SU1553296A1 - Method of abrasive grinding - Google Patents

Abstract

The invention relates to the field of mechanical engineering, in particular, to methods for grinding abrasive conducting circles of parts made of structural and tool steels with the initiation of electrical discharges strengthening the surface to be machined. The purpose of the invention is to improve the quality of hardening by increasing the depth and hardness of the hardened surface layer. The pretreated part is subjected to 2-8-fold impact of electrical discharges initiated between the abrasive disc binder 8-16 grains, containing 40-50% of graphite, and the workpiece in air at a gap excluding the mechanical contact of the grains with the surface being treated, with the amplitude voltage of the discharge is 140 ... 280 V, the amplitude of the current is 56 ... 112 A and the duration of the discharge is 10 ... 20 ms, after which the final grinding is carried out before removing the traces of erosion and obtaining the required size. 7 tab.

Description

The invention relates to mechanical engineering, in particular, to abrasive conductive grinding methods for grinding parts of structural and tool steels with the initiation of electrical discharges strengthening the surface to be machined.

The purpose of the invention is to improve the quality of hardening by increasing the depth and hardness of the hardened surface layer.

The proposed method is carried out as follows.

The pre-grinded part without a circle is subjected to a 2-8-fold electric spark treatment with the discharge initiated between the abrasive wheel bind with a grain size of 8-16, containing 40-50% of graphite, and the workpiece in an air gap at the gap excluding the mechanical contact of the abrasive grains with the treated surface to remove the surface layer with a depth equal to 2-8 depths of holes from the impact of a single discharge, with an amplitude value of the discharge voltage of 140-280 V, the amplitude of the discharge current of 56-112 A and the duration of the discharge Yes 10 - 20 ms.

When processing the part, the following sequence of operations should be observed: pre-grinding; surface bombardment with spark discharges initiated between the conductor wheel bind and the workpiece; final grinding to remove traces of erosion.

All three processing steps are carried out, on the same machine, without re-installing the part.

Providing the necessary multiplicity of spark exposure is carried out, based on the experimental formula

5pa6 5max -, (2-8) A ,, (1)

where spae is the working electrode gap

um;

Svakc - maximum penetrative clearance, µm;

SP

ate

with you

SE

/ hl - depth of the hole;

(2-8) - the multiplicity of spark exposure (number of passes) is necessary.

In a single pass, the thickness of the layer removed by the electrospark effect is approximately equal to the depth of a single well / gA.

In order to provide the necessary multiplicity of action by the discharges of the surface of the circle link, at the initial moment of time it is necessary to install the gap 5rab from the surface of the parts. When the number of passes of the electrospark effect (multiplicity) reaches its specified value (2-8 bits), the thickness of the removed layer will be equal to (2-8) / gL, respectively, and the interelectrode gap reaches its maximum penetration value of 5 "ax, at which the spark the impact stops automatically.

In tab. Figure 1 shows the average values of the maximum penetration gap and the depth of the well corresponding to the specified electrical conditions.

Represent the values of 5max, or zero in the formula given, by calculating the size of the working gap to obtain the necessary degree of spark action.

The surface treatment of the discharges is carried out under certain electrical conditions. The proposed amplitude values of the current strength, voltage, and duration of the discharges cause intense heat generation followed by hardening of the surface layer. The intensification of the electrical parameters of these values leads to an increase in the energy of the pulse, and with heme to an increase in the depth of the hardened layer, but with increasing energy, the hardness of the hardened layer decreases as a result of erosion and partial tempering. Reducing the values of the electrical modes reduces the intensity of heat generation, which leads to a significant reduction in the depth of thermal exposure.

In tab. Figure 2 shows the averaged values of the microhardness and depth of the hardened layer, depending on the electrical conditions.

As can be seen from the table. 2, an increase in the current and voltage parameters has an ambiguous effect on the hardening efficiency, namely, the depth of the hardened layer increases, and the microhardness decreases.

Similar dependences can be traced as the pulse duration changes.

In tab. Figure 3 shows the microhardness and depth of the hardened layer, depending on the duration of the impact of the discharge.

Exodus from table. 3 it can be concluded that in order to obtain a strengthened layer with optimal microhardness and depth, the treatment must be carried out in a given range of electrical parameters, i.e., U, 140-280V; 4 56-112 A; 20 ms

The magnitude of the spark effect has a significant effect on the microhardness and depth of the hardened layer.

In tab. Figure 4 shows the microhardness and depth of the hardened layer, depending on the magnitude of the effect of the discharge.

A range of 2-8 is selected from the table. 4, since with an increase in the multiplicity of the spark effect above 8, a significant decrease in the microhardness occurs, and the depth of the hardened layer remains almost unchanged.

The process of abrasive-electric spark grinding grinding should be carried out at the specified electrical parameters and multiplicity combined with conductive abrasive wheels with a grain size of 8-16, containing as a filler 40-50% carbon

An increase in the grain size of the circle above the recommended values leads to the removal of a part of the hardened layer, and a decrease in the grain size leads to a decrease in its grinding ability.

° Table 5 shows the relationship between the grain of the abrasive wheel and the working layer of the circle

As a result of the analysis of experimental data, it was established that the magnitude of the working

The layer of grinding wheel А «аКС (tab. 5), located between the outer surface of the wheel and the surface of the bundle, must be less than the size of the working interelectrode gap between the coupling of the current-conducting abrasive disc and the surface of the workpiece (Table 1)

Otherwise, the working layer of the grinding wheel comes into contact with the surface to be treated and removes part of the hardened layer (Table 6).

The change in the percentage of carbon in the abrasive wheel below or above the recommended values is also impractical, since in the first case the reduction of the conductivity of the wheel and a significant deterioration in the hardening effect, and

5 in the second case, a decrease in the concentration of abrasive grains, a deterioration in the cutting ability of the grinding wheel and a decrease in its durability.

In tab. Figure 7 shows the effect of the percentage of carbon on the micro hardness and depth of the hardened layer.

When grinding by the proposed method, hardening occurs due to the simultaneous flow of three processes: nitriding of the surface layer of the product due to dissociation of atmospheric nitrogen in the discharge of electric current and its connection with elements of the surface layer, cementation due to polar transfer of carbon present in the current graphitized circle in given proportions (40-50%), and high-speed quenching.

Claims (1)

formula of invention The method of abrasive grinding of parts from structural and tool steels with a conductive wheel with the initiation of electrical discharges for hardening the surface to be machined, characterized in that, in order to improve the quality of hardening by increasing the depth and hardness of the hardened surface layer, an abrasive wheel with grain size 8- is used for processing. 16, on a soft bond containing 40–50% carbon, and before the final grinding, the surface to be treated is treated with discharges in air at to prevent contact of the abrasive grains with the surface to be treated before removing a layer of depth 2-8 depths of the well from a single discharge, with an amplitude value of discharge voltage 140-280 V, discharge current amplitude 56-116 A and duration of discharge 10- 20 ms eight 45 28 42 56 70 84 98 112 126 140 28 42 56 70 84 98 112 126 140 70 105 140 175 210 250 280 315 350 70 105 140 175 210 250 280 315 350 Table 1 table 2 0.081 0.090 0.145 0.168 0.194 0.250 0.280 0.310 0.315 0.071 0.084 0.134 0.157 0.192 0.234 0.284 0.295 0.300 50 63 80 100 125 160 200 250 315 Table 3 Table 4 Table 5 ten 21 26,6 33.3 41.6 53.3 66.6 83.3 105 St45 70 175 Table 6 Table 7 721 732 809 936 941 948 0.081 0.114 0.148 0.157 0.158 0.158