Investigation of Optimum Grinding Condition Using Cbn Electroplated End-Mill for CFRP Machining

https://doi.org/10.20965/ijat.2021.p0004 Yamashita, S. et al.

Paper: Investigation of Optimum Grinding Condition Using cBN Electroplated End-Mill for CFRP Machining

Shinnosuke Yamashita∗, Tatsuya Furuki∗,†, Hiroyuki Kousaka∗, Toshiki Hirogaki∗∗, Eiichi Aoyama∗∗, Kiyofumi Inaba∗∗∗, and Kazuna Fujiwara∗∗∗

∗Gifu University 1-1 Yanagido, Gifu, Gifu 501-1193, Japan †Corresponding author, E-mail: [email protected] ∗∗Doshisha University, Kyotanabe, Japan ∗∗∗Kamogawa Co., Ltd., Ritto, Japan [Received May 10, 2020; accepted July 29, 2020]

Recently, carbon fiber reinforced plastics (CFRP) have Keywords: CFRP, cBN electroplated end-mill, cutting, been used in various applications such as airplanes grinding, oscillating grinding and automobiles. In CFRP molding, there are unnecessary portions on the outer area. Therefore, a machining process is required to remove them. Cutting 1. Introduction and grinding are conventionally used in the finish machining of CFRPs. End-milling allows the removal of Carbon fiber reinforced plastics (CFRPs) have been most of these portions. However, uncut fibers easily used since the late 1960s. Their demand has increased in occur during end-milling. In contrast, a precise ma- various fields such as the aerospace or automotive indus- chined surface and edge are easily obtained using a tries. This is because CFRPs have many desirable charac- grinding tool. Therefore, this research has developed a teristics such as light weight, high rigidity, heat resistance, novel cubic boron nitride (cBN) electroplated end-mill and good corrosion resistance. CFRPs are convention- that combines an end-mill and a grinding tool. This ally fabricated by an autoclave molding method. While is a versatile tool that can cut and grind CFRPs by molding CFRPs, unnecessary portions are created as the changing the direction of rotation of the tool. In this resin that flows into the outer area hardens as shown in study, the effectiveness of the developed tool is investi- Fig. 1. Therefore, a machining process is required to re- gated. First, the developed tool machined the CFRP by move unnecessary portions after molding. Examples of side milling. Consequently, cBN abrasives that were machining of CFRPs are discussed below. Abrasive wa- fixed on the outer surface of the developed tool did not ter jet machining has high machining efficiency. How- detach in certain cutting conditions. Next, in order to ever, this method has many disadvantages including the generate a sharp edge on the CFRP and restrict the in- machine being expensive, and dry processing is neces- crease in the CFRP temperature with the cBN electro- sary [1, 2]. Meanwhile, end-milling is often applied as plated end-mill, the optimum abrasive size and grind- a highly efficient machining method using a machining ing condition were investigated through the design of center, which is a conventional machining device. How- experiments. Moreover, the effectiveness of the devel- ever, end-milling tends to generate uncut fibers or burrs at oped tool was verified by comparing it with a conven- the CFRP edge [3]. It has been clarified earlier that the tional tool. As a result, smaller burrs and uncut fibers electroplated router is able to remove uncut fibers or burrs were observed after final machining with the devel- generated by end-milling with cubic boron nitride (cBN) oped tool under the derived optimum condition than abrasives fixed to the outside of the tool [4]. Therefore, if those with conventional tools. However, the desired an end-mill and electroplated router are used simultane- surface roughness could not be achieved as required ously, a high quality and highly efficient machining pro- by the airline industry. Therefore, oscillating grinding cess is possible. However, when changing tools, the non- was applied. In addition, the formula of the theoretical machining time increases in order to use multiple tools. surface roughness while using the developed tool was In addition, diamond coated end-mills with high wear derived using the theory of slant grinding. As a result, resistance that are conventionally used as end-mills for the oscillating condition that led to the required sur- CFRP machining are more expensive than conventional face roughness was obtained by theoretical analysis. coated end-mills such as TiAlN. To solve these problems, In addition, the required value for the airline industry we have attempted to develop a new tool combining the was achieved by oscillating grinding. mechanisms of an end-mill and a cBN electroplated tool. This is a versatile tool that can cut and grind CFRPs. This tool was fabricated by electroplating cBN abrasives on an

4 Int. J. of Automation Technology Vol.15 No.1, 2021

© Fuji Technology Press Ltd. Creative Commons CC BY-ND: This is an Open Access article distributed under the terms of the Creative Commons Attribution-NoDerivatives 4.0 International License (http://creativecommons.org/licenses/by-nd/4.0/). Investigation of Optimum Grinding Condition Using cBN Electroplated End-Mill for CFRP Machining

F%1DEUDVLYH &)53 5DNH %DVHPHWDO )ODQNIDFH IDFH PP 8QQHFHVVDU\SRUWLRQ )ODQN IDFH 5DNHIDFH Fig. 1. Photograph of CFRP after autoclave molding. PP PP (a) Cutting edge (b) Cross sectional surface = < (QGPLOOW\SH = < Fig. 3. SEM images of cBN electroplated end-mill. EDVHPDWHULDO *ULQGLQJ URWDWLRQ ; &XWWLQJ ; URWDWLRQ Table 1. Speciﬁcation of developed cBN electroplated end-mill.

Base metal Cemented carbide %XUU %XUU Diameter φ6mm &)53 &)53 Number of cutting edge 2blades PP Blade length 13 mm ◦ (a) Cutting process (CW rota- (b) Grinding process (CCW Rake angle +6 ◦ tion) rotation) Clearance angle 0

