aluminum /CFRP/titanium Diameter tolerances caused by dissimilar lastic moduli of the materials Major CFRP flank Shim-lay C=10° Intense tool wear Delaminations, erosion Figure 19: Aspects concerning drilling of composite-metal MateriaL: Al/ CFRP/ TiAI6V4 hickness 10/10/10mm Figure 18: Influence of clearance angle on burr generation after drilling 1000 holes on GFRP(V+=60% d=6.0 mm Work thickness: 10 mm: drill fish tail carbide drill diam Tools 12 mm; cutting speed: 181 m/min; feed: 0.05 mm [30] Carbide K10 Carbide K30F In [34] the authors emphasize that in many aerospace Diameter D 91mm85/91mm pplications dissimilar material stack-ups of composites ind aluminium and/or titanium are used for wing No, of flutes 3 tailplane structures. Such structures contain holes for various purposes. The machining characteristics of these materials, when sandwiched together, introduce a unique Point angle o set of drilling problems(Figure 19). Apart from the intense Rake angle y 0° tool wear caused by the high loads during the process, the erosion and abrasion in the cfrp layer are also critical for uncoated aerospace fabrication In addition, industrial needs such as Boring parameters the avoidance of cooling lubrication also increase the efforts for successful machining and require highly efficient Cutti d machining technology. Therefore, extensi ge set-up of Feed reverse after 5/10/15/20/25/30 mm e experiments Feed f 0.15mm ere undertaken to find solutions conomic drilling processes on multi-layer materials(Table 4). Different drill configurations were selected and MQL(fattyalcohol/ester) investigated by characterising cutting forces, tool wear hole quality and chip formation. The investigations showed Table 4: Experimental conditions in the drilling of an that drilling of multi-layer composites requires adapted aluminium/CFRP/titanium sandwich structure [34] utting parameters tools and cooling lul brication Figure 20 shows the feed forces for a drilling process on an AlCuMg2/CFRP/Al6V4 sandwich structure using a N Fatty alcohol onventional drilling tool with a diameter d =9. 1 mm and stigations have shown that dry machining of titanium involves increased ip formation problems [35 onsequently, the drilling experiments were carried out with minimum quantity lubrication. The increase of feed 3 forces clarifies that the forces vary considerably between le material layers. The feed force when drilling the titanium layer is clearly higher and increases with growing 公 N+(additivated umber of holes caused by extensive tool wear 200 igure 21 shows the course of tool wear for a conventional tool and a tool with optimised geometry. The latter was designed with a diameter step of 8.5 to the carbide specification was changed to a micro-grain carbide and the tool surface was treated by micro-blasting 2 For conventional drilling tools, the number of holes is Number of holes limited to 15 no matter what cutting fluid is used. The optimised tool shows a significantly better wear behaviou Figure 20: Feed force when drilling the aluminium/CFRP/titanium sandwich structure [34]Figure 19: Aspects concerning drilling of composite-metal sandwich materials [34] Process Workpiece a = 20" Figure 18: Influence of clearance angle on burr generation after drilling 1000 holes on GFRP (Vf = 60%). Work thickness: 10 mm; drill: fish tail carbide; drill diam.: 12 mm; cutting speed: 181 m/min; feed: 0.05 mm [30]. Drilling Material: Al / CFRP / TiA16V4 In [34] the authors emphasize that in many aerospace applications dissimilar material stack-ups of composites and aluminium and/or titanium are used for wing or tailplane structures. Such structures contain holes for various purposes. The machining characteristics of these materials, when sandwiched together, introduce a unique set of drilling problems (Figure 19). Apart from the intense tool wear caused by the high loads during the process, the erosion and abrasion in the CFRP layer are also critical for aerospace fabrication. In addition, industrial needs such as the avoidance of cooling lubrication also increase the efforts for successful machining and require highly efficient machining technology. Therefore, extensive experiments were undertaken to find solutions for the set-up of economic drilling processes on multi-layer materials (Table 4). Different drill configurations were selected and investigated by characterising cutting forces, tool wear, hole quality and chip formation. The investigations showed that drilling of multi-layer composites requires adapted cutting parameters, tools and cooling lubrication. Figure 20 shows the feed forces for a drilling process on an AICuMg2/CFRP/TiAIGV4 sandwich structure using a conventional drilling tool with a diameter D = 9.1 mm and two different cutting fluids. Several investigations have shown that dry machining of titanium involves increased tool wear and chip formation problems [35, 361. Consequently, the drilling experiments were carried out with minimum quantity lubrication. The increase of feed forces clarifies that the forces vary considerably between the material layers. The feed force when drilling the titanium layer is clearly higher and increases with growing number of holes caused by extensive tool wear. Figure 21 shows the course of tool wear for a conventional tool and a tool with optimised geometry. The latter was designed with a diameter step of 8.5 to 9.1 mm. Moreover, the carbide specification was changed to a micro-grain carbide and the tool surface was treated by micro-blasting. For conventional drilling tools, the number of holes is limited to 15 no matter what cutting fluid is used. The optimised tool shows a significantly better wear behaviour. Tools d = 6.0 mm Conventional I Optimized Cutting speed vc Feed f 1 Carbide K10 1 Carbide K30F 20 m/min 0.15 mm Diameter D I 9.1 mm I 8.5/9.1 mm No. of flutes I 3 I 3 Helix angle 6 Point angle o Rake angle y Coating uncoated uncoated Boring parameters I Feed reverse after I 5/10/15/20/25/30 mm Cooling I MQL (fatty alcohol / ester) Table 4: Experimental conditions in the drilling of an aluminium/CFRP/titanium sandwich structure [34]. Number of holes Figure 20: Feed force when drilling the aluminium/CFRP/titanium sandwich structure [34]