Cutting Tool Materials Various cutting materials has been used in industry for different applications. The important characteristics expected of cutting tool material 1- Higher hardness 2 -Hot hardness 3- Wear resistance- 4- Toughness 5- Low friction 6- Thermal characteristicsTypes of Materials Carbon Tool Steel -0.6 -1.5% carbon and very small alloy additions such as manganese -Speed 6- 9 m/min High speed steel Carbon, Tungsten, Molybdenum, Chromium Speed 30 - 45m/min Cemented carbides - High hardness - Higher young's modulus -Speed 70-120 m/min Ceramics -Speed 250-300 m/min Diamond - Can be used as a cutting tool material - High tool lifeRequirements When Machining with Ceramics: © Using the highest cutting speed recommended ¢ Use rigid machines ¢ Machining rigid work-pieces ¢ Ensuring adequate power supply ¢ Using negative rake angle * Keeping the overhang of the tool holder to minimum ¢ Using a large nose radius ¢ Taking a deeper cut with a light feed e Avoiding coolants with aluminum oxide based ceramics e Reviewing machining sequences while converting to ceramics and if possible introducing chamfers or reduce feed rate at entryTool Wear And Tool Life A tool gets worn out due to long term usage. There are two major types of wear found in tools: 1- Crater wear 2- Flank wear Rake face Crater wear Flank face Workpiece Flank wearCutting tools are subjected to extremely sever cutting conditions: - Metal to metal contact - Very high stress - Very high temperature - Virgin metal - Very high temperature gradients - Very high stress gradients TOOL LIFE e Tool life represented the useful life of the tool e The tool life can be specified by any of the Following measurable quantities: 1-Actual cutting time to failure 2-Length of work cut to failure 3- Volume of metal removed to failure 4-Number of components produced 5-Cutting speed for a given time to failureTool Failure Criteria ¢ Chipping or fine crack at the cutting edge © Wear land size ¢ Crater depth or width ¢ A combination of the above two © Volume or weight of material worn off the tool * Total destruction of the tool Based on Consequence of A Worn Tool * Limiting value of surface finish ¢ Limiting value of change in component Size Fixed increase in the cutting force or power required to perform a cut.Tool Life Equation Taylor equation based on his experimental work VT"'=C Where: V = Cutting Speed m/min T = Tool Life in Minutes Cand n = Constant This formula was extended by a number of researchers VT md =¢ Constants for extended tool life equation Tool Work Exponent for Constant marerial material a 1SO Grade Aisl__| Toollife.n | Feed, n, | Depth of cut, ny POl,P!I0. | 1020 | 038 0.06 0.10 1150 P20, P30 1020 0.38 -0.17 0.11 780 POI, P10 10s | ~0. 0.21 0.11 350 P20, P30 1045 | 0.22 0.34 0.12 226Example:1 In a tool wear test with a high speed steel cutting tool. The following values of tool life were obtained: : Tool Life Cutting Speed : min Meter / min Pp SCT CtOC“‘(SN”CSC#S@d;S Calculate the values of n and C of Taylor’s equation Solution VT"=C log V + n*log T = log C when: T=30 and V =25 log25 +n log30 = log C 1.3979 +n*1.477= log C (equation-1) when: T=1.5 and V=70 log70 +n log1.5 = log C 1.8451 +n*0.176= log C (equation-2)Equation-1 = Equation-2 1.3979 +n*1.477 =1.8451 +n*0.176 n=0.34472 Substitute in equation-1 1.3979 +0.344*1.477 = log C log C =1.9059 C= 80.50 vT°*- 80.50Example:2 A carbide cutting tool lasted for (2) hours while machining mild steel work material at 45 meter / min. a-Compute the tool life if a similar tool is used for machining mild steel at 20% higher speed. b-Also, what will be the value of cutting speed if the tool required to machine for (3) hours without failing. (Assume that n=0.27) Solution VT"=C log V + n log T= log C log 45 + 0.27 log 120 = log C 1.6532 + 0.27*2.0791= log C log C = 2.215 C=163.89 V 1°77 =163.89 #a-When speed increases