, Plzeň, Czech Republic, EU

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1 PRO-BEAM TECHNOLOGY - HEAT TREATMENT OF METALS Václav HOŠEK a, Filip VRÁBLÍK a, Uwe CLAUß b, Pavel STOLAŘ a a ECOSOND s.r.o., Čerčany, Czech Republic, EU, ecosond@ecosond.cz b pro-beam AG & Co.KgaA, Neukirchen, Germany, EU Abstract This paper deals with electron beam technology as a technology for heat treatment of metals. In the field of applications belong welding, hardening, drilling, alloying and coating. Wide range of material could be treated: (steel, steel alloys, aluminium, titanium etc.). The process of electron beam heat treatment and its advantages were discussed, examples of applications were shown. 1 INTRODUCTION The electron beam as a quasi mass free power source has over the years developed into a flexible and economic manufacturing tool. Due to the deep welding effect the electron beam is able to generate narrow welds with minimum thermal distortion. With the advanced development of computer control the number of electron beam applications has significantly increased. For the EB welding technologies new applications have been developed, where material combinations unweldable until recently can now be welded without the usage of welding consumables. Fast beam deflection enables beam splitting in order to process with up to 60 beams simultaneously - multibeam technology, or multiple processes like heating and welding - multi-process technology. For drilling applications the parameter range has increased to larger drilling diameters up to 2 mm and thicker material up to 10 mm. As of today, the electron beam has developed into a truly software controlled manufacturing tool with high efficiency and excellent reproducibility. Technological data gathered during the process enable quality monitoring and support to improve the testing process of the manufactured components. 2 MULTI-BEAM TECHNOLOGY Multi-beam technology is the ability of the electron beam to be split up into independent beam spots placed at different locations. Because of the fast deflection of the electron beam it is possible to leave the keyhole and return after a specific period of time without collapse of the keyhole. Requirement for the technology is a high bandwidth function generator and beam control electronic in order to achieve accurate timing and positioning of the electron beam. For industrial applications the multi-beam technology is already successfully used. Welding of diesel particle filters with up to 60 welding pools significantly reduces the processing time and resolves problems with thermal distortion of conventional single spot welding technologies (Fig. 1.). In particular, gear welding for automotive gear boxes benefits enormously from multi-beam welding (Fig. 1.). Numerous applications in automotive industry already use the multi-beam technology, like the adjustable turbo charger component (Fig. 2.). All 8 circular welds are performed simultaneously. Not only the welding time is reduced by 2/3, but also the radial deformation of the gears, caused by thermal distortion, improved resulting in better concentricity and less noise emission of the gear box.

2 Fig. 1. Particle filter welded with 60 simultaneous beam spots (left) synchronizing gear of automatic gear box welded with three electron beams (right) Fig. 2. Multi-beam welding, turbo charger control ring (left) heat exchanger (right) For surface treatment the multi-beam technology opens up a wide range of applications. The ability to position specific amounts of energy onto particular areas of a parts surface is used for selective hardening and surface modification. Fig. 3. Beam deflection patterns for multi-beam EB welding and hardening Possible beam deflection patterns for welding and hardening applications are shown in (Fig. 3.). The ability to deflect the beam into practically any form of geometric pattern and the correlated control of the power density by controlling the beam current enable exact predefined hardness patterns (Fig. 4.).

3 Fig. 4. Mikrographs of solid phase hardened cam (left) face of extruder screw (right) 3 MULTI-PROCESS TECHNOLOGY The multi-process technology uses the capability of the fast electron beam deflection to split the beam into individual beams performing different processes. Besides welding the electron beam can be used for preand post-heating and cosmetic treatment of the weld bead. For example, part of the electron beam trails ahead of the welding beam as preheating pattern in order to increase the temperature of the joint (Fig. 5.). Fig. 5. Multi-process technology side view of the beam arrangement (left) top view with separation of spots (middle) weld profile of multi-process weld (right) The main welding beam then penetrates the joint and performs the weld. That opens up a wide field for innovative process developments. Implementations of the technology are used for the development of a welding process for welding of cast iron material without external preheating or filling material. By selective, simultaneous heating at different locations, significant progress could be established in avoiding pores and cavities. Further interesting applications are elimination of hot cracking for welding of blank sheets. The tensile stress of the material in the mushy-zone forces the weld to crack. By compensating the force cracking can be avoided. The internal compensating force is generated through thermal expansion caused by a heat spot lagging behind the main weld spot (Fig. 6.). Practical tests, where the plate was clamped on one side, demonstrated positive results in avoiding hot cracking. Fig. 6. Elimination of hot cracking: weld beat is forced to crack due to tensile force (left) internal force of additional heat spot compensates the tensile force (right)

