Workpiece properties Benefits of solid forming .1 Economic aspects

6.2.2 Workpiece properties

Du e t o t h e h igh d egree o f geo m et rical accu racy, su rface q u alit y an d h igh ly favo rable m ech an ical p ro p ert ies, t h e wo rkp iece ch aract erist ics o f co ld fo rged co m p o n en t s are gen erally very go o d . Th e m ech an ical ch aract erist ics d ep en d o n p h ysical fact o rs an d can o n ly be in flu en ced t o a lim it ed d egree. Th e fact o rs in flu en cin g o p erat in g accu racy in t h e p ro d u ct io n o f p recise geo m et ries an d su rface p ro p ert ies, wh ich are list - ed in Table 6.2.1 , m u st be t aken in t o co n sid erat io n in t h e fo rge p lan t . In p rin cip le, t h e p rim ary req u irem en t is fo r a h igh ly p recise an d rela- t ively rigid fo rgin g p ress. If su ch a p ress is n o t available, even fu ll co m - p lian ce wit h all t h e o t h er fact o rs su ch as excellen t d ie d esign can n o t co m p en sat e fo r t h is d eficien cy. Next , in o rd er o f im p o rt an ce are t h e vo lu m e co n t ro l o f t h e billet , t h e p ro cess co n cep t , et c. Co m p lian ce wit h an d m o n it o rin g o f all t h e p ro cess p aram et ers t h u s en su re t o ach ieve t h e req u ired service ch aract erist ics o f a co m p o n en t . Ho wever, it is n eces- sary t o co n sid er t h at at t h e sam e t im e p ro d u ct io n co st s also in crease. Desp it e t h e h igh d egree o f co st red u ct io n ach ieved in au t o m at ed fo rgin g lin es, it is o n ly wit h well t rain ed st aff, wh o are cap able o f en su r- in g co rrect o p erat io n o f t h e eq u ip m en t , t h at it is p o ssible t o ach ieve a sat isfact o ry ret u rn o n su ch a large cap it al in vest m en t . To h igh ligh t t h e 443 Benefits of solid forming Fig. 6.2.2 Oil filter housing – extruded single component compared to three-part w elded configuration extruded w elded flange cup connecting piece Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 im p ortan ce of th e h u m an factor h ere, th is h as been in clu d ed as a sep a- rate item in Table 6.2.1 . Th e skill of th e p ress op erator is p aram ou n t in th e su ccessfu l op eration of th e p rod u ction system . He sh e takes th e in flu en cin g factors in to accou n t an d evalu ates th em . Tolerances Ach ievable ISO t o leran ces fo r d ifferen t t yp es o f co ld fo rgin g an d co m - p lem en t ary p ro cesses are su m m arized in Table 6.2.2 . Th e “variat io n 444 Solid forming Forging Table 6.2.1: Classification of process parameters that affect the geometrical accuracy and surface quality of a forged part Line: M achine kinematics, stiffness, off-center load capacity, gib precision, heating behavior w arm, natural frequency Automation w eight control, careful feed and discharge, positioning accuracy, transfer, press force control Heating type, temperature, temperature control Cooling temperature control Billet: Starting material analysis, strength, microstructure M aterial form wire, bar, thick sheet; rolled, peeled or drawn M anufacturing process shearing, saw ing, blanking Pre-treatment possibly soft-annealing, pickling, phosphating, coating Process : Processing sequence No. of steps single-step, multiple-step, process combination Temperature hot h, cold c, w arm w Intermediate treatment recrystallization, normalization w arm, pickling, phosphating, coating Lubrication and cooling additional lubrication, spraying, flooding w arm, lubricant and coolant w arm Clearance for part transport Die: Precision die concept, details, production process, adjustment of upper and