Fig. 2. Change of machining methods of cBN electroplated end-mill. groove of the end-mill, air cooling is expected by inter- mittent grinding [5]. Thus, the developed tool can carry end-mill. Therefore, it is expected that the machining ef- out CFRP machining and grinding by switching the rota- ficiency would be improved and the tool cost would be tional direction of the tool. Therefore, this tool is expected reduced by using the cBN electroplated end-mill that en- to be less expensive than conventional methods for trim- ables cutting and grinding with a single tool. In this study, ming of CFRPs. The fabrication method of the cBN elec- we investigated the cutting and grinding characteristics of troplated end-mill is described below. First, a carbide rod the trimming of a CFRP with the developed cBN elec- was formed into an end-mill shape using a tool grinder. troplated end-mill. Next, the optimum grinding condition Then, cBN abrasives were fixed to the outer surface of the was derived using the design of experiments (DOE). Fur- end-mill by the electrolytic method. The scanning elec- thermore, the effectiveness of the cBN electroplated end- tron microscopy (SEM) images of the developed tool are mill under the optimum condition was verified by com- shown in Fig. 3. The cBN abrasives were fixed to the paring the surface quality with that of a diamond coated outer surface of the tool as shown in Fig. 3(a). In addition, end-mill. the surface of the developed tool was cut by wire elec- tric discharge machining (EDM) as shown in Fig. 3(b). As cBN abrasives were fixed to the tool surface by nickel 2. Fabrication of the cBN Electroplated plating, the diameter of the developed tool was larger than that of a conventional end-mill. The specifications of the End-Mill developed tool in this study are shown in Table 1. A pos- itive rake angle is effective for reducing the cutting force The concept of the developed cBN electroplated end- during CFRP machining [5]. In this study, the rake angle mill is shown in Fig. 2. The developed tool cuts the CFRP of the developed tool was set to +6◦. In addition, carbon with the rake angle. Therefore, the end-mill rotates in the fibers with high hardness are likely to cause abrasive wear clockwise (CW) direction as shown in Fig. 2(a) to cut the due to repeated rubbing of the tool surface and powdery CFRP. Thus, machining is carried out by the developed chips in CFRP machining [6]. tool without an expensive tool such as a diamond coated Hence, the clearance angle is set to a pre-determined end-mill. However, as mentioned earlier, the machining value to decrease the amount of contact between the flank causes burr formation on the edges because the cutting face of the tool and the CFRP in conventional end-mills force deforms the resin. Therefore, a finish machining for CFRP machining. It has earlier been found that fewer such as grinding is necessary. When the tool rotates in the burrs and uncut fibers are generated at the edge of the ma- counterclockwise (CCW) direction as shown in Fig. 2(b), chined surface when the clearance angle of the developed cBN abrasives are fixed to the flank face of the ground tool is small [7]. Therefore, the clearance angle was set CFRP. The CFRP temperature is likely to increase be- ◦ to 0 and the contact amount between the cBN abrasives cause of the electroplated router in grinding because the and CFRP was increased in this study. CFRP and the tool always contact during grinding. How- ever, as the developed tool has slits such as the cutting

Int. J. of Automation Technology Vol.15 No.1, 2021 5 Yamashita, S. et al.

ႏ Table 2. Speciﬁcation of fabricated CFRP.

Matrix resin Epoxy resin = ; ◦ ,QIUDUHGWKHUPRJUDSK\FDPHUD Glass transition temperature Tg Approx. 200 C < 7RRO Carbon ﬁber PAN based CF &)53 7RRO Diameter 7 μm Weaving method Twilled weave 3URWHFWLRQ Workpiece size 50 × 30 × t5.7 mm SODWH &D) &)53 = < ; ([SRVHGEDVHPDWHULDO '\QDPRPHWHU (YDOXDWHGDUHD

(a) Photograph of machining setup (b) Thermographic image PP

Fig. 4. Overview of machining experiment. Fig. 5. Microscopic image of delamination of nickel on ﬂank face. 3. Experimental Methods and Results

3.1. Overview of CFRP Machining Experiment 3.2. Evaluation of Cutting Characteristics of the In this study, the CFRP was cut and ground using the cBN Electroplated End-Mill developed tool through the experimental setup shown in The developed tool is assumed to be a versatile tool that Fig. 4(a). The evaluation parameters viz. the machin- can cut and grind CFRP. First, we investigated whether ing force, CFRP temperature during machining, average the developed tool could cut the CFRP without dropping length of the uncut fibers, and the surface roughness of the cBN abrasives. If cBN abrasives fixed to the outer sur- machined CFRP were measured. The experimental con- face are dropped from the developed tool, the base ma- ditions were set and included the size of the cBN abra- terial of the cutting edge is exposed as shown in Fig. 5. sive As, cutting speed V, feed rate per tooth f ,andthe Then, the effective number of cBN abrasives decreases in radial depth of cut Rd. As side milling was conducted in the grinding process. The cBN abrasives must not drop this experiment, the axial depth of cut was the same as out. In the developed tool, half of the cBN abrasives were the thickness of the workpiece. In side milling, down- filled with nickel plating. Therefore, for lesser cBN abra- cut milling should be applied due to large vibration of the sives, the nickel plating was thinner. Hence, it was found workpiece and tool wear in up-cut milling [8]. Therefore, that the abrasives were dropped during cutting in order to in all machining processes in this study, we used down- decrease the holding force of the cBN abrasives (#400), cut milling. As the mechanical properties of CFRPs are which concurred with a previous study [9]. Therefore, degraded due to water absorption, cutting oil should not the cBN abrasives of the developed tool were changed be used as the coolant. Therefore, dry machining was ap- from #30 to #200, which had a larger abrasive diameter plied. A vertical 3-axis machining center (NV4000DCG, than #400. The cutting condition was set to 200 m/min, Mori Seiki Co., Ltd.) was used as the machining device. feed rate 25 μm/tooth, and radial depth of cut 0.7 mm by The maximum spindle rotation speed of this machine −1 referring to the cutting condition of a conventional end- was 12,000 min . An infrared thermography camera mill for CFRP machining. The total cutting distance was (SC7000, FLIR Inc.) was used to measure the maximum 2.5 m. The CFRP temperature, grinding force during cut- temperature of the CFRP machined surface. The CFRP ting, and the flank face state of the tool were applied as temperature was the highest temperature of the CFRP sur- the evaluation parameters. The force in the X+ direction face measured during machining as shown in Fig. 4(b).A is the principal force, and the force in the Y + direction is 3-axis dynamometer (9347C, Kistler Co., Ltd.) was used the feed force in Fig. 2. to measure the machining force. The surface roughness A microscopic image of the cutting edge of the devel- was measured with a 3D laser microscope (OLS4100, oped tool after CFRP cutting is shown in Fig. 6.ThecBN OLYMPUS Corp.). Length of uncut fibers were measured abrasives did not drop from the cutting edge of the de- with an optical microscope (BX53M, OLYMPUS Corp.). veloped tool after machining. The maximum CFRP tem- A digital microscope (Dino-Lite AM7013MT, Opto Sci- perature and grinding force measured during cutting are ence Inc.) was used for tool photography. The specifi- shown in Fig. 7. Usually, in end-milling, the load applied cations of the workpiece in this study are shown in Ta- to the workpiece during cutting increases due to wear and ble 2. Prepregs of 16 sheets were laminated on cross ply ◦ ◦ rounding of the cutting edge. Consequently, the cutting (0 –90 ) considering the anisotropy of carbon fiber orien- force and workpiece temperature increase [10]. In this ex- tation. periment, the CFRP temperature and grinding force were constant regardless of the cutting distance. Therefore, it is clarified that the developed tool can cut CFRPs with-

