General steps for fixture design

by:Top Talent     2020-07-14
First of all, we must analyze the workpiece with reference to the part drawing, preliminarily formulate the design plan of the inspection tool, determine the reference surface, unevenness of the inspection tool, detect the cross section, positioning surface, etc., and simply draw its two-dimensional schematic diagram. In the design of inspection tools, the specific design modeling of inspection is the key, which directly affects whether the inspection tools can accurately detect the quality of the workpiece. Due to the characteristics of body panels with free-form surfaces, 'reverse object' is the current general method of modeling. Reverse seeking is a method of constructing a prototype model with a specific shape and structure based on the existing workpiece or physical prototype, collecting data with a laser scanner, and after data processing, three-dimensional reconstruction and other processes. We use a laser scanner to scan the standard workpiece surface, collect the surface characteristic information of the workpiece mainly with point clouds, convert the point coordinates to the body coordinates, and use the surfacer software to process the point information to obtain the characteristic curve of the surface of the workpiece surface To generate the final free-form surface model; at the same time, the generated prototype model can be detected by the maximum and minimum distance from the point cloud to the surface. It should be noted that the model obtained at this time is a sheet model with no thickness. It is necessary to distinguish the model as the inner or outer surface of the workpiece according to the surface scanned by the scanner. This is particularly important for the specific design of the inspection.

In order to realize the inspection of the free-form surface of the workpiece by the inspection tool, the specific surface of the inspection and the inner surface of the workpiece are generally kept at a constant gap of about 2 to 3 mm. The numerical control processing machine tool can meet the requirements of higher accuracy according to the designed surface model. During the inspection, the deviation of the workpiece surface can be measured by the reciprocating movement of the inspection tool surface and a special measuring tool. There are two main methods for detecting the outer contour of the workpiece. When designing the corresponding inspection tool: ① the inspection surface extends tangentially outward about 20mm along the outer contour of the workpiece; ② extends downward about 20mm along the normal direction of the outer contour of the workpiece. In general CAD software (such as UG), offset the workpiece surface inward by a distance of 2 to 3 mm (if the generated workpiece model is an outer surface, the thickness of the workpiece must be added when making the offset), and then the surface It extends 20mm along the tangential or normal direction of its outline to obtain the specific inspection surface, and then stretches a certain distance to the reference plane to check the specific model. Due to the complexity of the body cover, most of the above two methods are required to generate the specific inspection surface. For some special profiles, this is still difficult to achieve.

Figure 2 shows a schematic diagram of the processing of complex surfaces. In the figure, the surface of the workpiece of the inner engine support obviously self-intersects and interferes at two places.In order to ensure that the main contour of the workpiece is detected, the detection at the corner with a vertical height difference is sacrificed to generate the inspection as shown in the figure. Concrete surface, and finally inspect the concrete surface along the contour of the workpiece and double scribe lines at intervals of 3mm to facilitate the detection of the contour of the workpiece. Of course, many similar problems will be encountered in the design of inspection tools (especially inspection concrete), and it is necessary to deal with the penetrating understanding and experience of inspection tool principles.
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