Yasutsune Ariura

An investigation of surface failure of surface-hardened gears by scanning electron microscopy observations

Abstract The tooth surface of surface-hardened gears often becomes grey stained under a heavy load before pitting or spalling occur. The grey-stained area increases with running time and this failure causes degradation of the tooth profile. The nature of grey staining and the influence of surface conditions on the phenomena are investigated by scanning electron microscopy observations of the surfaces of gear teeth and rollers. It is established that the grey staining consists of many microcracks and micropits. Their formation and wearing off occur successively. It is reconfirmed that surface roughness has a significant influence on grey staining.

Automatic leveling procedure by use of the spring method in measurement of three-dimensional surface roughness

Leveling of specimen surfaces is very important in measurement of surface roughness. If the surface is not leveled, the measured roughness has large distortion and less vertical measurement range. It is convenient to utilize some automatic leveling procedures instead of manual leveling which needs longer adjustment time. In automatic leveling, a new algorithm is proposed, which is named the spring method superior to the least square method. The spring method has an advantage that a part of tentative data points is used to calculate the surface inclination, so the obtained results are less influenced by local pits for example. As examples, the spring method was applied to actual engineered surfaces, which were milled, shot-peened, and ground surfaces, and also an artificial ditched surface. The results went well for the calculation of the surface inclinations and consequently the specimen surfaces were leveled with less distortion and large vertical measurement range can be achieved. It is also found the least square method is a special case of the spring method with using all sampling data points. That means the spring method is a comprehensive procedure including the least square method. This must become a very strong and robust method in automatic leveling algorithm

Evaluation of shot peened surfaces using characterization technique of three-dimensional surface topography

Objective parameters to characterize global topography of three-dimensional surfaces have been derived. The idea of this evaluation is to separate the topography into two global form deviations and residual ones according to the degree of curved surfaces. A shot peened Almen strip is measured by profilometer and concrete parameters of inclination and circular-arc shaped global topography are extracted using the characterization technique. The arc height is calculated using the circular arc-shaped part and compared with a value measured by an Almen gauge. The relation between the coverage and roughness parameters is also investigated. The advantage of this evaluation is that it is possible to determine the arc height and the coverage at the same time from single measured topography. In addition, human error can be excluded from measurement results. This method has the wide application in the field of measurement.

Impact of High-Speed Image Recognition of Transition Phenomenon of Chip Formation and Chip Flow in Gear Hobbing Process

The transient phenomenon of chip generations and behavior in the gear hobbing process are investigated by using a high-speed video camera. The chip behavior generated in gear finish hobbing process is very complicated and one can not identify each chip from specified cutting edges. The authors have built up a new simulation method of the hobbing process using a flying tool and a special-shaped workpiece, which consists of one tooth space. Visual evidences of the chip interference on the rake face and some conditions of contact between generated chips and the work surface were visually obtained. In the case of dry cutting conditon with a high-speed steel (HSS) flytool without coating on the rake face, the flytool cuts the workpiece frequently with the stuck chip generated in the previous revolution on the rake face. The newly generated chip pushes out the previous stuck chip, which flies away eventually. The chip flow on the rake face interferes strongly at the corner of the cutting edge when both top and side cutting edges produce different chips at the same time, and the chips flow out in changing the shape. The moving speed of the chip was also measured.

Transient Phenomenon of Chip Generation and Its Movement in Hobbing : 4th Report, The Relationship Between the Jamming of Chips on the Finished Surface and the Chip Form in Generating in Flytool Simulation Tests(Machine Elements and Manufacturing)

The degradation of tooth surfaces and the abnormal tool wear sometimes occurs in dry hobbing. This paper investigates the transient phenomenon of chip formation and behavior in simulation tests of hobbing by using a high-speed video camera. The jamming of the chip between the tooth surface and the cutting edge causes scratches on the tooth surface and the chipping of a cutting edge so on. The figures of chips produced by hobbing are classified roughly into the “U”, “J” and “I” types. This paper presents findings of the “J” and “I” type-chip movements in flytool simulation tests. The “J” type-chip is removed with the two cutting edges both top and a side edge. In the “J” type-chip, a part of end side of the chip produced by the top cutting edge is often jammed into the finished surface by pushing from the chip at the side cutting edge. The “I” type-chip flows from the root to the tip side of the cutting tooth, and the pointed end of the chip is jammed into the space between the finished surface and the relief face of the cutting tooth, in down cut. In up cut, the chip flows to the root side of the rake face, and possibility of jamming is shown as well as the case of down cut.