6 Int. J. of Automation Technology Vol.15 No.1, 2021 Investigation of Optimum Grinding Condition Using cBN Electroplated End-Mill for CFRP Machining

(a) cBN abrasive size: #200 (average abrasive size φ74 μm)

&)53WHPSHUDWXUHႏ PP 7RWDOFXWWLQJOHQJWKP (b) cBN abrasive size: #100 (average abrasive size φ149 μm) (a) CFRP temperature

PP (c) cBN abrasive size: #60 (average abrasive size φ250 μm)

3ULQFLSDOIRUFH1 PP 7RWDOFXWWLQJOHQJWKP (d) cBN abrasive size: #30 (average abrasive size φ590 μm) (b) Principal force Fig. 6. Microscopic images of cutting edge after rough machining with cBN electroplated end-mill. out dropping the cBN abrasives and incurring significant wear of the cutting edge under the cutting conditions set in this experiment. However, as shown in Fig. 8, burrs and uncut fibers were generated on the machined surface )HHGIRUFH1 for all abrasive sizes. 3.3. Evaluation of Grinding Characteristics with 7RWDOFXWWLQJOHQJWKP the Experimental Design (c) Feed force Grinding is necessary to remove burrs and uncut fibers generated by cutting to create a good machined surface. Fig. 7. Measured CFRP temperature and grinding force dur- However, the developed tool has less cBN abrasives that ing cutting process with cBN electroplated end-mill. operate in the grinding process than in a conventional grinding tool (the electroplated router) in CFRP grinding, because cBN abrasives fixed on the flank face function in the grinding process as shown in Fig. 9. Therefore, it is PP 8QFXWILEHU %XUU thought that uncut fibers and burrs tend to be left on CFRP edges as compared to a conventional tool during CFRP Fig. 8. Microscopic images of CFRP surface after cutting. grinding. Consequently, the developed tool cannot apply the recommended condition for the conventional tool. Therefore, it is necessary to clarify the grinding characteristics of the developed tool and derive the optimum tal results (objective variables) were evaluated through a grinding condition. Grinding characteristics change in a main effect graph [11]. The conditions in this experiment complicated manner according to the grinding conditions are shown in Table 3. The explanatory variables were such as the abrasive size, feed rate, radial depth of cut, and the cBN abrasive size As, grinding speed V, feed rate per the grinding speed. Therefore, it is difficult to understand tooth f , and the radial depth of cut Rd.TheL16 orthog- the grinding characteristics by a simple grinding experi- onal table was used because four levels were set for each ment in which the condition parameters are changed one explanatory variable. The smallest abrasive size used in by one. Therefore, DOE was applied in this study. By us- this experiment was As = #200. The recommended con- ing this method, the relationship between the experimen- dition of the electroplated router that was marketed from tal conditions (explanatory variables) and the experimen- the tool maker for CFRP grinding was As = #60 (average

Int. J. of Automation Technology Vol.15 No.1, 2021 7 Yamashita, S. et al.

3ULQFLSDOIRUFH3ULQFLSOHIRUFH )HHGIRUFH &)53WHPSHUDWXUH

(a) Electroplated router (b) Electroplated end-mill *ULQGLQJIRUFH1

&)53WHPSHUDWXUH& Fig. 9. Difference of effective abrasive number between

the conventional tool and the developed tool in the grinding

process. As f ȝPWRRWK Rd P V PPLQ

Table 3. L16 orthogonal table in the grinding experiment. (a) Grinding force and CFRP temperature

Radial depth Grinding /HQJWKRIXQFXWILEHU 6XUIDFHURXJKQHVV Abrasive Feed rate No. μ of cut speed size As f [ m/tooth] μ Rd [ m] V [m/min] ȝP

a 1 #200 2 5 100 R 2 #200 10 10 120 3 #200 25 20 150 4 #200 50 30 200 6XUIDFHURXJKQHVV 5 #100 2 10 150 /HQJWKRIXQFXWILEHUP

6 #100 10 5 200 As fȝPWRRWK RdP VPPLQ 7 #100 25 30 100 8 #100 50 20 120 (b) Length of uncut fiber and surface roughness Ra 9 #60 2 20 200 Fig. 10. Main effect graph of each evaluated results of char- 10 #60 10 30 150 acteristic value. 11 #60 25 5 120 12 #60 50 10 100 13 #30 2 30 120 procedure prior to grinding, a pre-stage machined surface 14 #30 10 20 100 was generated under certain cutting conditions. The cut- 15 #30 25 10 200 ting conditions were set as cBN abrasive size #200, cutting speed 100 m/min, feed rate 25 μm/tooth, and radial 16 #30 50 5 150 depth of cut 0.5 mm. The surface roughness Ra after cutting was 8.2 μm and the average length of the uncut fiber was 283 μm. abrasive size = φ250 μm), f = 25 μm/rev, Rd = 100 μm, The effects of each explanatory variable on each ob- and V = 200–300 m/min. It was found that the feed rate jective variable are shown in Fig. 10. The main effect was smaller than the abrasive size. Therefore, the feed graph is a graph that plots the average of the character- rate of the developed tool was also set smaller than the istic value at each level of the explanatory variable. For abrasive size based on the above condition. Half of the larger change in the characteristic value, there is a larger cBN abrasives were filled with nickel plating in the de- effect on the objective variable. As an example, the CFRP veloped tool. Therefore, the radial depth of cut was set to temperature for As = #200 in Fig. 10(a) is the average less than half of #200. The grinding speed in this experi- result of the measured grinding temperature values for ment was lower than that of conventional grinding (CFRP Nos.1–4, where the grinding condition is As = #200. First, grinding with electroplated router, V = 200–300 m/min). the grinding force and maximum CFRP temperature are This was because the developed tool was assumed to be evaluated. The force in the X+ direction is the principal used in conventional machining centers. These machin- force, and the force in the Y+ direction is the feed force ing centers with a maximum spindle speed from 10,000 to in Fig. 2. In conventional grinding, the grinding force 20,000 min−1 are used in many machining plants. There- and grinding temperature increase in accordance with the fore, the maximum grinding speed was set to 200 m/min abrasive size [12]. However, in this experiment, the prin- (10,610 min−1). The cBN abrasives were used from #30 cipal force reduced with abrasive size. When the abra- to #200, which were applicable in the cutting experiment. sive size is small, the chip pocket located in each abra- As the objective variables, the CFRP temperature during sive becomes small. Therefore, as chips tend to accumu- grinding, grinding force, average length of uncut fibers late among abrasives after grinding, the principal force after grinding, and the surface roughness Ra of the CFRP increases [4]. When the abrasive size is large, the volume machined surface were measured. With a rough cutting of the chip-pocket is also large. Thus, as the chips that are

