Valk Welding: 2000

The Honda plant in Aalst was established in 1963 to produce motor cycles, involving the machining of steel, and hence welding was done manually and with robots. In 1985, the plant was converted into a supplier for Honda and Rover, supplying dashboards, fuel injection systems and very recently drive systems.

In '98, the production of the new Honda Accord was started. For the first time ever, the dashboard of this model has an integrated steel safety frame, providing extra protection in case of a side impact. This resulted in a totally new design of the dashboard and … welding again became important. Together with the Japanese mother company, a robot cell was designed, containing two integrated Panasonic robots (supplied by Valk Welding). This robot cell started working in April 1998. Recently, a wire problem was solved by using a new wire transport system that was developed by Valk Welding.

The Technical Management spoke about the welding cell and the renovation with Johan The Vuyst, manager engineering and maintenance of Honda Belgium in Aalst.

Robot welding
The base for the new dashboard of the Honda Accord is a rod system consisting of 23 parts, assembled by MIG-welding under CO2 protection gas. Because the management is of the opinion that no constant quality can be guaranteed if such structure is not welded by robot system, a robot cell was developed for this job containing two robots that simultaneously weld one part. The parts are clamped by the operator in a jig and welded by the robot without manual position welding. In the meantime, the operator has the time to clamp the parts in the second jig (clamping is done with pneumatic cylinders), resulting in a production time of 120 seconds.

The robot cell that started working in 1998 in Aalst, was adjusted using Japanese engineering. That is why the robot has another structure than most "European" automatic welding cells. A European welding robot mostly consists of the welding robot(s) and a turn table. On one side, the operator prepares the pieces, and the robot will weld them on the other side. When the piece is welded, the table turns,  while the robot is stopped. And that can take some time: at Honda the jig weighs 700 kg.

In Japan they are of the opinion that machines must deliver maximum performance. That is why the robots are put in one cell and two shuttle tables with a jig mounted onto them are used to move in and out of the cell. Once the robots are finished welding, the new part is ready at the other side of the robot, and hence no welding time is lost. The table with the welded pieces leaves the cell, can be unloaded and again loaded with new parts and again move into the cell; the table is ready when the welding robots have finished the other part.

Feeding problem with welding wire
With such a structure with one welding cell and two moving tables for the workpieces, feeding of the welding wire has to be done from a certain distance. From the wire drum (drums of 200 kg and a wire thickness of 1.2 mm) to the welding torch, the welding wire has to be transported over 6 m.

At first, the supplied metal flexible tube was used thereto. However, due to the movements of the robot this often resulted in the wire guide being twisted and worn wire at the feeding points. As a result, the wire could suddenly get blocked, wire feeding started jolting, leading to bad welding quality. This did not happen frequently, but mostly at times when no production loss could be afforded (the robot cell was already working in two to three shifts per day, hence there was little space for defects).

During the Welding Week in the Bouwcentrum in Antwerp October last one of the collaborators saw the new Wire Wizard system of Valk. And Honda is always open to new things; they already found and implemented an improvement to avoid contamination of the gas tube, due to which cleaning the gas tube no longer led to downtimes. In the case of wire guides, money was invested to mount the Wire Wizard system on one of the two robots.

Solved with better wire guides
With the Wire Wizard "weld wire dispensing" wire guide system, the complete wire transport between bulk packaging and wire feeding systems to welding robots is done in an efficient way. A steel guide sleeve was replaced by a more flexible synthetic tube provided with a patented Teflon coating. This coating is applied on all contact areas of the tube, resulting in minimum frictional resistance during wire transport. Wear and tear of the wire is strongly reduced, even completely avoided. The application of this coating also resulted in a faster wire transport.

In addition, the wire guide system contains flexible couplings, due to which they can turn, and the Teflon sleeve can no longer be twisted. Finally, the cone form cover contains a turning wire guide, so that the wire ends up in the Teflon flexible in one streamlined movement. Wire feeding will no longer jolt. This seemed to solve the problem, and a second system for the second robot was purchased.

One problem remained, namely to install the wire guide in the cover of filled drums: there was not enough space to do this in a practical (and fast) way. As a solution, a cylindrical spacer is fitted on the drum between conic cover and drum. This should solve the problem.

(Source: Technisch Management - January 2000)