UA134189U - METHOD OF PLASMA-MECHANICAL PROCESSING - Google Patents

Abstract

The method of plasma-mechanical processing involves heating without melting the plasma arc of the cutting surface of the workpiece with a given current, moving the arc along the cutting surface. The heating is performed by an arc directed front to the cutting surface and oscillating relative to its average position with the frequency of the external alternating magnetic field across the velocity vector, with an amplitude equal to the width of the cutting surface. The cutting speed value is: EMBED Equation.3, where EMBED Equation.3 is the cutting speed, m / min; EMBED Equation.3, EMBED Equation.3 - current and voltage of the plasma arc; EMBED Equation.3 - thermal efficiency of plasma arc; EMBED Equation.3 - maximum allowable heating temperature (EMBED Equation.3); EMBED Equation.3, EMBED Equation.3 - width and length of heating spot on cutting surface, mm; EMBED Equation.3 - coefficient of thermal conductivity, W / cm EMBED Equation.3 ° C; EMBED Equation.3 - coefficient of thermal conductivity cm2 / s.

Description

The useful model belongs to mechanical engineering, namely to mechanical processing, including the field of machining electrically conductive materials with allowance heating, and can be used in the processing of cast and forged ingots and billets with a hard foundry crust or from difficult-to-machine alloys.

The well-known "Method of mechanical treatment with heating" of the cutting zone with a plasma arc, which includes applying a chip-separating groove to the cutting surface under the influence of plasmatron current pulses (AS 5) 860936, publ. 09/07/81, bulletin Mo 33).

The above-mentioned method has a number of disadvantages. Thus, the metal melted by the pulse of the plasmatron in the chip formation zone is not removed from it in all cases, which worsens the chip formation process. In addition, in order to prevent crystallization (packaging) of the molten metal in the area of the chip-separating groove, the cutter must be placed in the immediate vicinity of the heating spot (2-5 cm), which leads to overheating of the carbide tool, its increased wear, and a general decrease in the technological capabilities of this method .

The closest in technical essence, chosen as an analogue, is the "Method of mechanical processing with heating of the cutting zone by a plasma arc" (AS ZO 872035, publ. 15.10.81, bulletin Mo 38), which includes the application of chip-splitting grooves on the cutting surface under the influence of pulses plasmatron current and removal of the heated allowance with a cutter.

Heating is carried out by a compressed electric arc, which is oscillated by an external alternating magnetic field, and, in order to increase the efficiency of the cutting process, part of the allowance is melted by a plasma arc and the molten metal is removed from the cutting zone by increased consumption of plasma-forming gas.

Disadvantages of the method are: low quality of the finished surface, because additional finishing mechanical processing is required; increased power consumption because all the metal being removed must be heated to the melting point. In addition, the melting of the workpiece material leads to the formation of harmful aerosols from metal oxides in the atmosphere of the production premises, which is limited by sanitary standards. There are also a number of hard-to-machine materials, for example, titanium alloys, in the surface layer of which, when heated with melting according to an analog scheme, a defective layer is formed in the form of a 9-modification of titanium with a very low machinability coefficient, which reduces technological

From the possibility of the method.

The basis of the useful model is the task of improving the method of plasma-mechanical processing of workpieces from difficult-to-process materials, due to pre-heating, without reflow, allowance for processing with a scanning plasma arc, which allows to realize the maximum efficiency of heating, increase the machinability of the workpiece material, as a result of which the period of stability of the tool is increased .

The technical result from the use of the proposed useful model of plasma-mechanical processing of cast and forged ingots and billets with a hard casting crust or from difficult-to-machine alloys provides an improvement in their machinability by creating an austenite structure that has significantly lower physical - mechanical properties, than the starting material of the workpiece. As a result, the period of stability of the cutting tool also increases.

The task is solved by the fact that the method of plasma-mechanical processing includes heating without plasma arc melting of the cutting surface of the processed part with a given current strength, moving the arc along the cutting surface. Heating is carried out by an arc directed frontally to the cutting surface and oscillating, relative to its average position, with the frequency of an external variable magnetic field across the cutting speed vector, with an amplitude equal to the width of the cutting surface. The value of the cutting speed is equal to:

IhOh p Y o x Vp

Mr -0--- 52 ;fЖ- - - - - | x--

Otah x p x ad x X x

Ii; where - cutting speed, m/min;

I, O - current and plasma arc voltage; 7 - thermal efficiency of the plasma arc;

Otakh - the maximum temperature of heating the allowance (Utakh 2 Oplavl);

would app. width and length of the heating spot on the cutting surface, mm;

X is the coefficient of thermal conductivity, W/cm. "WITH;

Ф - coefficient of thermal conductivity, cm/s.

The claimed utility model is explained by a diagram showing the location of the heating source and the heating zone relative to the workpiece.

