RU1780951C - Method for simultaneous electro-erosion machining of conjugated parts - Google Patents

Abstract

Usage: simultaneous electrical discharge cutting with a wire electrode-tool of mutually interfacing parts. SUMMARY OF THE INVENTION: the processing is carried out in two passes, moving the electrode-tool in the second pass along the same path as in the first pass. The diameter of the tool electrode for the second pass is selected from co {di + Ј) il-Z2 (zi ratios S2 - Z2) +2 (Rmaxi-Rmax2) where di and J2 are the diameters of the wire tool electrode used for the first and second passes respectively mm; zi and rh are the predefined values of the interelectrode gaps in the first and second passes, respectively, for these processing modes, mm; si and S2 are predefined values of productivity by area on the first and second passes, respectively, for these processing modes, CM2 / MIN; Rmaxl and Rmax2 are predetermined heights of microroughnesses in the cut surface after the first and second passes, respectively, for these processing conditions, / mm /. 4 ill., 1 tab. to C

Description

The invention relates to mechanical engineering technology, in particular to electrical discharge machining of complex-profile parts with a non-profiled wire electrode on cutting machines.

Known methods for electrical discharge machining, including electrical discharge cutting in one pass at the same time two mutually mating parts. A common disadvantage of these methods is the insufficiently high quality of the machined surfaces, since cutting is performed, as a rule, in rough modes, cutting in finishing modes is so laborious that it is practically not used.

The closest in technical essence and the achieved positive effect to this method is the method consisting in making a jumper holding the cut part of the workpiece, and repeated passes are carried out by moving the electrode-wire in the specified groove. However, for the vast majority of materials, the interelectrode gap during cutting in finishing conditions is less than in rough ones. Therefore, the completion of finishing passes along the same path along which the rough pass was made, without increasing the diameter of the wire electrode, leads to the fact that the movement of the electrode wire along the groove in the finishing pass is practically without discharges, or with

about

s

the action of the bits is only local. This means that the surface roughness after processing by the specified method is not reduced as much as the technological modes allow, and for a number of materials it remains almost at the level of the rough pass, i.e. the quality of the processed surfaces is low.

The execution of subsequent passes along an equidistant trajectory with simultaneous electroerosive cutting of two interconnected parts leads to a doubling of the number of subsequent passes (slotted groove machines are processed sequentially first one and then the other) and causes an increase in the total complexity of cutting and. accordingly, its low productivity, on the one hand, and, on the other hand, leads either to unilateral impact of discharges or to the unbalance of their force impact on the electrode-wire, because different sizes of allowance will be removed from different sides of the cut. And this contributes to the spin. the wire electrode from the machined surface with a large allowance causes vibration of the wire electrode, which ultimately leads to a decrease in accuracy and deterioration in the quality of the treated surfaces.

The aim of the invention is to improve the quality of the machined surfaces during EDM cutting of two interconnected parts at the same time and to increase the cutting performance when the desired quality is achieved.

This goal is achieved in that in a method of electrical discharge machining, including two-pass electrical discharge machining at the same time two mutually interconnected parts from one workpiece, the cutting is carried out by moving the electrode-wire at each pass along the same path, and the second, finishing pass is performed by the electrode- wire diameter d2 satisfying the relation

(Ch + 21) S1 (zi.Z2) + S2

+2 (Rmaxi-Rmax2);

where di is the diameter of the electrode wire used in the first (rough) transition;

zi and Z2 are the interelectrode gaps in the first and second passes, respectively;

si and S2 are the productivity of EDM cutting the area on the first and second passes, respectively;

Rmaxl and Rmax2 are HIGHER THAN MICRO-Roughnesses of the surface after the first and second passes, respectively. The invention is illustrated in FIG. 1-4.

The circuitry of FIG. 1, 2 illustrate the nature of the force acting on the electrode wire 1 when performing the second pass of EDM cutting of part 2 along an equidistant path with respect to

to the path of the first pass (Fig. 1) and along the same path as the path of the first pass (Fig. 2). Surface quality during EDM cutting along with electric modes is significant

the degree is determined by the magnitude of the vibrations of the electrode wire in the p plane, perpendicular to the direction of processing. The magnitude of these oscillations, in turn, depends on the degree of equilibrium of the force effects of some discharges to the left and to the right of the wire electrode. If the effect of spark discharges is represented as the distributed load q acting on the sector

of the electrode-wire, limited by the angle a, the force acting on the electrode-wire on one side of the cut is proportional to q and a,. When performing the second pass along an equidistant path,

offset by the value of S relative to the path of the first pass, the allowance removed from the workpiece 1 from the left and right will differ by 2S (Fig. 1). For example, a shift to the right of the path of the electrode-wire 1 in the second pass will increase the allowance removed on this aisle, on the right,

Those. And right. Alev.

