Iwao Yamaji

Measurement of Contact Stiffness for Stiffness Estimation of Machine Tool Supports

The contact stiffness is measured at interfaces of several materials that are often used for the machine tool support. Models of machine tool supports and contact stiffness are described. Then, a measurement method of the contact stiffness is proposed according to the model and demonstrated. The unit normal contact stiffness is 1-2×106 N/mm/mm2 for general steel and cast iron. The unit normal contact stiffness is pSuperscript textositively correlated with the longitudinal elastic modulus. The unit tangential contact stiffness is 1/10-1/5 of the unit normal contact stiffness and not correlated with the elastic shear modulus. The surface roughness of the specimen should be small to reduce the dispersion of the measured unit contact stiffness.

Linked Ball Bar for Flexible Motion Error Measurement for Machine Tools

A measuring instrument, Linked Ball Bar (LBB), is developed to measure machine tool motion errors quickly, flexibly, and robustly. The LBB employs the concept of double ball bar (DBB) and measures the distance between two balls attached to the spindle and table. The problem of short measurement range, the drawback of the DBB, is solved using a link. The measurement accuracy of the LBB is investigated. The analytical resolution of displacement measurement using the LBB is under 30 nm when the displacement direction coincides with the sensitivity direction. The difference between the LBB and the laser interferometer is less than 1 μ m in the center measurement range of 75 mm. The repeatability of the LBB is±0.4 μm and is at the same level as the interferometer. The kinematic error of a five-axis machine tool is measured using the LBB to demonstrate its validity. The parallelism between the C-axis and Z-axis identified using the LBB agrees with the result measured using the cylindrical square. The difference between the LBB and the cylindrical square is about 10 μ m/m at the maximum. The LBB can provide quick and flexible measurements of the motion errors of five-axis machine tools.

Discrimination of the Tool Failure Patterns in Machining Hardened die Steel with End Mill.

In cutting hardened die steel with carbide end mill, the criterion for judging a tool failure are divided broadly into three categories, that is, wear, chipping or breakage. Among them, the prediction of the tool failure caused by wear is relatively easy, but it is difficult to estimate the tool failure caused by the remaining two. Thus it is desirable to select the cutting conditions which lead a tool failure caused by the wear. In this study a mathematical model for predicting the tool failure patterns is identified by applying simultaneous approach to fuzzy cluster, principal components and multiple regression analysis. In the approach the kind of machine, spindle speed, feed, radial depth of cut, axial depth of cut, free length and run out are chosen as predictor variables from the tool failure tests using carbide radius end mill, and the tool failure patterns (wear, chipping and breakage) as response variables. As the results, three clusters are obtained and from each cluster input variables affecting the tool failure patterns are extracted. According to the approach it is possible to predict the tool failure patterns and to select the cutting conditions leading to the tool failure caused by wear.

Heat Treatment Using Small Power Laser on-the-Machine Tool.

This study describes laser heat treatment of die steels using YAG laser on-the-machine tool. An optical fiber has been used in order to transmit the laser light from a source to workpieces at this system. At first, the temperatures based on a theoretical model during laser irradiation were estimated in order to predict the hardened range of workpieces. Second, experiments of laser heat treatment were carried out for various die steels in order to grasp the relationship between the hardened depth and irradiation conditions. Finally, a method to repeat laser irradiation at the same area was proposed to increase the hardened depth. As a result, the detail of the hardened depth for various die steels becomes clear under various laser irradiation conditions. It is found that this heat treatment of die steels with YAG laser on-the-machine tool is an effective method.