1. 4. Extrusions Brief introduction
Compression forming process in which the work metal is forced to flow through a die opening to produce a desired cross‑sectional shape
Process is similar to squeezing toothpaste out of a toothpaste tube
In general, extrusion is used to produce long parts of uniform cross-sections
Can be hot or cold
Hot – steels
Cold –soft metals

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

3. Extrusion Process Direct – Indirect –
Hydrostatic – billet is smaller in diameter than chamber and fluid pressure forces billet by a ram
Side (lateral) – extrusion forced at right angle to billet

4. Schematic illustration of the direct extrusion process.

5. Types of extrusion: (a) indirect; (b) hydrostatic; (c) lateral.

6. Metal Flow in Extrusion
Elongated grain structure
Can test with grid test

7. Types of metal flow in extruding with square dies
Types of metal flow in extruding with square dies. (a) Flow pattern obtained at low friction, or in indirect extrusion. (b) Pattern obtained with high friction at the billet-chamber interfaces. (c) Pattern obtained at high friction, or with cooling of the outer regions of the billet in the chamber. This type of pattern, observed in metals whose strength increases rapidly with decreasing temperature, leads to a defect known as pipe, or extrusion defect.

8. Extrusion-Die Configurations
(b)
(c)
Typical extrusion-die configurations: (a) die for nonferrous metals; (b) die for ferrous metals; (c) die for T-shaped extrusion

9. Hot Extrusion
Dies can be preheated to reduce wear and to reduce cooling of the billet
Oxide film can form so a dummy block smaller in diameter is placed ahead of ram
Square dies used for non-ferrous metals
Work piece has high plasticity and low deformation resistance
Used for parts with big sizes and high strength

10. Cold Extrusion Improved mechanical properties by work hardening
Good dimensionals
Improved surface finish
Elimination of billet heating
Competitive production rates
High stresses on tooling

11. Two examples of cold extrusion
Two examples of cold extrusion. Thin arrows indicate the direction of metal flow during extrusion.

12. Production steps for a cold extruded spark plug.
A cross-section of the metal part above, showing the grain flow pattern.

13. (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. (b)-(d) Components of various dies for extruding intricate hollow shapes.

14. Poor and good examples of cross-sections to be extruded
Poor and good examples of cross-sections to be extruded. Note the importance of eliminating sharp corners and of keeping section thicknesses uniform.

15. Impact Extrusion
Punch descends rapidly on the blank and extruded backward
Collapsible tubes
Thin walled parts

16. Impact Extrusion
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.

17. (a) Two examples of products made by impact extrusion
(a) Two examples of products made by impact extrusion. These parts may also be made by casting, by forging, or by machining; the choice of process depends on the dimensions and the materials involved and on the properties desired. Economic considerations are also important in final process selection. (b) and (c) Impact extrusion of a collapsible tube by the Hooker process.

18. Hydrostatic Extrusion
No container wall friction
High pressure
Defects can be reduced by fluid-to-fluid extrusion
Vegetable oils used at room temperature
Waxes, polymers, glass used for high temp
Limited use due to complex tooling, high pressures, special equipment, and long cycle times

19. Extrusion Defects Surface cracking Pipe Internal cracking
Temperature, friction, or speed too high
Sticking along die land
Pipe
Impurities drawn toward center of billet
Can be minimized by controlling flow and by eliminating impurities
Internal cracking
Tensile stresses
Increases with increased impurities
Decreases with increased extrusion ratio and friction

20. (a)
(a) Chevron cracking (central burst) in extruded round steel bars. Unless the products are inspected, such internal defects may remain undetected, and later cause failure of the part in service. This defect can also develop in the drawing of rod, of wire, and of tubes.

21. Extrusion Equipment Horizontal hydraulic press
Can control stroke and speed
Vertical can be used for cold extrusion

22. General view of a 9-MN (1000-ton) hydraulic-extrusion press.

23. 5. Drawing Brief introduction
Cross-section of wire or rod reduced by pulling through die
Limit is 63% reduction in cross section
Shapes such as flat strips can be drawn

24. Process variables in wire drawing
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.

25. 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).

