GB1598323A - Welding with filler material - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO WELDING WITH FILLER MATERIAL (71) We, STEIGERWALD STRAHL TECHNIK GmbH, a joint stock company organised under the laws of the Federal Republic of Germany, of la, Haderunstrasse, 8000 Munich 70, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to welding with filler material.

For the automatic welding with filler material (which may be in wire or sheet form or any other applicable form e.g., particles) or workpieces which form a gap of varying width along the welding line because of inaccurate preparation of their edges we have considered introducing filler material at a controlled rate while maintaining constant beam parameters. The problem then arises of adapting the rate of the supply of additional or filler material which may, e.g, have the form of a wire or sheet metal to the varying gap width in order to avoid the overlying weld bead sinking in or too great an increase in the height thereof.

The present invention relates to a method of obtaining a measure of the amount of filler material which must be supplied to the welding zone during the joining, by beam welding, e.g., electron beam welding, of the edges of two workpieces separated by a gap the width of which varies in an irregular manner as it is usual with workpieces of greater thicknesses, e.g., 50 to 60 mm and more. It is generally not feasable or at least not economical to machine the workpieces to be joined so that they abut continuously or form a gap of constant width. Thus, filler material must be supplied to the welding zone and the amount of filler material supplied to each increment of the gap length must be controlled so that the volume of the gap is made up by the filler material supplied. It is difficult to measure the width of the gap in advance of the welding zone (which is moved along the gap), since the width of the gap may vary not only in the direction of the length of the gap but also in the direction of the depth of the gap, i.e., in the direction of the electron beam. Thus, the present invention proposes to measure the height or cross-sectional area of the overlying solidified weld bead, relative to the surfaces of the workpieces being joined, immediately after the solidification has occurred, i.e., a short distance behind the welding zone. The measurement may be effected by means of a mechanical probe as will be described. Such a proceeding is practical since the gap width, or better the cross-sectional area of the gap which must be made up by a filler material, does not vary abruptly and since an exactly constant height of the solidified weld bead is in most cases not required.

The cross-sectional area of the overlying weld bead can be measured by a mechanical probe which is periodically drawn across the solidified seam, or by other means, e.g., an inductive probe which may consist of a solenoid coil comprising a rod-shaped magnetic core which is oscillated transversely at a short distance above the seam and which is energized by an alternating current, so that the inductive reactance of the solenoid coil varies with a distance between the front face of the magnetic core and the probed surface area of the weld bead.

Since, in particular in the case of large workpiece thicknesses, measurement of the gap width prior to welding is especially difficult, the present invention starts from the idea of measuring the cross-sectional area of the overlying weld bead immediately after solidification of the melt. Since it is not important to obtain an absolutely constant cross-sectional area. of the overlying bead, but it is only important to keep this area between certain lower and upper limits, it is sufficient to control the supply of additional or filler material after the result of the measurement of the cross-sectional area of the overlying bead which is described hereinafter in such manner that the rate of supply can be increased (or reduced) when a certain minimum value (or maximum value) of this area is not reached (or is exceeded).

Moreover, this minimum or maximum value must be so chosen that it incorporates sufficient reserve as regards a certain control delay, since in fact the corresponding measurement of area can be carried out only after a certain period of delay between the welding of the joint and the formation of the overlying bead.

An embodiment of the invention will now be described with reference to the accompanying drawing in which: Figure I is a schematic view of a measuring system and a cross-section of a weld seam, and Figure 2 is a circuit diagram of electronic apparatus for use in the embodiment of Figure 1.

In the embodiment illustrated by the drawing, the basis of the measurement of cross-sectional area is a measuring system 10 which can measure the height h of the overlying bead above the otherwise plane workpiece surface 20 at various points. Such a measuring system may either be based in known manner on a mechanical probing of the height as shown schematically, or, in likewise known manner, the determination of this height h by an inductive method.

What is important here, in addition to the combination of such a measuring system 10 with a welding apparatus (in particular an electron beam welding apparatus), is that the measuring system 10 can be moved reproducibly at the same time transversely of the overlying bead 30 in the direction x, the increase in length at any given time dx being detected with the aid of an incremental length measuring device likewise known per se (not shown here) utilizing, for example, photo-optical adaptation of a length scale, which is fixedly connected to the system 10.

The value dx at any given time, if necessary after electronic conversion, and the value h measured at the same time and, for example converted into an electronic signal by means of a rotation value pick-up coupled in the case shown in the drawing to the axis of rotation or pivot 50 of the probe 40 are multiplied electronically. This product dx. h supplies an incremental area element of the cross-sectional area 30.

After electronic integration (summation) of all the increments dx. h(x), an electronic measurement value is obtained which is proportional to the wanted cross-sectional area. Thus there is provided a system of weld bead probing with distance-height integration for process control in welding with filler material.

Such an area measurement is repeated intermittently during the welding process and, in the case of mechanical probing, the ball probe 40 is raised automatically during return.

The filler material may have essentially the same composition as the workpiece material, or alternatively it may comprise or consist of another material or the materials to modify the properties of the area welded.

The filler material may be supplied in any appropriate form, e.g., in form of a wire, a rod, a sheet or band or even in particulate form.

