Forging Outline Forging Types of forging Forging analysis Examples Oldest of te metal forming operations, dating from about 5000 B C Components: engine cranksafts, connecting rods, gears, aircraft structural components, jet engine turbine parts In addition, basic metals industries use forging to establis basic form of large components tat are subsequently macined to final sape and size Hot or warm forging most common, due to te significant deformation and te need to reduce strengt and increase ductility of work metal Cold forging - advantage is increased strengt tat results from strain ardening Forge ammer (impact) - applies an impact load Forge press (press) - applies gradual pressure Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/ Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/2 Types of Forging Dies Open-Die Forging Open-die forging: work is compressed between two flat dies, allowing metal to flow laterally witout constraint Flasless forg g: piece is completely constrained in die and no excess flas is produced Impression-die forging: die contains a cavity or impression tat is imparted to workpiece, tus constraining metal flow - flas is created Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/3 Compression of work wit cylindrical cross-section between two flat dies Similar to compression test Deformation operation reduces eigt and increases diameter of work Common names include upsetting or upset forging If no friction occurs between work and die surfaces, ten.. deformation occurs, so tat radial flow is uniform trougout workpart eigt and true strain is given by: ε = ln o o = starting eigt = eigt at some point during compression Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/4
Open-Die Forging wit Friction Impression-Die Forging Friction between work and die surfaces constrains lateral flow of work, resulting in effect In ot open-die forging, effect is even more pronounced due to eat transfer at and near die surfaces, wic cools te metal and increases its resistance to deformation Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/5 Flas must be later trimmed from part, but it serves an important function during compression: - As flas forms, friction resists continued metal flow into gap, forcing material to fill die cavity - In ot forging, metal flow is furter restricted because te tin flas cools quickly against te die plates Several forming steps often required, wit separate die cavities for eac step - Beginning steps redistribute metal for more uniform deformation and desired metallurgical structure in subsequent steps - Final steps bring te part to its final geometry - Impression-die forging is often performed manually by skilled operator under adverse conditions Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/6 Impression-Die Trimming Advantages compared to macining from solid stock: - Higer production rates - Conservation of metal (less waste) -.. strengt - Favorable grain orientation in te metal Limitations: - Not capable of close tolerances - Macining often required to acieve accuracies and features needed, suc as oles, treads, and mating surfaces tat fit wit oter components Cutting operation to remove flas from workpart in impression-die forging Usually done wile work is still ot, so a separate trimming press is included at te forging station Trimming can also be done by alternative metods, suc as grinding or sawing Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/7 Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/8
Flasless Forging Forging Hammers (Drop Hammers) Starting workpart volume must equal die cavity volume witin very close tolerance Process control more demanding tan impression-die forging Best suited to part geometries tat are simple and symmetrical Often classified as a precision forging process Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/9 Apply an impact load against workpart - two types: - Gravity drop ammers - impact energy from falling weigt of a eavy ram - Power drop ammers - accelerate te ram by pressurized air or steam Disadvantage: impact energy transmitted troug anvil into floor of building Most commonly used for impression-die forging Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/0 Forging Presses Upsetting and Heading wire stock is fed to te stop gripping dies close on te stock and te stop is retracted punc moves forward bottoms to form te ead Apply gradual pressure to accomplis compression operation - types: Mecanical presses - converts rotation of drive motor into linear motion of ram Hydraulic presses - ydraulic piston actuates ram Screw presses - screw mecanism drives ram Forging process used to form eads on nails, bolts, and similar ardware products More parts produced by upsetting tan any oter forging operation Performed cold, warm, or ot on macines called eaders or formers Wire or bar stock is fed into macine, end is eaded, ten piece is cut Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/ Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/2
Upsetting and Heading Swaging Radial Forging eading a nail using open dies round ead formed by punc two common ead styles for screws formed by die carriage bolt ead formed by punc and die Wire or bar stock is fed into macine, end is eaded, ten piece is cut For bolts and screws, tread rolling is ten used to form treads Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/3 Accomplised by rotating dies tat ammer a workpiece radially inward to taper it as te piece is fed into te dies Used to reduce diameter of tube or solid rod stock Mandrel sometimes required to control sape and size of internal diameter of tubular parts Radial forging: is similar to swaging except tat te workpiece rotates instead of te forging dies. Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/4 Oter Forging Processes Force required: F = K f Y f A F: force A: cross-sectional area K f : forging saping factor Forging - Analysis Ideal Actual Orbital forging Roll forging 0.4µD K f =+ Impression Simple w/ flas Complex w/ flas µ: coefficient of friction Very complex w/ flas 0.0 D: work-part diameter Flasless (or oter dimension representing contact lengt wit die surface) Coining 6.0 : work-part eigt Complex sape 8.0 K f 6.0 8.0 Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/5 Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/6
Hot Forging - Analysis Teoretically, a metal in ot working beaves like a perfectly plastic material, wit strain ardening exponent n = 0 However, an additional penomenon occurs during deformation, especially at elevated temperatures: (strain rate becomes important) Strain rate is defined:. ε = v V = deformation velocity = instantaneous eigt of workpiece being deformed As strain rate increases, resistance to deformation increases Tis effect is known as strain-rate sensitivity Y f = Cε& m were C = strengt constant m = strain-rate sensitivity exponent te deformation force is: te work is: F = C W v assume constant strain rate: te power consumed is: Hot Forging - Analysis m = F o. m W = CV ε P = CV t. m ε ε ε A d V is te volume of te work piece t is te time Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/7 Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/8 Example : Cold Upsetting A 302 stainless steel cylinder of eigt 2 cm and diameter 7 cm at room temperature is compressed to a eigt of 2 cm between large platens. Mineral oil is used as a lubricant between te cylinder and platens. Calculate te force necessary and stress on te platens. Example 2: Hot Upsetting Te 302 stainless steel cylinder of te previous example is ot upset at 000 C to a eigt of 2 cm by a platen moving at 2 cm/s. Grapite is used as a lubricant between te platens and workpiece. Calculate te forging force. Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/9 Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/20
Next time Rolling Dr. M. Medraj Mec. Eng. Dept. - Concordia University Mec 42/65 lecture 4/2