GB2118878A

GB2118878A - Electric arc stud welding

Info

Publication number: GB2118878A
Application number: GB08305022A
Authority: GB
Inventors: Ernst-Gunther Jordan
Original assignee: Obo Bettermann OHG
Current assignee: Obo Bettermann OHG
Priority date: 1982-04-24
Filing date: 1983-02-23
Publication date: 1983-11-09
Also published as: GB8305022D0; FR2525510A1; IT1152872B; IT8223585A0; NL8203603A; DE3215453C1

Abstract

Electric-arc stud-welding apparatus for welding a stud to a workpiece comprises a stud-retaining device (4) connected to a ram (3) mounted to reciprocate in the apparatus housing (1) with axial limitation and connectable to a welding-current source, and a motor (8) operable to act linearly on the ram (3). In use, the stud is applied to the workpiece, with the formation of an electric arc between the stud and workpiece, is then lifted off from the latter, and, after fusion zones have been produced, the stud is re-applied to the workpiece, with the electric arc being quenched, and is kept in that position until the fused mass solidifies. With this apparatus and welding method, it is possible to achieve better welding quality and efficiency, as well as attaining a correct position for the effective length of the welded-on stud, the ram movements being positively and adjustably controlled in both directions of movement, as regards the in displacement paths and speeds. <IMAGE>

Description

SPECIFICATION Electric arc stud welding The invention relates to electric-arc studwelding apparatus, a method and a process for welding a stud to a workpiece, the apparatus comprising a stud-retaining device which is located at the front end of the apparatus and is connected to a ram reciprocably mounted in the apparatus housing with axial limitation and connectible to a welding-current source, and a motor operable to act linearly on the ram, wherein the stud is applied to the workpiece, with the formation of an electric arc between the stud and the workpiece, is then lifted off from the latter, and after fusion zones have been produced, the stud is re-applied to the workpiece, with the electric arc being quenched, and is kept in that position until the fused mass solidifies.

In the electric-arc stud-welding apparatus known from German Patent Application P 3032 829, which works according to the socalled drawn-arc process, the ram carrying the stud is retracted by means of an electromagnet and a compression spring pre-stressed at the same time ensures that the stud is inserted into the fused mass.

In this prior art method there are two movements in different directions at different speeds and with different paths.

In the known electric-arc stud-welding types of apparatus working according to the drawn-arc process, these three parameters cannot be controlled exactly and therefore have substantial influence on the quality welding.

For example, the lifting-off dimension of the stud has to be corrected by adjusting the spring element, whenever this is necessary.

In addition, the lifting-off speed is provided by the magnetic force and likewise can be varied only by means of a variable lifting-off path. However, when the lifting-off path is the same, it is not possible to regulate the speed.

An even greater disadvantage arises when the stud moves towards the welding location, since when this happens the speed of the stud is determined exclusively by the force of the spring.

Although, in the known electric-arc studwelding apparatus described above, the advance of the stud can also be braked by means of pneumatic damping, in order to ensure, when the stud is inserted too quickly into the fused mass, that the latter is prevented from splashing off, the effect of this damping on the speed is not always the same, since influences, such as temperatures and the degree of soiling, lead to variations even here.

Furthermore, at the same time, the path distance of the stud in the direction of the welding location depends on the size and depth of the fused mass into which the stud is inserted as far as possible as a result of the pressure of the spring, so that the length of the welded-on stud, as measured from the workpiece, can vary greatly.

It is an object of the invention to improve apparatus, a method and a process which, whilst preserving the advantages already achieved in the state of the art, it is possible furthermore to obtain a substantial improvement in the welding quality and in efficiency as well as a hitherto unattained arrangement of the welded-on stud in the correct position as regards its effective length.

