From pneumatic screwdrivers to EC servo screwdrivers - reliable and precise

On the look out for new trends - Focus on the latest in screw assembly / High-tech manufacturer provides optimal screwdriving technology for any application

Amberg, (PresseBox) - In order to discover the latest trends in screwdriving technology, I visited the AUTOMATICA trade fair; the leading platform for automation innovations. In Hall A6, Stand 310 at the DEPRAG exhibition stand three slogans caught my eye: "Technical - Clean - Screwdriving - DEPRAG", "Intelligent - Manual - Assembly - DEPRAG", "Sheet Metal - Direct - Screw Assembly - DEPRAG". This seemed to be the right place to get all my questions answered. At the exhibition stand I met Jürgen Hierold, long-standing Sales Manager at DEPRAG SCHULZ GMBH u. CO.

Q: Mr Hierold, can you answer my questions about the latest trends in screw assembly?

A: Yes, you've come to the right address. To be able to appreciate the current trends in screw assembly you need also to have an understanding of past innovations and developments. I have been specialising in screwdriving technology and automation since the end of the seventies and so can look back on years of experience. One must also take into consideration, the differences in the development of screwdriving technology on an international level and for example, how in Asia there are different requirements to those in the USA. And in the same way, how the market in the USA was already displaying many trends in the eighties which only later reached Europe and vice versa.

Q: Which specific trend do you mean, can you give me an example?

A: I can well remember the increased demand for fully-automated assembly processes. In order to provide for the increase in quality consciousness, these fully automatic assembly systems were seen as the best option for efficient and reliable manufacturing. Expressed simply, people sometimes make mistakes and their work is not repeatedly accurate (without additional measures been taken). The possibility of using, for example, a robot to minimise errors and increase processing reliability is of course attractive. However despite the advantages of fully-automated processes for processing reliability and efficient production we have learned that a fully-automated system cannot react so flexibly as semi-automatic or manual processes when it comes to short-term changes in factors such as changing numbers of parts.

Q: What does that mean? Have fully-automated systems gone out of fashion?

A: Yes and no. Of course fully-automated systems are still used. But in the last few years we have seen a trend towards intelligent manual work stations which combine flexibility from the human aspect with processing accuracy. In comparison with today, back in the past it was only possible to guarantee processing reliability and precision with high additional costs. Today the situation is different: standardised, intelligent modules guarantee processing reliability, which is why, depending upon the specific requirements, it is profitable to select flexible manual work stations as an automation concept.

Q: What kind of standardised intelligent modules do you mean?

A: One example of an intelligent component is the positioning control in combination with a part fixture and integrated sensors. The processing sequence is thereby predetermined, visually displayed and the correct working sequence can be controlled. Positioning control concepts from DEPRAG are based on diverse solutions, for example position control stands or portals in varying designs for all kinds of applications. Optimal processing reliability is guaranteed with the MINIMAT® EC screwdriver. The torque, angle, speed, waiting time and rotational direction can be freely programmed within the performance range of each spindle and thereby adapted to each individual screwdriving task. The integrated torque and angle measurement ensures precise control of screw tightening as well as documentation of important processing parameters. Together the position control stand and EC screwdriver are an effective method of coordinating processing. The screwdriver will only start if the selected sequence is adhered to.

Q: Is the move towards intelligent manual work stations the only noticeable trend?

A: No. For many years there have been developments towards electronic screwdriving tools. They are used ever more frequently for assembly work. The screwdriving system selected ultimately depends on a variety of factors. EC systems are programmable and adjustable and capable of the kind of documentation required in the assembly of high quality products, such as for the automobile industry. Our sensor-controlled EC servo screwdrivers are therefore used in the assembly of airbags. Screw joints in the automobile industry are divided into the risk categories A, B and C in accordance with the VDI directive 2862.

Q: What do these risk categories mean and what kind of screwdriving technology must be used?

