2 BULK DEFORMATION PROCESSES IN METALWORKING RollingOther Deformation Processes Related to RollingForgingOther Deformation Processes Related to ForgingExtrusionWire and Bar Drawing
3 ForgingDeformation process in which work is compressed between two diesOldest of the metal forming operations, dating from about 5000 BCComponents: engine crankshafts, connecting rods, gears, aircraft structural components, jet engine turbine parts
4 Classification of Forging Operations Cold vs. hot forging:Hot or warm forging – most common, due to the significant deformation and the need to reduce strength and increase ductility of work metalCold forging – advantage: increased strength that results from strain hardeningImpact vs. press forging:Forge hammer - applies an impact loadForge press - applies gradual pressure
5 Types of Forging Dies Open‑die forging Impression‑die forging With frictionWithout frictionOpen‑die forgingImpression‑die forgingFlashless forging
6 Open-Die ForgingWork is compressed between two flat dies, allowing metal to flow laterally with minimum constraint.Common names include upsetting or upset forgingDeformation operation reduces height and increases diameter of work (similar to compression test)Figure Three types of forging: (a) open‑die forging.
7 Open‑Die Forging with No Friction If no friction occurs between work and die surfaces, then homogeneous deformation occurs, so that radial flow is uniform throughout workpart heightTrue strain is given by:where ho= starting height; and h = height at some point during compressionNo frictionFigure Homogeneous deformation of a cylindrical workpart under ideal conditions in an open‑die forging operation:
8 Open-Die Forging with Friction Friction between work and die surfaces constrains lateral flow of work, resulting in barreling effectIn hot open-die forging, effect is even more pronounced due to heat transfer at and near die surfaces, which cools the metal and increases its resistance to deformationFigure Actual deformation of a cylindrical workpart in open‑die forging, showing pronounced barreling:Friction(1) start of process(2) partial deformation(3) final shape
9 Impression-Die Forging Compression of workpart by dies with inverse of desired part shapeMetal flow is constrained so that flash is createdFigure Three types of forging: (b) impression‑die forging.
10 Impression-Die Forging Impression-die forging is often performed manually by skilled operator under adverse conditionsForging dieFigure Sequence in impression‑die forging: (1) just prior to initial contact with raw workpiece, (2) partial compression, and (3) final die closure, causing flash to form in gap between die plates.
11 Impression‑Die Forging Compression of workpart by dies with inverse of desired part shapeFlash is formed by metal that flows beyond die cavity into small gap between die platesFlash must be later trimmed, but it serves an important function during compression:As flash forms, friction resists continued metal flow into gap, constraining material to fill die cavityIn hot forging, metal flow is further restricted by cooling against die plates
12 Advantages and Limitations Advantages of impression-die forging compared to machining from solid stock:Higher production ratesLess waste of metalGreater strengthFavorable grain orientation in the metalLimitations:Not capable of close tolerancesMachining often required to achieve accuracies and features needed
13 Examples One step of several steps of manufacturing the coins Various mechanical partsKnives
14 Figure 19.9 Three types of forging (c) flashless forging. (Also known as precision forging)Workpart is completely constrained in die( No excess flash is created )Figure Three types of forging (c) flashless forging.
15 Flashless ForgingCompression of work in punch and die tooling whose cavity does not allow for flashStarting workpart volume must equal die cavity volume within very close toleranceProcess control more demanding than impression‑die forgingBest suited to part geometries that are simple and symmetrical
16 Flashless ForgingFigure Flashless forging: (1) just before initial contact with workpiece, (2) partial compression, and (3) final punch and die closure.
17 Flashless forging Computer simulation of a connecting rod This is an animated gif file.Wait to see the whole process.Computer simulation of a connecting rodBlue shows the area with the least deformation (smallest strain and stress values) and yellow shows the areas with highest amount of stress and strain
18 Test yourself Name the following 4 forging operations: Impression‑Die ForgingFlashless ForgingOpen Die Forging (with Friction)Open Die Forging (without friction)
20 Forging Hammers (Drop Hammers) Apply impact load against workpartTwo types:Gravity drop hammers - impact energy from falling weight of a heavy ramPower drop hammers - accelerate the ram by pressurized air or steamDisadvantage: impact energy transmitted through anvil into floor of buildingCommonly used for impression-die forging
21 Figure Drop forging hammer, fed by conveyor and heating units at the right of the scene (photo courtesy of Chambersburg Engineering Company).
22 Drop Hammer DetailsFigure Diagram showing details of a drop hammer for impression‑die forging.
23 Forging PressesApply gradual pressure to accomplish compression operationTypes:Mechanical press - converts rotation of drive motor into linear motion of ramHydraulic press - hydraulic piston actuates ramScrew press - screw mechanism drives ram
24 Upsetting and HeadingForging process used to form heads on nails, bolts, and similar hardware productsMore parts produced by upsetting than any other forging operationPerformed cold, warm, or hot on machines called headers or formersWire or bar stock is fed into machine, end is headed, then piece is cut to lengthFor bolts and screws, thread rolling is then used to form threads
25 Heading (Upset Forging) Figure An upset forging operation to form a head on a bolt or similar hardware item The cycle consists of: (1) wire stock is fed to the stop, (2) gripping dies close on the stock and the stop is retracted, (3) punch moves forward, (4) bottoms to form the head.
26 Heading (Upset Forging) Figure Examples of heading (upset forging) operations.(a) heading a nail using open dies(b) round head formed by punch(c) and (d) two common head styles for screws formed by die(e) carriage bolt head formed by punch and die
27 How do they make the slot in screw’s head?! Left: The cold heading machine cuts a length of wire and makes two blows on the end, forming a head.Right: In the head slotting machine, the screw blanks are clamped in the grooves around the perimeter of the wheel. A circular cutter slots the screws as the wheel revolves.
28 SwagingAccomplished by rotating dies that hammer a workpiece radially inward to taper it as the piece is fed into the diesUsed to reduce diameter of tube or solid rod stockMandrel sometimes required to control shape and size of internal diameter of tubular partsIn radial forging, the workpiece rotates while the dies remain in a fixed orientation as they hammer the work.Figure Swaging process to reduce solid rod stock; the dies rotate as they hammer the work.
29 TrimmingCutting operation to remove flash from workpart in impression‑die forgingUsually done while work is still hot, so a separate trimming press is included at the forging stationTrimming can also be done by alternative methods, such as grinding or sawing