Awareness on Plastics &Moulds
H & GT - GTCI - Bangalore - July 2005
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Contents
> > > > > > > > > H & GT - GTCI - Bangalore - July 2005
Introduction Materials Mould Manufacturing Advanced Moulding Technology Injection Moulding Machine Moulding defects and remedies Design Considerations Design Guidelines Design for Manufacturing and Assembly Guidelines
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Introduction to Moulds What is mould? Moulding is a manufacturing technique for making parts from plastic material. •Molten plastic is injected at high pressure into a mold, which is the inverse of the desired shape. •The mould is made by a mold maker from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part.
4 M’s to be considered Man Material Manufacturing Machine
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•Injection moulding is very widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars.
Why is injection moulding awareness needed for Product Designing ? Considerable thought should be put into the design of moulded parts and their moulds, to ensure that the parts will not be trapped in the mould, that the moulds can be completely filled before the molten resin solidifies, and to minimize imperfections in the parts, which can occur due to peculiarities of the Design Process.
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Materials
> General Definition of Materials Material is the substance or matter from which something is or can be made, or also items needed for doing or creating something. Materials for moulding: 1. Natural Rubber. 2. Synthetic Rubber 3. Thermoset Plastic. 4. Thermo Plastic.
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Materials
> Criteria for selecting Materials Physical & Mechanical Considerations •What are the overall part dimensions (diameter, length, width, thickness)? •What load will the part have to carry? •Will the design carry high loads? •What will the highest load be? •What is the maximum stress on the part? •What kind of stress is it (tensile, flexural, etc.)? •How long will the load be applied? •Will the load be continuous or intermittent? •Does the part have to retain its dimensional shape? •What is the projected life of the part or design
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Materials
> Criteria for selecting Materials Thermal Considerations •What temperatures will the part see and for how long? •What is the maximum temperature the material must sustain? •What is the minimum temperature the material will sustain? •How long will the material be at these temperatures? •Will the material have to withstand impact at the low temperature?
Note: Materials filled with friction reducers (such as PTFE, molybdenum disulfide, or graphite) generally exhibit less
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•What kind of dimensional stability is required (is thermal expansion and contraction an issue)? Bearing and Wear Considerations •Will the material be used as a bearing? Will it need to resist wear? •Will the material be expected to perform as a bearing? If so, what will the load, shaft diameter, shaft material, shaft finish, and rpm be? •What wear or abrasion condition will the material see?
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Materials
> Criteria for selecting Materials Chemical Considerations •Will the material be exposed to chemicals or moisture? •Will the material be exposed to normal relative humidity? •Will the material be submerged in water? If so, at what temperature? •Will the material be exposed to steam? •Will the material be painted? If so, what kind of paint? •Will the material be glued? If so, what kind of adhesive will be used? •Will the material be submerged or wiped with solvents or other chemicals? If so, which ones? •Will the material be exposed to chemical or solvent vapors? If so, which If so, which ones? •Will the material be exposed to other materials that can outgas or leach detrimental materials, such as plasticizers or petroleum-based chemicals?
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Materials
> Criteria for selecting Materials Other Miscellaneous Considerations Will the part have to meet any regulatory requirements? Is UL94 Flame retardant rating required? What level? Should the material have a special color and/or appearance? Natural | White | Black | Other Colors Color match to another part or material? Window-Clear | Transparent | Translucent | Opaque Smooth | Polished | Textured | One-Side or Both Will the part be used outdoors? Is UV Resistance needed? Is static dissipation or conductivity important? Insulator | Static Dissipative | Conductive
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Materials
> Rubber 1. A naturally gifted plastic. 2. Has many applications in industrial and consumer goods. 3. Only group of materials able to provide elastic properties across a wide range of temperatures. The rubber family includes a diverse range of materials - as varied as "metals" or "plastics".
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Materials Rubber
> Introduction to Rubber Manufacturing The two types of rubber in common use today are Natural and Synthetic. Natural rubber comes from the rubber tree (Hevea brasiliensis). When a tree matures at the age of six or seven years, the latex is collected from a diagonal incision in the tree trunk. The tapping process does not affect the health of the tree and the tree wound later heals itself. Synthetic rubber is made by man from petrochemical feedstock. Crude oil is the principal raw material.
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Materials Rubber
> Uses of Rubber Designers choose rubber because of its wide range of properties It can be used over a temperature range from -80°C to +300°C
It can be electrically insulated, conductive or anti-static
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Materials Rubber
> Uses of Rubber It is available in a wide range of colors and textures
It can withstand extremes of weather and outdoor environment
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Materials Rubber
> Uses of Rubber It can withstand exposure to fuels, oils and chemicals while retaining its properties It can be made flame retardant and self extinguishing, with halogen free and smoke suppressant types available
It can absorb vibration and noise and act as an insulator
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Materials
> Uses of Rubber
Rubber
It can maintain tension and compression forces indefinitely - for example in seals. It can be gas tight and used as a fluid seal or separator
Gaskets and Oil Seals used in Engine
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Materials Rubber
> Uses of Rubber It has low thermal conductivity and can be used to reduce heat transfer
It has friction properties similar to human skin and is comfortable to grip
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Materials
> Uses of Rubber
Rubber
It can have a clean, smooth surface which is non-stick and suitable for hygienic applications
It is compatible with other engineering materials (e.g. metals, plastics and ceramics) and can be combined with them in many different ways, including bonding.
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Materials
> Plastics The term plastics covers a range of synthetic or semi-synthetic organic condensation or polymerization products that can be molded or extruded into objects or films or fibers. •Their name is derived from the fact that in their semi-liquid state they are malleable, or have the property of plasticity. •Plastics vary immensely in heat tolerance, hardness, and resiliency. •Combined with adaptability, the general uniformity of composition and lightness of plastics ensures their use in almost all industrial applications today. •Plastic may also refer to any material characterized by deformation or failure under shear stress. •Plastics offer extraordinary advantages in product manufacturing. Because they are easily softened or melted, they can be molded into almost any shape. •Plastics have replaced traditional materials like metals and wood in countless applications because of their cost effectiveness and property attributes.
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Materials
Plastics can be divided into two processing groups
Plastics
Thermoplastics and Thermosets
Thermoplastic 1.It is heated and pressed into a mould. 2.No chemical reaction of any kind takes place. 3.Once the plastic has cooled and hardened in this shape, it could be reheated and remoulded without any perceptible change in its properties.
Granules
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Products
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Materials
Thermosets
Plastics
1. Undergo chemical change while they are being formed. 2. They react by polycondensation and cross-link to form a three-dimensional lattice. 3. Once a thermoset has achieved its final shape, it cannot be reformed. 4. Examples of thermosets are phenolic resins, melamines and urea resins
Granules
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Products
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Materials
Advantages of Plastics
Plastics
Plastics can provide the following advantages for product designers and manufacturers: •Design Flexibility •High Strength and Toughness •Corrosion Resistance •Reduced Manufacturing Costs •Almost Any Color or Surface Texture •Waterproof •Stiffness or Ductility •Low Weight •High Manufacturing Throughput •High Reproducibility of Parts •Electrical Insulation •Thermal Insulation
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Materials
Different types of Plastics
Plastics
•Polyethylene (PE) •Polyurethane (PU) •Polypropylene (PP) •Polyethylene Terephthalate (PETE) •Polyamide (PA) or Nylon •Polyester •Polyvinyl Chloride (PVC) •Polycarbonate (PC) •Acrylonitrile Butadiene Styrene (ABS) •Acetal
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Materials
Polyethylene (PE)
Plastics
Polyethylene or polyethene is one of the simplest and most inexpensive polymers. It is a waxy, chemically inert plastic. Properties:
Uses
•Thermoplastic.
Film, bags, pipe and tubing, insulating sleeves, bottle stoppers, lids, plastic wrap, toys.
•Toughness •Ease of processing •Chemical resistance •Abrasion resistance •Electrical properties •Impact resistance •Low coefficient of friction •Near-zero moisture absorption •Translucent.
