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Anti-loosening bolted joints were developed with an innovative double-thread mechanism composed of coaxial single and multiple coarse threads. The number of coarse threads of the multiple-thread was set to 3 (denoted as 3thread DTB-II), and its thread structure was fundamentally modified as follows: (i) one of the three multiple-thread grooves was removed for 3thread DTB-II specimens and one of the two remaining grooves shifted downwards by a half pitch (denoted 3-1thread DTB-IIB) and (ii) the depth of the multiple-thread grooves was reduced by up to 50% of the thread height (denoted 3-1thread DTB-IIC). FEM thread rolling simulations were performed using a dedicated die. The two kinds of modified DTB-II specimens were rolled precisely and the thread heights reached the target value at all cross sections. The forming states in the thread rolling experiments well matched the FEM simulation states. The performance evaluation tests demonstrated that the 3-1thread DTB-IIC specimens had sufficient tensile strength, and its anti-loosening performance exceeds the reference level given in DIN25201.

We have devised new bolt fasteners based on an innovative double thread mechanism composed of a coarse single thread and coarse multiple threads (called DTB-II). In order to improve the rolling formability and the strength, the screw-thread of the DTB-II was fundamentally modified in this study. The number of multiple threads was reduced by one from the 3thread DTB-II (called 3-1thread DTB-II). The FEM thread rolling simulations were first performed using dedicated dies having a groove that followed the same outline as the thread profile of the modified DTB-II. The 3-1thread DTB-II was rolled precisely and the thread heights completely reached the target level at any cross-section, and the difference in the rolled filling rate remarkably decreased due to the material flow in the circumferential direction. The equivalent plastic strain was intensively high at the groove bottom where a coarse single thread was traversed by bottom of multiple threads, that might cause some surface defects. The actual forming states in the thread rolling experiments well reproduced the FE-simulation results. The performance evaluation tests show that the 3-1thread DTB-II with the double nut structure has a practically sufficient tensile strength and its anti-loosening performance clearly exceeds that of the conventional DTB-I composed of a coarse-single thread and a fine-single thread.

Surface rolling experiments and surface durability tests were carried out using Cr−Mo and Ni−Mo pre-alloyed sintered steel spur pinion gears with different densities fabricated by powder metallurgy (P/M). The P/M gear specimens were machined from sintered packs made from the single-press single-sinter route and some were surface-rolled using a high-precision CNC form-rolling machine of two roller-dies transverse-type. A fully densified surface layer less than 2% porosity was obtained on the tooth flank approximately 0.5 mm thick when P/M pinions with a density of 7.4 Mg/m 3 or more were surface-rolled using the amount of stock rolled at 0.15 mm. The load bearing capacity of P/M pinions were estimated by gear running tests using a power re-circulating type testing rig. A counter gear was made of standard grade Cr−Mo wrought steel. All test gears were case-carburized under identical conditions and finished by grinding. The representative damages for every P/M pinion were pitting near the pitch point. The experimental results show that the load bearing capacity of surface-rolled pre-alloyed P/M gears with a density 7.40 Mg/m 3 or more completely matches that of a case-carburized Cr−Mo wrought steel gear.

Surface rolling experiments and surface durability tests were carried out using powder metallurgy (P/M) gears made of 1.5Cr-0.2Mo single-press single-sinter (1P1S) high density (7.55×103 kg/m3) sintered steel. The fundamental densification properties of this P/M material were first examined using P/M rollers. A high precision form rolling machine of two roller-dies transverse type was employed. The porosity became nearly zero from the surface down to a depth of at least 0.5 mm when the amount of decrease in the roller radius was more than 0.15 mm. Next, the gear tooth profile analysis was done by finite element simulation (FE-simulation) to optimize some shape parameters of a modified convex tooth profile of P/M spur gears before rolling. Simulation results agree well with the experimental data and gears with good tooth profile accuracy and a fully densified surface layer of about 0.5 mm in depth on the gear flank could be obtained. The gear running tests were finally conducted using a power re-circulating type gear testing rig with a counter pinion gear made of Ni-Cr-Mo wrought steel. Both P/M gears and counter pinions were case-carburized and finished by grinding under the same conditions. The test results confirmed that high density 1.5Cr-0.2Mo P/M gears had sufficiently high load bearing capacity as an automotive power transmission gear and those surface durability tended to increase by surface rolling.