According to a first aspect of the invention, there is provided a method of welding a stud to a workpiece by means of an electric-arc studwelding apparatus comprising a housing, a studretaining device which is located at the front end of the apparatus and is connected to a ram displaceably mounted in the housing with axial limitation and which can be connected to a welding-current source, and an actuating means comprising a motor operable to act linearly on the ram, in which method the stud is applied to the workpiece, with the formation of an electric arc between the stud and the workpiece, is then lifted away from the workpiece, and, after fusion zones have been produced, the stud is applied to the workpiece again, with the electric arc being quenched, and is kept in that position until the fused mass solidifies, the movement of the ram being positively adjustably controlled in the two directions of ram movement, both with regard to the ram displacement paths and with regard to the ram displacement speeds.

Thus, the ram movements are positively and adjustably controlled in both directions of ram movement, both with regard to the displacement paths and with regard to the displacement speeds.

Furthermore, it is advantageous if during the return of the ram and/or the advance of the ram the ram is accelerated or decelerated variably under positive control.

This results, for the first time, in the possibility of varying all the welding parameters and adapting them exactly to the particular requirements.

According to a second aspect of the invention there is provided apparatus for carrying out the method of said first aspect of the invention, the apparatus comprising a rotatable dynamo-electric motor with an adjustable speed and adjustable direction of rotation, which motor is connected positively to a ram, for both directions of movement of the ram, via a gear converting the rotary movement into a linear movement.

Actuators comprising motors of this type can meet the requirements desired. In addition, there is no need for the spring elements which were hitherto necessary nor for damping devices which are susceptible to faults.

It is also advantageous, to use a direct-current motor which can be regulated relatively easily. It is also advantageously possible to provide a frequency-controlled alternating-current motor.

An alternative which may be preferred under certain circumstances involves providing a rotating stepping motor.

Preferably, for converting the rotary movement into a linear ram movement, the rotating part of the motor is connected to the ram via a screw gear. This permits a compact design of the apparatus as a whole and slip-free conversion of the movements in both directions.

In this respect, in an advantageous embodiment the ram is mounted non-rotatably in the apparatus housing, and also there projects from its rear end part a spindle aligned with the latter, and a screw nut, which can be made to rotate directly by the motor, is screwed on the spindle.

An alternative form which may be preferred under certain circumstances, which does away with additional means for arranging the ram fixed against rotation, is characterised in that the spindle and the screw nut corresponding to it extend parallel to the axial displacement direction of the ram.

A further possibility, preferred under certain circumstances, for carrying out the process described above involves connecting the ram to a dynamo-electric linear motor reversible in the direction of movement and adjustable as regards the displacement paths and the displacement speeds.

To achieve a compact three-dimensional form for the apparatus as a whole, and to simplify production, it is advantageous, here, if the ram and the linear motor are aligned with one another as regards their directions of movement and are connected directly to one another.

When an electrical actuator of this type is used, there is also no need for the hitherto necessary gear for converting a rotary movement into a linear ram movement.

To improve welding further, it is advantageous if there is associated with the electric-arc studwelding apparatus a path-measuring system which senses the displacement path of the ram and which acts in response on a control system of the motor actuator.

In this respect, it is advantageous, to simplify production, if there is a path-measuring system with a non-contact action which ensures exact adherence to the preselected ram strokes, above all when the ram is inserted into the fused mass.

The path-measuring system can be designed as a resistive, inductive or optical system.

