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Study on Quality Improvement of Machine Tools
Available online at www.sciencedirect.com
ScienceDirect Procedia CIRP 59 (2017) 156 – 159
The 5th International Conference on Through-life Engineering Services (TESConf 2016)
Study on quality improvement of machine tools Makoto Fujishima1, Masahiko Mori1, Kimiyuki Nishimura1, Katsuhiko Ohno1 1 DMGMORI Co,. Ltd., Nagoya, Japan, * Corresponding author. Tel.: +81-52-587-1811; fax: +81-52-587-1818. E-mail address:[email protected]
Abstract Quality management of machine tools is the key to reducing downtime of customers’ machines and the manufacturers’ service cost. This paper introduces DMG MORI’s systematic workflow from designing, procurement, manufacturing, and acceptance inspections to the delivery of machines, which contributes to improvement of machine quality. Two quality management systems, one for before shipment and the other for after shipment, are described in this paper. Various workflow systems, data analysis, remote monitoring, continuous Kaizen approaches are integrated in the systems. However, defects of machines cannot be completely eliminated, so proactive maintenance and strong service networks are vital for business success. Especially, proactive maintenance is favorably accepted in the industry as a solution to minimize machine downtime and the repairing cost. This paper introduces various sensing technologies to improve the functions of proactive maintenance. 2016 The Authors. Published by Elsevier B.V. ©©2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Programme Committee of the 5th International Conference on Through-life Engineering Services Peer-review responsibility of the scientific committee of the The 5th International Conference on Through-life Engineering Services (TESConf 2016) (TESConfunder 2016). Keywords: machine tools; smart manufacturing; sensing
1. Introduction Until recently, machine tools utilizing the state-of-the-art technologies such as 5-axis machines and mill turn centers and the machining methods using those machines were mainly studied in research and development of the machine tool industry. However, new approaches to technical development have been drawing attention lately, e.g. various technologies such as machine tools, peripheral equipment, control units, and applications are combined. To be more specific, systems utilizing the IoT technology and the concept of Industry 4.0 and the latest machining methods such as additive manufacturing are incorporated into new solutions. The authors have been working to employ the above-mentioned technologies to machine tools. However, among customers’ demands, having machines that do not break down once they are installed and start operating at their factories are still the most important. The number of DMG MORI’s machine tools installed at customers’ factories is approximately 200,000 machines of
DMG MORI CO (DMG MORI in Japan) and 130,000 machines of DMG MORI AG (DMG MORI in Germany) are in operation. Moreover, according to the survey, 230,000 companies are potential customers of DMG MORI. Large-scale manufacturers have installed hundreds of thousands of machine tools at customers’ factories worldwide, so they need to provide meticulous services to customers to keep those machines constantly operating. If a machine tool of a customer breaks down, service engineers must visit the customer’s factory to repair the machine, and the production at the customer’s factory stops until the machine recovers. In most of such cases, customers demand that the manufacturer should recover the machine as promptly as possible. Furthermore, the average life span of machine tools is considered to be as long as 15 years and maintenance services are required during the same period. To provide maintenance services to customers for such a long period, it is necessary to carry spare parts with short life cycles such as electrical parts in stock or modify machines so that the latest spare parts can be used.
2212-8271 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the The 5th International Conference on Through-life Engineering Services (TESConf 2016) doi:10.1016/j.procir.2016.09.029
157
Makoto Fujishima et al. / Procedia CIRP 59 (2017) 156 – 159
The key to providing customers with machine tools which do not break down is to improve quality during the production processes. This is the common target for most of the divisions in the entire plant including development and manufacturing divisions. The following are the items to be achieved. 1. Common items Lean manufacturing Education/training PDCA cycle 2. Design section Design review Design verification Customer point of view evaluation 3. Manufacturing section Before shipment quality management Kaizen Inspection 4. Procurement section Supplier management Acceptance inspection Cost management Delivery management If these items are rigorously pursued, drastic improvement in the quality can be expected, defects on machine tools cannot be completely eliminated. So efficient and highly-qualified services are important, and the following two solutions are the key to providing such services.
