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 0°
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),