by 20% V =1.2*45 = 54 meter/min log 54 +0.27 log T = log C log 54 +0.27 log T = log 163.89 1.7324 + 0.27 log T= 2.215 0.27 log T = 0.4826 log T =1.7874 T= 61 minutes b-When T =3 hours = 180 minutes log V + 0.27 log 180 = log C log V + 0.27 * 2.255 = 2.215 log V = 1.606 V = 40.27 meter/ min V = 40 meter/ minExample:3 In a laboratory test on turning operation, the following data have been recorded at a depth of cut of 2mm: A tool life equation is to deduced by computing the values of n1, n2, n3 in the relationship: v7 d= Where C= 2.22 Solution: Tool life equation: VT" f™ d™=C100*120"*0.1"*2™ =C Equation -1 130*50"*0.1"*2"=C Equation-2 100*70"*0.1"*2"=C Equation -3 Equation 1 = Equation 2 100*120"*0.1"*2" = 130*50"*0.1""*2"" Then: 100*120"=130*50" log 100 + n log 120= log 130 +n log 50 # n=0.3 Equation 2 = Equation 3 #n1=0.4 Substitute in Equation-1 # n2=-6.236Machinability ¢ Machinability is the characteristic of the work material expressing its ease of machining. © Hard work material are difficult to machine e Hardness alone would not be able to specify the machinability It depends on the other characteristics such as tool materials used, process parameters. ,.., .... Surface Finish The actual surface finish obtained depends on the factors such as: The cutting process parameters, speed , feed, and depth of cut. © The geometry of the cutting tool Application of cutting fluid © Work and tool material characteristics © Rigidity of the machine tool and consequent vibrationMACHINE DESIGN SRF- x= s a8 28 oe o< es <8 ° § 02 68- id yS1y Jo stuswnnsu, Buunsoay - saojins Buu09q Busjoy . sayp Buyin 10) #990)005 = eINOgIe ‘tajpuids vIoW ; KoeinD20 YBIy jo T92B}:0F BuNIUED, soysund Buijs 10) sa90}295 - yiaa; 1998 pus spoaiy! ma:>s pUNDID 19> Buyany2 US teinyxy Jo sa20}4N5 BUVIU9D, = tepuyk> 2ynasphy jo sa20}:n5 wousiul - Buyoaq Buipys papool-Airoay paads-yBiy oan pause) yum se20}105 BuIpNS + sasojint 6u0ag (,.u2/dy ¢ 04 da) ainstoxd wnipaw (294/41 ¢ o} dn) paods wnipey ‘sa29}ins Buss09g aunssaid moj paads my -uouow anyoja1 noyim s230pin5 Bussua> oyounaDy ‘Aoein330 (20u02 19 Buyjoas Ov “YoHou anio{91 Ou Yim sarojins Bujow jowioN 9908 0 01 pajag t929):9§ » Suipuns hq paysuy 9q oF tas9pIng = Buwysou juanbasgns 10) winjop $9 LAPD). s8I5}ing Guipun6 voys s9yio Buwrypaw sayusy Sussieras saz0pi9g - s22a}:06 Bunow-uoyy puoy a4) Aq payanas 2 01 ing suawesinbos lasedi ou yim sa0ojng - sousieadde a3u yum 593 suonosyddy jarehy een suaquinny ss2uyBnoy requits yes 2304395 PIOAccuracies achievable in machining operations Machining operation Accuracy Turning +25 um Shaping, Slotting +25 jum/side Planing + 65 um/side Milling £12025 wm Drilling in drill press Location +250 tm Hole + 125 um Jig hole +50 um Drilling in lathe Location +12 um Hole + 2.5 um Boring 42.5 wm Internal grinding +2.5 um Reaming + 25 jum Reaming with jig + 12.5 um Jig boring Hole 42.5 um Location +5 um Cylindrical and surface grinding 42.5 um ‘Thread cutting products +50 pm Broaching + 12.5 pm Lapping +5 um Honing + Super finishing + Achievable surface finishes Roughness (R.M.S.) microns Operations 25 [12.5|625| 32 | 16 0.8 | 04 0.20] 0.10 | 0.05 |o.025| Flame cutting, Sawing Hand grinding |_ Filing, Disc grinding Turning, Shaping, Milling Boring Drilling Surface grinding Cylindrical grinding Honing, Lapping Polishing ‘Super finishing [_ButtingCutting fluid Why?? ¢ To reduce the friction between the tool and the work-piece and chips ¢ Absorb heat generated ¢ Wash way chips Results?? e Reduce power consumption ¢ Improve the surface finish ¢ Increase the tool lifeSpecifications ¢ It heat absorbed © Good lubricant ° Stability ¢ Neutral © Odorless ¢ Harmless to scale e Harmless to bearing © Non corrosive * Low viscosity to separate © Low priced Types of cutting fluids ¢ Water ¢ Soluble oil ¢ Straight oils ¢ Mixed oils * Chemical additive oils Solid (wax) ¢ Stream of compressed air