1. EXTRUSION
Ch. 5

2. Extrusion
A compression forming process in which the work metal is forced to flow through a die opening to produce a desired cross-sectional shape.
Pros:
variety of sections possible (hot extrusion)
grain structure and strength enhancement (cold)
close tolerance (cold)
no material wastage.

3. EXTRUSIONS

4. STANDARD EXTRUSIONS

5. Extrusions
Figure Extrusions, and examples of products made by sectioning off extrusions.

6. Types of Extrusion Direct Extrusion Indirect Extrusion
The ram forces the work billet metal to move forward to pass through the die opening.
Indirect Extrusion
The die is mounted to the ram rather than at the opposite end of the extruder container housing.

7. Direct Extrusion
Figure Schematic illustration of the direct extrusion process.

8. Direct Extrusion Friction increases the extrusion force.
Hollow section is formed using a mandrel.

9. Indirect Extrusion
Figure Types of extrusion: (a) indirect; (b) hydrostatic; (c) lateral.

10. Indirect Extrusion
Metal is forced to flow through the die in an opposite direction to the ram’s motion.
Lower extrusion force as the work billet metal is not moving relative to the container wall.

11. Hydrostatic Extrusion

12. Hydrostatic Extrusion
Using hydrostatic system to reduce the friction and lower the power requirement.
Sealing is the major problem.

13. Ram Force
Variation of Ram Force with ram stroke and die angle.

14. Lateral Extrusion

15. Extrusion-Die Configurations
(b)
(c)
Figure Typical extrusion-die configurations: (a) die for nonferrous metals; (b) die for ferrous metals; (c) die for T-shaped extrusion, made of hot-work die steel and used with molten glass as a lubricant.

16. Hydraulic-Extrusion Press
Figure General view of a 9-MN (1000-ton) hydraulic-extrusion press.

17. Extrusion Equipment

18. EXTRUSION

19. EXTRUSION

20. Cross-Sections to be Extruded
Figure Poor and good examples of cross-sections to be extruded. Note the importance of eliminating sharp corners and of keeping section thicknesses uniform. Source: J. G. Bralla (ed.); Handbook of Product Design for Manufacturing. New York: McGraw-Hill Publishing Company, Used with permission.

21. Components for Extruding Hollow Shapes
Figure (a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders. This part is 8 mm (5/16 in.) thick and is sawed from the extrusion (see Fig. 15.2). (b)-(d) Components of various dies for extruding intricate hollow shapes. Source: for (b)-(d): K. Laue and H. Stenger, Extrusion--Processes, Machinery, Tooling. American Society for Metals, Metals Park, Ohio, Used with permission.

22. Extrusion Processes Hot extrusion Cold extrusion
Keeping the processing temperature to above the re-crystalline temperature. Reducing the ram force, increasing the ram speed, and reduction of grain flow characteristics. Controlling the cooling is a problem. Glass may be used as a lubricant.
Cold extrusion
Often used to produce discrete parts. Increase strength due to strain hardening, close tolerances, improved surface finish, absence of oxide layer and high production rates.

23. Extrusion Temperature Ranges for Various Metals

24. Extrusion Defects
a) Centre-burst: internal crack due to excessive tensile stress at the centre possibly because of high die angle, low extrusion ratio.
b) Piping: sink hole at the end of billet under direct extrusion.
c) Surface cracking: High part temperature due to low extrusion speed and high strain rates.

25. Process Variables in Direct Extrusion
Figure Process variables in direct extrusion. The die angle, reduction in cross-section, extrusion speed, billet temperature, and lubrication all affect the extrusion pressure.

26. Extrusion Analysis Extrusion ratio, Assuming all sections
are circular, ideal
deformation, no friction,
no redundant work:
Ram pressure
Taking into account friction,
where a =0.8 and b =1.2 to 1.5.

27. Extrusion Analysis
For direct extrusion, additional pressure, pf, required by the extruder to overcome the wall friction is related as follows:
For the worst case that the friction shear stress at the wall equals to the shear yield strength of the work metal:
The additional pressure:
The total ram pressure:
The power required:

28. Extrusion Dies
For the case of non-circular extruded section, a shape factor has to be introduced:
where Kx = shape factor
Cx = perimeter of the non-circular extruded section
Co = perimeter of a circle that has the same cross- sectional area as the extruded section.
For direct extrusion, the extrusion force

29. Impact Extrusion
Impact extrusion is performed at higher speeds and shorter strokes than conventional extrusion.
It is for making discrete parts.
For making thin wall-thickness items by permitting large deformation at high speed.

