When the Swiss market leader for powerful gear pumps plans the overhaul of its manufacturing operations, everything is going to be called in question. The production of high-pressure displacement pumps calls for maximum precision. At the same time the greatest possible flexibility needs to be maintained in the turning and milling of the various components for the different product variants. The combination of a DMG / MORI SEIKI processing centre with a powerful clamping chuck from RÖHM for high table loading was the solution chosen by Maag Pump Systems, and has been giving the company the desired flexibility and enhanced productivity since January. Up till the point of decision, the pump experts' deliberations had proceeded consistently on two parallel tracks.
'Critical for the decision in the last resort was the compact design of the machine, and the perfect dovetailing offered by the clamping chuck solution,' stresses Bruno Lutz, a programmer at Maag Pump Systems AG. Up till this point he and his brother Thomas Lutz had consistently investigated two possible options for transferring the manufacture of the pump components from the old processing centre, now more than 20 years old, to a new machine. 'Turning machines that can also perform milling operations came into consideration, as well as milling machines capable of turning,' explains team leader Thomas Lutz. Since January a DMC 80 FD duoBLOCK processing centre from DMG MORI SEIKI, capable of both turning and milling and equipped with 3-jaw Duro-T-500 key bar chucks from the clamping specialist RÖHM, has been giving the engineers in Oberglatt every cause for satisfaction. With just two easily effected clamping operations, unfinished parts weighing up to 550 kg can be processed into precise slide bearings, flanges and spiral gaskets for maximum-efficiency pumps. The processing time involved in turning, milling and drilling operations has been reduced by more than 30%. There is no longer any need to lose time in transferring the workpiece from one machine to another.
Pumping fluid also functions as a lubricant
The gear pumps of Maag Pump Systems optimise the thermoplastic extrusion process by ensuring a constant material flow, supplying the required tool pressure and so taking the strain off the extruder unit. In this way the pumps can increase the pressure between inflow and outflow from 100 to 300 bar. They can be used both as feed pumps and in direct conjunction with the injection moulding machine. This boosts the performance of the production system, reduces the melting temperature and so improves the quality of the end product as well as prolonging the service life of the extruder. In addition, the pulsations and pressure peaks of the extruder are balanced out or eliminated altogether by the damping effect of the pump.
The special feature of the pumps, however, is to be seen in the lubrication of the slide bearings for the shafts with the toothed wheels. Because any risk of contaminating the pumping fluid would be unacceptable, no oil or grease can be used for lubricating purposes. So Maag Pump Systems has developed a solution whereby the bearings are lubricated by the pumping fluid, i.e. by the thermoplastic medium itself. An elaborately calculated and designed spiral oil groove distributes the plastic in the bearing, and so ensures the necessary lubrication. The geometry and sizing of the groove are crucial in this connection. If the groove is too large, too much lubricant will be supplied. This results in a 'dead circuit' and impairs the effectiveness of the pump. If the groove is too small, too little lubricant will be supplied to the bearing, and there is a risk that the shaft will seize up.
Rapid change of the prepared workpiece
The bearings, flanges and spiral gaskets for these pumps are now being made by Maag Pump Systems on the compact DMC 80 FD processing centre from DMG MORI SEIKI. The table can be loaded with workpieces weighing up to 1200 kg. In Bruno Lutz's view, this is a convincing solution: 'The machine is very compact nonetheless, and needs little surface area. Moreover, the heavy workpieces can be more efficiently handled with the horizontal workpiece clamping system.' Another cause for satisfaction is the way in which the entire process of milling, turning and drilling can be carried out in just two clamping operations. 'Rapid all-round processing is also supported by the powerful tool changer, incorporating 120 tools,' stresses Patrick Tresch, Managing Director of DMG MORI SEIKI Switzerland. To do this, the tool measurements are passed to the machine with maximum precision, using the machine's own laser measuring system. In addition, the changing unit takes no more than 14 seconds to substitute a new tool, which has been got ready for action in parallel to the main processing time.
Massively powerful 3-jaw Duro-T 500 key bar chucks are used to clamp the workpieces, which are made of different materials and can weigh up to 550 kg. The chucks have a diameter of 500 mm, and with a 220-250 Nm tightening torque in the top jaws can apply a total clamping force of as much as 220 kN to the workpiece. As a result of various improvements, RÖHM has again increased the clamping force as compared with the earlier model by 20%. 'Which is more than enough,' declares Damiano Casafina, Deputy Managing Director of RÖHM Spanntechnik AG [RÖHM Clamping Technology plc] in Switzerland. 'With some clamping operations, we actually have to hold back and avoid unleashing the full clamping force available.'
Splash water edge is ideal for directing the flow of coolants and lubricants
The design of the statically balanced and user-friendly manual clamping chuck has also been improved. For example, RÖHM's designers have introduced a splash water edge, which is ideal for directing the flow of cooling and lubricating media. The chuck works with extreme precision when it is a matter of repeating results after a change of jaw. And the concentric and axial runout accuracy is twice as good as required by DIN Accuracy Class 1. The rigid body of the chuck has a hardened surface overall, and its functionally optimised expendable parts (like the safety lock slide) promise a long service life with a high standard of precision. 'Rapidity and ease of operation are a priority for us,' says Thomas Lutz. 'As from a certain size up our pumps are practically unique specimens, specific to the customer or application, the flexibility of the machine and clamping tools used are crucial,' Bruno Lutz adds.
The people at Maag Pump Systems also welcome the modest height of the chuck, which still allows enough air to pass upward even though it is mounted on a changing unit. The swivelling processing head of the machine has the free space required at all times. If the combination of the machine and the clamping chuck works so well, that is not a coincidence - as is shown by RÖHM's longstanding and effective partnership with DMG MORI SEIKI in the design and installation of essential equipment. The DMC 80 FD at Maag Pump Systems, for instance, incorporates a RÖHM solution for the clamping of the tool pallets. The massive pull-in force makes it possible for prepared pallets to be clamped on the clamping cones with speed, safety and precision. The solution can be used even in a tightly confined space. The high degree of accuracy in the axial runout and positioning are the reasons why the system has become standard. Since 2005 every new series has been equipped with spring-activated clamping cones developed by the clamping specialist RÖHM, so as to hold the pallets securely in place.
Trade fair contacts grew to become a partnership
Patrick Tresch and Damiano Casafina in Switzerland are committed to ensuring that users can always count on an ideal combination of the mechanical equipment and the clamping solution. First contacts with Maag Pump Systems meanwhile came about as a result of Casafina's meeting the Lutz brothers at the AMB trade fair in 2010. 'Just when we were in the throes of the decision process,' Bruno Lutz recalls. Casafina smiles: 'Sometimes it is just the lucky moment of an initial contact which is going to pave the way to a successful "three-way relationship".' If Maag Pump Systems is not just dependent on luck when it comes to the magic triangle of machine / clamping chuck / application, not to mention the excellent results it gives rise to, that has to be down to the skills and the expertise of all the companies and individuals involved.