8 Int. J. of Automation Technology Vol.15 No.1, 2021 Investigation of Optimum Grinding Condition Using cBN Electroplated End-Mill for CFRP Machining

)ODQNIDFH

PP (a) Abrasive size is small (a) #200 (Grinding condition: No.2)

/RDGHGFKLS )ODQNIDFH

(b) Abrasive size is large PP Fig. 12. Difference of abrasive trajectory caused abrasive size on the flank face. (b) #60 (Grinding condition: No.12) Fig. 11. Observation images of the flank face after grinding. sive size and shortening the abrasive distance. In conventional grinding, the surface roughness increases with feed rate [13]. However, in this experiment, the feed rate did not significantly affect the surface roughness due to the re- placed in the chip-pockets are not compressed, they are moval mechanism of CFRP grinding, which was different easily removed by the air-blow during the machining pro- from conventional grinding. It is known that shear failure cess and the flank face does not contact the CFRP. In this occurs due to compression of brittle carbon fibers in the experiment, the loading chips formed while using small grinding process using cBN abrasives with a large nega- abrasive such as #200 are shown in Fig. 11.However, tive rake angle. Therefore, the failure extends deeper than loading chips did not form when using large abrasive such the actual depth of cut [14, 15]. Therefore, CFRP grind- as #60. Consequently, the principal force and CFRP tem- ing is unlikely to be affected by the trajectory of the tool perature decreased as the abrasive size became smaller. movement. The feed rate and radial depth of cut affected the grinding force and CFRP temperature. As the feed rate and radial depth of cut increased, the grinding time per tooth 3.4. Derivation of the Optimum Grinding and the removal amount of the workpiece increased. It Condition by Actual Grinding Results is inferred that as the friction time and frictional force per In this section, the optimum grinding conditions are in- tooth increased, the grinding force and CFRP temperature vestigated using experimental grinding results. The op- also increased. Next, the length of the uncut fibers and the timum grinding condition in this experiment is the con- surface roughness were evaluated. The average length of dition in which the required surface quality is achieved the uncut fibers and the surface roughness reduced as the and the grinding efficiency is high. If the CFRP tempera- cBN abrasive size became smaller. Fig. 12 shows that ture during grinding exceeds the glass transition tempera- the difference of the abrasive trajectory led to the abra- ture Tg, the epoxy resin deteriorates [16]. Therefore, car- sive size. When the abrasive size was small, the distance bon fibers and softened resins are pulled up to the CFRP of each abrasive trajectory reduced. The remained area edge. Consequently, uncut fibers or burrs are likely to be that shown in Fig. 12 where the abrasives did not contact generated on the CFRP edges. Therefore, the CFRP tem- the workpiece becomes smaller. From this figure, it is in- perature should not exceed Tg.TheTg of the CFRP used in ferred that the average length of the uncut fiber and the this experiment is 200◦C. However, thermoplastic CFRPs surface roughness reduced because more uncut fibers and (CFRTPs), which are expected to be extensively used in surface irregularities were removed by reducing the abra- future as a material for automobile parts, use nylon-based

Int. J. of Automation Technology Vol.15 No.1, 2021 9 Yamashita, S. et al.

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ODUJHUWKDQ& n F PLQ PP ,QDGHTXDWHFRQGLWLRQ

*ULQGLQJIRUFHUDWLR MRR

&)53WHPSHUDWXUH *ULQGLQJFRQGLWLRQQXPEHU Fig. 15. Evaluated grinding force ratio of each grinding *ULQGLQJFRQGLWLRQQXPEHU condition. Fig. 13. Relation between grinding stock removal rate and CFRP temperature under each grinding condition. ,QDGHTXDWHFRQGLWLRQ

$YHUDJHEXUUOHQJWK 6XUIDFHURXJKQHVV ,QDGHTXDWHFRQGLWLRQ ȝP a R *ULQGLQJIRUFH1 *ULQGLQJFRQGLWLRQQXPEHU 3ULQFLSDOIRUFH )HHGIRUFH /HQJWKRIXQFXWILEHUȝP 6XUIDFHURXJKQHVV Fig. 16. Measured principal force and feed force under each *ULQGLQJFRQGLWLRQQXPEHU grinding condition.

Fig. 14. Measured surface roughness Ra and average length of uncut fiber under each grinding condition. ness. Therefore, these conditions are considered inappropriate for grinding. The grinding force ratio (principal force Fn / feed force Ft ) under each experimental con- thermoplastic resin as the matrix for high productivity. dition is shown in Fig. 15. Feed force is the force re- ◦ However, the Tg of most of these materials is 100 Cor quired to cut the workpiece in grinding. Meanwhile, as less. Therefore, it is necessary to maintain the CFRP tem- the principal force presses the workpiece, it causes the perature at 100◦C in CFRP grinding. The measured val- workpiece and tool to deform elastically due to decrease ues of the CFRP temperature and material removal rate in the grinding accuracy. Therefore, the grinding force under each grinding condition are shown in Fig. 13.The ratio must be small. Consequently, the conditions hav- grinding stock removal rate (MRR) that has a correlation ing low grinding force ratio except for the inappropriate with the grinding temperature and grinding force is calcu- conditions in this experiment are Nos.10 and 12. Nos.10 lated by the following formula: and 12 are close to the optimum condition from Figs. 13– V 15. Therefore, the grinding force under both conditions MRR= fR t ...... (1) are compared. Fig. 16 shows the measured values of the d πd principal force and feed force under each grinding condi- d is the tool diameter and t is the workpiece thickness. tion. The principal force in No.10 is more than twice as It has been found that the grinding temperature under large as that in No.12. Therefore, No.12 is more suitable the grinding conditions (Nos.3, 4, 7, and 8), where the than No.10 as the optimum grinding condition. The CFRP 3 ◦ MRR exceeds 40 mm /min, is more than 100 Candex- temperature of the No.12 grinding condition is 91.2◦C ceeds the Tg of the CFRTPs. Therefore, these conditions as shown in Fig. 13.IftheMRR increases as compared do not seem to be appropriate for grinding. Next, the to this condition, the CFRP temperature is assumed to ◦ measured values of the surface roughness Ra and aver- exceed 100 C. Therefore, the optimum grinding condi- age length of uncut fibers under each grinding condition tion for CFRP with the cBN electroplated end-mill is the are shown in Fig. 14. The average length of uncut fibers No.12 grinding condition (As = #60, f = 50 μm/tooth, for airplane parts is required to be less than 0.2 mm [17]. Rd = 10 μm, V = 100 m/min). The average length of uncut fibers under all conditions in this experiment satisfies the required value. The re- 3.5. Verification of Effectiveness of the Grinding quired value of surface roughness Ra of airplane parts is less than 3.2 μm [16]. However, the required value with cBN Electroplated End-Mill could not be achieved under all conditions in this exper- Next, the effectiveness of the developed tool and the de- iment. In addition, the grinding conditions with large rived optimum grinding condition were verified by com- abrasive size (Nos.13–16) deteriorated the surface rough- paring the quality of the machined surface with that of

