加工中心鏈式刀庫及控制系統(tǒng)設計5張CAD圖,加工,中心,鏈式,控制系統(tǒng),設計,CAD Applied Mechanics and Materials Vols 271-272 (2013) pp 461-465 Online: 2012-12-27 ? (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.271-272.461 Reliability Evaluation of Chain-type Tool Magazine and ATC Xiaohong Lua, Pengzhuo Hanb,Wenyi Wuc Key Laboratory for Precision and Non-traditional Machining Technology of Ministry of Education, Dalian University of Technology, Dalian 116024, China. a lxhdlut@dlut.edu.cn, b hanpengzhuo@mail.dlut.edu.cn, c wuwenyiwwy@mail.dlut.edu.cn Keywords: Chain-type tool magazine, ATC, Reliability, Mean tool change numbers between failures, Mean time to repair Abstract. As the tool magazine and automatic tool changer (ATC) are the important function units to reserve and change tools for the machining center, the tool-changing rate affects their reliability life which directly influences the performance level of the machining center. However, the reliability of the tool magazine and ATC has not yet got a reasonable evaluation index. Directing at the features of the tool magazine and ATC system, the mean tool change numbers between failures evaluation index is proposed, which is used to calculate the mean time to repair and estimate the collected failure data of the chain-type tool magazine and ATC. It can be seen that the tool magazine with continuous tool-changing adopts the mean tool change numbers between failures as the reliability evaluation index. Introduction Reliability evaluation is the one of the most important section of the reliability study on CNC machine tool. The purpose of it is to master the status of the tool, put forward the goals and tasks of the reliability design work and make a direction to the further studies on reliability. In studies of CNC machine tool reliability evaluation, Huazhong University of Science and Technology[1,2] and Tianjin Vocational and Technical Normal University proposed a reliability assessment based on performance degradation data. Shanghai Jiaotong University[3,4] research the reliability evaluation about the time-terminated test on a variety of CNC machine tool in use of Weibull mixture model and then put forward some model of time-terminated test on CNC machine tool as well as parameter estimation of time between failures' methods. Jilin University and Dalian University of Technology[5,6] took the fuzzy theory into the research on reliability of CNC machine tool and came up with a comprehensive fuzzy reliability allocation method oh CNC machine tool. Wang Guiping[7] studied the machining center failure analysis methods which are faced on reliability and green, evaluation methods and growth strategy. As the tool magazine and automatic tool changer (ATC) are the important function units to reserve and exchange tools for the machining center, their tool-changing rate affect their reliability life which directly influences the performance level of the machining center. However, the reliability has not yet get a reasonable evaluation index. The tool-changing rate of the tool magazine and ATC affects their reliability life greatly. To the same product, its lifetime difference is great between in one processing with changing tools frequently and in another with changing tools seldom. It can’t evaluate