Patent Application
20080179305
The invention relates generally to the field of automotive component manufacture and more specifically to a method of welding the components that make up a torque arm assembly for an automotive vehicle.
A torque arm is normally used in an automotive suspension system for stabilizing and maintaining the geometry of the rear end of such system under cornering loads, while allowing the driveshaft and other components to function as intended. Typically, a torque arm is an assembly that is constructed of two preformed panels of sheet metal. The metal panels are mated together and welded along overlapping joints formed along their lengths. The assembly also includes metal spacer elements tack welded within and between the mated panels to provide cylindrical passages co-axial with pre-formed and opposing bolt-through holes in the metal panels and separating support for the panels.
In a conventional manufacturing process for such torque arm assemblies, the spacers are tack welded to one of the panels and the mated preformed metal panels are welded together using traditional MIG or TIG welding methods. Several problems have been persistent in using such welding methods and have been difficult to overcome. Primarily, conventional MIG or TIG welding methods generate excessive heat on the metal. When used to tack weld the spacers in place, dimpled distortions are often created which appear on the external surface of the panel. Such distortions in appearance may be a sign of induced weakness in the panel structure. These welding methods also can cause other distortions. When welding the lap joint between the panels, these welding methods tend to cause an excessive amount of heat to be introduced into the weld area and cause spattering of the molten material onto the work piece and surrounding area. Spattering provides a sloppy appearance to the work piece which requires additional steps to clean the part for quality acceptance. Additionally, the high heat generated by these welding methods at the lap joint can cause distortion of the metal panels that, in some cases, is sufficient to cause the un-welded gap between metal panel and one or more of the respective spacers to be out of tolerance.
The present invention is directed to a method of welding a torque arm assembly utilizing a spatter-free and relatively cold hybrid MIG welding process to tack weld spacers in place and to weld lap joints created between mated metal panels.
The technique described herein utilizes a cold hybrid MIG welding process. It involves controlling the voltage, current and wire movement in a precise manner to achieve a solid weld between adjacent metal surfaces, without spattering and with reduced heat distortion of the sheet metal. Such results are advantageous from the standpoint of eliminating the requirement of removing spattering residue and a lower rejection rate due to dimpling. Additionally, this cold hybrid MIG welding process has been found to cause much less heat to be generated in the affected weld zone and therefore allows for more consistent dimensional control of the work pieces. Another advantage is a reduction in energy costs for the welding process due to the fact that it is not a continuous weld, but rather a series of pulsed or intermittently generated welds, generally at lower voltage and/or amperage.
It is an object of the present invention to provide an improved method of manufacturing a torque arm assembly of preformed sheet metal panels by utilizing a cold hybrid MIG welding process to achieve high quality results.
This object is achieved on a torque arm assembly that includes an outer metal panel and an inner metal panel, the outer metal panel is formed to have upward extending edges along its length and the inner metal panel is formed to have downwardly extending edges along its length. The inner metal panel has width dimensions that are slightly less than the corresponding width dimensions of the outer metal panel. The outer metal panel and the inner metal panel are mated together along their upward and downward extending edges so that a narrow gap or joint is formed between the inner surface of each of the upward extending edges and the corresponding portion of the opposing outer surface of the inner metal panel. The method further includes the steps of utilizing a cold hybrid MIG welding process by control moving the end tip of the sacrificial weld wire to contact the outer surface of the inner metal panel adjacent the gap; applying a predetermined value of electrical energy between the wire and the metal panel for a predetermined amount of time to cause conduction therebetween and the end of the wire to become molten; upon terminating the application of electrical energy, pulling back the weld wire tip to break contact with the panel and allowing the molten drop to enter the gap and form a weld. The steps of contacting, applying and terminating electrical energy, and pulling back are repeated at pre-selected points along the gap until each gap is filled and welded along its length.
It is another object of the present invention to provide a method of manufacturing the elements of a torque arm assembly by attaching spacer elements to the inside surface of one of the metal panels utilizing a cold hybrid MIG welding process to achieve high quality results.
That object is achieved in a method that includes placing at least one metal spacer element at a predetermined location on the inner surface of one of the panels prior to welding the panels. The method further includes the steps of utilizing a cold hybrid MIG welding process by touching the end tip of the sacrificial weld wire of the weld gun to the joint formed at the point of contact between the spacer and the inner surface of the metal panel; applying a predetermined value of electrical energy between the wire and the joint to cause conduction therebetween and allowing the end of the wire to become molten. After a predetermined period of time, the application of electrical energy is terminated and the weld wire tip is pulled back to break contact with the joint. The molten drop falls onto the joint and forms a tack weld between the spacer and the panel. Of course, the steps of touching, energizing and pulling back at pre-selected points along the joint can be repeated if it is desirable to tack weld the spacer at additional points around the joint.
Applying the cold hybrid MI weld process to the tack welding of spacers also allows the manufacturer to utilize dissimilar materials for the panel and the spacer, and therefore allows one to design for the optimization of strength or weight improvements.
The torque arm assembly of the present invention is shown in
Assembly 100 also includes at least one spacer for each through-bolt location. In this case, four such spacers 206, 208, 212 and 214 and are provided in alignment with opposing though-holes 107-108, 109-110, 111-112 and 113-114, respectively. The spacers are hollow metal cylinders and function to maintain the desired thickness of the torque arm assembly and prevent distortion when the through-bolts are tightened. In order to hold the spacers in place throughout the manufacturing process of the torque arm and thereafter, the spacers must be welded to one of the panels. In
The cold hybrid MIG welding method utilized in this invention is described in conjunction with FIGS. 4 and 5A-5C. A modified MIG type welding apparatus is provided with a controllable and movable weld gun 502 and that includes a sacrificial weld wire 504 that is controllably advanced and retracted from a supply spool (not shown). Although not shown, the inert gas utilized in a conventional MIG welder is used in this method also to saturate and protect the weld zone.
One step of the weld method, represented in
Another step in the weld method, represented in
A subsequent step in the weld method is for the application of voltage to be terminated and weld wire 504 to be pulled back or drawn into the gun 502. As is represented in
The period of energy application (i.e., on time of the duty cycle) is determined according to several factors including the material used for the weld wire, the material being welded, as well as the voltage and current produced during the period. Once it is set, it can be repeated for each weld that occurs during each duty cycle (i.e., the period defined by the time between each applied energy step). In this embodiment, it has been found that duty cycles having a 60 HZ repetition rate are desirable, but may be increased as improvements in equipment are made.
During the step in which tip 506 is being placed in contact with surface 104 adjacent gap 302, a downward force can be exerted on the tip. This results in a favorable lateral force on the welding tip.
The same series of steps, as stated above with respect to
It should be understood that the foregoing description of the embodiments is merely illustrative of many possible implementations of the present invention and is not intended to be exhaustive.