This paper describes a study on the load bearing capacity of high density sintered metal gears with surface-densification. High density sintered metal gears were hobbed, and then surface-rolled. These gears were case-carburized after surface-rolling. The effect of surface-rolling on the surface property was examined by measuring porosities and hardness near surfaces of rolled gears. Running tests for these gears were performed, for the cases when these gears were used as a driver or follower. A failure mode and load bearing capacity of high density sintered metal gears and the effects of surface-rolling on the load bearing capacity of sintered metal gears were determined, and the results were compared with those of carburized wrought steel gears. The experimental results show that the load bearing capacity of high density sintered metal gear with surface-densification is comparable to that of a carburized wrought steel gear.

This paper investigates the characteristic of single-layered and multi-layered compacts made by selective laser sintering using titanium powder. The surface texture and tensile strength were investigated by using single-layered compacts. There were few defects in surface of specimen laser sintered in vacuum, and the roughness was smoother than that of the specimen laser sintered in argon. Maximum tensile strength of single-layered compact laser sintered in vacuum was about 200MPa. The shrinkage and mechanical strength were investigated by using multi-layered compacts. There was a unique tendency in the shrinkage of multi-layered compacts, which the density was around 75% and the adhesive bonding was not observed between layers, resulted in 70MPa of maximum bending strength and 50MPa of maximum tensile strength.

The final objective of this study is to establish the optimized manufacturing method of herringbone microgrooves for fluid dynamic spindles. In this article, two kinds of fundamental coining experiments of a simple indentation are carried out to create microgrooves of 5∼10μm depth. In order to compare the coining performance, two kinds of materials are used. One is an austenitic stainless steel (SUS303) of the wrought material and the other is also an austenitic stainless steel (SUS304L) of metal injection molded (MIM) material which has 5% porosity. In experiment-1, a flat head punch with three micro projections of 10μm height is pushed into a hexahedral specimen with or without the ultrasonic vibration. The groove depth of the MIM material increases in proportion to the punch load in the static indentation and its maximum value is about 80% larger than that of the wrought material. The imparting of the ultrasonic vibration is effective to increase the amount of groove depth especially for the MIM material under the lower punch load. In experiment-2, a circular punch and a circular anvil are statically pushed into a cylindrical specimen to produce 18 parallel grooves with an equal pitch in the circumferential direction. The groove profiles become almost uniform and the burr formation at tips of groove shoulder is effectively suppressed under the excessive amount of die indentation.

The purpose of this study is to optimize the finish rolling process of sintered Fe alloy gears (P/M gears) using a screw-shaped tool to improve the tooth profile accuracy and the load carrying capacity. In this article, finish rolling experiments of unmodified P/M gears using an unmodified screw-shaped tool are firstly carried out to investigate the fundamental rolling properties. The porosity in the surface layer of rolled gear teeth is reduced to the target level, but the tooth profile becomes heavily concave. Secondary, modified P/M gears with a convex tooth profile are rolled to improve the tooth profile accuracies. Gears with a good tooth profile and a good surface finish are obtained by optimizing the amount of radial feed of the tool. Finally, simultaneous rolling of tooth and fillet surface of unmodified gears using a modified screw-shaped tool are carried out. It is confirmed that the rolled tooth profile are scarcely affected by the amount of rolling stock and the tooth surface and the fillet at the root of gears are successfully consolidated in one rolling pass using this method.

This paper investigates the characteristic of single-layered and multi-layered compacts made by selective laser sintering using blended bimodal titanium powders. The surface texture and tensile strength were investigated by using single-layered compact. There were few defects in the surface of specimen sintered in vacuum, and the roughness was smoother than that of specimen sintered in argon. Maximum tensile strength of single-layered compact sintered in vacuum was about 200 MPa. The shrinkage and mechanical strength were investigated by using multi-layered compact. There was a unique tendency in the shrinkage of multi-layered compacts, which the density was around 76% and the adhesive bonding was not observed between layers, resulted in 70 MPa of maximum bending strength and 50 MPa of maximum tensile strength.

