CONTENTS: What is sand casting? .......................................................................................................2 The three primary casting processes……………………….…………………………...3 Pattern…………………………………………………………………………………….3 Sprues and Runners ..................................................................................................…... 4 Design considerations…………………………………...……………………………….5 Sand casting procedure………………………………………………………………….7 Procedure Photos……………………………………………………………..………….8 Mass properties………………………………………………………..………………..11 Calculation…………...………………………………………………………………….12 Conclusion…………………...………………………………………………………….13 Reference………………………………………………………………………………..15
What is Sand Casting? This technique is usually used for high production volume processes. Sand moulds are created using various materials, the sand must be bonded together using either synthetic compounds or clay and water and moulds must be rebuilt after each casting. The design of moulds is a very complicated process; however, in general, they are filled simply by gravity without the need for any pressure differentials or mechanical action. Casting is generally the quickest way to produce either a small amount pf prototypes or very production quantities. The casting process is used by almost every industry as all metal can be cast. Common mill forms such as bar and plate are product from cast metal. Sand casting is used to make large parts(typically Iron, but also Bronze, Brass, Aluminum). Molten metal is poured in to the mold cavity formed out of sand (natural or synthetic). The processes of sand casting are discussed in this section; include patterns, sprues and runners, design considerations, and casting allowance. Many casting processes use patterns that form the cavity of the mold and can be made of wood, plastic, or metal. Pattern which are expandable (consumed by the mold making process or by the poured metal during casting) are made of wax, plastic, or polystyrene foam. Patterns are oversized to make up for metal shrinkage as it solidifies. They will also have taper (Draft) to ease pattern release and make allowance for finishing and metal transfer through the mold. Cores are also needed to create any recesses, undercut, and hollows required in the part.
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The three primary casting processes are: •
Expandable mold/reusable pattern. The expandable mold/reusable pattern method includes the sand mold, plaster mold, and ceramic mold casting.
•
Expandable mold/expandable pattern. Expandable mold/expandable pattern method includes investment casting and evaporative-foam casting.
•
Permanent mold/ no pattern.
Pattern: The cavity in the sand is formed by using a pattern (an approximate duplicate of the real part), which are typically made out of wood, sometimes metal. The cavity is contained in an aggregate housed in a box called the flask. Core is a sand shape inserted into the mold to produce the internal features of the part such as holes or internal passages. Cores are placed in the cavity to form holes of the desired shapes. Core print is the region added to 3
the pattern, core, or mold that is used to locate and support the core within the mold. A riser is an extra void created in the mold to contain excessive molten material. The purpose of this is feed the molten metal to the mold cavity as the molten metal solidifies and shrinks, and thereby prevents voids in the main casting. In a two-part mold, which is typical of sand castings, the upper half, including the top half of the pattern, flask, and core is called cope and the lower half is called drag. The parting line or the parting surface is line or surface that separates the cope and drag. The drag is first filled partially with sand, and the core print, the cores, and the gating system are placed near the parting line. The cope is then assembled to the drag, and the sand is poured on the cope half, covering the pattern, core and the gating system. The sand is compacted by vibration and mechanical means. Next, the cope is removed from the drag, and the pattern is carefully removed. The object is to remove the pattern without breaking the mold cavity. This is facilitated by designing a draft, a slight angular offset from the vertical to the vertical surfaces of the pattern. This is usually a minimum of 1° or 1.5 mm (0.060 in), whichever is greater. The rougher the surface of the pattern, the more the draft to be provided.
Sprues and Runners: The molten material is poured in the pouring cup, which is part of the gating system that supplies the molten material to the mold cavity. The vertical part of the gating system connected to the pouring cup is the sprue, and the horizontal portion is called the runners and finally to the multiple points where it is introduced to the mold cavity called the gates. Additionally there are extensions to the gating system called vents that provide the path for the built up gases and the displaced air to vent to the atmosphere. The cavity is usually made oversize to allow for the metal contraction as it cools down to room temperature. This is achieved by making the pattern oversize. To account for shrinking, the pattern must be made oversize by these factors, on the average. These are linear factors and apply in each direction. These shrinkage allowance are only approximate, because the exact allowance is determined the shape and size of the casting.
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In addition, different parts of the casting might require a different shrinkage allowances and castings generally have a rough surface sometimes with surface impurities, and surface variations. A machining (finish) allowance is made for this type of defect.
Design considerations: Location of the parting line/plane. By properly locating the parting plane. The number of cores can be reduced. The gating can be made less elaborate. The material wasted can be reduced. The dimensional accuracy can be increased. Use of uniform thicknesses in a casting, where possible. Uniform thicknesses lead to uniform cooling and solidification. This leads to stress free and distortion free castings. Heavier sections cool more slowly, and may have shrinkage cavities, porosities and large grain structures. Voids, porosities and cracks can be sites of subsequent failures and should gestation be prevented by minimizing variations in cross sections. When uniform crosssections cannot be maintained, then changes in cross-sections must be gradual. A recommended way to achieve this is to use a transition radius of 1/3 of the thicker section and blend in the radius with a 15degree slope line.