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Materials
Polyurethane (PU)
Plastics
Polyurethane is a unique material that offers the elasticity of rubber combined with the toughness and durability of metal Properties:
Uses
•Abrasion resistant
Belts, Metal forming pads, Wear strips, Bumpers, Gears, Bellows, Machinery mounts, Cutting Surfaces, Sound-dampening pads, Chute and hopper liners, Prototype machined parts, Foam, Gaskets, Seals, Rollers, Roller covers, Sandblast curtains, Diaphragms
•Oil and solvent resistant •Load bearing capacity •Tear resistant •Weather resistant •High flex-life •Electrical insulating properties •Heat and cold resistant
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Materials
Polypropylene (PP)
Plastics
Polypropylene is an economical material that offers a combination of outstanding physical, chemical, mechanical, thermal and electrical properties not found in any other thermoplastic. Properties: Uses •Thermoplastic • Lightweight •High tensile strength •Impact resistant
Household items, plastic wrap, automobile parts, batteries, bumpers, garden furniture, syringes, bottles, appliances
•High compressive strength •Excellent dielectric properties •Resists most alkalis and acids •Resists stress cracking •Retains stiffness and flex •Low moisture absorption •Non-toxic •Non-staining •Easily fabricated •High heat resistance
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Materials
Polystyrene (PS)
Plastics
Polystyrene is a polymer made from styrene, a liquid that is commercially manufactured from petroleum, although it is also found in plants. Properties:
Uses
•Thermoplastic
Plastic wrap, kitchen utensils, furniture covers, thermal insulation, toys, office supplies, disposable razors
•Transparent •Nontoxic •Optical and electrical properties •Easy to color •Resistant to X rays, oils, and grease
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Materials
Polyethylene Terephthalete (PETE)
Plastics
Polyethylene terephthalate (aka PET, PETE, PETP) is a plastic resin of the polyester family, used to make some thermoforming applications. It is also one of the most important raw material for man-made fibers. Its main virtue is that it is fully recyclable as you can recover its polymer chains, unlike most other plastics Properties:
Uses
•Thermoplastic
Soft drink bottles, peanut butter jars, salad dressing bottles, non breakable bottles
•Extremely hard •Wear-resistant •Dimensionally stable •Resistant to chemicals •Good dielectric properties.
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Materials
Polyamide (PA) or Nylon
Plastics
Nylon is a condensation polymer made of repeating units with amide linkages between them: hence it is frequently referred to as a polyamide. It was the first synthetic fibre to be made entirely from inorganic ingredients: coal, water and air. Properties:
Uses
• Very good physical properties
Electrical connectors, gear, slide, cams and bearings, cable ties and film packaging, fluid reservoirs, fishing line, brush bristles, automotive oil pans, fabric, carpeting, sportswear, sports & recreational equipment
• Moisture has significant effect on properties • Very good heat resistance • Excellent chemical resistance • Excellent wear resistance • Moderate to high price • Fair to easy processing
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Materials
Polyester
Plastics
Polyester is a category of polymers which contain the ester functional group in their main chain. Properties:
Uses
• Strong
Filters, conveyor belts, sleeping bag insulation, coat insulation, tire cords.
• Resistant to stretching and shrinking • Resistant to most chemicals • Quick drying • Crisp and resilient when wet or dry • Wrinkle resistant • Abrasion resistant • Easily washed
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Materials
Polyvinyl Chloride (PVC)
Plastics
Polyvinyl chloride is produced from its monomer, vinyl chloride. PVC is a hard plastic that is made softer and more flexible by the addition of phthalates. Polyvinyl chloride (PVC) is a flexible or rigid material that is chemically non reactive.. Properties:
Uses
• High strength
Nuts, filters, signs, tanks, pipes, bolts, valves, bushings, tank and pool liners, laboratory equipment ducts, sprinkler systems, photo mounting, wall coverings, pump parts, fittings
• Economical • Dimensional stability • Good weather resistance • High impact strength • Clarity • Colorability • Flexible or rigid • Chemically inert • Ease of fabrication • Tasteless, odorless, non-toxic • Good electrical properties
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Materials
Polycarbonate (PC)
Plastics
Polycarbonates are a particular group of polymers that are moldable under heat; as such, these plastic are very widely used in modern manufacturing. This versatile thermoplastic maintains its properties over a wide range of temperatures, from -40"F to 280"F. Uses Properties: • Thermoplastic • High dielectric strength • Unbreakable
Lenses, high temperature and pressure windows,face shields industrial equipment and housing components, medical equipment components, instrument components, electrical insulators and connectors
• Machinability • High impact strength • Dimensional stability • Thermal stability • Stain resistant • Non-toxic • Low water absorption
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Materials
Acrylonitrile Butadiene Styrene (ABS)
Plastics
Acrylonitrile butadiene styrene, or ABS is a common thermoplastic used to make light, rigid, moulded products. Properties:
Uses
• Good chemical resistance
Machine parts, prototypes, tote bins and trays, automotive parts, business machine housing and parts, aircraft interior trim, industrial enclosures
• Stress cracking resistance to inorganic salt solutions, alkalis, acids, and some oils • Excellent abrasion resistance • Electrical properties • Moisture • Creep resistance .
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Materials
Acetal
Plastics
Acetal is a crystalline thermoplastic polymer with a high melting point. It is suitable for mechanical parts or electrical insulators that require structural strength at above normal temperatures. Uses Properties: Pump and valve components,gears,bearings, • High modules of elasticity. bushings, rollers, fittings,electrical insulator parts • High strength and stiffness. • Low coefficient of friction. • Good abrasion and impact resistance. • Low moisture absorption. • Excellent machinability. • Natural lubricity. • Resistant to gasoline, solvents, and other neutral chemicals.
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Materials
Special Purpose Materials
Sheet Moulding Compound
SMC or Sheet Moulding Compound Definition: •A fiber glass reinforced thermosetting compound in sheet form, usually rolled into coils interleaved with plastic film to prevent auto adhesion. •Made by dispensing mixed resin, fillers, maturation agent, catalyst and mold release agent onto two moving sheets of polyethylene film. •The lower one also contains chopped glass roving or glass mat. SMC can be molded into complex shapes with little scrap. Advantages •Processing of SMC by compression or injection moulding enables the production of bodywork or structural automotive components, and electrical or electronic machine housings in large industrial volumes. •The process also penetrates sectors such as sanitary ware (baths) and urban furniture (stadium and cinema seating) etc.
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Materials
Composition of SMC
Sheet Moulding Compound
SMC or Sheet Moulding Compound
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SMC Manufacturing Process
Sheet Moulding Compound
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Materials Sheet Moulding Compound
Advantages of SMC Part Consolidation: A well designed composite part can easily eliminate the assembly of many metal parts by allowing you to mold them as one complete piece. In addition, inserts can be molded into the SMC material to aid in the assembly process. Design Flexibility: Parts molded in polyester or vinylester composite materials can reproduce almost any shape desired. Dimensional Stability: Products made from composite materials offer a greater degree of dimensional stability when compared to thermoplastics, wood, and some metals. Light Weight: Composite parts offer more strength per unit of weight than any un-reinforced plastic and most metals. High Strength: Composite parts can be designed to provide a wide range of impact, tensile, and flexural strength properties, depending on the specific requirements of the application.
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Materials
Advantages of SMC
Sheet Moulding Compound
Corrosion Resistance: Composites do not rust or corrode, and offer various levels of chemical and environmental resistance. Low Electrical and Thermal Conductivity: Composites can offer a wide range of insulating properties to meet specific requirements for electrical and thermal resistance.
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Materials
SMC Components
Sheet Moulding Compound
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Special Purpose Materials
Bulk Moulding Compound
DMC or Dough Moulding Compound Also called as BMC or Bulk Moulding Compound Definition: Molding compound consisting of thermosetting plastic resins mixed with stranded reinforcement, fillers, and other additives. This viscous compound can be used for compression or injection molding. DMC is a combination of chopped glass strands with resin in the form of a bulk prepreg. BMC is suitable for either compression or injection moulding. Injection moulding of BMC is used to produce complex components such as 1. Electrical equipment 2. Car components (headlamps are an important application for BMC) 3. Housings for electrical appliances 4. Tools, in large industrial volumes.