When the above-described electric-arc studwelding appliance with which an electrical control is preferably associated, is used in a fully automatic production system, it is advantageous, to achieve a fault-free process cycle, if the procedure is as follows, namely that a) before the motor is actuated the stud is kept in its initial position spaced from the workpiece, b) after the motor has been started and the stud has advanced by the amount of a preselectable stroke, its making contact with the workpiece is checked, and, if contact is not obtained, the advancing path is increased and contact-making is checked again, c) when the maximum advancing position is reached, a "stud-missing" signal is given and the welding process is stopped, d) when the stud makes contact with the workpiece, a pilot electric-arc current of variable current intensity and adapted to the stud crosssection is applied, and the stud is lifted off from the workpiece along a preselectable path at a preselectable speed, e) the ignition of the electric arc is checked, and, in the event of non-ignition of the pilot electric arc, the stud is applied to the workpiece again and the ignition operation repeated, f) when the pilot electric arc has ignited, a welding current of variable current intensity and burning time and adapted to the stud crosssection is applied, g) a check is made that the preselected welding parameters are obtained, and if appropriate readjustment is carried out, h) after the preselected welding parameters are obtained, the stud is moved towards the workpiece at a preselectable speed over a preselectable distance and inserted into the fused mass, the stud insertion depth is checked and, if appropriate, the latter is readjusted, and the welding current is switched off, i) the stud is kept in the fused mass for an adjustable time, j) solidification of the fused mass is checked, and if appropriate the length of dwell time of the stud in the fused mass is increased, and k) the device is then moved into the initial position.

To shorten the work cycle according to feature e), it is advantageous, if to repeat the operation of igniting the pilot electric arc the stud is returned into the initial position at a higher speed than during its advance.

Furthermore, an oxide layer which may be present at the point of impact is broken up at least partially as a result of the hammer-like advance of the stud during the pilot ignition operation, so that ignition can at least take place more easily.

Likewise, to shorten the work cycle according to feature h), whilst improving the welding quality at the same time, it is advantageous if the study is moved towards the workpiece and inserted into the fused mass with progressive deceleration.

To acquire even more checking possibilities than hitherto, it is advantageous if after the welding operation has ended the preselected welding parameters and those obtained are printed out.

By means of these measures, it becomes possible, for the first time, to preselect exactly the stud lifting-off dimension, the stud lifting-off speed, the moment in time of the forward movement of the stud, the impact speed of the stud, the path of the stud during insertion into the fused mass, the length of dwell time of the stud in the fused mass up to solidification of the latter, and the most favourable welding currents at a particular time.

Furthermore, it is also guaranteed that the preselected parameters will be adhered to exactly.

Also, the electric-arc stud-welding apparatus according to the invention allows a rapid programmable changeover to particular welding requirements.

Embodiments of the invention will now be described by way of example only, and with reference to the accompanying drawings, in which:~ Figure 1 shows, in longitudinal section, one embodiment of electric-arc stud-welding apparatus in accordance with the invention; Figure 2 shows, in a longitudinal section, an alternative embodiment of electric-arc studwelding apparatus according to the invention, with an automatic stud feed: Figure 3 shows a programming chart; and Figure 4 shows a ram path diagram.

Referring to Figure 1 there is shown one embodiment of electric arc stud welding apparatus comprising, mounted displaceably, with axial limitation, in a housing 1 having a pistol grip 2, a ram 3 which carries on its front end part a stud-retaining device 4, which is preferably fastened on said front end part of the ram so as to be replaceable.

The ram 3 is mounted non-rotatably in the housing 1 in a tongue-and-groove manner.

The stud-retaining device 4 is connected to an electrical supply lead (not shown) which can be connected to an electrical current source also (not shown).

A spacer 5 is also provided at the front end of the apparatus. From the rear end part of the ram 3 projects a spindle 6, coaxially aligned therewith, and onto which a screw nut 7 is adjustably threadingly mounted. The screw nut 7 is connected releasably to the output shaft of a direct-current motor 8 located in the housing. This motor can rotate in both directions of rotation and its speeds are variable. Also located in the housing is a ram displacement path measuring system 9 which is disposed parallel to the direction of movement of the ram and with which is associated a feeler 10 connected to the ram.

The motor 8 and the path-measuring system 9 are connected electrically to an electronic control system located in the grip 2. On the grip 2 there is also a trigger 11 which acts on the electronic control system (not shown).