A: Category A covers those safety-critical screw connections whose failure could result in loss of life or limb. For these the highest processing reliability and dependability is required. Torque and angle measurement and control via sensors is compulsory in order to fulfil the minimum requirements of category A. An EC screwdriver which is classified in category B can have torque and angle measurement and control via motor current analysis. For category C however a screwdriving system with mechanical shut-off suffices. The reliable pneumatic screwdrivers of the MICROMAT® and MINIMAT® series are used today internationally in their tens of thousands for the most varied of assembly tasks such as assembly of mobile phones. They have an extremely precise mechanical shut-off. As soon as the preset torque is reached the clutch disconnects from the drive. The standard deviation is ±3 percent an outstanding value.

Q: You are getting nostalgic...

A: Hold on, that's not quite true! The move towards electronic screwdriving tools is without question a legitimate one. However it is a fact that pneumatic screwdriving systems are today still very often used. That the DEPRAG pneumatic screwdrivers are still being used in such numbers speaks for itself. We are of course again talking about screw assembly of high quality products here as well.

Q: And which prerequisites are there for using pneumatic screwdrivers?

A: Basically electricity or compressed air are both workable drive mediums. A system is selected depending on the individual features and criteria required. One such factor is flexibility, if the torque, angle, speed, rotational direction or screw depth parameters must be altered during the application task, then an electric system makes sense. EC screwdriving systems can be freely programmed to take these parameters into consideration and can easily make changes to processing. If there is no requirement to alter parameters then a pneumatically driven shut-off screwdriver is usually sufficient. An additional factor is the processing reliability which has a decisive influence on the scope and costs of the screwdriving system to be chosen. The requirements for processing reliability must be clearly defined in advance. For some applications the transfer of signals will suffice, for others all assembly steps must be precisely documented. In this case the intelligent EC screwdriving system is predominantly used. Additional criteria include torque precision, operating data recording and statistical processing guidance. To incorporate these features a screwdriving system is required which can communicate with a superior processing data storage device and fulfil documentation requirements. The EC or EC servo technology is again in this case most suitable. Both systems allow recording of torque and angle values. The EC and EC servo technology can therefore be seen as the more attractive solution, although the investment needs must also be considered.

Q: That is very interesting. What are the differences in purchase prices?

A: If a screwdriving system controlled by motor current is selected then this is five times as expensive as a pneumatic system. Sensor controlled screwdriving systems can even be up to ten times as expensive. The price gap between the different technologies is therefore relatively wide and selection should be considered carefully.

Q: You are right, but leaving the purchase price to the side for a moment, is it not correct that the operating costs for pneumatic systems are very high?

A: Yes of course compressed air is expensive, but this alone should not be decisive for the selection of a system. The operating costs cannot only be judged on the drive medium but also the incurred costs over the complete life cycle must be taken into account. Generally during screw assembly the effective power-on time of the motor is often very short, the actual required energy is a lot less than assumed in the nominal performance data. Within the operating costs one should not only consider the comparison of energy prices but also the maintenance costs. Pneumatic screwdrivers can be simply and inexpensively repaired and maintained by on-site maintenance staff. EC screwdrivers usually will need expert service personnel and specific measurement equipment. One must not forget that the EC and EC servo screwdrivers are not only assembly tools but also measurement instruments. If they fall under EN ISO 9001/2000, they must be regularly inspected and calibrated. Pneumatic screwdrivers are heavy duty tools for continuous industrial use and are insensitive to external influences. We often receive pneumatic screwdrivers back for maintenance which were last returned thirty years previously and have in the meantime carried out several million screw assemblies.

Q: Thank you, the latest situation in assembly is much clearer to me now. How do you see the future, in your opinion which trends are currently on their way to us?

A: Screw assembly continues to be challenging. The project "Industry 4.0" in the German market and the computerisation of the entire industrial process is a one such challenge which we are involved with. The scope is not yet determined but its goal is the creation and promotion of intelligent networks in classic industry e.g. production technology. Logistics, stock and purchasing, overall communication between all internal as well as external areas and processes so that customers or business partners are all interlinked. Modern factories will therefore be intelligent, efficient, flexible and sustainable. In order for this computerisation of industry to function Manufacturing Execution Systems (MES) are needed for transparent production. The basis for this is consistent documentation of machine data logging and product data acquisition. If all goes to plan then "Industry 4.0" will be the fourth industrial revolution. We are on the edge of our seats!

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