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Composition of BMC
Bulk Moulding Compound
BMC or Dough Moulding Compound BMC Manufacturing Machine
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Advantages of BMC
Bulk Moulding Compound
Technical Advantages: •Very rigid and stiffer than thermoplastics •Ability to integrate all the housing functions •No mechanical rework needed •No paint: BMC can be mass coloured •Reduced cycle time compared to aluminium •Longer life of BMC tools •Dimensional stability and higher precision compared to aluminium •Noise reduction : BMC has a dampening effect on vibrations
Economic Advantages: •50 % total cost savings in comparison to cast aluminium
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Materials Bulk Moulding Compound
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BMC vs. Thermoplastics •Dimensional accuracy •Dimensional stability (creep resistance) over a broad range of temperatures •Good property retention over long term / high temperature conditions (ageing) •Low thermal linear expansion (same as steel) •High mechanical properties (strength, stiffness and impact) •Excellent electrical properties •Design flexibility, thin to thick variable component sections •Inserts can be integrated in the moulding process •Direct screw assembly without previous threading •Corrosion resistance in aggressive environments including solvents •Non-melting, flame retardant , low smoke density, low toxicity and no halogens •Fire resistant UL94 V-0; glow wire 9600 •Customizing to meet specific needs, good speed to market •BMC can be mass coloured to match customer specifications •Lower mould cavity pressure •Faster cycle time (at medium to high wall thickness) •Machine workability •Low cost per litre
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BMC Components
Bulk Moulding Compound
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Types of Moulds
Mould (Manufacturing)
1. Compression Mould 2. Transfer Mould 3. Extrusion Mould 4. Injection Mould 5. Hot Runner Mould. 6. Blow Mould
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Types of Moulds
Compression Moulds Compression Moulding is one of three processes used to mold parts. Compression molding is the oldest and simplest way to make products. In some specific applications, compression molding is still the best way. To put it simply, compression molding involves squishing a chunk of uncured material into a pocket in the mould. After time, heat and pressure the material cures in the shape of the pocket. The mold can then be opened and the part removed Step #1 - A piece of uncured material is placed in the mold. Step #2 & 3 - The mold is closed up and held under hydraulic pressure while the material cures. Step #4 - When the mold opens the part can be removed. The excess material, called flash, needs to be trimmed off the part.
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Types of Moulds Compression Moulds
Parts of Compression Moulds Compression Mould - Closed
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Types of Moulds Compression Moulds
Advantages & Disadvantages Advantages of Compression Molding Lowest cost molds Little "throw away" material provides advantage on expensive compounds Often better for large parts
Disadvantages of Compression Molding Offers least product consistency Difficult to control flash Not suited for some types of parts
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Types of Moulds
Transfer Moulds Transfer Molding involves having a "piston and cylinder"-like device built into the mold so that the rubber may be squirted into the cavity through small holes. Pot Transfer Molding
Step #1 - A piece of uncured material is placed into a portion of the mold called the "pot." The plunger (on the top-most part of the mold) fits snugly into the "pot." Step #2 - The mold is closed up and under hydraulic pressure the material is forced through the small hole (the ”sprue") into the cavity. The mold is held closed while the material cures. Step #3 - The plunger is raised up and the "transfer pad" material may be removed and thrown away. Mold is opened and the part can be removed. The flash and the gate may need to be trimmed.
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Types of Moulds Transfer Moulds
Plunger Transfer Molding
Step #1 - A piece of uncured material is placed into a portion of the mold called the "pot." The plunger (on the top-most part of the mold) fits snugly into the "pot." Step #2 - The mold is closed up and under hydraulic pressure the material is forced through the “cull” and to the gate into the cavity. The mold is held closed while the material cures. Step #3 - The plunger is raised up, Mold is opened and the part can be removed. The flash and the Cull may need to be trimmed.
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Types of Moulds Transfer Moulds
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Movie - Transfer Mould Operation
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Types of Moulds Transfer Moulds
Advantages & Disadvantages Advantages of Transfer Molding •Provides more product consistency than compression molding •Cycle times are shorter than compression molding •Better than compression molding for rubber-to-metal bonding
Disadvantages of Transfer Molding •The transfer pad is scrap •Cycle time is longer than injection molding •Product consistency is poorer than injection molding
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Types of Moulds
Extrusion Moulds Extrusion moulding is a method used to form thermoplastic materials into continuous sheet film, tubes, rods, and other shapes, and to coat wiring and cable. The process produces continuous two dimensional shapes like sheet, pipe, film, tubing, gasketing, etc. The material is fed into the extruder where it is melted and pumped out of the extrusion die.
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Types of Moulds Extrusion Moulds
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Movie - Extrusion Mould Operation
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Types of Moulds
Blow Moulds Blowing molding is the primary method to form hollow plastic objects such as soda bottles. Blow molding is another common type of plastic molding. In this process a plastic tubular form, produced by extrusion or injection molding, is used to form the part. This form, called a parson, is softened inside a mold and then injected with air or other compressed gas. This expands the parson against the sides of the mold cavity, forming a hollow object the size and shape of the mold.
Step #1 - The Parision is Extruded from injection Unit Step #2 - The mold is closed onto Parision and then the Parision is inflated against the walls of the Mould by using a Air. Step #3 - The Mould is opened and the Part is collected
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Types of Moulds Blow Moulds
2 Movies - Blow Mould Operation
Blow Mould
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Types of Moulds
Injection Moulds Injection Molding is the most advanced typical method of molding plastic products. Injection molding produces the most consistent results by automating all aspects of how the material gets into the mold. In injection molding, the material is worked and warmed and then squirted into the mold at controlled speeds, pressures and temperatures.
Step #1 - Mold is closed and clamped. Step #2 - A shot of melt is injected under high pressure into the mold cavity. Step #3 - The screw is rotated and retracted and the polymer in the mold has completely solidified. Step #4 - The mold is opened, and the part is ejected and removed.
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Types of Moulds Injection Moulds
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4 major steps in Injection Moulding
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Types of Moulds Injection Moulds
Advantages & Disadvantages Advantages of Injection Molding •Provides the maximum product consistency •Allows the most control of flash •Because the material is warmed before going into the mold, fastest cycle times. Disadvantages of Injection Molding •Not suited for all compounds •Most expensive molds •Typically has some runners or other "throw away" portion in each shot
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Types of Moulds Injection Moulds
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Parts of a typical mould base
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Types of Moulds Injection Moulds
Parts of a typical mould base
Top Half
Locating Ring: This part is fitted on to the front face of the mold to serve the purpose of locating the mould in the correct position in alignment to the machine nozzle and directly align the sprue bush hole. Sprue Bush: It is the connecting member between nozzle and the runner system.The plasticized material is transferred to the impression through a passage termed as a “Sprue”. The Sprue Bush radius is always more than the nozzle radius to avoid leakage of plastic material. Top Clamp Plate: It is the top most part of the mould assembly and is used for clamping top assembly on the machine platen.
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Types of Moulds Injection Moulds
Parts of a typical mould base
Top Half
Cavity Plate ( A Plate) This plate incorporates the cavity inserts and also help to incorporate cooling media into the mold Guide Pillars The accurate mould assembly need the perfect alignment between top half and bottom half at any point of time in a mould cycle.The needed services is provided by guide pins which guided into the guide bush in other half. Cavity The space inside a mold into which material is injected. The material injected will take the form of the cavity profile.
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Types of Moulds Injection Moulds Bottom Half
Parts of a typical mould base Core Plate ( B Plate) This plate incorporates the Core inserts and also help to incorporate cooling media into the mold Guide Bush The accurate mould assembly need the perfect alignment between top half and bottom half at any point of time in a mould cycle.The needed services is provided by guide bush which guides the guide pillar in other half. Support Plate This plate will give extra support for core plate. Which reduces the deflection caused by injection force.
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Types of Moulds Injection Moulds Bottom Half
Parts of a typical mould base Ejector Pins Pins that are pushed into a mold cavity from the rear as the mold opens to force the finished part out of the mold. Ejector Return Pin Pins that push the ejector assembly back as the mold closes. Also called surface pins or return pins Sprue Puller Pin This member pulls the Sprue from the Sprue Bush. This can also be used as a cold slug well by reducing the height from parting line.
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Types of Moulds Injection Moulds Bottom Half
Parts of a typical mould base Ejector Retainer Plate This plate will retain the ejector pins in its position as the ejector assembly is pushed back. Ejector Plate The Ejector Plate is clamped to Ejector Retainer Plate. As the mold opens the ejector rod pushes the ejector plate (assembly), which results in ejection of component Ejector Housing This is the bottom most part of the mould assembly and is used for housing the ejector assembly and also for clamping to the moving platen of the moulding machine
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Types of Moulds Injection Moulds
Parts of a typical mould base Locating Ring
Sprue Bush
Plastic Part A-Plate Guide Pillar Cavity
Core
Guide Bush
B-Plate Retainer Pin Ejector Pin Ejector Retainer Plate
Ejector Housing
3D View of the Mould Parts
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Ejector Plate Guided Ejection
Support Pillar
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Types of Moulds Injection Moulds
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Types of Injection Moulds
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Types of Moulds Injection Moulds
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Two Plate Mould A two plate mould is the simplest type of mould. It is called a two plate mould because there is one parting plane, and the mould splits into two halves. The runner system must be located on this parting plane; thus the part can only be gated on its perimeter.
