AU628222B2 - The welding of sheet metal - Google Patents

Description

COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION NAME ADDRESS OF APPLICANT: Linde Aktiengesellschaft Abraham-Lincoln-Strasse 21 D-6200 Wiesbaden Federal Republic of Germany NAME(S) OF INVENTOR(S): ians HOHENBERGER Dieter BOHME ADDRESS FOR SERVICE: a DAVIES COLLISON Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

"o COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: S The welding of sheet metal The following statement is a full description of this invention, including the best method of performing it known to me/us:o 0 4 I t I LINDE AKTIENGESELLSCHAFT la- 07. September 1990 G 89/76-AU Background of the Invention This invention relates to welding, particularly to a process for welding coated, especially galvanized, thingage sheet metal.

Heretofore, resistance spot welding has been especially utilized for welding together coated thingage metal sheets (sheet thicknesses around 1 mm), for example in automobile construction. This welding method, despite irrefutable advantages, aloo has drawbacks mainly in manufacturing, for example: comparatively high investment costs, and deficiencies in the mechanical strength of the structural parts produced thereby.

(Force transmission between spot-welded structural parts takes place in a punctiform manner!).

For this reason, other welding processes, especially fusion welding methods, are utilized for joining thin metal panels, capable of yielding a higher mechanical stability based on continuously producible weld bonds.

Conventional methods here include, above the use of MAG (metal active gas) welding with a melt-consumable electrode. As additional materials, unalloyed wire electrodes accoLJing to DIN 8559 or bronze wire electrodes are utilized. However, in the performance of this process, especially in case of the wire electrodes, there is frequently extensive spatter formation which can lead to unacceptable structural parts or to expensive follow-up work. Moreover, especially with rather thin 2 i metal sheets, pool breakouts are often encountered during i the welding step since welding is carried out approximately perpendicularly to the metal sheets into the angle formed by the projecting bottom sheet and the top sheet lying on the former. The second-mentioned version with a bronze electrode wire, in contrast thereto, represents a possibility which is applicable only in special cases because of its expense.

Summary of the Invention Therefore, an object of the present invent,. is to provide an advantageous fusion welding method for bonding sheet metal, especially coated thin-gage sheet metal, which will overcome the disadvantages of the known methods.

Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.

These objects are attained by conducting the welding step by the plasma arc welding process along the provided welding groove, utilizing, besides argon as the central gas, an argon-oxygen mixture with 87-97 vol.% of argon and 3-13 vol.% of oxygen as the external or shielding gas This is the volume ration under which the shielding gas is Stored in the pressure vessel.

Fot details of the conventional plasma arc welding process, reference is made to, for example, the article "Feinschweissen nach dem Mikroplasmaverfahren", from SchwAisstechnik (1970) Heft 9.

This welding method yields, when welding coated thin-gage sheet metal, an excellent weld which could not be expected from a knowledge of the conventional welding processes. This is true because, even though gaseous mixtures corresponding to the mixtures according to this invention are generally known and used in welding processes, for example in MAG welding, the utilization of the. aforementioned gaseous mixture has, however, not heretofoce been suggested for the plasma welding method.

3 Prior to this invention, external sjoe;domg gases known in the plasma welding process have been solely mixtures of argon with hydrogen, helium or nitrogen. In addition, the use of oxygen as a component of the external gas would have been considered as unfavorable on account of the danger of oxidizing the electrode. It has furthermore been discovered in experiments in this regard that the plasma welding process does not give satisfactory welding results with the conventional external gases, but that surprisingly, with the oxygencontaining external gas mixture, qualitatively highly satisfactory weld seams are obtained. Furthermore, the welding process of this invention is stable.

Therefore, contrary to expectations, the process of this invention, utilization of the plasma arc welding method with the aforementioned gas mixture in the disclosed way, provides a very good weld with securely welded-on, regular ,smooth and corrosion-proof weld seams produced, in a stable welding operation, practically without any welding spatter.

An especially advantageous version of the process according to this invention resides in the use of the plasma arc welding method with a pulsed current whereby the so-called plasma pulsed arc welding can be regulated with special precision for the introduction of heat into the workpieces to be welded together. This version of the process is thus particularly advantageous for welding thin-gage metal sheets, especially sheets below 1 mm wall thickness.

In a preferred embodiment of the invention, an especially advantageous gas composition was found to be a shielding gas mixture ,ith 91-93 vol.% argon and 7-9 vol.% oxygen. Smoothness and uniformity, as well as stability of the weld seam are here attained in an optimum manner, while maintaining otherwise conventional welding parameters.

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-1 4 It is furthermore particularly advantageous to conduct the welding step so that the metal sheets or their folded-over rims are made to lie one on the other without projecting to any appreciable extent, and the welding unit is aligned toward the end faces of the metal sheets and then guided so that the plasma arc root is always located approximately on the contact line or in a possibly present gap between the superimposed sheet rims.

Brief Description of the Drawing Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawing, in which like reference characters designate the same or similar parts throughout the several views, and wherein: The attached figure is a half-section schematic view of a welding apparatus according to the invention, and an exemplification of the operation of the apparatus is discussed below.