10 Int. J. of Automation Technology Vol.15 No.1, 2021 Investigation of Optimum Grinding Condition Using cBN Electroplated End-Mill for CFRP Machining

Fig. 17. Whole image of a diamond coated end-mill.

PP 8QFXWILEHU

(a) Before grinding (with developed tool) (a) With diamond coated end-mill

PP 6PDOOXQFXWILEHU

(b) After grinding (grinding condition: No.12, As = #60, f = 50 μm/tooth, Rd = 10 μm, V = 100 m/min)

Fig. 18. Microscopic images of ﬁnish machined surface of CFRP with cBN electroplated end-mill.

(b) With cBN electroplated end-mill PP 8QFXWILEHU Fig. 20. Schematic illustrations of ﬁnish machining with (a) Before ﬁnish cutting (with developed tool) diamond coated end-mill and developed tool.

PP *HQHUDWHGXQFXWILEHU mond coated end-mill, respectively. The developed tool (b) After finish cutting could obtain high quality CFRP edges. There are two rea- sons. First, as the radial depth of cut of the developed tool Fig. 19. Microscopic images of finish machined surface of was one tenth of the diamond coated end-mill, the uncut CFRP with diamond coated end-mill. fiber length also reduced spontaneously. Second, when using the end-mill tool, the fibers experienced an upward (thrust) force as shown in Fig. 20(a). Asthefibersthat a conventional tool. As a conventional tool, a diamond were fixed on the upper surface did not provide support, it coated end-mill was used. This tool is generally applied was difficult for the cutting edges to cut the fibers. Addi- in CFRP finish machining. The diamond coated end-mill tionally, as the cutting edges of the base material of the de- shown in Fig. 17 had high wear resistance. Therefore, it veloped tool did not involve the grinding of the CFRP, the was easy to maintain a sharp cutting edge even after cut- lateral (feed) force was dominant as shown in Fig. 20(b). ting [18]. In the experimental method, after rough cutting The thrust force when using the developed tool and the di- with the developed tool, finish machining was executed amond coated end-mill was 11.6 and 81.3 N, respectively. under the optimum condition with each tool. Regarding Thus, the uncut fiber length reduced while using the de- the specifications of the diamond coated end-mill, the rake veloped tool. angle was +6◦, clearance angle was 17◦, the width of the Next, the surface roughness of the machined CFRP flank face was 0.5 mm, and the number of cutting edges when using the diamond coated end-mill and developed was 4. The recommended finish cutting condition of the tool were 1.2 and 18.7 μm, respectively. The unevenness diamond coated end-mill is f = 25 μm/rev, Rd = 100 μm, of the developed tool was large as shown in Fig. 6(c), and V = 200 m/min. Subsequently, the length of the uncut and the unevenness of the diamond coated end-mill that fibers and the surface roughness of the machined surface coated the fine diamond abrasive onto the tool surface were measured. Fig. 18 shows the microscopic images of was small as shown in Fig. 21. This difference in the un- the CFRP surface before and after finish machining with evenness had an impact on the surface roughness. From the developed tool. Fig. 19 shows the same with the di- the above, the surface roughness Ra of the developed tool amond coated end-mill. The average uncut fiber length could not achieve the required value of surface roughness was 44 and 66 μm using the developed tool and the dia- of airplane parts (Ra ≤ 3.2 μm).

Int. J. of Automation Technology Vol.15 No.1, 2021 11 Yamashita, S. et al.

&XWWLQJHGJH 5DNHIDFH Table 4. Nomenclature of Eqs. (2)–(9). )ODQNIDFH fy Feed rate in the Y direction fz Feed rate in the Z direction φ Virtual expansion amount of tool periphery α Angle of the abrasive tip h(θ) Valley height D Tool diameter P V Grinding speed θ Tool rotation range Fig. 21. SEM image of diamond coated end-mill. n¯ Random coefﬁcient

Wo Average volume of an abrasive Am Amplitude T Cycle

lF Flank width of developed tool ∗ Rzt Theoretical ultimate roughness Rzt Theoretical surface roughness with electroplated router Rztc Theoretical surface roughness with developed tool Rz Measured maximum height roughness Ra Measured arithmetic mean roughness

section are shown in Table 4. To derive the theoretical surface roughness in oscillating grinding using the cBN Fig. 22. Schematic illustration of an oscillating grinding electroplated end-mill, the theory of slant grinding using method. a conventional grinding tool (an electroplated router) [20] was used. The differences between slant grinding and oscillating grinding are shown in Fig. 23. Slant grinding is a 3.6. Improvement of Surface Roughness of CFRP grinding method in which the tool is fed obliquely in the by Oscillating Grinding Y direction. Therefore, the process of removing the workpiece is similar to that in oscillating grinding. Therefore, The required surface roughness R of airplane parts a the theoretical surface roughness in oscillating grinding could not be achieved by CFRP grinding with the cBN using the electroplated router R was calculated by ap- electroplated end-mill. To solve this problem, oscillating zt plying the theory of surface roughness of slant grinding. grinding was applied. A schematic illustration of the os- This theory was analyzed by a statistical method in con- cillating grinding process is shown in Fig. 22.Thisisa sideration of all the abrasives being randomly arranged finish machining method in which the tool is moved as on the surface of the grinding tool. First, the theoretical a sine wave along the Z-axis and Y -axis directions only formulae of slant grinding are shown below. by the machine tool [19]. The developed tool has lesser number of abrasives operating during grinding than an φ = fzV α 2 cot ...... (2) electroplated router because the developed tool has slits. fy However, it is expected that the required surface rough- D f 2 ness of the machined surface can be achieved by oscillat- h(θ)= y θ 2 ...... (3) 4 V ing grinding that moves the tool in the axial direction and increases grinding marks. The important factors in oscil- nW¯ R∗ = 0 cotα ...... (4) lating grinding are not only the feed rate per tooth f and zt θD grinding speed V, but also the cycle T and amplitude Am. The cycle T implies the feed rate in the Y direction per cy- R zt⎧ cle. The amplitude A implies the vertical movement of 2 m ⎪ 5 ⎪ 15 ∗ 2 15 ∗ the tool in the Z direction during cycle T . Thus, it is dif- ⎪ (R ) h(θ) h(θ) ≥ R ⎪ 8 zt 8 zt ficult to select the grinding conditions that satisfy the re- ⎨⎪ quired surface roughness. Therefore, we derived the the- = 1 (θ)+ ( ∗ )2 − 4 { (θ)}2 oretical formulae of the surface roughness in oscillating ⎪ h Rzt h ⎪ 3 45 grinding using the cBN electroplated end-mill. In addi- ⎪ ⎪ (θ) < 15 ∗ tion, the values of the amplitude Am and cycle T satisfy- ⎩ h Rzt ing the required surface roughness and high grinding effi- 8 ciency were calculated. The variables that are used in this ...... (5)