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Types of Moulds Injection Moulds
Two Plate Mould
Functioning of two plate mould
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Types of Moulds Injection Moulds
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Three Plate Mould A three plate mould differs from a two plate in that it has two parting planes, and the mould splits into three sections every time the part is ejected. Since the mould has two parting planes, the runner system can be located on one, and the part on the other. Three plate moulds are used because of their flexibility in gating location. A part can be gated virtually anywhere along its surface.
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Types of Moulds Injection Moulds
Three Plate Mould
Functioning of three plate mould
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Types of Moulds Injection Moulds
Three Plate Mould
Functioning of three plate mould
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Types of Moulds Injection Moulds
Three Plate Mould
Functioning of three plate mould
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Types of Moulds Injection Moulds
Different Types of Mould - Movies
Two Plate mould (Pin ejection)
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Types of Moulds Injection Moulds
Different Types of Mould - Movies
Two Plate mould (Stripper ejection)
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Types of Moulds Injection Moulds
Different Types of Mould - Movies
Two Plate mould (Core Side Stripper ejection)
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Types of Moulds Injection Moulds
Different Types of Mould - Movies
Three Plate mould (Pin ejection)
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Types of Moulds Injection Moulds
Different Types of Mould - Movies
Stack mould (Stripper ejection)
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Types of Moulds Injection Moulds
Different Types of Mould - Movies
Shuttle mould (Pin ejection)
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Types of Moulds Injection Moulds
Different Types of Mould - Movies
Unit mould (Pin ejection)
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Types of Moulds Injection Moulds
Hot Runner Moulds Hot runner molds are two plate molds with a heated runner system inside one half of the mold. A hot runner system is divided into two parts: the manifold and the drops. The manifold has channels that convey the plastic on a single plane, parallel to the parting line, to a point above the cavity. The drops, situated perpendicular to the manifold, convey the plastic from the manifold to the part.
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Types of Moulds Injection Moulds
Hot Runner Moulds
Hot Runner Mould
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Types of Moulds Injection Moulds Hot Runner Mould
Advantages & Disadvantages While Hot Runner Molds are typically more expensive than "Cold Runner" molds, the cost of the mold can be offset in other ways. Thermoplastic Hot Runner Molds can reduce costs due to : •No scraping of the the runner. •Reducing the cycle time. •Injection time is reduced due to the shot size being reduced by the elimination of the runner. •Improves both part and mold design with flexibility of gating locations, which provides options for cavity orientation. •Pressure drops are greatly reduced due to the balanced melt flow as the temperature is consistent from the machine nozzle to the gate. •Precise material temperature control is critical to successful Hot Runner processing.
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Types of Moulds Injection Moulds Advanced Moulding Technologies
Over Moulding Overmoulding is an injection molding process using two separate moulds of which you mould one material over another to create or touch appeal such as a handle or knob.
Over molding
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Types of Moulds Injection Moulds Advanced Moulding Technologies
Types of Over Moulding •Two color Over Molding
•Two Material Over Molding
•Insert Over Molding
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Types of Moulds Injection Moulds Advanced Moulding Technologies
Over Moulding Technologies Double Injection Molding This process produces a soft feel to the product as well as improved impact properties and an increased value.
Two Shot Injection Molding This process has been used for keycaps and buttons on telephones and other products for many years. The moldedin graphics are embedded in the part and will not wear off with use. Clear sections can be utilized with back lighting for readability in dim or dark applications.
In Mold Decoration This application is relatively new to the plastics industry. Using IMD, multiple colors and graphics can be added in a single operation.
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Types of Moulds Injection Moulds
Over Moulds
Advanced Moulding Technologies
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Types of Moulds Injection Moulds Advanced Moulding Technologies
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Advantages & Disadvantages • Grabs consumer attention - a proven concept to build market share • Improved feel and appearance • Provides a soft grip or feel • Improved ergonomics • Provides a safe, tactile grip in wet environments • Eliminates / reduces assembly labor • Eliminates need for mechanical fasteners and adhesives • Ease of color match with no secondary painting required • Improved impact resistance • Sealing in fluid environment • Provides high friction surface • Vibration damping • Sound absorption
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Types of Moulds Injection Moulds Advanced Moulding Technologies
Gas Injection Moulding The gas injection technique (GIT) is a special injection molding method. After the actual injection molding operation, a permanent cavity is created in the molding as a second step by means of an inert compressed gas (nitrogen). The plastic is pressed against the mold wall by maintaining the gas pressure during the solidification process, thus defining the external contour of the component. Gas Injection Method
Blow Out Method
Gas Injection Technology
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Types of Moulds Injection Moulds
Advantages & Disadvantages - Gas Injection Moulding Advantages
Advanced Moulding Technologies
•Greater design freedom (thick-walled, rod-shaped parts possible) •High degree of rigidity due to larger closed cross-section profiles •Reduction of sink marks •Uniform shrinkage and thus less distortion •Shorter cycle times as compared to thick-walled compact parts •With rod-shaped parts weight savings of up to approx. 50% Disadvantages •Additional costs for gas, gas pressure system and injection device •Higher expenditure for quality assurance may be necessary •Risk of surface faults (e.g. switchover markings) •Possibly greater startup losses with more complex moldings •Restrictions in the selection of material and with subsequent material changeovers •Composite molds more difficult than in the case of conventional injection molding
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Types of Moulds Injection Moulds Advanced Moulding Technologies
Rotational or Roto Moulding Rotational or rotomoulding is an extremely popular and well-used process for producing items that are usually hollow. •Used for very large articles which are usually made in small quantities. •Items such as children's toys, garden furniture are manufactured by rotational moulding. Roto moulding uses PVC in paste ( plastisol ) form which is introduced into the mould along with any additives such as pigments or finishers. The mould is closed and then spun both vertically and horizontally and moved into an oven. As the paste starts to melt and the mould continues rotating, it's flung to the walls of the mould by centrifugal force where it forms a skin. After a fixed period, the mould is removed from the oven and allowed to cool carefully to avoid the product shrinking or warping.
Movie on Roto Moulding
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Injection Moulding Machine
Injection Moulding Machine The injection molding machine converts granular or pelleted raw plastic into final molded parts via a melt, inject, pack, and cool cycle. Zones in Injection Moulding Machine
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Injection Moulding Machine Moulding Cycle
Plasticizing the Resin • The cycle begins with the extruder plasticizing the resin and accumulating it in the forward section of the barrel. • The heater bands maintain the melt's temperature as the shot it built up. • The mold is closed. • The cycle is typically timed so that there is minimal time between the closing of the mold and the next shot
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Injection Moulding Machine Moulding Cycle
Injecting the Resin • Once the shot is ready, a valve is opened at the nozzle and the melt is quickly injected into the mold. • This part of the process only takes a few seconds. • As the melt enters the cavity, the displaced air is vented out through the holes for the ejection pins and along the parting line. • Proper filling of the cavity is dependant on part design as well as good gate location and design and proper venting.
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Injection Moulding Machine
Cooling the Part
Moulding Cycle
Once the cavity is filled, the part is allowed to cool.
This is the longest portion of the molding cycle.
If an accumulator is not used, the extruder continues to push material into the mold and maintain the proper amount of pressure until the material cools (or "freezes").
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Injection Moulding Machine Moulding Cycle
Ejecting the Part •Once the part has cooled enough (so that it will hold its shape out of the mold, and the ejection pins won't deform the part), the mold is opened. •The moving platen has moves backwards and the ejector pins strike the rear plate (or "ejector plate"), ejecting the part.
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Injection Moulding Machine
Movie of Moulding Cycle
Moulding Cycle
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Injection Moulding Machine
Components of Injection Moulding Machine A typical injection molding machine consists of the following major components, Injection system Hydraulic system Mold system Clamping system Cooling System Control system
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Injection Moulding Machine
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Injection Moulding Machine
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Injection Moulding Machine Injection System
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Injection System The injection system consists of a hopper, a reciprocating screw and barrel assembly, and an injection nozzle, as shown in figure. This system confines and transports the plastic as it progresses through the feeding, compressing, degassing, melting, injection, and packing stages.
