1. David Ortegel Steven Neidigk Tim Ngo Jason Maestas
Group 9 3 / 1 / Ch. 15: Extrusion and Drawing of Metal Ch. 16: Sheet-Metal Forming Process
David Ortegel
Steven Neidigk
Tim Ngo
Jason Maestas

2. Extrusion and Drawing Of Metals
CHAPTER 15
Extrusion and Drawing Of
Metals

3. 15.1 Introduction Extrusion
Rooted From Latin Term “Extrudere”(To Force out).
A Cylindrical Billet is Forced Through A Die
Same Concept as forming Play-Doe
Die Geometry remains constant throughout the operation
Forms a constant extruded cross-section
Aluminum, copper, Steel Magnesium, lead are the most common material used in the Extruding process

4. Products Made by Extrusions
Railings for Sliding Doors
Window Frames
Aluminum Ladders
Extrusions can be cut into desired lengths, allowing for discreet parts such to be produced as Gears, and Brackets

5. Economics of Extrusions
Extrusions can be economical for Large productions runs as well as short ones.
Tool cost is generally low
Manufactures are able to produce quantity because of the ability to cut individual parts from a single extrusion

6. Drawing
Drawing – Cross-sections of solid rod, wire, or tubing is reduced or changed in shape by pulling through a die.
Developed between AD
Used to from shafts, automobile components, spindles, fasteners.

7. Depending on the ductility pf the material used extrusions can be caries out various ways:
Cold Extrusion – Extrusion carried out a ambient temperature. Often combined with forging operations
Hot Extrusions – Extrusions carries out at elevated temperatures
Impact extrusion – punch is rapidly descends on billet material
Hydrostatic extrusion – pressure is applied by a piston through incompressible fluid medium surrounding the billet

8. 15.2 The Extrusion Process 3 Basics Types of Extrusion:
Direct or Forward Extrusion: A billet is placed in a chamber and forced hydraulically through a die by a ram. Fig a
Indirect Extrusion (Reverse, Inverted, Backward Extrusion): The Die Moves Toward the billet material. fig b

9. Hydrostatic Extrusion:
A Billet that is smaller that the chamber is used.
The Chamber is filled with a fluid. Pressure is then applied to the pressing stem
There is no friction to overcome

10. Variables Die Angle A ۪ – Initial cross-sectional Area
A – Final cross-sectional Area

11. k = Constant determined experimentally
Extrusion Force
The force required for extrusions
F = A*k*ln( A ۪ / A )
k = Constant determined experimentally
The force required depends on:
Strength of Billet Material
Extrusion Ratio: A ۪ /A
Friction between the billet material and the chamber
Temperature
Speed of the Ram
Type of lubricants used

12. Extrusion constant k for various metals at different temperature

13. Metal Flow
Flow patterns influence the quality and mechanical properties of the extruded product
Material flows longitudinally (ex. Fluid flowing in a channel)
The extruded product has a elongated grain structure

14. A common technique in investigating a flow is to section the round billet in half
Dead-Metal Zone – The corner of the material stays stationary. Bright finishes result due to material flowing past the die angle
Fig a – flow patterns attained with low friction
Fig b – flow patterns attained with high friction
Fig c – flow pattern attained with high friction or cooling of the billets outer regions in the chamber

15. 15.3 Hot Extrusion Extrusions carried out at elevated temperatures
Used for metals that do not have sufficient ductility at room temperature.
Used when wanting to reduce forces on billet material

16. Special Requirements
Due to excessive heat die wear becomes excessive and rapid cooling of the product after extrusion causes deformations.
Pre-heated dies prolong the life of the die done my hot forging. This also reduces rapid cooling if the material
Billet develops an oxide film. Oxides can result in a finished product that is unacceptable.
Placing a dummy block, a little smaller than the chamber ahead of the ram, results in a thin shell of the oxide layer left in the container.

