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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 ProcessDavid OrtegelSteven NeidigkTim NgoJason Maestas
2 Extrusion and Drawing Of Metals CHAPTER 15Extrusion and DrawingOfMetals
3 15.1 Introduction Extrusion Rooted From Latin Term “Extrudere”(To Force out).A Cylindrical Billet is Forced Through A DieSame Concept as forming Play-DoeDie Geometry remains constant throughout the operationForms a constant extruded cross-sectionAluminum, copper, Steel Magnesium, lead are the most common material used in the Extruding process
4 Products Made by Extrusions Railings for Sliding DoorsWindow FramesAluminum LaddersExtrusions 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 lowManufactures are able to produce quantity because of the ability to cut individual parts from a single extrusion
6 DrawingDrawing – Cross-sections of solid rod, wire, or tubing is reduced or changed in shape by pulling through a die.Developed between ADUsed 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 operationsHot Extrusions – Extrusions carries out at elevated temperaturesImpact extrusion – punch is rapidly descends on billet materialHydrostatic 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 aIndirect 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 stemThere 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 ForceThe force required for extrusionsF = A*k*ln( A ۪ / A )k = Constant determined experimentallyThe force required depends on:Strength of Billet MaterialExtrusion Ratio: A ۪ /AFriction between the billet material and the chamberTemperatureSpeed of the RamType of lubricants used
12 Extrusion constant k for various metals at different temperature
13 Metal FlowFlow patterns influence the quality and mechanical properties of the extruded productMaterial 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 angleFig a – flow patterns attained with low frictionFig b – flow patterns attained with high frictionFig 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 RequirementsDue 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 materialBillet 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 angle2) 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 chamberonly suitable for aluminum and its alloys because of their capacity to create strong welds.
20 Die Materials Hot Worked dies Steels are used for hot extrusion Coatings such as zirconia used to extend die lifeNot suitable for dies used for complex shapes because of the sever stress gradients that develop in the die.
21 LubricationLubrication Is important in hot extrusions because of major effects on:Material flowSurface finish on extrusionProduct qualityExtrusion 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 entranceThe 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 dieAlso used or toxic and radioactive material. The jacket that is formed over the extruded material acts as a protected barrier
24 15.4 Cold ExtrusionDeveloped 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 productsAppliancesFasteners
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 DefectsSurface Cracking: Cracking on billet materials occurs due to temperature, friction, punch speed.High TemperaturesCrack from along the grain boundaries. Typically occur in aluminum, magnesium, zinc alloysCold TemperaturesCaused by sticking of billet material at the die landKnown 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 billetInternal Cracking: Center of extruded product develops cracks.Attributed to a state of hydrostatic tinsel stressCracks increase with increasing die angle, impurities, and decreasing extrusion ratio and friction
29 15.6 Extrusion EquipmentBasic horizontal press: Suitable because the stroke and speed of the press can be controlledVertical Hydraulic press: used for cold extrusions. Take up less floor space
30 15.7 The Drawing ProcessA 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 stressA ۪ – initial cross–sectional areaA – 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 radiansU – Frictional forces
33 15.8 Drawing PracticeBundle Drawing: Drawing many wires simultaneouslyProduces wire in polygonal cross-sectionsTheses types of wire are cut into many shapes. Used in medical implant, electrically conductive material, filter mediaReduces 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 errorDie Materials:Die are made out of typical tool steels and carbidesCast steels are used for hot extrusionsDiamond dies are used for drawing extremely fine wireInsert 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 finishParticular in tube drawing, because of its difficulty to maintain for a thick lubrication film at the mandrelWet drawing – Dies and rod are completely immersed in lubricantDry 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 extrusionInternal Cracking with are longitudinalSeam may openCold–drawn products have residual stresses, this causes stress-corrosion cracking over a period of timeQuality control becomes a major problem in drawn defects and residual stresses
37 15.10 Drawing Equipment Draw Bench: Contains a single die, design is longPulling 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 13mmA large drum is rotated
39 Introduction We utilize sheet metal for products such as CansCookwareAppliancesCar bodiesLow carbon steel is the most commonly used sheet metal for its strength and formabilityThe most general sheet forming operationsPress workingPress forming
40 ShearingShearing metal is like punching holes in paper with a hole punch.It can also be compared to using a cookie cutterThe punch must be harder and stronger that the metal being sheared
41 ShearingTypical features of sheared edges are not smooth nor perpendicular to the cutting planeEdge quality can be improved by increasing punch speedShearing 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 roughToo little and tools can be damagedBurr is a thin edge or ridge an the punched out piece of metalCan be caused by dull tool edgesThe size and shape of the burr can change subsequent forming operations
43 Shearing OperationsDie cutting- perforating, parting, notching, lancingParts produced by die cutting are commonly used in assembly with other componentsFine blanking- used to produce smooth and square edgesNibbling- moves a small straight punch up an down rapidly into a die. One advantage of this technique is intricate slots and notches.
44 Shearing OperationsSlitting- a pair of circular blades follow a line or path cutting as they go.much like a can openerScrap in shearing- The sheets of metal that are not used.Can be as large as 30% of large stampingsIncreases manufacturing cost
45 Shearing OperationsTailor-Welded Blanks- Can be used of sheet metal with different shapes and thicknesses (often used in automotive industry)Reduction in scrapEliminate need for subsequent spot weldingBetter control of dimensionsImproved 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 DiesProgressive dies- good for making parts that require multiple operations to produceUse a series of punchesOther operations includeLaser beam cuttingWater-jet cuttingFriction sawingFlame cutting
48 Sheet-Metal Characteristics and Formability After a blank is cut into a sheet it is formed into various shapesElongation- Stretching the metalHigh elongation is desirable for good formabilityYield-Point Elongation- Happens in low carbon steel and aluminum-magnesium alloys. Causes stretcher-strain marks, or wormsElongations, 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 deformationWays 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 failureMay undergo two basic modes of deformation- stretching and drawingCupping Tests- earliest tests to determine formabilityErichsen 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 operationAdds 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 removedUsually 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 FormingProcess 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 EaringNeckingSeaming
70 Deep DrawingProcess 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 RedrawingOperations used to redraw containers that are too difficult to draw in one operation.IroningIf 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 EaringA 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.SeamingJoining 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 spinningAlso 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 SpinningThe 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.
80 Explosive formingFirst 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 costLabor and skill requiredTimeMachining and tooling operationsLevel of automation and computer control required