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When two or more uniform sections intersect, they create a region of heavy crosssection, resulting in the problems mentioned earlier. One way to minimize this is to core the intersection by a hole, similar to a hub hole in a wheel with spokes.
When sections intersect to form continuous ribs, contraction occurs in opposite directions as the material cools down. This leads to a high stress area at the intersections, causing cracking immediately, or in service. The way to avoid this is to stagger the ribs and thereby maintain uniform cross-sections.
Large unsupported areas tend to warp, so they should be avoided.
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Sand Casting Procedure:
2. The cope and drag are then 1. The pattern first makes an impression in the cope and drag.
combined and are ready to accept the metal.
The impression created includes the gating system as
3. The metal is heated and prepared metallurgic ally. It is transferred to a crucible just before pouring.
5. The part is allowed to sit and
4. The molten metal is then poured into the mold.
6. The casting is then sent to the
cool. Once cooled the casting and
finishing department where any
gating system are removed from
remains of the gates are ground
the mold and the sand is
off.
recycled.
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7.
The part is the cleaned and ready
to ship.
Procedure Photos: Main Part (pattern):
Core’s sand preparation:
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Mold making:
Pouring:
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Cleaning:
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Mass properties: Mass properties of casting drawing ( Part Configuration - Default ) Output coordinate System: -- default -Density = 0.00 grams per cubic millimeter Mass = 18.70 grams Volume = 18700.06 cubic millimeters Surface area = 15050.22 square millimeters Center of mass: (millimeters) X = 0.00 Y = -2.80 Z = 0.00 Principal axes of inertia and principal moments of inertia: (grams * square millimeters) Taken at the center of mass. Ix = (0.00, 1.00, 0.00) Px = 4461.49 Iy = (-1.00, 0.00, -0.00) Py = 14488.47 Iz = (-0.00, 0.00, 1.00) Pz = 16603.46 Moments of inertia: (grams * square millimeters) Taken at the center of mass and aligned with the output coordinate system. Lxx = 14488.47 Lxy = 0.00 Lxz = 0.04 Lyx = 0.00 Lyy = 4461.49Lyz = 0.00 Lzx = 0.04 Lzy = 0.00 Lzz = 16603.46 Moments of inertia: (grams * square millimeters) Taken at the output coordinate system. Ixx = 14634.90 Ixy = 0.00 Ixz = 0.04 Iyx = 0.00 Iyy = 4461.49 Iyz = 0.00 Izx = 0.04 Izy = 0.00 Izz = 16749.89
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Calculation: Some important equations in pouring:
Velocity of the liquid metal at the base of the sprue: v = 2.g .h
v=
2.( 9.81 m / s 2 ).( 0.03534 m) = 0.83268889
m/s
Volumetric flow rate: Q = v. A
Q = (0.000914415 ).( 0.83268889 ) = 7.614182 x10 −4 m 3 / s
Mold filling time: MFT = V / Q
MFT = 0.83268889 /( 7.614182 x10 −4 ) = 1093 .6 sec ond
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CONCLUSION: In this report we have tried to explain our casting project.We discussed our casting process in this report,also we put some solidwork and autocad drawings about our part. As a first step we choosed our casting part ,and then we made a core for sand casting.After we finished making core ,we started to doing sandmold .Step by step we made our mold.First of all we sieved the sand and then we hardened the sand with water. After these steps we prepare our mold .And then we molt metal ,and we poured the molten metal in our sand mold.When we finished our casting and opened the mold. We saw some errors in our part,already our aim is not producing excelent parts.Our aim is just analysing the errors in our casted part . When we are doing our core we did some error because of this errors we haven’t got enough place between core and mold so we have empty surface in our product.
Because of the wrong riser and runner calculations we have some shrinkage problem.And again because of the this calculation error we found wrong solidification time value so we have misrun problem.We have some desıgn fault ,we used 3 riser so we losed metal.If we use 2 riser and runner we lose lower metal then using 3 risers and runner . As a conclusion we can say that we saw our mistakes ,we analysed our errors and we finished our casting project.
Casting Drawing:
Reference: http://www.world-aluminium.org/production/processing/casting.html. http://www.efunda.com/processes/metal_processing/permanent_mold.cfm. http://www.efunda.com/processes/metal_processing/sand_casting_design.cfm. http://www.mccannsales.com/book/sandcasting.pdf. http://me.emu.edu.tr/majid/ME%20364/ME364_casting_overview.PDF