Fig. 1 shows how the processes of the manufacturing management, quality management, and acceptance inspection are combined. These processes and the quality of machines tools are all managed at one central system by computers. Fig. 2 shows the flow of assembly work in a vertical space utilizing the 3D model and BOM system to create standard procedures for assembly work and test procedures. 2.1 Quality management before shipment Quality inspections are conducted to detect problems including potential problems at the factories before shipment to prevent problems from occurring after machine tools are delivered to the customers’ factories. Fig. 3 shows the flow of the product inspections including the positioning accuracy test, cutting test, product inspection, running test, and shipment inspection. In the quality inspection processes actions for improvement are continuously taken, contributing to the quality improvement of machine tools. 㻵㼚㼢㼑㼚㼠㼛㼞㼥㻌 㼙㼍㼚㼍㼓㼑㼙㼑㼚㼠 Parts preparation
Digital picking
㻼㼞㼛㼏㼑㼟㼟㻌 㼙㼍㼚㼍㼓㼑㼙㼑㼚㼠 VPS䠖Virtual product simulator Operation indication
Process management
WEB DMG MORI 4.0
Acceptance
Process Production check management
Web order MRP Test procedure Operation monitor
NET Inspection
(1) (2)
Detect failures before parts broken Preventive maintenance with sensing technologies Repair as soon as possible after failure Remote monitoring and maintenance system Strong service network Parts supply system
㻽㼡㼍㼘㼕㼠㼥㻌 㼙㼍㼚㼍㼓㼑㼙㼑㼚㼠
㻻㼞㼐㼑㼞㼞㻌 㼙㼍㼚㼍㼓㼑㼙㼑㼚㼠
Fig.1 Smart manufacturing at Iga facility of DMGMORI Development
3D CAD DATA
Preparation 䠄Virtual Product Simulator䠅
Quality management
Check sheet
BOM
Traceability
This paper introduces approaches to the above-mentioned contents as a machine tool manufacturer.
Barcode reader
Interference check
Standard Transfer
2. Quality management at the factory DMG MORI has 13 main factories in seven countries. This global production system, with factories in Europe, the U.S.A., and China, as well as four factories in Japan and three in Germany, reduces risks of volatile currency exchange rates, and enables optimal machine tool delivery for the customers worldwide in terms of transportation costs and lead time. Additionally, high accuracy magnescales and laser scales are produced in Isehara, and Taiyo Koki's grinding machines are produced in Nagaoka. At the factory in Iga, the largest one among the 13 main factories, medium-size and large-size machine tools are manufactured. The quality management divisions in Iga, which consists of two divisions: the before shipment quality management division and after shipment quality management division. The before shipment quality management division is responsible for inspecting machines before shipment to provide customers with high-quality machine tools, whereas the after shipment quality management division is responsible for improving the quality of machine tools after they are installed at customers’ factories.
Manufacturing
VPS
Process managem management me t me
Operation recor
ORiN
Feed back
Fig. 2 Utilization of Design data In-process inspection Self inspection by the assembly personnel
Shipment
Positioning accuracy test ISO standard test
Cutting test Cutting accuracy test
Shipment inspection
100-hours running operation
Product inspection
Inspection of packaging and bundled items at shipm shipment
Overall running operation of 100 hours in total, covering all roces oces oc o ce c e es sses ses se processes
specifications, functions, embedded software and safety
Fig.3 Product inspection
158
Makoto Fujishima et al. / Procedia CIRP 59 (2017) 156 – 159
3.