the property of the tool magazine and ATC product only by adopting MTBF (Mean Time between Failures) as the reliability evaluation index. Therefore, based on the science and technology major projects “The Development Study of the Large Chain-type Tool Magazine, the High-speed Disk-type Tool Magazine and the Automatic Tool Changer” in the All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 132.174.254.159, Pennsylvania State University, University Park, USA-23/05/15,09:58:33) 462 Frontiers of Manufacturing and Design Science III national “High-grade NC machine tools and basic manufacturing equipment”, this paper summarizes and analyses the study of reliability evaluation to the domestic and overseas CNC and their key function units. Through the laboratory accelerated test on the large-scale chain-type tool magazine and ATC, the tool-changing times is recorded, and their reliability is evaluated based on the MTCNBF (mean tool change numbers between failures) and MTTR (Mean Time to Repair). This paper explored the reliability evaluation methods on the large-scale chain-type tool magazine and ATC, expecting to provide reference for the development of the CNC and their function units’ reliability level. Reliability Evaluation of Chain-Type Tool Magazine and Automatic Tool Changer Chain-type tool magazine and ATC system includes tool magazine, ATC, CNC system and simulation spindle, shown as Fig.1. The operation of tool magazine is realized by servomotor, planetary reduction gear drives chain wheel and chain to choose the tool. In the ATC of tool magazine, the exchange of the tool and the switch motion of protective door is achieved through the chain drives roller type of rotor cambered surface multiple mounted cam. The power producer of chain driving comes from gear motor, transducer controls the rate of manipulator tool changing, and time of tool changing can be adjusted. In the reliability test of tool magazine system, the tool changing time of tool- to-tool is 3.0 seconds. The process of tool changing includes choosing the tool, tool cylinder sends separating cover and tool to the location of tool changing. The technical parameters of the studied chain-type tool magazine and ATC system are in Table.1. Fig. 1 The chain-type tool magazine and ATC for testing Table 1 The technical parameters of the studied chain-type tool magazine system Item The technical parameters Tool warehouse capacity 40/60[T] Largest cutter length 500[mm] Maximum tool weight 25[kg] Tool- to-tool changing time 3.0[s] The largest knife storage capacity 600/900[kg] Applied Mechanics and Materials Vols. 271-272 463 The failure data of Table 2 comes from the accelerate reliability test of MDH-80 Chain-type tool magazine system in Dalian Golden CNC Group CORP... According to the sampling principle, 3 chain-type tool magazine and ATC system is chosen to perform the accelerate reliability test, the testing time of each chain-type tool magazine and ATC is 30 days, and 8 hours per day, in total, the circle of tool changing is 60 circles, changing tool 80 times per circle. So the tool changing times is 4800 in one day, equally, tool changing 10 times per minute. 