Lecture 31

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



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



Joining


Surface Treatment

Process Selection Flow Chart


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


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


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


Process-size chart


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


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


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


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

Documents

Lecture 31