A basic component essential to the successful performance of today's high oompreosion engine is the %Tangshaft, The loads imposed on.the crankshaft have placed great impor- tance on its fatigue'life. A prime facto'r affecting the fatigue life of a crankshaft in the size of the crankshaft fillet radiuu area. Beginning with the 1964 model produotion, Oldsmo- bile Division initiated ,the practice of tangentially rolling crankshaft fillcte. Tho result kas been a 50 per cent increaoc in fatigue life. The deep fillet rolling proooas, originally develoflcd in 'West Germany, das selected by Oldsmobile after aeveral years of investi- gating various metal working processing methods.

N 1959, a program was started at completed in 1961, involved running ' $1ol&mobile to investigate ways to many tests on various type dressers in increase the fatigue life of the crankshaft, cooperation with diamond dressing tool with particular attention being given to companies, diamond tool manufacturers, the crankshaft's critical radii. Various and machine builders in an attempt to manufacturing methods and variations develop the type of dresser required. of existing processes pertaining to crank- Everything from cam dressing with grit shaft production were studied and tested, tools to carbide form rolls, both recipro- including rolling, shot blasting, shot cating and plunger type, was tried. peening, and liquid peening. Impregnated and set-stone formed The methods and processes studied all diamond wheels also were used in the had various shortcomings. For example, attempt to precision dress the crankpin the shot blasting method for increasing grinding wheels. Single point diamond fatigue life was rejected because of the tools following a profile cam were put size of the equipment required, the high through various tests with a minimum maintenance costs, and the uneven force amount of success. Eventually, a rotary reactions on the crankshaft radii sub- diamond wheel dresser following acproi;k:- jected to this process. The basic design msdeveloped. This development of a crankshaft also made this process mavea major role in the suc- unpredictable and unreliable because of cessful practice of tangentially rolling interferences which blocked the various crankshaft fillets. shot and media lines of force-inter- ferences such as those caused by the Preliminary Tests Proved Worth counterweights and sidewalls of the of Tangentially Rolled Fillets

crankshaft. I In early 1962, Oldemobile's Product Another process considered was under- Engineering Group. was developing a '' cutting as well as rolling of the fillets. new engine of lightweight design, with The equipment and tooling concepts prime importance being givcn to econ- available at that time indicated that this omy of opera tion and weight-to-horlic- process would be impractical. Various power ratio. The dcvclcpmcntal program tests performed showed that distortions did not cail for a major redesign of the resulted which were unacceptable by crankshaft but did require the crankshaft Oldsmobile quality utandards. Distortion to have rr higher factor of safety. The job Fig, I -CRANKSHAFT FATIGUE TEST

9 of the crankshaft bearing nrcas, as well of meeting this requirement was givcn EQUIPMENT,A crankshaft rpcclmcn I, havlnK as the entire crankshaft, would rcquire to the Production Ihgineering Croup, tangentially rolled fillets, war held by a roonant tuning fork assembly 2 whore frcqucncy of vibrn- a straightening operation, which ruicd which has as onc of its reuponsibilitics tion wcrr controlled by an clcctro-magnetic out further devclopmcntal testing. thc proccsuing of cr;inkshafu. Previously excitation unit 3. The tcrt equipment wus opcr- ateci at 200 cyclea per recond to reduce tcrting Concurrent wit11 the Oldsxnobilc pro- tricd rnctlrodu to increirsc the fatigue: lifc timc. A control war dcvclo~~edto operate thc gram to increase crankshaft fatigue life of crankshafts were I-cinvcstigatcd, New excitation unit at the 200 cpr nuturd frequency was a program to obtain Ixttcr control trials were run, new tcotti wcrc made. of the tuning fork arcernbly at a rct load. Data r, obtained from thc tent wcrc plotted (bottom) to of the radii on crankpin diameters. 'l'his I he results wcrc not encouraging, determine the effect varioun fillet hydraulic rolling program, started in 1956 and succcsufully It then was brought to Oldsrnobilc's prcsrurcs had on crankahaft endurance limits.

