Competitive advantage through stable and efficient processes


Against a background of increasing automation, process and machine monitoring is becoming ever more important. Last year's praxisFORUM+ held by the KOMET GROUP was therefore directed at users and manufacturers of machine tools, control systems and automation systems. Contributors presented areas in which modern monitoring systems are used, and analysed current and future challenges. The result: Stable machining processes offer more benefits than just longer tool life and a production area which allows low manning levels. When the process is ideally under control, even limits in terms of product design can be extended.

MTU Aero Engines, one of the few suppliers in the aerospace industry that machines critical components for engines built by Rolls Royce, Pratt & Whitney, GE and others, has a quite particular reason for investing in process monitoring: The company would like to extend the limits of its product designs. Dr. Martin Eckstein, who is responsible for process monitoring at MTU Aero Engines, recently explained this strategy at the praxisFORUM+, which was organised by the KOMET Group in Besigheim. Because if lighter engines are to be manufactured, limits have to be determined. For this, reports known as damage tolerance assessments are required. "When certain limit values are reached, a risk assessment has to be undertaken," argues Dr. Martin Eckstein. "The designer must demonstrate what level of safety we build into the process, because we're working at the limit. Process monitoring is one solution for that."

Dr. Dražen Veselovac, who leads the Product and Process Monitoring Group at the WZL machine tool laboratory in Aachen, sees the requirement for optimum proportionality between productivity, tool life and costs as an extremely important driving force. "The industry is looking for stable processes that are productive. How far can we go with work when close to the limit?" In his opinion, it is essential to know what happens during machining. His belief: First, understand the process, next establish the process monitoring system and only then regulate. Only in this sequence and no other.

Tools as the decisive factor

In their Munich plant, MTU machines, amongst other things, high-pressure compressors for aircraft engines. The materials used for this include titanium and nickel materials, such as Inconel 718. A production run of five pieces is already seen as considerable. Customers place high demands on the integrity of surfaces and on component edges. According to Eckstein, the decisive factor is tool wear: "This is the biggest change that occurs during the process." In the aircraft industry, forged parts are often handled that do not always have identical properties. As a result, two forged parts which, at first sight, are identical can show a difference in wear of up to 30 per cent. With material variations as large as these, a monitoring system that, for example, only measures spindle torque statically would produce too many incorrect signals.

Embedded system

In collaboration with a research team from the machine tool laboratory (WZL) in Aachen, Dr, Martin Eckstein has therefore developed an algorithm that compensates for the variations in the material properties in signal processing. Several machines have now been equipped with an embedded PC that contains this algorithm. The signals are read directly from the Siemens 840D sl machine control system, because Eckstein does not want to build any additional sensors or other devices into the machines. Due to the process signals, conclusions can now be drawn about tool wear, so that machining can be performed closer to the critical limit, in the knowledge that the machining is free of faults. "Through this development, MTU has received the highest of approbation from the FAA in the aircraft industry. It gives us a competitive advantage," explains Eckstein with satisfaction. At present, he is working with his team on implementing these embedded systems into the five-axis machining centres in the new production hall that was additionally built for machining blisks. He also intends to use the system in turning and milling centres. One of the suppliers of MTU Aero Engines also uses the system. Martin Eckstein: "We have built more reliability into our process without using additional sensors. We want to use this monitoring system to positively determine the limits of tool wear." But not to exceed them – this form of process monitoring provides this certainty.

Process monitoring from the machining specialist

KOMET BRINKHAUS GmbH, a subsidiary of the tool manufacturer KOMET GROUP, develops systems for monitoring machining processes on the basis of data that is already available in the machine control system. This data includes tool torques, spindle power requirement, machine axis speed and tool and workpiece numbers. All these are data that can be read out and analysed, and then used for process monitoring. "Without sensors," emphasises Dr. Jan Brinkhaus, Managing Director of KOMET BRINKHAUS GmbH. Low defect levels, expensive tools, short cycle times and the call for consistent manufacturing quality are, in his opinion, the reasons why increasingly more machining companies are in search of a form of process monitoring.

