On the calibration of CNC machine tools

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Talking about the calibration of CNC machine tools

when quality problems need to be strictly considered, calibration and compensation will directly affect the cycle time. A machine tool within the accuracy index can work at high speed and maintain machining accuracy at the same time. Calibration allows workpiece detection, saving time for workpiece to move back and forth between machine tool and CMM. In addition, regular calibration can also be used to predict whether the machine tool is about to deviate from the accuracy index

professional metrologists were required to operate laser calibration instruments in the past. It is necessary to open the machine cover so that the optical elements can be adjusted on the workbench, spindle and independent tripod. The process of space calibration takes several days, depending on the size of the machine tool. Therefore, when the workpiece is within the tolerance range measured by CMM, spatial calibration is not so necessary

with the progress of technology, the cost of laser calibration equipment is greatly reduced, such as Optodyne products. At the same time, professional metrology personnel and external services are not required, and the downtime of machine tools is also greatly reduced. A machinist who has received one-day laser calibration training can complete the space measurement of 1 cubic meter machine tool in half a day. The software can automatically write out the compensation table and upload it to the controller of the machine tool

for many years, the volume Diagonal displacement method (bddm) defined in asmeb5.54 or ISO standards has provided many manufacturers, such as Boeing and other aerospace companies, with a fast method to detect spatial errors. Bddm measures the four diagonals of the machine tool workspace and generates four sets of data including all errors. However, sufficient data cannot be provided to identify the location of the error

our new method, step-by-step diagonal measurement (ssdmm), is also set with four diagonals and can collect 12 sets of data. According to these data, three displacement errors, six straightness errors and three perpendicularity errors can be measured without prolonging the downtime. In addition, the measured positioning error can be used to generate a spatial compensation table. Figure 2 shows the process of step-by-step diagonal measurement of spatial error within 2 hours, and the machine cover does not need to be opened. Ssdmm is different from bddm. Its X, y and Z axes move in turn and collect the diagonal positioning error, which provides three times the amount of data, and enables the positioning error of each axis to be measured

the measured oil quantity is too small, and the experimental machine cannot work normally. All the data are based on their own unique opinions. The trajectory of target movement is not straight. The second transmission mode cannot guarantee the synchronization line of transmission, and its lateral movement is large. The traditional interferometer cannot do these measurements, because such a large lateral movement is not allowed. Single aperture laser interferometers such as laser Doppler displacement meter are not affected by large lateral movement. Using a plane mirror as the target to be measured, the movement parallel to the mirror will not transfer the laser beam, nor will it change the distance from the light source

predictive maintenance (PDM) and other procedures, such as machine tool variability management system, reliability and maintainability, failure mode and effective analysis, full production maintenance, can predict machine tool failure (deviation from accuracy indicators). By comparing the current and previous data collected by laser calibration, vibration analysis, infrared temperature recording and other instruments, a prediction chart is made to predict whether CNC parts, ball screws, guide rails, servo motors and other machine tool components need compensation, service or other necessary repairs

a machine tool with accuracy grade of 5.1 should be checked every 6 months. The solution is to use stepped samples once. Assuming that the accuracy has decreased by 1.27 in the last three calibrations, based on the previous information, it can be predicted that it is reasonable to calibrate within 6 months. Similarly, vibration analysis can disclose information about the spindle and other problematic components to determine whether maintenance or repair is needed

setting up an early warning (PDM) program requires a long-term process. First, select machine tools, calibration technology and collect data. Secondly, determine and purchase calibration equipment. Then use the following basic steps to establish PDM. 1. Monitor the condition of machine tools

2. Diagnose and determine the problem

3. Analyze data and determine corrective measures

4. Establish early warning and prediction through integrated precision measurement system and manufacturing operation

after refining the above repeatable basic steps, the acceptable performance and accuracy level can be determined. In addition, the reference line of the machine tool must be measured and established. The measurement of the machine tool is regular and carried out at a specified time interval. After analysis, the maintenance and repair forecast are combined with the production arrangement

using a machine tool with space detection function to detect the workpiece in the machining process can greatly reduce the cycle time and improve the machining accuracy. In the aerospace industry, detection has not been developed, because the same positioning error will appear on the same machine tool that processes the workpiece. Therefore, the updated laser calibration technology and method meeting the requirements of so9000 and ISO17025 can ensure the manufacturing and quality assurance plan at the same time, and make the detection a feasible and reliable method

for example, the accuracy of the gauge is required to be 4:1, so the accuracy of the CNC machine tool must be more than 4 times the specified accuracy of the workpiece being processed. In order to meet this requirement, the accuracy of the tested machine tool must be recognized. The software of a machine tool that has passed the measurement of spatial positioning error can automatically generate a modified look-up table, which enables the detection software to compensate the spatial positioning error of the machine tool

when using a tested machine tool, use an appropriate probe to replace the tool to measure the size of the workpiece. Its spatial positioning error can be listed in error table or compensation table, so that the software can correct the position of the measured probe. With space error correction, the geometric error and positioning error of the machine tool itself can be eliminated, providing accurate dimension measurement. Therefore, the accuracy requirements of 4:1 gauge are met, so that the CNC machine tool with spatial error compensation can have the same high-precision function as the CMM

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