اندازه گیری انتخابی از سطوح فرم آزاد برای کنترل کیفیت و نگهداری انتخابی از ابزار خمش

Bending tools are frequently used to manufacture freeform surfaces. In such cases, the geometry of the workpiece is determined wholly or in part by that of the tool (e.g. die forming). The quality of the finished product depends largely, therefore, on the geometry of the tools. Tool geometry is changed in the course of the manufacturing process by wear and optimisation. When the time comes for repairs or the manufacture of new tools, there is no record of the geometrical modifications which have been carried out. A model in the form of a quality control loop to feed back geometrical modifications to CAD and CAM systems is presented in this contribution. A means of creating the individual components in the quality control loop is described. Particular care has been taken to ensure that both the measurement and the feedback are limited to selected areas in order to minimise the cost and time involved.

Freeform surfaces of many of the sheet metal products in our daily lives are important to us for both functional and aesthetic reasons. Their uses range from that of a soap dish, formed so as to be aesthetically pleasing to the shell of an aircraft, designed from an aerodynamic point of view. As a result of technical advances in the techniques used to manufacture such surfaces (e.g. hydroforming [1], 3D-laser forming [2]) and ever higher customer expectations in terms of product design, such parts will become increasingly important. Requirements relating to the quality of the surfaces, in particular, will become more exacting. The quality of bend parts depends largely on process control and on the quality of the tools used. Research conducted in this field concentrates on these two areas. In this context, digitisation and geometric reconstruction (reverse engineering) are among the subject areas relevant to metrologists. In contrast, the techniques applied in the quality assurance and implementation of quality control loops assume a subordinate role. However, this is the area in which improvements stand to be made, particularly in view of the rising expectations in terms of the quality of bend parts. The concept and the technical tools presented here illustrate how a quality control loop for the production of bend parts can be developed, taking into account the changes of tool geometry during the use of the tools.

Due to geometrical changes to bending tools during the period of tool deployment, the actual tool geometry does not correspond to the geometry specified in the tool design. These geometrical changes can be measured rationally using modern measuring methods such as coordinate measuring technology. It is vital that the measurement data are processed in a suitable manner if the results of the measurement operations are to be used effectively in CAD and CAM systems. There are special extensions for CAD systems which adapt CAD data to the measurement data. In those cases in which the CAD data do not need to be adapted and the tool geometry should be reconstructed in accordance with the target data, the boundaries of the areas of deviation should be defined. These boundaries can be used in the form of polylines in CAM systems for selective machining of areas of deviation which have occurred as a result of wear, for example.