Robot Welding. Exhaust Hanger Brackets and Panasonic Equipment.

For me it was another one of those annoying Japanese, automotive robot applications, thanks to the engineers we had complexity rather than simplicity. After six weeks the Panasonic personnel and Panasonic robot integrator could not get their robot to consistently place two small welds, 15 mm in length on a carbon steel rod to a thin gage galvanealed part (commonly called, exhaust bracket).

The exhaust hanger bracket was designed by engineers at Honda. I am sure the engineer who designed the part had no idea how their MIG weld process ignorance contributed to some of the welding issues generated. The round carbon steel rod was 5/16 diameter and the thin gage, galvanealed bracket the rod was welded to was only 0.047 thick. Think about it, weld penetration concerns for the round component 5/16 thick, and weld burn through concerns for the thin part 0.047.

Poor MIG weld design is common in the auto / truck industry. I have yet to meet a designer who has a weld process expertise. Its a sad reflection today, that few designers of auto components take the time to read about the weld processes they recommend on the parts they design.

The poor weld design of this part was not the only reason for the inconsistent welds attained by the Panasonic robot. After six weeks of playing around with the weld settings, the Panasonic and integrator team could only produce inconsistent weld profiles, welds with porosity, welds with burn through and welds with lack of weld fusion. After wasting thousands on unnecessary labor costs and extensive weld frustration for the robot customer, the robot customer gave me a call.

After spending a few hours of reviewing the welds I made the following observations.

* The welds recommended by the Pansonic personnel and intergrator were too small. The fast freeze, short circuit, undersize welds were the primary cause of the weld porosity. I changed the weld size, this change resulted in more forgiving welds that had less less opportunity for weld porosity, however the welds were still inconsistent.

* The weld inconsistency was readily noted in the arc sounds. This inconsistency was a direct result of the performance of the Panasonic Invertor power source. This power source provides two outputs one for CO2 and the other for argon mixes. With welds that have an arc on time of less than 3 seconds, its important that the weld equipment used has the capability of providing "consistent out put" for the robot weld start data, weld data, and end weld data. This power source could not provide this basic function with the low parameters utilized. I changed the weld mode and settings on the equipment, and was able to find settings that although were not recommended by Panasonic proved to be more consistent. The new data improved the consistency and stability for the small welds.

* The fixture designed by the integrator did not allow for ideal positioning of the MIG gun. As the integrator gave up on his responsibility the changes were eventually made by the customer.

* The Panasonic MIG gun contact tip bore was on the minus size while the USA made MIG wire diameter was on the plus size. Occasionally the MIG wire was restricted by the gun contact tip. I relieved this situation by drilling and increasing the tip bore on the Panasonic tips. I recommended a change to a Tregaskis, North American gun.

* Small welds require a higher degree of weld accuracy. The Panasonic cell lacked an automatic TCP control for the robot. When Panasonic develops one, they will provide.

After all the changes were made and the weld process data was recorded. The robot process control program was implemented. After seven weeks the robot finally attained consistent welding results. However thanks to the designer that recommended galvanealed parts 0.047 thick, and round hanger bars rather than square bars, this part will always create a challenge and generate concern with the company producing these parts.

FOR MAJOR AUTOMOTIVE MANUFACTURES, AUTO PART DESIGNERS AND WELD PROCESS IGNORANCE MAY RESULT IN WELD PROCESS BLISS, HOWEVER FOR THE SUPPLIERS OF WELDED PARTS, DESIGN AND WELD PROCESS IGNORANCE CAN SOON TURN INTO WELDING NIGHTMARES.