1 Introduction
CNC machine tools and machining centers use digital control systems to digitally control the movement of the tool to achieve the cutting of the workpiece. In the machining process, the geometry of the tool used (such as the length and diameter of the tool) must be input to the CNC system. And control the trajectory of the tool. If the machine tool is not equipped with a tool measuring device, only the real cutting method can be used to determine the geometry of the tool used (that is, the tool tool compensation value), that is, the tool compensation parameter in the numerical control system is corrected by measuring the actual size of the machined workpiece and the corresponding Control program. For the processing of small batches of workpieces that require frequent tool change, a large number of machine cuts will be added, which will greatly reduce the processing efficiency and will not be conducive to automated processing. For this reason, most CNC machine tools and machining centers are equipped with various types of tool setting devices, such as external tool setting devices, in-machine optical tool setting devices, and contact type automatic tool setting devices. Because the degree of standardization of tool clamping in turning centers is not high, the accuracy of tool setting using external tool setting tools is relatively low, and its practicality is poor. However, the use of internal contact type automatic tool setting devices is undoubtedly a simple and quick method. With the tool setting method, it can automatically measure the fixed tool compensation value of the tool, greatly reducing the tool setting time and improving the machining efficiency of the machine tool. This paper takes the Renishaw HPA high-precision tool automatic measurement system configured on the SCHAUBLIN 130-CNC turning center as an example to introduce the composition and specific application of the automatic tool measurement system.
2. Composition of automatic tool measurement system
The contact center tool automatic measurement system of a turning center is generally composed of a touch probe, a link arm, a mounting base, and measurement software, as shown in FIG. 1 . The shape of the touch probe is a 10mm x 10mm x 4mm carbide block with a measurement accuracy of 0.001mm. The probe is fixed to the spindle of the machine tool by the coupling arm and the base. The vertical centerline of the probe is parallel to the X and Z axes of the machine tool. When measuring, move the tool holder. When the tip of the tool contacts with the probe, measure the trigger signal. Use the signal cable to trigger the CNC system to record the position of the tool. Then calculate the tool by the corresponding measurement software. The fixed compensation value is directly transmitted to the corresponding tool compensation unit. After the measurement is completed, the operator can use the tool for machining.
Fig.1 Schematic diagram of automatic measuring system for contact tool in turning center
3. Calibration of automatic tool measurement system
The automatic tool measurement system is not generally manufactured by a machine tool manufacturer, but is purchased as a measurement tool, and can be purchased according to the user's different needs like a numerical control system. The measurement software is also designed by a numerical control system or a machine tool manufacturer according to their own needs. Before the tool automatic measurement system is used, the initial calibration must be performed according to the specific machine zero point and reference point. The calibration procedure is as follows.
(1) Select the calibration tool that can touch the four sides of the square probe. It is best to select two finishing tools with tool types 1 and 3 or 2 and 4, as shown in Figure 2.
Figure 2 Selection of calibration tools
(2) Estimate the tool length (tool offset value) used to calibrate the probe, as shown in Figure 3. The length of X and Z directions of each tool can be roughly measured manually, and the measurement accuracy should be controlled within 0.5mm.
(3) Estimate the coordinate position of the probe on the machine tool. Manually move the tool holder so that the tool is in contact with the probe, and record the coordinate values ​​at this time. After calculation, you can roughly obtain the X and Z coordinate values ​​of the two sides of the probe and the machine zero, as shown in Figure 4.
Fig. 3 Evaluation of tool compensation
Figure 4 Estimation of probe coordinate position
(4) Accurate tool length value (tool offset value) is obtained by test cutting. Among them, the X direction tool compensation value (ie diameter error value) = ideal size - the actual size, as shown in Figure 5, the tool's exact length (ie, new tool compensation value) = old tool compensation value + (± error value/2); The length error value in the Z direction can be obtained by dimensional errors of the workpiece end face to the chuck end face or the three-claw surface before and after the trial cut.
Figure 5 Accurate Calculation of Tool Compensation Value
Through the above steps, the corresponding parameters in the measurement software are corrected according to the requirements of the automatic tool measurement software of the numerical control system, and the initial calibration of the automatic measurement system of the numerical control machine tool is completed.
4. Automatic measurement of turning center tools
In the actual machining of the turning center, the processing of some parts often requires several or even several tens of tools to complete. For each tool, the specific size (ie, tool compensation value) relative to the reference point of the tool holder must be determined. Processing. In the turning center machining, according to the processing needs, each tool can select one or several tool compensation value storage units. The numerical control system has a number for each tool compensation unit, and the CNC system will call the used tool according to the tool compensation unit number. The knife compensation value. When using the automatic tool measurement system, you must first select the tool compensation unit for each tool, and then fill in the corresponding contents in the tool compensation unit. There are generally 10 items in the tool compensation unit, as shown in the following table.
Table tool compensation unit content
Cutter compensation numberDn 0 Tool number 1 Tool type 2 X axis direction fixed tool offset value L1 3 Z axis direction fixed tool offset value L2 4 Tool nose radius value Ra 5 L1 Tool wear compensation value 6 L2 Tool wear compensation value 7 Ra Tool wear compensation value 8 L1 lengthened tool correction 9 L2 lengthened tool correction
The definitions of the L1 and L2 values ​​in the table are shown in Fig. 3. The L1 and L2 values ​​must first give a rough measurement (error ≤ ±2mm). The tool types in the table can be generally divided into 8 categories, as shown in Figure 6. For single-axis turning centers, only types 2, 3, 4, 7, and 8 are generally used, and the rest are used for the lower tool holder of a turning center with double tool carriers. Among them, the second category is the boring tool, the third category is the external turning tool, the fourth type is the reverse-mounted external turning tool, the seventh type is the drilling type tool, and the eighth type is the cutter, the thread turning tool and the diameter Drilling tools. After filling relevant contents in the table in the tool compensation unit, the automatic tool setting device is installed and the tool automatic measurement cycle is invoked to quickly and conveniently implement the automatic measurement of the tool. The measured value is directly input into the tool in the corresponding tool compensation unit. Compensate for L1 and L2.
Fig. 6 Schematic diagram of turning center tool type
5. Conclusion
The turning center tool automatic measurement system can automatically realize the measurement of the tool tool compensation value on the machine tool, and automatically input the measurement result into the CNC system without manual intervention, avoiding human error and tool change errors, and some software also has tool damage. Automatic detection and other functions. The automatic tool measurement system can greatly reduce the processing auxiliary time, improve the machining accuracy, reduce the reject rate, obtain the qualified products at the first cutting, and at the same time increase the intelligent degree of the numerical control machine tools. Therefore, the automatic tool measurement system has become a numerical control. One of the essential basic options for machine tools.