1 Introduction

Wirecut Electrical Discharge Machining (WEDM), sometimes referred to as wire cutting. The basic working principle is to use a continuous moving thin wire (called a wire) as an electrode, and perform pulse spark discharge on the workpiece to remove metal and cut. Wire cutting is mainly used to process various shapes and delicate workpieces, such as punches, dies, embossing dies, fixing plates, unloading plates, etc. for forming dies, forming tools, stencils, and metal for EDM processing. Electrodes, various micro-holes, narrow slits, arbitrary curves, etc., have outstanding advantages such as small machining allowance, high machining precision, short production cycle and low manufacturing cost. They have been widely used in production, and are currently used at home and abroad. Spark wire cutting machines account for more than 60% of the total number of electric machine tools.

2 slow wire processing machine

2.1 wire cutting machine classification

According to the operating speed of the wire, the WEDM machine is usually divided into two categories: one is the high-speed wire EDM machine (WEDM-HS), the wire is used for high-speed reciprocating motion, the general wire speed is 8 ~10m / s, the electrode wire can be reused, the processing speed is higher, but the quick wire is easy to cause the wire to shake and the pause in the reverse direction, so that the processing quality is degraded. It is the main machine produced and used in China, and it is also the original in China. The electric discharge wire cutting processing mode; the other is the low speed wire-cut wire electric discharge machine (WEDM-LS), the electrode wire is used for low-speed one-way movement, the general wire speed is less than 0.2m/s, and the wire is not discharged after discharge. Reuse, work is smooth, uniform, small jitter, good processing quality, but low processing speed, is the main machine for foreign production and use. This paper introduces the application case of Delta ASD-AB servo on the slow wire processing machine.

2.2 wire cutting machine structure

Slow wire and fast wire as the main components of the machine tool include:

(1) Host: including bed, coordinate workbench, wire-traveling mechanism, etc.;

(2) Pulse power supply: converts the alternating current into a unidirectional pulse current of a certain frequency;

(3) The control system controls the movement of the machine tool, which is the focus of this paper;

(4) Working fluid circulation system: Provide a clean, pressurized working fluid.

3 Motion control based on Delta servo technology

3.1 Hardware Introduction

The control part is the host computer system and the servo system:

(1) Host computer: It is a dedicated NC controller for slow wire-cutting machine based on PC architecture;

(2) Servo system: two sets of Delta ASD-AB10212MA servo controller and Delta ECMA-G31309ES large inertia servo motor.

(3) Mechanical transmission: The servo motor is directly connected with a screw with a pitch of 6 mm.

3.2 technical difficulties

The main technical difficulty of the servo application on the slow wire machine is to maintain a stable tracking error during the ultra-low speed operation of 0.5~0.2 rpm, and the tracking error must be less than 2 pulses. Such ultra-low speed technology requirements are actually closely related to the processing characteristics of slow wire machine tools.

The wire diameter of the slow wire-cutting machine is usually 0.03~0.35mm, and the total area of ​​the centerline cut on the workpiece when machining the workpiece is up to about 350mm2/min. The workpiece processed by the slow wire machine is different from the wire. It is usually required for both machining accuracy and processing thickness. This has a high requirement for the feed speed of the slow wire machine. The speed must be within a certain range. Too fast speed will result in incomplete processing, leaving a rough trace of different depth on the surface of the workpiece to make the surface roughness. The deterioration will also cause the vibration of the wire to increase, which is easy to cause broken wire. As for the tracking error of the servo system less than 2 pulses, the processing principle of the wire cutting is to continuously discharge the surface of the workpiece between the positive and negative electrodes. That is to say, the two electrodes must maintain a certain distance between them, and they can neither contact each other to cause a short circuit, nor can they be too far away to cause an open circuit!

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