SU952499A1 - Tool-electrode for electric discharge cutting out - Google Patents

Description

(54) ELECTRODE INSTRUMENT FOR ELECTROEROSION

CUTTING

. one

The invention relates to electrical discharge machining, specifically to wire cutting.

There is a known method of electroerosive cutting of rewinding wire, in which an electrode-tool is used in the form of uninsulated, without surface coatings, wire of tungsten and other metals. This method can be implemented, for example, on the EDM cutting machine model ME-320.

The method consists in the fact that the part and the electrode-wire are placed in the working fluid, kerosene, and connected to the source of the technological current — the generation of the Copy-RC. Under the action of the electroerosive removal, the rewinding electrode-wire produces in the part a cutting along the given contour 1.

The disadvantage of this method is low processing capacity, which limits the use of EDM cut-off machines, especially for the manufacture of serial parts.

Low processing performance due to the use of generator-RC.

Processing performance can be increased by switching to pulsed power sources. In this case, narrow pulses with a duration of the order of 0.1 -10 MCS are used, which drastically reduces the likelihood of an electrical breakdown of the gap. To maintain the EDM process, the breakdown distance of the interelectrode gap is reduced to units of micrometers. At the same time, there is a danger of the transition of the process of electroerosive breakdown into a short circuit, which sharply destabilizes the process of electroerosion.

The aim of the invention is to increase the performance of EDM.

This goal is achieved by using wire with a coating containing gra () IT (carbon) obtained by drawing through diamond dies as an electrode tool.

With such a coating, there can be practically no gap between the front side of the wire and the part, i.e. the wire is rewound, in contact with the part. Due to the roughness of the contact does not occur over the entire surface. When a current pulse appears at one of the swing points, the coating layer will heat up, evaporate and the contact will break, and a breakdown will occur in its place. The degree of contact can vary within fairly wide limits, ensuring the transition of the gap to its negative area — nat g. Nat g is limited by the amount at which the contact turns into an EDM breakdown. The gap, as in the case of treatment with uncoated wire, is determined by the breakdown distance at a given idling voltage.

Due to the coating of the wire, which ensures the expansion of the range of permissible values of the gap - tension g, stable initial conditions of the spark erosion gap are achieved.

The presence of coating particles in the interelectrode gap facilitates electrical discharge testing, forming additional bridges along which it occurs. The combination of these factors allows processing with a high pulse utilization rate - no less than 80-90%. Thus, a sharp increase in productivity is achieved.

A number of experiments were performed for verification. In one of them, the resistance of the contact between the wire and the steel part, 0.5 mm thick, was measured with a step-by-micrometer each, bringing them closer together. Wire with graphite-known

VA-1G

Proposed

VA-1A

Wire brand BA-1A is produced by dragging through diamond dies. The wire is pre-dipped in a suspension of graphite in water, called in the technical literature, aquadag. With a wire drawing on the surface of the wire, a durable layer of graphite serves as a working coating. Wire brand BA-1G is obtained from BA-1A by cleaning its surface, as it was believed, from harmful aquadag.

The coating is not insulated, as well as a goal. In both cases, rewinding caused contact instability. When using a wire without coating, the contact resistance with a decrease in the gap of 1-2 µm, starting from a certain value, varied abruptly from 5 kΩ (water leakage resistance) to 0.02-0.04 kΩ. In the experiment with a wire with a graphite coating, the contact resistance decreased gradually from 5 kΩ to 0.25 kΩ while reducing the gap by 5-10 μm. A further reduction in the gap did not affect the contact resistance. It remained at the level of 0.2-0.3 kΩ. It can be considered that this range is the coating resistance, since if the wire is wiped with force to the part, destroying the coating, the contact resistance drops to 0.01-0.02 kΩ, as in the case of bare, uninsulated wire.

In other experiments, repeated processing was carried out with the same piece of graphite-coated wire, which gives it a black color. Processing capacity began to fall in some cases after the 5th, in others, after the 15th time, using the same wire segment. At the same time, the surface of the wire is light, in the middle of the coating.

Example. It was made by EDM cutting a shel in a spinneret for producing artificial fiber.

1-3Generator-Kerosene 20-30

RC

10-20 Impulse - Waterborne 2-3 generators water

The table presents comparative data processing wire known and proposed methods.

The increase in wire rewinding speed is caused by the intensification of the EDM process. With fast forwarding

the EDM gap is drawn in by more water, more heat and eroded particles are removed. Wire consumption due to growth

performance does not increase, and reusability even reduces it.

The power source of technological current is a specially designed generator, pulses with inductive energy storage.

Its characteristic is: Frequency of working impulses, kHz 800 ± 5 Duration of operating current pulses, MKS0.3 ± 0.5 Amplitude of a short-circuit current pulse, A 2.5 ± 0.1 Amplitude of a no-load voltage pulse, not less, B80

Coated wire processing is characterized by increased productivity, which makes it possible to economically use EDM cut-off machines for the manufacture of mass-produced parts.

Claims (1)

Invention Formula Dragging application through diamond dies wire of conductive material with graphite coating as an electrode tool for electroerosive cutting. Sources of information taken into account during the examination 1. Artamonov B. A. Size of electrical processing of metals. M., 1978, p. 152.