1. EPT 221 Engineering Design
Manufacturing Process Selection

2. Objectives of Lecture
Differentiate and select primary, secondary , and tertiary processes
Understand and apply methods to select appropriate manufacturing processes
Estimate the costs of manufacturing a product.

3. How would we manufacture a mountain bike ?
Handle Bar
Top
Tube
Seat
Post
Saddle
Fork
Rear Brake
Down
Tube
Front Brake
Rear
Derailleur
Pedal
(Courtesy of Trek Bicycle, 2002)

4. Manufacturing process decisions
How do we choose the specific manufacturing processes?
How do the selected materials influence the choice of manufacturing processes?
Would product function or performance issues influence our choice of processes?
What criteria should we use to select processes?
Which criteria are more important?
Who will make the final decisions?

5. Parts undergo sequence of processes
Changes?
Parts undergo sequence of processes
Primary - alter the (“raw”) material’s basic shape or form.
Sand casting
Rolling
Forging
Sheet metalworking
Secondary - add or remove geometric features from the basic forms
Machining of a brake drum casting (flat surfaces)
Drilling/punching of refrigerator housings (sheet metal)
Trimming of injection molded part flash
 Tertiary - surface treatments
Polishing
Painting
Heat-treating
Joining

6. Part / Mfg. Process Considerations
1. Production Volume
2. Part Size (overall)
3. Shape Capability (features)/ geometric complexity
boss/depression 1D
boss/depression >1D
holes
undercuts (int./ext.)
uniform walls
cross sections - uniform/regular
rotational symmetry
captured cavities

7. Types of manufacturing processes
How is the input material changed?

8. Bulk Deformation
To change the shape or form of bulk material caused by compressive or tensile yielding.
Rolling
Extrusion
Drawing
Forging

9. Rolling
Two or more cylindrical rollers plastically compress material, forming sheets, bars and rods.
Hot rolling requires less work but an oxidized surface finish
Cold rolling requires more work but increases the yield strength of the material and produces superior surface finish.

10. Rolling
slab
bloom
billet
sheet
coil
bar
rod
structural
ingot

11. Extrusion
Heated metal plastically yields as it is pushed through a die, producing long pieces with a constant cross-section.
Size: 40-foot in length
Economical production quantities: 1,000 to 100,000 pieces
Materials: ductile metals (e.g. aluminum, steel, zinc, copper, magnesium)
Ram
Cross
sections
Extrusion die
Billet

12. Drawing
Process of producing a wire, bar or tube by pulling on a material until it increases in length accompanied with a reduction in its cross-sectional diameter.
Size: bar size range 1/8 to 6 inches in cross-section, wire size range to 3/8 inches.
Material: ductile metals (e.g. aluminum, steel, copper)
Pulling force
Cross
sections
Drawing die
Billet

13. Forging (closed-die)
Blocked
preform
Gutter
Ram pressure
Flash
A process in which material is plastically compressed between 2 halves of a die set by hydraulic pressure or the stroke of a hammer.
Size: maximum size limit roughly 36 inches
Economic production quantity: 1,000 to 100,000 pieces

14. Casting Processes
The process in which molten metal is poured into a cast to solidify.
Sand casting
Die casting
Investment casting

15. Sand casting (closed-mold)
Core
Riser
Sprue
Runner
Drag
Flask
Cope
Gate
Parting
line
Uses sand mold. The mold is destroyed to remove the part.
Mold size ranges from inches to feet. (e.g. as mold cast for industrial engine blocks as large as 12 feet in cross section and 30 feet long)
Economical production quantity: very small i.e. 1 to 10
Material: all ferrous and nonferrous metals
Parts produced have a granular surface finish.

