Under Graduate Course on
Mach Machin inee Design Design-I -I Design of Machine Elements Dr. S. S. Roy Assistant Professor Robotics & A.I Lab. (RAIL) Department of Mechanical Engineering
1/18/2012
1
Reference Books 1.
V.B. .B. Bhan Bhand dari, ari, “Design of Machine Elements ”, Elements ”, , >, Tata McGraw McGraw Hill.
2.
J.E. J.E. Shig Shigle ley, y, C.R. C.R. Misc Mischk hke, e, “Mechanical Engineering Design ”, ”, Tata McGraw McGraw Hill.
3.
M.F. Spotts Spotts & T.E. T.E. Shoup, Shoup, “Desig “Design n of Machin Machine e Elements” Elements”,, Pearson Pearson Educa Education tion..
Machine Design Handbook 1.
“ Design Design Data”, Data”, Compiled Compiled by Faculty Faculty of Mechani Mechanical cal Enginee Engineering, ring, PSG PSG Colleg College, e, Coimbator Coimbatoree
2.
“ CMTI CMTI Hand Hand Book”, Book”, Compiled by by Scientists Scientists of Centra Centrall Manufac Manufacturing turing technology technology Institute Institute,, Bangal Bangalore ore
1/18/2012
2
1
Design of Machine Element Gear Drive
Pressure vessel
Clutch IC engine parts
C-frame
Brake
Coupling Spring
Bearing
Belt, Rope, chain Drive
Connecting rod Power Screw
Cam
Shaft & Axle
Key Cotter & Knuckle Joint
Riveted Joint
Welded Join t
Bolted Joint
1/18/2012
3
Introduction Design is the process of problem solving Design is a decision making process Design is an iterative process Design is an innovative or creative process
Machine Design
In Mechanical Engineering Objective of a Designer is to design & develop a product (devices, machinery, mechanical system) or process that is functional, safe, reliable, usable, manufacturable, competitive & marketable by using different engineering tools [ like Mathematics, CAD-CAE etc .] 1/18/2012
4
2
Mechanical Design Energy Stem Mechanical Engineering Systems Structures & Motion Stem Energy Stem in Mechanical Engineering
Design of heat exchangers Design of IC engines Design of boilers Design of air compressors, gas turbine etc…
They rely on the use of technical materials from thermodynamics, heat transfer, combustion etc.
Structures & Motion Stem in mechanical Engineering Design of gear box Design of belt drive, chain drive system Design of suspension systems Design of machine structure etc…
They draw on technical materials from solid mechanics, kinematics, dynamics etc. Mechanical design applies to d esign in mechanical engineering systems where both stems can be involved Machine Design is a sub-set of mechanical design where the focus is on Structur es & Motion stem only 1/18/2012
5
Mechanical Engineering Design/ Machine Design the use of scientific principles, technical information, skill & imagination in the description of configuration of a mechanical system/ machine to perform specific functions with maximum economy & efficiency Designer
uses principles of basic engineering sciences has technical information of basic elements of machine like fasteners,
gear, belt drive, bearing etc. - Relative advantages & disadvantages of basic elements & their suitability in different applications. uses skill & imagination to produce a configuration, which is a
combination of basic elements. - Intellectual part of constructing a proper configuration iscreative in nature
1/18/2012
6
3
Machine Design Kinematic Link
transfers Motion
Mechanism transforms
Kinematic Pair
Primary Objectives
Kinematic Chain
One link fixed
Mechanism
transfers
Machine
Energy
Machine
Machine Tool
transforms
All Machines are Mechanism but all Mechanisms are not Machine
All Machine Tools are Machine but all Machines are not Machine Tool
Mechanism
Machine
-
-
-
1/18/2012
assemblage of resistant bodies, connected by joints, to form a kinematic chain with one link fixed & having the purpose of transmitting & transforming motion. Combination of resisting bodies having definite motions & capable of performing useful work. Combination of resistant bodies with successfully constrained relative motions which is used to transform, transmit & modify available energy to do some useful work
7
Machine Design Design Design Analysis
Inputs
Mechanism
Design Synthesis decision –making process Outputs
is given
Given Configuration, material & assume mode of failure
determines the dimension
process of creating new
configuration/ mechanism Selecting optimum/best
configuration from no. of existing mechanism Selecting materials from no. of
alternative materials Determination of optimum shape
& dimensions of the component on the basis of design analysis
1/18/2012
8
4
Type of Design Adaptive Design - This is based existing design.