14 failure data have been gotten. Description of the failure Number Failure start Failure end Failure Failure Failure repair date date start time end time time[min] The tool magazine stalls 1 2011.12.05 2011.12.05 14:35 14:40 5 The abnormal noise appears in 1 2011.12.14 2011.12.14 7:40 9:20 100 The tool falls in ATC 1 2011.12.18 2011.12.18 8:10 8:30 20 Tool magazine stuck 1 2011.12.23 2011.12.23 9:45 12:10 145 Splined shaft and bushing wear 1 2011.12.28 2011.12.28 9:30 12:00 150 Tool magazine stop turning 2 2012.02.04 2012.02.04 10:00 10:05 5 Grasping tool is not in place 2 2012.02.10 2012.02.10 13:20 13:35 15 Inserting tool is not in place 2 2012.02.20 2012.02.20 15:55 16:15 20 Pocket impact is too large 2 2012.02.27 2012.02.27 14:50 18:40 230 Inserting the tool is not in place 3 2012.03.08 2012.03.08 13:05 13:30 25 Pocket is stuck 3 2012.03.19 2012.03.19 9:30 12:00 150 The tool falls in ATC 3 2012.03.21 2012.03.21 15:30 15:35 5 Splined shaft and bushing wear 3 2012.03.26 2012.03.26 10:40 12:50 130 The abnormal noise appears in 3 2012.03.30 2012.03.30 9:00 10:30 90 Table 2 The failure data of MDH-80 chain-type tool magazine system ATC and tear and tear ATC Mean Tool Change Numbers between Failures MTCNBF (Mean Tool Change Numbers between Failures) is proposed as a reliability evaluation index of the tool magazine and automatic tool changer, which indicates the average number of tool change between the adjacent two failures. It calculates as follows: MTCNBF = k  n ?S j j =1 n ?rj j =1  (1) n:number of samples, Sj: the cumulative tool change number of the j set sample in an assessment cycle, rj: the cumulative fault number of the j set sample in an assessment cycle, k: Correction factor and its value is as follows in Table.3 Cumulative times of tool change for each chain-type tool magazine and ATC can be drawn from the processed and calculated failure data in Table 2. 464 Frontiers of Manufacturing and Design Science III Table 3 The correction factor of MTCNBF Cumulative times of tool changes of the first chain-type tool magazine and ATC: Serial Number Maximum Weight of tool [Kg] Tool Magazine Capacity [T] Tool Change Time [s] k 1 ≤20 ≤60 ≥3 1.1 2 ≤20 ≤60 <3 1.0 3 ≤20 >60 ≥3 1.0 4 ≤20 >60 <3 0.9 5 >20 ≤60 ≥3 1.0 6 >20 ≤60 <3 0.9 7 >20 >60 ≥3 0.9 8 >20 >60 <3 0.8 S = 30 ′ 4800 - (5 + 100 + 20 + 145 + 150（′10 = 139800 （ 1 S = 30 ′ 4800 - (5 + 15 + 20 + 230) ) （ Cumulative times of tool changes of the second chain-type tool magazine and ATC: ′10 = 141300 2 S = 30′ 4800 - (25 +150 + 5 +130 + 90 Cumulative times of tool changes of the third chain-type tool magazine and ATC: 3 ) ′10 = 140000 According to the data in Table 2, a total of 14 failures in 3 chain-type tool magazines, the sample number is 3, the correction factor is 1.0. S1=139800, S2=141300, S3=140000, bringing them into Eq. 1: MTCNBF = 1 3 S ? j 14 j=1 = 1 (139800 + 141300 + 140000) = 30078 14 Take 9 sets chain-type tool magazine and ATC developed by Dalian Golden CNC Group Corp. for example, the average tool change times of the studied chain-type tool magazine and ATC is about 30000 applied on horizontal machining center. It will last one more year to obtain the MTCNBR, if the user evaluates the reliability in the course of machining. However, by exposing the weak spots of the chain-type tool magazine and ATC based on reliability tests, it will only last one month. Consequently