Positioning of workpieces in machining operations has a direct influence on the machined features. Workpiece datum errors are one of the error sources that affect the workpiece positioning in the fixture. In this article, a systematic method is presented for eliminating the effect of datum errors on the workpiece machined features in five-axis machining. In this method, the effect of datum errors on the machined features is mathematically modelled using homogenous transformation matrix, and the error vector on the workpiece machining surface is obtained. The error vector consists of position and orientation errors of the tool in workpiece coordinate system. In this work, a compensation module is developed, which is applied to the machining codes of the workpiece. The input to this module is the datum errors and initial NC-codes. The output of the module is the modified NC-codes. For verifying the method, two cases are studied, which are related to five-axis drilling and five-axis free-form milling. Using the compensation method, the position, orientation and form errors are decreased considerably. The results confirm that this method can be used for compensating the datum errors effectively.
One of the major sources of error in machining operations is the inaccurate positioning of the workpiece in the fixture. Generally, the surface of the workpiece that is in contact with the fixture locators is used as a workpiece reference surface (WRS). Errors in the WRS can lead to improper placing of the workpiece in the fixture and, in turn, to inaccurate machining operations. In this paper, a method is introduced that eliminates the effect of WRS errors on machined features produced in a milling operation. In the proposed method the positioning of the workpiece with consideration of WRS errors is mathematically modelled using homogenous transformation matrices. This model is then used to compensate the effect of WRS errors by modifying the machining toolpath. A post-processing workpiece error compensation module is developed that modifies the initial NC-codes that are generated from a CAM system. The presented method is verified using the simulation software NX and VERICUT and experimental studies. The results confirm that this method can be used to successfully compensate these kinds of errors.
Selecting materials and alloys, fabrication methods, surface characteristics and coatings, and topology design, all affect the mechanical properties, biocompatibility, and functionality of dental implants. The success in embedding implants in mouth and improving biocompatibility and consequently useful life of implants depends directly on proper adhesion of tissue to implant surface of a biocompatible alloy. In this research, experimental surface hardness and in vitro tests are carried out on samples with different alloys and different manufacturing methods. Various fabrication techniques, such as machining and 3D printing (Selective laser melting (SLM)), are considered for steel and titanium specimens. Results show that the hardness values of specimens made by the SLM method are higher than machined samples about 8% and also stainless steels samples have higher hardness than titanium specimens. A comparison of scanning electron microscopy (SEM) surface pictures indicates that applying modern fabrication methods for production which includes SLM improves the performance of implants in terms of mechanical and biocompatibility by increasing cell adhesion up to 21 times. In addition, results indicate that titanium alloys have almost 13% higher adhesion property than stainless steel and generally exhibit a higher balance of adhesion and cell growth.
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