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Authored by: P T Mativenga & K K B Hon

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1 Authored by: P T Mativenga & K K B Hon
A Study of Cutting Forces and Surface Finish in High-Speed Machining of AISI H13 Tool Steel Using Carbide Tools With TiAIN Based Coating Authored by: P T Mativenga & K K B Hon Presented by: Ted Hand October 27, 2004

2 Introduction Purpose of the paper:
“Process improvement should not compromise but should enhance product quality.” Purpose of the paper: Address the effects of increasing machining speeds as well as the effects of different advanced coatings on surface finish.

3 Background Coatings TiC coatings
Reduce cutting T, forces, and increase abrasion resistance as well as acting as a diffusion barrier. Expand the region of machining conditions which reduces wear rates Coatings are expected to result in lower wear regions occurring at higher spindle speeds, promoting the use of HSM.

4 Surface Roughness Definition: relatively closely spaced or fine surface irregularities, mainly in the form of feed marks left by the cutting tool. Surface roughness: Ra = S2z / (18 x (3(D/2 + SzNt/ pi)).5) D = tool diameter Sz = Vf / Nt N = chip load Nt = number of edges that advance in a revolution of the cutter N = spindle speed in r/min Vf = feed rate

5 Parameters Machine tool: Cutting tools: Mikron HSM 700
42000 r/min 12 kw spindle capable of a 20m/min cutting feed and 40 m/min rapid feed Cutting tools: 6mm ball-nose end mills PVD coated Micrograin alloy WC 10% Co

6 Table 1: Geometrical properties of the ball-nose end mill used in the experiments
Tool parameters Symbol Value Number of flutes 2°° Helix angle λ 30° Rake angle γ Shank diameter d 6mm Overall tool length lt 57mm Nominal length below chuck lnorm 20mm Cut length lc 7mm Cutter diameter Corner Radius r 3mm Setting angle χ

7 Table 2: Properties of PVD coatings
Coating material TiN TiCN CrN 2TiAlN TiAlN TiAlN + WC/C Microhardness (HV 0.05 2300 3000 1750 3500 Coefficient of friction against steel (dry) 0.4 0.5 0.2 Coating thickness (μm) 1--4 1--5 1--3 2--6 Maximum working temperature (°C) 600 400 700 800

8 Cont. Work material: Finishing operations use the following coatings:
Mid range hot work tool steel AISI H13 Finishing operations use the following coatings: TiN TiCN CrN TiAlN 2TiAlN TiAlN + WC/C Three components of the cutting forces were sampled and averaged.

9 Milling Strategy Table 3: Cutting parameters for AISI H13 tool steel HSM experiments Tool diameter D 6mm Depth of cut a .06mm Width of cut b Rapid feed Vf-rapid 10,000 mm/min Ramp feed Vf-ramp 500 mm/min Cutting feed Vf 6000 mm/min Direction of linear interpolation x axis Direction of tool step-over y axis

10 Evaluation Surface finish was evaluated using a Mitutoyo SURFTEST 301 with a cut-off value of .8mm and a span of .5mm 25 measurements taken Surface integrity studied with a optical microscope and an SEM

11 Results Table 4: Correlation coefficients of surface finish to cutting forces Step-over direction G01 direction Fx Fy Fz Peak Fz TiN 0.83 0.84 1.00 0.99 0.81 0.98 TiCN -0.14 0.90 -0.20 0.87 0.96 0.95 CrN 0.93 0.62 0.97 0.89 0.59 0.94 TiAlN 0.42 0.49 0.88 0.44 0.31 0.73 Uncoated 0.74 0.71 0.50 0.57 2TiAlN -0.09 0.80 TiAlN + WC/C -0.03 0.19 0.35 0.38 -0.30 -0.21 -0.05

12 Graphs Figures 2-10 How the surface finished is affected by the spindle speed.

13 Cont. HSM with TiCN, TiN, CrN, single and double layered TiAlN produced a better surface finish TiAlN gave the best results, but need to minimize interaction with steel CrN didn’t present an advantage

14 Conclusions PVD tool coatings improved the surface finish compared to uncoated tools Coatings had the smallest wear zone promoting higher cutting speeds Higher cutting speeds and PVD coatings are pushing the frontiers in surface finishing's.

15 Implications Reducing die making lead times
Cutting costs with smaller lead times Industries affected: Aerospace Precision machine labs Auto industry Etc.

16 References: Edwards, R. Cutting Tools, 1993, pp (The institute of Materials) ISO 368 Surface Roughness—Parameters, Their Values and General Rules for Specifying Requirements Lim, S.C. and Lim, C.Y.H. Effective use of coated tools—the least wear map approach. Surface and Coatings Technol., 2001, 139, Konig, W., Komanduri, R., Tonshoff, H.K. and Ackershott, G. Machining of hard materials—Key Note papers. Ann. CIRP, 1984, 33(2), DeVries, W.R. Analysis of Material Removal Processes, 1992, p.138 (Springer - Verlag, Berlin). Da Silva, M.B. and Wallbank, J. Lubrication and application method in machining. Ind. Lubric. Technol., 1998, 50(4),

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