Tolerance(䡚 䡚2013䠅 New Tolerance(2014 䡚䠅
Fig. 4 Accuracy improvement process Fig. 4 shows the sampling of measurement results of the Xaxis positioning accuracy of horizontal machining centers. The accuracy of 80% within the allowable range is constantly achieved thanks to daily efforts to take actions for accuracy improvement. The allowable range of accuracy is reviewed every year and an even more challenging target is set depending on the measurement result. 2.2 Quality management after shipment In the quality management after shipment, problems which have occurred at customers’ factories are managed, so solving those problems and taking countermeasures to prevent recurrence of the same problems are important. If a problem occurs at a customer’s factory, the service engineer in the region issues the product problem report system (PPR). The After Shipment Quality Management Group receives the report, and forwards it to the related division(s) with instructions about what need to be done. When a critical problem occurs or the same type of the problem occurs on multiple machines, the After Shipment Quality Management Group instructs to change design or change the procedure in the manufacturing process to prevent recurrence of the same problem. Remote monitoring is efficiently utilized in the quality management after shipment. Approximately 10,000 machine tools are connected to the DMG MORI’s network and these machine tools are monitored remotely [1]. When a problem occurs at DMG MORI’s customer’s factory, detailed information about the machine such as the diagnosis result by CNC and the alarm history can be checked at offices of DMG MORI to promptly solve the problem (Fig. 5). Customer’s Factory Problem
Machine Tool Manufacturer’s Service Center
mobile phone network
Diagnostic requests can be automatically sent by machine or manually sent by machine operator.
Problem is diagnosed and repaired
Screen information (Data is compressed)
Operate and monitor CNC screen One screen information can be displayed in 3sec
Fig. 5 Remote monitoring system
Sensing technologies for machine tool The paper has explained quality management and services to be provided after shipment so far. As a next challenge, the paper introduces preventive maintenance and predictive maintenance [2], [3] in which sensing technologies are utilized. Many sensors have been effectively used lately in various fields such as consumer appliances, health care, transportation, and businesses. Numerous sensors actually function these days, many of which were once thought to be inconceivable to be put into practice. Consequently, the production volume of sensors increased, while production costs per unit decreased. According to the 2013 TSensors Summit, the volume in the mobile sensor market grew exponentially, exceeding annual increases of 200% between 2007 and 2012. Visionary organizations foresee the number of sensors will reach trillions within the next decade [4], exceeding the sales of billions in 2012 due to the recent growth of the demands for sensors.. More and more sensors will be utilized for machine tools in the near future. Members of CIRP have been studying various types of monitoring technologies by using sensors [5] , [6], and determined that some of the technologies will be effective, if they are put into practice. The goal of this study is, therefore, to develop a test machine equipped with various sensors and utilizing practical applications in the industry by employing sensing technologies that were studied in the past. In this study, acceleration sensors embedded in the spindle unit were used to measure chatter vibration, collision impact, and abnormal bearing vibration. A coolant level sensor, developed by ourselves, is advantageous in terms of cost and performance. Electric current and voltage sensors were used to measure energy consumption of the entire machine tool. Temperature sensors embedded in the spindle unit and table were used to compensate thermal displacement or diagnose spindle bearings. Motor power and spindle speed obtained from the NC unit were utilized as well. Machine tool input-output (I/O) signal lines are usually connected to the Programmable Logic Controller (PLC). I/O signals are mostly digital binary at DC24V. Analogue signals can be received by the PLC, but a generic PLC is not suitable to receive high-speed analogue signals in sensing technology studies. The sampling rate required for acceleration sensors exceeds several kHz, which is several fold of chatter vibration frequency. Since generic PLC control cycles commonly perform only in the millisecond range, a platform that allows machine tool manufacturers to utilize sensor data without limitations of the PLC or NC unit was developed [7]. The backbone route of the sensing network was structured with the 100BASE-TX Ethernet. Because sensors cannot be connected to the Ethernet directly, four types of interface boards for sensor signal inputs and Ethernet outputs were developed. The Data Acquisition FFT Board (DAQF) has three acceleration sensor interfaces and two temperature sensor interfaces. In addition, the real time FFT function is embedded in this circuit board. The Data Acquisition Temperature Board (DAQT) is a general A/D converter board with the voltage input terminal and thermistor interface. The Electrical Power Monitor Board (EPM) is connected to electrical current sensors and voltage sensors, which were placed at three-phase