In the embodiment of electric-arc stud-welding apparatus illustrated only partially in Figure 2, there extends through the apparatus housing (not shown) an axially disposed channel means 12 through which the studs are fed by means of compressed air into the stud-retaining device (not shown) located at the front end of the ram 3'.

Located in a flange 13 provided at the rear end of the ram 3', which ram 3' is mounted in the housing to be axially displaceable, is a screw nut 7' which extends with its axis parallel to the direction of movement of the ram 3' and into which is screwed a spindle 6' which extends co-axially with the supporting shaft of the motor 8' and which is coupled to the output shaft. Arranged parallel to the spindle 6' and fixed to the frame is a path-measuring system 9 which interacts with a feeler 10 fastened to the screw nut 7'.

Figure 3 shows a programmed operating method of welding a stud by means of either of the above-described types of electric-arc studwelding apparatus, with which an electronic control is associated, the stud being held in the initial position spaced from the workpiece to which the stud is to be fastened.

Subsequently, once the trigger 1 1 has been actuated, the command "advance of the ram towards the workpiece" is first given by the electronic control, and a check is made as to whether the stud rests against the workpiece, and if appropriate the preselected displacement path of the ram or of the stud is increased until the stud has come in contact with the workpiece.

The command "switch on the pilot electric arc current" is then given, the current intensity adapted to the stud cross-section being preset, and the stud is lifted off from the workpiece along a preselected path at a preselected speed.

Should the pilot electric arc not yet ignite after that, the pilot electric arc is reignited, the advance of the ram towards the workpiece taking place at maximum speed so as to shorten the work cycle and to destroy an oxide skin possibly present on the workpiece at the point of impact, this having a positive effect on the ignition operation.

If the electric arc has then ignited, the command "switch on welding current" is given, the current intensity and arc burning time adapted to the stud being preset.

A check is also made, at the same time, as to whether the predetermined conditions are satisfied. If not, readjustment takes place automatically to obtain the preset parameters.

Subsequently, after the distance, speed and direction have been preset, the command "insert and switch off the welding current" is given, and a check is made as to whether the creselected parameters have been obtained. After a preselectable dwell time of the stud in the fused mass up to solidification of the latter, the ram is then lifted off from the welded-on stud. When this condition is satisfied, the ram returns into the initial position. It may be advantageous, moreover, to store and print out all the preselected parameters and those obtained.

The diagram illustrated in Figure 4 shows the paths to be covered by the ram or by the stud, the lifting-off speed and the insertion speed being programmable, and also, among other things, the ram movement being decelerated increasingly during insertion of the stud into the fused mass.

The ram movement for igniting the pilot electric arc can also start initially with reduced acceleration and only then be increased gradually to shorten the work cycle.

Claims

1. A method of welding a stud to a workpiece by means of an electric-arc stud-welding apparatus comprising a housing, a stud-retaining device which is located at the front end of the apparatus and is connected to a ram displaceably mounted in the housing with axial limitation and which can be connected to a welding-current source, and an actuating means comprising a motor operable to act linearly on the ram, in which method the stud is applied to the workpiece, with the formation of an electric arc between the stud and the workpiece, is then lifted away from the workpiece, and, after fusion zones have been produced, the stud is applied to the workpiece again, with the electric arc being quenched, and is kept in that position until the fused mass solidifies, the movement of the ram being positively adjustably controlled in the two directions of ram movement, both with regard to the ram displacement paths and with regard to the ram displacement speeds.

2. A method according to Claim 1, wherein, during the return of the ram and/or during the advance of the ram, the ram is accelerated or decelerated variably under positive control.

3. Apparatus for carrying out the method according to Claim 1 or 2, comprising a rotatable dynamo-electric motor with an adjustable speed and adjustable direction of rotation, which motor is connected positively to a ram, for both directions of movement of the ram, via a gear converting the rotary movement into a linear movement.

