Perfect cold welding of hot exhaust system parts

Cloos CP process provides significant advantages

The new CP welding provides high welding speeds with low heat input into the component. (Photos: Dieter Holler/Cloos Schweisstechnik)
(PresseBox) ( Haiger, )
The company PWS, who are located in the town of Struthütten in Westphalia, have strengthened their market position providing components for the automotive industry. They have also proven that even in a high-wage country like Germany healthy company growth can be realised through a network of system partners and high-tech production technology. The latest evidence of opportunities for effective co-operation between the system supplier and manufacturer is the innovative CP welding process which was integrated into series production in record time by the manufacturer Cloos and the end user PWS.

Any company in Germany wanting to produce exhaust system parts for international automotive manufacturers competitively has to come up with something special. "We specialise in the hot side of exhaust systems", Michael Jud, technical managing director of Messrs. Presswerk Struthütten GmbH explains. "Here the parts for the manifolds must withstand hot exhaust gases of up to 900 degrees over many years without any problems occurring." These requirements can only be fulfilled by using high-quality materials, optimum design and the appropriate production technology. PWS therefore only use stainless steel plate for these "hot products".

"In order to be able to respond to the cost pressures from the automotive manufacturers, we first modified the parts to enable them to be produced as punched parts and not by using the costly hydroform technology", Jud explains. However the welding technology requirements increased so considerably that PWS could not achieve the required quality and production throughput with the conventional process. According to Michael Jud: "These three-dimensional punched parts with plate thicknesses of around 1 mm naturally show very different gap dimensions". "In addition the automotive manufacturers demand spatter-free components because under the extremely hot conditions spatter can be released in the exhaust and destroy the catalysers for example."

As the processes of different manufacturers did not produce the required results, PWS decided on the new Cold Process (CP) from the Cloos welding specialists in Haiger. This process was adapted for the customers' requirements within a record time of about two weeks. "This emphasises the importance for complex processes of having the system partners located close by, so that improvements can be quickly achieved," Gundolf Braun, the commercial manager of PWS, says. "With a functioning network of system supplier and manufacturer even Germany can compete successfully in the international marketplace." But naturally the abilities of the service partner play a major role. "Here we are well looked after by the Cloos representative Lixfeld in Siegen."

Cold Process (CP): colder, faster, better

While current pulsed arc welding processes are unipolar / positively poled, the Cloos Cold Process uses changing polarities. Thus the relative heat input in the wire electrode or workpiece becomes controllable. This results in a considerably reduced heat input in the weld and in the welded material itself. This again reduces component distortion and the problem of crack formation which for example with exhaust system components on cars would lead to many complaints. "Since CP welds are nearly spatter-free, rework on the components is considerably reduced," Gundolf Braun explains, who, in his commercial function, always keeps an eye on the costs.

Whether high-strength sheet steel, aluminium or thin stainless steel plate - the Cold Process can join materials of up to 3.5 mm wall thickness with as low as possible heat expenditure. In the pulse phase there is maximum spatter-free deposition from the wire. During the negative phase the arc surrounds the wire end, directing the heat into the wire and cooling the weld pool. Due to the lower heat input with the "Cold Welding Process" penetration is minimised, resulting in a significant reduction in surface discolouration. Even in the case of coated plate the surface remains in good condition.

Better gap bridging ability - higher weld speed

"Another benefit is the improved gap bridging ability which enables our punched parts to be welded", explains Tim Oppermann, who is in charge of welding technology at PWS. A tour of the production department shows what he is talking about: the two punched / extracted T half shells of stainless steel plate have differing gap dimensions from 0 to more than 2 mm when assembled. "However with CP there's no problem."

At the same time the Cloos Cold Process makes considerably higher welding speeds possible, resulting in shorter cycle times in production. At present, PWS manufactures about 15,000 manifold components a month. Mr. Oppermann knows from the many tests and optimisation trials with other processes that "this is only possible with CP". This new process achieves welding speeds of an astonishing 2.2 meters per minute - even with the complex PWS components which have welds with numerous bends and narrow radii. The manufacturer's and customer's experts will not give exact details but under certain circumstances it is possible to achieve twice the speed.

Production cell - compact and complete

The PWS operator is kept extremely busy operating the Z2 compact production cell with its two stationary work tables. While he unloads one finished component from the first work table and loads two new half shells, the ROMAT® robot is already welding again at the second work place.

"This production cell enables us to react extremely flexibly to the requirements of our customers", Michael Jud says. On an area of only 3.90 x 2.25 m the Z2 contains all the necessary components such as a ROMAT® 320 robot with water-cooled welding equipment, Duo Drive wire drive unit and torch clean unit. The ROTROL® controller and the Quinto CP pulsed arc power source are also mounted on the base frame. The cell has a protective housing with integrated safety technology. On the front side the two work tables are located behind two sliding doors which are opened alternately. "When welding is complete, the door opens automatically and the operator can remove the finished component".

Conversions for other components can be carried out very quickly via the user-friendly operating surface of the ROTROL® controller and the co-ordinated characteristic curves of the Quinto CP pulsed arc power source. For this purpose this modern system has the so-called TSM, True Synergy Mode, which enables suitable welding parameters to be easily called up for the relevant component. "It is only in this way that we can achieve the required quantities for the different manifold parts" Gundolf Braun emphasises.

The complete cell can be easily moved via forklift truck if any changes to the production run are required, as the appropriate facilities for transportation are located underneath the base frame. The cell only needs to be connected to the electric supply, compressed air and shielding gas to be ready to work. The PWS experts use an argon/oxygen mixture with 2% O2.

According to Managing director Michael Jud: "The decision for the Cloos Cold Process was the right one in all respects because we produce parts which are technically and visually fault-free and we have been able to significantly increase output due to fast welding and minimal rework." Being near to the manufacturer also proved to be very positive. Hardly surprising then that Cloos have now delivered the fifth robot welding system to Struthütten.

The PWS group -
Partner for difficult forming and welding technology

Founded in 1939 as a tool manufacturing company for forming equipment, the PWS group today consists of the Presswerk Struthütten GmbH, the Werkzeugbau Struthütten GmbH and the AST Apparate und Schweisstechnik GmbH. This technology network specialises in the production of metal based components, the forming of which constitutes a serious challenge and requires complex welding tasks. As a system partner Presswerk also offers solutions in the field of wire and pipe brackets, hydro forming and the provision of operating resources. The efficiency of the group can also be seen in the achievement of certification to TS 16949 by the automotive industry. The company, based in Siegerland,produces exhaust system parts and turbo-supercharger steering boxes for various brands, silencer covers and brackets for BMW motorbikes, catalyser reinforcements for Opel, exhaust manifolds for Porsche and Toyota and shielding plates for DaimlerChrysler. The electrical and the mechanical engineering industry are also part of the growing PWS customer base.

The group-owned tool manufacturer produces about 70% of the tools for Presswerk. High quality, strong prototype development and short optimisation times are the advantages of this concept. The third business division AST provides customer-related solutions in the field of pressure tanks, heat exchangers and agitator tanks with the main emphasis on complex welding tasks.
In a production area of more than 5000 sqm approx. 130 employees achieve an annual turnover of more than 20 million Euro. About a third is attributable to exports.
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