Makoto Fujishima et al. / Procedia CIRP 59 (2017) 156 – 159
ATC, Magazine Preventive Maintenance 䞉 Motor load and torque
Chattering control
Balance monitoring/ control
䞉XYZ Vibration sensors 䞉Motor load
䞉SP Balancing data 䞉Bearing temp. and vibration data
B Axis automatic rotation adjustment 䞉 Servo data from motor drivers
Hydraulic management 䞉 Pressure 䞉 Controller alarm
Power monitor
䞉Contamination of oil
䞉Power consumption
(Voltage & current)
Oil cooler management
Remote monitoring 䞉Alarm signal 䞉Operation monitor 䞉sensing data
䞉 M/C body temp. 䞉 Oil Temp. 䞉 Atmosphere temp. 䞉 Motor load 䞉 Controller alarm
Automatic servo tuning
Distortion Compensation
Machine leveling
䞉Servo data from motor drivers 䞉Vibration data
䞉Load cell data
䞉Vibration data 䞉Temp. data
Coolant quality 䞉Coolant level 䞉 Water level and temp. data 䞉 Contamination level
Fig.6 Sensing items for machining center power supply. Aside from calculating electrical power consumption, this function monitors power supply quality. The EPM is also connected to the coolant level sensor. Fig. 6 shows all the sensing items which could be mounted on a machining center, e.g. sensors for the spindle, table, ATC, magazine, coolant, power consumption and so on. The coolant level sensor and power consumption sensor are introduced. A new approach for the measurement of the coolant level is introduced here. This system uses a capacitance-type original level sensor shown in Fig. 7. The electrodes of this sensor fall into nine areas. Each electrode pair has different capacitance values depending on whether the electrode is in the air or submerged in coolant. The collected capacitance values were converted to voltage values and transferred to the EPM through the RS485 interface. Nine electrode pairs as the sensor device and the control circuit are on one circuit board, which makes the sensor cost less expensive than a currently available level sensor.
The coolant level in the tank can be easily detected with this sensor. That is, monitoring the clean tank and dirty tank enables us to predict when the filter between the tanks needs cleaning or replacing. The timing is when the difference between coolant levels of both tanks becomes higher than a certain level. Reducing the power consumption of a machine tool is one of the most important themes. The authors have studied power saving and experienced that power consumption was actually reduced on actual machine tools by employing some of the technologies that were studied. The next step is to monitor and visualize power consumption of each machine tool. A digitalcomputing-type power meter was developed for this. The voltage sensor and electric current sensor were attached to the three-phase power input area so that samples of the voltage and electric current are collected simultaneously at a high speed, analog data is converted to digital data, and instantaneous power is calculated by multiplying the data with the microprocessor(Fig.8). The result is processed by the averaging procedure for a period of one cycle (T), the active power P is calculated, and the active power P is displayed on a HMI via the Ethernet. This system measures power consumption and detects abnormal power consumption as well, which enables us to determine machining processes and predict potential problems for machine tools. Though many sensor technologies have been widely used on machine tool, the security of such application is still a concern. This includes the integrity of sensing data transmission, customer specific data protection and reliable sensing acquisition system to prevent harmful attack. The security issue needs further investigation, and this paper does not cover the topic. 4. Conclusion (1) Smart manufacturing enables us to efficiently manage the quality of machine tools before shipment in the factory. (2) Remote monitoring enables us to efficiently perform maintenance work for customers’ machines after shipment. (3) Sensing enables us to improve functions of preventive maintenance. References
Fig. 7 Level sensor and inner circuit Machine
PCB board
Sensor data
Ethernet
Controller 0䠉440V
0䠉6V ADC
㽢
+
ADC ADC
P1
㽢
Ptotal
P2 Data collection
ADC
Ptotal = P1 + P2 Factory server
i1
5 i2
6 V1
V2
LOAD
Fig.8 Power consumption monitoring system
159
[1] Mori, M. Fujishima, M. Komatsu, Bingyan Zhao, Yadong Liu, 2008, Development of Remote Monitoring and Maintenance System for Machine Tools, Annals of the CIRP, 57/1 [2] Jay Lee, Machine performance monitoring and proactive maintenance in computer-integrated manufacturing: review and perspective, International Journal of Computer Integrated Manufacturing, 4/3/2007 [3] Cunha, P.F. Caldeira Duarte, J.A. Alting, L. 2004, Development of a productive service module based on a life cycle perspective of maintenance issues, Annals of the CIRP, 53/1, 13-16 [4] N.N, 2013, The TSensors Roadmap, www.tsensorssummit.org/Resources/TSensors%20Roadmap%20v1.pdf, [5] H.C. Möhring, K.M. Litwinski, O. Gümmer, 2010, Process Monitoring with Sensory Machine Tool Components, CIRP Annals, 59/1:383-386 [6] R. Teti, K. Jemielniak, G. O'Donnell, D. Dornfeld, 2010, Advanced monitoring of machining operations, CIRP Annals, 59/2:717-739. [7] Fujishima, M., Ohno, K., Nishikawa, S., Nishimura, K., Sakamoto, M., & Kawai, K. 2016. Study of sensing technologies for machine tools. CIRP Journal of Manufacturing Science and Technology.