GENERAL MOTORS ENGINEERING JOURNAL controlled by varying the rolling pressure. This meant that reliability couId be T By ROBERT 0. MARKLEWITZ controlled. The results of the preliminary tests were used in a further testing Oldsmobile Division program of a more intense nature. Final Tooling Developed The concept of the present prod#wtion equipment used by Oldsmobile to tangen- tially roll crankshaft fillets was observed Cold rolling operation firsthand in West Germany and France provides 50 per cent where rolling equipment of a similar nature was in operation. increase in fatigue life The first crankshafts experimentally rolled in thc West German plant werc

returned to Oldsmobilc for fatiguc tcsts. + LIFE CYCLES , Test resuits indicated that the cranklihafts attention that a manufacturcr in West Fig. 2-EFFECT OF VARIOUS HYDRAULIC ., had excellent fatigue life. Inspired by ROLLING PRESSURES ON CRANKSHAFT Germany had dcvelopcd a process of ENDURANCE. These data were obtained from thcse results, a group of newer model deep rolling fillcts and contours on tests run at a constant bending moment of crankshafts was shipped to the West crankshafts, stecring knuckles, and var- 5,000 in-lb. Confidence bands ..were extremely German manufacturcr. After being clone and werc omitted from the,graph for pur- ious automotive parts that wcrc bcing poses of clarity. returned to Oldsmobile and tested, no produced in France, West Germany, improvemen t in fatigue Iifc was noted, Holland, and Italy. It also was lcarned performed to detcrminc information on The reason for the fatigue lifc increase that the crankshaft fillets bcing rolled physical properties. Samples were used on the earlier model crankshaft and the were undercut. 'l'his application was of from several crankshafts to measure lack of it on the newer model crankshaft interest to Olcismobilc, even though the tensile strength, yield strength, and was not immediately apparent. particular fcaturc of undercutting was enduiance limit (Fig. 3). After reviewing the various tests and not desirable. While static tests were being performed, visually inspecting the fillets that had Thc possibility of developing a mcthod a crankshaft was. comple tcly strain gaged been' rolled, it was discovered that the . for tangentially rolling both the crankpin for dynamic testing. This crankshaft was center section of the fillet radius had not and main journal radii of the Oldsmobile placed in an engine which operated at been cold worked. This was observed in crankshaft was studied and thought various rpm and throttle openings. The photomicrographs taken at a magnifi- feasible. Arrangcrnents were made to recorded traces were analyzed and max- cation of 100X. The problem was ship crankshafts to Wcst Germany for imum operating stresses logged. From resolved into one of rolling tool design. deep fillct rolling, then return thcm to A temporary tooling setup duplicating the fatigue data and material properties I Oldsmobile to undcrgo fatiguc tcsts. obtained, modified Goodman diagrams the West German setup was installed in Preliminary tcsts were performed by were constructed. On these diagrams, the Product Engineering and Dcsign dynamic stresses were plotted and safety Reliability Groups. One of the tcsts for factors dcterrnined . fajigue used a resonant tuning fork .and Based on test results, Oldsmobile knew associated equipmcnt that was sct up to that a crankshaft with tangentially rolled opera tc at 200 cycles per second to rcducc fillets was reliable and would perform testing time (Fig. 1-top). This equipment well. Also, the safety factor could be cnablcd thc computation of endurance limit curvcs (Fig. 1-bottom) in a rnini- mutn of t inw. Once* cranks1i;tft filtip,ti(: lifc rrquirc- ments wcrc cst;d)iisllcd, thc exact p-cssurc nccticd to roll thc fillets had lo be detcrminccl. Several groups of identical crankshafts wcrc rolled at various hychulic pressures. Thesc shafts then wcrc subjected to resonant fatigue tcsts to cvaluatc each group. All tcsts wcrc run at a constant bending moment, which produced failure in a rclativcly Fig. 3-ENDURANCE LIMIT CURVE, The short period of time. Data from the testa steel wed far ex erimentsl crankshafts having Fig, 4-TEMPORARY TOOLING TO ROLL CRANKSHAFT FlLLETS. wcrc plotted to determine the cflcct tansentially .d'hh8 war S.A.E. 1045 modi- The fixture inatallcd hed having e tenrile rtrength oi 105,000 pri and a by Oldrrnobilc to hold the toolin8 for tanrentirlly diffcrcnt rolling prcaaurea had on crank- yield atren t'h of 73,000 pi, Thr hrrdnar, rrnre tolling the filletr 18 rhown poritioned on the shaft cndurancc (Fig, 2), Teats also were w.. 96-99 &. crmkrhrft,

