General steps in the design of automotive inspection fixtures

The design and production of automobile inspection tools is one of the main businesses of Beijing Jingke Xingye Technology Development Co., Ltd. Jingke has been committed to the design, manufacture, measurement and maintenance of automobile inspection tools. With its excellent product quality and perfect after-sales service system, Beijing Jingke has won the high evaluation and trust of Beijing Benz, Beijing Hyundai, BAIC Foton, FAW Volkswagen, FAW Toyota, Great Wall Motor, Wuling Automobile, Land Rover, Jaguar and other well-known automobile enterprises at home and abroad. Jingke provides professional and precise inspection tools for all kinds of automobile companies to provide guarantee for all aspects of automobile production. Let's introduce the general steps of Jingke automobile inspection tool design in detail.

Part of the design process of (I) automobile inspection tools: design modeling of workpieces and inspection details

First of all, the workpiece should be analyzed with reference to the drawings of the parts, the design scheme of the automobile inspection fixture should be preliminarily drawn up, the datum plane and concave and convex conditions of the automobile inspection fixture should be determined, the cross section and positioning plane should be detected, and the two-dimensional schematic diagram should be simply drawn.

In the design of automobile inspection tools, the specific design modeling is the key, which directly affects whether the automobile inspection tools can accurately detect the quality of the workpiece. Due to the free-form surface-based characteristics of body panels, "physical reverse" is a common method of modeling. Reverse is the method of constructing a prototype model with a specific shape structure based on the existing workpiece or physical prototype, using a laser scanner for data acquisition, and through the process of data processing, three-dimensional reconstruction, etc. We use a laser scanner to scan the standard workpiece surface, collect the workpiece surface feature information based on point cloud, convert the point coordinates to body coordinates, process the point information with surfacer software, and obtain the characteristic curve of the workpiece surface, thus generating 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, and the model should be distinguished as the inner or outer surface of the workpiece according to the surface scanned by the scanner, which is particularly important for the specific design of the automobile inspection tool.

In order to realize the detection of the free-form surface of the workpiece by the automobile inspection tool, a constant gap of about 2-3mm is generally kept between the specific surface to be inspected and the inner surface of the workpiece. The numerical control machining machine tool can meet the requirement of higher precision according to the designed surface model. During actual detection, the deviation of the curved surface of the workpiece can be measured by the reciprocating movement of the automobile inspection tool surface with a special measuring tool. There are two main methods for detecting the outer contour of the workpiece. When designing the corresponding automobile inspection fixture: ① The specific surface of the inspection extends outward about 20mm along the tangential direction of 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), the distance by which the workpiece surface is offset2-3mm inward (if the generated workpiece model is the outer surface, the thickness of the workpiece should be added when making offset), then the curved surface is extended by 20mm along the tangential or normal direction of its contour to obtain the inspection specific inspection surface, and then stretched to the reference surface for a certain distance is the inspection specific model of the automobile inspection tool. Due to the complexity of the body cover, the combination of the above two methods is mostly required when generating a specific inspection surface, which is still difficult to achieve for some special profiles. Figure 1 shows a schematic diagram of complex profile treatment. In the figure, the workpiece surface of the inner engine support obviously produces self-intersection and interference at 1 and 2 places. 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 inspection specific surface as shown in the figure. Finally, the inspection specific surface is double-scribed along the workpiece contour and at an interval of 3mm to facilitate the inspection of the workpiece contour. Of course, many similar problems will be encountered in the design of automobile inspection tools (especially inspection specific), which need to be dealt with by the penetration understanding and experience of the principle of automobile inspection tools.

Fig. 1 Treatment of Complex Surface

Design and Modeling of Section Template of (II) Automobile Inspection Fit Design

The detection of the critical surface of the workpiece is generally realized through the cross-section template. The cross-section template of the automobile inspection tool is divided into two types: rotary type and plug-in type. When the span of the cross-section template exceeds 300mm, it is usually designed as plug-in type to ensure the detection accuracy in the vertical direction. The specific surface is inspected to detect the inner surface of the workpiece, and the section template is used to detect the outer surface of the key section. Generally, the working surface is 2-3mm away from the outer surface of the workpiece. The modeling method is similar to that of the specific surface. The plate body material of the section template is generally steel or aluminum and other metals, and the working surface part can be made of aluminum or resin. The cross-sectional template of complex profile will interfere when rotating or inserting, which can be processed in sections in actual design, as shown in fig. 2.