The force acting on the electrode wire on the right will be proportional to an, and the forces acting on the left will be proportional to op, but since if an and ap are determined by the values of the allowances Ll and Al, it follows from Dn Al that On Zn. And that means the force acting

on the electrode wire on the right, there will be more force acting on the left, which leads to an imbalance of the force effects on the electrode wire, causing it to be pressed to the left and causing oscillations of the electrode wire in the plane P. If the second pass is performed along the same path, then the values of the allowances removed on the right and on the left are equal (Al Al), and therefore On «l (Fig.

2), which leads to a balance of power effects on both sides of the wire electrode and thereby improves the quality of the treated surfaces. Thus, the implementation of the second pass along the same path as the first allows to improve the quality of surfaces after EDM cutting by eliminating the imbalance of force effects on the electrode-wire in the plane,

perpendicular to the cutting direction.

In FIG. 3,4 presents conditional patterns of forming microroughnesses on the surface of the workpiece 1 during the second pass by the electrode-wire 2. As is known, the electric mode of electroerosive cutting quite unambiguously determines the interelectrode gap Z, as well as the smallest microroughness of the surface Rmax, which can be achieved on this electric mode. However, the use of certain electrical modes in the second EDM cutting process alone does not guarantee that the surface roughness obtained as a result of it will have the smallest possible roughness height Rmax2 for these electrical modes. To explain this position, we consider two possible cases of the formation of surface irregularities during the second pass. Let the first pass be carried out by an electrode-wire 3 of diameter di in electric modes characterized by an interelectrode gap ZL. The height of the surface roughness was Rmaxi, and the width of the groove B along the lines of microroughness a-a and a - a - EY. As can be seen from FIG. 3.4

Bi di + 2Zv + 2Rmax1

When performing the second pass further with the electrode-wire 2 of diameter d2 in electrical modes providing an interelectrode gap of 2 g, the process of forming surface irregularities can proceed in two ways. In the first case, the lines of cavities b-c and b-c formed in the second pass of the micro-irregularities will lie closer to the groove axis by a certain amount of h than the lines of the basins a-a and a-a of the micro-irregularities formed in the first pass (Fig. 3). Then the microrelief of the surface formed after the first pass will be a combination of the microroughnesses Rmax2 formed by the spark discharges of the second pass and the remnants of the microroughness troughs formed on the first pass. In this case, the total height of the microroughnesses of the second pass

Will make R max2 Rmax2 + h. OTHER Case

the lines of cavities in-in and in-in, formed on the second pass of microroughnesses will either coincide with the lines of cavities aa-a and aa of microroughnesses after the first pass, or will be shifted relative to aa and aa by a certain amount in the body details 1 (Fig. 4). In this case, the heredity of the roughness obtained after the first pass will be eliminated, the microroughness will be completely formed by the bits of the second PASS, and their height will be Rmax 2 As can be seen from the diagrams of FIG. 3, 4 for the first case, there is a relation, while the second case is characterized by the relation

B2 W, (1),

where B2 is the width of the slot to be cut along the lines of the in-in and microroughness after the second pass.

Taking into account that B2 d2 + 2Z2 + 2Rmax2, we can write relation (1) in the form

d2 + 2Z2 + 2Rmax2 dl + 2Zl + 2Rmax1

Hence, we determine that, in order to ensure that, after the second pass, the surface microroughness height is the smallest Rmax2 that can be achieved in the electric modes of the second pass, it is necessary to perform the second pass with a wire electrode whose diameter satisfies the relation

d2 dl + 2 (Zi-Z2) +2 (Rmax1-Rmax2) (2)

Since the second pass is the last, the failure of relation (2) leads to a deterioration in the quality of the surfaces after EDM cutting.

An increase in the performance of EDM cutting during the second pass will be achieved if the execution time of the first t and second pass t2 is no more than the time t-time of the EDM cutting in one pass at the finish pass modes, i.e. at ti + t2 t (3) From this condition we determine the boundary value of the diameter of the electrode-wire for the second pass, at which equality of performance is achieved.

The time of the first pass is determined as follows:

 - (4)

 -Ј

where I is the length of the cut contour,

vi is the linear cutting speed in the first pass.

Volumetric productivity of the first pass, performed by an electrode-wire with a diameter di on technological

modes characterized by the gap di

Vi (dt + Zi) -h + vi (5)

where h is the height of the cut part.

From here

v - VI v (di + Zi) -h

Using formulas similar to (4) and (5), the time t and the linear velocity V are determined when cutting the mating parts in one pass at the finishing (second) pass modes

(6) V2

1 7

V

(7)

(d2 + 2.2} h where Va is the volumetric cutting performance at the finish pass modes;

d2 is the diameter of the electrode wire used on the finishing pass;

7.2 - interelectrode clearance of the fair passage

To simplify the subsequent transformations, we introduce the notation

Ai di + Zi (8)

A2 d2 + Z2 (9)

The physical meaning of AI and A2 is the width of cuts obtained in the first and second passes, made respectively by wire electrodes of diameters di and d2.