this characteristic provides timely reference for the design of reliability growth of chain-type tool magazine and ATC. Mean Time To Repair Traditional MTTR (Mean Time To Repair) indicates the average time interval from the beginning of failure to maintenance end. It calculates as follows. MTTR = 1 N  n ?Ti =  n ?Ti i =1 n  (2) 0 i =1 ?ri i =1 N0: Cumulative fault frequency of system in an assessment cycle, n: Sample number of system, Ti: Corrective maintenance time of the i system in an assessment cycle, ri: fault frequency of the i system in an assessment cycle. According to the data in Table 2, the cumulative corrective maintenance time for each chain-type tool magazine and ATC can be calculated: T1= 7 [h], T2= 4.5 [h], T3= 6.7 [h]. There are 14 failures in 3 chain-type tool magazines. Bringing them into Eq. 2, the MTTR is 1.30 [h]. It can be concluded that the MTTR is about 1.3 [h] of the studied chain-type tool magazine and ATC. Applied Mechanics and Materials Vols. 271-272 465 Summary Directing at the features of the chain-type tool magazine and ATC system, the mean tool change numbers between failures evaluation index is proposed. It is adopted to evaluate the failure data received by experimenting on type MDH-80 chain-type tool magazine and ATC whose MTTR are calculated. It can be seen that the mean tool change numbers between failures is a reasonable evaluation index to describe the reliability of the tool magazine and ATC. The failure data of the tool magazine without tool-changing times should be evaluated by the traditional method. While in the experiment on continuous tool-changing or in the circumstance that the tool magazine has a counter, the reliability can be evaluated based on the mean tool change numbers between failures. Acknowledgments The research is supported by the high-grade CNC machine tool and the basic equipment manufacturing industry major science and technology project (No. 2011ZX04011-022) and Dalian science and technology project (No. 2010A16GX091). References [1] Wu Jun, Deng Chao, Shao Xinyu, Xie S Q, A reliability assessment method based on support vector machines for CNC equipment [J]. Science in China Series E: Technological Sciences, Jul. 2009, vol. 52, no. 7, 1849-1857. [2] Bin Li, Hailong Lu, Methods of Reliability Estimation for Numerical Control Machine Tool Based on Performance Parameters [J]. 2011 2nd International Conference on Mechanic Automation and Control Engineering, MACE 2011-Proceedings, p 4144-4147, 2011. [3] Wang Zhiming, Yang Jianguo, Reliability assessment of numerical control machine tools using Weibull mixture models [J]. Advanced Materials Research, v 181-182, p 161-165, 2011, Advanced Materials Science and Technology. [4] Wang Zhiming, Yang Jianguo, Wang Guoqiang, Zhang Genbao, Reliability evaluation of multiple NC machine tools with time truncation [J]. Harbin Gongye Daxue Xuebao/ Journal of Harbin Institute of Technology, v 43, n 3, p 85-89, March 2011. [5] Yang Zhaojun, Hao Qingbo, Chen Fei, Xu Binbin, Li Xiaobing, Zhao Hongwei, A comprehensive fuzzy reliability allocation method of NC machine tools based on interval analysis [J]. Beijing Gongye Daxue Xuebao/ Journal of Beijing University of Technology, v 37, n 3, p 321-329, March 2011. [6] Yang Zhaojun, Zhu