How to judge the accuracy of equipment when buying used CNC machine tools?

When buying used CNC machine tools, you can judge the accuracy of the equipment from the machine's own accuracy test report, the condition of the key components, the performance of the trial machining, etc., the following is the specific method:

First, check the accuracy test report

Factory report: Check the factory accuracy inspection report of the machine tool to understand the precision indicators of the machine tool in the factory, including geometric accuracy, positioning accuracy, repeat positioning accuracy and so on whether it meets the standard. But pay attention to the timeliness of the report, time may not reflect the current accuracy.

Recent test report: If the seller can provide a recent accuracy test report issued by a professional testing organisation, the credibility is higher. This report usually lists in detail the measured data of various precision indicators, according to which the current precision status of the machine tool can be judged.

Second, check the key components

Guide rail: the guide rail is one of the key components affecting the accuracy of the machine tool. By observing the guideway surface whether there are obvious signs of wear, scratches, strains, etc., but also can be touched to feel the flatness and smoothness of the guideway surface. If the guide rail is seriously worn, it will lead to unstable movement of the table, affecting the machining accuracy.

Screw: the accuracy of the screw directly affects the positioning accuracy and feed accuracy of the machine tool. To check whether the screw is worn or deformed, you can shake the table or coordinate axis by hand to feel whether the screw rotates smoothly and whether there is any phenomenon such as stagnation and excessive clearance. Can also use the percentage table and other tools to measure the axial runout and radial runout of the screw.

Spindle: the rotary accuracy of the spindle is critical to the machining accuracy. Check the radial runout and axial runout of the spindle, can be fixed in the machine bed or other fixed parts of the per centimeter, the head contact spindle end or journal, rotate the spindle, observe the per centimeter reading changes. Generally speaking, high-precision machine tool spindle radial runout and axial runout should be within a few microns.

Third, the trial machining test

Processing simple shape parts: let the machine tool to process some simple shape parts, such as square, cylinder, etc., and then use the gauge (such as calipers, micrometers, coordinate measuring machine, etc.) to measure the dimensional accuracy of the parts, shape accuracy and positional accuracy, to check whether the processed parts meet the design requirements.

Detection of complex contour machining: carry out complex contour machining tests, such as machining a part with a variety of curves and surfaces, and observe the performance of the machine tool in the machining process, such as whether it can accurately process according to the programmed trajectory, and whether there is any distortion of the contour, surface roughness and other problems. By testing the machining of complex contours, the accuracy and performance of the machine can be more comprehensively assessed.

Evaluation of machining surface quality: Observe the surface quality of the machined parts, such as whether there are cut marks, ripples, burrs, etc.. Good machine accuracy usually produces parts with a high surface finish and uniform texture. If the surface quality is poor, it may be insufficient machine tool accuracy, or it may be the tool, cutting parameters and other issues that need to be further analysed and judged.

Fourth, running performance testing

Coordinate axis motion accuracy detection: through the CNC system commands, so that the coordinate axis for rapid movement and positioning operations, to observe whether the movement of the coordinate axis is smooth, accurate, there is no vibration, creep and other abnormal phenomena. Professional equipment such as laser interferometer can be used to measure the positioning accuracy and repeat positioning accuracy of the coordinate axes.

Automatic tool changer system testing: For CNC machine tools with automatic tool changer function, check the accuracy and reliability of the automatic tool changer system. Carry out multiple tool change operations and observe whether the tool exchange is accurate, whether there are any problems such as dropped tools and tool positioning deviation.