Fig. 2 Segmented Treatment of Section Template

If it is set as an inserted section template, it will interfere with the workpiece positioning pin. If it is set as a single rotary type, due to the multi-folding surface of the workpiece itself, it will interfere with the inspection details or the workpiece. If it is designed as two independent rotary section templates, it can meet the requirements of comprehensive inspection.

(III) Auto Gauge Design: Positioning and Clamping of Workpiece

The correct and reasonable positioning of the workpiece is the basis of accurate measurement. The positioning mode of the body cover on the automobile inspection fixture is mainly completed by the positioning hole and the clamping and positioning of the chuck or the clamping and matching of the permanent magnet. With the wide application of automobile inspection tools in body manufacturing, lever-type movable chucks and permanent magnets are available for selection, and movable chucks are also equipped with brackets or brackets of different types and sizes. Most body covers have two main and auxiliary positioning holes. The main positioning pin is generally a cylindrical pin (round hole) or a diamond pin (waist hole), and the auxiliary positioning pin is a tapered pin or a diamond plug pin. When designing the automobile inspection tool, punch the positioning hole on the inspection site (subject to placing the positioning pin bushing), and give the body coordinates of the positioning hole. At the same time, the positioning gasket and movable chuck are arranged at the position with good rigidity and reasonable distribution of the workpiece to ensure the firm positioning of the workpiece. The number of clamping points should be reduced as much as possible during design to ensure that the movable chuck does not interfere with other components during operation. Taking into account the convenient operation of workers, the body coordinates of the center of the upper surface of the positioning gasket are finally given.

Fig. 3 Degrees of Freedom of Workpiece Restricted by Chuck

For a workpiece with only one positioning hole, since the main positioning hole can only limit two degrees of freedom, the positioning pad also acts to limit the degree of freedom of the workpiece to prevent the workpiece from rotating around the main positioning pin (see Figure 3).

Design of (IV) automobile inspection fixture: design of base plate assembly

The specific upper surface of the inspection is stretched for a certain distance along the normal direction of the reference plane, so that the lowest point is greater than 150mm to ensure that the inspection specific has sufficient strength, and at the same time, try to make the specific bottom surface of the inspection, that is, the upper surface of the floor assembly (base surface), At the integer position of the body coordinate system. The base plate assembly is generally composed of base plate, channel steel (I-steel is added in the middle if necessary), positioning block and universal wheel. After the base plate and the base plate are fixed, other parts can be selected as standard models according to the actual situation.

Hole Detection of (V) Automobile Gauge Design

Many important holes and flanging in body stamping parts need to be inspected separately. In the design of automobile inspection tools, a boss with a thickness of about 1mm is usually added to the upper surface of the inspection tool. The center of the boss is on the same axis as the center of the workpiece hole, and the diameter is 5mm larger than the hole diameter. The boss is detected by double scribing (see Figure 4). When the accuracy requirement of the measured hole is relatively high, the plug gauge and bushing are used to detect the positioning hole.

Fig. 4 Hole detection method

Jingke Conclusion

The above is the general steps of the design of the automobile inspection fixture of Beijing Jingke Xingye Technology Development Co., Ltd. It should be noted that: in the large body covering parts, due to the complex shape, large volume, high production cost, single detection object and poor flexibility of this kind of automobile inspection fixture, it is difficult to obtain a large amount of accurate information quickly, and it has been gradually replaced by advanced automatic detection means (such as online detection system), however, for the detection of small stamping parts produced in large quantities, at present, China's automobile manufacturers still rely mainly on such automobile inspection tools. Jingke Company is committed to providing customers with verification and trial production solutions that shorten the cycle and save costs for the design and development of new products. It insists on providing customers with 10-point high-quality products and 100-percent considerate service, and makes unremitting efforts to become a world-class enterprise trusted by customers, proud of employees and respected by others!