New developments in advanced welding
Electron beam welding machines
Apart from the further development of beam generators, adaptation of the equipment to varying demands is of considerable importance to the industrial applications of electron beam welding. For example, the evacuation times in the vacuum chambers may be reduced so that the welding downtimes do not deter the use of electron beam technology. Different working chamber systems are currently available to equip electron beam welding machines.
The most flexible variant is the universal working chamber where the workpiece is moved in two or three directions. Revolving devices with horizontal or vertical axes of rotation can be used instead of an NC coordinate table. Typical chamber sizes are from 0.1 m3 to 20 m3 and some machines can have a chamber volume of up to 3500m3. However when using vacuum chambers there can be comparatively high downtimes because such procedures as ‘clamping the tool’, ‘entering the recipient’, ‘evacuation’, ‘welding’, ‘airing’, and ‘workpiece release’ must be carried out one after another. Figure 7.8 shows a typical 2.5 m3 chamber with an x-y-coordinate table.
In order to fulfil the demand for shorter cycle times, machine systems such as double chamber machines, lock chamber machines, cycle system machines and conveyor machines have been developed.
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7.8 2.5m3 universal vacuum chamber. |
7.3.2 Double chamber and lock chamber machines
Double chamber machines have two working chambers that are placed side by side. The beam generator is either moved between the two chambers or the beam is deflected to one chamber at a time. Thus welding may be carried out in one chamber while the other chamber is loaded or discharged as well as evacuated. If the welding time exceeds the workpiece change and evacuation time, the capacity of both chambers is fully utilised. A disadvantage of these machines is that both chambers have to be equipped with separate movement devices and pumping units. Figure 7.9, left, shows one of the variations of a double chamber machine.
The lock welding machine is illustrated in Fig. 7.9, right. A high vacuum is permanently maintained in the chamber where the welding is carried out. Manipulation devices pass the workpieces through one or two prechambers. The machines have a position for loading and discharging, a lock for airing and de-aerating and a welding lock (von Dobeneck et al., 2000). Figure 7.9 shows one type of a lock welding machine system.
7.9 Double chamber and lock chamber machine.
7.3.3 Cycle system machines and conveyor machines
Cycle system machines are suitable for welding similar parts with equal weld geometries and axial welds; an example is shown in Fig. 7.10. Underneath the chamber is fixed a rotating jig, usually small-volume and demanding only short evacuation times, with vertical, horizontal or swivelling axes; this jig is equipped with one or several loading stations. This means that loading and discharging as well as welding may be carried out at the same time. In new cycle system machines there is a low vacuum in the area where the jig rotates all the time. This leads to shorter evacutaion times from free atmosphere to low vacuum at the loading position and from low vacuum to high vacuum at the welding positions, as shown in Fig. 7.10, right.
Small, workpiece adapted vacuum chamber
7.10 Cycle system machine (Source: PTR).
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Electron beam welding 209 |
Conveyor machines are now available on the market especially for the manufacture of saw bands. This type of equipment is very productive but also very inflexible. Conveyor machines work on the the same operating principles as do lock welding machines. The workpiece is continuously transported over centring lips through the pressure locks into the working chamber and from there through a pressure lock. Any inevitable leakage is compensated by the vacuum technique.
