Hermos Schaltanlagen GmbH in Mistelgau works exclusively with Desoutter screwdrivers.
With the ergonomic cordless screwdrivers in the Elit range, the employees can tighten the sensitive connections to the exact torque specified by the customer. The quality of the screw connections has increased since Elit screwdrivers have been used.
“Components are assembled in our company for which the sensitivity is unknown”, explains Armin Birner as he makes his way through the production facilities of Hermos Schaltanlagenbau GmbH in Mistelgau. Here, the company manufactures distribution boards, power distributors up to 6,300 amps (A), UL-certified switchgear and complex control cabinets. The Production Department manufactures some of the switchgear for inhouse projects at Hermos AG, which amongst other things develops solutions for building automation and building management systems as well as IT solutions for the manufacturing and process industries.
External customers order the switchgear for mechanical and plant engineering, assembly lines for the automotive industry or robot applications. “The orders range from a production batch of one to small batches and batches of up to several thousand copies”, says Birner. The planning brought together all the areas required for control cabinet construction: mechanical processing, including assembly, wire and cable manufacturing and labelling. Many work steps are automated; the assembly of the components, on the other hand, involves manual work, without which it would not be possible to achieve high flexibility. “When it comes to tools, however, we rely on high-quality screwdriving technology provided by Desoutter”, says Birner.
Electrical connections have different characteristics to mechanical ones
Armin Birner is responsible for process optimisation in switchgear engineering at Hermos. Together with his colleagues Volker Breit and Ronny Messinger, he oversees the Assembly Department, which employs around 180 people. “The big difference compared to other industries is that we don't create a purely mechanical connection between components, rather an electrical connection between the component and the conductor”, he explains. This connection has a completely different characteristic. “It's not just about whether the screw holds or not. Smooth clamping points and smooth surfaces predominate. The contact pressure must be sufficient in the long run and the contact resistance must not too high”. There are components that are very large but require almost no torque. “If, for example, clamps are tightened too firmly, the clamping point is weakened in the long run. The terminal or conductor will be damaged. ”If the electrical connection is too loose because it has not been tightened enough, it either does not work or, in the worst case, poses a fire risk if the contact resistance becomes too high.
You don't have torque in your wrist
For every system that is assembled at Hermos, it is therefore precisely specified which connection must be tightened with which torque. “In terms of clamping point technology, we supply our customers with exactly what the component manufacturer demands”. A torque of 0.5 Newton metres (Nm) is "not in the wrist”, as Birner emphasises. With manual assembly with a simple screwdriver, the manufacturer's specifications would tend to be exceeded. “Therefore, we prefer to rely on modern screwdriving technology”.
The team quickly agreed on the selection of the latter. “We tested various models from different manufacturers and then decided on the screwdrivers from Desoutter GmbH in Maintal”. The first tools that were purchased in 1995 were pneumatic screwdrivers, which Hermos still uses today. “When the workpieces are horizontal, they can be conveniently assembled using the baton screwdrivers”, says Volker Breit. “Completion in the cabinet is more difficult. Because when the control cabinet goes through the final wiring phase, it is in a vertical position. Managing the screw contacts neatly is not an easy task with the baton screwdrivers. Hermos tried it out with compressed air offset screwdrivers from Desoutter, but they also have the handicap of using air. “The operation is relatively exhausting and I have to use greater force to put the bit on and hold it in the correct position", are the disadvantages that Birner mentions. The speed may be too high, the bit grip is not optimal, and in the worst case scenario you slip and wreck components. And there is always a tube in the way.
Cordless screwdrivers enable ergonomic work on the control cabinet
Hermos first used Desoutter's cordless screwdrivers from the Elit range a few years ago. They have now become an integral part of assembly process. The ergonomic and quiet cordless screwdrivers with pistol grip convinced the team from their very first use: “I don't have a bothersome tube, the basic machine is more ergonomic, the release button is easier to operate, I can lock the torque setting and have the option of reducing the speed - that's a completely different way of working”, Ronny Messinger and Volker Breit also affirm. Two positions are also possible for the lithium-ion batteries for optimal access to the screw connection.
