How to judge whether the thickness tolerance of stamping parts raw materials meets the requirements?

To judge whether the thickness tolerance of raw materials for stamping parts meets the requirements, the process of "standard comparison-detection method-data determination-batch sampling inspection" should be followed. The core is to ensure that the material thickness deviation is within the design allowable range through accurate measurement and standard comparison. The specific steps are as follows:

A, clear the criterion of thickness tolerance.

Determine the implementation standard first.

The stamping raw materials with different materials have corresponding national standards or industry standards, and the thickness tolerance should be based on this:

Cold-rolled steel plates (such as SPCC and DC04): According to GB/T 708-2006, tolerances are classified into ordinary precision (P), high precision (H) and high precision (HH). Precision stamping parts usually require high precision or high precision, such as cold-rolled plates with a thickness of 1.0mm, with a high precision tolerance of ±0.03mm and a high precision of 0.0.

Stainless steel plates (e.g. 304 and 316L): According to GB/T 3280-2015, stainless steel plates for precision stamping mostly adopt Class A tolerance, with a tolerance of ±0.02mm for thickness of 0.5mm and ±0.05mm for thickness of 2.0 mm..

Aluminum alloy plates (such as 1060 and 5052): According to GB/T 3880.3-2012, high-precision tolerances are commonly used for precision parts, and the tolerance of 1.5mm thickness is 0.04 mm.

Check product design requirements

If the product drawings have special requirements for thickness tolerance that are stricter than the national standard (such as the tolerance of precision electronic shrapnel of ±0.01mm), the drawing requirements should be the final criterion, not the lower limit of the national standard.

Second, choose accurate detection tools

According to the thickness and accuracy requirements of raw materials, select corresponding measuring tools to ensure that the measuring accuracy is 2~3 times higher than the tolerance requirements (error traceability principle);

The measurement accuracy of the detection tool is suitable for the scene.

Micrometer (spiral micrometer) 0.001mm thin/medium plate with thickness of 0.1~10mm, suitable for single-point accurate measurement.

Digital display thickness gauge can be used for fast multipoint measurement of 0.001~0.01mm large area plates, and some models can measure curved surfaces.

Raw materials (such as steel belts for precision elastic parts) required by laser thickness gauge with ultra-high accuracy of 0.0001mm are measured in a non-contact manner without indentation error.

High-precision full-scale detection of 0.001mm batch sampling of three-coordinate measuring instrument can record measurement data and generate reports.

Note: Before measurement, the tool should be calibrated (for example, the micrometer should be zeroed with a calibration rod) to avoid the error of the tool itself from affecting the result.

Third, standardize the measurement operation to avoid human error.

Selection of measuring points

The thickness of raw materials is uneven, so it needs to be measured according to the principle of "multi-point sampling" to avoid measuring only one point:

Small-sized plate (≤500mm×500mm): measure 5 points (1 point in the center+1 point in each corner);

Large-size coiled material/plate (> ＞1000mm): measure one group every 1m along the length direction, and measure three points (left, middle and right) in each group to ensure that the whole area of the plate is covered.

Key points of measurement operation

When measuring, keep the tool perpendicular to the surface of the plate to avoid the measured value being too large due to inclination;

For soft materials (such as aluminum alloy and copper), the micrometer should lightly press the probe to prevent the material from deforming and producing false readings;

Avoid defects such as scratches, scales and burrs on the surface of the plate, which will affect the measurement accuracy.

Four, data judgment and batch sampling rules

To judge and calculate the thickness of all measuring points for a single sheet, two conditions must be met:

Thickness deviation of any single point ≤ tolerance range specified in drawings/national standards;

The thickness fluctuation value (maximum-minimum value) of the plate is ≤ 1/2 of the tolerance range (to avoid the deformation of stamping parts caused by uneven thickness of the plate).

Example: The required thickness of a cold-rolled plate is 1.0±0.03mm, and the measured thicknesses of five points are 0.98, 0.99, 1.00, 1.01 and 1.02mm → the deviation and fluctuation values of one point meet the requirements, so it is judged as qualified.

Sampling inspection of incoming materials in batches follows GB/T 2828.1 sampling standard, and the sampling proportion is determined according to the batch size of incoming materials:

Batch ≤100 sheets/roll: sampling ratio ≥ 20%;

Batch > 100 sheets/roll: the sampling ratio is ≥10%, and the sampling number is not less than 30 sheets/roll;

If one piece is unqualified in the sampling inspection, the sampling inspection shall be doubled; If double sampling still fails, the whole batch of incoming materials is judged to be unqualified.

V. Supplementary judgment of special circumstances

Thickness consistency of coil material

The thickness difference of the same coil for stamping needs to be measured additionally, so as to avoid the mismatch of the gap between stamping dies and the occurrence of material jamming or size deviation due to the excessive thickness deviation of the coil head and tail.

Raw materials with coating/plating

If the surface of raw materials is coated with zinc, nickel, etc., it should be clear whether the tolerance includes the coating thickness:

If the tolerance is the thickness of the substrate: the coating should be removed before measurement;

If the tolerance is the total thickness: directly measure the overall thickness.