Xiaocui, Jia Yazhou, Wang Liding, Xu Binbin, Li Xiaobing, Lu Jianwei, Fuzzy-comprehensive evaluation of use reliability of CNC machine tools [J]. Key Engineering Materials, v 464, p 374-378, 2011. [7] Wang Guiping. Study on Evaluation System and Increasing Technology of Reliability and Green in CNC Machining Center[D]. Changchun: Jilin University, 2008.in Chinese. Frontiers of Manufacturing and Design Science III 10.4028/www.scientific.net/AMM.271-272 Reliability Evaluation of Chain-Type Tool Magazine and ATC 10.4028/www.scientific.net/AMM.271-272.461 鏈式刀庫和ATC的可靠性評估盧曉紅a，彭卓漢b，吳文義c 教育部精密非傳統(tǒng)加工技術重點實驗室，大連理工大學，大連116024。 關鍵詞：鏈式刀庫，ATC，可靠性，故障間平均刀具變化數(shù)，平均修復時間 摘要 由于刀庫和自動換刀器(ATC)是為加工中心儲備和更換刀具的重要功能單元， 換刀率影響其可靠性壽命，直接影響加工中心的性能水平。 然而，刀庫和ATC 的可靠性還沒有得到合理的評價指標。 針對刀庫和ATC系統(tǒng)的特點，提出了故障評價指標之間的平均工具變化數(shù)，用于計算鏈式刀庫和ATC收集的故障數(shù)據(jù)的平均修復和估計時間。 可以看出，具有連續(xù)換刀的刀具雜志采用故障間的平均刀具變化數(shù)作為可靠性評價指標。 導言 可靠性評價是數(shù)控機床可靠性研究的重要內(nèi)容之一。 目的是掌握該工具的現(xiàn)狀，提出可靠性設計工作的目標和任務，為可靠性的進一步研究指明方向。 在數(shù)控機床可靠性評估研究中，華中科技大學[1,2]和天津職業(yè)技術師范大學提出了基于性能退化數(shù)據(jù)的可靠性評估。上海交通大學[3,4]利用威布爾混合模型對多種數(shù)控機床進行時間終止試驗的可靠性評價進行了研究，并提出了數(shù)控機床時間終止試驗的一些模型以及故障間時間的參數(shù)估計方法。 吉林大學和大連理工大學[5,6]將模糊理論引入到數(shù)控機床可靠性研究中，提出了一種綜合模糊可靠性分配方法。 王貴平[7]研究了加工中心失效分析方法的可靠性和綠色化、評價方法和增長策略。 由于刀庫和自動換刀器(ATC)是加工中心儲備和交換刀具的重要功能單元，其換刀率影響其可靠性壽命，直接影響加工中心的性能水平。 但可靠性尚未得到合理的評價指標。 刀具雜志和ATC的換刀率對其可靠性壽命有很大影響。 對于同一種產(chǎn)品，它的壽命差異很大，在一個經(jīng)常更換工具的加工過程中，在另一個很少更換工具的加工過程中。 采用MTBF（平均故障時間）作為可靠性評價指標， 不能對刀庫和ATC產(chǎn)品的性能進行評價。 因此，基于科技重大項目“大鏈式刀具雜志、高速盤式刀具雜志和自動換刀器的發(fā)展研究”在本文對國內(nèi)外數(shù)控及其關鍵功能單元的可靠性評價研究進行了總結和分析。 通過對大型鏈型刀庫和ATC 的實驗室加速試驗，記錄了換刀時間，并根據(jù)MTCNBF（故障間的平均刀具變化數(shù)） 和MTTR（平均修復時間)對其可靠性進行了評價）。 本文探討了大型鏈式刀具雜志和ATC的可靠性評價方法，以期為數(shù)控系統(tǒng)及其功能單元的可靠性水平的發(fā)展 提供參考。 鏈型刀庫和自動換刀器的可靠性評估 鏈式刀庫和ATC系統(tǒng)包括刀庫、ATC、數(shù)控系統(tǒng)和仿真主軸，如圖所示。 1. 通過伺服電機，行星減速齒輪帶動鏈輪和鏈條來選擇刀具來實現(xiàn)刀庫的操作。 在刀庫的ATC中，通過轉子形成面多安裝凸輪的鏈條驅動滾子式實現(xiàn)刀具的交換和保護門的開關運動。 鏈條傳動的動力源來自齒輪電機，換能器控制機械手換刀速度，換刀時間可調(diào)節(jié)。 在刀庫系統(tǒng)可靠性測試中，刀庫換刀時間為3.0秒。 換刀過程包括選擇刀具，刀缸將分離蓋和刀具送至換刀位置。 所研究的鏈型刀庫和ATC系統(tǒng)的技術參數(shù)見表 1. 圖1 鏈式刀庫和ATC進行測試 表1所研究的鏈式刀庫系統(tǒng)的技術參數(shù) 表2故障數(shù)據(jù)來自大連金數(shù)控集團公司MDH-80鏈型刀庫系統(tǒng)加速可靠性試驗... 根據(jù)采樣原理，選擇3個鏈型刀庫和ATC系統(tǒng)進行加速可靠性測試，每個鏈型刀庫和ATC的測試時間為30天，每天8小時，總共換刀圈為60圈，換刀80次/圈。因此，一天內(nèi)工具更換次數(shù)為4800次，平均每分鐘更換工具10次。 已獲得14個故障數(shù)據(jù) 表2 MDH-80鏈式刀庫系統(tǒng)的故障數(shù)據(jù) Description of the failure Number Failure start date Failure end date Failure start time Failure end time Failure repair time[min] The tool magazine stalls 1 2011.12.05 2011.12.05 14:35 14:40 5 The abnormal noise appears in 1 2011.12.14 2011.12.14 7:40 9:20 100 The tool falls in ATC 1 2011.12.18 2011.12.18 8:10 8:30 20 Tool magazine stuck 1 2011.12.23 2011.12.23 9:45 12:10 145 Splined shaft and bushing wear 1 2011.12.28 2011.12.28 9:30 12:00 150 Tool magazine stop turning 2 2012.02.04 2012.02.04 10:00 10:05 5 Grasping tool is not in place 2 2012.02.10 2012.02.10 13:20 13:35 15 Inserting tool is not in place 2 2012.02.20 2012.02.20 15:55 16:15 20 Pocket impact is too large 2 2012.02.27 2012.02.27 14:50 18:40 230 Inserting the tool is not in place 3 2012.03.08 2012.03.08 13:05 13:30 25 Pocket is stuck 3 2012.03.19 2012.03.19 9:30 12:00 150 The tool falls in ATC 3 2012.03.21 2012.03.21 15:30 15:35 5 Splined shaft and bushing wear 3 2012.03.26 2012.03.26 10:40 12:50 130 The abnormal noise appears in 3 2012.03.30 2012.03.30 9:00 10:30 90 平均工具改變數(shù)字之間的失敗 提出了一種刀庫和自動換刀器的可靠性評價指標MTCNBF（故障間平均刀具變化數(shù)），它表示相鄰兩次故障之間刀具變化的平均次數(shù)。 