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Injection Moulding Machine
Injection System
Injection System
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Injection Moulding Machine
Movie of Injection System
Moulding Cycle
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Injection Moulding Machine Injection System
Components of Injection System The Hopper: Thermoplastic material is supplied to molders in the form of small pellets. The hopper on the injection molding machine holds these pellets. The pellets are gravity-fed from the hopper through the hopper throat into the barrel and screw assembly.
Granules in Hopper:
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Injection Moulding Machine
Components of Injection System
Injection System
The Barrel: The barrel of the injection molding machine supports the reciprocating plasticizing screw. It is heated by the electric heater bands.
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Injection Moulding Machine
Components of Injection System Reciprocating Screw
Injection System
The reciprocating screw is used to compress, melt, and convey the material. The reciprocating screw consists of three zones: •the feeding zone •the compressing (or transition) zone •the metering zone •the injection zone
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Injection Moulding Machine
Components of Injection System Reciprocating Screw
Injection System
The injection zone
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Injection Moulding Machine Injection System
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Components of Injection System The Nozzle The nozzle connects the barrel to the sprue bushing of the mold and forms a seal between the barrel and the mold.
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Injection Moulding Machine Hydraulic System
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Hydraulic System The hydraulic system on the injection molding machine provides the power to open and close the mold, build and hold the clamping tonnage, turn the reciprocating screw, drive the reciprocating screw, and energize ejector pins and moving mold cores. A number of hydraulic components are required to provide this power, which include pumps, valves, hydraulic motors, hydraulic fittings, hydraulic tubing, and hydraulic reservoirs.
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Injection Moulding Machine Mould System
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Mould System The mold system consists of tie bars, stationary and moving platens, as well as molding plates (bases) that house the cavity, sprue and runner systems, ejector pins, and cooling channels, as shown in figure. The mold is essentially a heat exchanger in which the molten thermoplastic solidifies to the desired shape and dimensional details defined by the cavity.
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Injection Moulding Machine
Mould System
Mould System
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Injection Moulding Machine
Mould System
Mould System
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Injection Moulding Machine Delivery System
The delivery system The delivery system, which provides passage for the molten plastic from the machine nozzle to the part cavity, generally includes: •a sprue •cold slug wells •a main runner •branch runners •gates
The delivery system design has a great influence on the filling pattern and thus the quality of the molded part.
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Injection Moulding Machine
The Delivery System
Delivery System
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Injection Moulding Machine Delivery System
Sprue A sprue is a channel through which to transfer molten plastics injected from the injector nozzle into the mold. It is a part of sprue bush, which is a separate part from the mold
Sprue Gate
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Sprue Bush
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Injection Moulding Machine
Runner A runner is a channel that guides molten plastics into the cavity of a mold.
Delivery System
Runner System
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Injection Moulding Machine
Gate A gate is an entrance through which molten plastics enters the cavity.
Delivery System
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Injection Moulding Machine
Functions of Gate •Restricts the flow and the direction of molten plastics.
Delivery System
•Simplifies cutting of a runner and moldings to simplify finishing of parts. •Quickly cools and solidifies to avoid backflow after molten plastics has filled up in the cavity. •Generates shear heat by going through the narrow gate, raising the temperature of molten plastics and improving the filling in the cavity. •Reduces residual stress, and thus reduces part defect such as warpage. •As the cooling solidification time is shortened, molding cycle is also shortened. •As the gate trace is less, it is possible to complete finishing process in a short time.
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Injection Moulding Machine
Sprue Gate •The Sprue gate is mainly used for cylindrical parts
Delivery System Types of Gate
•The Parts are balanced and concentric •Have very good weld-line strength
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Injection Moulding Machine
Edge Gate
Delivery System Types of Gate
•Put to the side of parts.
•The most common gate.
•The gate trace will be left. •Often used for the structure with more than two cavities.
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Injection Moulding Machine
Fan Gate
Delivery System Types of Gate
•Finishing is difficult and cost is high due to the wide gate.
•Suitable for large and flat plate parts.
•The gate trace will be left.
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Injection Moulding Machine
Point Gate
Delivery System Types of Gate
•The position is relatively flexible.
•Suitable for molding multiple parts.
•The structure is complicated due to Three Plate method of die
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Injection Moulding Machine
Ring Gate
Delivery System Types of Gate
•The part consistency is more..
•Suitable for Round Hollow parts.
•The Material loss is more.
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Injection Moulding Machine
Submarine Gate
Delivery System Types of Gate
•The position is flexible (front, side, or back of parts).
•The gate will be automatically cut off during mold opening.
•The gate needs to be thought about not to be left inside the cavity.
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Injection Moulding Machine
Film Gate
Delivery System Types of Gate
•Finishing is difficult and cost is high due to the wide gate.
•Suitable for thin plate parts.
•The gate trace will be left.
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Injection Moulding Machine Delivery System Types of Gate
Cold Slug Well Cold Slug Wells are are highly desirable in an Injection Mold. The Cold Slug Well provides a small reservoir (well) to trap air, and impurities before they enter the Runner, Gate and Cavity. A Cold Slug Well is located above the Sprue Puller Pin. Typically, as the runner changes from a primary to secondary, and, secondary to tertiary there is also a cold slug well at each intersection.
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Injection Moulding Machine Clamping System
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Clamping System The clamping system opens and closes the mold, supports and carries the constituent parts of the mold, and generates sufficient force to prevent the mold from opening. Clamping force can be generated by a mechanical (toggle) lock, hydraulic lock, or a combination of the two basic types
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Injection Moulding Machine Cooling System
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Cooling System Cooling time is by far the most dominate time consumer in the injection molding cycle. A long cycle time means that the molder must charge more for the same part. During Product Design we should use thermal analysis capabilities to specify the cooling design for the tools. The result will be a low cost tool that will run fast and keep your cost per part as low as possible.
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Types of Cooling System Cooling channels or lines
Cooling System Types of Cooling System
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Most commonly used cooling design.Cooling channels should be placed close to the mold cavity surface with equal center distances in between.
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Types of Cooling System Baffle cooling
Cooling System Types of Cooling System
A baffle is actually a cooling channel drilled perpendicular to a main cooling line, with a blade that separates one cooling passage into two semi-circular channels.
This design is used for core insert
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Injection Moulding Machine
Types of Cooling System Bubbler cooling
Cooling System Types of Cooling System
A bubbler is similar to a baffle except that the blade is replaced with a small tube.
This design is used for slender core insert
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Injection Moulding Machine
Types of Cooling System Spiral Cooling
Cooling System Types of Cooling System
A spiral is similar to a bubbler except that the coolant flow in a spiral slots.
This design is used for long large core (above 40mm)
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Injection Moulding Machine
Types of Cooling System Thermal pins
Cooling System Types of Cooling System
A thermal pin is an alternative to baffles and bubblers. It is made of copper or sealed cylinder filled with a fluid.
This design is used for long slender core
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Injection Moulding Machine
Types of Cooling System Air Cooling
Cooling System Types of Cooling System
Air is blown at the cores from the outside during opening or flows through a central hole from inside.
This design is used for very slender core (less than 5mm)
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Injection Moulding Machine Ejection System
Ejection System After the molding solidified and cooled down, it has to be removed from the mold, however, by undercuts, adhesion and internal stress the molding does not fall due to gravity. Therefore it has to be separated and removed from the mold by special means. Ejection equipment is usually actuated mechanically by the opening stroke of the molding machine
The Ejector rod in turn hits the Ejector plate in the mold base and it will move towards the parting line and to eject the molded part.
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Injection Moulding Machine Ejection System
Methods of Ejection The method of ejection has to be adapted to the shape of the molding to prevent damage. In general, mould release is hindered by shrinkage of the part on the mould cores. Large ejection areas uniformly distributed over the molding are advised to avoid deformations. Ejector system is normally in movable mold half, assuming the molding is connected to the movable side of the mold in initial ejection. Several ejector systems can be used: Pin Ejection Sleeve Ejection Blades Ejection Air valve Ejection Stripper plate Ejection Threads Ejection
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Injection Moulding Machine
Ejector Pins •Straight, cylindrical pins are most common.
Ejection System Methods of Ejection
•Used where little force is needed.
