Processes Forging

1 processes

1.1 temperature
1.2 drop forging

1.2.1 open-die drop forging
1.2.2 impression-die forging

1.2.2.1 design of impression-die forgings , tooling




1.3 press forging
1.4 upset forging
1.5 automatic hot forging
1.6 roll forging
1.7 net-shape , near-net-shape forging

1.7.1 cold forging
1.7.2 cost implications


1.8 induction forging
1.9 multidirectional forging
1.10 isothermal forging

processes

a cross-section of forged connecting rod has been etched show grain flow

there many different kinds of forging processes available; however, can grouped 3 main classes:

drawn out: length increases, cross-section decreases
upset: length decreases, cross-section increases
squeezed in closed compression dies: produces multidirectional flow

common forging processes include: roll forging, swaging, cogging, open-die forging, impression-die forging, press forging, automatic hot forging , upsetting.

temperature

all of following forging processes can performed @ various temperatures; however, classified whether metal temperature above or below recrystallization temperature. if temperature above material s recrystallization temperature deemed hot forging; if temperature below material s recrystallization temperature above 30% of recrystallization temperature (on absolute scale) deemed warm forging; if below 30% of recrystallization temperature (usually room temperature) deemed cold forging. main advantage of hot forging can done more , precisely, , metal deformed work hardening effects negated recrystallization process. cold forging typically results in work hardening of piece.

drop forging


boat nail production in hainan, china

drop forging forging process hammer raised , dropped onto workpiece deform according shape of die. there 2 types of drop forging: open-die drop forging , closed-die drop forging. names imply, difference in shape of die, former not enclosing workpiece, while latter does.

open-die drop forging

open-die drop forging (with 2 dies) of ingot further processed wheel

open-die forging known smith forging. in open-die forging, hammer strikes , deforms workpiece, placed on stationary anvil. open-die forging gets name fact dies (the surfaces in contact workpiece) not enclose workpiece, allowing flow except contacted dies. operator therefore needs orient , position workpiece desired shape. dies flat in shape, have specially shaped surface specialized operations. example, die may have round, concave, or convex surface or tool form holes or cut-off tool. open-die forgings can worked shapes include discs, hubs, blocks, shafts (including step shafts or flanges), sleeves, cylinders, flats, hexes, rounds, plate, , custom shapes. open-die forging lends short runs , appropriate art smithing , custom work. in cases, open-die forging may employed rough-shape ingots prepare them subsequent operations. open-die forging may orient grain increase strength in required direction.

advantages of open-die forging

reduced chance of voids
better fatigue resistance
improved microstructure
continuous grain flow
finer grain size
greater strength

cogging successive deformation of bar along length using open-die drop forge. commonly used work piece of raw material proper thickness. once proper thickness achieved proper width achieved via edging . edging process of concentrating material using concave shaped open-die. process called edging because carried out on ends of workpiece. fullering similar process thins out sections of forging using convex shaped die. these processes prepare workpieces further forging processes.

impression-die forging

impression-die forging called closed-die forging . in impression-die forging, metal placed in die resembling mold, attached anvil. usually, hammer die shaped well. hammer dropped on workpiece, causing metal flow , fill die cavities. hammer in contact workpiece on scale of milliseconds. depending on size , complexity of part, hammer may dropped multiple times in quick succession. excess metal squeezed out of die cavities, forming referred flash . flash cools more rapidly rest of material; cool metal stronger metal in die, helps prevent more flash forming. forces metal fill die cavity. after forging, flash removed. in commercial impression-die forging, workpiece moved through series of cavities in die ingot final form. first impression used distribute metal rough shape in accordance needs of later cavities; impression called edging , fullering , or bending impression. following cavities called blocking cavities, in piece working shape more closely resembles final product. these stages impart workpiece generous bends , large fillets. final shape forged in final or finisher impression cavity. if there short run of parts done, may more economical die lack final impression cavity , instead machine final features. impression-die forging has been improved in recent years through increased automation includes induction heating, mechanical feeding, positioning , manipulation, , direct heat treatment of parts after forging. 1 variation of impression-die forging called flashless forging , or true closed-die forging . in type of forging, die cavities closed, keeps workpiece forming flash. major advantage process less metal lost flash. flash can account 20 45% of starting material. disadvantages of process include additional cost due more complex die design , need better lubrication , workpiece placement. there other variations of part formation integrate impression-die forging. 1 method incorporates casting forging preform liquid metal. casting removed after has solidified, while still hot. finished in single cavity die. flash trimmed, part quench hardened. variation follows same process outlined above, except preform produced spraying deposition of metal droplets shaped collectors (similar osprey process). closed-die forging has high initial cost due creation of dies , required design work make working die cavities. however, has low recurring costs each part, forgings become more economical more volume. 1 of major reasons closed-die forgings used in automotive , tool industries. reason forgings common in these industrial sectors forgings have 20 percent higher strength-to-weight ratio compared cast or machined parts of same material.

