GB2231521A

GB2231521A - Welding machine controllers

Info

Publication number: GB2231521A
Application number: GB8911181A
Authority: GB
Inventors: Rudolf Drucker; Geoffrey Elliot Wilson
Original assignee: SUPERTECH ENGINEERING Co
Current assignee: SUPERTECH ENGINEERING Co
Priority date: 1989-05-16
Filing date: 1989-05-16
Publication date: 1990-11-21
Anticipated expiration: 2009-05-16
Also published as: GB2231521B; GB8911181D0

Abstract

In a controller for electrical resistance welding machines, especially for spot welding using a welding transformer and a weld gun, a delay is preset in the reset line from the welding timer to the trigger that initiates the welding timer, so that the welding timer cannot be triggered to commence a fresh weld immediately the previous weld has been completed. The delay, which can be accomplished by an R.C. time delay network, is calculated to determine a maximum frequency of making welds at which sufficient cooling time exists between welds to render it unnecessary for the welding operation to be stopped periodically for a prolonged cooling period to avoid over-heating. <IMAGE>

Description

"IMPROVEMENTS IN WELDING MACHINE CONTROLLERS" This invention relates to controllers for electrical resistance welding machines, especially for spot welding.

Resistance welding machines and welding guns heat up during use and must be operated in a manner to prevent overheating of the transformer and secondary circuit. Although water cooling is normal for larger units, smaller hand welding guns for work such as motorbody repair are air-cooled only and therefore must not exceed the safe limits, or serious damage can result. In any case if welding is carried out too fast, the power losses prevent the making of sound welds.

It has been suggested to provide a thermostat switch in the transformer to switch off the primary current on reaching a pre-set safe temperature limit in the windings, so that damage will be avoided, but a long time then has to elapse before the gun cools down enough for the work in hand to be resumed.

According to the present invention, the problem of having to stop the work for an extended cooling period is solved by setting the maximum frequency with which successive welds can be made at a rate that allows sufficient aircooling of the transformer between welds. In effect, the heating up and cooling down equal out at the optimum number of welds per hour. Thus, work can be uninterrupted and jobs can be completed without having to wait for overheated weld guns to cool down.

Preferably, this is achieved by providing a time delay network, which may be adjustable, in the reset line that supplies the reset signal from the weld timer at the completion of a weld to the trigger that initiates the weld timer for the next weld.

One arrangement in accordance with the invention will now be described in more detail by way of example and with reference to the accompanying drawings, in which: Figure 1 is a block diagram of an electrical resistance welding machine controller, and Figure 2 is the corresponding circuit diagram.

Referring to the drawings, in existing welding machine controls the operation is basically as follows: a microswitch trigger 1 activates a weld timer 2 and when the time set by this timer has elapsed a reset circuit 3 transmits a reset signal to cause the trigger 1 to activate the weld timer 2 again.

To implement the invention, the reset signal is time delayed to prevent the operator from making more than a pre-set number of welds per hour. In the arrangement illustrated, an RC time delay network 4 receives the reset signal (logic hi) and goes to logic hi after a pre-set interval. The signal output of the delay network 4 is then processed through two inverter gates 5, 6 to give the same logic level at the actual reset signal output 7.

The two inverters 5, 6 are necessary to prevent the capacitor in the RC delay network 4 from being discharged by the circuit which is being reset and thus shortening the time delay.

The resistor 9 in the RC delay network is variable to enable the delay time to be set in relation to the user's weld time to limit the speed of operation to 400 welds per hour.

e.g. squeeze time = 32 cycles threshold = 3 cycles backstop = 38 cycles 73~ = 1.46 sec delay = 7.54 sec total = 9.00 sec welds per minute = 6.66 welds per hour = 400 The threshold is the time taken to reach the minimum pre-set welding current necessary to start the weld timer running.

As well as supplying the reset signal to the trigger 1, the output of the second inverter gate 6 is connected to light an indicator lamp (LED) 8 to show whether the machine is ready to make another weld.

Claims

CLAIMS:

1. A method of making a succession of electrical resistance welds, such as spot welds, using a welding transformer and a weld gun, wherein the maximum frequency with which the successive welds can be made is preset at a rate that allows sufficient aircooling of the transformer and weld gun between welds to avoid having to stop the work for an extended cooling period.

2. A method according to Claim 1, wherein a weld timer is triggered to initiate each weld and the time delay between welds that is demanded by the aforesaid maximum frequency is achieved by automatically delaying the triggering operation after the completion of each weld.

3. A method according to Claim 2, wherein a reset signal that is sent from the weld timer to a trigger circuit for the weld timer at the completion of a weld traverses a time delay network.

4. A method according to Claim 1, and substantially as described with reference to the accompanying drawings.

5. A welding controller for performing the method of any preceding claim, comprising a weld timer, a trigger for initiating the weld timer, a reset line supplying a reset signal from the weld timer to the trigger at the completion of each weld, and an R.C. delay network in the reset line.

6. A controller according to Claim 5, and substantially as described with reference to the accompanying drawings.