16. Die casting
Parting line
Plunger
Sprue
Moving die
Stationary die
Ejector pins
Molten
metal
Molten metal is injected under high pressure into permanent die set usually made of steel.
Die casting is faster than sand casting but can more expensive.
Smoother surface finish than sand-cast parts.
Size: maximum part size 30 x 30 inches to parts less than an inch.
Economic production quantity: over 10,000
Material: low-melting-point metals (e.g. aluminum, zinc, magnesium, brass)

17. Investment casting (lost wax casting)
Molten metal solidifies in a ceramic cast made by coating a wax pattern with liquid slurry, then dried.
Wax is melted out and ceramic mold is destroyed after part solidifies.
Material: alloy of aluminum, zinc, magnesium, brass, steel, stainless steel.
Economic production quantity: less than 10,000 pieces

18. Investment casting Ceramic mold (hardened slurry) 4-part pattern tree
Wax pattern
is cast
Wax removed
by melting
Molten metal solidifies in cast
Ceramic mold is removed

19. Polymer Processes
Part shapes are created by solidification of thermoplastic polymers or curing of thermosetting polymers.
Results in little waste of raw material and require few, if any, finishing operations
Compression molding
Transfer Molding
Blow molding
Injection molding

20. Compression molding
Charge
Heated mold
Part
Ram Pressure
Charge of thermoset or elastomer is formed between heated mold halves under pressure while the polymer cures.
Compression molds are simpler than injection molds (no sprue, runners, risers)
Size: minimum part size of the order of 1/8 to ¼ inch in cross-section
Economic production volume: more than 10,000 pieces

21. Transfer molding
Charge
Ram
Heated
mold
Sprue
Part
Ram pressure

22. Molten parison is extruded
Blow molding
Extruder
air injector
parison
Part is
removed
Air
blown
into
Mold halves
close
Molten parison is extruded

23. Blow moulding
A molten parison of thermoplastic material injected with air, then expands to the shape of the mold.
Is used to produce hollow parts within thin walls.
Size: maximum size of about 3 feet in diameter

24. Injection moulding
Thermoplastic pellets are melted and injected under high pressure into a metal mold.
Size: maximum part size less than 24 x 24 inches, minimum part size are of the order of 1/8 to ¼ inch in cross-section
Economic production quantity: more than 10,000

25. Sheet Metalworking
The permanent deformation of thin metal sheets by bending and shearing forces produced by mechanical or hydraulic forces.
Often called stamping forces.
Produces parts of moderate complexity.
Size: less than 24x24inches
Economic production quantity: more than 10,000
Material: alloys of steel and aluminum
Bending
Blanking
Drawing
Punching
Shearing
Spinning

26. Shearing : cutting or separating sheet metal along a straight line.
Blanking: shearing of a smaller, shaped piece, called a blank, from the stock.
Punching: produces slots, notches, extruded holes, and holes.
Embossing: forming plastic indentations to form ribs, beads, or lettering on the surface of metal.

27. Sheet metal drawing
Blank
Drawn part
Clamp
force
Blank holder
Die
Punch
Punch ram
Punch plastically deforms a blank sheet material into a die, forming cupped-, box-, or hollow-shaped parts
Products: soda cans, ammunition cartridge casings, and pots and pans.

28. Solidification processes
solid Part
molten material
freezing
Casting Processes
Sand Casting
Die Casting
Investment Casting
Centrifugal
Polymer Processes
Injection Molding
Blow Molding
ThermoForming
Compression Molding
Recall
Flow (voids, flash)
Cooling time (cycle time)
Temperature
Mold complexity
Warpage
Post processing
Costs (materials, tooling, processing)
considerations
Add to your notes

29. Machining
The removing of material from the workpiece by a sharp cutting tool that shears away chips of material to create a desired form or features.
It is a subtractive process that produces manufactured waste and can, therefore be expensive.
Often used as a secondary process to true-up critical dimensions or surfaces or to smooth the surface finish.
Often used for low-volume production.

30. Machining processes
ECM : electro chemical machining

31. Machining – removal of material…
Sawing –using a toothed blade.
Milling – from a flat surface by a rotating cutter tool.
Planing – using a translating cutter as workpiece feeds.
Shaping - from a translating workpiece using a stationary cutter.
Boring - increasing diameter of existing hole by rotating the workpiece.
Drilling- using a rotating bit forming a cylindrical hole.
Reaming – to refine the diameter of an existing hole.
Turning - from a rotating workpiece.
Facing - from turning workpiece using a radially fed tool.
Grinding - from a surface using an abrasive spinning wheel.
Electric discharge machining (EDM) - by means of a spark.

