New electro-pneumatic welding drive (EPS)
Constant welding force over the complete welding process
Excellent repositioning behaviour, constant welding force, precise adjustment of the welding electrodes, gentle and impact-free electrode placement on the workpiece - the new electro-pneumatic welding drive (EPS) from DALEX Schweißmaschinen GmbH & Co. KG combines enormous advantages with its fast and dynamic properties and ensures excellent welding quality. At the same time, it opens up great energy saving potential for the user - thanks to minimal compressed air consumption and targeted adjustment of parameters.
„A good indicator of the welding quality in resistance welding is the force level during the current flow. The more evenly the force is applied during welding, the better the parts will weld together. If the weld projection begins to melt after the welding current has been applied, the welding force suddenly collapses - a completely normal phenomenon. However, in order to prevent the resulting unwanted weld spatter and an unclean weld, the drive must correct this collapse as quickly as possible and reposition the electrode practically without delay,“ explains Marcel Groß, M. Eng., SFI, group leader for mechanical design at DALEX Schweißmaschinen GmbH & Co. KG
To make this simple and energy efficient, DALEX has developed a new electro-pneumatic welding actuator for resistance welding systems. It ensures an almost constant and effective welding force over the entire weld.
Short cycle times and comfortable operation
The new EPS from DALEX consists of a servomotor linear unit designed as a spindle drive and a tracking unit attached to it, in which a pre-tensioned spring filled with compressed air transfers the welding force to the welding spot. With the servo motor drive stroke, the welding electrodes can be adjusted precisely, quickly and continuously in relation to each other according to the required welding task and component geometry. A speed of up to 200 mm/s can be set. Perfect for achieving a clean weld even with short cycle times.
Marcel Groß: „ For the design of the EPS, comfortable operation was important to us. The user simply adjusts the welding force to the respective task by entering the required values via the user interface. After setting the parameters, the machine control system then automatically determines the spring or welding pressure based on stored sets of characteristic curves and determines the required spring compression. No further intervention by the operator is necessary for this“.
When the welding electrode is fed to the welding point with the linear unit, the „pneumatic spring“ is only subjected to a fraction of the welding pressure, which is defined and set beforehand. This ensures that the electrode is placed on the workpiece gently and without impact. When the electrode is in contact, a sensor in the tracking unit gives the signal to adjust the spring travel until the defined spring compression is reached. Thanks to the pre-control of the pressure, the welding force is already at the required level and the welding process can begin without delay.
High dynamics in the welding process
If the welding projection starts to melt due to the welding current supplied, the tracking device immediately follows, expanding the spring and the welding force acts almost constantly on the welding point. This is achieved by the fact that during the actual welding process only the components directly connected to the tracking unit - i.e. only a very small mass due to the pneumatic spring - need to be accelerated.
A direct comparison of the EPS with a linear drive with additional pressure compensation via elastomer springs clearly shows the superiority of the DALEX system. Both drives were used on a capacitor discharge machine (KE) for welding a ring projection. When the welding force collapses due to melting of the annular projection, the linear actuator only reaches the original force level when the welding current has already fallen to about 20 percent of the maximum (see Figure 2). This means that the welding process is practically completed electrically before the full welding force is available again. The EPS operates much more efficiently. If the welding force reaches its initial value again, the welding current has just exceeded its maximum value and is still around 80 percent (see Figure 3). The welding force is therefore at a uniform level almost over the entire weld.
Low energy consumption and wear
It is not only the quality of the welding that is right with the new EPS from DALEX, the system also has advantages in terms of operating costs: „The pneumatic drive only needs compressed air to adjust the electrode force and only in very small quantities to regulate the pressure of the pneumatic spring. This minimises compressed air consumption and saves energy. Also, only a small amount of air escapes, so that noise is greatly reduced,“ adds Marcel Groß. In addition, welding force and current can be kept as low as possible by adjusting the parameters in a targeted manner.
Because the drive concept also works without sliding seals, but with roller-bearing guides, frictional effects are almost completely eliminated. This supports the high dynamics of the drive and significantly reduces wear.
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