RU2772410C9 - Method for electric discharge wire cutting machining - Google Patents

Abstract

FIELD: metal working.

SUBSTANCE: invention relates to electric discharge machining, in particular, to electric discharge wire cutting machining of hard-to-process layered fibre composites. The method includes electric discharge wire-cutting machining of a sheet non-conductive or weakly conductive workpiece when a conductive medium in the form of metal sheets is applied to the upper and lower surfaces of the workpiece. The workpieces and conductive metal sheets are therein collected in a package prior to machining, alternating conductive and conductive layers. Sheets of stainless steel or aluminium providing intensive heat removal from the machined surface of the workpiece are used as conductive layers.

EFFECT: expansion of the technological capabilities of electric discharge wire cutting machining with the increased productivity of electric discharge machining of hard-to-process dielectrics, such as carbon fibre.

1 cl, 5 dwg

Description

The invention relates to electroerosive processing, in particular to electroerosive wire cut processing of difficult-to-machine layered-fiber composites, which include carbon-fiberglass and can be used to cut the contours of complex-shaped products from layered-fiber plastics, in particular carbon, fiberglass, mainly in sheet any thickness of products that are used in aircraft and rocket manufacturing, and in the machine-building industry.

A known method of electroerosive processing of dielectrics (patent RU No. 2024367, IPC V23N 1/00, 05/07/1992), which consists in exposing the workpiece to a microwave field. The pre-treated section of the surface of the workpiece is subjected to energy impact, localizing the zone of dissipation of the microwave field, before the occurrence of a local electric discharge. The energy impact is carried out by an ion beam in a vacuum, a beam of ultraviolet radiation or thermal radiation.

The method is designed for processing a homogeneous, isotropic, continuous material with dielectric properties, which is difficult to apply to anisotropic hard-to-machine layered-fiber composites, materials, such as carbon-fiberglass. Its use does not allow obtaining a high-quality surface in these materials either on the front side of the product or inside the hole. The method is structurally complicated. Accordingly, technologically it is a complex system. It provides only the accuracy and controllability of the process of electroerosive removal of material from the surface of the part.

A known method of processing a composite material having an epoxy resin matrix reinforced with carbon-containing fibers (A.A. Uglov. Status and prospects of laser technology "Physics and Chemistry of Materials Processing", 1992, p. 342-343), according to which it is proposed to use the first, the second and third harmonics of the radiation of a solid-state laser on an yttrium aluminum garnet with neodymium operating in a Q-switched mode. The treatment is carried out under a nitrogen atmosphere. The material being processed is affected by laser radiation with a wavelength of 265, 530, 1060 Nm or a combination of these wavelengths (US patent No. 2002).

The methods are complicated in terms of design and technology. When they are used in the processing of dielectrics with a high fracture temperature and a large difference in fracture temperatures, which are layered sheet products (the same ones having an epoxy polymer as a binder, type VSE-12-1, and as a filler - carbon fiber located in the layers of the composite in the form of a fabric (with a temperature difference of 220-2800 C - respectively), to create through or blind holes in the sheet, they will lead to the appearance of burns on the surface of the product (blank), around the holes, opening the binder layer on the edges of the hole and fluffing the carbon fiber fabric. The methods are difficult to implement for dimensional electroerosive drilling of holes.

A known method of electroerosive cutting with a non-profiled electrode-wire (author's certificate SU No. 709305 A1, IPC V23R 1/08, 01/15/1980), according to which, together with the workpiece, additional technological plates are processed, which are located on both sides of the workpiece. The workpieces are collected in a package, alternating them with technological plates, while using plates from a material with increased erosion machinability relative to the material of the part, i.e. low melting and evaporation temperature.

Despite the fact that this method has a high productivity, due to the processing of workpieces with a package, its use is limited. The method is designed for the processing of metallic materials with limited erosion machinability and is difficult to apply to polymers, and even more difficult to dielectrics in the form of an anisotropic fiber-layer composite, for example, carbon fiber reinforced plastics. In addition, due to the excessively high temperature in the cutting zone caused by the technological plate exceeding the evaporation temperature, it leads to swelling and withdrawal of the binder from the surface of the workpiece.

The closest method of the same purpose to the claimed invention in terms of the combination of features is a method of cutting semiconductor materials or non-conductive materials using electroerosive wire cut processing (Taiwan patent TW103138441A, IPC B23N 7/02, 05.11.2014), which consists in electroerosive wire cutting a sheet non-conductive or weakly conductive workpiece by applying a conductive medium in the form of metal sheets to the upper and lower surface of the workpiece. To create a conductive medium in the cutting zone, under the action of high-current electric discharges, short pulses melt the metal layers and release metal slag. Metal slag adheres to the surface of a weakly conductive or non-conductive workpiece. The cutting process is carried out as a result of the joint melting of metal slag and the surface of a non-conductive workpiece in the interelectrode gap under the action of electric discharges at an instantaneous high temperature. This method is taken as a prototype.

Signs of the prototype, coinciding with the essential features of the proposed method, - a method of electroerosive wire cut processing sheet non-conductive or weakly conductive workpiece; a conductive medium in the form of metal sheets is applied to the upper and lower surfaces of the workpiece.

