How to Make Part Measurement More Accurate

In the process of product testing, if it is found that the test data of the same program or the same part during multiple tests are greatly different, the output is inconsistent, or it is different from the actual assembly situation, it needs to be checked and analyzed from several aspects. Here are the main points.

A. Fixing and clamping of parts

Most users, when measuring parts, think that the weight of the workpiece can make it shift without position during measurement. In fact, the granite countertop is very smooth, if the workpiece is directly placed on the countertop, it will move because the center of gravity of the machine moves or vibrations, resulting in changes in the measurement results. Especially when the workpiece is small or light.

For batch testing, a scientific fixing method must be adopted, that is, 3-point bracket positioning, and there must be a reliable and convenient positioning reference to ensure the accuracy of clamping repetition.

B. Reasonable selection of stylus configuration

1. Reasonable choice of measuring stylus measuring ball diameter

Some "blanks" are not grinded or burred. Due to the large self-error, it will also cause greater repeatability. In this case, it is recommended to choose a larger diameter stylus and collect more points on the feature to get a relatively average effect and get good repeatability.

2. Choose the length of the measuring stylus reasonably

The length, weight and elongation of the contact have a great influence on the measurement accuracy and repeatability. The load capacity of the probe and the sensitivity of the probe (that is, the accuracy of the measurement probe) are often contradictory values. Contacts and contacts that exceed the load of the probe will cause interference errors and shorten the service life of the probe. Therefore, when using a longer stylus, select a corresponding suction cup or measuring probe with a larger load.

3. Probe calibration

The correctness of the probe calibration is the guarantee of the measurement accuracy, especially the probe position and star probe calibration, must be checked to ensure the accuracy of the measurement.

When the sphere is used, we need to increase the calibration points of each layer in the case of high measurement accuracy; In the case of complex surface and curve characteristics, it is necessary to increase the number of checking layers appropriately.

C. Select appropriate measurement and evaluation methods

The first is to determine which sector to use the measurement for, how to do it, and choose reasonable benchmarks based on these. If the measurement results provide a reference for adjusting the parameters of the next process, that is, the measurement results are used for process adjustment, the measurement basis needs to be unified with the process basis; If the measurement results are used for assembly or final acceptance of the workpiece, the measurement basis needs to be consistent with the design basis. Design information is usually given in drawings. The process data is based on the enterprise process and needs to be confirmed with the processing personnel.

D. View measuring machine accuracy and repeatability

The method to check whether the measuring machine is normal is simple. The accuracy and repeatability are checked by using standard detectors, such as measuring blocks, spheres, ring gauges, square boxes and parts processed by high-precision grinding machines, etc., as long as the length and diameter of repeated measurements are issued, and then the measurement results are compared with the theoretical standard dimensions, if these readings are consistent with the theoretical dimensions and the repeatability is good, the measuring machine itself is without any problems. Then continue to analyze the root cause of the problem.

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