THIRD QUARTER 1964 the Oldsmobile plant (Fig. 4). It was 0.065-in. radius (Fig. 8-left), which is the soon discovered that the radius of the mean radius of the Oldsmobile crank- rolling tool had to be identical to the shaft's crankpins and main bearing crankshaft fillet radii and that these radii journals. The rollers are machined using had to be held. It then was realized that a 3/16-in. diameter hole in the center. the crankshah sent from Oldsmobile to This allows the roller to be placed upon West Germany for rolling had been made a mandrel for circular grinding as well with tool room type equipment and their as circular relieving and polishing to fillet radii had been machined to approx- obtain the RMS finish required. The imately 0.060 in. while the original radii of the roliers are relieved 0.014 in. rolling toolslon the German equipment off.center which gives an eccentric relief were 0.070 in. This difference caused the to the rollers, making the constant radius rolling tool to straddle the fillet and of 0.065 in. decrease in width to 0,045 in. accounted for the center section of the at the thinnest section. The reason for fillet not being adequately cold worked. the arch width varying from the mean Final tool development was eventually radius of 0.065 in. to the relieved radius completed by Oldsmobile that gave a 50 of 0.045 in. is to give a side thrust, or MAIN BEARING JOURNAL per cent increase in fatigue life for the kneading action, to the material being FILLET ROLLING LNER newer model crankshaft. The ,process of cold worked. ARM ASSEMBLIES MASTER tangential fillet rolling became a reality. Work rollers retained in the upper tool cartridge are forced against the 385- Ton Rolling Force back-up roller and into the corner radii Apllied to Crankshaft Fillets of the crankpin or main bearing journal The design of the tangential fillet sidewall and diameter when pressure is rolling machine is basically quite simple. applied st a work angle of 43" to the It consists mainly of a driving unit, two vertical centerline (Fig. 8-right). To date, master cranks to drive lever arms that the life of the work rollers has been in hold the rolling tool assemblies, a loading excess of 20,000 cycles. The life of the and unloading device, and necessary back-up rollers and needle bearing hydraulic cylinders and hydraulic supply assemblies has not been determined, to apply pressure to the tooling for the since no replacements have been made cold rolling operation (Fig. 5). The to date. Their life so far is in excess of hydraulic cylinders put the lever arms 50,000 cycles, through a moment of leverage and make it possible to apply 624 lb of squeeze pres- Special Tooling Developed sure to the rolling tool assemblies (Fig. 6). for Dressing Grinding' Wheels The tooling used for tangential rolling It is essential that the quality of the of the crankshaft fillets consists of an crankshaft prior to tangential rolling of Fig. 5-PRODUCTION SETUP FOR TAN-' upper and lower cartridge assembly the fillets be well within the process CENTIAL FILLET ROLLINC OPERATION. (Fig. 7). The upper cartridge assembly tolerances. The crankshaft must be The rolling machine has two master crankshafts from which are suspended four lever arm assem- c6ntains the work rollers and the lower straight, the index and spacing must be blies that contain tool cartridges used to roll the cartridge the support, or back-up, rollers. of high quality, and the radii prior to crankpin fillets (bottom). The master crankshafts The work rollers, made of M-2 high rolling must be within f0.005 in. max- are rotated by a driving unit. Suspended from an overarm arrongemcnt are four lever arm assem- speed steel, are machined then hardened imum of the mean dimension. Any blies with the tooling used for the main bearing through thrce draws. The final draw is attempt to roll crankshafts having toler- journal fillets. made at a temperature of WOF, The rollers then are hand poiished to a Fi . 6-PRINCIPLE OF OPERATION OF TAN- surface finish of 2 to 3 Iih4S. This RMS GENTIALFILLET ROLLINC MACHINE. When a crnnkmhaft is loaded into the machine, the main surfrice finish is ncccssary to prolong the bearing journal and crankpin fillet rolling tools con. life of the work rollers at the high pres- taincd-in their rerpective lever arms we rn a definite HYOMULIC sures involved. This surface finish also index porition, The lever armr then close the tooling CYLINDLR around the crankghaft journals and crankping, Tha rrrurcr the cold flow of mmtcrid with the main bowing journal lover arnr arrambllac rro the . least arnoun t of resistance, provides a basic support that maintains the crankshaft on its MAIN 1tMINO geometric' centerline. When all lever arm assernblier K)UN*I LNU ARMS good finish in the fillet being rolled, and are closed, the driving mechanism for the master minimizes the chance of material adhcr- crankshafts causes the lever arms to reciprocate, ing to the work roller. forcing the crankshaft (workpiece) to follow the same path of motion it does when installed in an The work rollers are 0.610 in. in engine assembly. The hydrauh cylinders apply a diamctcr and are the main working squeeze presaure that reacher 624 Ib during the first components of the fillet rolling operation. five revolutions of the crankshaft, which rotates at 60 rprn, This pressure is held for the next ten revolu- Their basic geometry consists of an 85" tiona, then reduced during the last five revolutionr. included angle that blends into a The crankshaft is unloaded in apredetermined position.

