What are the requirements for accuracy of automobile fixture customization?

The core of the precision requirement of automobile fixture customization is to follow the principle of "the precision of fixture is higher than the precision of parts", which usually needs to reach 1/3 to 1/10 of the tolerance requirement of parts, and the specific value needs to be determined comprehensively in combination with the type of parts, functional importance and testing standards.

1. Core accuracy requirements: divided by inspection object.

The accuracy requirements of different inspection objects are significantly different, so it needs to be set accordingly to ensure that the inspection fixture can accurately identify whether the parts are qualified or not.

dimensional accuracy

According to the key dimensions of parts (such as aperture, shaft diameter and length), the dimensional error of the fixture should be strictly controlled. For example, if the tolerance of an aperture of a part is ±0.05mm, the dimensional tolerance of the measuring pin corresponding to the fixture usually needs to be controlled within 0.01 mm..

Non-critical dimensions can be appropriately relaxed, but it is still necessary to ensure that the error of the fixture does not exceed 1/3 of the tolerance of the parts to avoid misjudgment.

Form and position accuracy

Covering parallelism, verticality, coaxiality, etc. Taking the engine block as an example, if the plane parallelism tolerance is 0.03mm/100mm, the reference plane parallelism of the checking fixture should reach 0.01mm/100mm, so as to ensure that the shape and position deviation of the parts can be accurately captured.

positioning accuracy

The locating pins, locating blocks and other parts of the fixture should be accurately matched with the locating datum of the parts. The positioning error is usually required to be ≤0.02mm to prevent the detection result from being distorted due to the positioning offset.

Second, the influencing factors of accuracy: need to focus on control.

In the process of customization, the following factors will directly affect the accuracy of checking fixture, so it is necessary to plan ahead and avoid risks.

Material selection: materials with high stability and strong wear resistance are preferred, such as No.45 steel (quenched) and aluminum alloy (suitable for lightweight requirements). Avoid the use of deformable materials to prevent the accuracy from decreasing after long-term use.

Processing technology: The key components need to be processed with high precision, such as CNC precision milling (accuracy up to ±0.005mm) and wire cutting (accuracy up to ±0.002mm), so as to ensure that the processing error meets the design requirements.

Assembly accuracy: When assembling the checking fixture, it is necessary to control the assembly clearance of each component, for example, the fitting clearance between the locating pin and the pin hole should be ≤0.005mm to avoid affecting the overall accuracy due to loose assembly.

Third, the accuracy verification standard: to ensure compliance

After the fixture is made, it is necessary to confirm that the accuracy reaches the standard through standardized verification, and the common basis includes industry standards and enterprise specifications.

Industry standard: Follow the international standard ISO 8015 (geometric tolerance labeling principle) and China automobile industry standard QC/T 300 (design and manufacturing specification of automobile inspection tools) to ensure the accuracy of inspection tools meets the general requirements of the industry.

Enterprise specification: Large automobile manufacturing enterprises usually set internal standards of fixture accuracy, such as Volkswagen, Toyota and other brands, and set stricter enterprise limits on the dimensional tolerance and shape tolerance of fixtures, which need to be verified according to customer requirements.