Measurement of Tooth Pair Deflections With Ultra High Resolution Encoders and Prediction of Transmission Error Under Load in High Precision

The purpose of this research is to predict transmission error under loading conditions in high accuracy. Transmission error is very important information in the evaluation of gear engagement and the prediction of vibration and noise from gear boxes. In some experiments, measurement of transmission error is sometimes performed to grasp an actual situation of gear static engagement. However, it is impossible to measure all of gear pairs in mass production for actual transmission manufacturers. The prediction of transmission error by the simulation in high accuracy should be powerful and effective means in application. The most important and indispensable information to simulate accurate transmission error under load is the deflection of a gear tooth and the displacement in tooth pair contact. One of conventional approaches is to predict bending deflections with FEM analysis. However it is very difficult to calculate the deflections in high accuracy by FEM because of less grid density, inadequate constraint conditions, the lack of information of actual loading conditions, and so on. To overcome the difficulty, the authors try to measure tooth pair deflections directly by experiments using a couple of ultra high precision encoders. The measurement strategy is to obtain the deflection of only single tooth pair during a whole period of tooth engagement. It can be achieved by use of a specially manufactured gear which has large and intentional pitch deviations. Experimental formulas of gear tooth pair deflections are derived from measured results. Putting assumption that tooth deflections with respect to applied loads can be expressed approximately as a curve of the second order, the stiffness of single-tooth engagement is evaluated. Transmission error is simulated with the obtained formula of the tooth stiffness and the result is compared with the measured transmission error and discussed.© 2007 ASME

Transient Phenomenon of Chip Generation and its Movement in Hobbing (3rd Report, The Relation of the Ending Point of Cut of Chip Movements)

The degradation of tooth surfaces and the unusual tool wear sometimes occurs in dry hobbing. This paper investigates the transient phenomenon of chip generations and behavior in hobbing by using high-speed video camera. The location of the ending point of cut on a cutting edge influences chip movements at the take-off from the tooth flank. Many chips rotate around the fulcrum of the ending point of cut. Some chips produced with the regular cutting tooth flow to the opposite side frequently when the ending point of cut exists at the trailing side in the conventional hobbing. When the chips flow to the opposite side flank, though the chips do not jam into the space between tooth surface and cutter relief surface, the chips strike against the tooth surface. This phenomenon gives suggestions to the degradation of tooth surfaces. In the climb hobbing, the chip movements are similar to the case of the conventional hobbing. However, many chips flow away to the direction of the tool revolution because the both flanks facing each other guide chips at the root just after the end of cut.

Gear Finishing With a Nylon Lap

The objective of this research is to develop a new lapping process which can efficiently make tooth flanks of hardened steel gears smooth as a mirror. The lapping is carried out using a nylon helical gear as a lap and a simple mechanical device. This paper first shows the lapping machine designed and manufactured by the authors and the procedure and principle of the lapping. And as a result of the lapping tests, it becomes clear that the process can make tooth flanks of hardened steel gears smooth in a short time and it is important to carry out the lapping for a short time using a nylon gear which has a large helix angle and high-teeth under a condition of high rotating speed and light load in order to prevent increases of tooth profile errors. Moreover the lapping process accompanied by micro vibrations of a nylon gear is tested. From the result, it is found that the addition of micro vibrations enables this process to reduce also tooth profile errors of work gears. The running noise and the load carrying capacity of lapped gears are considered.Copyright

The Experimental and Analytical Evaluation of High Speed Bevel Gears.

To reduce the size of reduction gears where big power is transmitted through crossed shafts, it is necessary to increase rotational speed and decrease the transmitted torque and load. To know dynamic behaviour of high speed bevel gears, the experiments were carried out and tooth root stress and temperature were measured. Also a spiral bevel gear set analysis has been developed that makes use of mesh stiffness calculations based on finite-element methods. The analysis enables the calculation of dynamic loads. And then, the following results were obtained. (1) A power absorbing gear testing machine (960 kW) could be operated up to high pitch line velocity (∼110 m/s) and it is found that dynamic loads is nine times as much as static loads under the condition of 110 m/s. (2) Analytical results of dynamic load agreed with the experimental results. It was confirmed that the analytical method has practical accuracy and usefulness.

A Study on Cutting Forces in Gear Cutting. A Theory of Cutting with Two Continuous Symmetrical Cutting Edges.

In hobbing the cutter has many cutting teeth. Each hob tooth has two or three cutting edges. When a hob cuts a gear, each chip is simultaneously produced with two or three cutting edges of one tooth. Then the interference occurs among the parts produced by those butting edges, and the specific cutting forces become larger than those in orthogonal cutting. In this paper, the interference of chips is theoretically investigated. The simplest model of the interference of chips is the cutting of full-depth or non-full-depth triangular cuts. So the specific cutting forces in non-full-depth triangular cuts with a point nose straight tool are theoretically investigated with various included angles. The result shows that the specific cutting forces become large when the included angle is small. The specific cutting forces with an included angle of 90 degrees are about 1.3∼1.35 times as large as those with a flat tool.