Taking into account that the size of the allowance removed on the second pass when cutting in this way (in two passes) is determined as Ai-A2, the linear cutting speed on the second pass will be

"-Fr-A,).

Transforming the boundary expression ti + t2 t (11) of condition (3), taking into account the introduced notation and relations (4-10), we obtain I- Ai -h, I (Aa-AiV h l -A2 h

Vi

, (A2-AiVh -

V2

V2

(12)

We make the necessary transformations

I At h V2 -I (A2-AQ h Vi

Vi -V2 HA2 h

I -h - (Al V2 + (A2-Ai) -Vi-A2Vi)

Vi V2 U

Given that I &0; h 0, we obtain AiV2 + A2Vi-AiVi-A2V2 0 or AiV2-AiVi 0 (13)

those. boundary condition (11) is fulfilled only if the volumetric capacities are equal, and for all (14) the producer will increase

5

0

5

0

5

0

5

0

5

nosti. Applying transformation (5), we obtain inequality (14) in the form (di + Zi) -h-vi (d2 + Z2) - h- V2 Bearing in mind that the products h (15)

h (16)

there are generally accepted when electroerosive cutting performance by area, we get

(di + Zi) -Si (d2 + Z2) -82

d2 Ј L ± | l i-Z2 (17)

and there is that range of values of the diameter of the electrode wire used in the second pass, which provides an increase in cutting performance when it is performed according to this method.

Combining inequalities (2) and (17) into a single double inequality

() Sl-Z2 d2 di-f2 (Zi-Z2) + +2 (Rmax1-Rmax2) (18)

and determines the range of diameters of the wire electrode in which when cutting in two passes by the proposed method, both an improvement in the quality of cutting of two mating parts and an increase in the productivity of their cutting will be achieved.

Example. Comparative electroerosive processing of tool electrodes was carried out for subsequent electroerosive stitching of mold parts for pressing metal powders. Tool electrode material was copper M1 GOST 859-78, height 16 mm. The processing was performed in two passes on an EDM cutting machine model 4732FZ with a pulse generator GKI 300-200A. The electrical modes of the passages and the corresponding technological characteristics are given in table. 1.

According to this method, the first one was made with a wire electrode with a diameter of 0.2 mm, and the diameter of the electrode wire for performing the second pass was determined from the relation (18)

(0.2-f-0.065)., 0; 2, + 2 (0.065 - 0.036) + 2 (0.023 - 0.008) 0.525 d2 0.288

The diameter of the electrode wire for making the second pass was taken to be 0.3 mm.

After processing the filed method, the surface roughness Ra was 1.4 ... 1.6; the surfaces were smooth (no marks) and uniform in height. The processing time amounted to a total of 10.5.

Cutting by a known method was carried out in two ways. In the first version, both passes were made along the same trajectory by the electrode-wire of the same diameter (0.2 mm). In this case, the second pass was characterized only by a rare local passage of discharges, and the surface roughness was Ra 4.5 μm in the upper part, Ra 3.4 μm in the lower part, which can be explained by the smaller cut width after the first pass in the lower part due to wear electrode and more frequent passage of discharges in the lower part during the second pass.

In the second embodiment, the finishing pass is carried out first along one wall of the cut, and then along the other with a correction of 0.045 mm to each side. The total labor intensity in this case was 13.5 hours, and the surface roughness was Ra 1.7 ... 1.9 μm, and in some areas the surface is viscous, resulting in the repulsion of the electrode wire and its vibrations under the action of spark discharges.

As can be seen from the foregoing, this method of electric discharge machining allows to improve the quality of the machined surfaces of two mating parts at the same time when electrically cutting from one workpiece, which is manifested in a decrease in the surface roughness by 1.8 ... 3.0 times in comparison with the known way. In addition, it allows you to increase the productivity of EDM cutting by reducing by 1.5 ... 2 times the execution time of the second pass while simultaneously treating the surfaces of both mating parts resulting from the implementation of this method.

Claims (1)

The formula is invented and, A method for simultaneous electrical discharge machining of interconnected parts by a wire electrode-tool, in which the processing is carried out in two passes, the electrode-tool being moved along the same path as in the first pass, characterized in that the second one; that, in order to improve the quality and productivity of processing, the second pass is carried out by an electrode-tool, the diameter of which is selected from the ratio (di + zi) si (zi-z2) + S2 +2 (Rmax1-Rmax2) where di and dz are the diameters of the wire electrode tool used for the first and second passes, respectively, mm; zi and Z2 are the predefined values of the interelectrode gaps in the first and second passes, respectively, for these processing modes, mm; si and S2 are predefined values of productivity by area on the first and second passes, respectively, for these processing modes, cm / min;  Rmaxi and Rmax2 — preliminary determination of the heights of microroughnesses of the cut surface after the first and second passes, respectively, for these processing conditions, mm. Electrical modes and technological characteristics of EDM cutting FIG. g Fig.Z Fts & 4