The major product of KOMET BRINKHAUS is called ToolScope. It is used both for process monitoring and for adaptive process control. The special feature about this system is its self-learning behaviour based on statistical analyses, e.g. using the 6 Sigma strategy. It was developed for fast processes, since monitoring and adaptation are performed in real time. ToolScope uses its own hardware which is built into the control cabinet. A further highlight is the uninterrupted storage of sensor data throughout several days. Although the system gathers the data present in the machine, external sensors, such as structure-borne sound or acceleration sensors, can also be connected. Dr. Jan Brinkhaus has witnessed a trend towards increasingly deeper integration of process monitoring into the control system of the machine: "The more you know, the better you can react."

The challenge in this regard is, in his opinion, that of keeping the software accessible to the operator: "Although things can also be taken to an academic level, the operator at the machine still has to have an understanding." As a case in point, it remains essential that the CNC operator understands the meaning of a signal. If this is not taken into account, the system will soon no longer be used. Furthermore, it is important that systems can always be adapted to customer requirements. That is really easy to do with the ToolScope system. In collaboration with MTU, the algorithms tested by Martin Eckstein have therefore also been successfully implemented on the ToolScope system.

Dynamic breakage detection

One of the monitoring tasks assumed by the KOMET BRINKHAUS software is tool breakage detection. This is performed dynamically with the Dynamic Monitoring Module. The system calculates the upper and lower limit from the interaction between material and tool. When the material is changed, the system performs a calibration in the first seconds of the new machining operation. If material from another batch is being cut with the machine, the limits are dynamically adjusted. As soon as the torque measured exceeds one of the limits, the system knows that the tool is broken. Torque is also the parameter that is used by the Adaptive Control Module. Among other things, this module ensures process acceleration when air cuts are detected. Using this module and an external vibration sensor, it is also possible to react appropriately to chatter vibration.

More than tool breakage detection

When used correctly, however, process monitoring performs significantly more than just tool breakage detection. It also ensures correct tool life utilisation, prevents the machine from starting to vibrate, monitors the condition of machine parts and, most recently, even provides a module for energy monitoring. ToolScope can be compared to a sports car with various different tuning kits, the full potential of which can only be exploited by a good driver. In order to guarantee this, the KOMET Group offers intensive training courses for these topics. Alternatively, the optimal process setting can also be provided as a service. The KOMET GROUP is the manufacturer of process monitoring systems with the highest level of market penetration by tool and process experts directly at the end customer.

Expert knowledge from a single source

The praxisFORUM+ follows on from the successful tradition of the IDEEN-FORUM+ and provides expert knowledge from a single source. With this activity, the KOMET GROUP has, in collaboration with selected co-operation partners, established a series of events in which the focus falls on current developments and practical tips and advice. The praxisFORUM+ scores points with a professional profile and focuses entirely on practical topics such as "Process reliability – competitive advantages through stable and efficient processes." This topic was discussed by experienced practitioners and participants as part of the last praxisFORUM+ held in 2013: From "Use of online process monitoring for safeguarding safety-related components" (Dr. Martin Eckstein, MTU Aero Engines AG) to "Possibilities of tool monitoring for supporting process reliability" (Dr. Klaus Nordmann, Nordmann GmbH und Co. KG) through to "Industrial practice in using artificial intelligence in process monitoring" (Dr. Jan Brinkhaus, KOMET BRINKHAUS). Other topics were "Adaptive TNC functions for increasing the process reliability of machine tools" (Peter Topol, Dr. Johannes Heidenhain GmbH), "Working with actuating tools with flexibility and process reliability" (Ewald Hasselkuss, KOMET GROUP) and "Process reliability – competitive advantages through stable processes" (Dr. Dražen Veselovac, WZL RWTH Aachen).

The around thirty participants – among them, the author of the article, the Dutch journalist Franc Coenen – showed just as much enthusiasm for the scope and range of the event, that was held in the IDEEN-FABRIK+ in Besigheim, as for the practice-oriented supporting programme.

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Author: Franc Coenen,


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