30. Impact Extrusion
Figure Schematic illustration of the impact-extrusion process. The extruded parts are stripped by the use of a stripper plate, because they tend to stick to the punch.

31. Impact Extrusion
Forward
backward
combination

32. Examples of Cold Extrusion
Figure Two examples of cold extrusion. Thin arrows indicate the direction of metal flow during extrusion.

33. Examples of Impact Extrusion
Figure (a) Two examples of products made by impact extrusion. (b) and (c) Impact extrusion of a collapsible tube by the Hooker process.

34. Cold Extruded Spark Plug
Figure Production steps for a cold extruded spark plug.
Figure A cross-section of the metal part in Fig , showing the grain flow pattern.

35. Factors Influencing the Forces
Friction
Material Properties
Reduction In Area
Speed
Temperature
Geometry Of The Die

36. WIRE DRAWING

37. WIRE DRAWING

38. WIRE DRAWING

39. WIRE DRAWING

40. Process Variables in Wire Drawing
Figure Process variables in wire drawing. The die angle, the reduction in cross-sectional area per pass, the speed of drawing, the temperature, and the lubrication all affect the drawing force, F.

41. Draw Dies
Approach angle about 6 to 20
Back relief angle about 30

42. Die for Round Drawing
Figure Terminology of a typical die used for drawing round rod or wire.
Figure Tungsten- carbide die insert in a steel casing. Diamond dies, used in drawing thin wire, are encased in a similar manner.

43. Die Materials Overview
Tungsten Carbide:
Lowest cost, shock resistance, ease of production, large sizes available.
Lower life expectancy.
Natural Diamonds:
Wear resistance, gives excellent wire surface, high thermal conductivity, longer life expectancy
Susceptible to fractures from shock or wear, limited availability in required high quality and quantity, constantly escalating price.
Synthetic Single Crystal:
Consistently uniform material, gives excellent wire surface, high thermal conductivity, predictable wear schedule, uniform wear pattern gives longer life expectancy.
Larger size ranges are still costly at this time.
Polycrystalline Diamond:
Excels in life expectancy, wear resistance of diamond, shock resistance of carbide, high availability, cost effectiveness
Higher drawing force, smaller fines requires more filtration, may be damaged by temperatures above 700ºC, wire surface condition less than from natural diamond.

44. Examples of Tube-Drawing Operations
Figure Examples of tube-drawing operations, with and without an internal mandrel. Note that a variety of diameters and wall thicknesses can be produced from the same initial tube stock (which has been made by other processes).

48. Drawing Equipment Good dimensional control Good surface finish
Improved mechanical properties
economic for mass production

49. Cold Drawing
Figure Cold drawing of an extruded channel on a draw bench, to reduce its cross-section. Individual lengths of straight rod or of cross-sections are drawn by this method. Source: Courtesy of The Babcock and Wilcox Company, Tubular Products Division.

50. Multistage Wire-Drawing
Figure Two views of a multistage wire-drawing machine that is typically used in the making of copper wire for electrical wiring. Source: H. Auerswald.

51. Roll Straightening
Figure Schematic illustration of roll straightening of a drawn round rod (see also Fig. 13.7).

52. Wire and Bar Drawing
Reducing the cross section of a bar, rod or wire by pulling it through a die.
Bar drawing is generally in a batch mode while the wire drawing is in general in a continuous mode.

53. Fig. 5.2 Stress and strain development in wire and rod drawing processAf Ao ε
ε =
ln(Ao/Af)
s pd σ
Stresses and drawing pressure variation in deformation zone.
Drawing
die angle α
Drawing die
(deformation zone) 2 3 1 pd
Effective strain variation in deformation zone.
Fig. 5.2 Stress and strain development in wire and rod drawing process

54. Fig. 5.4 Stresses and drawing pressure for maximum reduction of area.
s pd=K/(n+1)e n+1
s* s=Ke n
e* e
Fig. 5.4 Stresses and drawing pressure for maximum reduction of area.

55. Mechanics of Drawing Area reduction in drawing ; Draft
No friction and true strain
The ideal stress
Taking into account friction and die angle,
where , ,
The drawing force

56. Maximum Reduction
Assume perfectly plastic material (n=0), no friction, no redundant work,
Then
The maximum possible area ratio
The maximum possible reduction