low er die, mechanical die deflection, thermal die expansion Wear die material, surface, coating, change interval Human element: Die designer, die manufacturer, operating staff, training and instruction specialized skills Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Table 6.2.2: ISO tolerances for the cold extrusion and complementary processes VDI 3138 ran ge” o f a fo rgin g p ro cess in d icat ed h ere sh o u ld be in t erp ret ed so t h at sm aller, ligh t er-weigh t co m p o n en t s fall in gen eral t o t h e left -h an d sid e o f t h e bar lo wer t o leran ce field s an d larger, h eavy-d u t y co m p o n en t s fall m ain ly t o t h e righ t -h an d sid e wid er t o leran ce field s. Th e red sec- t o rs are t o leran ces wh ich can be ach ieved u n d er n o rm al co n d it io n s. Th e o ran ge areas are ISO t o leran ces wh ich can be ach ieved in sp ecial cases bu t wit h larger effo rt an d co st . Th is in fo rm at io n also in d icat es t h at t h e iro n in g an d red u cin g p ro cesses p erm it t h e im p ro vem en t o f accu racy levels by as m u ch as t wo q u alit y levels. Th e h igh d egree o f d im en sio n al accu racy is n o t ach ieved eq u ally fo r all t h e d im en sio n s o f a co m p o n en t , bu t sh o u ld be rest rict ed t o d im en sio n s t h at are crit ical fo r fu n ct io n al o r m at erial rem o val co n sid erat io n s. Th e ach ievable d im en sio n al t o leran ces n o rm al, n arro w fo r co ld ext ru sio n o r t h e p ro cess co m bin at io n warm ext ru sio n an d su bseq u en t co ld sizin g are in d icat ed fo r t h e t h ree m o st freq u en t fo rm in g p ro cesses, so lid fo rward ext ru sio n , cu p backward ext ru sio n an d iro n in g Tables 6.2.3 t o 6.2.5 . Th is in fo rm at io n is given relat ive t o t h e m ain d im en - 445 Benefits of solid forming form ingprocess hot e trusion warme trusion warmcold e trusion cold e trusion ironing upsetting open die forward e trusion ITspecification as per INI uality 6 7 6 3 achie able withspecial m easures achie able without special m easures Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 Table 6.2.4: Diameter, concentricity, w all and w eb thickness tolerance of backw ard extruded cups, in mm D tolerances up to diameter run-out mm normal narrow normal narrow D d D d 25 0.20 0.15 0.10 0.03 0.25 0.10 50 0.30 0.20 0.125 0.035 0.30 0.15 75 0.35 0.30 0.15 0.04 0.35 0.20 100 0.40 0.50 0.175 0.06 0.40 0.25 s, h tolerances up to w all thickness s bottom thickness h mm normal narrow normal narrow 2 0.10 0.075 0.25 0.15 5 0.15 0.10 0.35 0.20 10 0.25 0.15 0.45 0.30 15 0.35 0.25 0.55 0.40 446 Solid forming Forging Table 6.2.3: Diameter, length and deflection tolerance of solid forw ard extruded parts, in mm D tolerances L up to diameter D up to length deflection B mm normal narrow narrow narrow mm normal normal 25 0.10 0.02 150 0.25 0.20 0.15 0.03 50 0.15 0.08 200 0.75 0.50 0.25 0.05 75 0.20 0.15 300 1.50 1.00 0.35 0.07 100 0.25 0.18 450 2.00 1.50 0.50 0.10 Table 6.2.5: Diameter, concentricity, w all thickness tolerance in mm of tubular components produced by ironing D up to mm diameter run-out s up to mm w all thickness s normal narrow normal D d D d 25 0.15 0.10 0.075 0.025 0.25 0.10 1 0.075 50 0.25 0.20 0.10 0.03 0.30 0.15 2 0.075 75 0.30 0.25 0.125 0.35 0.035 0.20 4 0.10 100 0.35 0.30 0.15 0.45 0.045 0.25 6 0.10 0.035 0.04 0.05 0.07 narrow normal narrow tolerances Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 sio n s fro m Fig. 6.2.3 . As alread y in d icat ed , clo ser t o leran ces can be ach ieved as a resu lt o f sp ecial m easu res su ch as cen t erin g o f