32. Machining process considerations
solid material
machining
material removed
sawing, turning, boring, milling,
drilling, grinding, ECM
Recall
hardness, strength of material
shear forces = strong jigs & fixtures
tool/bit wear, replacement
size of workpiece, fit machine?
volume removed
rate of removal, hp needed
tolerances
operator skill, CNC
costs (materials, tooling, processing)
considerations
Add to your notes

33. Finishing
Preparing the final surface for aesthetics and protection from the environment.
Cleaning: wire brushing is used to remove grit and scale, and chemical solutions, including acid baths, are used to remove oily films
Protection: polymers and ceramics requires little protection from the environment. Metals, however, require some surface treatment with oil-and-water based painting providing the least expensive coating. Steels are often plated with chrome, cadmium, or zinc). Aluminum alloys are usually anodized (a chemical surface treatment).

34. Finishing processes
protection?

35. Surface roughness

36. Assembly
The process of putting together all the components of a product before shipping.
Operation include handling, insertion, and/or attachment of parts.
Handling: grasping, moving, orienting, and placing parts, before insertion or attachment.
Attachment: either
- Permanent: welding, brazing, soldering, adhesive bonding, rivets, eyelets, staples, shrink fits, press fits, or
- Temporary: threaded fasteners such as screws, nuts and bolts, snap fits.

37. Assembly processes – fastening / joining of 2 or more components
permanent?

38. Process / Material Screening

39. Product function is interdependent
Material
Properties
Product
Function
Manufacturing
Processes
Product
Geometry

40. Are materials compatible with mfg. process?
Properties
Manufacturing
Processes
compatible
materials & processes

41. Material-Process Compatibility

42. Shape generation capability (of processes)

43. Manufacturing costs
Total Manufacturing Cost = Material + Tooling + Processing
raw mat’ls molds labor 
fixtures electricity
jigs supplies
tool bits O/H
(deprec.)
TMC = M T P

44. Material costs per part, cM
Let M = total materials costs (raw, bulk)
q = production quantity
Then material costs per part, cM is
cM = M/q = (cost/weight x weight) / number of parts
Let’s reorganize the variables in the equation above
cM = [cost/weight] [weight/number of parts]
= (cost/weight) (weight/part), and therefore
cM = cost/part

45. Material cost per part (continued)
Let
cw = material cost per unit weight, and
wp = weight of finished part
ww= weight of wasted material, scrap
 = ratio of wasted material weight / finished weight
= ww / wp
Then the material cost per part, cM is
cM = cw (wp + ww ) = cw (wp +  wp )
cM = cw wp (1+ )

46. Tooling cost per part, cT
Let
T= total cost of molds, fixtures per production run
q = number of parts per run
Then tooling cost per part, cT
cT= T/q
e.g. sand casting
cT = ($10,000/run) / (5000 parts/run) = $2.00/part

47. Processing cost per part, cP
Let
ct = cost per hour, (machine rate + labor)
t = cycle time (hours per part)
then cP = ct t
e.g. sand casting
cP = ($30/hr) (0.3 hrs/part) = $9/part
Processing cost: labor, energy, floor space, machine usage
Cycle time: time needed to make a part

48. Total cost per part Cost per part, c = cM + cT + cP
c = cw wp (1+ ) + T/q + ct t (6.6)
e.g. sand casting
c = $ $ $9.00
c = $12.05 / part

49. Example
Assume that our company is considering making a part out of low-strength metals or thermoplastics. Three processes appear compatible with the required feature shapes: sand casting, injection, and machining. The marketing department estimates that the company should produce about 5,000 pieces. Data gathered to select the material and manufacturing process are shown in the table below. Determine the cost per part.

50. Run quantity is important!
A-Sand casting B-Inj.Molding C-Machining

51. How can we lower the cost of parts?
c = cw wp (1+ ) + T/q + ct t (6.6)
      
purchase less expensive materials,
keep our finished part weight low
produce little manufactured waste
design simple parts that result in less expensive tooling
make many parts production run (i.e. batch)
choose a manufacturing process that has a low cycle time & cost per hour
Goal: minimize the sum of the terms!
(not any one term in particular)

52. Case Study- Aero engine

53. Summary Manufacturing process decisions Deformation processes
Casting processes
Sheet metalworking
Polymer processing
Machining
Finishing
Assembly
Material compatibilities / Process capabilities
Material costs, Tooling costs, Processing costs