Consideration of the economic and efficiency aspects of vacuum gripping systems for handling sheet-metal parts are of enormous importance, particularly in the automotive industry, which is very sensitive to costs and quality.

Unfortunately, recent publications on the subject of vacuum generation have frequently compared apples with oranges, and many wild statements have been made and circulated.
In fact, it is not possible to compare the varies technologies and methods with each other.

It is true that a basic distinction can be made between centralised and decentralised vacuum generation. For centralised vacuum generation, for example with compact ejectors which have integrated vacuum monitoring and valves, the so-called "air-saving function" has been the state of the art for many years now. This air-saving function – switching off the compressed-air supply when a defined vacuum level is reached – is extremely important if the high costs for this medium are to be reduced.

In many cases, however, it is forgotten that the cost reductions for compressed air in press shops and bodyshell assembly are only a part of the possible cost savings, and that far greater potential savings are being ignored.

Typical "cost-eaters" are tooling errors or vacuum leaks in the gripping systems which are very difficult to identify and localise. Such problems result in idle times or, in the worst case, to an uncontrolled stoppage of the system – a crash. And it goes without saying that such events cause very high costs.
The company Schmalz in Glatten/Germany, world market leader in the area of vacuum technology for the automotive industry, considered how this large cost-generators can be avoided and developed new vacuum generators with a special "Condition Monitoring System".

Amongst others, a well-known German-American car manufacturer was convinced by the benefits of the new generation of Schmalz vacuum generators for a press line in which several presses are linked together by robots. This press line runs in three shifts and produces various bodyshell parts made of sheet steel and aluminium, and it is thus frequently necessary to convert the line several times during each shift.

The company wanted to use new vacuum generators for this press line, and these had to be faster, more efficient and more fault-resistant than the previously used ejectors. Since the various vacuum spiders were frequently affected by faults which resulted from wear and tear, and caused very high costs, the company was looking specifically for a solution which would improve the process reliability.

High-performance ejectors with integrated condition-monitoring functions

They found the solution in the from of the high-performance ejectors of the type X-Pump from Schmalz which, due to their integration concept and their significant reductions in the consumption of compressed air, are becoming increasingly popular.

These X-Pump ejectors are characterised, on the one hand, by their extremely high suction and blow-off power (30% higher than conventional compact ejectors with the same nozzle size), their very fast generation of high vacuum levels (0.05 seconds), their very short reaction times and their compact and light design.

These properties made very short cycle times possible (>8 parts/minute although the presses are positioned 8 metres apart), resulting in considerable improvements in the productivity and efficiency of the complete press line.

On the other hand, the high-performance ejectors X-Pump are designed as integrated compact units and include both air-saving and condition-monitoring (diagnosis) functions.
For many years now, the vacuum specialist J. Schmalz GmbH has placed confidence in the technology of automatic air-saving and has continually optimised it, with the result that the consumption of compressed air by up to 98%, compared with conventional vacuum generators without air saving, are today the state of the art.
In practice, the automatic air-saving function switches off the flow of compressed air when a specific vacuum level is reached. When handling airtight workpieces, this means that the air consumption is only a fraction of that needed in the past.

The above-mentioned integrated condition monitoring functions offer further benefits which are decisive for the user. They permit major improvements in the availability and thus in the process reliability of vacuum gripping systems used for handling sheet-metal parts. Defects in the system – vacuum leaks – are indicated even in the idle positions of the presses (suitable indicator lamps display the current status of the vacuum gripping systems), which means that preventative maintenance can be carried out during the next set-up phase of the press line.

This technology makes it possible to completely eliminate faults which result from the gripper-tooling or from wear and tear.

In contrast: conventional vacuum generators can signal a leak or a fault only when the system has already stopped or crashed. According to a high-ranking member of the staff who is responsible for the mechanisation of the press shop, this aspect deserves great attention, because the stresses on the gripping systems in a press shop are very high and wear and tear frequently causes leaks or defects which, in the worst case, can paralyse the complete press line.

Satisfied customer

On the subject of cost savings, one of the responsible employees in the press shop said: "We are very satisfied with the new high-performance ejectors X-Pump, which we use in all gripping systems (loading, linking and unloading robots) of the press line.

In particular, the extremely high gripping and blow-off power, combined with the monitoring and error-compensation possibilities, are unbeatable arguments for the X-Pump, and this is why we will, in future, invest increasingly in the innovative and profitable concept for vacuum generation in gripping systems. The single-stage nozzle of the X-Pump generates a noticeably higher vacuum than multi-stage ejectors, and much faster, and this permits us to further reduce the handling cycle times (the non-productive idle times) and to increase the throughput.

This does not mean that we are taking any risks with respect to the process reliability, since the integrated condition-monitoring functions completely eliminate any possible tooling errors and vacuum faults. This reduces fault times caused by the presses to a minimum and reliably avoids crashes of the system."

A final note

He also described a situation which recently occurred during setting up for a new workpiece and the related vacuum spider with new suction pads.

"During commissioning, the condition-monitoring (diagnosis) function immediately indicated, with a flashing red light, that the required vacuum was being built up too slowly. At first, we could not understand why this was so, since we were using new suction pads. A closer inspection then showed that the problem was caused by leaks in some old couplings which were being re-used. Thanks to the integrated "immediate diagnosis", we were thus able to avoid a costly system crash, and we did not have to waste time on further fault-finding and rectification measures.

" The "condition-monitoring made by Schmalz" can thus be regarded as an elementary component for reliable handling of sheet-metal parts in the press line of the German-American car manufacturer.

In conjunction with the considerable reductions in operating and maintenance costs and the improved process reliability, the high-performance ejectors of the X-Pump series are thus more than an economic alternative to conventional vacuum generation with compressed-air ejectors. This is particularly true since the time and costs for initial equipment of vacuum spiders or conversion of existing vacuum spiders are relatively low and can easily be calculated and since amortisation of the necessary investments is guaranteed within a short period, just be the lower consumption of expensive compressed air.