Extrusion and Drawing Processes and Equipment

IE 3130 Material Processing

Module 3: Metal Extrusion and Drawing Processes and Equipment

Reading 1. Chap 15, Manufacturing Engineering & Technology, 6th Edition, Serope Kalpakjian & Steve Schmid Objective of this module Upon completion of class activity, lecture, and homework, student should be able to do the following: 1. Sketch and describe an open-die forging with simple tools and complex process sequences. 2. Describe Impression and closed-die forging with complex tools and simple process sequences. 3. Sketch and describe extrusion and drawing of wire, tube and shaped sections. 4. Estimate die pressure, force, and power requirement of forging, extrusion, drawing, and rolling processes. 5. List different processes of cutting parts for further working or immediate assembly. 6. Sketch and describe bending on presses or roll-forming lines. Extrusion

Extrusion – Latin root (Extrudere: to thrust out)

Initially non-steady state, then steady state process Hot extrusion of aluminum is capable of producing a large variety of often very complex shape, including multihole sections, gearing, and tubing, with thin walls and significant wall-thickness variations. 80/20 – T Slotted Aluminum - Erector Set for Adults Hose Reel Assembly System – Graco Pump Minn

Deburring – Parker Hannifin Load Carrying Device – Air Force Extrusion

• Two types of Extrusion • Direct or forward extrusion: the product emerges in the same direction as the movement of the punch. Container friction plays big role. • Indirect or reverse extrusion: the product travels against the movement of the punch. Container friction plays no role. Billet is at rest in container. Extrusion process: (a) forward or direct without lubrication (and the associated extrusion-pressure/stroke curve; (b) forward with full lubrication; c) reverse or (indirect or backward); (d) reverse can (impact); (e) hydrostatic extrusion. Hyrdostatic extrusion - Cold extrusion of copper tubes and of composite cu-Al billets FIGURE 15.3 Types of extrusion: (a) indirect; (b) hydrostatic; (c) lateral. Hollow products may be extruded with (a) fixed or (b) piercing mandrels or with c) bridge or spider-type dies. Forward Extrusion - Classification

▪Extrusion of semifabricated products ▪Extrusion of finished components ✓Remnant in container cutoff ✓Remnant in container is integral head of part ✓Primary ✓secondary

• Unlubricated (primary) • Lubricated (primary and • With a die of flat face (180 die secondary) opening) Conical entrance zone • Pb, Zn, Al, Mg and other alloys Hot: • Materials that form hard oxides • Graphite (solid lubricant) that might result in smearing the surface of the product during • Glass (solid lubricant that melts lubricated extrusion at the extrusion temperature) Cold: • Semisolids (phosphate + soap) Forward Extrusion l

d1, A1

Ao Forward Extrusion with Full Lubrication

• No dead metal zone Reverse Extrusion

• Lubricated or unlubricated • Primary or secondary • Hot or Cold Extrusion Analysis Extrusion Ratio:

Ao RE = A1 a A1 A  = ln o A1

Extrusion Force: Ao  A  F = A k ln 0  0    Af  K is the extrusion constant which is determined experimentally. It is a measure of the strength of the material being extruded and frictional conditions FIGURE 15.4 Process variables in direct extrusion. The die angle, reduction in cross section, extrusion speed, billet temperature, and lubrication all affect the extrusion pressure. FIGURE 15.5 Extrusion constant k for various metals at different temperatures. Source: After P. Loewenstein.

Extrusion Force  A  F = A k ln o  o    Af  Flow Stress (Schey) n+1 K  Ao •  = ln Cold:  fm = [ ] A  n +1 1

6vd2 tana • Hot: m  = o   f = C m 3 3 do - d1 Frictionless Extrusion Pressure

pe =  fmQe =  fm (0.8 +1.2) for frictionless extrusion Includes inhomogeneous deformation Extrusion Force

Pe = pe Ao Effect of Container Friction • Friction in container:

4 l l is the length of the billet p = p + i l e d do is the initial diameter of the o billet where: m* = 1 for sticking friction

i   f

 f = 0.5 fm m*  = f i 2 Metal Flow in Extrusion Metal Flow in Extrusion has influence on the quality and mechanical properties of extruded parts, Technique of investigating flow pattern is slice, grid, and braze before extruding.