計算如下： n：樣本數(shù)，Sj評估周期中j集樣本的累積工具變化數(shù)rj評估周期中j集樣本的累積故障數(shù)k：校正因子及其值如表3所示。 每個鏈型刀庫和ATC的刀具變化累積時間可以從表2中處理和計算的故障數(shù)據(jù)中提取。 表3 MTCNBF的校正因子 Serial Number Maximum Weight of tool [Kg] Tool Magazine Capacity [T] Tool Change Time [s] k 1 ≤20 ≤60 ≥3 1.1 2 ≤20 ≤60 <3 1.0 3 ≤20 >60 ≥3 1.0 4 ≤20 >60 <3 0.9 5 >20 ≤60 ≥3 1.0 6 >20 ≤60 <3 0.9 7 >20 >60 ≥3 0.9 8 >20 >60 <3 0.8 第一鏈型刀庫和ATC的刀具變化累積次數(shù)： S,= 30×4800-(5+100+20+145+150)(×10=139800 第二鏈型刀庫和ATC的刀具變化累積次數(shù)： S, =30×4800-(5+15 +20+230)(×10 =141300 第二鏈型刀庫和ATC的刀具變化累積次數(shù)： S; = 30×4800-(25+150＋5+130＋90)(×10= 140000 根據(jù)表2中的數(shù)據(jù)，3個鏈式刀庫共發(fā)生14次故障，樣本數(shù)為3，修正因子為1.0。 s1=1398002=1413003=140000，把他們帶到等式1 以大連金控集團公司開發(fā)的9套鏈型刀庫和ATC為例，研究的鏈型刀庫和ATC在水平加工中心上的平均換刀次數(shù)約為30000次。如果用戶在加工過程中對可靠性進行評估，則獲得MTCNBR將再持續(xù)一年。 然而，通過基于可靠性測試的鏈式刀庫和ATC的弱點暴露出來，它只會持續(xù)一個月。 因此，這一特點為鏈式刀庫和ATC 的可靠性增長設計提供了及時的參考。 同時修理 傳統(tǒng)的MTTR（平均維修時間）表示從故障開始到維修結束的平均時間間隔。它計算如下。 n0評估周期內(nèi)系統(tǒng)的累積故障頻率，n：系統(tǒng)樣本數(shù)，Ti*i系統(tǒng)在評估周期內(nèi)的糾正維修時間，ri評估周期內(nèi)i系統(tǒng)的故障頻率。 根據(jù)表2中的數(shù)據(jù)，可以計算出每個鏈型刀庫和ATC的累計糾正維護時間： T1=7[h]，T2=4.5[h]，T3=6.7[h]。 在3個鏈式刀庫中有14個故障。 把他們帶到情商里。 2、MTTR為1.30[h]。 它可以得出結論，MTTR約為1.3[h]的研究鏈型刀庫和 ATC。 摘要 針對鏈式刀庫和ATC系統(tǒng)的特點，提出了故障評價指標間的平均刀具變化數(shù)。通過對MDH-80 型鏈型工具庫和ATC型工具庫的試驗，對所接收的失效數(shù)據(jù)進行了計算。 可以看出，故障間的平均刀具變化數(shù)是描述刀具雜志和ATC可靠性的合理評價指標。 采用傳統(tǒng)方法對無換刀次數(shù)的刀庫失效數(shù)據(jù)進行評價。 在連續(xù)換刀實驗中，或在刀庫有計數(shù)器的情況下，可以根據(jù)故障間的平均換刀次數(shù)來評價可靠性。 致謝 本課題研究以高檔數(shù)控機床和基礎裝備制造業(yè)重大科技項目（No. 2011ZX04011-022)和大連科技項目(No. 2010A16GX091)為支撐。 參考文獻 [1] Wu Jun, Deng Chao, Shao Xinyu, Xie S Q, A reliability assessment method based on support vector machines for CNC equipment [J]. Science in China Series E: Technological Sciences, Jul. 2009, vol. 52, no. 7, 1849-1857. [2] Bin Li, Hailong Lu, Methods of Reliability Estimation for Numerical Control Machine Tool Based on Performance Parameters [J]. 2011 2nd International Conference on Mechanic Automation and Control Engineering, MACE 2011-Proceedings, p 4144-4147, 2011. [3] Wang Zhiming, Yang Jianguo, Reliability assessment of numerical control machine tools using Weibull mixture models [J]. Advanced Materials Research, v 181-182, p 161-165, 2011, Advanced Materials Science and Technology. [4] Wang Zhiming, Yang Jianguo, Wang Guoqiang, Zhang Genbao, Reliability evaluation of multiple NC machine tools with time truncation [J]. Harbin Gongye Daxue Xuebao/ Journal of Harbin Institute of Technology, v 43, n 3, p 85-89, March 2011. [5] Yang Zhaojun, Hao Qingbo, Chen Fei, Xu Binbin, Li Xiaobing, Zhao Hongwei, A comprehensive fuzzy reliability allocation method of NC machine tools based on interval analysis [J]. Beijing Gongye Daxue Xuebao/ Journal of Beijing University of Technology, v 37, n 3, p 321-329, March 2011. [6] Yang Zhaojun, Zhu Xiaocui, Jia Yazhou, Wang Liding, Xu Binbin, Li Xiaobing, Lu Jianwei, Fuzzy-comprehensive evaluation of use reliability of CNC machine tools [J]. Key Engineering Materials, v 464, p 374-378, 2011. [7] Wang Guiping. Study on Evaluation System and Increasing Technology of Reliability and Green in CNC Machining Center[D]. Changchun: Jilin University, 2008