17. Die Design Main types of die designs:
1) Square dies: Used in extruding nonferrous metals
- Develops dead metal zones that form the dies angle
2) Solid or Hollow Dies: Used in extruding tubing products
- The ram is fitted with a mandrel that pierces a hole in the billet
-Wall thickness is limited to 1 mm for aluminum. 3mm for stainless steels, 5mm to stainless steels

18. 3) Spider, porthole dies ,and bridge dies: Used in creating hollow cross-section extrusions
-Created by welding chamber methods
-Metal divides and flows around the supports for the internal mandrel
-The extruded strands become welded back together by the high internal pressure existing in the chamber
only suitable for aluminum and its alloys because of their capacity to create strong welds.

19. (a)
(b)
(c)

20. Die Materials Hot Worked dies Steels are used for hot extrusion
Coatings such as zirconia used to extend die life
Not suitable for dies used for complex shapes because of the sever stress gradients that develop in the die.

21. Lubrication
Lubrication Is important in hot extrusions because of major effects on:
Material flow
Surface finish on extrusion
Product quality
Extrusion forces

22. Sejournet process was developed in the 1940s uses Glass as a lubricant on high temperature steels.
A circular glass pad is placed in the chamber at the die entrance
The head conducted cause the glass to melt around the extruded product acting as a lubricant

23. Jacketing: also known as canning, uses softer and lower strength metals metals such as copper or a mild steel.
Used for materials that have a tendency to stick to the container and die
Also used or toxic and radioactive material. The jacket that is formed over the extruded material acts as a protected barrier

24. 15.4 Cold Extrusion
Developed in the 1940’s, are extrusion produced at ambient temperature.
Denotes combinations of operations, that consist of indirect extrusions and forgings

25. Cold extrusions are widely used
Automobile products
Appliances
Fasteners

26. Advantages cold extrusion has over hot extrusion
- Improved mechanical properties
- Control over dimensional tolerances
- Improved surface finishes
- production rates and cost are competitive
- magnitude of stress is extremely high

27. 15.5 Extrusion Defects
Surface Cracking: Cracking on billet materials occurs due to temperature, friction, punch speed.
High Temperatures
Crack from along the grain boundaries. Typically occur in aluminum, magnesium, zinc alloys
Cold Temperatures
Caused by sticking of billet material at the die land
Known has the “Bamboo Defect” because of its similar appearance to bamboo

28. Internal Cracking: Center of extruded product develops cracks.
Pipe: The metal-flow pattern tends to draw oxides and impurities toward the center of the billet
Internal Cracking: Center of extruded product develops cracks.
Attributed to a state of hydrostatic tinsel stress
Cracks increase with increasing die angle, impurities, and decreasing extrusion ratio and friction

29. 15.6 Extrusion Equipment
Basic horizontal press: Suitable because the stroke and speed of the press can be controlled
Vertical Hydraulic press: used for cold extrusions. Take up less floor space

30. 15.7 The Drawing Process
A long rod or wire is reduces or changes by pulling through a die called a “draw die”
Rod and wire is used in many applications such as drive shafts, machine and structural components, welding electrodes, spokes.

31. Drawing Force: used under ideal and frictionless conditions
F = YA * ln(A ۪ / A)
Y- average true stress
A ۪ – initial cross–sectional area
A – Final cross-sectional area

32. F = Y*A* [(1 + u/s) * ln(A ۪ / A) + (2/3)*s]
Drawing Force used under frictional forces:
F = Y*A* [(1 + u/s) * ln(A ۪ / A) + (2/3)*s]
S – Die angle in radians
U – Frictional forces

33. 15.8 Drawing Practice
Bundle Drawing: Drawing many wires simultaneously
Produces wire in polygonal cross-sections
Theses types of wire are cut into many shapes. Used in medical implant, electrically conductive material, filter media
Reduces cost of production by producing 100 or more.