FIGURE 15.6 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. Process Parameters

• Materials: wrought alloys including aluminum, magnesium, copper, steels, stainless steels. Titanium and refratory materials are extruded with some difficulty. • Extrusion ratios: 10 to 100, up to 400 for special non ferrous alloys, at least 4 to deform the material. • Ram speeds: up to 0.5 m/s. Lower speed for aluminum, magnesium, copper. Higher speed for steels, titanium and refractory alloys. • Dimensional tolerance: E0.25 – 2.5 mm. They increase with increasing cross section. • Geometry: Extruded products less than 7.5 m (25 ft) long because of difficult handling. Can be up to 30 m (100 ft). • Handling: Most extruded products require straightening and twisting especially small cross sections. 15.3 Hot Extrusion • Application on low ductile metals • Excessive die wear. To prolong die life, die is preheated. • Low tolerance because of oxidation layer. Minimized by using dummy block placed ahead of the ram (Fig 15.1). Die Design • Square dies. • Angled dies. • T-shaped dies

FIGURE 15.7 Typical extrusion–die configurations: (a) die for nonferrous metals; (b) die for ferrous metals; (c) die for a T-shaped extrusion made of hot-work die steel and used with molten glass as a lubricant. Source: (c) Courtesy of LTV Steel Company. Die Design • Tubular extrusion. • Hollow cross sections.

FIGURE 15.8 Extrusion of a seamless tube (a) using an internal mandrel that moves independently of the ram. (An alternative arrangement has the mandrel integral with the ram.) (b) using a spider die (see Fig. 15.9) to produce seamless tubing.

FIGURE 15.9 (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) through (d) Components of various dies for extruding intricate hollow shapes. Source: (b) through (d) after K. Laue and H. Stenger. Die Material and Lubrication

Hot worked die steels are used for hot extrusion Coatings such as partially stabilized zirconia may be applied to the die to extend their life.

➢Used widely for components in automobiles, motorcycles, bicycles, and appliances in the transportation and farm equipment.

➢Uses slugs cut from cold-finished or hot- rolled bars, wire, or plates.

➢Advantages include: ✓Improved mechanical properties. ✓Good control of dimensional tolerances. ✓Improved surface finish due to absence of an oxide film. ✓Competitive production rates and costs with other methods.

FIGURE 15.12 Two examples of cold extrusion. Thin arrows indicate the direction of metal flow during extrusion. FIGURE 15.13 Production steps for a cold-extruded spark plug. Source: Courtesy of National Machinery Company. FIGURE 15.14 A cross section of the metal part in Fig. 15.13, showing the grain- flow pattern. Source: Courtesy of National Machinery Company. 15.4.1 Impact Extrusion

