General methods and steps for the design of inspec

Abstract: starting from the automobile structure, combined with examples, this paper expounds the general methods and steps of the design of the inspection tool for small stamping parts of the car body and the new idea of checking the specific design and building a general graphene automatic decomposition mold at high temperature, and puts forward the solutions to the common problems in the design of small inspection tools

key words: gauge design, small stamping parts

1 introduction

body stamping parts, sub assemblies (welded by stamping parts), body skeleton, various interior trim parts, etc. are collectively referred to as body covering parts. The manufacturing quality of covering parts has a great impact on the quality of the whole vehicle, especially the welding production of cars and all kinds of passenger cars and the appearance of the whole vehicle, so the inspection of its quality has become an indispensable work for automobile manufacturers. For important small stamping parts in China, special inspection fixtures (hereinafter referred to as inspection fixtures) are generally used as the main inspection means to control the product quality between processes. The United States, Germany, Japan and other highly automated countries in the automotive industry have begun to use testing equipment to efficiently and quickly respond to product quality problems. China's Shanghai Volkswagen Automobile Manufacturing Co., Ltd. introduced two sets of testing equipment in 2001, but it has not been effectively used due to technical and management reasons. Moreover, due to the high cost and technical requirements of the testing equipment, it is difficult to be widely used in the testing of small body stamping parts in China. In recent years, with the rapid development of the car and bus industry, the application of body panel inspection tools in the domestic automotive industry has been quite extensive. The State Economic and Trade Commission has listed the production capacity of inspection tools in the production condition assessment procedure of vehicle enterprises. Therefore, designing and manufacturing special inspection tools with convenient operation and high inspection accuracy has become an urgent problem to be solved by many automobile manufacturers

2 composition and characteristics of the inspection tool for small stamping parts of the car body

the inspection tool for small stamping parts of the car body is mainly composed of the bottom plate assembly, inspection details, section templates, main and auxiliary positioning pins and clamping devices (see Figure 1). The main elements of the detection are the positions of the workpiece shape (including the contour of the workpiece and the shape of the surface, etc.) with the characteristics of holes, flanges, etc. During the design of the gauge, the dimension datum is generally placed in the body coordinate system, and the setting line is drawn every 100mm in the X, y and Z directions. The coordinate system of the gauge is established with the datum block and datum hole on the bottom plate

Figure 1 main structure diagram of the inspection tool

most of the body stamping parts have space 2 The balance of the universal experimental machine itself and the balance during installation are very important. There are many local features, such as non axisymmetric and poor rigidity, so it is difficult to locate, support and clamp. At present, most of the inspection of body stamping parts are automatically completed by CNC machine tools at one time according to the digital simulation and the predetermined processing program. The specific materials are mostly epoxy resin. After the specific design is completed, the position and size of the bottom plate assembly are determined according to the specific inspection, and the section template is set in the key section to be inspected

3 general steps of fixture design

3.1 workpiece and specific design modeling of inspection

first, analyze the workpiece with reference to the part drawing, preliminarily draw up the fixture design scheme, determine the datum plane, concave convex condition, detection section, positioning surface, etc. of the fixture, and simply draw its two-dimensional schematic diagram

in the design of the inspection tool, the specific design modeling is the key, which directly affects whether the inspection tool can accurately detect the quality of the workpiece. Because the body panels are mainly free-form surfaces, "reverse engineering of real objects" is a general method of modeling at present. Reverse engineering refers to the method of using laser scanner to collect data according to the existing workpiece or physical prototype, and then constructing the prototype model with specific shape and structure through data processing, three-dimensional reconstruction and other processes. We use a laser scanner to scan the standard workpiece surface, collect the workpiece surface feature information mainly based on point cloud, convert the point coordinates to the vehicle body coordinates, and process the point information with surfacer software to obtain the feature curve of the workpiece surface surface surface, so as 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 without thickness. It is particularly important to distinguish the model from the inner or outer surface of the workpiece according to the scanned surface of the scanner

in order to realize the inspection of the workpiece free-form surface by the inspection tool, the constant gap between the specific inspection surface and the inner surface of the workpiece is generally maintained at about 2 ~ 3mm. The NC machining machine tool can meet the requirements of high accuracy according to the digital simulation of the designed profile. During the actual inspection, the deviation of the workpiece surface can be measured by the reciprocating movement of the inspection tool profile with the special measuring tool. There are mainly two kinds of inspection methods for the outer contour of the workpiece. When designing the corresponding inspection tool: ① the specific inspection surface extends outward about 20mm along the tangential direction of the outer contour of the workpiece; ② Extend downward about 20mm along the normal direction of the outer contour of the workpiece. In general CAD software (such as UG), the workpiece surface is offset inward by a distance of 2 ~ 3mm (if the generated workpiece model is the outer surface, the thickness of the workpiece should be added when making offset), and then the surface is extended 20mm along the tangent or normal direction of its contour to obtain the specific inspection surface, and then stretch a certain distance to the datum plane to inspect the specific model. Due to the complexity of body panels, the combination of the above two methods is mostly required when generating specific inspection surfaces, but for some special surfaces, this is still difficult to achieve. Figure 2 shows the schematic diagram of complex profile processing. In the figure, the workpiece surface of the inner engine support obviously produces self intersection and interference at 1 and 2. In order to ensure that the main contour of the workpiece is detected, the detection at the corner with vertical height difference is sacrificed to generate the specific inspection surface as shown in the figure. Finally, double lines are drawn along the workpiece contour and at an interval of 3mm on the specific inspection surface to facilitate the detection of the workpiece contour. Of course, if oil leakage is found in the design of the inspection tool (especially the specific inspection tool), many similar problems will be encountered, which requires the penetration understanding and experience of the inspection tool principle

