Wed Jun 08 16:04:48 CST 2022
The continuous upgrading of the tapered cutting precision puts forward higher requirements. For this reason, a high-precision taper device is designed to solve the problems of rigidity, reliability, transmission accuracy and protection in terms of structural performance. Through application and verification, its geometric accuracy and numerical control motion accuracy have been steadily improved, and it can complete high-precision taper cutting and multiple cutting processing.
With the rapid development of aerospace, defense technology and mold industry, mold manufacturing is constantly upgrading, and the dimensional accuracy and surface quality requirements of supporting parts are getting higher and higher. Ordinary reciprocating wire cutting machine tools can no longer meet the requirements of precision mold manufacturing. The requirements have promoted the industrialization and technology improvement of CNC middle-line wire-cutting machine tools.
As one of the core components of the wire cutting machine tool, the taper device has higher requirements than ordinary reciprocating wire cutting machine tools. The newly released and implemented JB/T11999.1-2014 "Numerical control reciprocating wire type multiple cutting electric discharge wire cutting machine tools Part 1: Accuracy inspection" stipulates that the U (V) axis movement is opposite to the X (Y) axis movement. The tolerances of parallelism in the vertical and horizontal planes are 0.030mm and 0.015mm, respectively, which are higher than the 0.040mm and 0.020mm specified in the accuracy standards of ordinary reciprocating wire-cutting machine tools; and the taper processing inspection items in the processing inspection are specified The big end size difference and taper deviation are 0.020mm and 1', respectively, which are also higher than the 0.030mm and 1'30" stipulated in the accuracy standards of ordinary reciprocating wire-cutting machine tools. From this point of view, the requirements of the accuracy inspection standards are improved. The essence is the control of product quality and the promotion of technology improvement. How to further improve the accuracy of taper cutting and multiple cutting accuracy has become a new topic and research direction for the majority of industry technicians.
1. Taper processing principle and related elements
The taper processing of the reciprocating wire cutting machine tool moves through the U and V coordinates and moves with the X and Y coordinates, so that the electrode wire produces a spatial displacement trajectory along the central axis between the upper and lower main wheels, and realizes the taper cutting and upper and lower different surfaces. Processing.
The main factors that affect the taper processing accuracy and surface quality are the positioning accuracy of X, Y, U, and V coordinates, the rotation accuracy of the guide wheel and the guiding accuracy of the V-groove. In the taper processing, in view of the opening of the V-groove, the tangent point of the electrode wire will change, which will cause the inevitable taper cutting error; in addition, the displacement and repeated positioning of the U and V coordinates are more important. This plays a decisive role in taper processing and multiple cuts.
2. Analysis of taper device structure and machining error
The taper device of the ordinary reciprocating wire cutting machine tool generally adopts a cross slide structure (Figure 1), a rigid ball guide, a stepping motor driving a reduction gear, and a small pitch micro screw to achieve displacement. Because the thickness of the two-layer slide plate is relatively thin, the movement of the guide rail is along the straight line formed by the two tangent points of the steel ball, and the force of the vertical plane falls completely on the steel ball, so the rigidity and load-bearing capacity of the guide rail are poor, and the miniature small-pitch sliding screw It is also difficult to control the accuracy and clearance; coupled with the drive characteristics of the stepper motor, the UV axis has low positioning accuracy, small transmission torque, no pitch and gap compensation functions, and large cumulative transmission error, so it can only meet the accuracy of 0.05 Taper processing of about mm. In addition, the overall installation is close to the processing area, and the protection performance, accuracy retention and service life are all affected.
3. Design of high-precision taper device
3.1 Overall structure of high-precision taper device
The design idea is to design the taper device as an independent whole, avoid the processing area to install, solve the protection problem, adopt precision linear guide, precision ball screw and special bearing, AC servo motor direct drive, ensure sufficient rigidity, and achieve high Precision transmission.
3.2 Brief description of mechanical structure
The taper head device is a T-shaped sliding table structure (Figure 2). The UV shaft slides are made of box-type precision castings, which are connected at 90° to each other. The installation of the linear guide rail adopts the installation method of the cross beam guide rail of the CNC gantry milling machine. The two linear guide rails are installed on two perpendicular planes respectively, so that the vertical force when connecting the guide wheel seat or other parts is resolved, and a larger amount can be obtained. Load and torsion resistance. The servo motor directly drives the ball screw through the coupling, which is reliable in connection and accurate in transmission.
The device can be used as an independent component for assembly and testing of geometric accuracy and motion accuracy on the platform. Therefore, manufacturing and accuracy adjustment are extremely convenient. In addition, the overall installation is in front of the main spindle head, away from the discharge area, effectively preventing the pollution of erosion products such as water mist, discharge oxidation mist, cutting fluid, etc., and the comprehensive protection performance is improved.
3.3 Improve control and repair capabilities
By improving the numerical control system and software control function, the pitch and backlash errors of the ball screw are compensated, the accuracy error of the screw itself and the human error factors generated during the assembly process are eliminated, and the positioning accuracy and repeated positioning of the UV axis are improved. Accuracy. In terms of taper processing and multiple cutting control, the numerical control system and software have also made corresponding circuit improvements and technical upgrades, so that the taper processing accuracy has been steadily improved.
Through the inspection and verification of more than ten batches of the company's full-ac servo drive wire series products, the geometric accuracy of the U (V) axis movement to the X (Y) axis movement in the vertical and horizontal planes are less than 0.015. mm and 0.010mm; the measurement values of the CNC accuracy of the UV axis are: two-way positioning accuracy ≤0.015mm, one-way repeat positioning accuracy ≤0.008mm, backlash ≤0.005mm (measurement length ≤100mm). When processing 40mm thick 40Cr, the average cutting efficiency is 3200mm2/h; the accuracy of processing straight octagonal is ±0.005mm, the size difference of the large end of the processing regular octagonal table is 0.002mm, and the taper deviation is 36"; the best surface rough mallet The degree is Ra0.78μm.
This independent suspension sliding table taper device has been applied to the wire-moving series products in our company's full AC servo drive. The assembly and debugging are easy to master, and the maintenance is very convenient. After half a year of verification, workers responded well. Practice has proved that the servo taper device has high transmission and positioning accuracy, stable and reliable processing, and the accuracy of taper plus and multiple cuts is greatly improved compared with the stepper taper device.