Optimization of rotor shaft shrink fit method for motor using “Robust design”

Journal of Industrial Engineering International https://doi.org/10.1007/s40092-018-0255-9 (0123456789().,-volV)(0123456789().,-volV) ORIGINAL RESEARCH Optimization of rotor shaft shrink fit method for motor using ‘‘Robust design’’ Eiji Toma1 Received: 5 August 2017 / Accepted: 10 January 2018  The Author(s) 2018. This article is an open access publication Abstract This research is collaborative investigation with the general-purpose motor manufacturer. To review construction method in production process, we applied the parameter design method of quality engineering and tried to approach the optimization of construction method. Conventionally, press-fitting method has been adopted in process of fitting rotor core and shaft which is main component of motor, but quality defects such as core shaft deflection occurred at the time of press fitting. In this research, as a result of optimization design of ‘‘shrink fitting method by high-frequency induction heating’’ devised as a new construction method, its construction method was feasible, and it was possible to extract the optimum processing condition. Keywords Robust design  Quality engineering  Shrink fitting  High-frequency induction heating Introduction In recent years, there are frequent cases of recall problems due to quality problems of consumer electronics products and automobiles in the market and betrayal of consumer confidence. The way of manufacturing is also the problem solving type in most cases, and the recurrence preventiontype development occupies mainstream in actuality. Especially the recall problem of automobiles, such as the complicated structure of the products themselves, the fact that consumers’ eyes became more severe and that it was impossible to break down all the problems in the design process in shortening the development period, it shows the limit of conventional quality control in the market environment. The reason why the recall cannot be prevented in terms of quality control is because the factors of the recall problem are put in the design and development stage (Taguchi 1992). Therefore, it can be said that it is difficult to reduce this problem unless innovating the way of design and thinking into ‘‘prevention’’ concept. To prevent problems in & Eiji Toma 1 National Institute of Technology, Tsuruoka College, Tsuruoka, Japan advance, to speed up the development of new products and strengthen the constitution of production technology capabilities, it is desired to advance technology development with high versatility and high reproducibility. For that purpose, it is important for engineers to acquire the idea of quality engineering and how to proceed and fulfill the role and responsibility of engineers. Therefore, ‘‘Robust design’’ is utilized in technology development and product design that account for most of design responsibility (Koshimizu and Suzuki 2007; Hasebe 2009). Research purpose This research is a collaborative with a motor manufacturer, and we tried approach to optimization of construction method by applying Quality engineering for the purpose of reviewing construction method in production process. Figure 1 shows the rotor core and the shaft which are the main components of the motor used in this study (Yano 2004). In the process of joining the rotor core and the shaft, the press-fitting method has been adopted conventionally, but as shown in Fig. 2, the quality defect of ‘‘rotor runout’’ of the rotor shaft occurring at the time of press fitting has occurred. Simulation analysis reveals that the factor is 123 Journal of Industrial Engineering International Fig. 1 Rotor core and shaft p¼ • d22  d12  E  D; 2d1 d12 where E is the Young’s modulus ð¼ 201½GPaÞ and D is the interference. Area of junction (A) A ¼ pd1 L; • where L is the insertion length. Transmission torque (T) T ¼ lpAd1 =2; where l is the coefficient of friction (= 0.15). Materials Fig. 2 Inferior quality model caused by an unbalanced load at the time of press fitting the shaft (Mori 2005; Taguchi 1992). Figure 3 shows the calculation model of the strength of the required interference at the time of press fitting. Formula • Internal pressure between cylinder and shaft after joining (p) • • Rotor core: aluminum alloy and electromagnetic steel. Shaft: carbon steel for machine construction. Specification • • • • Required rotation transmission torque: T = 70 [N m]. Drawing load: F = 5000 [N]. Core inner diameter: d1 = [ 12 [mm]. Core outer diameter: d2 = [ 47.6 [mm]. Fig. 3 Press-fitting model L (Insertion length) Rotor core Shaft Press fitting 123 Journal of Industrial Engineering International • Insertion length: L = 40 [mm]. Calculation result • • • • • Area of junction: A ¼ pd1 L ¼ 1:51  103 ½mm2 . Internal pressure between cylinder and shaft after joining: p ¼ 51:5½N=mm2 . Interference: D ¼ 64:5½lm. Required heating temperature: DT. D ¼ d1  a  DT ! DT ¼ D=ða  d1 Þ ¼ 444½ C   a: Coefficient of linear expansion ¼ 12:1  106 ½= C : As a result of the previous research, it was possible to optimize the press-fitting method by setting the ideal function (Fig. 4) by applying the quality engineering, and extract the processing condition to reduce the occurrence of core runout of the rotor shaft (Yano 2002; Koshimizu and Suzuki 2007). A summary of research on the optimization of the pressfitting method applying the quality engineering in the previous research is described below. Experimental system The outline of the experimental apparatus in the previous research is shown in Fig. 5. Set the shaft and the core in the upper and lower jigs, and semi-automatic press fitting with hydraulic pneumatic actuator. The press-fitting process conditions (each parameter) were set, and the measurement results of the press-fit load and deflection, which are characteristic values, were analyzed and evaluated. Experimental method Tables 1 and 2 show various factors and level tables. ‘‘Control factor’’ assigns press-fitting conditions to each level, and ‘‘Noise factor’’ is accuracy of core inner diameter. Based on these level tables, experiments were conducted based on ‘‘L18 orthogonal array’’ which is a statistical tool for constructing an experiment plan. Experimental result Figure 6 shows the SN ratio calculated from experimental results as a factorial effect diagram. A diagram showing the effect of combinations of factors on characteristic values is called a factorial effect diagram (response graph). The vertical axis of the graph represents the SN ratio, and the horizontal axis represents the level of the factor. Reliability of experiment Table 3 shows the evaluation results on reliability of the experiment in the response graph. Based on the benchmark condition and the estimation result of the SN ratio of the condition considered to be optimum, it was judged that the experimental result is reliable. This means that the selected optimum condition is an appropriate level out o (...truncated)