CN112388079B

CN112388079B - Composite pulse working method of wire cut electrical discharge machining pulse power supply

Info

Publication number: CN112388079B
Application number: CN202011301393.1A
Authority: CN
Inventors: 刘庆丰; 冷朝霞; 李瑞康
Original assignee: Xian University of Technology
Current assignee: Xian University of Technology
Priority date: 2020-11-19
Filing date: 2020-11-19
Publication date: 2022-08-05
Anticipated expiration: 2040-11-19
Also published as: CN112388079A

Abstract

Composite pulse work of electrospark wire-electrode cutting pulse power supplyThe method comprises the following steps: step 1, a wire cut electrical discharge machining pulse power supply is sequentially conducted by using a plurality of switching tubes to realize the output of composite pulses, and the process of machining gap electrical discharge machining at one time is completed; step 2, in the generation process of the composite pulse in one period, each switching tube is triggered and conducted once, the pulse width of a triggering signal of the switching tube which is conducted first is longest, the breakdown of a processing gap is realized during the conduction period, and a discharge channel is established; and 3, after the spark discharge is started in the machining gap, conducting the rest switch tubes in sequence, wherein the pulse width of the trigger signal of each rest switch tube is narrow, the pulse intervals between the trigger signals of two adjacent switch tubes are the same, and the interval time is t _d The pulse power supply outputs a composite pulse containing a series of narrow pulses at the machining gap; the gap machining control process is simplified, and the energy utilization rate and the machining quality of the pulse power supply are improved.

Description

Composite pulse working method of wire cut electrical discharge machining pulse power supply

Technical Field

The invention belongs to the technical field of power electronics, and particularly relates to a composite pulse working method of a wire cut electrical discharge machining pulse power supply.

Background

The gap state of wire cut electrical discharge machining is mainly divided into three states of open circuit, spark discharge and short circuit. In order to ensure normal spark discharge, a proper gap needs to be kept between the electrode and the workpiece, and only the machining gap is moderate, namely when the feeding speed and the erosion speed of the machine tool are equal, the probability of generating spark discharge is increased, the erosion speed of the material is increased, and the energy utilization rate is improved. If the processing gap is too large, the material is not easy to break down and is in an open circuit state, and the material is not corroded and removed. If the machining gap is too small, the workpiece is easy to be in a short circuit state, and the phenomenon of wire electrode burning is easy to occur due to long-time short circuit, so that the machining efficiency and the surface quality are influenced; in addition, in the short-circuit state, the short-circuit current of the processing gap is very high, but the workpiece material is not corroded, so that the energy is wasted.

Therefore, at present, the improvement of the energy utilization rate of wire electric discharge machining is mostly realized by judging the machining gap state through a machining gap detection method, then controlling the feeding speed of a machine tool, and reducing the occurrence of a short-circuit state, or controlling the reverse retraction of the machine tool, and reducing the duration of a short circuit.

For the resistance type pulse power supply, fixed threshold discharge state detection is adopted. The method comprises the steps that a voltage threshold value is set, machining gap voltage is periodically sampled, if the average machining gap voltage is lower than the set threshold value, the current machining gap or pulse width is considered to be not appropriate, the occurrence frequency of a short-circuit state is large, and the occurrence of a short-circuit condition is reduced by reducing the feeding speed of a machine tool or changing the pulse width of a pulse power supply; the inductance type pulse power supply replaces a current-limiting resistor with inductance, and the common machining gap detection method is to directly count the pulses output by the discharge state judging circuit and calculate the open-circuit rate, the spark rate and the short-circuit rate within the counting time. The open circuit rate is large, which indicates that the machining gap state tends to open circuit and the feeding speed needs to be increased. The short-circuit rate is high, which indicates that the machining gap tends to be short-circuited, and the feeding speed needs to be reduced or even reversed. However, the simple method for calculating the relative time utilization rate of each state according to the number of the signals has large error and low discrimination precision, so that the feeding of the machine tool cannot be accurately controlled, and the energy utilization rate is improved.

In addition, after detecting the short-circuit state of the machining gap, the wire cut electric discharge machine waits for a period of time and then controls the machine to retreat to eliminate the short-circuit state; when the short-circuit state is not detected, the feeding is performed rapidly or normally according to the discharge state. The quality of the processed surface is affected by the forward and backward movement of the machine tool, and the processing system transmits commands such as detection/movement/feedback, so that the waiting time is long, and the cutting efficiency is reduced.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a composite pulse working method of a wire cut electrical discharge machining pulse power supply, which solves the problems that detection errors exist in the process of forward and backward control of a machine tool by means of machining gap short-circuit state detection, and the energy utilization rate and the machining quality of the pulse power supply are reduced by adopting machine tool backward operation to eliminate the machining gap short-circuit state.

In order to achieve the purpose, the invention adopts the technical scheme that: the composite pulse working method of the wire cut electric discharge machine pulse power supply comprises the following steps:

step 1, a wire cut electrical discharge machining pulse power supply is sequentially conducted by using a plurality of switching tubes to realize the output of composite pulses, and the process of machining gap electrical discharge machining at one time is completed;

step 2, in the generation process of the composite pulse in one period, each switching tube is triggered and conducted once, the pulse width of a triggering signal of the switching tube which is conducted first is longest, the breakdown of a processing gap is realized during the conduction period, and a discharge channel is established;

and 3, after the spark discharge is started in the machining gap, conducting the rest switch tubes in sequence, wherein the pulse width of the trigger signal of each rest switch tube is narrow, the pulse intervals between the trigger signals of two adjacent switch tubes are the same, and the interval time is t _d The pulse power supply outputs a composite pulse comprising a series of narrow pulses at the machining gap.