ScienceDirect Procedia CIRP 59 (2017) 156 – 159
The 5th International Conference on Through-life Engineering Services (TESConf 2016)
Study on quality improvement of machine tools Makoto Fujishima1, Masahiko Mori1, Kimiyuki Nishimura1, Katsuhiko Ohno1 1 DMGMORI Co,. Ltd., Nagoya, Japan, * Corresponding author. Tel.: +81-52-587-1811; fax: +81-52-587-1818. E-mail address:[email protected]
Abstract Quality management of machine tools is the key to reducing downtime of customers’ machines and the manufacturers’ service cost. This paper introduces DMG MORI’s systematic workflow from designing, procurement, manufacturing, and acceptance inspections to the delivery of machines, which contributes to improvement of machine quality. Two quality management systems, one for before shipment and the other for after shipment, are described in this paper. Various workflow systems, data analysis, remote monitoring, continuous Kaizen approaches are integrated in the systems. However, defects of machines cannot be completely eliminated, so proactive maintenance and strong service networks are vital for business success. Especially, proactive maintenance is favorably accepted in the industry as a solution to minimize machine downtime and the repairing cost. This paper introduces various sensing technologies to improve the functions of proactive maintenance. 2016 The Authors. Published by Elsevier B.V. ©©2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Programme Committee of the 5th International Conference on Through-life Engineering Services Peer-review responsibility of the scientific committee of the The 5th International Conference on Through-life Engineering Services (TESConf 2016) (TESConfunder 2016). Keywords: machine tools; smart manufacturing; sensing
1. Introduction Until recently, machine tools utilizing the state-of-the-art technologies such as 5-axis machines and mill turn centers and the machining methods using those machines were mainly studied in research and development of the machine tool industry. However, new approaches to technical development have been drawing attention lately, e.g. various technologies such as machine tools, peripheral equipment, control units, and applications are combined. To be more specific, systems utilizing the IoT technology and the concept of Industry 4.0 and the latest machining methods such as additive manufacturing are incorporated into new solutions. The authors have been working to employ the above-mentioned technologies to machine tools. However, among customers’ demands, having machines that do not break down once they are installed and start operating at their factories are still the most important. The number of DMG MORI’s machine tools installed at customers’ factories is approximately 200,000 machines of
DMG MORI CO (DMG MORI in Japan) and 130,000 machines of DMG MORI AG (DMG MORI in Germany) are in operation. Moreover, according to the survey, 230,000 companies are potential customers of DMG MORI. Large-scale manufacturers have installed hundreds of thousands of machine tools at customers’ factories worldwide, so they need to provide meticulous services to customers to keep those machines constantly operating. If a machine tool of a customer breaks down, service engineers must visit the customer’s factory to repair the machine, and the production at the customer’s factory stops until the machine recovers. In most of such cases, customers demand that the manufacturer should recover the machine as promptly as possible. Furthermore, the average life span of machine tools is considered to be as long as 15 years and maintenance services are required during the same period. To provide maintenance services to customers for such a long period, it is necessary to carry spare parts with short life cycles such as electrical parts in stock or modify machines so that the latest spare parts can be used.
