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AWL-Techniek laser welds tracks for car seats

03 October 2013

Harderwijk, September 2013 – Two tracks are placed per seat in every car, each consisting of an upper and a lower part, meaning 8 parts needing to be placed in the average car. Considering that the European automobile industry is still producing more than 10,000,000 cars each year, the volume of tracks is extremely interesting.

AWL has secured a substantial number of projects over the last few months, projects which involve these products being welded in an innovative way. Because of the large numbers, laser welding is being used, a technique which is much faster than conventional welding methods.

AWL first began applying laser welding in 2003, since when it has built up a leading position, particularly in the car seat and body part sectors. But that expertise is different than the expertise needed for laser welding tracks. Laser welding tracks involves specific features which make guaranteeing the quality of the welded end-product a challenge. AWL has done extensive research into the characteristics of the track, the required welding quality and other details. By carrying out the research and various tests, AWL has proven that it is able to make a successful laser weld in the tracks.

Tracks form the connection between the car seat and the base plate and ensure that the seat can slide backwards and forwards, allowing the driver to adjust the ideal position. In the event of a crash, it is essential that the tracks are crash-resistant in order to guarantee the safety of driver and passengers. The track must therefore be able to resist heavy stress loads. To ensure this, larger sheet thicknesses are used than are usual in the design of seats and rests. When laser welding, this sheet thickness results in different welding seams being needed than for thinner sheet, without the heat input negatively effecting the straightness of the material.

Contrary to the lap joints which are normally used for both seats and rests, T-joints and flange joints are normally used when laser welding tracks.

With lap joints the joint between the sheets is relatively narrow. This is not a problem for thin sheets; the width of the weld is sufficiently proportionate to the thickness of the sheet, but a broader joint between weld parts is necessary for thicker sheets. This can be achieved by using the T-joint and the flange joint. The weld joint is thereby stronger than the parts, making optimal use of the material. An additional advantage of the T-joint is that no flange is required for this type of seam, as opposed to the lap joint. This results in material being saved and the weight of the part minimized.

When welding the T-joint and the flange joint, the position where the weld has to be made is extremely narrow. This defines the quality of the weld. There is more margin with a lap joint; even if the seam in not exactly in the correct position, it has no effect on the strength of the welded seam. Welding T-joints and flange joints therefore imposes higher demands on the accuracy of the welding machine.

AWL-Techniek B.V. Visiting adress Nobelstraat 37 | 3846 CE Harderwijk | The Netherlands T. +31 (0)341 411811 F. +31 (0)341 411822 Postal address P.O. Box 245 | 3840 AE Harderwijk | The Netherlands E. info@awl.nl I. www.awl.nl

In extensive research, AWL has shown that it is possible to achieve the required tolerances and good welding results by means of robotised laser welding. However, consideration must be given to the high demands on the positioning accuracy for the weld seam. This precision is achieved by critically testing the complete chain of position-determining parts. This chain consists of the robot with optics, of course, the fixture, the turntable on which the fixture is mounted and the precision of the parts to be welded. Various tests showed that with a T-joint the permitted tolerance on robot movement is extremely restricted, but what was also evident was that this tolerance is obtainable and that extremely good reproducible welding results are achievable.

AWL has now processed its findings in a number of technical measures. The fixture must be so constructed that the parts to be welded are exactly clamped. The robot also has to be extremely carefully programmed with a camera, mounted on the optics, assisting the robot programmer.

In addition, optics should be used with a short focal length in order to optimally utilize robot precision. All this results in good, reproducible laser quality and production of high-quality laser-welded tracks.