34. Die Design: Die Materials: Die angles range from 6 -15 degrees
Die designs go through many period of trial and error
Die Materials:
Die are made out of typical tool steels and carbides
Cast steels are used for hot extrusions
Diamond dies are used for drawing extremely fine wire
Insert and nibs are used to support carbide and diamond dies because of their lack of tensile strength

35. Lubrication:
Proper lubrication is essential to improve die life and product surface finish
Particular in tube drawing, because of its difficulty to maintain for a thick lubrication film at the mandrel
Wet drawing – Dies and rod are completely immersed in lubricant
Dry Drawing – Rod is coated in a lubricant by passing through a box filled with lubricant

36. 15.9 Drawing Defect and residual Stresses
Typical defects in a drawn rod or wire are similar to extrusion
Internal Cracking with are longitudinal
Seam may open
Cold–drawn products have residual stresses, this causes stress-corrosion cracking over a period of time
Quality control becomes a major problem in drawn defects and residual stresses

37. 15.10 Drawing Equipment Draw Bench:
Contains a single die, design is long
Pulling for is supplied by a chain drive that is hydraulically activated

38. Rotating Drum:
Used in producing long rods and wires of smaller cross-sections less that 13mm
A large drum is rotated

39. Introduction We utilize sheet metal for products such as
Cans
Cookware
Appliances
Car bodies
Low carbon steel is the most commonly used sheet metal for its strength and formability
The most general sheet forming operations
Press working
Press forming

40. Shearing
Shearing metal is like punching holes in paper with a hole punch.
It can also be compared to using a cookie cutter
The punch must be harder and stronger that the metal being sheared

41. Shearing
Typical features of sheared edges are not smooth nor perpendicular to the cutting plane
Edge quality can be improved by increasing punch speed
Shearing is most commonly done with a punch and die

42. Shearing Having the correct between the punch and die is important
Too much and the sheared edge can become rough
Too little and tools can be damaged
Burr is a thin edge or ridge an the punched out piece of metal
Can be caused by dull tool edges
The size and shape of the burr can change subsequent forming operations

43. Shearing Operations
Die cutting- perforating, parting, notching, lancing
Parts produced by die cutting are commonly used in assembly with other components
Fine blanking- used to produce smooth and square edges
Nibbling- moves a small straight punch up an down rapidly into a die. One advantage of this technique is intricate slots and notches.

44. Shearing Operations
Slitting- a pair of circular blades follow a line or path cutting as they go.
much like a can opener
Scrap in shearing- The sheets of metal that are not used.
Can be as large as 30% of large stampings
Increases manufacturing cost

45. Shearing Operations
Tailor-Welded Blanks- Can be used of sheet metal with different shapes and thicknesses (often used in automotive industry)
Reduction in scrap
Eliminate need for subsequent spot welding
Better control of dimensions
Improved productivity

46. Punches and Dies Compound dies-Limited to simple shapes
Several operations on the same sheet may be performed in one stroke at one station with a compound die

47. Punches and Dies
Progressive dies- good for making parts that require multiple operations to produce
Use a series of punches
Other operations include
Laser beam cutting
Water-jet cutting
Friction sawing
Flame cutting

48. Sheet-Metal Characteristics and Formability
After a blank is cut into a sheet it is formed into various shapes
Elongation- Stretching the metal
High elongation is desirable for good formability
Yield-Point Elongation- Happens in low carbon steel and aluminum-magnesium alloys. Causes stretcher-strain marks, or worms
Elongations, depressions along the surface

49. Sheet-Metal Characteristics and Formability
Dent-Resistance of sheet metal- refers to the dynamic yield or yield stress under high rate of deformation
Ways to improve dent-resistance is to increase sheet thickness of decrease the metals elastic modulus

50. Formability Tests for Sheet-Metals
Formability- The ability to of the sheet-metal to undergo the desired shape without failure
May undergo two basic modes of deformation- stretching and drawing
Cupping Tests- earliest tests to determine formability
Erichsen test- Sheet clamped between two circular dies then a steel ball of round punch is forced into the sheet until it cracks

51. Formability Tests for Sheet-Metals
Forming Limit Diagrams- They are made by marking a flat sheet with a grid pattern of circles, then it is stretched over a punch. The deformation of the circles is measured in regions where the sheet has failed.
The information gathered from the test is then turned into a diagram.