GENERAL MOTORS ENGINEERING JOURNAL Fig. 7-UPPER AND LOWER TOOL CAR- TRIDGES. The upper cartridges (top left) con- tain the work rollers and the lower cartridges . (top right) the back-up rolls. The section drawing shows the const~ctionof the work rollers and back-up rolls. The upper tool cartridge consists of a magazine that contains a center mandrel, a series of needle , bearings, an outer support roll shell, two work rollers, and a work roller retainer. The radius of the work roller is form ground in a backup roller having a Rockwell C hardness between 62 and 63. The two work rollers that contact the back-up roll are retained in a bronze cage in the magazine assembly merely to hold them in position. The hardness of the work rollers is between 58 and 69 Rockwell C. The lower tool cartridge consists of four center mandrels, four sets of needle bearings, and four back-up rollerr sct in pairs at a 45" included angle. This angle is, 22-1/2O off the centerlinc of the crankpin or main bearing journal of the crankshaf t. Riding in contact with each pair of back-up rolls ia .another roller approximately 0.500 in, in ROLLER BOG BACK-UP ROLL FOR diameter, which bears tangent against the two WORK ROLLERS work rollers and against the crankpin or journal diameter, Thus, the lower tool cartridge provides two support pointa to the crankpin diameter or journal diameter.

ROLLER ances not within specified limits will result in distortion of the crankshaft or WORKPIECE malformed radii. During early attempts to improve the process tiobtain better fillets and spacing, gaging was developed to check the spacing and counterweight location 'at BACK-UP ROLL RETAINING CLIP the bearing shoulder in rough crankshaft machining operations. Tooling also was

I \ / developed for the main bearing journal \ / ROLL \ and crankpin turning operations that SUPPORT ROLL would leave the correct fillet shoulder MANDREL ROLLER BODY A height. This assured the proper amount

t 1

1 I

Fig. 8-WORK ROLLER AND i 60 RPM TQOLINC GEOMETRY, Prcssurc is ap21icd nt an angle of 43' to force the work rollcrs into thc corncr radii of the I fillets being rolled on either thc crnnk- ; pin or main Lcaring journals of n i crankshaft. Thc 43" anglc allows the 1 work rollers to npproach the unrollcd 1 fillet at an angle less than 45". The i ultimatc position of the work rollers i at the end of the rolling cycle is 45", or i siightly leas duc to part to\cranccs. j The aqueczc prcssure of 62%Ib excrtcd , by the lever arms in which the rollerr 1 arc contained !gives a resultant work- I ing contac! pressure of approximately j

385,000 pal. 1 I 1

THIRD QUARTER 1964 Fig. 10-PROJECTING COMPARATOR. This comparator checks main bearing journal spacing and radius contours for both journals and crankpins. The accuracy of the comparator at a magnification of I5 times enables rigid quality control to be maintained over the forms and tangential blending of all radius areas,

of stock so that a full radius, according journals and crankpins, a special com- to process tolerances, could be finish parator was developed (Fig. 10). The ground. The width of the main bearing accuracy of the comparator enables rigid journal rough grinding wheels was made quality control to be maintained over 0.020 in. narrower than the wid!h of the the forms and tangential blending of all finish grindi.ng wheels. This variation in radius areas. width, along with proper spacing toler- ances, assured that the finish grinding operation on the jourr,als would leave The introduction of the cold working- ample stock to produce a quality radius, method for tangentially rolling the fillets To grind a precise radius on main of crankshaft radii has provided excellent bearing journal fillets, Oidsmobile uses results in increasing fatigue life. The cold a diamond radius dressing bar (Fig. 9). working concept also is being considered This bar is constructed of a series of nine for future application to other areas of diamond-impregnated radius form dress- the crankshaft. For cxamplc, a testing ing whccls whose diameter and spacing program is currently in cffcct at 01th- are the same as the diameter and spacing ... mobilc to roll the diameters of crankpins of the journals of the crankshaft, After and main bearing journals instcad of the periphery of the grinding wheels arc using an abrasive finishing process, Good finish dressed, the diamond dressing bar results from st geometric and finish is placed in the grinding fixture in the standpoint have been obtained. On same manner as the crankshaft. The experimental parts proccsscd to date, it fixture then is run through an automatic has been possible to roll surfaces on cycle similar to that uscd when grinding crankpin and journal diameters from 60 crankshaft journals. During this one to 70 RMS down to two to three RMS Fig. 9-DRESSING BAR. This bar precision dresser the grinding wheels used to grind the cycle, all nine radii of the crankshaft in ten seconds. The program on cold crankshaft journals. The bar is constructed of a journal grinding wheels are precision rolling diameters also is expected to series of nine diamond-impregnated dressing wheels whose diameter and spacing are the same dressed. provide further improvements in round- as the diameter and spacing of the journals of To check the bearing journal spacing ness, surface characteristics, anti elimina- the crankshaft. and radius contours of both the bearing tion of barrel or hourglass configurations.

4 6 GENERAL MOTORS ENGINEERING JOURNAL