Figure 2 shows a possible circuit useful in the probe system shown in Figure 1. The probe arm 40 is connected to a potentiometer which produces an output signal proportional to h. The measuring system 10 is moved in steps (dx) by a stepping motor controlled by a pulse generator which produces a series of stepping pulses. The stepping pulses are shaped to have constant width and amplitude and are multiplied with the signal h. The output signal h . dx is integrated and applied to the input of a gate.

The gate is enabled by a counter which counts the stepping pulses and produces an output when the device 10 has completed its path across the weld seam. The output of the gate is supplied to upper and lower limit threshold devices which produce output signals which slow down and accelerate, respectively, the feeding of the filler material. The output of the counter is used to reset the stepping motor and to actuate a device, e.g., an electron magnet which lifts the probe 40 during the reset motion.

Alternatively, the probe 40 may be constructed such that it can effect measuring in both directions.

WHAT WE CLAIM IS: 1. A method of obtaining a measure of the amount of filler material which must be supplied to a welding zone during the joining, by beam welding, of the edges of two workpieces separated by a gap the width of which varies in an irregular manner, filler material being supplied to the welding zone, the method including the step of measuring the height or cross-sectional area of the overlying solidified weld bead relative to the surfaces of the workpieces being joined, immediately after the solidification has occurred, i.e., a short distance behind the welding zone.

2. A method according to claim 1, wherein the said cross-sectional area is measured by a mechanical probe which is periodically drawn across the solidified weld bead.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. between certain lower and upper limits, it is sufficient to control the supply of additional or filler material after the result of the measurement of the cross-sectional area of the overlying bead which is described hereinafter in such manner that the rate of supply can be increased (or reduced) when a certain minimum value (or maximum value) of this area is not reached (or is exceeded). Moreover, this minimum or maximum value must be so chosen that it incorporates sufficient reserve as regards a certain control delay, since in fact the corresponding measurement of area can be carried out only after a certain period of delay between the welding of the joint and the formation of the overlying bead. An embodiment of the invention will now be described with reference to the accompanying drawing in which: Figure I is a schematic view of a measuring system and a cross-section of a weld seam, and Figure 2 is a circuit diagram of electronic apparatus for use in the embodiment of Figure 1. In the embodiment illustrated by the drawing, the basis of the measurement of cross-sectional area is a measuring system 10 which can measure the height h of the overlying bead above the otherwise plane workpiece surface 20 at various points. Such a measuring system may either be based in known manner on a mechanical probing of the height as shown schematically, or, in likewise known manner, the determination of this height h by an inductive method. What is important here, in addition to the combination of such a measuring system 10 with a welding apparatus (in particular an electron beam welding apparatus), is that the measuring system 10 can be moved reproducibly at the same time transversely of the overlying bead 30 in the direction x, the increase in length at any given time dx being detected with the aid of an incremental length measuring device likewise known per se (not shown here) utilizing, for example, photo-optical adaptation of a length scale, which is fixedly connected to the system 10. The value dx at any given time, if necessary after electronic conversion, and the value h measured at the same time and, for example converted into an electronic signal by means of a rotation value pick-up coupled in the case shown in the drawing to the axis of rotation or pivot 50 of the probe 40 are multiplied electronically. This product dx. h supplies an incremental area element of the cross-sectional area 30. After electronic integration (summation) of all the increments dx. h(x), an electronic measurement value is obtained which is proportional to the wanted cross-sectional area. Thus there is provided a system of weld bead probing with distance-height integration for process control in welding with filler material. Such an area measurement is repeated intermittently during the welding process and, in the case of mechanical probing, the ball probe 40 is raised automatically during return. The filler material may have essentially the same composition as the workpiece material, or alternatively it may comprise or consist of another material or the materials to modify the properties of the area welded. The filler material may be supplied in any appropriate form, e.g., in form of a wire, a rod, a sheet or band or even in particulate form. Figure 2 shows a possible circuit useful in the probe system shown in Figure 1. The probe arm 40 is connected to a potentiometer which produces an output signal proportional to h. The measuring system 10 is moved in steps (dx) by a stepping motor controlled by a pulse generator which produces a series of stepping pulses. The stepping pulses are shaped to have constant width and amplitude and are multiplied with the signal h. The output signal h . dx is integrated and applied to the input of a gate. The gate is enabled by a counter which counts the stepping pulses and produces an output when the device 10 has completed its path across the weld seam. The output of the gate is supplied to upper and lower limit threshold devices which produce output signals which slow down and accelerate, respectively, the feeding of the filler material. The output of the counter is used to reset the stepping motor and to actuate a device, e.g., an electron magnet which lifts the probe 40 during the reset motion. Alternatively, the probe 40 may be constructed such that it can effect measuring in both directions. WHAT WE CLAIM IS:

1. A method of obtaining a measure of the amount of filler material which must be supplied to a welding zone during the joining, by beam welding, of the edges of two workpieces separated by a gap the width of which varies in an irregular manner, filler material being supplied to the welding zone, the method including the step of measuring the height or cross-sectional area of the overlying solidified weld bead relative to the surfaces of the workpieces being joined, immediately after the solidification has occurred, i.e., a short distance behind the welding zone.

2. A method according to claim 1, wherein the said cross-sectional area is measured by a mechanical probe which is periodically drawn across the solidified weld bead.

3. Apparatus for carrying out a method

according to claim 2 and substantially as described hereinbefore with reference to the accompanying drawing.