In this parameter design study, we examined the effect of a solid film lubricant coating on the contact zones of mechanical parts in preventing fretting fatigue failures, which occur frequently in the structural members of machines that experience varying loads. In conventional evaluation of the fatigue strength of materials, fatigue tests are performed at various stress levels and fatigue life is evaluated, but fatigue life evaluation takes considerable time. For the fretting fatigue strength evaluation in this study, instead of performing life tests to measure the time taken for a test piece to break under fatigue, we measured the contact force waveform affecting the contact zone in a fatigue test with up to 105 stress cycles, and evaluated stability of the waveform over the test time using the standard S/N ratio. As a result, by using an optimized solid lubricant,we improved the fatigue strength characteristic and greatly shortened the test time.

In the cutting of aluminum alloy round-bar when smaller sizes of bar were cut,a good surface finish could not be obtained because the maximum speed of the NC lathe was lower than the cutting speed recommended by the tool bit manufacturer. In this study, the authors optimized the machining conditions for finish cuting in order to achieve good surface finish even at low rotational speeds. Variation in power consumption was evaluated for the cutting and idling states by dividing the time axis into on and off intervals. In calculation of the S/N ratio, in particular, reproducibility of the gain was improved by adding the mean variance over these intervals to the denominator. Also, by using work-piece rigidity as a noise factor, chatter-free machining conditions were obtained.

At present, many manufacturers use control charts to study the stable states of their manufacturing processes. There are several problems with this, however,because a control chart evaluates a process in terms of only a single parameter. To address these problems, the MT system was applied to control charts, and the Mahalanobis distance and orthogonal arrays were put to work to study the stable state of a process, using multiple variables. The results achieved included the discovery of problems and their causes, and improved detection of abnormalities in the process and product, making it possible to detect problems even when the process was unstable.

The proper operating conditions for a spinning machine depend on the material to be spun (e.g., cotton or wool) and the required properties of the spun yarn. In many cases, the conditions are set by skilled experts proceeding by hunch and experience through a series of trial spinning operations. One of the conditions to be set is the spacing between the multiple rollers that feed the material out. If the appropriate spacing for each job could be estimated in advance, the large number of man-hours required for trial spinning could be reduced, and whether to readjust when changing lots could be decided reasonably and efficiently. In the usual MT method, how much a pattern represented by multiple items resembles the unit space data is evaluated by the Mahalanobis distance(MD). In this study, however, useful results were obtained by treating the quantity to be estimated, which was the optimal spacing between rollers, as one of the items and performing a true-value estimation, taking the value that minimized the Mahalanobis distance of the whole system as an estimate of the optimal roller spacing. The concepts and speciflc methodology applied when the MT method is utilized to estimate optimal adjusted values by the type of estimation described above wlll be reported, together with actual results.