• Usually lubricated • Usually secondary • Usually cold

Pe = Ao pe or

Pi = 3 fm Ap Take larger of two

Similar to Piercing or Forging FIGURE 15.15 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. FIGURE 15.16 (a) Impact extrusion of a collapsible tube by the Hooker process. (b) and (c) Two examples of products made by impact extrusion. These parts also may be made by casting, forging, or machining. The choice of process depends on the materials involved, part dimensions and wall thickness, and the properties desired. Economic considerations also are important in final process selection. 15.4.2 Hydrostatic Extrusion • The pressure required in the chamber is supplied via a piston through an incompressible fluid medium surrounding the billet. • Pressures are typically in the order of 1400 Mpa (200 Ksi). • No need for lubrication, some of the fluid transmitted to the die surface due to high pressure act as lubricant. • Typically conducted at room temperature with vegetable oils as fluid. Castor oil is a good lubricant and its viscosity is not influenced significantly by pressure. • Brittle materials can be extruded successfully by this method. • Extrusion ratios can be as high as 14,000. 1-m billet becomes 14 km-long wire. • It’s application in the industry is not common because: complex nature of tooling, experience needed with high pressures and design of specialized equipment, and long cycle times required. • Process is uneconomical for most materials and application. 15.5 Extrusion Defects 1. Surface Cracking. Too high extrusion temperature, friction, or speed will cause high surface temperature, which may cause surface cracking and tearing. Occurs in Aluminum, magnesium, and zinc alloys. Occurrence at low extrusion temperature is due to sticking of extruded part along the die land. 2. Pipe. Inhomogeneous metal flow will draw surface oxides and impurities toward the center of the billet-much like a funnel. Or too much extrusion into the die. 3. Internal Cracking. The center of the extruded product can develop cracks, called center cracking, centre-burst, arrowhead fracture, or chevron cracking (Fig 15.17a. These are attributed to hydrostatic tensile stress at the centerline in the deformation zone in the die (Fig 15.17 b). This is similar to necking in a tensile- test specimen. Tendency increases with (a) increase in die angle, (b) increase in amount of impurities and c) decrease in extrusion ratio and friction. 4. Subsurface defects caused by lubricant trapped at the boundary of the dead- metal zone. FIGURE 15.17 (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. (b) Schematic illustration of rigid and plastic zones in extrusion. The tendency toward chevron cracking increases if the two plastic zones do not meet. Note that the plastic zone can be made larger either by decreasing the die angle, by increasing the reduction in cross section, or both. Source: After B. Avitzur. 15.5 Extrusion Defects Process Capabilities and Design Aspects

h Use L  1.8 An Example A 6061 Al Alloy billet is extruded at 500C without lubrication on a hydraulic press at a ram speed of 0.5 m/s. Find the basic pressure for extruding a bar of 15-mm diameter, assuming that the half angle of the dead-metal zone is 15  and 45 . The original bar diameter is 200-mm.

This is hot working extrusion because Temperature, T = 500C From Table 8-2, find mechanical properties of A 6061 Al Alloy: C = 37 MPa, m = 0.17

Known conditions are: Velocity = 500 mm/s, do = 200 mm, d1 = 15 mm

2 2 2 2 Ao = do /4 = 31416 mm , A1 = d1 /4 = 176.7 mm , Ao − A1 31416 −176.7 ee = = = 0.994 Ao 31416

Ao 31416 Re = = =177.8 A1 176.7

Ao  = ln Re = ln = ln(177.8) = 5.18 A1 for a =15 for a = 45 6vd 2 tana 6vd 2 tana  o  = o  = 77.7  = 3 3  = 20.8 3 3 do − d1 do − d1 a =15 m 0.17 2  f = C = 37(MPa)*20.8 = 62.0N / mm a = 45 m 0.17 2  f = C = 37(MPa)*77.7 = 77.6N / mm Qe = 0.8 +1.2 = 7.02 for a =15 2 2 pe =  fmQe = 62.0(N / mm )*7.02 = 435.0 N / mm for a = 45 2 2 pe =  fmQe = 77.6(N / mm )*7.02 = 544.2 N / mm

for a =15 2 2 Pe = pe Ao = 435.0 (N / mm )31416(mm ) =13667KN or a = 45 2 2 Pe = pe Ao = 544.2 (N / mm )31416(mm ) =17096KN Drawing Process

1. Material is deformed in (a) Tension or (b) Compression 2. Deformation mode is (a) Direct Compression or (b) Indirect 3. Drawing force is by (a) Pushing or (b) Pulling 4. Drawing can be used to produce (a) Cylinders (b) wires c) Tubes 5. In drawing process, is die moving or stationary 6. Is drawing process (a) Steady state process or (b) non-steady process. 7. Similar to Extrusion, five variables are identified to analyze drawing process: Drawing The material is deformed in compression, but the deformation force is now supplied by pulling the deformed end of the wire. Therefore, it is often said that the deformation mode is that of indirect compression.

▪Stationary draw dies are made of tool steel, cemented WC, or diamond. ▪The wire is pointed usually by swaging, fed through the die and is drawn on a drum. ▪The task is speeded up with multiple draw machines in which the wire is passed through several dies. ▪Constancy of volume again applies and individual drums are driven at increasing speeds to compensate for reduction in area.

