Today, I will share with you a summary of the key points in the design, manufacture, and inspection of large-scale trim check fixtures by senior designers, as well as the general methods and techniques used. The research and development of more efficient automotive trim inspection tools is of great significance to meet the needs of the rapidly developing automotive market.
Large automotive trim parts are generally made of chemical materials or textile fabrics, which have many different characteristics compared to body parts. It has the characteristics of large size, complicated surface and structure, poor rigidity of parts, and mostly space size. Therefore, it is necessary to make comparison and measurement with the aid of a fixture to quickly and accurately judge the quality of product parts. At the same time, the inspection fixture can help the discovery of parts manufacturing problems and ensure the continuous improvement of the product manufacturing process. The inspection fixture plays an important role in the smooth production of automobiles. A preliminary discussion was made on the large-scale trim inspection fixture in automobile production.
One. concept of design
Before the design of the fixture, the concept of the fixture design should be clarified, and the following factors should be fully considered.
1.1 Fully understand GD & T
G D & T is a descriptive document for automotive product design. Product specifications, product positioning benchmarks, key product characteristics (KPC), and product tolerance characteristics will be reflected on GD & T. Therefore, G D & T must be fully understood before the design of the fixture.
1.2 Determine product positioning and inspection content
Based on a full understanding of the product GD & T, analyze the benchmark characteristics of the product positioning, consider the optimal placement of product parts, understand the meaning of various tolerances, determine the test content that product parts must implement on the fixture, and do not need to achieve even Content that cannot be achieved at all.
1.3 Statistics of Process Control Capability (SPC)
Identify whether the product has KPC requirements, understand the purpose of the fixture, correctly understand the requirements of quantitative measurement and qualitative measurement, and ensure the reliability of SPC data collection.
1.4 Understanding requirements and processes
Fully understand the customer's requirements for product inspection tools, learn from past success or failure cases, fully understand the customer inspection tool review and approval process, and understand the required documents.
two. Design Principles
The fixture should have sufficient rigidity; it should have sufficient stability; it should have sufficient measurement accuracy to ensure the quality of the car; operation should be convenient to ensure sufficient measurement efficiency; the structure should be as simple as possible to use; it should have a good appearance; it should have sufficient The economic guarantee is convenient to control the cost of the whole vehicle; at the same time, it should be easy to measure and calibrate.
three. Design points of large-scale decorative fixtures
The inspection of large-scale automobile parts has the same features as the inspection parts of automobiles, and also has its own characteristics. Its structure is mainly composed of the following parts: base plate and frame part, positioning device, clamping device, measuring device, auxiliary device, etc. As shown in Figure 1, Figure 2.
Dashboard check fixture
Front bumper checkout for a certain model
3.1 Design of bottom plate and frame
The bottom plate and the frame part are the basic parts of the entire fixture. Although it is not the working part of the fixture, its stability is directly
Affects the accuracy of the entire gage. Because the inspection fixtures for large decorative parts are relatively large, we must pay attention to their rigidity and processability and stability of the selected materials when designing the structure of the bottom plate and the frame. Now generally use cast aluminum material, using ribbed structure or box structure
结构。 Structure. The bottom plate should be set with the detection and calibration benchmark of the inspection tool, which can be related to the vehicle coordinates. At the same time, a lifting or handling structure should be set. The bottom plate should have the coordinate lines of the car parts, as shown in Figure 3. Because the size of the product itself is relatively large, the design of the bottom plate should not be too large, otherwise it will cause inconvenience in operation, as long as it can ensure that the flipping parts do not protrude from the bottom plate.
A door panel interior inspection fixture floor
3.2 Positioning device design
Automotive parts are generally space parts, and their positioning in space plays a decisive role in the accuracy and stability of their detection. For rigid parts or small parts, the basic principle of '3-2-1' is generally used, that is, the first Three points for one benchmark, two points for second benchmark,
The third benchmark point, a popular point is to use different numbers of points to form surfaces, lines, and points to limit the degree of freedom of space objects. In actual production, it is impossible to have real points and lines. Generally, the 'points' and 'lines' are approximated by the unit 'surface'. The size of the unit surface should depend on the size of the product. For large decorative parts, the placement state on the inspection fixture should be based on the loading state to avoid the impact of the gravity state of the flexible body on the detection result.