Developmental Design on
- Existing standard product or systems with/ without minor modification, are adapted for a new application.
- Starts with an existing design, but the final product may differ quite markedly from the original product. - A new model of a car
New Design
- This is an entirely new one but based on existing scientific principles. - Needs lot of r esearch, technical ability & creative thinking.
1/18/2012
9
Type of Design based on Methods Rational Design
- This depends upon mathematical f ormulae of mechanics. - This is based on determining the stresses and strains of components and thereby deciding their dimensions.
1/18/2012
Empirical Design
Industrial Design
- This is based on empirical formulae which in turn is based on experience and experiments.
- These are based on industrial considerations and norms viz. market survey, external look, production facilities, low cost, use of existing standard products.
10
5
Manufacturer
General Procedur e in Machine Design
Customer
Identification of Need Problem definition, Design specification Collecting relevant design information & feasibility study Design Conceptualization/ Preliminary design i.e. Mechanism synthesis
Design Synthesis
Modeling & Simulation Engineering Analysis CAD/CAE
Design Analysis
Design Optimization Design Evaluation Detail Design of Components Design Communication & Documentation 1/18/2012
11
Basic Procedure of Design of Machine Element Specify functions of element Determine forces acting on element Select suitable material for element Determine failure mode (s) of element Determine geometric dimensions of element based on above failure mode Check & modify dimensions for assembly & manufacture Check design at criti cal cross-sections Prepare detail engineering drawing of element 1/18/2012
12
6
Basic Requirements of Machine Elements Broad objective of designing a machine element is to ensure that it preserves its operating capacity during the stipulated service life with minimum manufacturing & operating costs. In order to achieve these objectives, the machine element should satisfy following basic requirements.
Strength
- should have sufficient strength to avoid failure (fracture/ general yielding) due to force.
Rigidity
- should not deflect or bend beyond permissible limit due to forces/moments.
Wear Resistance
- Machine components like gear, cam should have sufficient wear resistance. Wear leads to the loss of accuracy, puts the part out of order.
Minimum Dimensions & Weight Manufacturability
- Machine part should be sufficiently strong, rigid & wear resistant & at the same time, with minimum possible dimensions & weight.
- ease of fabrication & assembly. - shape & material of the m/c part should be selected in such a way that it can be produced with minimum manufacturing cost
1/18/2012
13
Basic Requirements of Machine Elements Safety
- shapes & dimensions of the machine parts should ensure safety to the user/operator.
Reliability
- is probability that a machine part will performits intended functions under desired operating conditions over a specified period of time. - machine part should be reliable i.e. it should perform its function satisfactorily over its lifetime.
Maintainability
Conformance to Standards
- ease with which a machine part can be serviced or repaired. - machine part should be maintainable
- machine part should confirm to the National or International standard.
Minimum Life Cycle cost
1/18/2012
- Total cost to be paid by the purchaser for purchasing the part and operating & maintaining it over its life span. 14
7
“ Standards ” in Machine Design Standardization
Standardization is defined as obligatory norms, to which various characteristics of a product should conform. The characteristics include materials, dimensions and shape of the component, method of testing and method of marking, packing and storing of the product.
Standard Standard is defined as a set of specifications for parts, materials or processes Purpose of Standard
to reduce the variety & limit the no. of items to a reasonable level
Code Code is defined as a set of specifications for the analysis, design, manufacture, testing and erection of the product
Purpose of Code
to achieve a specified level of safety
1/18/2012
15
“ Standards ” in Machine Design Advantages of Standardization The
reduction in types & dimensions of identical components, to a rational number, makes it possible to manufacture the standard component on mass scale in a centralized process.
