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 unnec- essary portions on the outer area. Therefore, a ma- chining process is required to remove them. Cutting 1. Introduction and grinding are conventionally used in the finish ma- chining 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.