Before your machine makes precision parts, it is extremely important to know in advance whether it will produce good parts for you. This is very effective in reducing the number of scraps and machine downtime. Many companies have realized this. They have begun to adopt the international standard ISO230, the American ASME B5.54 machine standard or the Chinese.B standard to ensure that CNC machine tools can work “healthyâ€, thus increasing productivity.
1 Common precision requirements of CNC machine tools and traditional detection methods
Geometric accuracy includes straightness, verticality, flatness, pitch and torsion, and parallelism. The traditional method uses marble or metal flat ruler, angle gauge, dial gauge, spirit level, collimator and other tools. It is manually operated, manually recorded data and calculation, and has low precision, and is mostly used in small machine tools.
Position accuracy CNC machine tool position accuracy includes positioning accuracy, repeat positioning accuracy and micro-displacement accuracy. Traditional methods use metal wire scales or step gauges, electronic micrometers, and collimators to measure. When the machine tool size is slightly larger, the corresponding standard device of the traditional method is very heavy, and the precision is too low, which is greatly affected by the ambient temperature. The inspection method is extremely tedious and the test repeatability is also very poor, which is difficult to reflect the true condition of the machine tool being inspected. Precision. Data processing must be done manually, cumbersome and error-prone.
Work Accuracy The US NAS (National Aerospace Standard) 979 developed a standardized "circular-diamond-square" test (now the CMTBA logo) 20 years ago. When implementing, prepare cast iron or aluminum alloy test pieces, milling cutters and CNC cutting programs. The accuracy of the test piece is checked by a high-precision roundness meter and a high-precision coordinate measuring machine. This method requires careful definition of the cutting method of the test piece and measurement of the cutting result, which may take several days and depends on the conditions of the measuring chamber.
2 new technology realizes old ideas
For any factory, buying CNC machine tools is a considerable investment. Therefore, it is crucial to make CNC machine tools play a strong role in production and to recover costs as soon as possible.
In general, it is often too late to find the quality of machine tool processing after the parts have been processed. For those responsible for the efficiency of the shop, the ideal solution is to test the machine performance before the workpiece is machined. The Renishaw ML10 laser interferometer and QC10 ballbar provide a powerful tool for achieving this goal.
Characterizing machine performance is not a new idea, it just doesn't work. The US NAS (National Aerospace Standard) 979 cannot evaluate all the performance of the machine. Most of the cutting motion of the "Curve-Rhombus-Square" test is performed on the XY plane, so most of the accuracy along the XZ and YZ planes is not measured. An aerospace factory found that the machine tool with the "circular-diamond-square" test was found to have a tracking error of 800 μm on the XZ and YZ planes after inspection with the QC10 ballbar.
The “one-day test†is proposed in American National Standard B5.54. It is actually a simplification of multiple tests, taken from the standard as a whole. This test is for machine tools with three linear axes. The most important part of this test with a ballbar and laser interferometer is the verification of size and accuracy. The modified NAS still needs to be tested to verify that the machine is functioning properly, but it is not a test of whether the machine can achieve accuracy. “One-day test†includes: linear displacement accuracy: bidirectional repeatability: spatial position accuracy, laser-based diagonal displacement accuracy measurement: two-axis linkage contour performance.
A set of basic hardware and software to complete the B5.54 "one-day test" is about $40,000, including the ballbar and laser interferometer system. This is a complete system that collects and reports machine performance data according to B5.54 (can also be analyzed according to the Chinese GB/T17421-2000 standard) and has a fully traceable machine performance evaluation program in accordance with ISO230. The laser system in the system can use automatic error compensation software, which generates G code to drive the machine, acquire and compare the positioning data and rewrite the CNC pitch error compensation file of the machine.
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