Metal fusion bonding – Process – With clamping or holding
Reissue Patent
2000-10-18
2002-06-11
Ramsey, Kenneth J. (Department: 2879)
Metal fusion bonding
Process
With clamping or holding
Reissue Patent
active
RE037735
ABSTRACT:
The invention relates to a
tack
gripper for a
tack
welding gun, a workpiece which can be
tack
welded to a component by means of a
tack
welding gun with a
tack
gripper and a process for connecting a preferably strip-shaped workpiece to a component.
BACKGROUND OF THE INVENTION
Welding has evolved in mechanical engineering to a production process with broad applications which is adopted in particular in the case of light construction. Welding also affords an excellent opportunity to reduce the assembly cost of components. In the production of motor vehicles, in particular, welding is the main process for body assembly. Workpieces which serve as fastening and/or holding elements are welded on the body.
It is known to arrange, for example, solid bolts on the body by welding. The welding process as such is substantially automated. The positioning of the workpieces, in particular in the vehicle body region, also takes place substantially automatically. Apparatuses which combine a welding device and a supply device for workpieces are also known.
For the
tack
welding of workpieces, in particular strip-form workpieces, welding guns are provided with
tack
grippers. These
tack
grippers are designed in the manner of tongs. As a result, these
tack
grippers have a plurality of mechanically moving parts. Welding spatter which impairs the operability of the mechanically moving parts of the
tack
gripper can be formed during the welding process. In addition to such welding spatter, the mechanically moving parts are contaminated so the mechanically moving parts are subject to increased wear in the course of time. It may also happen that the holding force of the
tack
gripper no longer suffices as the tong-form
tack
gripper is inaccessible. It has also been found that contamination on the surfaces of the
tack
gripper adversely affect the reliable supply of current owing to welding spatter and that the desired resultant weld is not therefore always obtained. As a result, the welds have to be reworked under certain circumstances.
Also, similar results are experienced during the tack welding of workpieces, when tong-
like tack grippers and tack welding guns are used.
SUMMARY OF THE INVENTION
The purpose of this invention is to provide an improved gripper for holding a workpiece as it is presented to a metal body and welded thereto. The gripper may be used to hold the workpiece while the workpiece is completely welded to the body, or only while the workpiece is temporarily attached by localized spot welds. In this case, if necessary, a more extended weld may be performed later in the manufacturing process.
On the basis of the foregoing, an object of the present invention is to develop a
tack
gripper which has a smaller number of moving parts. The
tack
gripper is also to be almost self-cleaning in design. A further object is to provide a process by means of which a strip-form workpiece can be reliably and economically connected to a component. A further object of the invention is to design a workpiece in such a way that it can be gripped reliably and positioned exactly by a
tack
gripper.
The
tack
gripper according to the invention for a welding gun is distinguished in that the
tack
gripper is U-shaped in design with two arms connected via a base, at least one free arm of the
tack
gripper being resilient. The formerly adopted route is abandoned with this design of the
tack
gripper according to the invention. In contrast to the known
tack
gripper, the
tack
gripper according to the invention has at least one resilient free arm instead of mechanically moving parts. With this design of a
tack
gripper, a frictional joint is created between the
tack
gripper and a component which is clamped between the arms. The distance between the arms is dimensioned in such a way that the arms are automatically spread during the gripping of the workpiece.
During the gripping process, the surfaces of the arms rub against the surfaces of the workpiece so the surfaces of the arms, which also act as contact surfaces for the welding current to be introduced are cleaned. The cleaning process is repeated when the
tack
gripper is removed from the workpiece so two cleaning processes invariably take place during one welding process.
Each arm is preferably detachably connected to the base. Therefore, the arms can easily be exchanged. A further advantage of this design is that the distance between the arms can be increased by spacer members arranged between the base and the arm. The
tack
gripper can therefore easily be adapted to workpieces of various thicknesses.
According to a further idea, it is proposed that at least one arm be designed with at least one hole in its region adjacent to its free end. If several holes are provided, they are aligned in a line extending transversely to the length of the arm. The design of the
tack
gripper has the advantage that a workpiece can be provided with catch knobs which engage at least partially in a hole in the arm. This allows, on the one hand, reliable transmission of the welding current and, on the other hand, exact positioning of the workpiece in the
tack
gripper.
Since the arms are provided with holes, they cannot be clogged by contamination or the like.
At least one arm of the
tack
gripper has, at its free end, a portion which is bent over itself, the portion being arranged between the arms. If holes are provided in the arms, they are formed in the bent over portion. The bent over portion has the advantage of simplifying introduction of a workpiece into the space between the arms or the portions. The bent over portion also increases the spring action of the arms.
The welding current is transmitted through the arms. The electric resistance of the arms should therefore be as low as possible. Bronze can be considered as a suitable material for forming the arms and/or the base. The spring strength or spring rating of the material of which the arms consist can sometimes be considered as too low to produce an adequate holding force. It is therefore proposed that at least one arm be spreadable against an additional spring force. At least one spring element arranged on an arm is provided for this purpose. This spring element can be a spring subjected to bending stress, the spring element being fixed at one end in a region of the arm in which the arm at least partially overlaps the base. A spring element which is a leaf spring is preferred. The leaf spring can also consist of spring steel. To increase the spring force exerted on the respective arm by the spring element it is proposed that the spring element be designed in such a way that it is curved in an arc toward the arm at least at its free end.
The welding current is preferably introduced into the workpiece via the base and the arms. For this purpose, the base is formed by a cuboid carrier having a connection to the welding head of the
tack
welding gun on one of its end faces. The arms and optionally the spring element or the spring elements are preferably screwed to the cuboid carrier.
In order to center the arms on the carrier, each arm has a groove in which a respective base formed on the carrier engages. The centering of the arms is particularly important if each arm has, in a region adjacent to its free end, at least one hole which cooperates with catch knobs formed on the workpiece.
To minimize the production costs of the
tack
gripper according to the invention, it is proposed that the arms of the
tack
gripper be identical in design. The storage of spare arms is therefore also minimized. The leaf springs can be standard springs.
The thermal stress on the
tack
gripper during the welding process can be considerable. If the tack gripper is used in a handling device, the time interval between two welding processes is sometimes too small to allow adequate cooling of the
tack
gripper. It is therefore proposed that the
tack
gripper be designed so as to allow the fastest possible discharge of heat and therefore cooling of the
tack
gripper. It is proposed for this purpose t
Emhart LLC
Murphy Edward D.
Ramsey Kenneth J.
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