Hot forging Rule based DFM analysis for forging

1 hot forging

1.1 advantages
1.2 disadvantages
1.3 cold forging

1.3.1 advantages
1.3.2 disadvantages


1.4 categories of tolerances

1.4.1 group 1
1.4.2 group 2
1.4.3 group 3
1.4.4 group 4


1.5 deviations of forms
1.6 design procedure

1.6.1 information required forger
1.6.2 preparation
1.6.3 indication of dimensions on drawings
1.6.4 indication of tolerances on drawings
1.6.5 importance of drawings


1.7 processes

1.7.1 open-die drop-hammer forging
1.7.2 impression-die drop-hammer forging
1.7.3 design of impression-die forgings , tooling
1.7.4 press forging
1.7.5 upset forging
1.7.6 automatic hot forging
1.7.7 roll forging
1.7.8 net-shape , near-net-shape forging
1.7.9 equipment

hot forging

hot forging defined working metal above recrystallization temperature. main advantage of hot forging metal deformed strain-hardening effects negated recrystallization process.

advantages

disadvantages

cold forging

cold forging defined working metal below recrystallization temperature, around room temperature.

advantages

disadvantages

categories of tolerances
group 1

(see table 2.1 , table 2.2) :

a) length, width , height tolerances. b) mismatch tolerances. c) residual flash (and trimmed flat) tolerances. d) pierced hole tolerances.

group 2

(see table 2.3 , table 2.4) : thickness tolerances. ejector mark tolerances.

group 3

(table 2.5.jpg , table 2.6) : straightness , flatness tolerances. tolerances centre-to-centre dimensions.

group 4

fillet , edge radii tolerances (see table 2.7). burr tolerances (see table 2.7). surface tolerances. tolerances on draft angle surfaces. eccentricity tolerances deep holes. eccentricity tolerances pierced holes. tolerances on concentric bosses. tolerances unforged stock. tolerances deformation of sheared ends.

deviations of forms

the tolerances lengths, widths, heights, , thicknesses cover il diligences of dimensions, deviations of form are: a) out of round, b) deviations cylindricity c) deviations parallelism, , cl) other deviations specified contour. deviations arc not exceed limits given tolerances. iii extreme cases may cover whole fields of tolerances unless other agreed between supplier , purchaser. restrictions deviations of form have been agreed, shall noted on drawing.

design procedure
information required forger

in order assist forging supplier utilize experience best effect, both in designing dies , tools , in establishing forging inspection procedures, rt in purchaser’s interest supply following

information: a) finished machined drawing; b) details , dimensions of machining locations (prior notice should given of subsequent changes in these location points) c) anv other relevant information on machining operations , function of component.

preparation

it recommended drop drawing should submitted forger should prepare forging purchaser approval,and, if necessary, joint consultation.

in instances purchaser wishes prepare own dimensioned forging drawing, no less necessary drawing of finished machined component , other information referred above should made available supplier.

indication of dimensions on drawings

it imperative note that, exception concerning draftangle surfaces tolerances indicated in standardshall npplicd dimensions indicated on agreed forging drawing.

for reason method of indicating dimensions on forgingdrawing has vital bearing on dimensional control of forging.

tolerances dimensions not shown on forging drawing may not taken standard may determined, if required, calculation based on dimensions , tolerances shown on agreed forging drawing.

indication of tolerances on drawings

all forging drawings should endorsed, ‘tolerances conform is : 3469 (part ii)-1974 unless otherwise indicated

for correct endorsement of forging drawings following form of presentation of tolerances @ foot of drawing recommended:

category: 1. lengths , overall diameters 2. widths 3. heights 4. mismatch 5. residual flash , trimmed flat 6. thickness 7. straightness 8. flatness 9. fillet , edge radii 10. surfaces

any tolerances applicable specific dimensions shall indicated on drawing against particular dimensions concerned. ejector mark tolerances , burr tolerances should shown on forging drawing against specific locations. special tolerances agreed between purchaser , supplier shall indicated on forging drawing , shall, wherever possible entered against specific dimensions concerned.

importance of drawings

the drawing of forged part has been accepted purchaser valid document inspection of forged part. drawing valid document tolerances on parts of forging remaining unmachined

processes

there many different kinds of forging processes available, can grouped 3 main classes: 1. drawn out: length increases, cross-section decreases 2. upset: length decreases, cross-section increases 3. squeezed in closed compression dies: produces multidirectional flo 4. common forging processes include: roll forging, swaging, cogging, open-die forging, impression-die forging, press forging, automatic hot forging , upsetting.

open-die drop-hammer forging

open-die forging known smith forging. in open-die forging hammer comes down , deforms workpieces, placed on stationary anvil. open-die forging gets name fact dies (the working surfaces of forge contract workpiece) not enclose workpiece, allowing flow except contacted dies. therefore, operator needs orient , position workpiece desired shape. dies flat in shape may have specially shaped surface specialized operations; instance die may have round, concave, or convex surface or tool form holes or cut-off tool. open-die forging lends short runs , appropriate art smiting , custom work. other times open-die forging used rough shape ingots prepare further operations. can orient grains increase strength in required direction.

impression-die drop-hammer forging

impression-die forging called closed-die forging. in impression-die work metal placed in die resembling mold, attached anvil. 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; called 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 trimmed off.