design of impression-die forgings , tooling

forging dies made of high-alloy or tool steel. dies must impact resistant, wear resistant, maintain strength @ high temperatures, , have ability withstand cycles of rapid heating , cooling. in order produce better, more economical die following standards maintained:

the dies part along single, flat plane whenever possible. if not, parting plane follows contour of part.
the parting surface plane through center of forging , not near upper or lower edge.
adequate draft provided; @ least 3° aluminium , 5° 7° steel.
generous fillets , radii used.
ribs low , wide.
the various sections balanced avoid extreme difference in metal flow.
full advantage taken of fiber flow lines.
dimensional tolerances not closer necessary.

the dimensional tolerances of steel part produced using impression-die forging method outlined in table below. dimensions across parting plane affected closure of dies, , therefore dependent on die wear , thickness of final flash. dimensions contained within single die segment or half can maintained @ greater level of accuracy.

a lubricant used when forging reduce friction , wear. used thermal barrier restrict heat transfer workpiece die. finally, lubricant acts parting compound prevent part sticking in dies.

press forging

press forging works applying continuous pressure or force, differs near-instantaneous impact of drop-hammer forging. amount of time dies in contact workpiece measured in seconds (as compared milliseconds of drop-hammer forges). press forging operation can done either cold or hot.

the main advantage of press forging, compared drop-hammer forging, ability deform complete workpiece. drop-hammer forging deforms surfaces of work piece in contact hammer , anvil; interior of workpiece stay relatively undeformed. advantage process includes knowledge of new part s strain rate. controlling compression rate of press forging operation, internal strain can controlled.

there few disadvantages process, stemming workpiece being in contact dies such extended period of time. operation time-consuming process due amount , length of steps. workpiece cool faster because dies in contact workpiece; dies facilitate drastically more heat transfer surrounding atmosphere. workpiece cools becomes stronger , less ductile, may induce cracking if deformation continues. therefore, heated dies used reduce heat loss, promote surface flow, , enable production of finer details , closer tolerances. workpiece may need reheated.

when done in high productivity, press forging more economical hammer forging. operation creates closer tolerances. in hammer forging lot of work absorbed machinery; when in press forging, greater percentage of work used in work piece. advantage operation can used create size part because there no limit size of press forging machine. new press forging techniques have been able create higher degree of mechanical , orientation integrity. constraint of oxidation outer layers of part, reduced levels of microcracking occur in finished part.

press forging can used perform types of forging, including open-die , impression-die forging. impression-die press forging requires less draft drop forging , has better dimensional accuracy. also, press forgings can done in 1 closing of dies, allowing easy automation.

upset forging

upset forging increases diameter of workpiece compressing length. based on number of pieces produced, used forging process. few examples of common parts produced using upset forging process engine valves, couplings, bolts, screws, , other fasteners.

upset forging done in special high-speed machines called crank presses. machines set work in horizontal plane, facilitate quick exchange of workpieces 1 station next, upsetting can done in vertical crank press or hydraulic press. initial workpiece wire or rod, machines can accept bars 25 cm (9.8 in) in diameter , capacity of on 1000 tons. standard upsetting machine employs split dies contain multiple cavities. dies open enough allow workpiece move 1 cavity next; dies close , heading tool, or ram, moves longitudinally against bar, upsetting cavity. if of cavities utilized on every cycle, finished part produced every cycle, makes process advantageous mass production.