12 Int. J. of Automation Technology Vol.15 No.1, 2021 Investigation of Optimum Grinding Condition Using cBN Electroplated End-Mill for CFRP Machining

P z R URXJKQHVV 0D[LPXPKHLJKW

$ULWKPHWLFPHDQURXJKQHVVRa P

(a) Slant grinding Fig. 24. Relationship between surface roughness Rz and Ra on conventional grinding results using the developed tool.

worse than that with a conventional grinding tool. There- fore, the theoretical maximum height roughness in oscillating grinding with the developed tool Rztc is πD Rztc = Rzt ...... (8) 2lF

Here, lF is the flank width (primary clearance land) of the cBN electroplated end-mill. As the calculation of the (b) Oscillating grinding arithmetic mean roughness Ra is complicated even with the theory of conventional grinding, the maximum height Fig. 23. Differences between slant grinding and oscillating roughness was converted to the arithmetic mean rough- grinding. ness using the relational formula derived from experimental results. The maximum height roughness and arithmetic mean roughness are linearly related [23]. There- f is the feed rate in the YZ direction, V is the grinding fore, the relational expression between the maximum speed, D is the tool diameter, Wo is the average volume height roughness and arithmetic mean roughness was de- of an abrasive cutting edge, and α is the angle of the rived using the measured values in the conventional grind- abrasive tip.n ¯ is a random coefficient, which is 3.3 re- ing experiment with the developed tool. The measured gardless of the type of abrasive [21]. h(θ) is the valley values of the maximum height roughness and arithmetic height, which is the cutting height of the abrasive that average roughness in the conventional grinding experi- draws a trochoid locus in grinding [22]. The theoretical ment using the developed tool are shown in Fig. 24.It surface roughness in slant grinding is calculated by apply- is clarified that the maximum height roughness and arith- ing the theoretical surface roughness formulae of conven- metic mean roughness have the following relationship. tional grinding, considering the increase in the effective Rz − 14.437 number of abrasives due to the axial movement of the tool Ra = ...... (9) 4.6093 with increase in the tool rotation range. The tool rotation range during grinding was converted from −π ≤ θ ≤ π The maximum height roughness is converted to the to −π − φ ≤ θ ≤ π + φ. Here, φ is the virtual expansion arithmetic mean roughness using Eq. (9) for deriving the amount of the tool periphery in slant grinding compared theoretical value. In order to investigate the validity of the ∗ derived formula, it was verified whether the Eqs. (2)–(9) to conventional grinding. Rzt is the ultimate roughness in which the surface roughness is zero for feed rate in the could be applied for oscillating grinding. In this experi- γ Y direction. The feed direction in oscillating grinding is ment, an angle of wave was considered as the experi- γ = −1( / ) approximated to a triangular wave. When the feed rates mental parameter. ( tan 2Am T ) is the angle between the feed direction and Y direction when the feed in the Y direction fy and Z direction fz in slant grinding are reflected in oscillating grinding, they are converted to direction in oscillating grinding is approximated from the sine wave to the triangular wave. γ was changed from 45◦ the following formulae. ◦ to 76 . Then, Am was changed from 0.1 to 3.0 mm. For the T other conditions, the optimum grinding conditions were fy = f ...... (6) 4A2 + T 2 used as derived in the previous section. It was investigated m whether the experimental and theoretical value coincided 2Am in oscillating grinding using the developed tool. The mea- fz = f ...... (7) 4A2 + T 2 sured and theoretical values of arithmetic mean roughness m by oscillating grinding are shown in Fig. 25.Thethe- As mentioned above, as the developed tool grinds with oretical and measured values in the experimental condi- abrasives fixed to the flank face, the surface roughness is tions for Am between 0.5 to 3.0 mm were almost the same.

Int. J. of Automation Technology Vol.15 No.1, 2021 13 Yamashita, S. et al.

7KHRUHWLFDOYDOXH $P PP developed tool was evaluated. As a result, the following $P PP $P PP $P PP $P PP conclusions are drawn. $P PP P

R 1) CFRPs can be machined by the cBN electroplated end-mill without dropping cBN abrasives during cutting. 2) The effect of grinding conditions on the grinding results has been clariﬁed by the design of experiments. For CFRPs, the optimum grinding condition for creating a machined surface with good sur- $ULWKPHWLFPHDQURXJKQHVV face quality with low grinding load and CFRP tem- Ȗ GHJ perature is cBN abrasive size As = #60, feed rate = μ = μ Fig. 25. Comparison result of theoretical and measured f 50 m/tooth, radial depth of cut Rd 10 m, value on an oscillating grinding. and grinding speed V = 100 m/min. 3) Regarding the result of comparison between the developed tool and a diamond coated end-mill (conventional tool), the developed tool can obtain short

P uncut ﬁbers. However, the surface roughness is large a

R because of the inﬂuence of the unevenness of the tool surface. 7KHRUHWLFDOYDOXH $ULWKPHWLFPHDQ URXJKQHVV 4) The theoretical formulae of oscillating grinding have 0HDVXUHGYDOXH been derived, and their validity is conﬁrmed. As a result, it is observed that the theoretical and measured Ȗ GHJ values almost coincide. The required value of surface roughness of airplane parts (Ra ≤ 3.2 μm) is Fig. 26. Derived result of the optimum grinding condition achieved at γ ≥ 85.9◦. on an oscillating grinding.