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 workpiece working shape more , more 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 , rather machine final features.

impression-die forging has been further improved in recent years through increased automation includes induction heating, mechanical feeding, positioning , manipulation, , direct heat treatment of parts after forging.

one 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 included: additional cost due more complex die design, need better lubrication, , better workpiece placement.

there other variations of part formation integrate impression-die forging. 1 method incorporates casting forging preform liquid metal. casting removed after cooled solid state, while still hot. finished in single cavity die. flash trimmed , quenched room temperature harden part.

another variation follows same process outlined above, except preform produced spraying deposition of metal droplet 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 reoccurring costs each part, forgings become more economical more volume. 1 of major reasons forgings used in automotive , tool industry. reason forgings common in these industrial sectors because forgings have 20% higher strength 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 rules should followed:

1. dies should part along single, flat plane if @ possible, if not parting plan should follow contour of part. 2. parting surface should plane through center of forging , not near upper or lower edge. 3. adequate draft should provided; guideline @ least 3° aluminum , 5° 7° steel 4. generous fillets , radii should used 5. ribs should low , wide 6. various sections should balanced avoid extreme difference in metal flow 7. full advantage should taken of fiver flow lines 8. dimensional tolerances should not closer necessary dimensional tolerances of steel part produced using impression-die forging method outlined in table below. should noted dimensions across paring plane affected closure of dies, , therefore dependent die wear , thickness of final flash. dimensions contained within single die segment or half can maintained @ greater level of accuracy. lubricant used when forging reduce friction , wear. used thermal barrier restrict heat transfer workpiece die. lubricant acts parting compound prevent part sticking in 1 of dies.

press forging

press forging variation of drop-hammer forging. unlike drop-hammer forging, press forges work applying continuous pressure or force. amount of time dies in contact workpiece measured in seconds (as compared milliseconds of drop-hammer forges). main advantage of press forging, compared drop-hammer forging, ability deform complete workpiece.

drop-hammer forging deforms surfaces of workpiece in contact hammer , anvil; interior of workpiece stay relatively undeformed. there few disadvantages process, stemming workpiece being in contact dies such extended period of time. 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.

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. upset forging done in special high speed machines; machines set work in horizontal plane facilitate quick exchange of workpieces 1 station next. initial workpiece wire or rod, machines can accept bars 25 cm (10 in.) in diameter. 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 utilizes on every cycle finished part produced every cycle, why process ideal mass production.

a few examples of common parts produced using upset forging process engine valves, couplings, bolts, screws, , other fasteners.

the following 3 rules must followed when designing parts upset forged:

1. length of unsupported metal can upset in 1 blow without injurious buckling should limited 3 times diameter of bar. 2. lengths of stock greater 3 times diameter may upset provided diameter of upset not more 1.5 times diameter of stock. 3. 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 or 24 ft long) 1 end of machine @ room temperature , hot forged products emerge other end. occurs quickly; 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 (12 lbs), , 18 cm (7 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 1050 °c (1900 °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 6/100 of second.

the downside process feasible on smaller symmetric parts , cost; initial investment can on $10 million, there large quantities required justify process. process starts heating bar 1200 1300 °c (2200 2350 °f) in less 60 seconds using high power induction coils. descaled rollers, sheared blanks, , transferred several successive forming stages, during upset, preformed, final forged, , pierced (if necessary). process can couple high speed cold forming operations. generally, cold forming operation finishing stage advantages of cold-working can taken advantage of, 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 or more shaped grooves. bar inserted rolls , when hits stop rolls rotate , bar progressively shaped rolled out of machine.

the workpiece transferred next set of grooves or turned around , reinserted same grooves. continues until desired shape , size achieved. advantages 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. process developed minimize cost , waste associated post forging operations. therefore, final product precision forging needs little 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 or draft, 1° 0°. downsize of process cost, therefore implemented if significant cost reduction can achieved.

equipment

the common thought of forging equipment hammer , anvil. principles behind hammer , anvil still used today in drop-hammer equipment. principle behind machine simple, raise hammer , drop or propel workpiece, rests on anvil. main variations between drop-hammers in way hammer powered; common being air , steam hammers. drop-hammers operate in vertical position. main reason because excess energy (energy isn t used deform workpiece) isn t released heat or sound needs transmitted foundation. moreover, large machine base needed absorb impacts. overcome of shortcomings of drop-hammer counterblow machine or impactor used. in counterblow machine both hammer , anvil move , workpiece held between them. here excess energy becomes recoil. allows machine work horizontally , consist of smaller base. other advantages include less noise, heat , vibrations. produces distinctly different flow pattern. both of these machines can used open die or closed die forging. forging press, called press, used press forging.

there 2 main types: mechanical , hydraulic presses.

mechanical presses function using cams, cranks or toggles produce preset (a predetermined force @ location in stroke) , reproducible stroke. due nature of type of system difference forces available @ different stroke positions. mechanical presses faster hydraulic counterparts (up 50 strokes per minute). capacities range 3 160 mn (300 18,000 tons). hydraulic presses use fluid pressure , piston generate force. advantages of hydraulic press on mechanical press flexibility , greater capacity. disadvantages slower, larger , more costly operate. roll forging, upsetting, , automatic hot forging processes use specialized machinery.