Standard parts are easy to replace when worn out due to interchangeability. The application of standard machine elements & especially the standard units reduce the time &
effort needed to design a new machine. Standardization results in substantial saving in Designer’s effort The standards of specifications & testing procedures of machine elements improve their quality &
reliability. In designing, the aim is to use as many standard components as possible for a given machine Company Standards
Types of Standards
National Standards
I.S / B.I.S B.S A.I.S.I / S.A.E D.I.N
India UK USA German
International Standards 1/18/2012
16
8
“ Standards ” in Machine Design Indian Standards in Mechanical Engineering Design SP 46
Bureau of Indian Standards on “Engineering Drawing Practice for Schools & Colleges
I.S. 210
Seven grades of grey cast iron
I.S. 1570
Chemical composition of various grades of alloy steel
I.S. 733 : 1983
Mechanical Properties of wrought Al. & Al alloy Bars, Rods for general purposes
I.S. 736 : 1986
Mechanical Properties of wrought Al. & Al alloy Plates for general purposes
I.S. 919
Recommendations for Limits & Fits for Engineering
I.S. 2709
Guide for selection of fits
I.S. 8000
Geometrical tolerancing on technical drawings
I.S. 4218 : 1996
Designation & Dimension of screw threads, bolts & nuts
1/18/2012
17
Preferred Numbers When a machine is to be made in several sizes with different powers or capacities, it is necessary to
decide what capacities will cover a certain range efficiently with minimum number of sizes. For example, a company want to manufacture six different models of electric motors ranging from 1.0
HP to 105 HP to cater to the need of different customers. Preferred numbers are used to specify the ‘sizes’ of the product in these cases.
French Engineer Charles Renard first introduced Preferred Numbers in the 19th century.
The system is based on the use of geometric progression to develop a set of numbers.
Basic series
Common Ratio
% increase in steps
Preferred Numbers [in between 1 to 10]
R 5 series
101/5
1.58
58%
1.0, 1.6, 2.5, 4.0, 6.3, 10.0
R 10 series
101/10
1.26
26%
1.0, 1.25, 1.6, 2.0, 2.5, 3.15, 4.0, 5.0, 6.3, 8.0,10.0
R 20 series
101/20
1.12
12%
1.0,1.12,1.25,1.4,1.6,1.8,2.0,2.24,2.5,2.8,3.15,3.55,4.0,4.5,5.0,5.6,6.3,7.1,8.0,9.0,10.0
R 40 series
101/40
1.06
6%
1.0,1.06,1.12,1.18,1.25,1.32,1.4,1.5,1.6, ……………………………………, 10.0
R 80 series
101/80
1.03
3%
1.0,1.03, 1.06,1.09, 1.12,1.16, 1.18, 1.21,1.25,1.29,1.32,1.36,1.4,…..1.6, ………, 10.0
1/18/2012
18
9
Aesthetic Considerations in Machine Design When there are a number of products in the market, having the same qualities of efficiency, durability and cost, the customer will naturally attracted towards the most appealing product. The external appearance is an important feature, which not only gives grace and luster to the product but also dominates the sale in market.
Automobiles
Industrial Design
Household Appliances
Audio Visual Equipments
The job of an Industrial Designer is to create new forms & shapes, which are aesthetically pleasing.
The external appearance of the products is a cumulative effects of number of factors : Form
Step Stream
Colour
Surface finish & Tolerances
Materials
Manufacturing Methods
Taper Shear Sculpture
Relationship between Functional requirement & Appearance of the Product
In many cases, functional requirements result in shapes, which are aesthetically pleasing. The evolution of the streamlined shape of the boeingis the result of studies in aerodynamics for effortless speed. Chromium plating on the household appliances is for corrosion resistance rather than for pleasing appearance 1/18/2012
19
Ergonomic Considerations in Machine Design Ergonomics is defined as the relationship between Man & Machine and the application of anatomical, physiological and psychological principles to solve the problems arising from Man-Machine relationship.
Topics of Ergonomic studies in Machine Design
Anatomical factors in design of driver’s seat.
Layout of instrument dials & display panels for accurate perception by the operators
Design of hand levers & hand wheels.
Ergonomists have carried out experiments to determine the best dimensions of driver’s seat, the most convenient hand or foot pressure or dimensions of levers and hand wheels.
1/18/2012
20
10
Manufacturing Considerations in Machine Design Design Consid erations of Castings General Principles : Round all external corners All
sections in a casting should be designed of uniform thickness, as far as possible. If variation is unavoidable, it should be done gradually
Avoid very thin section : Minimum thickness for CI component in sand casting is about 6 mm. The cast components should be designed in such a way that it will require a simpler pattern &
its mouldingis easier.
In designing a casting, the various allowances must be provided in making a pattern.
The casting should be designed as simple as possible,
but with a good appearance.