Detailed Description of the Drawin The figure shows schematically a welding torch unit 8 with an associated electrode 9 and feed ducts for the central gas and external gas 10, as well as the thingage sheet metal parts 1, 2 to be joined, with associated folded-over rims or flanges 3, 4. As in the case of the re-sistance spot welding method or corresponding MAG welding processes, folded-over flanges 3, 4 are provided at the bonding site of the metal sheets 1, 2; these flanges are aligned flush to one another for purposes of welding them together. However, in contrast to the conventional methods, the flanges 3, 4 can be designed to be markedly shorter since the welding of the metal sheets can also be executed at the end face.

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i 1 .i__lLI1_~11 5 shorter flanges have dimensions of 0.5 to preferably 1 to For welds provided at the end face, the welding torch unit 8 is arranged with respect to its longitudinal axis in an approximately perpendicular orientation with regard to the plane determined by the end faces 5, 6 of the superaligned flanges. For the welding operation, the torch 8 is then guided along the welding groove, i.e., along the contact line 7 of the two flanges, or, if present, along a small gap between the two flanges, at a suitable spacing from the workpiece. This means that the footpoint of the produced plasma arc always comes to lie on the contact line or the gap between the metal sheets to be bonded. By footpoint of the produced plasma arc is meant the point, where the tip of the plasma arc meets the workpiece.

The figure shows the plasma torch unit in a halfsectional view so that it can be seen that the electrode 9 which is a non melting tungsten electrode, is concentrically surrounded by gas feed ducts 10, 11, of which the inner duct 10 serves for introducing the argon central gas and the outer duct 11 delivers the external gas.

As the external gas, a gaseous mixture of 92 vol.% Ar and 8 vol.% 02 is supplied, flowing approximately in the area denoted by reference numeral 13. The zone of the central or plasma gas, which somewhat constricts the arc 15, is denoted by 14.

Moreover, the torch is moved forward into the direction denoted by arrow 16 and operated with a basic current with superimposed current pulses supplied at a frequency in the range from 3 to 5 Hz. The feeding rate is in the range from 45 to 55 cm/min, and the torch is advantageously maintained at a distance of between 5 and mm from the workpiece.

With these settings, the very good welding resulNs described in greater detail above are achieved. Even those settings which deviate therefrom but are within 'n.v _Il--^IIIIIIIC11~---- 1~ 6 scope of reasonable welding parameters will in all normal cases yield good results as well, for example a stabbing or touching torch guidance, or also the projection of a flange due to unavoidable dimensional fluctuations of the individual structural parts. In addition to galvanized thin-gage sheets, the process of this invention also produces advantageous welding of metal sheets, particularly those coated with other materials, for example aluminum-coated thin-gage metal sheets. By metal sheets is meant any weldable metal, steel. It is also contemplated that in place of argon, other inert gases, e.g. helium, may be used, but generally they are expensive compared to argon.

In general the volumetric ratio of the external shielding gas to the central gas depends on the geometry of the torch and the nozzle in the torch.

There is no defined ratio of the gas flow rate of the two gases. The usual central gas flow rate can be 0.5 to 3 1/min, by an external gas flow rate from 5 to 15 1/min.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

The entire disclosures of all applications, patents and publications, if any, cited above and below, and of the.

corresponding application F.deral -Rep-ul- f Crma- P-O 17 5q 5 330 30 64G.1, fild ptbe_--em9, are hereby incorporated by reference.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

Claims (12)

1. A process for welding metal sheets comprising conducting the welding with a plasma arc having a central gas and a concentric outer shielding gas wherein the central gas is argon and the shielding gas is an argon- oxygen mixture of 87-97 vol.% argon and 3-13 vol.% oxygen.

2. A process according to claim 1, wherein the metal sheets are coated.

3. A process according to claim 1, wherein the metal sheets are galvanized.

4. A process according to claim 1, wherein a pulsed current is utilized.

A process according to claim 1, wherein the shielding gas is a mixture of 91-93 vol.% argon and 7-9 vol.% oxygen.

6. A process according to claim 2, wherein the shielding gas is a mixture of 91-93 vol.% argon and 7-9 vol.% oxygen.

7. A process according to claim 3, wherein the shielding gas is a mixture of 91-93 vol.% argon and 7-9 vol.% oxygen. I IIIFiliil 8

8. A process according to claim 4, wherein the shielding gas is a mixture of 91-93 vol.% argon and 7-9 vol.% oxygen.

9. A process according to claim 1, wherein the metal sheets to be welded together, or folded-over rims thereof, are aligned flush to one another without substantial projection, and resultant plasma arc is oriented toward the end faces of the metal sheets and is then guided so that the plasma arc root is substantially maintained on a contact line between the metal sheets or on a gap between the aligned sheet metal rims.

A process according to claim 8, wherein the metal sheets to be welded together, or folded-over rims thereof, are aligned flush to one another without substantial projection, and resultant plasma arc is oriented toward the end faces of the metal sheets and is then guided so that the plasma arc root is substantially maintained on a contact line between the metal sheets or on a gap between the aligned sheet metal rims. -9-

11. A process for welding metal sheets substantially as hereinbefore described with reference to the drawings.

=12. The stipsA. faA-Hirp 'rnompositionsqnd-n ponds---- disclosed herein or referred to ndicated in the specification and/or c of this application, individually ollectively, and any and all combinations of a..y4 or moor.e- r -s-fce ps-ea^u-E. DATED this 15th day of November, 1990 Linde Aktiengesellschaft by DAVIES COLLISON Patent Attorneys for the applicant(s) I. t,