A direct action plasmatron 1 was chosen as the source of the plasma arc C. The plasmatron is equipped with a magnetic deflection system 2, which consists of two cooled magnetic conductors, the ends of which are located near the plasmatron nozzle and are perpendicular to the cutting speed vector.

The magnetic deflection system is connected to a regulated AC power supply.

The method is implemented as follows. The workpiece is installed on a lathe, on which a plasma generator in the form of a single-arc direct current plasmatron is mounted.

The plasma-forming gas is air. According to the location of the plasma arc Z in relation to the arc channel, as well as the impact of the arc on the processed material, it belongs to direct action plasmatrons.

The locality of plasma arc heating is reduced by applying an external variable magnetic field to the generated plasma flow. To create an external variable magnetic field, the serially produced air cutting plasmatron 1 (PVR-401) is equipped with a special magnetic system. The plasmotron generates an electric arc that burns between the cathode of the plasmotron and the cutting surface on the workpiece, and at the point of contact, it realizes thermal power through the reference spot of contact with the dimensions ap and Br. In addition, in the gap between the ends of the magnetic conductor 2, the arc C is affected by the magnetic field. And since the electric arc is a current-carrying conductor, the Lorentz force acts on it in the magnetic field, which deflects the arc in a plane parallel to the ends of the magnetic conductor 2 and perpendicular to the cutting speed vector during turning of the workpiece. Thus, by changing the voltage on the coils of the magnetic system, it is possible to change the magnitude of the Lorentz force and, as a result, the magnitude of the deflection of the plasma arc in the magnetic field changes. As a result, when scanning the plasma arc with the current frequency in the network (50 Hz), the heating spot increases in size, the locality of heating decreases, which allows heating the workpiece without melting its surface and ensures the stability of the parameters of the plasma-mechanical processing process.

When implementing this method for processing workpieces made of alloy steels, heat-resistant and corrosion-resistant titanium alloys, the heating spot is stretched across the entire width of the cutting surface and along the cutting speed vector, and the arc is directed frontally to the cutting surface at an angle of 90. The orientation of the plasma arc frontally at a given angle allows to ensure the largest heat investment in the workpiece material, since a smaller value of the angle leads to an increase in the reflection of the heat flow into the air and a decrease in the heating efficiency below 4095, which reduces the efficiency of the process. At the same time, the arc scan amplitude (ap) is set equal to the width of the cutting plane. A smaller value of the plasma arc scan amplitude is set for workpiece materials with a higher value of the thermal conductivity coefficient (alloy steels), and a smaller value - for workpieces with a lower value of the thermal conductivity coefficient (titanium alloys) in order to avoid defects on the machined surface.

Experimental results make it possible to consider a conventional heating spot as a linear, uniformly distributed, fast-moving heat source during processing with heating by a plasma arc that scans cast and forged ingots and billets with a hard cast crust or hard-to-machine alloys. As a result of the analysis of the obtained experimental studies, we write down the formula for determining the speed of movement of the plasma arc relative to the workpiece, equal to the cutting speed (P): 2

IhOh p F x Va «uni tt

Otah x ba x aa x X x u de R - cutting speed, m/min;

And, MO. current strength and plasma arc voltage; 7 - thermal efficiency of the plasma arc;

Otakh - the maximum temperature of heating the allowance (Utakh 2 Oplavl);

would app. width and length of the heating spot on the cutting surface, mm;

X is the coefficient of thermal conductivity, W/cm. "WITH;

Ф - coefficient of thermal conductivity, cm/s.

As a result, an area of thermally weakened metal appears on the processed surface of the workpiece, which allows to increase the productivity of mechanical processing with the cutter while ensuring the stability of the parameters of the plasma heating process due to the absence of melting of the surface of the workpiece, reducing the degree of overheating of the cutter and, as a result, increasing its stability period.

The use of a useful model, which is claimed, ensures an increase in the productivity of processing blanks from difficult-to-process materials used in shipbuilding, power engineering.

Claims (1)

USEFUL MODEL FORMULA A method of plasma-mechanical processing, which includes heating without plasma arc melting of the cutting surface of the processed part with a given current strength, moving the arc along the cutting surface, which is characterized by the fact that the heating is carried out by an arc directed frontally to the cutting surface and oscillating with respect to its of the average position with the frequency of the external variable magnetic field across the cutting speed vector, with an amplitude equal to the cutting width, while the value of the cutting speed is equal to: x M higher where - cutting speed, m/min; Yi, Oh. current strength and plasma arc voltage; 7. thermal efficiency of the plasma arc; - k Otakh - the maximum heating temperature of the allowance (Utakh 2 Oplavl); Would; app. width and length of the heating spot on the cutting surface, mm; X is the coefficient of thermal conductivity, W/cm. "C; e - coefficient of thermal conductivity, cm/s.