Ejector Pins
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Movie of Pin Ejection
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Injection Moulding Machine
Blade Ejector Pins •Used to eject narrow, slender, intricate shaped parts
Ejection System Methods of Ejection
•Avoids deep impression in the molded part during ejection in pin ejector
Blade Ejector Pins
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Movie of Blade Ejection
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Injection Moulding Machine Ejection System Methods of Ejection
Sleeve Ejection Ejector Sleeve is basically an ejector pin with a hole through the center.The hole is used for a core pin to form a portion of the desired part. The core pin touches the part, the other end of the core pin runs through the ejector housing and terminate near the bottom of the mold base.
Sleeve Ejector Pins
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Movie of Sleeve Ejection
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Injection Moulding Machine Ejection System Methods of Ejection
Stripper Ejection Stripper Plates are used to strip the part off the core steel. The stripper plate is actuated via stripper bolts from the A side of the mold, or by the ejector mechanisms in a variety of ways.
Stripper Plate
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Movie of Stripper Ejection
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Injection Moulding Machine Ejection System Methods of Ejection
Air Valve Ejection Air Poppets are standard components that aid the ejection of a part by using compressed air within the mold. The timing of the actuation of the air is controlled by the controller of the moulding machine.
Air poppets
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Movie of Air Valve Ejection
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Injection Moulding Machine
Threads Ejection •Used to eject threaded components.
Ejection System Methods of Ejection
•Too costly method but it is the only method
Movie of Collapsible Core Ejection
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Movie of Rotary Core Ejection
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Injection Moulding Machine Control System
Control System The control system provides consistency and repeatability in machine operation. It monitors and controls the processing parameters, including the temperature, pressure, injection speed, screw speed and position, and hydraulic position. The process control has a direct impact on the final part quality and the economics of the process.
Moulding Machine Control System
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Injection Moulding Machine
Control System
Control System
Onboard External Control System
Internal Control System
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Moulding defects and remedies
Moulding defects and remedies •Problems can occur at all stages in the injection moulding process.The origins of these problems are often difficult to identify thanks to the complex interrelationship between the moulded part and the mould. •Successful troubleshooting should begin at the design stage not on the shop floor so that mistakes can be identified and remedied before they become critical.As a part designer it is a very good Idea to be aware of your options in tooling and to consider those while designing your part. •For example, have potential gate locations in mind. Try to guess where knit lines will occur and how different gate locations will affect them.
Areas which are concentrated during Product Design to get a defect free component
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Moulding defects and remedies
Blush Dull discolored or whitish area on the surface of the part, usually at the gate. May also occur where there is a sudden change in part thickness.
Burn Discoloration usually black, brown or dark yellow/brown depending upon severity. Feels rough and crunchy. Most often seen in deep, blind ribs where a lot of air can be forced into a small space.
Cold Flow Wavy or streaked appearance on part surface. Looks like a fingerprint or small waves like you would see on the surface of water. Low melt temperature, low injection speed or low injection pressure.
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Moulding defects and remedies
Cold Slug Cold piece of plastic that has been forced into the part along with the melt. Add a cold slug well at each intersection in the runner
Contamination Foreign particles embedded in the part
Delamination Separation of plastic surface layer giving a flaking or onion skin effect. Due to contaminated resin.
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Moulding defects and remedies
Discolouration Deviation from the original intended color of the material as compared to the manufacturers color chip. Contaminated resin / Overheated resin / Incorrect regrind ratio / Incorrect color mixing or blending.
Gloss Smooth shiny areas on the part surface. Hard to fill areas.
Jetting Squiggly line in part pointing to gate. Looks like a worm in the part.Incorrect gate placement or size.The gate is positioned in such a manner as to aim the plastic straight into an open area.The plastic launches out into the open like a piece of "silly string" and then stacks up in squiggles.
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Moulding defects and remedies
Knitline A line where the molten polymer flow fronts meet in the mold. Incomplete adhesion occurs along the knit line and causes a weak point in the plastic part. Mould is not preheated to moulding temperature.
Pinpush Circular or semicircular white stress rings on the side of the part opposite an ejector pin. May even be raised circular bumps. Unpolished core or less draft on core side of component. Inadequate ejector pins for ejection
Drag Fine, straight lines scraped in the line of draw. Cavity Side happens usually from insufficient draft for the texture. Core side drag happens usually from inadequate draft, rough core, or overpacking.
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Moulding defects and remedies
Sink Marks Depressions or dimples in the part that are usually adjacent to thick areas. In clear parts, bubbles can be seen in thick areas. As the plastic cools it shrinks. If there is an area that is proportionally thicker than the rest of the part, then the plastic will shrink more in the thick spot causing it to collapse inward. Wall perpendicular to ribs or bosses that don't conform to the 66% rule. Inconsistent wall thickness. i.e. thick areas adjacent to thin areas.
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Moulding defects and remedies
Warpage The failure to maintain flatness of a plastic part that was intended to be flat. Distortion from the intended shape of the plastic part. The underlying cause of most part warpage is the shape of the part itself. The pattern, shape, and thickness of ribs on the part as they undergo shrinkage have the greatest effect upon warpage. Present to some degree in most Injection molded parts but most easily detected on large flat parts. Differential mold cooling can get you parts that are flatter. Your best bet is to follow the 66% rule and minimize rib height. Flat parts are more susceptible to warpage than curved parts.
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Design Consideration
Parting Surface Parting Surface is a line at which the two halves of mould meet and form a seal to prevent the escape of material. The shape of the component, method of ejection, etc. largely influence the selection of parting surface.
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Design Consideration
Avoid round edges along the Parting Line
Parting Surface
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Design Consideration
Always look for simple tooling solutions
Parting Surface
Design to avoid side cam moulding
Movie of Side Cam Moulding
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Design Consideration
Always look for simple tooling solutions
Parting Surface
Design to avoid side cam moulding
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Design Consideration
Always look for simple tooling solutions
Parting Surface
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Design Consideration
Always look for simple tooling solutions
Parting Surface
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Design Consideration
Always look for simple tooling solutions
Parting Surface
Extending vent slots over the corner edge eliminates the need for a side action in the mold
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Design Consideration
Shrinkage In the production of plastic components melt is injected into the mold cavity. After completion of the injection phase and the hold period the molding is cooled down to the temperature for removal from the mold during the cooling period. Due to physical factors, the plastic component undergoes a dimensional change during the cooling process that is specific to the material used. This dimensional change is called shrinkage.
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Design Consideration
Effects of Shrinkage in design
Shrinkage
Wall thickness differences may lead to varying shrinkage behavior that is weaker or stronger depending on the plastic used. In the case of semi-crystalline materials, a large wall thickness results in slower cooling, which then leads to greater shrinkage. The resulting shrinkage differences in the molding lead to internal stresses in the molding, which are either absorbed through the inherent rigidity of the structure or reduced through special processing conditions.
Distortions due to differences in basic rib wall thickness
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Distortion in non-reinforced components
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Design Consideration
Effects of Shrinkage in design
Shrinkage
Incorrect
Correct
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Design Consideration
Draft The purpose of draft is to first provide release from the cavity side of the mold upon tool opening. Then upon ejection, draft allows instant release of the plastic part without dragging. If plastic parts have completely vertical walls, drag marks will occur on the plastic as it scrapes along the metal tool face. If money is no object vertical faces may be obtained however with the use of slides and lifters
stuck Without Draft
free With Draft
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Design Consideration
Where should you give Draft ?
Draft
The answer is it should start from parting surface. Draft must fall away from the parting lines on ALL vertical faces in the plastic part. The widest point on the part is thus the parting line. The location of parting line and subsequent application of draft to the plastic part are design decisions that affect both the aesthetics and functionality of the part. These decisions should be made before the part is sent to the mold maker if time to market is critical.
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Design Consideration
What is the correct draft angle?
Draft
The answer is it should start from parting surface. Draft must fall away from the parting lines on ALL vertical faces in the plastic part. The widest point on the part is thus the parting line. The location of parting line and subsequent application of draft to the plastic part are design decisions that affect both the aesthetics and functionality of the part. These decisions should be made before the part is sent to the mold maker if time to market is critical.
Industrial designers want 0.0 degrees, mold designers want 45.0 degrees…. Use the adjacent write up as a guide.