52. Bending Sheets, Plates, Tubes
Bending is the most common industrial forming operation
Adds stiffness to the part without adding weight (car door panels)
Minimum bend allowance- refers to the radius at which a crack first appears at the outer fibers of a sheer being bent

53. Bending Sheets, Plates, Tubes
Bendability can be increased by heating the metal or by bending in a high-pressure environment.
Edge cracking can be decreased by minimizing cold working when the part is sheared.
Anisotropy of the metal is another important factor in bendability.
(a)
(b)

54. Bending Sheets, Plates, Tubes
Springback- when a sheet or tube recovers elastically when load is removed
Usually compensated for by overbending the part

55. Ch.16 Sections
– Miscellaneous Bending and Related Operations
– Deep Drawing
– Rubber Forming
– Spinning

56. 16.6 Miscellaneous Bending and Related Operations
Press-brake forming.
Bending in a four-slide machine.
Roll bending.
Beading.
Flanging.
Roll forming.
Tube bending and forming.
Dimpling, piercing, and flaring.
Bulging.
Stretch forming.

57. Press-brake forming.
Easily bends sheet metal or plates that are 7m (20ft) or longer, which is suitable for small production runs.
This machine uses long dies in a hydraulic press, to create an up and down motion to bend the metals.

58. Material of the die: Hardwood – used for low strength materials and small production runs; Carbides- used for strong and abrasive sheet materials and last longer than other dies. Carbon-steel and gray iron is the most commonly used.

59. Bending on a four-slide machine.
Uses dies to bend short pieces of metal into tubing and conduits, bushings, fasteners, and various machinery components.

60. Roll bending. Plates are bent using a set of rolls.
By adjusting the rolls various curvatures can be obtained.
The metals created can be use for boilers, cylindrical pressure vessel, and other curved structures.

61. Beading.
A technique utilizing the cavity of a die to bend the periphery of the sheet metal.
The purpose of the bead is to create stiffness and better appearance of the part and eliminates hazardous sharp edges.

62. Flanging.
A process of bending the edge of a sheet metal into a 90o angle.
Periphery wrinkling may occur in shrink flanging, due to excessive compressive hoop stress.
Periphery cracking may occur in stretch flanging, due to excessive tensile stress.

63. Dimpling, piercing, and flaring.
Dimpling is a type of flanging operation that punches a hole in the sheet metal and expanded into a flange with a shaped punch.

64. Roll forming.
Process where sheet metal strips are passed through consecutive set of rolls and bent in consecutive stages and then sheared into specific lengths and stacked continuously.
Sheet thickness: – 20mm(0.005–0.75 in.)
Forming speed: below 1.5 m/s (300 ft/min)
Examples: Door panels, picture frame, and gutters.

65. Tube bending and forming.
Several methods are implemented to prevent buckling and folding of the tubes, such as filling the tubes with sand or the use of mandrels.
Relatively thick tubes have a low tendency to buckle so it can be bent safely without the use of fillers.

66. Bulging.
Process involving the expansion of a poly-urethane plug within the tube, and once the punch retracts, the plug goes through elastic recovery.
Examples: coffee or water pitchers, beer barrels and bellows.

67. Stretch Forming
Process where a sheet metal is clamped along it’s edges and stretched over a male die (form die or form punch).
Examples: aircraft wing-skin panels, fuselages, and boat hulls.

68. 16.7 Deep Drawing Blanking Deep Drawing Redrawing Ironing Doming
Earing
Necking
Seaming

69. Process in Manufacturing an Aluminum Can

70. Deep Drawing
Process where a round sheet-metal blank is placed over a circular die and is held in place with a blank-holder, which is then forced downward into a die cavity by a punch; forming a cup.

71. Redrawing
Operations used to redraw containers that are too difficult to draw in one operation.
Ironing
If clearance between the punch and the die is sufficiently large, the drawn cup will have thicker walls at its rim than its base.
The thickness can be controlled by ironing, a process which the drawn cup is pushed through one or more ironing rings

72. Earing
A phenomenon where the edges of cups become wavy during the drawing process.
The ears have to be trimmed off since it serves no useful purpose and interferes with further processing of the cup.
Earing is caused by planar anisotropy of the sheet.