2212-8271 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the The 5th International Conference on Through-life Engineering Services (TESConf 2016) doi:10.1016/j.procir.2016.09.029
157
Makoto Fujishima et al. / Procedia CIRP 59 (2017) 156 – 159
The key to providing customers with machine tools which do not break down is to improve quality during the production processes. This is the common target for most of the divisions in the entire plant including development and manufacturing divisions. The following are the items to be achieved. 1. Common items Lean manufacturing Education/training PDCA cycle 2. Design section Design review Design verification Customer point of view evaluation 3. Manufacturing section Before shipment quality management Kaizen Inspection 4. Procurement section Supplier management Acceptance inspection Cost management Delivery management If these items are rigorously pursued, drastic improvement in the quality can be expected, defects on machine tools cannot be completely eliminated. So efficient and highly-qualified services are important, and the following two solutions are the key to providing such services.
Fig. 1 shows how the processes of the manufacturing management, quality management, and acceptance inspection are combined. These processes and the quality of machines tools are all managed at one central system by computers. Fig. 2 shows the flow of assembly work in a vertical space utilizing the 3D model and BOM system to create standard procedures for assembly work and test procedures. 2.1 Quality management before shipment Quality inspections are conducted to detect problems including potential problems at the factories before shipment to prevent problems from occurring after machine tools are delivered to the customers’ factories. Fig. 3 shows the flow of the product inspections including the positioning accuracy test, cutting test, product inspection, running test, and shipment inspection. In the quality inspection processes actions for improvement are continuously taken, contributing to the quality improvement of machine tools. 㻵㼚㼢㼑㼚㼠㼛㼞㼥㻌 㼙㼍㼚㼍㼓㼑㼙㼑㼚㼠 Parts preparation
Digital picking
㻼㼞㼛㼏㼑㼟㼟㻌 㼙㼍㼚㼍㼓㼑㼙㼑㼚㼠 VPS䠖Virtual product simulator Operation indication
Process management
WEB DMG MORI 4.0
Acceptance
Process Production check management
Web order MRP Test procedure Operation monitor
NET Inspection
(1) (2)
Detect failures before parts broken Preventive maintenance with sensing technologies Repair as soon as possible after failure Remote monitoring and maintenance system Strong service network Parts supply system
㻽㼡㼍㼘㼕㼠㼥㻌 㼙㼍㼚㼍㼓㼑㼙㼑㼚㼠
㻻㼞㼐㼑㼞㼞㻌 㼙㼍㼚㼍㼓㼑㼙㼑㼚㼠
Fig.1 Smart manufacturing at Iga facility of DMGMORI Development
3D CAD DATA
Preparation 䠄Virtual Product Simulator䠅
Quality management
Check sheet
BOM
Traceability
This paper introduces approaches to the above-mentioned contents as a machine tool manufacturer.
Barcode reader
Interference check
Standard Transfer
2. Quality management at the factory DMG MORI has 13 main factories in seven countries. This global production system, with factories in Europe, the U.S.A., and China, as well as four factories in Japan and three in Germany, reduces risks of volatile currency exchange rates, and enables optimal machine tool delivery for the customers worldwide in terms of transportation costs and lead time. Additionally, high accuracy magnescales and laser scales are produced in Isehara, and Taiyo Koki's grinding machines are produced in Nagaoka. At the factory in Iga, the largest one among the 13 main factories, medium-size and large-size machine tools are manufactured. The quality management divisions in Iga, which consists of two divisions: the before shipment quality management division and after shipment quality management division. The before shipment quality management division is responsible for inspecting machines before shipment to provide customers with high-quality machine tools, whereas the after shipment quality management division is responsible for improving the quality of machine tools after they are installed at customers’ factories.
Manufacturing
VPS
Process managem management me t me
Operation recor
ORiN
Feed back
Fig. 2 Utilization of Design data In-process inspection Self inspection by the assembly personnel
Shipment
Positioning accuracy test ISO standard test
Cutting test Cutting accuracy test
Shipment inspection
100-hours running operation
Product inspection
Inspection of packaging and bundled items at shipm shipment
Overall running operation of 100 hours in total, covering all roces oces oc o ce c e es sses ses se processes
specifications, functions, embedded software and safety
Fig.3 Product inspection
158
Makoto Fujishima et al. / Procedia CIRP 59 (2017) 156 – 159
3.
