Safe welding in volume production

The fail-safe version of this controller is used by welding machine and special equipment manufacturer Dalex to meet the high safety requirements of the EU’s Machinery Directive.
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Safety first

In order to protect operators, the safety requirements for welding machines are extremely high – and that’s why the fail-safe version of the SIMATIC S7-1200 was the control system of choice for Dalex Schweissmaschinen GmbH & Co. KG. 

“Certain functions, including the movement of the welding cylinder, must be designed according to performance level D in order to meet the high safety requirements of the Machinery Directive,” says Dirk Schneider, Deputy Chief of Electrical Design at Dalex. The F functions also include an emergency stop, and two-hand operation for projection welding. Schneider says that in order to protect the operator’s hands from inadvertent contact with the machine, projection welding can only be started from a two-hand control desk.

The programmable logic controller (PLC) replaces a combination of LOGO! modules and safety relays, making it a future-proof solution with many advantages for this German manufacturer – and its customers worldwide.


From past to present – and into the future

For more than 100 years, Dalex GmbH & Co. KG has been developing and building welding machines and special equipment, offering its customers customized solutions for increasing productivity, optimizing processes and increasing quality.

Whether for standard or special machines, robot cells or high-tech tools, this welding machine manufacturer in Wissen, Germany, specializes in resistance welding – and it is one of the foremost manufacturers worldwide when it comes to this technology. Dalex GmbH is internationally known for its industrial plants, the PMS series for spot, projection, and seam welding. However, the company now generates more than 60% of its annual sales from special systems such as automatic rotary indexing machines, interlinked plants, and robot cells. Their clients range from the automotive industry and its suppliers, to the electrical industry, to manufacturers of punch and bending parts as well as door and window fittings – and even to the aerospace industry.


SIMATIC S7-1200F – fast and flexible

Previously, safety relays along with LOGO! and a welding controller were required to ensure safety and automation of the welding machine. The safety relays provided the safety functions and were wired to LOGO! which in turn communicated with a specific welding controller and started the actual welding process. Because the expansion of this system was complex and prone to causing faults, the company looked for a new solution.
SIMATIC S7-1200F is exactly what we had been looking for.
Dirk Schneider, Deputy Chief of Electrical Design at Dalex

The solution has proven itself over many years, but the wiring was very complex,” explains Schneider. “If a requirement was added, we needed another safety relay and had to rewire it, which was prone to causing faults. And so we started looking for a more flexible solution.”

When the fail-safe versions of the SIMATIC S7-1200 control system came onto the market in 2015 – and in particular the SIMATIC CPU 1214FC – they corresponded to the precise needs and requirements of the machine manufacturer Dalex. “This PLC was exactly what we had been looking for,” says Schneider. “It allows us to dispense with the safety relays and take care of the wiring in the software, so to speak, which also saves our design engineers drawing time. Now, if we need an additional safety function, we can simply use additional inputs of the controller. The rest is programming.”

The system can also be easily expanded, if, for example, the customer requires additional tool functions for his machine six months later. The CPU version 1214FC can be extended by up to eight standard or fail-safe signal modules. “This also allows us to use them for larger machines,” notes Schneider. Thanks to communications taking place within the machine, such as via Profinet between the SIMATIC S7-1200 and the welding control, no additional wiring is required.


Ready for Industrie 4.0

The bottom line is that the solution is no more expensive than the old one and will even save costs in the future. The standardized engineering with TIA portal makes it possible to use the library of standard modules developed for the PMS series and SIMATIC S7-1200 – even for the most demanding special machines. 
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