Single Tooth Bending Fatigue Research Articles

Ni–Mo 系低合金鋼粉を適用した焼結転造浸炭歯車の特性

Finish gear rolling experiments, single tooth bending fatigue tests and gear running tests were carried out using P/M gears made of Ni–Mo pre-alloyed steel powder. A high precision CNC form rolling machine of two-roller dies transverse type was employed. The entire gear tooth flank was successfully densified from the tip to the root fillet by surface rolling. The durability test results show that the test case-carburized P/M gears with a density of 7.5 g/cm3 can achieve bending and surface fatigue strengths of 1.0 GPa and 2.0 GPa, respectively, which completely match with those of case-carburized SCM415 (0.15C–1.0Cr–0.2Mo–0.7Mn) wrought steel gears and those load bearing capacities tend to increase by surface rolling. The compressive residual stress near the gear flank surface is the level of 800 MPa, which is almost equivalent to that of wrought steel gear. The representative damages of P/M gears in gear running tests are pitting, which is the case with the wrought steel gear.

Improvement of Surface Densification and Fatigue Strength by Tooth Root Rolling of Sintered Ferrous Alloy Gear Added Mo

Surface rolling were carried out using P/M spur gears of 0.6Mo-0.2C partially alloyed sintered steel with the density of 7.18 g/cm3. A CNC form rolling machine of axis intersection type was employed, and an unmodified screw-shaped rolling tool was prepared. Then, porosity distributions in the surface layer of rolled gear teeth root were measured and the effects of the surface rolling on the selective surface densification behaviors were evaluated. Moreover, to obtain higher fatigue strength, reverse rolling was introduced to standard gears. As a result, the porosities in the tooth root were sufficiently reduced at 700 μm feed in rolling process. Furthermore, a profile shifted gear was prepared to increase the effect of surface rolling. After case hardening, the single tooth bending fatigue durability reached to about 83 % of the case hardened wrought steel gears of SCM415.

Development of High Precision and Strength Sintered Ferrous Alloy Gear by Rolling -3rd Report-

Surface finish rolling experiments were carried out using P/M spur gears of 0.6Mo-0.2Mn pre-alloyed sintered steel and of 0.8Mo-0.2Mn partially alloyed sintered steel with the density of 7.10 Mg/m3. A CNC form rolling machine of axis intersection type was employed, and a modified screw-shaped rolling tool was prepared: the modified concave tooth profile optimized by numerical tooth profile analysis for simultaneous rolling of tooth and fillet surface. Then, porosity distributions in the surface layer of rolled gear teeth were determined and the effects of the amount of tool radial feed R0 on the selective surface densification behaviors were evaluated. Besides, single tooth bending fatigue test was conducted. Gears with good tooth profiles were obtained by using the modified tools. As a result, the porosities in both the tooth flank and the fillet at the root were reduced to the target level at R0=600 μm in simultaneous rolling process. Furthermore, the single tooth bending fatigue durability was much improved to about 60 % of the case hardened wrought steel gears of SCM415.

Bending Durability and Impact Strength of Gear Tooth of 1.5Cr-0.2Mo Sintered Alloy Steel Gears for Automotive Transmission

Single tooth bending fatigue tests were carried out using spur gears of 1.5Cr-0.2Mo sintered steel having a density of 7.55 g/cm3 and the effects of surface rolled or shot peening (WPC) on bending fatigue strength were examined. P/M gears were case-carburized. The bending fatigue durability of this P/M gears not surface densified is equal to that of case-carburized wrought alloyed steel gears of SCM415. The bending fatigue limit of the P/M gear was much improved by WPC. The impact strength of P/M gear tooth was investigated using an impact testing machine for gears. The mean value of peak impact damage torque of the surface rolled P/M gears almost matches that of wrought steel gears of SCM415. Both test results indicate the feasibility of this high density Cr-Mo P/M gears to replace case-carburized wrought steel gears made of typical Cr-Mo alloyed steel.