The torque is set exactly according to the specifications of the component manufacturer
Each switchgear assembly station is usually equipped with at least three of the Elit screwdrivers. These have different torque settings in order to cover as many clamping points as possible. “This means we can operate around 80 to 90 per cent of the required values”, says Volker Breit, who uses the screwdrivers in the workshop. Manufacturers usually specify a tolerance range. Some components have to be screwed with torques between 1 and 1.5 Nm, others with values between 0.8 to 1.2 Nm. “In such a case, we set a screwdriver to one Newton metre, for example, to comply with both manufacturer’s specifications”, explains Breit. Appropriately adjusted screwdrivers are added for special cases. “The tools are marked with coloured rings when distributed - and the torque is on them”, says Breit. “This almost eliminates confusion completely”.
Two thirds of all connections are screwed using Elit tools
60 Elit cordless screwdrivers are now in use at Hermos Schaltanlagen GmbH. And this trend is on the increase. “If we invest in tools, they are only Elit screwdrivers”, the team agrees. 190 compressed air screwdrivers are also still regularly used for assembly on horizontal components. In a few cases they are also used for connections that require higher torques, such as load-break switches, or with larger cross sections. Torques over 6 Nm are also assembled by hand with a torque wrench - this affects about 10% of the screwing joints. “We usually use Desoutter's ELB and ELS pistol-grip screwdrivers that range from 0.4 to 6 Newton metres”, says Volker Breit. “This covers about two thirds of all connections”. With a daily output of 10,000 to 15,000 clamping points, almost all cordless screwdrivers are in principle always in production at their work groups. In order to ensure error-free processes, the entire production is structured in such a way that control cabinets and systems are divided into work groups. "The same teams are always responsible for the same customer or the same style and are therefore trained in certain work processes”, explains Birner.
Speed can be flexibly adjusted via a module
The tools are regularly readjusted for the upcoming tasks and handed over to the teams together with the project. "The Elit screwdrivers can be adapted as flexibly as the respective project requires”, says Birner. Whether it's about implementing special solutions or building complete project lines. Twelve of the screwdrivers are ELB models and have a fixed speed. In the ELS models, the speed can also be flexibly adjusted using a corresponding module. “We process torques over 2.2 Newton metres with 900 rpm, and over 3 Newton metres with 650 rpm. For all lower torques, the speed usually remains at 1,150 or 1,500 rpm”, says Volker Breit. The screwdriver offers the option of a solution approach for each individual screw joint. “When a project goes into series production, there are tests and evaluations to find the optimal tool parameters”.
The error rate and deviations are set at zero when testing screwdrivers
The quality of the screw connections has improved noticeably since Hermos started working with the Elit screwdrivers. There are hardly any complaints and there has even been some positive feedback. “When working with compressed air screwdrivers, it can happen that the bit does not grip 100 per cent due to the immediate start. That almost never happens with cordless screwdrivers”, says Birner. The ELS screwdrivers also provide an optical signal (green = OK) when the torque has been reached.
All screwdrivers are checked annually as standard. “At the start, we tested the screwdrivers every six months”, reports Ronny Messinger. But since the error rate and deviations was always zero, this interval was extended. “Of course this is not so ideal for Desoutter”, smiles Armin Birner. “If the tools always work perfectly, we won't buy new ones”. Maintenance and repairs are also kept to a minimum, as the screwdrivers are extremely robust thanks to the brushless motor and wear-free start button.
Goods dispatch area documents the "responsible" screwdriver
Depending on the customer's requirements, the connection points are currently checked either randomly or 100% using a torque gauge. The serial number of the screwdriver with which the connections were tightened is also recorded. "With the annual inspection of the screwdrivers, we have evidence that the tools were ok at the time of use”, says Ronny Messinger.
A higher degree of automation in production and documentation would be feasible for the innovative company and will also be discussed in the course of increasing demands of some customer groups, but "we don't want to make production more complicated than we need it to be”, emphasise the three Hermos employees. As it is now, you can intervene very flexibly in the continuous improvement process. “But if we have projects in the future that make the implementation of Industry 4.0 solutions in our production processes seem appropriate, we are always ready to do so. And we are happy to take this step with Desoutter”.