Tolerance(䡚 䡚2013䠅 New Tolerance(2014 䡚䠅
Fig. 4 Accuracy improvement process Fig. 4 shows the sampling of measurement results of the Xaxis positioning accuracy of horizontal machining centers. The accuracy of 80% within the allowable range is constantly achieved thanks to daily efforts to take actions for accuracy improvement. The allowable range of accuracy is reviewed every year and an even more challenging target is set depending on the measurement result. 2.2 Quality management after shipment In the quality management after shipment, problems which have occurred at customers’ factories are managed, so solving those problems and taking countermeasures to prevent recurrence of the same problems are important. If a problem occurs at a customer’s factory, the service engineer in the region issues the product problem report system (PPR). The After Shipment Quality Management Group receives the report, and forwards it to the related division(s) with instructions about what need to be done. When a critical problem occurs or the same type of the problem occurs on multiple machines, the After Shipment Quality Management Group instructs to change design or change the procedure in the manufacturing process to prevent recurrence of the same problem. Remote monitoring is efficiently utilized in the quality management after shipment. Approximately 10,000 machine tools are connected to the DMG MORI’s network and these machine tools are monitored remotely [1]. When a problem occurs at DMG MORI’s customer’s factory, detailed information about the machine such as the diagnosis result by CNC and the alarm history can be checked at offices of DMG MORI to promptly solve the problem (Fig. 5). Customer’s Factory Problem
Machine Tool Manufacturer’s Service Center
mobile phone network
Diagnostic requests can be automatically sent by machine or manually sent by machine operator.
Problem is diagnosed and repaired
Screen information (Data is compressed)
Operate and monitor CNC screen One screen information can be displayed in 3sec
Fig. 5 Remote monitoring system
Sensing technologies for machine tool The paper has explained quality management and services to be provided after shipment so far. As a next challenge, the paper introduces preventive maintenance and predictive maintenance [2], [3] in which sensing technologies are utilized. Many sensors have been effectively used lately in various fields such as consumer appliances, health care, transportation, and businesses. Numerous sensors actually function these days, many of which were once thought to be inconceivable to be put into practice. Consequently, the production volume of sensors increased, while production costs per unit decreased. According to the 2013 TSensors Summit, the volume in the mobile sensor market grew exponentially, exceeding annual increases of 200% between 2007 and 2012. Visionary organizations foresee the number of sensors will reach trillions within the next decade [4], exceeding the sales of billions in 2012 due to the recent growth of the demands for sensors.. More and more sensors will be utilized for machine tools in the near future. Members of CIRP have been studying various types of monitoring technologies by using sensors [5] , [6], and determined that some of the technologies will be effective, if they are put into practice. The goal of this study is, therefore, to develop a test machine equipped with various sensors and utilizing practical applications in the industry by employing sensing technologies that were studied in the past. In this study, acceleration sensors embedded in the spindle unit were used to measure chatter vibration, collision impact, and abnormal bearing vibration. A coolant level sensor, developed by ourselves, is advantageous in terms of cost and performance. Electric current and voltage sensors were used to measure energy consumption of the entire machine tool. Temperature sensors embedded in the spindle unit and table were used to compensate thermal displacement or diagnose spindle bearings. Motor power and spindle speed obtained from the NC unit were utilized as well. Machine tool input-output (I/O) signal lines are usually connected to the Programmable Logic Controller (PLC). I/O signals are mostly digital binary at DC24V. Analogue signals can be received by the PLC, but a generic PLC is not suitable to receive high-speed analogue signals in sensing technology studies. The sampling rate required for acceleration sensors exceeds several kHz, which is several fold of chatter vibration frequency. Since generic PLC control cycles commonly perform only in the millisecond range, a platform that allows machine tool manufacturers to utilize sensor data without limitations of the PLC or NC unit was developed [7]. The backbone route of the sensing network was structured with the 100BASE-TX Ethernet. Because sensors cannot be connected to the Ethernet directly, four types of interface boards for sensor signal inputs and Ethernet outputs were developed. The Data Acquisition FFT Board (DAQF) has three acceleration sensor interfaces and two temperature sensor interfaces. In addition, the real time FFT function is embedded in this circuit board. The Data Acquisition Temperature Board (DAQT) is a general A/D converter board with the voltage input terminal and thermistor interface. The Electrical Power Monitor Board (EPM) is connected to electrical current sensors and voltage sensors, which were placed at three-phase