Applications: electrical wiring, rivets, bolts, wire fencing, nails, etc.

➢The basic tube drawing processes are sinking, rod (mandrel) drawing, and several types of plug drawing ➢Sinking. Tube sinking is simply drawing the tube through a die to reduce the outside and inside diameters. Sinking does not use an internal support. ➢Rod Drawing. The rod drawing process draws the tube over a hardened steel rod, or mandrel, that passes through the die with the tube. The typical die angle for rod drawing is 36 degrees; the bearing length is short. This process reduces the OD, ID, and wall thickness. FIGURE 15.20 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). Fig 9.38 (a) Deformation in wire drawing takes place under the indirect compression developed by a conical die. (b) High h/L ratios can lead to center-burst in materials of limited ductility. The wire may be drawn on (c) a bull block or for higher productivity, (d) on a multiple-die wire-drawing machine. Wire Drawing

do + d1 h h =  2.0 2 L

Deformation in Wire Drawing Drawing Forces • : Drawing Strain A  = ln o A1

➢Steady State Process:

K   n+1   fm =    n +1 • Drawing Stresses:

exit = Qdr fm

• Qdr: Drawing Stress Multiplication Factor

Qdr = (1+  cota) •f • • f : Inhomogenity Factor is a function of h/L, extra work • µ: coefficient of friction between workpiece and die • a: is half angle of the draw die • h: is the mean diameter for a circular cross section material • L: is the length of contact zone Calculation of f • Round Bar: h d + d f = 0.88+ 0.12 (1) h = o 1 L 2 • Rectangular Sections: do = Initial wire diameter

d1 = Diameter of exit wire h f = 0.8 + 0.12 ( 1) L = length of contact zone L L = (d0 –d1)/2sinα Drawing Force

Pdr =  exit • A1 = Qdr fm A1

Pdr   0.2A1 (of the drawn wire)

Yield strength of the exit wire = Kn

The power required for drawing is obtained from the definition of power:

Power = Pdr v Die Materials and Design • Case 1: The interface pressures must not exceed a p  Hardness safe fraction of the yield strength of the die material. From the HRC values given in Table  h  9-3, the tensile strength can be estimated   1.0  L  Case 2: h  1.0 L

0.2 of die steel  1900 MPa for cold working  1100 -1700 MPa for hot working FIGURE 15.21 Terminology pertaining to a typical die used for drawing a round rod or wire.

Die angles usually range from 6° to 15°, 9-3

9-3 Drawing Lubrication

Proper lubrication is important in drawing in order to improve die life and product surface finish and to reduce drawing forces and temperature. Methods of lubrication are ➢ Wet drawing: die and rod are immersed completely in the lubricant. ➢ Dry drawing: surface of rod is coated with lubricant by passing it through a container. ➢ Metal coating: rod is coated with a soft metal, such as copper or tin, that acts as a solid lubricant. ➢ Ultrasonic vibration: dies and mandrels are vibrated to reduce forces, improve surface finish and die life and allow larger reductions per pass without failure. Process Capabilities and Design Aspects 1. Drawing is fairly limited in the variety of shapes produced, but it makes up for this in the low cost of dies and high productivity. Tolerances are tight. 2. Draw force must not exceed the strength of the drawn wire. The maximum reduction is typically below 50% (calculated as reduction of area, not as reduction of diameter). 3. A possibility of nonuniformity of deformation, just as in extrusion. h/L  2, leads to secondary tensile stress, and centerburst. 15.9 Drawing Defects and Residual Stresses

d + d h = o 1 h  2.0 2 L

Centerburst Due to High h/L ratio 15.10 Drawing Equipment Two types: draw bench and bull block

FIGURE 15.23 Cold drawing of an extruded channel on a draw bench to reduce its cross section. Individual lengths of straight rods or of cross sections are drawn by this method. FIGURE 15.24 An illustration of multistage wire drawing typically used to produce copper wire for electrical wiring. Source: After H. Auerswald.