26. Drawing Practice
Speeds of ft/min for heavy to 10,00 ft/min for thin
Reduction of 0-45%
Bundling – drawing many wires simultaneously
Material is usually tool steel or carbide
Wet drawing – completely immersed in lube
Dry drawing – surface of rod coated

27. Die for Round Drawing
Terminology of a typical die used for drawing round rod or wire.

28. Schematic illustration of roll straightening of a drawn round rod

29. 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.

30. Two views of a multistage wire-drawing machine that is typically used in the making of copper wire for electrical wiring

31. Questions
What are some of the attractive features of the cold extrusion process?
What is the unique capabilities and special limitations of hydrostatic extrusion?

32. 6. Sheet metalworking Brief introduction Cold-working
The starting stock is sheet metal
Higher deformation forces
Closer dimensional tolerances
Increased strength
High production rate
High die cost for small quantities

33. Sheet metal process
Shearing
Bending
Drawing
Sheet metal forming

34. Shearing
Mechanical cutting of materials without the formation of chips or the use of burning or melting.
Shearing process
Sheared edges
Burr
Break
Burnished land
Roll over

35. Sheared edge improvement
Clamping the starting stock firmly against the die
Maintaining proper clearance and alignment between the punch and the die
Restraining the movement of the workpiece
Simple shearing
Sheets of metal are sheared along a straight line
Shear angle is often used to reduce shear force on larger shear

36. Piercing and blanking Die design
Shearing operations where the shear blades are closed
In piercing, the punch-out piece is the scrap and the remaining strip is the workpiece.
In blanking, the piece being punched out becomes the workpiece and the remaining strip is the scrap.
Die design
The punch should fit within the die with a clearance between 5% to 7% of the stock thickness.
Punches and dies should be in proper alignment so that a uniform clearance is maintained.

37. Bending
The plastic deformation of metals about a linear axis with little or no change in the surface area.
Bending process
The metal on the outside is stretched while that on the inside is compressed.
The location that is neither stretched nor compressed is neutral axis.
The outside surface undertakes the maximum tensile stress

38. Bend radius Springback
The smaller the bend radius, the larger the deformation
Should be as large as possible to permit easier forming and wider variety of engineering materials
Springback
Elastic recovery occurs when the bending load is removed
The yield strength of the metal and the bending radius are involved in the amount of springback
The metal must be overbent by an amount equal to the subsequent springback

39. Design of bending The smallest bend radius
The metal is formed without cracking
The value is dependent on both the ductility and the thickness of the metal sheet
The process must provide springback compensation when the bend radius is greater than four times of the material thickness
The bend axis should perpendicular to the direction of grain flow

40. Drawing (sheet metal drawing)
The forming of closed-bottom cylindrical or rectangular containers from metal sheet
Drawing process
Shallow drawing and deep drawing
Shallow drawing The depth of the product is less than its diameter
Deep drawing The depth of the product is greater than the diameter

41. Trimming of drawn parts
Drawing defects
Wrinkle and tear
Can be limited by multiple operations when deep drawing parts are made
Trimming of drawn parts
Establish both the size and uniformity of the final part

42. Sheet metal forming Embossing Bulging Flanging
A pressworking process in which raised lettering or other designs are impressed in sheet material
Very shallow drawing operation where the depth of the draw is limited to one to three times the thickness of the metal
Bulging
Locally expand a metal blank or tube outward against a split die
Flanging
Flanges are rolled on sheet metal

43. Superplastic sheet forming
Metals achieve tensile elongations as high as 2000 to 3000%
Ultrafine-grain-size, low strain rates and elevated temperatures are required
Can be used to form material into large, complex-shaped products with compound curves by single operation
Can be extrusion, drawing, forging, etc.
The major limitation is the long cycle times

44. Questions
What is springback? What determines the amount of springback in bending?
What factors determine the smallest bend radius for materials?
What measures can be employed to improve the quality of a sheared edge?
What is the purpose of having a shear angle on a punch?
What is the major limitation of the superplastic forming of sheet metal? What are some of the attractive features?