these rules must followed when designing parts upset forged:

the length of unsupported metal can upset in 1 blow without injurious buckling should limited 3 times diameter of bar.
lengths of stock greater 3 times diameter may upset successfully, provided diameter of upset not more 1.5 times diameter of stock.
in upset requiring stock length greater 3 times diameter of stock, , diameter of cavity not more 1.5 times diameter of stock, length of unsupported metal beyond face of die must not exceed diameter of bar.

automatic hot forging

the automatic hot forging process involves feeding mill-length steel bars (typically 7 m (23 ft) long) 1 end of machine @ room temperature , hot forged products emerge other end. occurs rapidly; small parts can made @ rate of 180 parts per minute (ppm) , larger can made @ rate of 90 ppm. parts can solid or hollow, round or symmetrical, 6 kg (13 lb), , 18 cm (7.1 in) in diameter. main advantages process high output rate , ability accept low-cost materials. little labor required operate machinery.

there no flash produced material savings between 20 , 30% on conventional forging. final product consistent 1,050 °c (1,920 °f) air cooling result in part still machinable (the advantage being lack of annealing required after forging). tolerances ±0.3 mm (0.012 in), surfaces clean, , draft angles 0.5 1°. tool life double of conventional forging because contact times on order of 0.06-second. downside process feasible on smaller symmetric parts , cost; initial investment can on $10 million, large quantities required justify process.

the process starts heating bar 1,200 1,300 °c (2,190 2,370 °f) in less 60 seconds using high-power induction coils. descaled rollers, sheared blanks, , transferred through several successive forming stages, during upset, preformed, final forged, , pierced (if necessary). process can coupled high-speed cold-forming operations. generally, cold forming operation finishing stage advantages of cold-working can obtained, while maintaining high speed of automatic hot forging.

examples of parts made process are: wheel hub unit bearings, transmission gears, tapered roller bearing races, stainless steel coupling flanges, , neck rings lp gas cylinders. manual transmission gears example of automatic hot forging used in conjunction cold working.

roll forging

roll forging process round or flat bar stock reduced in thickness , increased in length. roll forging performed using 2 cylindrical or semi-cylindrical rolls, each containing 1 or more shaped grooves. heated bar inserted rolls , when hits spot rolls rotate , bar progressively shaped rolled through machine. piece transferred next set of grooves or turned around , reinserted same grooves. continues until desired shape , size achieved. advantage of process there no flash , imparts favorable grain structure workpiece.

examples of products produced using method include axles, tapered levers , leaf springs.

net-shape , near-net-shape forging

this process known precision forging. developed minimize cost , waste associated post-forging operations. therefore, final product precision forging needs little or no final machining. cost savings gained use of less material, , less scrap, overall decrease in energy used, , reduction or elimination of machining. precision forging requires less of draft, 1° 0°. downside of process cost, therefore implemented if significant cost reduction can achieved.

cold forging

near net shape forging common when parts forged without heating slug, bar or billet. aluminum common material can cold forged depending on final shape. lubrication of parts being formed critical increase life of mating dies.

cost implications

to achieve low-cost net shape forging demanding applications subject high degree of scrutiny, i.e. non-destructive testing way of dye-penetrant inspection technique, crucial basic forging process disciplines implemented. if basic disciplines not met, subsequent material removal operations necessary remove material defects found @ non-destructive testing inspection. hence low-cost parts not achievable.

example disciplines are: die-lubricant management (use of uncontaminated , homogeneous mixtures, amount , placement of lubricant). tight control of die temperatures , surface finish / friction.

induction forging

unlike above processes, induction forging based on type of heating style used. many of above processes can used in conjunction heating method.

multidirectional forging

multidirectional forging forming of work piece in single step in several directions. multidirectional forming takes place through constructive measures of tool. vertical movement of press ram redirected using wedges distributes , redirects force of forging press in horizontal directions.

isothermal forging

isothermal forging process materials , die heated same temperature (iso- meaning equal ). adiabatic heating used assist in deformation of material, meaning strain rates highly controlled. commonly used forging aluminum, has lower forging temperature steels. forging temperatures aluminum around 800 °f, while steels , super alloys can 1700-2300 °f.[1]

benefits:

near net shapes lead lower machining requirements , therefore lower scrap rates
reproducibility of part
due lower heat loss smaller machines can used make forging

disadvantages:

higher die material costs handle temperatures , pressures
uniform heating systems required
protective atmospheres or vacuum reduce oxidation of dies , material
low production rates




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