A comprehensive tool-wear/tool-life performance model in the ...

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ARTICLE IN PRESS P.W. Marksberry, I.S. Jawahir / International Journal of Machine Tools & Manufacture 48 (2008) 878–886 883 -Y (j) 4 80˚ +Y (j) 1 2 3 ~50-mm 5 16° +X (i) +X (i) 4 1 2 5 3 -Z (k) [1] Removable Hardened Steel Nozzle Holder [2] Stainless Steel Adjustable Nozzle [3] Tool Holder [4] Indexable Cutting Tool Insert [5] Tool Holder Carousel (4 qty) Nozzle to Cutting Tool Relationship (vector notation) i, j, k (+X, +Y, +Z) Vectors (+/- 2-mm) i. = -48-mm j. = -8-mm k. = -14-mm Fig. 3. Nozzle to cutting tool to workpiece orientation. Table 4 Fixed machining and mist spray delivery parameters Table 5 Design of experiments Parameter Description Control factors Levels Description of levels Cutting tool material Cutting tool geometry Cutting parameters Al 2 O 3 , aluminum oxide (supplier: Kennametal CNMG 432 ESA AC2000) Type: grooved chip breaker Relief angle: 01 (side), 01 (end) Cutting edge angle: 51 (side), 51 (end) Tool nose radius: 0.8 mm Depth of cut: 3.2 mm Cutting speed: 4 m/s Feed: 0.3 mm/rev Metal removal rate: 11,520 mm 3 /s MWF type Straight oil, Cooluble 2210 Soluble—water miscible, Cimperial 1011 Semi-synthetic—water miscible, TRIM SC235 Synthetic—water miscible, Hocut 763 Atomization system Atomization type: co-axial air blast atomization Machine: MSK-G 100—MicroJet Air pressure: 5 psi Nozzle: stainless steel The 95% confidence interval was determined at 0.85 and 1.00-mm for the dominant tool-wear pattern (W BL ) for dry cutting using a sample size of 20. Modifications to the ASTM tapping torque procedure were carried out to distinguish the primary MWF functions using two different reamed hole diameters 5.55 and 5.48 mm to characterize cooling and lubricity, respectively. Fig. 4 shows the ASTM tapping torque results for each of MWF volumetric flow rate (ml/h) 4 (1) 20 (2) 40 (3) 80 (4) 160 MWF type 4 (1) Straight oil (2) Soluble oil (3) Semi-synthetic (4) Synthetic oil Nozzle position 3 (1) Rake face (2) Flank face (3) Chip the MWFs used in this work while varying the reamed hole diameter. Test results were collected from a Microtap Megatap 2, Labtop II G8 machine using standard 1018 steel test bar. A forming tap type was used in the test at a size of M6 1 pitch. Tapping speed was held constant at 1000 rpm or 18.8 m/min. 5. Results A comprehensive study has been conducted to validate the new tool-life/tool-wear relationship for NDM. A summary of the study is presented in Tables 6–8 and Fig. 5.
884 ARTICLE IN PRESS P.W. Marksberry, I.S. Jawahir / International Journal of Machine Tools & Manufacture 48 (2008) 878–886 ASTMD 5619 Tapping Torque (N-cm) 550 500 450 400 350 300 250 Straight Oil 5.55-mm Reamed Hole (Lubricity) 5.48-mm Reamed Hole (Cooling) Soluble Oil Semisynthetic Oil Synthetic Oil MWF Type Fig. 4. ASTM tapping torque results varying MWF type and reamed holes. 6. Discussion Tool-life/tool-wear modeling using mist spray applications can be successfully and more accurately predicted than using dry machining equations for NDM. Fig. 5 shows that predicted tool-wear values mostly fall within actual 95% machining confidence intervals for actual results while varying MWF type and rate. Table 6 indicates that significant improvements in tool-wear (over 400%) can be achieved using NDM compared to dry machining. This study emphasis that models developed for dry machining conditions cannot accurately predict NDM performance. Equation accuracy over a broad range of MWFs, nozzle position(s) and MWF volumetric flow rates was observed to be less than 10% on the average. Linearization of MWF rate and type effect factors simplified model calculations, yet provided to be fairly accurate for shop-floor use. Modification of the tool coating effect factor allowed the Taylor equation to be extended without deteriorating chip groove or tool coating factor accuracy. Table 6 MWF rate and type effect factors for MWFs primary used for lubrication Dominant tool wear pattern Nozzle position MWF type MWF rate ( 10 4 ) M ZX ( 10 4 ) M ZY effect factor effect factor W BL R (rake face) 25.6 2.7 F (flank face) 1.3 6.2 C (chip) 5.1 18.9 Table 7 MWF rate and type effect factors for MWFs primary used for cooling Dominant tool wear pattern Nozzle position MWF type MWF rate ( 10 4 ), M ZX ( 10 4 ), M ZY effect factor effect factor W BL R (rake face) 23.4 10.4 F (flank face) 6.6 7.5 C (chip) 5.7 8.3 7. Conclusion It has been observed that the selection of ‘‘mist spray’’ delivery parameters represents an essential element in minimizing tool-wear/tool-life. The following is a summary of findings from the present work: A new tool-wear/tool-life relationship has been developed for NDM with coated grooved tools by extending the Taylor-type equation to include mist spray delivery parameters by modifying the tool coating effect factor. More accurate and consistent estimates of tool-wear are made by using the new predictive model for NDM compared to dry machining models. The G mapping function allows users of the empiricalbased model to customize the equation to consider a wide variety of mist-spray delivery parameters, including nozzle position, MWF volumetric flow rate and MWF type. Table 8 MWF rate and type effect factors for MWFs primary used for cooling MWF type New tool coating for mist factor (n mist ) NDM total effect factor (NDM) Predicted tool-wear W BL (mm) Actual test tool-wear W BL (mm) Error % Improvement % over dry machining Straight 0.078 0.140 0.88 0.91 3.30 102 Soluble 0.060 0.135 0.77 0.74 4.05 125 Semisynthetic 0.055 0.126 0.55 0.59 6.78 157 Synthetic 0.065 0.138 0.22 0.23 4.35 402 Dominant tool-wear pattern: W BL ; nozzle position: rake face; MWF volumetric flow rate: 180 ml/h; chip-groove effect factor (W g ): 0.89; tool coating effect factor (n c ): 0.56; empirical constants: k ¼ 0.32, m ¼ 1 for turning, n 1 ¼ 0.230, n 2 ¼ 0.642.
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