What Are The Steps In The Design Of Checking Fixture?

- Oct 09, 2018-

The specific design modeling of workpiece and seized 1 -- Automobile check out

The first reference to part drawing analysis of workpiece, initially seized with the design scheme, determine the inspection gauge datum, bump, a detection section, positioning surface, and the simple drawing 2D sketch map.

In the design of automobile inspection tools, design modeling seized concrete is the key, it directly affects the gage can detect the workpiece quality accurate.

Due to the characteristics of autobody panel with freeform surface, "reverse" is the general method of modeling the current real. Reverse namely on the basis of existing artifacts or physical prototype, data acquisition using laser scanner, and through data processing, 3D reconstruction process, method of structure with specific shape structure of the prototype model. We use a laser scanner to standard workpiece surface to sweep, acquisition to the surface feature information of point cloud based on coordinate transformation, will point to the body coordinate system, using surfacer software processing point of signal, get the characteristic curve surface of workpiece surface, thus generating a free surface model final; at the same time can be detected by the prototype model the generated by point cloud to the maximum and minimum distance surface. It should be noted that, the model is not the thickness of the sheet body model, according to the surface scanner sweep to distinguish the model for the inner or outer surface of the workpiece, which is particularly important for the design and inspection of concrete.

The realization of checking fixture workpiece detection on free surface, generally keep 3 or 5mm constant gap surface of workpiece surface and detecting specific, NC machine tools can be in accordance with the design type surface number mode to achieve higher accuracy requirements, the actual detection by checking fixture type surface with the special gauge reciprocating movement can be measured deviation curved surface of workpiece. There are two kinds of main methods for the detection of the workpiece outer contour, the corresponding design of fixture: check specific surface along the workpiece outer contour tangential extends outward to about 20mm; the workpiece outer contour along the normal direction extending down about 20mm. In the universal CAD software, the workpiece surface inward offset3 or 5mm distance (if the workpiece model generated for the outer surface, the offset plus the thickness of the workpiece), then the surface along the profile of tangential or normal extension 20mm, get the check specific detection surface, and then to the datum plane stretching a certain distance is specific model checking. Because the body covering parts of more complex, combination of the two methods are mostly needed in generating specific surface detection detection, but for some special surface, it is still difficult to achieve. Figure 2 shows a schematic diagram of complex surface processing. The surface of the workpiece in the figure inside the engine support in 1,2 two apparently has self intersection and interference, in order to ensure the main outline of workpiece is detected, at the expense of detection with the corner vertical height difference, generating examination concrete surface as shown in, finally seized the concrete surface along the contour of workpiece and interval of 3mm double crossed, in order to facilitate the detection of the contour of workpiece. Of course, the fixture (especially the inspection of concrete) many similar problems will be encountered in the design, all need to understand and experience permeating seized with the principle of the late treatment.

Modeling design of 2 section model

On the detection of the workpiece surface through the section of general key shape model to achieve, seized with the section model is divided into rotary and insertion type two, when the section model over a span of 300mm, in order to ensure the detection precision in the vertical direction, usually the design to insert. Detecting of concrete surface is the inner surface of the workpiece, section model is across the outer surface of the workpiece, outer surface for key section detection, generally the working surface of the outer surface of the workpiece distance 2-3mm, the modeling method and the inspection surface with a similar. Plate material section model for general steel or aluminum metal, made the work surface portion of the available aluminum or resin etc.. The complex cross section model to produce interference in rotation or inserted, the actual design can be segmented treatment, as shown in figure 3.

If set to insert the type section model, and the workpiece positioning pin interference; if set to single rotary, due to the workpiece itself multi fold surface, and by checking specific or workpiece interference occurred, its design into two independent rotary section model, can satisfy the requirements of comprehensive detection.

3 of the workpiece positioning and clamping fixture -- car

Correct positioning of the workpiece is the foundation for accurate measurement. A positioning fixture on the way in which is composed of a positioning hole and a clamp locating or permanent magnet for clamping with the completion of the body cover. With the inspection tool widely used in car body manufacturing, lever type movable clamping head and a permanent magnet are a series of products to buy, chuck is also provided with a bracket or activities of different types and sizes of bracket. Most of the body covering parts are the main, vice two positioning holes, the main positioning pin is generally cylindrical pin (hole) or diamond pin (waist hole), to limit the X. Y two degrees of freedom; positioning pin is a conical pin or diamond shaped plug pin, to restrict Z.X.Y.Z four degrees of freedom. Design of fixture, positioning holes punched in the examination of position specific (into the positioning pin bushing to prevail), and gives the body coordinate positioning hole. At the same time, position location of gasket and movable clamping head in workpiece rigidity is better and reasonable distribution, in order to ensure a solid workpiece positioning design to minimize the number of chuck clamping point, assurance activities when working with other components not produce interference, and considering the workers has the advantages of convenient operation, body coordinate Center eventually give location on the spacer surface.

Design of 4 plate assembly

In the examination of specific surface along the datum plane tensile certain distance, to its lowest point is greater than the thickness of 150mm, in order to ensure the detection of specific have sufficient strength, at the same time try to make inspection concrete bottom surface, i.e. the upper surface of the bottom board assembly (base), integer position in the body coordinate system on. Inspection of concrete baseplate assembly generally consists of substrate, channel (when necessary in the intermediate processing word steel), a positioning block and a universal wheel, when seized by specific substrate after fixing, other parts can be according to the actual situation, choose the standard model.

Detection of 5 holes

Body stamping on many important hole flanging and need separate detection. Usually in the examination of specific surface with about 1mm thick convex platform in the design of checking fixture, boss and the center of the workpiece hole center on the same axis, the diameter ratio of large aperture 5mm, and adopts double scribing methods on the boss

When the measured hole of the higher accuracy requirements, with plug and liner with positioning holes on the detection. In the body of large covering parts, because this kind of gauge complex shape, large volume, high manufacturing cost, the single object detection, poor flexibility, it is difficult to obtain accurate information on a large number of fast, has gradually been automation and advanced detection means (such as online detection system) are replaced, but for the detection of small punch mass production member, at present our country automobile manufacturers still rely mainly on this kind of fixture.

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