Group 9 3 / 1 / 2006 Ch. 15: Extrusion and Drawing of Metal Ch. 16: Sheet-Metal Forming Process - PowerPoint PPT Presentation

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Group 9 3 / 1 / 2006 Ch. 15: Extrusion and Drawing of Metal Ch. 16: Sheet-Metal Forming Process
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Group 9 3 / 1 / 2006 Ch. 15: Extrusion and Drawing of Metal Ch. 16: Sheet-Metal Forming Process

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  1. Group 93 / 1 / 2006Ch. 15: Extrusion and Drawing of MetalCh. 16: Sheet-Metal Forming Process David Ortegel Steven Neidigk Tim Ngo Jason Maestas

  2. 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 1000 -1500 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. Extrusion Force • The force required for extrusions F = A*k*ln( A۪/ 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) • (c) • (b)

  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. 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. 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 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. 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 Shearing

  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