Said interval time t _d The machining gap current is set to be short time to meet the requirement that the machining gap current is continuous, and the machining gap discharging process is ensured to be continued all the time. Even if the short-circuit state occurs in the machining gap during the conduction period of the switching tube, the pulse width of the switching tube trigger signal is narrow in the gap discharge process, the conduction time is shortened, the duration time of the short-circuit state of the machining gap is greatly shortened, and the machine tool does not need to retreat to exit the short-circuit state.

The invention has the beneficial effects that:

a composite pulse working method of a wire cut electrical discharge machining pulse power supply is characterized in that a series of narrow pulses among short pulses are output, forward and backward control of a machine tool is not required to be carried out according to detection of a short circuit state of a machining gap, inaccurate control of the machine tool caused by detection errors of the machining gap is avoided, the short circuit state is eliminated without controlling the backward operation of the machine tool, the gap machining control process is simplified, and the energy utilization rate and the machining quality of the pulse power supply are improved.

The energy-saving working method adopted by the invention avoids the machine tool rollback operation required for eliminating the short-circuit state, thereby achieving the purpose of improving the energy utilization rate and the processing quality of the pulse power supply.

Drawings

FIG. 1 is a schematic diagram of a main circuit of a pulse power supply according to the present invention.

FIG. 2 is a diagram of the composite pulse and gap voltage current waveforms of the present invention.

Detailed Description

The invention is described in detail below with reference to the drawings and the detailed description.

The composite pulse working method of the wire cut electric discharge machine pulse power supply comprises the following steps:

step 2, in the process of generating a periodic composite pulse, each switching tube in the pulse power supply main circuit diagram 1 is triggered to be turned on once, and first, a first switching tube G is triggered to be turned on ₁ Switch tube G ₁ Has the longest pulse width of trigger pulse in the switch tube G ₁ After the trigger pulse of (3) is over, interval t _d Time, sequentially triggering to turn on other switch tubes G in the main circuit diagram 1 ₂ ～G _n (n is more than or equal to 2), the pulse width of the trigger pulse of each switching tube is narrow, and after the trigger pulse of the previous switching tube is finished, the interval t is _d The narrow pulse width of the next switching tube is sent to trigger the pulse, so that the output end of the main circuit of the pulse power supply can provide composite pulse output shown in figure 2 for the machining gap, and the first pulse width is the largest to realize the breakdown of the machining gap and establish an electric spark discharge channel.

Step 3, before the processing gap is broken down, the gap state is an open circuit state, the gap voltage is an open circuit voltage, and the gap current is zero; after the machining gap breaks down, a spark discharge state is started, the gap voltage rapidly drops from the open-circuit voltage, and the gap current increases. Then a series of narrow pulses with the same inter-pulse interval of time t _d The machining gap is in a spark discharge state, the gap voltage and the gap current are increased step by step, and under the action of the composite pulse, the electric spark cutting power supply completes a complete discharge machining process. Interval time t _d The setting of (2) is set to be short time as far as possible, so that the discharge process can be continued all the time, and the machining gap current is not interrupted. Even if the short circuit state occurs in the processing gap during the conduction period of the switching tube, the conduction time is shortened due to the narrow pulse width of the trigger pulse of the switching tube, so that the short circuit state is causedThe duration of the short-circuit state is greatly reduced, and the machine tool does not need to back up to exit the short-circuit state.

See FIG. 1, G ₁ ～G _n (n is more than or equal to 2) is a switching tube in the main circuit of the pulse power supply, V is a direct current power supply, R is _d Is a distributed resistance in the main circuit of the pulse power supply, L _d Is a distributed inductance in the main circuit of the pulse power supply, C _d Is a distributed capacitor in the main circuit of the pulse power supply, and L is a current-limiting inductor in the main circuit of the pulse power supply.

Referring to fig. 2, 1 is a first switch tube G ₁ In the first pulse output period, the gap voltage is reduced from the open circuit voltage to the low voltage in the spark discharge operating state, and the gap current starts to increase from zero current in the open circuit state. 2 to n are each G ₂ ～G _n When the switch tube is sequentially conducted, the power supply outputs a series of narrow pulses to the machining gap, the machining gap is always in a spark discharge working state in the period, and the gap voltage and the gap current are increased in a step-by-step mode.

Claims

1. The composite pulse working method of the electric spark wire cutting pulse power supply is characterized by comprising the following steps of:

and 3, after the spark discharge is started in the machining gap, conducting the rest switch tubes in sequence, wherein the pulse width of the trigger signal of each rest switch tube is narrow, the pulse intervals between the trigger signals of two adjacent switch tubes are the same, and the interval time is t _d The pulse power supply outputs a composite pulse containing a series of narrow pulses at the machining gap;

said interval time t _d To satisfy the requirements of processingThe gap current is not discontinuous.