(1) Positioning surface (first datum)
That is, the '3' in the benchmark system. For large trim parts, because of its relatively poor rigidity and relatively heavy weight, three points are not enough to form a stable surface benchmark. Therefore, its positioning system must be at '3-2-1 On the basis of adding enough positioning points or auxiliary positioning points, a complete surface reference can be processed to ensure the reliability of the positioning. For example, the SGM980 front security inspection tool misjudges the product because the positioning of the product is too small because of too few positioning points. The first positioning plane should choose the center of gravity plane as much as possible. When possible, the center of gravity should fall within the polygon formed by the positioning surface's points so that the parts can be in stable contact with the positioning surface. Figure 4 shows the front bumper of a certain model. Due to its large size and poor rigidity, there are more than twenty positioning features on it.
Snugly. The clamping device must have a certain rigidity, and the clamping direction should be along the normal direction of the positioning surface, as shown in Figure 5. If two directions are clamped at the same time, the clamping direction should be along the bisector of the angle between the two sides as much as possible.
Front bumper of a model
(2) Locating pins (holes) (second and third datums) are '2' and '1' in the reference system. Generally, the main positioning holes (columns) are four-way positioning pins (holes), and the secondary positioning holes (pillars) ) Two-way positioning pins (holes) are used, and two-way positioning pins should have anti-rotation measures. For large decorative parts, because of their poor rigidity and heavy weight, they generally do not use tapered pin positioning. Instead, they use direct sales positioning. When designing, they can be designed to the maximum aperture value, and then based on the stable value of the actual product. To correct the size of the positioning pin (must meet the dimensional tolerance of the aperture), to ensure the stability of product positioning, so as to ensure the R & R of the fixture.
Of course, the shape of the actual positioning feature may also be the deformation of the positioning hole (column). Therefore, specific problems must be analyzed, and appropriate positioning forms should be used in combination with the characteristics of the parts to ensure the reliable positioning of the product on the inspection fixture.
3.3 Design of clamping device
Because of the characteristics of the large decorative parts and to ensure that the part is in the unique state of the fixture during testing, after the parts are placed on the fixture, a clamping device should be used. The zero positioning surface and the fixture positioning clamping device must have a certain rigidity. , The clamping direction should be along
The normal direction of the positioning surface is shown in Figure 5. If two directions are clamped at the same time, the clamping direction should be along the bisector of the angle between the two surfaces as much as possible. There are many types and structures of clamping devices, but the general principle is to ensure that the pressing parts and the structure of the check fixture allow the operation to be as convenient and fast as possible, and use standard parts as much as possible.
3.4 Measuring device design
The measuring device and the positioning device are also the core parts of the gage, and are an important part to realize the detection function of the gage. According to
How to determine the tolerance characteristics of the tested product can be divided into qualitative and quantitative. Qualitative measuring device only judges the conformity and
No, the product characteristic value cannot be obtained; and the quantitative measuring device can directly obtain the product characteristic value. Qualitative measurement is mainly obtained by the method of G o-N ogo, volume or area comparison. On the decoration inspection tool, it is mainly obtained by simulating blocks, section templates, stop gauges, position gauges, and delineating the tolerance zone. Yes, it has a great advantage when it is used in online detection, and has the function of quickly determining the product, as shown in Figure 6. Quantitative measurement is mainly used in the initial stage of product trial production or in the case of KPC testing requirements. The dial gauge is mainly used to obtain the dial gauge, oblique ruler or feeler gauge.
Door panel interior fixture of a certain model
With regard to the adoption and design of the gage detection device, the product GD & T must be carefully analyzed, and appropriate detection methods should be adopted according to different tolerance characteristics. For example, the position and contour monitoring methods are different. The maximum physical principle of position tolerance and independence The principles are also different, and tolerances should be treated differently with respect to different relative to small benchmarks.
Due to the rapid development of the automotive industry and the rapid development of new models, the demand for automotive inspection tools is increasing.
Development efforts, in-depth research on inspection tool technology, increase investment in inspection tool development, better serve the booming Chinese automobile industry, and enable China's automobile manufacturing industry to catch up with the advanced world level at an early date.