Electric heating – Metal heating – For bonding with pressure
Patent
1993-04-16
1995-02-14
Shaw, Clifford C.
Electric heating
Metal heating
For bonding with pressure
219 98, B23K 920
Patent
active
053897625
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a stud welding process in which a stud to be welded to a surface is pressed against the surface with an acceleration force and a welding current is triggered wherein a positioning pressure is applied to at least two points spaced away from the stud axis.
2. Description of Related Art
In principle, two forms of stud-welding processes are known. One employs a tip which is simultaneously subjected to a current and applied under force to the part to be welded on. This is referred to as tip ignition method. Here, large currents are built up and then discharged via the tip. Owing to the short time available during the discharge, it is not possible to accelerate the stud even further toward the part to be welded on and to immerses it deeper into the melt. As a result, this process cannot be used in the case of a stud diameter over 8 mm, as is known from specialist books (cf. Betterman "Bolzenchweisstechnik" [Stud-welding technique], page 4).
Thus, for example, JP-A-56-91 983 describes an apparatus for stud-welding, in which a guide device ensures the vertical guidance of a welding gun in relation to a surface onto which the stud is welded. The stud itself is pushed into a guide block which in turn is displaceable, by means of springs coordinated with it, in the axial direction of the welding gun. During the welding process, the stud is pressed against the surface by means of the welding gun. The guide block is provided for ensuring that the welding gun remains positioned at right angles to the surface during the welding process.
Although relatively large diameters can also be welded by means of the elevator ignition technique, this method requires an inert gas atmosphere, the energy requirement is higher, the welding time is longer and the tendency to burn through the stud on the part to be welded on is greater so that at least very strong welding discolorations always remain behind on the lower surface of the plate when such a stud is welded onto a thin plate. However, this is undesirable in many cases.
Consequently, it has not been possible to date to weld on studs having a diameter of more than 8 mm
This gives rise to an object of the present invention permit in particular a tang to be welded onto a trowel blade cleanly, without an inert gas and in a short period of time.
Extensive attempts have been made to achieve this object. An initial shown that an important phenomenon leading to the difficulties mentioned is the fact that, when the welding current is triggered, the stud has the tendency to "float away" on the end which has become liquid. This tendency cannot be counteracted by the conventional pressure-application devices acting exclusively axially, i.e. the investigations led to the discovery that this is not just a centering problem during the welding process, which may last a very short time where the tip ignition process functions within milliseconds.
Based on this discovery, according to a preferred embodiment of the invention, a positioning pressure is applied to at least two points spaced away from the axis of the stud. By virtue of the fact that the pressure now involves force components which are parallel and symmetrical in terms of the angle, decentering is not so easily possible, and any decentering tendencies due to the geometry of the stud or of the device can preferably be compensated by separately adjusting the pressure at the at least two points. For this purpose, all that is required is a test weld in order to be able to make the necessary adjustment, "separate" adjustment being intended to mean one in which an adjustment of one pressure does not necessarily result in an equally large adjustment of the other pressure.
Although the above statements indicate that the invention can be applied in principle to all embodiments of the stud-welding process, the object of the invention is preferably achieved when the tip ignition method is used.
An application of the process according to the invention in which the adv
REFERENCES:
patent: 2479092 (1949-08-01), Ainsworth
patent: 3539758 (1970-11-01), Ettinger
patent: 4988842 (1991-01-01), Van Allen
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