The known method, taken as a prototype, has the following disadvantages: firstly, it has limited performance due to the simultaneous processing of only one workpiece; secondly, the limitation of the claimed capabilities (the material of the workpiece is a semiconductor, of relatively small thickness), which creates big problems in the electroerosive piercing of dielectrics, layered-fiber composites (for example, carbon fiber reinforced plastics) with anisotropy and containing epoxy resin as a binder.

The objective of the invention is to increase the productivity of processing difficult-to-machine dielectrics such as carbon fiber, as well as to expand the technological capabilities of electroerosive wire cut processing.

The problem was solved due to the fact that in the known method of electroerosive wire cut processing of a non-conductive or weakly conductive sheet workpiece by applying a conductive medium in the form of metal sheets to the upper and lower surface of the workpiece, according to the invention, before processing the workpiece, conductive metal sheets are collected in a package, alternating conductive and non-conductive layers.

The features of the proposed technical solution, which are different from the prototype, before processing the workpiece and conductive metal sheets are assembled into a package, alternating conductive and non-conductive layers.

Distinctive features in combination with the well-known ones will increase the productivity of processing difficult-to-machine dielectrics such as carbon fiber, as well as expand the technological capabilities of electroerosive wire cut processing.

The applicant is not aware of the use in science and technology of the distinctive features of the method of wire EDM cutting to obtain the specified technical result.

The proposed method is illustrated by the drawings shown in Fig. 1-5.

In FIG. 1 shows a scheme for processing packaged blanks by the proposed method.

In FIG. 2 - packaged blanks from a composite with alternating conductive and non-conductive layers.

In FIG. 3 - a package of blanks from a composite with conductive layers superimposed only on two sides.

In FIG. 4 - control sheet of the composite overlaid with conductive layers of metal.

In FIG. 5 shows a table comparing processing parameters and processing speed by the proposed method.

The method is carried out as follows.

As a processing material, sheet blanks 1 made of polymer composite materials, carbon fiber or fiberglass are used - difficult-to-machine dielectrics. To perform the cutting operation, stationary equipment is used: an Electronica Ecocut EDM wire-cutting machine or another that is able to solve the difficult task - by EDM cutting out complex profile contours in sheets of anisotropic layered-fiber material, besides a dielectric. As a tool electrode, wire 2 of the required diameter is used, which is wound during processing. Before processing, plates of polymer composite materials are assembled into a package (Fig. 1), alternating conductive and non-conductive layers. As conductive layers, thin continuous sheets of metal 3 are used, which intensively remove heat from the treated surface (for example, silicon stainless steel, aluminum, etc.), provided that the surfaces fit snugly to each other. EDM wire cut processing is carried out by optimizing the processing modes so that the edges of the product retain their original properties, and the surface after processing is made without felting and fluffing of the fibers.

The method is illustrated by the following example.

The product was processed in the form of a sheet of a hard-to-cut dielectric, which is a layered fibrous material - a VKU-39 composite containing carbon fiber fabric impregnated with epoxy resin (VSE12-1) in layers. To obtain the desired properties, the composite was made with the front and back surfaces of high-quality pouring of a layer of epoxy resin, reliably isolating the carbon fiber from aggressive external influences and fluffing. A brass wire with a diameter of 0.25 mm was used as a tool electrode, which is wound during processing on an Electronica Ecocut wire-cut electroerosive machine. Composite sheets with a thickness of H=4 mm were collected in a package (Fig. 1). On both sides of the package and between the layers of the composite, layers of stainless steel with a thickness of h=0.75 mm were laid. The blank package was fixed on the machine table. The cooling medium (distilled water) was brought to the treatment zone under pressure from the nozzles so that it moved turbulently in the localized part where the treatment takes place directly. The processing was carried out at voltage U=50 V, pulse on time t=21 μs, pulse off time t=60 μs. Processing was carried out in the cross section of the workpieces. The control cut length L, regardless of the thickness of the package, is 20 mm.

To demonstrate the effectiveness of the proposed method, comparative experiments were carried out to evaluate performance. Composite blanks were packaged using three different methods. In the first case, the blanks were assembled into a package according to the proposed method in such a way as to ensure the alternation of conductive and non-conductive layers (Fig. 2). In the second case, conductive layers were applied only on both sides of a package of composite blanks (Fig. 3). In the third, processing of one control sheet of the composite overlaid with conductive metal layers was performed (Fig. 4). All experiments were carried out under identical modes and under the same processing conditions.

The results of experimental processing of blanks by the proposed method are presented in the table (Fig. 5).

The data in the table indicate an increase in the processing speed and, as a result, the productivity of the process in the implementation of the proposed processing method.

Thus, the proposed method, due to batch processing of workpieces with alternating conductive and non-conductive layers, increases the productivity of processing difficult-to-machine dielectrics such as carbon fiber, and also expands the technological capabilities of EDM wire cut processing.

Claims (1)

A method for electroerosive wire cut processing of a sheet non-conductive or low-conductive workpiece when a conductive medium in the form of metal sheets is applied to the upper and lower surfaces of the workpiece, characterized in that before processing the workpiece and conductive metal sheets are collected in a package with alternating conductive and non-conductive layers, while as The material of the conductive layers is stainless steel or aluminum.

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