u p p er an d lo wer d ies. Th e len gt h t o leran ces refer t o t h e sh o u ld er len gt h s wit h in t h e u p p er o r lo wer d ie, n o t t o t h e o verall len gt h o f t h e wo rkp iece in clu d in g excess m at erial. Surface finish O n n et sh ap e an d n ear n et sh ap e co m p o n en t s wh ich d o n o t n eed rem a- ch in in g, t h e su rface ro u gh n ess is an im p o rt an t q u alit y ch aract erist ic. Th e co n t act su rfaces o f t h e co re o f fo rm ed claw p o les, fo r exam p le, m u st n o t exceed a su rface ro u gh n ess o f R z = 10 m m , as o t h erwise t h e req u ired m agn et ic flu x ch aract erist ics can n o t be ach ieved . By t h e sam e t o ken , a sim ilar req u irem en t ap p lies t o fo rged gears. Table 6.2.6 p ro - vid es a su m m ary o f t h e ach ievable su rface ro u gh n ess p ro p ert ies R z an d R a fo r d ifferen t fo rm in g p ro cesses. Th e o ran ge areas are valu es wh ich are m easu red befo re, t h e red areas are valu es wh ich are m easu red aft er rem o val o f t h e lu brican t layer. Gu id elin e valu es o n t h e p h o sp h at e layer are R a = 0.3 – 0.8 m m an d aft er rem o val ap p ro x. R a = 0.6 – 2.5 m m . Th e su rface q u alit y is p o sit ively in flu en ced by a h igh sp ecific p res- su re, h igh relat ive velo cit ies an d su rface q u alit y p rio r t o fo rgin g. Fo rm in g p ro cesses wit h h igh sp ecific p ressu res an d relat ive velo cit ies 447 Benefits of solid forming Fig. 6.2.3 M ain dimensions in solid forw ard extrusion, backw ard cup extrusion and ironing process forw ard rod extrusion backw ard cup extrusion ironing s d D D D d h s d B L Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 are o p en d ie ext ru sio n , iro n in g an d so lid fo rward ext ru sio n . Th e su rface p ro p ert ies are in flu en ced h ere by t h e fo llo win g fact o rs: st art in g m at erial: h o t ro lled , san d blast ed , p eeled , co ld d rawn in t erface: sh eared , sawn in t erm ed iat e an n ealin g: scale free: u n d er in ert gas wit h scale: san d blast ed , p ickled Mechanical properties Th e h ard n ess, t en sile st ren gt h an d yield st ren gt h are in creased by p las- t ic flo w. Ho wever, at t h e sam e t im e t h e valu es fo r n o t ch im p act st ren gt h , elo n gat io n an d n eckin g are d ecreased . Dep en d in g o n t h e d egree o f t ru e st rain , in t h e case o f st eels wit h lo w an d m ed iu m carbo n co n t en t , t en sile st ren gt h can in crease by u p t o 120 , yield st ren gt h by bet ween 100 an d 300 , an d h ard n ess by bet ween 60 an d 150 . 448 Solid forming Forging Table 6.2.6: Surface qualities R z R a achieved using different forging methods form ingprocess hot e trusion warme trusion warmcold e trusion cold e trusion ironing upsetting open die e trusion 5 12 15 18 20 30 40 50 60 70 80 90 100 0,5 2 1 3 4 6 8 10 12 15 20 25 30 before rem o al of the lubricant carrier layer after rem o al of the lubricant carrier layer Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 W h ere n o h eat t reat m en t is carried o u t , t h is effect can be u t ilized in o rd er t o rep lace h igh -allo y st eels by lo wer-allo y grad es. Du rin g t h e d evelo p m en t o f t h e p ro cess p lan , it is p o ssible wit h in cert ain lim it s t o ach ieve sp ecified st ren gt h valu es in cert ain sect io n s o f a co m p o n en t by su it able ch o ice o f t h e billet d iam et er an d t h e p ro cess seq u en ce. 449 Benefits of solid forming Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998 6 Solid forming Forging

6.3 M aterials, billet production and surface treatment