1/18/2012
21
Design Considerations of Machined Components Machining is basically secondary & finishing manufacturing process. Dimensional Accuracy Geometric / Form Accuracy
Surface finish
Dimensional Tolerance Geometric Tolerance Surface roughness
General Principles : Avoid sharp corners Avoid too many shoulders & undercuts Avoid hard materials.
1/18/2012
22
11
Sequential Engineering Approach Vs. Sequential Design Process
Concurrent Engineering Approach
Prototype Development Stage
Customer
Marketing Department
Design Offic e Production Department
Sales & Service Department
1/18/2012
Sequential Engineering Approach
Concurrent Engineering
23
Vs. Concurrent Engineering Approach Concurrent Engineering is defined as the design process/approach that brings together a wide spectrum of expert/specialist from several functional areas (like R & D, Engineering, Manufacturing, Quality control, Marketing, sales & service etc.) during the early phases of the design process in new product development.
The team reviews the design from different aspects
1/18/2012
design for Manufacturing & Assembly (DFx)
quality assurance & standardization
aesthetics & ergonomics
maintenance
reliability & safety
process, facility, capacity planning
tool design
functional / performance testing
cost 24
12
Sequential Engineering Approach Vs. Concurrent Engineering App roach Concurrent Engineering
Any possible bottleneck/mistake is thoroughly studied & rectified. This results in small nos. of modification in the design at a later stage & reduce time interval from conceptual stage to marketing stage.
Customer’s requirement
Simultaneous Engineering Cross Functional Team Approach
Manufacturability Assembly & Testability
Parallel Engineering Cost, Sales & servicing
Design Engineering : Concurrent Engineering Approach
Ergonomics & Appearance
Reliability, Maintainability & safety
1/18/2012
25
1/18/2012
26
13
Motivation Most Economic
Requirements
Most Productive Improved Quality
Successful entry of a product into the market can best occur if it can complete the above cycle in the shortest possible time & at the lowest cost while maintaining very high product quality & reliability
CAD
Computer Aided Design
CAE
Computer Aided Engineering
CAM
Computer Aided Manufacturing
VP & VR
Virtual Prototyping & Virtual Reality
1/18/2012
27
Scope of CAD-CAM-CAE Design & Analysis Theories (FEM, CFD )
Automation Geometric Modeling
(Robot, FMS, CAPP )
CAD-CAM-CAE
Computer Graphics
1/18/2012
Manufacturing Process (RP&T, CNC)
28
14
CAD-CAM-CAE Software CAD/CAM/CAE software
Purpose
CATIA ( CATIA PLM Express ) 3-D modeling, Analysis & Simulation etc.
NX ( Siemens PLM ) PRO-ENGINEER SOLID WORKS SOLID EDGE INVENTOR Mechanical DESKTOP MasterCAM
3-D modeling & Manufacturing Simulation
SolidCAM SmartCAM
1/18/2012
29
CAD-CAE Software CAE software
Purpose
ADAMS
Multi-body dynamic analysis & simulation
SimDESIGNERMotion with CATIA
Multi-body dynamic analysis & simulation
Working Model
Multi-body dynamic analysis & simulation
ANSYS
Finite Element Analysis
NASTRAN
Finite Element Analysis
ABAQUS
Finite Element Analysis
LS-DYNA
Finite Element Analysis, Crash simulation
DEFORM
Finite Element Analysis, Crash simulation
PAMCRASH
Finite Element Analysis, Crash simulation
FLUENT
Computational Fluid Dynamics
Altair Hyper Mesh
Meshing for Finite Element Analysis
1/18/2012
30
15
Computational Tools Software MATLAB
Purpose Design calculation, dynamic analysis & simulation, design optimization, control
Mathematica MathCAD
Design calculation
Maple TK Solver Excel
1/18/2012
31
Assignment # 1 1. Explain with example, the different steps involved in m achine design process & in design of machine elements? What are the basic requirements of m achine elements? 2. Distinguish between design synthesis and design analysis. 3. What is Standardization & w hat are the advantages of standardization? Give examples of Indian s tandards for commonly used engineering materials. 4. What are preferred num bers? How many basi c series are used? What is R10 series? Develop R 10 series from 2 to 20. 5. What is an industrial design? What is the relationship between funct ional requirement and external appearance of the product. 6. Define ergonomics. What is the scope of ergonomics in machine design? 7. Distinguish between sequential design and concurr ent engineering.
Last date of submission : 08 th February, 2012
1/18/2012
32
16