Makoto Fujishima et al. / Procedia CIRP 59 (2017) 156 – 159
ATC, Magazine Preventive Maintenance 䞉 Motor load and torque
Chattering control
Balance monitoring/ control
䞉XYZ Vibration sensors 䞉Motor load
䞉SP Balancing data 䞉Bearing temp. and vibration data
B Axis automatic rotation adjustment 䞉 Servo data from motor drivers
Hydraulic management 䞉 Pressure 䞉 Controller alarm
Power monitor
䞉Contamination of oil
䞉Power consumption
(Voltage & current)
Oil cooler management
Remote monitoring 䞉Alarm signal 䞉Operation monitor 䞉sensing data
䞉 M/C body temp. 䞉 Oil Temp. 䞉 Atmosphere temp. 䞉 Motor load 䞉 Controller alarm
Automatic servo tuning
Distortion Compensation
Machine leveling
䞉Servo data from motor drivers 䞉Vibration data
䞉Load cell data
䞉Vibration data 䞉Temp. data
Coolant quality 䞉Coolant level 䞉 Water level and temp. data 䞉 Contamination level
Fig.6 Sensing items for machining center power supply. Aside from calculating electrical power consumption, this function monitors power supply quality. The EPM is also connected to the coolant level sensor. Fig. 6 shows all the sensing items which could be mounted on a machining center, e.g. sensors for the spindle, table, ATC, magazine, coolant, power consumption and so on. The coolant level sensor and power consumption sensor are introduced. A new approach for the measurement of the coolant level is introduced here. This system uses a capacitance-type original level sensor shown in Fig. 7. The electrodes of this sensor fall into nine areas. Each electrode pair has different capacitance values depending on whether the electrode is in the air or submerged in coolant. The collected capacitance values were converted to voltage values and transferred to the EPM through the RS485 interface. Nine electrode pairs as the sensor device and the control circuit are on one circuit board, which makes the sensor cost less expensive than a currently available level sensor.
The coolant level in the tank can be easily detected with this sensor. That is, monitoring the clean tank and dirty tank enables us to predict when the filter between the tanks needs cleaning or replacing. The timing is when the difference between coolant levels of both tanks becomes higher than a certain level. Reducing the power consumption of a machine tool is one of the most important themes. The authors have studied power saving and experienced that power consumption was actually reduced on actual machine tools by employing some of the technologies that were studied. The next step is to monitor and visualize power consumption of each machine tool. A digitalcomputing-type power meter was developed for this. The voltage sensor and electric current sensor were attached to the three-phase power input area so that samples of the voltage and electric current are collected simultaneously at a high speed, analog data is converted to digital data, and instantaneous power is calculated by multiplying the data with the microprocessor(Fig.8). The result is processed by the averaging procedure for a period of one cycle (T), the active power P is calculated, and the active power P is displayed on a HMI via the Ethernet. This system measures power consumption and detects abnormal power consumption as well, which enables us to determine machining processes and predict potential problems for machine tools. Though many sensor technologies have been widely used on machine tool, the security of such application is still a concern. This includes the integrity of sensing data transmission, customer specific data protection and reliable sensing acquisition system to prevent harmful attack. The security issue needs further investigation, and this paper does not cover the topic. 4. Conclusion (1) Smart manufacturing enables us to efficiently manage the quality of machine tools before shipment in the factory. (2) Remote monitoring enables us to efficiently perform maintenance work for customers’ machines after shipment. (3) Sensing enables us to improve functions of preventive maintenance. References
Fig. 7 Level sensor and inner circuit Machine
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Fig.8 Power consumption monitoring system
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