4 4 APPLICATIONS By means of electron beam is possible to weld aluminium alloys without pores, copper up to 50 mm depth or perform joining two dissimilar metals, like bronze and steel. In addition to it the processes are carried out in vacuum, which enables to weld reactive materials. Interesting applications (Fig. 7.). High power density and high temperature ensure high quality of welding joint. Welding depth is ruled by power of the generator. Welding rates reach from a few mm/s up to 1 m/s. The EB technology is suitable to solve challenging welding tasks in aerospace industry, series production of automotive safety parts or large-scale parts for shipbuilding industry. Fig. 7. Examples of different EB welding joints Bronze/steel, 30 mm Aluminium, 40 mm Copper, 35 mm Stainless steel, 2 mm 4.1 Welding of titanium parts for turbines A very strict quality control has always been required in branches like aviation, space and nuclear industry. In the last years also in mass production like in the automobile industry the quality requirements have immensely been increased. On the other hand we observe that in aviation and space industry also more and more automation of processes is requested. On one hand the cost pressure requires higher efficiency in production in this branch as well, but also the quality aspect drives automation. The individuality of the human hand is taken out of the process when it is operated automatically, with the result of a more stabile quality. More stabile process control allows a closer move to the edge of the technical feasibilities of process development. Modern production in some cases has meanwhile simply gotten to complex to be manually controlled by a human hand. As an example for modern production in aviation industry in (Fig. 8.) a machine is shown that produces front bearing housings (Fig. 8. front right side) for aircraft engines. The machine produces that kind of components fully automatic with significant reduction of production time. With higher stability of the process the need for repair welds could be significantly reduced. Fig. 8. (Left) Electron beam chamber machine for the aviation industry. (Right) Front bearing housing produced by automated EB-welding to be used in the engines of the A380

5 4.2 Low destortion EB welding in automotive industry Well known is EB welding of gears (Fig. 9.). The main advantage is, that welding process can be carried out as a last step in production cycle of gears, shafts or flanges. The design of the parts to be welded should prefer, regarding the low distortion, radial welds with full penetration. Nevertheless axial welds are more common in gear fabrication design as the parts are more cost effective to produce. In order to achieve symmetric shrinkage and thus avoid offset of the axes, simultaneous welding with three symmetric beams is an innovative solution. In materials that become hard and brittle after welding, the accumulated internal stresses may result in cracks. Therefore especially narrow seams welded with low power and low speed are preferred. Fig. 9. Gears, low distortion using the multi-beam welding EB technology 4.3 Small parts welding Highly sensitive parts like valves and sensors can be welded with EB technology as well. Two adverse requirements by EB welding of pressure sensors for Common Rail systems are needed to be fulfilled (Fig. 10.). Because of high pressures up to 2000 bar it is necessary to produce deep welds. At the same time the heat transfer into the weld should be minimalized. The only possibility is very narrow weld produced by electron beam. Deep/wide proportion can be reached 12:1. Fig. 10. Sensors are especially sensitive to temperature and distortion 5 CONCLUSIONS The development of multi-beam processes has not only made EB-applications faster and more precise, it has also made the EB equipment a lot smarter. Without jeopardizing product quality it reduces the dependence on qualified operators, which increase labor costs or often are not available. Summarizing, the described new developments strengthen the leading position of EB-welding as an ambitious and highly qualified welding process and result in a considerably improved productivity. Its position in economic competition has been strengthened and will further increase with new features already in development. As it

6 has been described above overriding advantages are the savings in processing time, high reproducibility, absence of welding consumables and simplified components design. But also improved quality, resulting in increased yield and lower costs for quality measures are beneficial. LITERATURE [1] Löwer T., von Dobeneck D.: Neue Verfahren in der thermischen Materialbehandlung mit dem Elektronenstrahl durch eine quasi trägheitslose Strahlbewegung, New methods in thermal material processing with the electron beam as a quasi inertia free beam deflection, 6th International Conference Beam Technology, 2004, pp [2] Böhme T.: The Electron Beam as a versatile tool for welding and drilling of aircraft components, Applied Production Technology APT 07, 2007 [3] Menhard C., Löwer T.: The electron beam geometry Definition, measurement and significance for the welding process, Welding and Cutting, 2009, 8, 3, pp [4] EN ISO Acceptance inspection of electron beam welding machines, part 1 6, July 2000