鉄系焼結合金歯車の転造による高精度化・高強度化―第２報―修整歯形工具による鉄系焼結合金歯車の各種転造特性

Surface finish rolling experiments were carried out using P/M spur gears of 0.6Mo-0.2Mn pre-alloyed sintered steel and of 0.8Mo-0.2Mn partially alloyed sintered steel with the density of 7.10 Mg/m3. A CNC form rolling machine of axis intersection type was employed. Three kinds of screw-shaped rolling tools were prepared: one was an unmodified tool and the others were the modified tools for simultaneous rolling of tooth and fillet surface having concave tooth profiles optimized by numerical tooth profile analysis. Porosity distributions in the surface layer of rolled gear teeth were determined and the effects of the amount of tool radial feed R0 on the selective surface densification behaviors were evaluated. Single tooth bending fatigue test was conducted. Gears with good tooth profiles were obtained by using the modified tools. The porosities in both the tooth flank and the fillet at the root were reduced to the target level at R0=600 μm in simultaneous rolling process. The single tooth bending fatigue durability was much improved to the same level as that of the wrought steel gears of SCM415.

Three point load application in single tooth bending fatigue test for evaluation of gear blank manufacturing methods

This study deals with the applicability of a single tooth bending fatigue test in the evaluation of gear blank manufacturing methods using three point bending loading. The “single tooth bending test” is an effective and rapid way of determination of the performances of gears instead of expensive and time-consuming life tests. Bending tests were applied to two groups of gears cut by hobbing and gear shaving from gear blanks. The first group of gear blanks was obtained by CNC-lathe machining from round bars and the second group of blanks was produced by closed-die upsetting. Both of the gear groups were additionally tested after case hardening by carburizing. It was shown that the three point bending test can easily be adapted and applied as an effective and rapid way of comparing the performances of such gears.

Increasing the bending fatigue resistance of spur gear teeth using a presetting process

The fatigue life of machine elements may be increased if beneficial compressive residual stresses are introduced. One mechanical method of introducing compressive residual stresses is prestressing or presetting. This paper discusses the application of a presetting process to AISI 1040 steel spur gear teeth. Gear teeth were individually preset using a single tooth bending fatigue fixture. Subsequent fatigue testing with R=0.10 using the same fixture demonstrated that presetting increased the bending fatigue life by an average of 670% and 95% for fatigue under an applied maximum unit load of U L=216 MPa and 253 MPa, respectively. Finite element analyses were performed to model the application of the presetting process to spur gear teeth, enabling prediction of residual stress and permanent tooth deformation.

Comparative bending fatigue strength of precision forged spur gears

To determine the bending fatigue strength of precision forged spur gears and to compare the results with those obtained from conventional cut gears, single tooth bending fatigue tests were carried out on both through-hardened and induction-hardened gear teeth. The gears were produced from rolled bar cut blanks, disc forged blanks or precision forged teeth blanks. For this purpose, a special test fixture was designed and built for an Amsler high-frequency vibrophore fatigue testing machine. The results show that the endurance limit of precision forged gears is significantly higher than those obtained from cut gears. The bending fatigue strength of forged gears was some 12.5 per cent higher than the cut teeth in a through-hardened condition and 8.4 per cent higher for the induction-hardened teeth. The effect of surface roughness at the tooth root area on the bending fatigue strength of the forged gears is also shown.

Bending fatigue and contact fatigue characteristics of carburized gears

In order to assure reliability, the manufacture of gears for power transmission in high load bearing applications requires precise control of a wide range of processing parameters during manufacture, aimed at achieving specific material properties. Process selection and control in forming and heat treatment operations plays a crucial role in gear production, and must start at the design stage. Material selection, choice of forming processes, thermochemical and heat treatment operations, surface finish and condition will ultimately determine the integrity and performance limits of the gears. An ongoing research programme by Birrana Engineering, Adelaide, and the University of South Australia involves the evaluation of materials, process route and process control used in the manufacture of a range of gears and relates these factors to fatigue resistance, with the aim to reduce production costs and improve gear quality and reliability. The results of single tooth bending fatigue, and contact fatigue tests on production gears manufactured from EN39B steel (steel A), and experimental steels B, C and D (heat treatment details restricted for commercial reasons) are presented and discussed.