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0.0 degree: Very small details under 0.040in tall that will get polished. The act of polishing will apply some draft. Faces to be 100% relieved with side actions. 1/4 degree: Emergency use only. Deep ribs, one internal side of a box where the other sides have good draft, bosses ejected by sleeves. 1/2 degree: Use sparingly and for good reason. Ribs, one internal side of a box, snaps, hooks, etc.. 1.0 degree: Standard draft, all features. 2.0 degree: Standard draft, very light texture, cavity side to ensure good release. 3.0 degree: Textured faces, faces that are in common with a shutoff.
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Design Consideration
Draft to Assembly Parts
Draft
Point to remember
Part mismatch due to improper draft
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Design Consideration
Importance of draft to the CAD model
Draft
-The failure to apply draft to a CAD file before sending it to the mold maker forces the mold designer to guess about what the part designer intended. Frequently the mold designer does not even know what your part is. -Time is consumed by someone unfamiliar with your parts applying draft arbitrarily without knowledge of your mating parts, sheet metal or components.
Designers who can't draft your parts you are costing your company time and money and should get a job doing something that you CAN do.
-Frequently your mold designer is using a different CAD package and if he sends back a drafted model, it may be difficult for you to do a good interference analysis. -Many toolers will simply slap some draft on and if the parts don't fit, its your problem. -When the mold is finished and your parts don't fit, time is lost reworking the tool.
Once you understand the basics of draft and shutoffs it is very simple to apply these to your model and save time to market. If you still have questions, get the Mold Designer to review your parts before tooling release.
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Design Guidelines
Design Guidelines 1. Use uniform wall thickness throughout the part. This will minimize sinking, warping, residual stresses, and improve mold fill and cycle times. 2.Use generous radius at all corners. The inside corner radius should be a minimum of one material thickness.
Much is written regarding design guidelines in latter slides. Yet, the design guidelines can be summed up in just a few design rules.
3.Use the least thickness compliant with the process, material, or product design requirements. Using the least wall thickness for the process ensures rapid cooling, short cycle times, and minimum shot weight. All these result in the least possible part cost. 4.Use ribs or gussets to improve part stiffness in bending. This avoids the use of thick section to achieve the same, thereby saving on part weight, material costs, and cycle time costs. 5.Design parts to facilitate easy withdrawal from the mold by providing draft (taper) in the direction of mold opening or closing.
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Design Guidelines
Wall thickness The typical plastic part may be considered to have a shell type configuration with a basic surface and features which are attached to it to meet functional requirements.
The actual determination of the wall thickness is based on a number of considerations. From a cost standpoint, the thinnest wall utilizes the least material and results in the fastest molding cycles
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1.Application Requirements Structural requirements including strength, impact, fatigue or deflection. 2. Moldability The size of the part and the ability of the material to fill the furthest point can determine the minimum wall
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Design Guidelines
Influence of wall thickness
Wall thickness
•Part characteristics •Mechanical performance •Cosmetic appearance •Mouldability •Economy Giving wall thickness should be carefully considered in the design stage to avoid expansive mold modifications and molding problems in productions The optimum thickness is often a balance between opposing tendencies, like:
Strength Vs Weight Durability Vs Cost
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Design Guidelines Wall thickness
Avoid designs with thin areas surrounded by thick perimeter sections as they are prone to gas entrapment problems
Maintain uniform nominal wall thickness through out the part
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Design Guidelines
Avoid sudden wall thickness variation that result in filling from thin to thick sections:
Wall thickness
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Design Guidelines
Core or redesign thick areas to create a more uniform wall thickness
Wall thickness
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Design Guidelines
Wall Thickness Design for Stiffness:
Wall thickness
Corrugation Corrugations can add stiffness to non cosmetic parts
Curved Side Walls Adding curvature to the sidewalls enhances stiffness and appearance
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Design Guidelines
Wall Thickness Design for Stiffness:
Wall thickness
Flexible
Stiffer
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Design Guidelines
Radius
Radius
Sharp corners greatly increase the stress concentration. This high amount of stress concentration can often lead to failure of plastic parts.
High molded in stresses Poor flow characteristics Reduced mechanical properties Increased tool wear Surface appearance problems, (especially with blends). Crack due to Stress
Uniform cooling Less warpage Less flow resistance Easier filling Lower stress concentration Less notch sensitivity.
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No Crack due to Radius
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Design Guidelines
What radius should you give?
Radius
Standard tables for stress concentration factors are available and should be consulted for critical applications.
As can be seen from the above chart, the stress concentration factor is quite high for R/T values less than 0.5. For values of R/T over 0.5 the stress concentration factor gets lower.
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Design Guidelines Radius
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Radius should be •Radius should be between 50% of the nominal wall thickness. •If the part has a load bearing function then the upper end is recommended. •A minimum radius of 0.5mm is suggested and all sharp corners should be broken with at least a 0.125 mm radius.
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Design Guidelines
Internal and external radii should originate from the same point
Radius
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Design Guidelines Ribs
Ribs Ribs increase the bending stiffness of a part. Without ribs, the thickness has to be increased to increase the bending stiffness. Adding ribs increases the moment of inertia, which increases the bending stiffness.
Functions of Ribs 1. The rib gives stiffness and strength in molded part without increasing overall wall thickness. 2. Locating and captivating components of an assembly. 3. Providing alignment in matting parts. 4. Acting as stops or guide for mechanisms
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Design Guidelines
Rib design issues
Ribs
•Thickness •Height •Location •Quantity •Moldability Consider these issues carefully when designing ribs
Proper Rib Design reduces the defects
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Design Guidelines
Rib thickness
Ribs
Many factors go into determining the appropriate rib thickness. Because thick ribs often cause sink and cosmetic problems on the opposite surface of the wall. If rib thickness is a constraint but not the cosmetic
Offset Rib to reduce Sink
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Design Guidelines
If rib thickness is a not a constraint but cosmetic
Ribs
1. The rib thickness should be less than the wall thickness 2. The thickness ranges from 40 to 60 % of the material thickness as per 66% rule 3. The rib should be attached to the base with .125 X thickness radius at the corners and .5 degree draft should be given for ejection,
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Design Guidelines
What is the 66% rule ?
Ribs
The divine 66% rule for ribs The thickness of ribs should never exceed 66% of the nominal wall thickness. If your ribs never exceed 50-66% of nominal wall thickness you will never have a problem with sink.
Sometimes you can get away with 66% to 75% of nominal wall, but it is risky. Don't do it unless you absolutely have to. If you do, be certain that the area gets better than average plastic flow.
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Design Guidelines
What happens if you ignore the 66% rule ?
Ribs
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Design Guidelines
Rib height
Ribs
Maximum rib height should not exceed 3 times the nominal wall thickness as deep ribs become difficult to fill and may stick in the mold during ejection.
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Design Guidelines
Effect of 1/8 rib on 1/4 thickness part
Ribs
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Design Guidelines
Rib location
Ribs
The rib location is based on providing maximum bending stiffness. Depending on orientation of the bending load, with respect to the part geometry, ribs oriented one way increase stiffness. If oriented the wrong way there is no increase in stiffness.
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Design Guidelines
Rib location
Ribs
Another issue to be considered If air is trapped, it will compress and create a burn mark on the rib, which probably won’t fill anyway. The best solution is to try to locate your ribs into the side walls or other features to help convey the plastic and air through the part. Another solution is to transition to a projection from the base wall with a gusset or ramped rib.
Rib A will trap air in the top corner Rib B has a better transition to the base wall. Rib C is the best since it's tied into the side wall.
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Design Guidelines
Rib quantity
Ribs
Multiple Ribs are better than one thick rib or one tall rib
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Design Guidelines
Rib mouldability
Ribs
Ribs are preferably designed parallel to the melt flow as flow across ribs can result in a branched flow leading to trapped gas or hesitation. Hesitation can increase internal stresses and short shots.
Position ribs in the line of flow to improve filling and prevent air entrapment.
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l Mo
l ow F d
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Design Guidelines
Rib design for stiffness
Ribs
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Design Guidelines
Now you know the standards of rib designing. Implement it with the help of these steps for better results.
Ribs
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Design Guidelines Holes
Holes Holes also are a major design element, The location of any holes may significantly affect the part's overall strength. Trying to create a hole in the side of a part is especially challenging, and the need for side holes should be minimized in the initial design. The functions of the holes 1. The holes are given in molded parts to accommodate rivets or pins. 2. Locating and captivating components of an assembly. 3. Providing alignment in matting parts.
