1. MANUFACTURING PROCESSES 5/27/2018 5/27/2018 1
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2. 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

3. Each of the three process families – shaping, joining, and surface treatment – has its own set of characteristic attributes
One process attribute applies to all three families – compatibility with material

4. There are limits to the size of a component that a process can make

5. Along with mass, there is a limiting value for section thickness that a given shaping process can handle

6. 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 too early solidification

7. Upper limits to size are set by problems of shrinkage
The outer layer of a casting or molding solidifies first, giving it a rigid skin
When the interior solidifies, the change in volume can distort the product or crack the skin
Keeping section thickness and cross-section uniform reduce the chances of differential shrinkage

8. Metal shaping processes such as rolling, forging, or extrusion involve flow – solid metals flow by plastic deformation or creep
The minimum thickness that can be achieved from these processes is limited by plastic flow
Very thin sections cause substantial friction forces and stick to the tools, even at very large pressures

9. 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

11. Measure of the irregularities of a surface specified as an
Tolerance
Dimension y specified
as y = 100 ± 0.1 mm
Roughness
Measure of the irregularities
of a surface specified as an
upper limit such
as R < 100 μm

13. Processing costs for precision and surface finish increase exponentially as the requirements are made more severe

14. Important joining-specific considerations are:
the geometry of the joint,
the thickness of the material they can handle,
the way the joint will be loaded

15. The most important finishing-specific attribute is the function of the treatment
Functions can range from protection, performance enhancement, or can be primarily aesthetic (for beauty)

16. The manufacture of a component consumes resources, each of which has an associated cost
The final cost is the sum of those of the resources it consumes

17. Material: material cost and mass per unit;
f is the scrap fraction for unused material
Tooling: cost is dedicated and written off for
production of n units; nt represents life of tool
in case replacement is necessary
Capital: non-dedicated cost; written off against time
for a given hourly rate; t wo is the write-off time, L is
the load factor, and ń is the production rate
Overhead: gross overhead costs divided by the
production rate

18. The most economical process for a part depends on the production size
At small batch sizes the unit cost is dominated by the ‘fixed’ costs of tooling
As batch size increases, the variable costs of material, labor, and other overhead become dominant

19. Each process has a range of batch sizes for which
it is likely to be economically competitive

20. Much of a cost model relies on user-defined parameters
Approximate values are used for cost modeling in computer based modeling
Default values can be replaced if more accurate data is available

23. Figure 18.21
Three process groups for ceramics, each able to handle the required shape, mass, section thickness, tolerance, and roughness
Constraint on economic batch size indicates
powder methods as the preferred choice

24. Screening the material, mass, and section thickness leads to three possible process: machining, injection molding, and compression molding
All three processes
can provide the proper
surface quality, but
a batch size of 50,000
is not economical
for machining

25. If a shaping process does not produce the required
Figure 18.22
If a shaping process does not produce the required
surface quality, a surface treatment process can
be used in addition if the combined processes are
more economical than a satisfactory single process
For the con-rod,
forging and
powder methods
do not provide
adequate tolerance
and roughness
values – following
with precision
machining would
satisfy the design
requirements

26. The final choice of process for the con-rod will be based on cost
Figure 18.23
The final choice of process for the con-rod will be based on cost
Based on a batch size of 10,000, forging is the cheapest process – as forging is likely to be followed by a machining process, the cost difference between forging and die casting is insignificant

27. SUMMARY Selecting a process involves 3 steps:
Translation of requirements
Screening of the possible options
Ranking of the processes
Further investigation of the ranked processes by detailed examination of the documentation is then performed.