Valk Welding: News

At Caterpillar Work Tools, NL, they would certainly agree with this sentiment; automation of thick metal plate welding has proven to be very worthwhile. Bucket components, incl. blades and top boxes, are welded by robot with a 24mm throat (a = 24mm in multilayer) in only 40% of the manual time.

There are relatively few examples of welding automation where it concerns processing of thick metal plate. The physical size of the system and the large investment required often pose a major hurdle. However, implementing automatic welding for smaller components rather than for complete assemblies can prove to be worthwhile and furthermore, can improve quality considerably.

At Caterpillar Work Tools in 's-Hertogenbosch, NL, they would certainly agree with this sentiment; automation of thick metal plate welding has proven to be very worthwhile. Bucket components, including blades and top boxes, are fillet welded by robot with a 24mm throat (a = 24mm) in 40% of the time. Welds are of higher and more consistent quality and the process requires less handling.

The complete system including programming application is supplied by Valk Welding. Peter Lauterslager, manufacturing engineer at Caterpillar Work Tools, had a stringent set of requirements.

Companies fabricating thick metal plate (> 25mm) are more than aware of the issues involved in welding such materials. The heat generated during the welding process causes material deformation, which in turn results in size discrepancies. Pre-heating and balanced welding are the best-known remedies in the welding arena. In addition, large fillet weld throats are often specified, which require multiple layers. Six layers are no exception. Quite often, welding must be carried out in a flat position because of the high fluidity of the weld pool.

A Panasonic welding robot welding a top box. (Photos: Erik Steenkist)

Welding By Hand is Heavy Work
Such procedures require a great deal of effort by someone welding by hand and temperatures above the welding area can become extremely high. Interruption of the welding process or too high an interpass temperature can lead to excessive power density, which can be detrimental to material properties and can result in sudden failures. In short, under such circumstances, welding by hand requires a lot of effort and is no guarantee for consistent quality.

This was reason enough for Caterpillar Work Tools to invest in an automated robotic welding and handling system. Their plan was to set up a production workcell for small-batch, customized buckets.


Bas van Haagen, Valk Welding, (left) and Peter Lauterslager, Caterpillar Work Tools, next to a CAT bucket.

For manufacturing engineer Peter Lauterslager, it was clear that welding a complete bucket was an ambitious plan. “Most of the work is involved in hand welding the sub-assemblies, so the implementation of robotic welding already generates a major saving on man-hours and makes the scope of the system somewhat more manageable. Valk Welding took our requirements for flat and balanced welding, pre¬heating, product handling and flexible programming, and came up with a workcell design with one track-mounted Panasonic VR robot serving two clamping beds where bucket blades and top box are welded in succession.”

Peter Lauterslager inspects the size of the fillet weld throat on one of the bucket blade teeth.

Dual-Axis Manipulator
Valk Welding incorporated a drop centre manipulator to facilitate a wide range of manoeuvrability for the heavy components during welding. The manipulators ensure that the component’s axis of rotation remains centred allowing the welding robot to weld in the weld pool. This range of manoeuvrability allows components and welding robot to move unhindered to the next reversed position, such that heat generation is evenly distributed. Balanced welding is then simply a question of configuring the program settings for the correct welding sequence.

The bucket blades and teeth are made of a wear-resistant material, which requires precision welding. During welding operations, the temperature may not exceed a set maximum, the interpass temperature, and the material must not be allowed to cool too rapidly. For this reason, the blades are pre-heated to 110°C. Valk Welding developed a special burner carriage, which is automatically deactivated on reaching the target temperature by an infrared temperature sensor mounted on the welding robot.

The welding workcell being set up at Caterpillar Work Tools in ‘s-Hertogenbosch.

Extreme Fillet Weld Throat Size
The Caterpillar Work Tools engineers specified fillet welds with a throat size of 24mm (a = 24mm) for attaching the teeth to the blade. Such an extreme throat size is quite exceptional and can only be achieved in multiple passes. The correct deposition rate places an important role in this process. To prevent the wire from burning out, the arc’s power density may not exceed 1.5kJ.

Based on trial and error, it was determined that a 1.4mm diameter wire and a 500A power source formed the optimal configuration to lay down the specified fillet weld in twelve passes. It is not possible to make twelve passes consecutively, but instead tooth by tooth and then layer by layer.

Peter Lauterslager, “It used to take more than eight hours to weld the bucket blade by hand, and due to a shift change mid assembly, the component always used to cool down and would then have to be re-heated. From now on, components must be welded in one go. The welding robot welds the sub-assembly 60% faster, so reaching that goal is easily achieved.”

“The welding robotwelds the sub-assembly 60% faster.”
Despite the fact that all the components are small-batch, customized runs, there is still a fair degree of standardization across the product range. For example, the teeth may be the same from product to product, but the positioning can vary greatly. Peter Lauterslager, “For this very reason, we use a programmable system. We create a subroutine for welding a tooth and then apply this subroutine wherever a tooth needs to be positioned. That saves on a lot of programming. Using this offline programming application, you have total flexibility and you can rapidly implement numerous variants. What’s more, you can simulate the whole welding process offline.”  
 

Detailed view of a twelve-layered fillet weld on a top box.

"Look for interrelated products”
Peter Lauterslager, “I think that a lot of companies in our industry are put off the idea of robotic welding because of the investment and technology involved. You do not have to be a rocket scientist to implement a robot into your production line, but it is essential that you are aware of the limiting factors. Always ask your supplier for advice about what is and what isn’t possible. It is just as important to understand precisely what benefits can be derived. Robotic welding is ideal for repetitive work, so look for interrelated products. Robots provide a higher and more consistent quality, and a shorter turnaround. The operator isn’t just a 'button pusher’; during welding operations, he can perform other duties within the production workcell so that his time is usefully spent.”

Competitive Advantage over Low-Wage Countries for One-Offs
‘s-Hertogenbosch based Caterpillar Work Tools concentrates on one-offs in a range of products including hoppers, backhoe buckets, grapples, shears, mechanical pulverizers etc. Peter Lauterslager, “Standard models are manufactured in Caterpillar’s Hungarian production plant. That plant is totally dedicated to high demand products and mustn’t be mixed with one-off, customized production work. That’s our speciality here in Den Bosch. In terms of one-offs and quality, we still have an edge on low-wage countries. We compensate for our higher labour costs with automation.”

(www.caterpillar.com and www.valkwelding.com)

Source: Metaalmagazine september 2006