Acknowledgements However, there was a large difference between the theo- This work was supported by JSPS KAKENHI Grant Number 17K14570. retical and measured value for Am ≤ 0.3 mm. As this area was applied with a small amplitude, the moving range of the tool in the Z direction became small. Therefore, it is References: inferred that this problem occurred because of the simi- [1] H. Hocheng, H. Y. Tsai, J. J. Shiue, and B. Wang, “Feasibility study larity of the tool trajectory in oscillating grinding under of abrasive-waterjet milling of fiber-reinforced plastics,” J. of Man- ufacturing Science and Engineering, Vol.119, No.2, pp. 133-142, these conditions to that in conventional grinding. There- 1997. fore, it was inferred these formulae can be applied under [2] J. Wang, “Machinability study of polymer matrix composites using abrasive waterjet cutting technology,” J. of Materials Processing certain amplitude for oscillating grinding. Next, we inves- Technology, Vol.94, No.1, pp. 30-35, 1999. tigated the range of γ in oscillating grinding with the de- [3] H. Hocheng, H. Y. Puw, and Y. Huang, “Preliminary study on veloped tool to achieve the required surface roughness for milling of unidirectional carbon fibre-reinforced plastics,” Compos- R ≤ μ A ites Manufacturing, Vol.4, No.2, pp. 103-108, 1993. airplane parts ( a 3.2 m). In this experiment, m was [4] H. Arisawa and S. Akama, “High-Performance Cutting and Grind- changed from 0.5 to 3.0 mm. T was changed from 8 to ing Technology for CFRP (Carbon Fiber Reinforced Plastic),” Mit- 200 μm. The measured and theoretical values of the arith- subishi Heavy Industries Technical Review, Vol.49, No.3, pp. 3-9, γ ≥ ◦ 2012. metic mean roughness by oscillating grinding for 84 [5] T. Furuki, T. Hirogaki, E. Aoyama, and K. Ogawa et al., “Investi- are shown in Fig. 26. The theoretical and measured values gation of cBN electroplated end-mill shape for CFRP machining,” are almost the same as the result in Fig. 25. Consequently, Materials Science Forum, Vol.874, pp. 463-468, 2016. [6] M. Senthilkumar, A. Prabukarthi, and V. Krishnaraj, “Study on Tool it was found that the required surface roughness for air- Wear and Chip Formation during Drilling Carbon Fiber Reinforced plane parts (R ≤ 3.2 μm) was achieved at γ ≥ 85.9◦. Polymer (CFRP) / Titanium Alloy (Ti6Al4V) Stacks,” Procedia En- a gineering, Vol.64, pp. 582-592, 2013. [7] T. Furuki, Y. Kabaya, T. Hirogaki, E. Aoyama et al., “Develop- ment of cBN electroplated end-mill combined cutting and grinding for precision machining of CFRP,” Int. J. of Abrasive Technology, 4. Conclusions Vol.8, No.3, pp. 188-202, 2018. [8] S. Kondo, C. Ohkawa, T. Hanawa, T. Sugawara et al., “Differences The cBN electroplated end-mill was fabricated, which in Surface Roughness between Up and Down Cutting and Grinding on Composite Resins,” Dental Materials J., Vol.4, No.2, pp. 223- was based on the concept of compatible rough cutting and 230, 1985. finish grinding of CFRPs. In this study, the cutting and [9] Y. Kabaya, T. Furuki, T. Hirogaki, E. Aoyama et al., “Influence of grit size in high speed milling of CFRP with cBN electroplated end- grinding characteristics of CFRP with the developed tool mill,” J. of the Japan Society for Precision Engineering, pp. 405- were investigated. In addition, the effectiveness of the 406, 2015 (in Japanese).

14 Int. J. of Automation Technology Vol.15 No.1, 2021 Investigation of Optimum Grinding Condition Using cBN Electroplated End-Mill for CFRP Machining

[10] T. Chen, J. Xiang, F. Gao, and X. Liu et al., “Study on cutting performance of diamond-coated rhombic milling cutter in machining Name: carbon fiber composites,” Int. J. of Advanced Manufacturing Tech- nology, Vol.103, No.9, pp. 4731-4737, 2019. Shinnosuke Yamashita [11] P. M. George, B. K. Raghunath, L. M. Manocha, and A. M. War- rier, “EDM machining of carbon-carbon composite – A Taguchi Affiliation: approach,” J. of Materials Processing Technology, Vol.145, No.1, Master Course Student, Gifu University pp. 66-71, 2004. [12] Y. H. Ren, B. Zhang, and Z. X. Zhou, “Specific energy in grinding of tungsten carbides of various grain sizes,” CIRP Annals, Vol.58, No.1, pp. 299-302, 2009. [13] R. L. Hecker and S. Y. Liang, “Predictive modeling of surface roughness in grinding,” Int. J. of Machine Tools and Manufacture, Vol.43, No.8, pp. 755-761, 2003. Address: [14] T. Tashiro, J. Fujiwara, S. Hanasaki, and S. Fujiwara, “Formation 1-1 Yanagido, Gifu, Gifu 501-1193, Japan mechanism of ground surface of CFRP,” J. of the Japan Society for Brief Biographical History: Abrasive Technology, Vol.49, No.2, pp. 99-104, 2005 (in Japanese). 2012- National Institute of Technology, Kagawa Collage [15] T. Kaneeda and M. Takahashi, “CFRP Cutting Mechanism (2nd Re- 2017- Undergraduate Course Student, Gifu University port),” J. of the Japan Society for Precision Engineering, Vol.56, No.6, pp. 1058-1063, 1990 (in Japanese). 2019- Master Course Student, Gifu University [16] H. Wang, J. Sun, J. Li, L. Lu et al., “Evaluation of cutting force Membership in Academic Societies: and cutting temperature in milling carbon fiber-reinforced poly- • Japan Society of Mechanical Engineers (JSME) mer composites,” Int. J. of Advanced Manufacturing Technology, • Japan Society for Precision Engineering (JSPE) Vol.82, No.9, pp. 1517-1525, 2016. • Japan Society for Abrasive Technology (JSAT) [17] H. Fukagawa, “Processing of the Hard to Cut Materials and Heat- resistant Alloys for Aircrafts,” J. of the Society of Mechanical En- gineers, Vol.115, No.1128, pp. 762-766, 2012 (in Japanese). [18] K. Kanda, S. Takehana, S. Yoshida, R. Watanabe et al., “Applica- tion of diamond-coated cutting tools,” Surface and Coatings Tech- nology, Vol.73, Nos.1-2, pp. 115-120, 1995. Name: [19] T. Nakajima, S. Tsukamoto, T. Teraoka, and Y. Ono, “Determina- Tatsuya Furuki tion of Oscillation Conditions for Optimizing Surface Roughness in Internal Grinding,” J. of the Japan Society for Precision Engineer- ing, Vol.65, No.4, pp. 604-609, 1999 (in Japanese). Affiliation: [20] K. Shimada, P. J. Liew, T. Zhou, J. Yan et al., “Statistical Approach Assistant Professor, Graduate School of Natural Optimizing Slant Feed Grinding,” J. of Advanced Mechanical De- Science and Technology, Gifu University sign, Systems, and Manufacturing, Vol.6, No.6, pp. 898-907, 2012. [21] N. Yoshihara and T. Kuriyagawa, “Statistical Approach to Ground Surface Roughness Formation Mechanism,” Proc. of JSPE Semes- trial Meeting, Vol.2005S, pp. 863-864, 2005 (in Japanese). [22] K. Ono, “Influences of Grit Profile and Grit Distribution on Ground Surface Roughness,” Japan Society of Mechanical Engi- Address: neers, Vol.30, No.211, pp. 361-368, 1964 (in Japanese). 1-1 Yanagido, Gifu, Gifu 501-1193, Japan [23] T. Mori, K. Tasaka, M. Ichimiya, and T. Ogasawara, “Surface Brief Biographical History: Roughness Parameter and Slip Coefficient of Friction Type of High 2016- Gifu University Strength Bolted Connections,” J. of Japan Society of Civil Engi- Main Works: neers, Ser. A1 (Structural Engineering & Earthquake Engineering • “Investigation on Magnetic Polishing Characteristics of Metal Additive (SE/EE)), Vol.67, No.2, pp. 446-453, 2011 (in Japanese). Manufactured Ti-6Al-4V,” Int. J. of Abrasive Technology, Vol.9, No.3, pp. 188-199, 2019. • “Development of cBN electroplated end-mill combined cutting and grinding for precision machining of CFRP,” Int. J. of Abrasive Technology, Vol.8, No.3, pp. 188-202, 2018. Membership in Academic Societies: • Japan Society of Mechanical Engineers (JSME) • Japan Society for Precision Engineering (JSPE) • Japan Society for Abrasive Technology (JSAT) • European Society for Precision Engineering and Nanotechnology (euspen)

