The productivity of a press shop for the series production of motor-vehicle parts no longer depends only on the performance of the presses, but also continuous feeding of the raw sheets and removal of the finished parts.

Regardless of whether (robot-) linked presses or vacuum transfer presses are used, it is not the maximum number of press strokes per minute which determines the working cycle. It is the practically achievable speed with which sheets can be inserted and the finished parts removed which determines how many cycles per minute can be used. The parts-handling speed, in turn, is determined not only by the traversing, positioning and transport speed, but above all by the quick and secure holding of the parts by the gripper system. The parts must also be released equally quickly when they are positioned in the press or reach the defined stacking position for finished parts.

 The factors speed, reproducible positioning, quick gripping, quick release and reliable parts transfer together are decisive for the performance in a press shop.

Whereas magnetic, mechanical and pneumatic gripper systems were widely used in the past, the emphasis today is on vacuum or combined vacuum/magnetic gripper systems.

Vacuum gripper spiders are generally lighter than mechanical grippers and can in many cases be constructed easily from standard components. They can also be modified easily and, in the worst case, damaged or worn suction pads can be replaced quickly without the need for tools.

The lower weight permits faster handling operations and the secure grip ensures reproducibly accurate handling and positioning. The optimum suction pads for the task can be selected and the fact that the pads can be changed quickly reduces the idle times of the expensive presses.

High-quality vacuum components
for demanding handling tasks

The decisive components for performance and process reliability when handling sheet-metal parts are the suction pads and the vacuum generator. The suction pads form the interface between the robot and the workpiece, while the vacuum generator must be capable of delivering the necessary vacuum under all conditions. But quick and reliable gripping are only half of the story: after removal from the stack or the press, the parts must be deposited as quickly as possible in the desired position and the handling device or robot must be withdrawn quickly from the working area of the press. In the case of vacuum gripper systems, the parts can be released quickly by blowing them off with a pulse of compressed air, while mechanical/pneumatic  grippers need a complex mechanical system.

In order to improve the performance of handling in press shops, the vacuum specialist J. Schmalz GmbH, 72293 Glatten, recently introduced a new series of high-performance ejectors for vacuum generation, called the Schmalz X-Pump. These ejectors have a very high suction capacity coupled with a powerful blow-off pulse, are very compact and robust, are easy to install and integrated into other systems and, above all possess many intelligent functions – the so-called Condition Monitoring – for more process reliability in vacuum handling.
Wolfhard Schmidt, responsible at DaimlerChrysler AG in Bremen for the mechanisation in the press shops, was so impressed by these features that the company now uses vacuum spiders equipped with the innovative vacuum ejectors X-Pump (SXP) and special sheet-metal suction pads of the type SAF 80/SAB 80 from J. Schmalz on the loading robots of press shop 9.

Wolfhard Schmidt said, "Our presses run in three shifts, 24 hours a day, and are converted two or three times in each shift. This of course means that the vacuum gripper systems (spiders) also have to be converted. Since the vacuum grippers are subjected to heavy loading, it can happen that they develop leaks or faults from time to time, which means that the parts can no longer be transported safely. In many cases, this becomes apparent only when a part is dropped and this can, in the worst case, stop the entire press line. The resulting costs are so high that we make every effort to ensure process reliability".

X-Pump = high-performance ejectors
with integrated diagnostic functions

As already indicated, the vacuum ejectors X-Pump are for many reasons ideal for use in series and mass production. In addition to their high suction and blow-off capacities, their primary advantage is their manifold diagnostic functions, called "Condition Monitoring", which permit permanent status monitoring and timely maintenance. The X-Pump detects faults in the vacuum system of the grippers, evaluates these and indicates them. For this purpose, the X-Pump has an optical status indicator in the form of easily visible indicator lamps which clearly signal the current status of the system.
The following states are indicated directly on the ejector:
o Steady green light = everything OK.
o Blinking green light = the system has a minor leakage, but can still be used without problems.
o Blinking red light = the required vacuum is being built up too slowly, because there is a major leakage in the system. The system must be inspected as soon as possible, since it will otherwise fail completely in the near future.
o Steady red light = there is no vacuum or the vacuum is far too low. The vacuum spider must be inspected immediately.

Wolfhard Schmidt says, "Until now, we had to stop the press line immediately in the case of a vacuum fault or a defective spider. This forced stoppage, whose duration was unknown, permitted us to repair the system, but always resulted in a loss of production. With the new X-Pump, this situation can never occur, since the diagnostic indicators clearly show how serious the problem is, permitting us to decide on the appropriate course of action.
A decisive advantage is that the X-Pumps continue to display the status of the vacuum gripper system, even when it is idle. A defective spider can thus be identified by the operator – for example, while the machine is being converted. It can then be removed and replaced by a functional spider. The defective spider can then be inspected and repaired in a workshop while the press continues to run."
The manifold diagnostic signals of the vacuum ejectors X-Pump can also be sent via a special data output to an external controller (such as that of the robot) or to a higher-level system (such as the central process control room). This provides the user with complete control and monitoring of the entire vacuum gripper system, including the vacuum supply.

High technical availability
at an affordable price

A further interesting function of the X-Pump concerns the automatic air-saving function, which normally ensures economical use of the available compressed air. If the Condition Monitoring function detects a problem in the vacuum system, such as an excessively high leakage rate, the diagnostic indicator is activated as described above and, in addition, the automatic air-saving function is deactivated. The vacuum generator then operates continuously at full power, compensating for the leakage an ensuring reliable operation of the process.

The X-Pumps are also extremely resistant to dirt (IP 65), have a friction-free piston system which suffers very little wear, require very little maintenance since the have no filters, operate quietly due to their silencers and have a very high availability.
 
As Wolfhard Schmidt said, "In Bremen, we have three press lines which use robots equipped with vacuum gripper systems. The vacuum- gripper system of loading robot 01 on press line 9 is equipped with a dual block with two X-Pumps (SXP). These X-Pumps have been running now for several months and we have had absolutely no faults or problems with them. Press line 9 is used to produce 27 different parts, which means that the press tools and the gripper have to be changed twice per shift. In addition, the presses run in three shifts under hard conditions, generally producing 7.6 parts per minute. We are very satisfied with the new X-Pumps, which provide a 30% higher suction capacity than the previously used compact ejectors with the same nozzle size and, thanks to the automatic air-saving function, ensure economical operation. The integrated Condition Monitoring permits us to detect possible faults in good time and to take the appropriate actions immediately. This provides us with a very high technical availability which, in turn, is a prerequisite for high process reliability."

As a result of the positive results obtained with the X-Pump at DaimlerChrysler in Bremen, the responsible persons are planning to completely equip a further press line with the new vacuum generators from Schmalz in the near future. In this case, the X-Pumps will replace the vacuum generators made by a competitor which are currently used. The primary reasons for this decision were the monitoring and fault-compensation functions, coupled with the high suction and blow-off capacities of the X-Pump.