From innovation to production
The relationship between the Alutech and Fronius welding experts is ex-tremely close. As the number of contact tubes required, and subsequent replacement on the automated welding systems in the production depart-ment, was very high (approx. two per shift), they were already swapping ideas on the new contacting system prior to the official presentation of Con-tec at Schweißen & Schneiden 2009. This was necessary as replacing con-tact tubes has serious side effects. Each change negatively impacts the work flow, process parameters may change, which in turn also affects process reliability. "This is comparable to the welding wire. In the past we fed it off a spool, then off a large spool and now we take it out of the drum. This mini-mises contamination, modifications to the wire-feed unit and especially inter-ruptions. The desired result is problem-free operation", explains welding expert Alexander Ottino on the practical progress that has been made.
For tests that are carried out before series production, SAG uses its own well-equipped technical centre. Robot welding cells with TIG, CMT and TimeTwin systems test alternative or new hardware and technologies. It was here that Contec had to first prove its capabilities, especially for the sensitive welds of air cell systems. "Our advantage is that our processes run problem-free. We were therefore able to concentrate on the differences between con-ventional contact tubes and Contec. One expectation was to achieve at least a fivefold increase in service life", recalls Wasle, the former Head of Devel-opment.
Concrete production task - air accumulators for premium vehicles
From premium saloons and sports cars to special commercial vehicles, great comfort is achieved from pneumatic and self levelling suspension. SAG and its subsidiary Alutech produce air accumulators for these systems as well as for use in braking systems on HGVs and rail vehicles. Technical require-ments include excellent resistance to corrosion, a lightweight design, the requisite amount of strength and good leakproofness (see box). When func-tioning correctly, they bring greater comfort, safety and environmental protec-tion. Depending on the design specifics of each vehicle, the accumulators can be manufactured with circular cross-sections or special profiles, in cus-tomised shapes or comprise Thixoforming parts produced by SAG. The ac-cumulators can also perform additional functions if attachments are welded on. They are suitable for operating pressures between 10 and 25 bar, and for burst pressures of up to 100 bar. The service life of the accumulators ex-ceeds that of the vehicles and they are 100 % recyclable. Common materials used at Alutech are AlMg3 or AlMg4.5Mn. The wall thicknesses are from 2.0 to 3.3 mm. Other marginal conditions when welding are similar filler metals or 1.2 mm diameter wires and argon as the shielding gas.
During testing in the technical centre, the Alutech and Fronius welding ex-perts optimised the technical details to the layout and design of the contact-ing system. Dr. Wasle adds: "The route from innovation to complete and flawless integration in the mass production line is often one long experiential and optimisation process. It's especially positive if there is constructive com-munication between the developer and the user. This successful concept of giving and taking very quickly produced the result we wanted. We can now safely assume that we'll reach the tenfold increase in service life. Perhaps we'll achieve even higher values by working together with Fronius." The quantitative and qualitative improvements also make a significant positive difference. In addition to fewer rejects, the improved contact between the welding wire and the contact shells also minimises the standard contact tube problems. Direct effects include a more stable arc, fewer pores and a subse-quently better leakproof properties.
It is also important to SAG, a supplier to the automotive industry, that the changeover to Contec does not mean a change in process. Such a change would have separate organisational, time and financial implications. It is therefore looking very likely that all welding cells in Lend, each with two CMT systems, will soon also be changed over to Contec.
SAG Motion and Alutech
The Salzburger Aluminium Group (SAG) AG is a leading international sup-plier of (aluminium) components for the automotive, aviation and rail vehicle industry. Another area of expertise is found in high-performance materials and molded parts (e.g. also following the Thixoforming process) for different industries. Energy storage and energy management systems represent the key activities of the subsidiary Alutech.
The group is divided into the SAG Materials and SAG Motion divisions. One of the 7 subsidiary companies of SAG Motion is Alutech GmbH. Based in Lend and Schwarzach-Pongau in Austria, Alutech also develops and manu-factures air cell and air suspension systems. Crucial to functionality are the welded pressure-resistant containers for compressed air, liquid fuel and hydraulic media.
From the contact tube to Contec
The geometry of a contact tube must be designed such that contact is only made towards the front of the tube. The welding wire should not melt prema-turely between the friction-heated point of contact and the arc. Secondly, the contact zone in its axial elongation should on the one hand be short enough that no arc variations occur when the point of contact is changed, and on the other hand, it should be long enough to minimise wear. This means that the desired target state is obtained with a contact surface that is as large as possible but no larger than required. Thirdly, the contact surface between the wire and contact shells should be constructed in such a way that optimal contact with the wire is achieved, but with minimal wear. As low as possible and as strong as required is the motto applied here too.
Contec provides the optimum contacting system geometry to fulfil these criteria. Two different external conical half shell elements with an interior cavity separate the welding current into two paths. At the same time they guide the welding wire, in which the separated welding current flows together again. The adjustable force of a spring pushes both half shells together and onto the wire passing between them. The design is such that the material is subjected to wear only at the front and in the middle during operation. As wear takes its toll, the conical half shells are gradually forced inside one another, while still making good contact with the wire in the intended area thanks to the defined spring force. The wire between them is still gripped with an even force without the outlet being subjected to bell-type deformation and without the contact surface being shifted backwards.
A standard unit of measure for leakproofness is the leak rate. It notes how much gas per unit of time escapes, or may escape, from the container. The permitted leak rate for the air accumulators is 1.6•10-4 mbar l/s. This corre-sponds to ½ millilitres an hour, or 12 millilitres a day.
Fronius International GmbH
Fronius International is an Austrian company with headquarters in Pettenbach, other sites in Wels, Thalheim and Sattledt, and production facilities in the Czech Republic and Ukraine. Fronius is active in the fields of battery charging systems, welding technology and solar electronics. The company employs 2,677 staff worldwide, 1,923 of whom are based in Austria. 93% of Fronius products are exported through its 14 sales subsidiaries, two agencies (Turkey/welding technology and China/solar electronics) and 130 sales partners around the world. 14.9% of the total turnover of 329 million Euro is re-invested (financial year 2009). With its outstanding products and services and 649 active patents, Fronius is world technology leader. 358 employees work in research and development.
Fronius International GmbH
Froniusplatz 1, A-4600 Wels
Tel. +43 / (0)7242 / 241 2590
Fax +43 / (0)7242 / 241 95 3940