Int. J. of Automation Technology Vol.15 No.1, 2021 15 Yamashita, S. et al.

Name: Name: Hiroyuki Kousaka Eiichi Aoyama

Afﬁliation: Afﬁliation: Professor, Graduate School of Natural Science Professor, Graduate School of Science and Engi- and Technology, Gifu University neering, Doshisha University

Address: Address: 1-1 Yanagido, Gifu, Gifu 501-1193, Japan 1-3 Tataramiyakodani, Kyotanabe-shi, Kyoto 610-0394, Japan Brief Biographical History: Brief Biographical History: 1997- Nissan Motor Corporation 1977- Technology Research Institute of Osaka Prefecture 2004- Nagoya University 1997-1998 Visiting Researcher, Queen Mary and Westfield College, 2016- Professor, Gifu University University of London Main Works: 1987- Doshisha University • “Effect of humidity on the friction properties of a-C:H and a-C:H:Si films Main Works: deposited by PECVD employing microwave sheath-voltage combination • “Mirror-Surface Finishing by Integrating Magnetic-Polishing plasma,” Japanese J. of Applied Physics, Vol.58, SAAC06, 2018. Technology with a Compact Machine Tool,” Int. J. Automation Technol., • “Analysis of Wear Track on DLC Coatings after Sliding with Vol.13, No.2, pp. 207-220, 2019. MoDTC-Containing Lubricants,” Tribology Online, Vol.12, Issue 3, • “Development of nanofibre abrasive buffing pad produced with modified pp. 110-116, 2017. melt blowing method,” Int. J. of Abrasive Technology, Vol.9, No.1, • “Spatio-temporal behavior of microwave sheath-voltage combination pp. 31-48, 2019. plasma source,” J. of Applied Physics, Vol.117, No.18, 183302, 2015. • “Whole Quenching of Small Thin Plate with Low-Power Semiconductor Membership in Academic Societies: Laser Based on Feed-Speed Combination Problem,” Int. J. Automation • Japan Society of Mechanical Engineers (JSME) Technol., Vol.10, No.6, pp. 923-933, 2016. • Japan Society of Tribologists (JAST) Membership in Academic Societies: • Japan Society of Applied Physics (JSAP) • Japan Society of Mechanical Engineers (JSME) • Japan Society for Precision Engineering (JSPE) • Japan Society for Abrasive Technology (JSAT) • Society of Materials Science, Japan (JSMS)

Name: Toshiki Hirogaki

Affiliation: Name: Professor, Graduate School of Science and Engi- Kiyofumi Inaba neering, Doshisha University Affiliation: Diamant Division, Kamogawa Co., Ltd. Address: 7-3-26 Tehara, Rittou, Shiga 520-3047, Japan Address: 1-3 Tataramiyakodani, Kyotanabe-shi, Kyoto 610-0394, Japan Brief Biographical History: 1990- Mitsubishi Motors Corporation 1993- Technology Research Institute of Osaka Prefecture Name: 1995- The University of Shiga Prefecture Kazuna Fujiwara 2003- Doshisha University 2006-2007 Visiting Researcher, University of California, Berkeley Main Works: Affiliation: • “Driving Performance of Natural Fiber Gears Made Only from Bamboo Diamant Division, Kamogawa Co., Ltd. Fibers Extracted with a Machining Center,” Int. J. Automation Technol., Address: Vol.14, No.2, pp. 280-293, 2020. 7-3-26 Tehara, Rittou, Shiga 520-3047, Japan • “Analysis of drilling conditions by a catalog mining method based on Fuzzy c-means algorithm,” J. of Advanced Mechanical Design, Systems, and Manufacturing, Vol.14, No.6, 20-00080, 2020. • “Investigation of Internal Thread Cutting Phenomena in Three Axes by Controlling Helical Interpolate Motion Considering Tool Position Information from Servo-Drive,” Int. J. Automation Technol., Vol.14, No.3, pp. 467-474, 2020. Membership in Academic Societies: • Japan Society of Mechanical Engineers (JSME) • Japan Society for Precision Engineering (JSPE) • Society of Materials Science, Japan (JSMS) • Japan Institute of Electronic Packaging (JIEP)

16 Int. J. of Automation Technology Vol.15 No.1, 2021