Figure 2 treatment of complex surface

3.2 design and modeling of section template

the detection of the key surface of the workpiece is generally realized through the section template. The section template of the inspection tool is divided into rotating type and plug-in type. When the span of the section template exceeds 300mm, it is usually designed as plug-in type to ensure the detection accuracy in the vertical direction. The specific surface inspection is the inner surface of the workpiece, and the section template spans the outer surface of the workpiece to detect the outer surface of the key section. Generally, its working surface is 2 ~ 3mm away from the outer surface of the workpiece, and its modeling method is similar to the surface of the inspection tool. The plate material of the section template is generally steel or aluminum, and the working surface can be made of aluminum or resin. The section template of complex surface will interfere when rotating or inserting, and it can be processed in segments in actual design, as shown in Figure 3

if it is set as an inserted section template, it will interfere with the workpiece locating pin; If it is set as a single rotating type, due to the multi fold nature of the workpiece itself, it will interfere with the specific inspection or workpiece. It can be designed into two independent rotating section templates to meet the requirements of comprehensive inspection

Fig. 3 sectional processing of section template

3.3 positioning and clamping of workpiece

correct and reasonable positioning of workpiece is the basis of accurate measurement. The positioning mode of the body cover on the inspection fixture is mainly completed by clamping and positioning the positioning hole and the collet or clamping and matching with a permanent magnet. With the wide application of inspection tools in body manufacturing, lever type movable collets and permanent magnets are available in a series of products, and movable collets are also equipped with brackets or brackets of different types and sizes. Most body covering parts have main and auxiliary locating holes. The main locating pins are generally cylindrical pins (round holes) or diamond pins (waist holes) to limit the degrees of freedom in X and Y directions; The auxiliary locating pin is a conical pin or a diamond plug pin, which is used to limit the degrees of freedom in the Z, x, y, z directions. When designing the inspection tool, punch a hole at the location of the positioning hole on the inspection (subject to the positioning pin bushing), and give the body coordinates of the positioning hole. At the same time, positioning shims and movable collets are arranged at the positions with good rigidity and reasonable distribution of the workpiece to ensure the firm positioning of the workpiece. During the design, the number of clamping points shall be minimized to ensure that the movable chuck will not interfere with other parts during operation, and considering the convenience of workers, the vehicle body coordinates of the center of the upper surface of the positioning gasket shall be finally given

for the workpiece with only one positioning hole, since the main positioning hole can only limit two degrees of freedom, the positioning gasket also limits the degree of freedom of the workpiece to prevent the workpiece from rotating around the main positioning pin (see Figure 4)

Figure 4 uses chuck positioning to limit the degree of freedom of the workpiece

3.4 design of the bottom plate assembly

stretch a certain distance along the direction of the reference plane on the specific upper surface of the inspection, so that its lowest point is greater than 150mm thick, so as to ensure that the specific inspection has sufficient strength. At the same time, try to make the specific bottom surface of the inspection, that is, the upper surface of the bottom plate assembly (base plane), on the integer position of the body coordinate system. The inspection base plate assembly is generally composed of base plate, channel steel (if necessary, machining the steel in the middle), positioning block and universal wheel. When the base plate is fixed by the inspection base plate, other parts can choose the standard model according to the actual situation

3.5 hole detection

many important holes and flanging in body stamping parts need to be detected separately. In the design of the inspection tool, a boss with a thickness of about 1mm is usually added to the upper surface of the inspection tool. The center of the boss and the center of the workpiece hole are on the same axis, and the diameter is 5mm larger than the hole diameter. The double scribed line method is used on the boss for inspection (see Figure 5). When the accuracy requirements of the measured hole are relatively high, the way of positioning hole is used to detect with plug gauge and bushing

Figure 5 hole detection method

4 conclusion

in large body panels, due to the complex shape, huge volume, high production cost, single detection object and poor flexibility of this kind of inspection tool, it is difficult to quickly obtain a large amount of accurate information, which has been gradually replaced by advanced automatic detection means (such as detection system), but for the detection of small stamping parts produced in large quantities, At present, China's automobile manufacturers still mainly rely on such inspection tools

references

1 Zhu Zhengde The principle and application of auto panel inspection fixture Tool technology, 2000 (1)

2 Ren Xueyan Surface quality control of automobile body panels Automotive Technology and materials, 2001 (2)

3 Yang Hua, Cao Libo Application of feature modeling in auto body panel design Bus technology and research, 2002 (4)

4 Zhou Baocheng Design, manufacture and application of comprehensive inspection tools Automotive appliances (end)