High-precision taper device for intermediate wire-feeding machine tools

As one of the core components of the wire cutting machine tool, the taper device has higher requirements than the taper device of the ordinary reciprocating wire cutting machine tool. The newly released and implemented standard of JB/T11999.1-2014 "CNC Reciprocating Wire Type Multi-Cutting Wire EDM Machine Part 1: Accuracy Inspection" stipulates that the movement of the U (V) axis is equal to the movement of the X (Y) axis. The parallelism tolerances 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 standard of ordinary reciprocating wire cutting machine tools; and the taper processing inspection items in the processing inspection stipulated 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" specified by the accuracy standard of ordinary reciprocating wire cutting machine tools. From this point of view, the requirements of the accuracy inspection standard 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 and development direction for the majority of technicians in the industry.

1. Taper machining principle and related elements

The taper processing of the reciprocating wire cutting machine is to move the U and V coordinates and move with the X and Y coordinates, so that the electrode wire generates a spatial displacement trajectory along the central axis between the upper and lower main wheels, so as to realize the taper cutting process and the upper and lower different planes. processing.

The main factors affecting the taper machining accuracy and surface quality are the positioning accuracy of X, Y, U, V coordinates, the rotation accuracy of the guide wheel and the guiding accuracy of the V-shaped groove. During taper machining, in view of the guiding defect of the openness of the V-groove, the change of the tangent point of the electrode wire will cause the inevitable taper cutting error; in addition, the displacement and repeated positioning of the U and V coordinates are more important. This is decisive for taper machining and multiple cuts.

2. Analysis of taper device structure and machining error

The taper device of an ordinary reciprocating wire cutting machine generally adopts a cross slide structure (Fig. 1), a rigid ball guide rail, a stepping motor driven reduction gear, and a small pitch micro screw to achieve displacement. Since the thickness of the two-layer sliding plate is relatively thin, the guide rail moves along the straight line formed by the two tangent points of the steel ball, and the force on the vertical plane completely falls on the steel ball, so the rigidity and bearing capacity of the guide rail are poor, and the miniature small pitch sliding screw It is also difficult to control the precision and gap of the UV shaft; coupled with the driving characteristics of the stepping motor, the positioning accuracy of the UV axis is low, the transmission torque is small, there is no pitch and gap compensation function, and the cumulative transmission error is large, so it can only meet the accuracy of 0.05. Taper processing about mm. In addition, the overall installation is close to the processing area, 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 installation in the processing area, solve the protection problem, adopt precision linear guides, precision ball screws and special bearings, and AC servo motors are directly driven to ensure sufficient rigidity. 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 and are connected at 90° to each other. The installation of linear guides adopts the installation method of beam guides of CNC gantry milling machine. load and torsion resistance. The servo motor directly drives the ball screw through the coupling, with reliable connection and accurate transmission accuracy.
The device can be assembled as an independent component and tested on the platform for geometric accuracy and motion accuracy, so it is extremely convenient to manufacture and adjust the accuracy. In addition, the overall installation is in front of the main shaft head of the main engine, away from the discharge area, which effectively prevents the pollution of water mist, discharge oxidation mist, cutting fluid and other erosions, 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 precision error of the screw itself and the human error factors generated in the assembly process are eliminated, and the positioning accuracy and repeated positioning of the UV axis are improved. In terms of taper machining and multiple cutting control, the numerical control system and software have also made corresponding circuit improvements and technical improvements, so that the taper machining accuracy has been steadily improved.

Through the inspection and verification of more than ten batches of the company's full AC servo drive wire-feeding series products, the parallelism tolerance of the U (V) axis motion of the geometric accuracy to the X (Y) axis motion in the vertical and horizontal planes is lower than 0.015 respectively. mm and 0.010mm; the measurement values of the numerical control accuracy of the UV axis are: bidirectional positioning accuracy ≤0.015mm, one-way repeat positioning accuracy ≤0.008mm, reverse clearance ≤0.005mm (measurement length ≤100mm). When processing 40mm thick 40Cr, the average cutting efficiency is 3200mm2/h; the precision of processing straight octagon is ±0.005mm, the size difference of the big end of the regular octagonal table is 0.002mm, and the taper deviation is 36"; the best surface rough hammer The degree of Ra0.78μm.

This independent hanging sliding type taper device has been applied to the wire-moving series products of our company's full AC servo drive. The assembly and debugging are easy to master, and the maintenance is very convenient. After six months of verification, the workers responded well. Practice has proved that the servo taper device has high transmission and positioning accuracy, stable and reliable processing, and the taper addition and multiple cutting accuracy are greatly improved compared with the stepping taper device.