PC-based control holds the key!

16 October 2016

Making key and locking mechanisms requires the use of very high-precision production technology that needs to be able to compensate for temperature fluctuations, even of a few degrees. 

Aumat and AST have opted to develop corresponding systems to address these requirements, based around PC-based control solutions from Beckhoff to help ensure manufacturing precision of 0.01 mm, while enabling easy implementation of customised special machinery – with minimal engineering effort.

Wilka Schließtechnik needs to be able to produce customized key and locking cylinder solutions for its customers. Olaf Witte, technical director, explains: “In a manner of speaking, we mass produce with a lot size of one. While an order can cover 1,000 identical items, each one is usually different – all the way down to a single order for a duplicate key.” Production therefore needs to be flexible in its structure, and it relies on a variety of special machines developed by Aumat Maschinenbau, combined with the Knowledge of its systems integrator, AST. 

According to Achim Ihlefeld, technical director at Aumat, a high degree of precision when machining the key blanks is vital. He said: “The maximum key tolerances lie in the hundredth of a millimeter range. In order to reliably meet this tolerance, the mechanical engineering has to be better by another order of magnitude. This requires the shortest possible control cycle times and servo axes with very high precision. Both of these can be produced by Beckhoff’s PC-based control solutions that even several parallel milling cycles can be achieved with several corresponding servo axes.” Tim Themann, software developer at AST, adds: “The precision requirements are so high that even temperature fluctuations of a few degrees can be critical for the machining results. This influence needs to be regulated via continuous temperature monitoring.”

The Wilka key production line consists of two stand-alone, specialised machines: “An existing key cutting machine for cutting the key bit was overhauled and equipped with control and drive technology from Beckhoff,” said Wilfried Wengenroth, Managing director at AST.  “Added to this was a profile milling machine, likewise controlled via PC Control, for the milling on the key side. The keys are manufactured to order during the run, first getting the longitudinal profile, then the notches. They are then finally delivered with the associated locks.” With the two Beckhoff controllers, Wilka benefits from a uniform user interface; if necessary, the company can continue running the second machine without interruption in the event of a machine stoppage.

The cutting machine has nine servo axes while the profile milling machine has 23 servo axes, which are implemented via Servo Drives and servomotors. Both machines are interlinked and communicate via two gateways programmed in C#. These each run on a control cabinet Industrial PC (IPC) on the corresponding machine and communicate via ADS with TwinCAT automation software. In addition, the IPCs are in charge of data transfer to the central data server of Wilka. Each milling spindle on the profile milling machine also has its own tool management.“In this way, the four milling spindles manage with 12 cutters each, in order to efficiently carry out the many and varied longitudinal milling operations from the thin master key to the thicker special keys that only fit specified locks of a locking system.

Conventionally, hundreds of specific cutters are often provided for this purpose. In our case we avoid this by intelligently coordinating usage of the 48 cutters via the tool management system,” said Ihlefeld. Themann adds: “Tool management is implemented via TwinCAT NC I. This makes it possible to select the appropriate cutters and cut ideal lines. Therefore, you can have a smoothed edge between deep and flat milling notches lying next to one another, and the finished key is reliably prevented from improperly catching in the lock cylinder.”

The specialised machines from Aumat have been using PC-based control from Beckhoff since 2005. Wengenroth said: “AST has been working with it since 2004. EtherCAT is a critical advantage, giving the ability to perform automatic scanning of the system, during initial commissioning in particular. EtherCAT also offers rapid and convenient diagnostics of all bus devices.” Mark Straka, manager of Electrical Maintenance at Wilka adds: “Our evolved controller landscape is, by nature, heterogeneous. The openness of the system is a vital as older legacy control technology can be integrated without great expense and the higher-level corporate network can be connected just as easily. The latter is increasing in importance to ensure that the entire production infrastructure is available via a standard network, from order entry to production, all the way to service.”

The more that production relies on networking, the more serious the potential damage in the event of a malfunction and so system availability and control technology service is becoming an even higher priority. “The speed with which we respond to inquiries is often crucial. Production downtime can be expensive, said Straka. “However, this is not only true in the case of service or procuring replacement parts. Just as critical is the speed with which Beckhoff has developed technical innovations over the years and accompanied those innovations with project support. Meanwhile, there is hardly an application that cannot be solved with PC Control. In addition, we save up to 50% in control cabinet space and about 20% in hardware costs compared to conventional PLC technology. Moreover, it is possible to respond rapidly and flexibly to new requirements via EtherCAT Terminals or Box modules, such as for subsequent temperature compensation.”

On the Wilka key production line PC Control handles all automation technology tasks – control of machine operation, HMI for setup and automatic operation, fault message display and data archiving, data handling via gateways as well as NC-control of the three-axis milling gantries. Five 3-axis stations controlled by TwinCAT NC I are used for the profile milling machine, while three stations are used for the key cutting machine. Added to this is key transport via 15 transfer stations and the supply of the key blanks with a total of 32 servo axes handled by drives that include system-integrated safety functions.

This is all controlled via a single control cabinet IPC per machine, which is connected to a 15in built-in control panel for visualisation programmed using TwinCAT PLC HMI. According to Wilfried Wengenroth, it offers sufficient power even for future system expansions: 

One Cable technology
Since 2014, Aumat machines has utilised One Cable Technology (OCT) aspect of Beckhoff Drive Technology. This puts power supply and feedback systems in a standard motor cable, helping to reduce hardware and commissioning costs. This solution has helped reduce labour requirement and has reduced sources of potential errors. In addition, the number of cables has been halved and there is more compact, more scalable cable routing, which offers cost savings of up to 30%. Further, the stable data transfer in OCT means that EMC is not an issue. 

Stefan Ziegler is marketing communications at  Beckhoff Automation.

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