# Reconditioning of Diamond Coated Tools and Its Impact on Cutting Performance for CFRP Laminates
## 1 Introduction  
It is well-known that the application of carbon-fiber-reinforced plastics (CFRPs) increases year by year in a wide range of industries, such as aircraft and automobiles. However, abrasion due to hard carbon fibers in CFRPs always leads to severe tool wear and, consequently, short tool life. Furthermore, when cutting tool conditions deteriorate due to wear and tear, the CFRP workpiece tends to show material-specific defects, such as delamination, burrs, and tearing of fibers. A well-known method of the tool life extension consists in the chemical vapor deposition (CVD) of polycrystalline diamond films on tungsten carbide (WC-Co) cutting tools [1; 2; 3].  
Moreover, studies reported that the utilization of special shape-designed WC-Co tools with CVD diamond coatings benefits CFRP machining, resulting in less burr formation and delamination effects [4; 5; 6]. Further, tool wear resistance can be improved by doping CVD diamonds with minute amounts of boron. The resulting boron-doped micro-crystalline diamond (B-MCD) film has shown excellent results in CFRP machining in our previous study [7]. On the other hand, such B-MCD-coated WC-Co tools with complicated shapes have a higher cost than conventional tools. Therefore, an effective method of the tool life extension is of great interest.  
Cutting tool reconditioning is one of the most efficient cost-saving strategies in the manufacturing industry [8]. For instance, [PERSON] reported that drills could be reconditioned and reused up to 10 times, thus significantly reducing costs and tool material wasting.  
Conventionally, reconditioning methods include sequential procedures, such as coating removal, tool regrinding, and film deposition [9]. Electrochemical etching (ECE) is commonly used for the decoating of metal-based composite films (e.g., TiN, TiAlN, TiAl-CrN, and CrN) [10]. However, the ECE is not effective for the stripping of diamonds due to its high chemical stability.  
The decoating of CVD diamond films by oxygen plasma has been studied by [PERSON] et al. [11; 12] and [PERSON] et al. [13]. However, these bulk plasma-based approaches have uniformity and scalability issues. A practically important method of CVD diamond decoating has been developed by [PERSON] [14]. The method consists in the reactive ion beam etching (RIBE) of a CVD diamond film with multiple closed electron drift ion sources (CDIS). The method has been shown to be able to strip both CVD diamonds and metal-based composite films from cutting tools with a complex geometry. On the other hand, the cutting performance of RIBE-reconditioned tools has not been studied. Indeed, energetic particle bombardment may alter the surface properties and the micro-geometry of the tools, negatively affecting the cutting performance of the reconditioned tools.  
In order to reuse the cutting tools after the decoating, the CVD diamond film must be re-applied, so the tools recover its mechanical properties. Typically, several extra steps are required prior to the film deposition: cleaning, Co wet-chemical etching (WCE) from the surface, and seeding [15]. The WCE is the most aggressive among these surface preparation steps and may negatively impact the WC-Co tool integrity. Therefore, the combined effects of RIBE decoating and WCE on various important tool properties have been investigated in the present work. The surface morphology, cutting edge geometry, B-MCD film adhesion and structure, and finally cutting performance were evaluated and discussed from the standpoint of the reconditioning approach.