4. Apparatus according to Claim 3, wherein the motor comprises a direct-current motor.

5. Apparatus according to Claim 3, wherein the motor comprises a rotatable stepping motor.

6. Apparatus according to any of Claims 3 to 5, wherein the rotatable part of the motor operates on the ram via a screw gear.

7, Apparatus according to any of Claims 3 to 6, wherein the ram is mounted non-rotatably in a housing, wherein there is provided, projecting from the rear end part of the ram, a spindle aligned with the latter, and wherein a screw nut, rotatable directly by the motor, is screwed on the spindle.

8. Apparatus according to Claim 7, wherein the spindle and the associated screw nut extend parallel to the axial direction of movement of the ram.

9. Apparatus for carrying out the method according to Claim 1 or 2, wherein a ram is connected to a dynamo-electric linear motor which is reversible in the direction of movement of the ram and which is adjustable in respect of the displacement paths and displacement speeds of the ram.

10. Apparatus according to Claim 9, wherein the ram and the linear motor are aligned with one another in their directions of movement and are connected directly to one another.

11. Apparatus according to any of Claims 3 to 10, wherein there is associated with it a pathmeasuring system which senses the displacement path of the ram and which acts in response on a control system of the motor.

12. Apparatus according to Claim 1 1, wherein a path-measuring system with a non-contact action is provided.

13. A process for carrying out the method according to Claim 1 or Claim 2, or using the apparatus according to any of Claims 3 to 12, by means of an electronic control system operates on the apparatus, wherein:~ a) before the motor is actuated, the stud is held in its initial position spaced from the workpiece, b) after the motor has been actuated and the stud has been advanced by the amount of a preselectable stroke, its making contact with the workpiece is checked and, if contact is not obtained, the advancing path is increased and contact-making is checked again, c) when the maximum advancing position is reached, a "stud-missing" signal is given and the welding process is stopped, d) when the stud makes contact with the workpiece, a pilot electric-arc current of variable current intensity and adapted to the stud crosssection is applied, and the stud is lifted off from the workpiece along a preselectable path at a preselectable speed, e) the ignition of the electric arc is checked, and in the event of non-ignition of the pilot electric arc the stud is applied to the workpiece again and the ignition operation repeated, f) when the pilot electric arc has ignited, a welding current of variable current intensity and burning time and adapted to the stud crosssection is applied, g) a check is made that the preselected welding parameters are obtained, and, if appropriate, readjustment is carried out, h) after the preselected welding parameters have been obtained, the stud is moved towards the workpiece at a preselectable speed over a preselectable distance and is inserted into the fused mass, the stud insertion depth is checked and, if appropriate, is readjusted, and the welding current is switched off, i) the stud is kept in the fused mass for an adjustable time, j) solidification of the fused mass is checked, and if appropriate the length of the dwell time of the stud in the fused mass is increased, and k) the apparatus is then returned to its initial state.

14. A process according to feature e) of Claim 13, wherein, to repeat the operation of igniting the pilot electric arc, the stud is returned to its initial position at a higher speed than during its advance.

15. A process according to feature h) of Claim 13, wherein the stud is moved towards the workpiece with progressive deceleration.

16. A process according to any of Claims 13 to 15, wherein, after the welding operation has ended, the preselected welding parameters and those obtained are printed out.

17. A method of welding a stud to a workpiece substantially as hereinbefore described, with reference to, and as illustrated by, Figures 1, 3 and 4, or Figures 2, 3 and 4 of the accompanying drawings.

18. Apparatus substantially as hereinbefore described, with reference to, and as illustrated by, Figure 1 or Figure 2 of the accompanying drawings.

19. A process for carrying out the method of Claims 1, 2 or 17, or using the apparatus of Claims 3 to 12 or 18 in which an electronic control system operates on the apparatus, substantially as hereinbefore described, with reference to and as illustrated in Figures 1, 3 and 4, or Figures 2, 3 and 4 of the accompanying drawings.