73. Hemming and Seaming Hemming Seaming Sheet metal is folded over itself.
Increases stiffness, improves appearance and eliminates sharp edges.
Seaming
Joining two edges of sheet metal by hemming.
Double seaming.

74. 16.8 Rubber Forming Rubber Forming
One of the dies in the set is made of polyurethane membrane, which is a type of flexible material.
Polyurethane is resistant to abrasion, cutting or tearing by the metal, and has a long fatigue life.

75. 16.9 Spinning Conventional Spinning
Process where a circular piece of sheet metal is placed and held against a mandrel and rotated while a rigid tool deforms and shapes the material over the mandrel.
May be performed at room temperature or at higher temperature for thicker metal.

76. Sheer spinning
Also called power spinning, flow turning, hydrospinning, and spin forging.
Process used to create axisymmetric conical or curvilinear shape, reducing the sheet’s thickness while maintaining its maximum diameter.
Applications: Rocket motor casings and missile nose cones.

77. Tube Spinning
The process where cylindrical blanks are reduced or shaped by spinning them on a solid, round mandrel using rollers.
Applications: Rocket, missile, and jet engine parts, pressure vessels, and car and truck wheels.

78. Diffusion Bonding/Superplastic Forming
Figure Types of structures made by diffusion bonding and superplastic forming of sheet metal. Such structures have a high stiffness-to-weight ratio. Source: Rockwell International Corp.

79. Specialized Forming Processes
Explosive forming
Magnetic-pulse forming
Peen forming
Laser forming
Microforming
Electrohydraulic forming

80. Explosive forming
First used to form metals in the 1900’s. A sheet metal blank is clamped over a die, and the entire assembly is lowered into a tank filled with water. The air in the cavity is evacuated, and an explosive is detonated at a certain height above.

81. Magnetic-pulse forming
Also called electromagnetic forming. Energy stored in a capacitor bank is discharged rapidly through a magnetic coil. Magnetic field crosses metal tube (conductor) creating eddy currents which have an opposing magnetic field.
(b)
(a)
Figure (a) Schematic illustration of the magnetic-pulse forming process used to form a tube over a plug. (b) Aluminum tube collapsed over a hexagonal plug by the magnetic-pulse forming process.

82. Other forming processes
Peen forming – A cast-iron or steel shot is discharged from a rotating wheel or by an air-blast from a nozzle. It is used for complex curvatures on thin sheet metals.
Laser forming – Laser beams are directed in certain regions causing thermal stresses , which are high enough to cause localized plastic deformation of the sheet.
Microforming – More recently developed for very small metallic parts and components. Typical components made include small shafts for micromotors, springs, screws, and a variety of cold-headed, extruded, bent, embossed, coined, punched, or deep-drawn parts.
Electrohydraulic forming – Also called underwater spark or electric discharge forming. In this process, the source of energy comes from a spark between two electrodes connected by a thin wire.

83. Manufacturing of Metal Honeycomb Structures
Figure Methods of manufacturing honeycomb structures: (a) Expansion process; (b) Corrugation process; (c) Assembling a honeycomb structure into a laminate.

84. Design Considerations in Sheet-Metal Forming
Blank design – Material scrap is the primary concern. Poorly designed parts will not nest properly.
Bending – Bending can cause material fractures or wrinkles. This is prevented with a flange, or relief notch which limit the stresses from bending. Do not put bends next to places with high-stress concentrations such as holes. A tab or ear can be used.
Stamping and progressive-die operations – Limit features so that tooling and machining costs are minimal. Narrow cuts and protrusions must be are also problematic.

85. Equipment for Sheet-Metal Forming
Type of forming operation, size and shape of the die, and tooling required.
Size and shape of workpiece.
Length of stroke, number of strokes per minute, operating speed, and shut height.
Number of slides.
Maximum force required.
Type of controls.
Safety features

86. Economics of Sheet-Forming Operations
Die and equipment cost
Labor and skill required
Time
Machining and tooling operations
Level of automation and computer control required

87. References http://www.amcastle.com/HTML/am_pr_alloy_tubing.html