Numerical tooth profile analysis of finish rolling process of sintered Fe alloy gears using screw-shaped tool are carried out to obtain some useful information for optimum design of the tool. P/M gears are approximated by a continuum model of a ductile porous material. Two kinds of 3 dimensional FEM models are proposed and the analytical results are compared with the experimental ones. In particular, the influence of the elastic deformation and the motion of the tool on the deformation of the workpiece are investigated in detail. The rotation motion of the tool during rolling cannot be ignored when evaluating the distribution of the amount of stock rolled of the workpiece precisely. An equivalent Young's modulus is adopted to the material properties of the workpiece to take into account the elastic deformation of the rigid tool indirectly. The analytical results about the amount of stock rolled and the tooth profiles of the rolled gear teeth are agree well with the experimental ones.

It has already been proven that bolt fasteners based on the double thread mechanism have an excellent anti-loosening performance. The purpose of this study is to establish a mass production method for these double thread bolts (DTBs) by thread rolling. The pitch ratio of the coarse thread and the fine thread of the target DTB is set as 2 to 1. A two-die roller with a plunge feed is employed as the rolling method due to its fine processing precision. The roller dies used in the experiments have special grooves on the external surface which follow the same outline as the thread profiles of the DTB. Using these special dies, the DTB can be successfully formed in the same process as single thread bolts. The deformation of a workpiece during rolling is examined, and the examination shows that the formed material smoothly fills the die grooves in each cross section. The rolled DTBs completely pass the loosening test with extremely severe vibration and impact, as specified in NAS3354. The tensile fatigue strength of the rolled DTB is about 100% greater than that of the cutting DTB.

The purpose of this study is to examine a practical application of a finish rolling process using a screw-shaped tool to consolidate the surface layer of sintered Fe alloy gears and to improve the tooth profile accuracy and the load carrying capacity simultaneously. These objectives are almost attained in the previous works except the crowning in tooth trace direction, which is the essential matter for gears in automotive transmissions. In this paper, a numerical control finish rolling machine is developed to enable the crowning process. In this new apparatus, the amount of radial feed of the tool is synchronized with the axial feed of the workpiece to put a specified crowning on the rolled gear teeth. A simple calculation method is proposed to decide the rolling orbit for crowning. The crowning profiles predicted in the analysis agree well with the experimental ones. Gears with a good tooth profile and a good surface finish can be obtained.

The load bearing capacities of sintered gears made of prealloy steel powder were tested. The P/M gears were machined from sintered packs, and some were surface-rolled. The bending durability was investigated using single tooth bending fatigue tests. The surface durability was evaluated using a power recirculation-type gear test rig with a counter gear made of Cr–Mo wrought steel. The test gears were case-carburized and finished by grinding. The test results showed that Ni–Mo P/M gears with a density of 7.5 Mg/m3 had sufficiently high durability to replace gears made of typical Cr–Mo wrought steel.

In conventional hot forging of connecting rods, the material wasted to the flash accounts approximately 20 to 40% of the original workpiece. In order to reduce the cost of forged products, the forging must be performed in a closed cavity to obtain near-net or net shape parts. In flashless forging, the volume distribution of the preform must be accurately controlled to avoid overloading the dies and to fill the cavity. Additionally, the preform must be simple enough to be mass produced. This study deals with the design of the optimum preform to forge a connecting rod without flash. The initial preform design was obtained from physical modeling experiments. The optimization of this preform was found through 3D FEM process simulations. The advantage of performing simulations is that no tooling has to be built and the number of experimental tryouts can be significantly reduced. A preform optimization methodology was derived for this investigation.

A new method of finish rolling is proposed to finish tooth surfaces and fillets at roots of gears in one pass, using a screw-shaped tool. A preliminary experiment of finish rolling of only tooth surfaces of spur gears is conducted with a trial constructed apparatus. Gears with good tooth profile accuracy and good surface finish are produced without any modification of the tooth profile of the tool or the work by this method. The rolled tooth surface of the work is markedly hardened.

This paper describes the effects of surface rolling on the load bearing capacity of sintered metal gears. Sintered metal gears and rollers were surface-rolled under various amounts of rolling. The effects of rolling on the surface properties were examined by measuring the porosities and hardness near the surfaces of the rolled gear teeth and rollers. Bending fatigue tests for the surface-rolled sintered metal gears and contact fatigue tests for the rollers were carried out. The effects of the amount of rolling on the load bearing capacity of sintered metal gears and rollers were determined, and these results were compared with the results for as-sintered and wrought steel gears and rollers.