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Design Guidelines Holes
Hole spacing The minimum spacing between two holes or between a hole and side wall should be one diameter.
Hole location Holes should be located three diameter or more from the edge of the part to avoid excessive stress.
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Design Guidelines
Blind holes
Holes
The depth of a blind hole should not exceed 3 times the diameter. For diameters less than 5 mm this ratio should be reduced to 2. Core pins supported by just one side of the mold tool create blind holes. The length of the pins, and therefore the depth of the holes, are limited by the ability of the core pin to withstand any deflection imposed on it by the melt during the injection phase.
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Design Guidelines
Blind holes
Holes
For blind holes the thickness of the bottom should be greater than 20% of the hole diameter in order to eliminate surface defects on the opposite surface. A better design is to ensure the wall thickness remains uniform and there are no sharp corners where stress concentrations can occur.
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Design Guidelines
Through holes
Holes
With through holes the cores can be longer as the opposite side of the mold cavity can support them.For through holes the length of a given size core can be twice that of a blind hole.
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Design Guidelines
Through holes
Holes
An alternative is to use a split core fixed in both halves of the mold that have a gap equal to wall thickness.
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Design Guidelines
Through holes
Holes
Another alternative is to use a split core fixed in both halves of the mold that interlock when the mold is closed.
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Design Guidelines
Through holes
Holes
In cases where even longer cores are required, careful tool design is necessary to ensure balanced pressure distribution on the core during filling to limit deflection. Doing this the core mismatch can be reduced
Incorrect
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Correct
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Design Guidelines
Bosses
Boss
Bosses are used for the purpose of registration of mating parts or for attaching fasteners such as screws or accepting threaded inserts (molded-in, press-fitted, ultrasonically or thermally inserted).
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Design Guidelines
The divine 66% rule for bosses
Boss
The thickness of boss wall should never exceed 66% of the nominal wall thickness Ideal Design
Bad Design
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Design Guidelines
Boss design standards
Boss
Nominal boss wall thickness less than 66% nominal wall thickness,
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Design Guidelines
Boss design standards
Boss
The boss height should be 3 times of the wall thickness.
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Design Guidelines
Boss design standards
Boss
The outer diameter should be within 2 to 2.4 times of internal diameter
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Design Guidelines
Boss design standards
Boss
A minimum radius of 25% the nominal wall thickness or 0.4 mm at the base of the boss is recommended to reduce stresses.
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Design Guidelines
Boss design standards
Boss
The core pin should be given a radius (min 0.25 mm) to reduce material turbulence during filling and to help keep stresses to a minimum.
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Design Guidelines
Boss design standards
Boss
A minimum draft of 0.5 degrees is required on the outside dimension and inside also (if required) of the boss to ensure release from the mold on ejection.
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Design Guidelines
Boss design standards
Boss
Greater wall sections for increased strength will increase molded-in stresses and result in sink marks. So use this method.
A recess around the base of a thick boss reduces sink.
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Design Guidelines
Boss design standards
Boss
Bosses located at corners can result in very thick walls causing sinks. Bosses can be isolated using the techniques illustrated.
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Design Guidelines
Boss design standards
Boss
Alternative boss design can be used for bosses near a standing wall.
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Design Guidelines
Strengthening a Boss
Boss
The boss can be strengthened by gussets at the base
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Design Guidelines
Strengthening a Boss
Boss
The boss can be strengthened by attaching it to nearby walls with connecting ribs.
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Design Guidelines
Rib design
Boss
Avoid bosses that merge into side walls by connecting ribs for support.
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Design Guidelines
Rib design
Boss
A minimum distance of twice the nominal wall thickness should be used for determining the spacing between bosses. If placed too close together thin areas that are hard to cool will be created. These will in turn affect quality and productivity..
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Design Guidelines
Failure of boss
Boss
Failures of a boss are usually attributable to: 1. Knit lines -these are cold lines of flow meeting at the boss from opposite sides, causing weak bonds. These can split easily when stress is applied.
Knit lines should be relocated away from the boss, if possible. If not possible, then a supporting gusset should be added near the knit line.
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Design Guidelines
Failure of boss
Boss
Failures of a boss are usually attributable to: 2. High hoop stresses caused because of too much interference of the internal diameter with the insert (or screw).
Hoop stresses are imposed on the boss walls by press fitting or otherwise inserting inserts.
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Design Guidelines
Mating of bosses
Boss
Excessively long bosses can often be replaced by two shorter bosses
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Design Guidelines
Gussets
Gussets
Gussets can be considered as a subset of ribs and the guidelines that apply to ribs are also valid for gussets. This type of support is used to reinforce corners, side walls, and bosses.
The height of the gusset can be up to 95% of the height of the boss or rib it is attached to. Depending on the height of the rib being supported gussets may be more than 4 times the nominal wall thickness. Gusset base length is typically twice the nominal wall thickness. These values optimize the effectiveness of the gusset and the ease of molding and ejecting the part.
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Design Guidelines
Gusset design
Gussets
Avoid sharp corners in your gusset design.
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Design Guidelines
Design for Manufacturability and Assembly (DFM/A)
DFM/A
Design for Manufacturability and Assembly (DFM/A) is a very broad topic covering many areas. Regardless, it can best be defined as any tool or process that helps a designer or engineer think about, and therefore avoid, manufacturing and assembly problems down the road. The design of plastic parts is good discipline for the application of DFM/A principles because designers must be in tune with all the factors that can cause a flawed design
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Design Guidelines
Design for ease of assembly
DFM/A
Simplify design and assembly so that the assembly process is unambiguous.
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Design Guidelines
Assembly alignment
DFM/A
Simplify design and assembly that can be easily aligned.
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Design Guidelines
Poka Yoke (Fail Proof design)
DFM/A
Components should be designed so that they can only be assembled in one way; they cannot be reversed. Roll pins, dowel pins or offset mounting holes can be employed.
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Design Guidelines
Design for orientation
DFM/A
Design for components orientation and handling to minimize non-value-added manual effort, ambiguity or difficulty in orienting and merging parts. Basic principles to facilitate parts handling and orienting are: •Parts must be designed to consistently orient themselves. Examples are dowel pins. •Product design must avoid parts that can become tangled, wedged or disoriented. •With hidden features that require a particular orientation, provide an external feature, guide surface or design alignment fixturing or tooling to correctly orient the part. •Design in fasteners large enough that are easy to handle and install
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Design Guidelines
Design Lettering for assembly
DFM/A
Base assembly component should have some sort of visual indicatives like lettering or embossing to show where other parts is to be assembled.
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Design Guidelines
Design for efficient joining and fastening
DFM/A
Threaded fasteners (screws, bolts, nuts and washers) can be time-consuming to assemble. Consider design alternatives that will reduce fastener count. Snap fits are very useful because they eliminate screws, clips, adhesives, or other joining methods. The snaps are molded into the product, so additional parts are not needed to join them together.
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Design Guidelines
Snap fit assembly
DFM/A Snap design
Use of snap-fit assemblies can deliver many benefits: •An integral element of the plastic part – no other components •Can replace screws, nuts, and washers •Easy automation can reduce assembly costs •No other fasteners, adhesives, solvents, welding, or special equipment •Design can minimize risk of improper assembly •Can be designed to engage and disengage Things To Be Aware of When Using Snap-Fits: •Some designs may require more complex or expensive tooling •Snap-fits that are assembled under stress will creep •It is difficult to design snap-fits with hermetic seals. If the beam or ledge relaxes, it could decrease the effectiveness of the seal. •Can be damaged by mishandling and abuse prior to assembly
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Design Guidelines
Types of Snap fits
DFM/A Snap design
Annular Snap Fit
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An annular snap is defined as involving a locator pair or the entire mating part-base part system they will constrain in more then one degree of motion.
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Design Guidelines
Types of Snap fits
DFM/A Snap design
Cantilever Snap Fit
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The Cantilever Snap design is the most popular when assembling two plastic parts. A cantilever beam snap-fit assembly consists of a cantilever beam with an overhang at the end of the beam.
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Design Guidelines
Types of Snap fits
DFM/A Snap design
Torsional Snap Fit
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A Torsional snap fit involves primarily torsional deflection for assembly although there is often some bending in the system as well. The torsional member is not necessarily round; they can be round or flat. A torsional snap fit is relatively uncommon but are useful as an alternative to the cantilever, the most used snap-fit, when clearances or access make the hook location for assembly difficult.
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Building
a New Electric World
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