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MATERIAL SCIENCE LECTURE SERIES
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Lecture 31: Processes and Process
Selection
Jayant Jain Assistant Professor,
Department of Applied Mechanics, IIT Delhi, Hauz Khas, 110016
Classification of processes
There are mainly three broad classes of manufacturing processes 1) Shaping 2) Joining and 3) Finishing
Note the shaping can further be divided into primary and secondary shaping processes Primary: creates shapes Secondary: modify shapes and properties
Classifying processes
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Similar to what we did for materials here we do a classification of
processes
Shaping family is expanded, each member is characterized by
a set of attributes, process selection involves matching of these
with design requirements
Classifying processes
Classifying processes
Depending on the type of process the attributes can be significantly different
Pictorial view of various key processes
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
Primary Shaping
Secondary Processes
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
Joining
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
Surface Treatment
Process Selection Flow Chart
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
The selection strategy for processes is similar to that for materials
Design requirements should be put
in terms of constraints and objectives to be used to screen, rank,
and finally select an appropriate process
Translation of process requirements
*Process chain option: may combine two or more processes to get the job done e.g. casting followed by machining
Selection Charts: Charts obtained by displaying
the process attributes
Why do we need them?? Required for screening!
Design constraints can be applied on process-selection charts to identify or to screen out the processes that meets the requirements
Similar to materials property charts, shape selection charts one can show the process selection charts Each process is characterised by set of attributes. Each attribute can be displayed as simple matrices or bar charts They provide the selection tool that we need for screening
Process-selection charts/matrix
Material Process Compatibility
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
Each of the three process families shaping, joining, and surface treatment has its own set of characteristic attributes
Diagonal alignment of process Red dot indicates that the pair are compatible
Do you envisage any problem in the current representation?? In my opinion the resolution of these charts is very limited e.g. It tells me for metals, welding is compatible. This is very vague statement For a particular metal may be a particular welding method might be good
Shape
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
A key attribute of a process is the families of shapes it can make there are three
generic classes of shape, each subdivided in two
Shape-Process Compatibility
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
Process-size chart
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
There are limits to the size of a component that a process can make: Size can be measured by mass
Processes that can make small size components
Processes that can make large size components
Inclusion of joining allows simple process chains to be explored
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
Along with mass, there is a limiting value for section thickness that a given shaping
process can handle
Physical Limits to Size and Section Thickness
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
Take an example of Casting What factors limits its size (both lower and upper limit) Lower limit: surface tension forces and viscous forces Upper limit: shrinkage cavity, internal defects due to residual stresses
Physical Limits to Size and Section Thickness
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon
Casting and molding rely on material flow in the liquid or semi-liquid state
Lower limits on section thickness are imposed by the physics of flow flow of liquid metal or polymer into thin sections is opposed by surface tension and viscous forces loss of heat into the mold increases viscosity and may result in premature solidification
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