Machine monitoring Switzerland: Unmanned production through process monitoring

Machine monitoring is a prerequisite for reliable, safe unmanned production. Bär und Mettler uses the monitoring system Artis CTM from Marposs.

Swiss Tool System is one of the world's most important manufacturers of system tools, specializing in spindle systems and holders for turning machining. Headquartered in Bürglen, Thurgau, Switzerland, Bär und Mettler AG is the production company for Swiss Tool System.

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Productivity is pivotal

For finishing in their grinding shop, Bär und Mettler requires quality expertise more than anything else. Here, precision and accuracy must be ensured to a micrometre-level. In preliminary turning and milling, on the other hand, the main focus is on productivity. "Of course precise production is also essential in turning and milling, but productivity is the crucial factor here", explains Peter Heinemann, CTO at Swiss Tool System. He adds: "The machines must work reliably and unmanned around the clock."

For this purpose, appropriate machine tools were purchased and equipped with assistance systems to support unmanned operation. Bär und Mettler have chosen three Doosan Puma MX 2100 multi tasking turning centres for this work. This machining centre allows for complete machining of a part in a machine and with the milling head in its B-axis also a very flexible manufacturing of complex components.

The Doosan machines were equipped with the Marposs Artis CTM monitoring system, because Doosan's own monitoring system did not meet the demands of Bär und Mettler’s production.

"The Doosan system was simply not sensitive enough for our small tools and diameters," says P. Heinemann. He adds: "Also, it is important for us to measure parallel to main time. Thus, tool monitoring with mechanical or tactile systems was not suitable for us. Furthermore, we have already used Artis systems on our old machines."

Monitoring of complex machining processes with CTM

Influences on processes from machine, tool and workpiece must be reliably recognized to prevent damage and unplanned shutdowns. Maximising tool usage and avoiding scrap are essential to ensure and increase productivity. Bär und Mettler for example always operate two parallel tools parallel, which are monitored simultaneously. The main requirement of the selected tool, process and machine condition monitoring system Artis CTM thus was to monitor all process-relevant spindles and axes parallel. It was integrated into the machine via existing standard interfaces (Ethernet with FOCAS2). The machining processes are dynamically monitored using the existing digital control signals (DTA = digital torque adapter) of both spindles and the relevant five feed axis. This means that the Artis CTM system automatically selects the four most appropriate spindle/axle signals for real-time monitoring from the eight control signals. This allows for selective monitoring of the various tools, without the need for additional external sensors.

Variation in the process can be detected immediately

The CTM system logs the entire process and creates appropriate curve diagrams via its statistics function. The data can be stored on the Artis Terminal (Windows) or in the network. The system basically "learns" the ideal process for each workpiece and processing step. Later variations (process anomalies) can be detected immediately at every moment of the process. Standard monitoring methods are breakage, lack, overload and tool wear, for which alarm and notification limits are individually set and parameterised. The monitoring works reliably from the first go. CTM's self-adjusting system (SAS) with self-calibrating segmentation and adjustment responds automatically to process variations, thus greatly simplifying settings and interventions.

"We notice any changes in the process immediately", says P. Heinemann. Not only potential tool breakage, but also tool wear can be identified. To achieve this, a trend in the development of the processes' total force is observed over a period of time. As soon as a set limit is reached, the process is either switched to a spare tool or another response is initiated depending on manufacturing strategy. Bär und Mettler for example do not use spare tools because of their small lot sizes.

"The global service network Marposs offers supports their clients’ monitoring: In case of questions, Marposs service staff can log into the Windows-based system via Team Viewer. The investment cost for an Artis-CTM system is about two or three percent of the machine tool’s total costs."

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Minimum 130 spindle hours per week

The manufacture of modular tool systems requires a high degree of flexibility. Lot sizes are usually between 20 and 500 pieces. "We want to achieve at least 130 spindle hours per week", says P. Heinemann. This requires a 24/7 production, where only one shift is manned. P Heinemann adds: "At the moment, we are at almost 115 hours. Machine- and system-wise, we already meet the requirements for a higher number of spindle hours, but we have only installed the systems in early 2015 and now the proper planning is crucial."

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