Machining Operations and Machine Tools PDF

INE 302 Manufacturing Processes for Industrial Engineers Lecture 3: Mach...

INE 302 Manufacturing Processes for Industrial Engineers Lecture 3: Machining Operations and Machine Tools ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Material Removal Processes  A family of shaping operations, the common feature of which is removal of material from a starting work part so the remaining part has the desired geometry  Machining – material removal by a sharp cutting tool, e.g., turning, milling, drilling  Abrasive processes – material removal by hard, abrasive particles, e.g., grinding  Nontraditional processes - various energy forms other than sharp cutting tool to remove material ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Machining Cutting action involves shear deformation of work material to form a chip, and as chip is removed, a new surface is exposed: (a) positive and (b) negative rake tools ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Machining Operations  Most important machining operations:  Turning  Drilling  Milling  Other machining operations:  Shaping and planing  Broaching  Sawing ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Cutting Tool Classification 1. Single-Point Tools  One dominant cutting edge  Point is usually rounded to form a nose radius  Turning uses single point tools 2. Multiple-Cutting-Edge Tools  More than one cutting edge  Motion relative to work achieved by rotating  Drilling and milling use rotating multiple-cutting- edge tools (a) Single‑point tool showing rake face, flank, and tool point; and (b) a helical milling cutter, representative of tools with multiple cutting edges ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Three Modes of Tool Failure 1. Fracture failure  Cutting force becomes excessive and/or dynamic, leading to brittle fracture 2. Temperature failure  Cutting temperature is too high for the tool material 3. Gradual wear  Gradual wearing of the cutting tool occurs at two locations  Crater wear – occurs on top rake face  Flank wear – occurs on flank (side of tool) ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Tool Wear vs. Time Tool wear (flank wear) as a function of cutting time ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Effect of Cutting Speed Effect of cutting speed on tool flank wear (FW) for three cutting speeds, using tool life criterion of 0.5 mm flank wear ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Taylor Tool Life Equation vTn = C where v = cutting speed; T = tool life; and n and C are parameters that depend on feed, depth of cut, work material, tool material, and tool life criterion  n is the slope of the plot  C is the intercept on the speed axis at one minute tool life  Relationship credited to Frederick W. Taylor ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Example  Turning tests using cemented carbide tooling resulted in a 1‑min tool life at a cutting speed = 5.0 m/s and a 30‑min tool life at a speed = 2.0 m/s. (a) Find the n and C values in the Taylor tool life equation. (b) Project how long the tool would last at a speed of 1.0 m/s. ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Example  Turning tests using cemented carbide tooling resulted in a 1‑min tool life at a cutting speed = 5.0 m/s and a 30‑min tool life at a speed = 2.0 m/s. (a) Find the n and C values in the Taylor tool life equation. (b) Project how long the tool would last at a speed of 1.0 m/s. Solution: (a) For data (1) T = 1.0 min, then C = 5.0 m/s = 300 m/min For data (2) v = 2 m/s = 120 m/min 120(30)n = 300 30n = 300/120 = 2.5 n ln 30 = ln 2.5 3.4012 n = 0.9163 n = 0.269 The tool life equation is vT0.269 = 300 (b) At v = 1.0 m/s = 60 m/min 60(T)0.269 = 300 (T)0.269 = 300/60 = 4.8 T = (5.0)1/0.269 = (5.0)3.712 = 393 min ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Tool Materials  Tool failure modes identify the important properties that a tool material should possess  Toughness ‑ to avoid fracture failure  Hot hardness ‑ ability to retain hardness at high temperatures  Wear resistance ‑ hardness is the most important property to resist abrasive wear ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Cutting Fluids  Any liquid or gas applied directly to the machining operation to improve cutting performance  Two main problems addressed by cutting fluids: 1. Heat generation at shear and friction zones 2. Friction at tool‑chip and tool‑work interfaces ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Cutting Fluids  Other functions and benefits:  Wash away chips (e.g., grinding and milling)  Reduce temperature of work part for easier handling  Improve dimensional stability of work part ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Dry Machining  No cutting fluid is used  Avoids problems of cutting fluid contamination, disposal, and filtration  Problems with dry machining:  Overheating of tool  Operating at lower cutting speeds and production rates to prolong tool life  Absence of chip removal benefits of cutting fluids in grinding and milling ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Roughing vs. Finishing Cuts  In production, several roughing cuts are usually taken on a part, followed by one or two finishing cuts  Roughing - removes large amounts of material from starting work part  Some material remains for finish cutting  High feeds and depths, low speeds  Finishing - completes part geometry  Final dimensions, tolerances, and finish  Low feeds and depths, high cutting speeds ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Machine Tool  A power‑driven machine that performs a machining operation, including grinding  Functions in machining:  Holds work part  Positions tool relative to work  Provides power at speed, feed, and depth that have been set  The term also applies to machines that perform metal forming operations ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Four Basic Types of Chip in Machining 1. Discontinuous chip 2. Continuous chip 3. Continuous chip with Built-up Edge (BUE) 4. Serrated chip ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Discontinuous Chip  Brittle work materials  Low cutting speeds  Large feed and depth of cut  High tool‑chip friction ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Continuous Chip  Ductile work materials  High cutting speeds  Small feeds and depths  Sharp cutting edge  Low tool‑chip friction ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Continuous with BUE  Ductile materials  Low‑to‑medium cutting speeds  Tool-chip friction causes portions of chip to adhere to rake face  BUE forms, then breaks off, cyclically ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Serrated Chip  Semicontinuous - saw- tooth appearance  Cyclical chip forms with alternating high shear strain then low shear strain  Associated with difficult- to-machine metals at high cutting speeds ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Power and Energy Relationships  A machining operation requires power  The power to perform machining can be computed from: Pc = Fc v where Pc = cutting power; Fc = cutting force; and v = cutting speed  In U.S. customary units, power is traditionally expressed as horsepower (dividing ft‑lb/min by 33,000) Fc v HPc  33,000 where HPc = cutting horsepower, hp ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Power and Energy Relationships  Gross power to operate the machine tool Pg or HPg is given by Pc HPc Pg  or HPg  E E where E = mechanical efficiency of machine tool  Typical E for machine tools  90%  Unit power, Pu or unit horsepower, HPu Pc or HP = HPc PU = u RMR RMR  Useful to convert power into power per unit volume rate of metal cut where RMR = material removal rate ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Specific Energy in Machining  Unit power is also known as the specific energy U Pc Fc v U = Pu = = RMR vtow where Units for specific energy are typically N‑m/mm3 or J/mm3 (in‑lb/in3) ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Example  In a turning operation on stainless steel, cutting speed = 150 m/min, feed = 0.25 mm/rev, and depth of cut = 6.0 mm. How much power will the lathe draw in performing this operation if its mechanical efficiency = 90%. ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Example  In a turning operation on stainless steel, cutting speed = 150 m/min, feed = 0.25 mm/rev, and depth of cut = 6.0 mm. How much power will the lathe draw in performing this operation if its mechanical efficiency = 90%.  Solution: From Table 17.2, U = 2.8 N-m/mm3 = 2.8 J/mm3  RMR = vfd = (150 m/min)(103 mm/m)(0.25 mm)(6 mm) = 225,000 mm3/min = 3750 mm3/s  Pc = (3750 mm3/s)(2.8 J/mm3) = 10,500 J/s = 10,500 W = 10.5 kW  Accounting for mechanical efficiency, Pg = 10.5/0.90 = 11.67 kW ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Cutting Temperature  Approximately 98% of the energy in machining is converted into heat  This can cause temperatures to be very high at the tool‑chip  The remaining energy (about 2%) is retained as elastic energy in the chip  High cutting temperatures result in the following:  Reduce tool life  Produce hot chips that pose safety hazards to the machine operator  Can cause inaccuracies in part dimensions due to thermal expansion of work material ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Cutting Temperature  Experimental methods can be used to measure temperatures in machining  Most frequently used technique is the tool‑chip thermocouple  Using this method, Ken Trigger determined the speed‑temperature relationship to be of the form: T = K vm where T = measured tool‑chip interface temperature, and v = cutting speed ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Classification of Machined Parts Rotational - (a) cylindrical or disk‑like shape Nonrotational - (b) block‑like and plate‑like ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Turning  Single point cutting tool removes material from a rotating workpiece to generate a cylindrical shape  Performed on a machine tool called a lathe  Variations of turning performed on a lathe  Facing  Contour turning  Chamfering  Cutoff  Threading ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Turning Operation ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Operations Related to Turning (a) Facing, (b) taper turning, (c) contour turning ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  More Operations Related to Turning (d) Form turning, (e) chamfering, (f) cutoff ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  More Operations Related to Turning (g) Threading, (h) boring, (i) drilling ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Engine Lathe Diagram of an engine lathe showing its principal components and motions ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Methods of Holding Workpiece in a Lathe (a) Holding the work between centers, (b) chuck, (c) collet, and (d) face plate ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e Summary of Turning Parameters and Formulas 38  Example  The 104-mm-diameter of a cylindrical aluminum workpiece is to be reduced to 100 mm in a turning operation, using a cutting speed of 5.0 m/s and feed of 0.40 mm/rev. The workpiece is 400 mm long. Determine the (a) time to complete the cut and (b) metal removal rate during the cut. ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Example  The 104-mm-diameter of a cylindrical aluminum workpiece is to be reduced to 100 mm in a turning operation, using a cutting speed of 5.0 m/s and feed of 0.40 mm/rev. The workpiece is 400 mm long. Determine the (a) time to complete the cut and (b) metal removal rate during the cut. Solution: (a) N = v/(πD) = (5.0 m/s)/0.104 = 15.303 rev/s fr = 15.303(0.4) = 6.121 mm/s Tm = L/fr = 400/6.121 = 65.35 s (b) Depth d = (104 – 100)/2 = 2.0 mm Rmr = 5.0(10)3(0.4)(2.0) = 4000 mm3/s ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Boring  Difference between boring and turning:  Boring is performed on the inside diameter of an existing hole  Turning is performed on the outside diameter of an existing cylinder  In effect, boring is an internal turning operation  Boring machines  Horizontal or vertical - refers to the orientation of the axis of rotation of machine spindle ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Vertical Boring Mill Applications: Large, heavy work parts that have low L/D ratio ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Drilling Creates a round hole in a work part  Compare to boring which can only enlarge an existing hole  Cutting tool called a drill or drill bit  Machine tool: drill press ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Through Hole vs. Blind Hole (a) Through hole - drill exits opposite side of work and (b) blind hole – drill does not exit opposite side ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Operations Related to Drilling (a) Reaming, (b) tapping, (c) counterboring ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  More Operations Related to Drilling (d) Countersinking, (e) center drilling, (f) spot facing ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Drill Press Upright drill press stands on the floor  Bench drill is similar but smaller and mounted on a table or bench ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Cutting Conditions in Drilling  Cutting speed v= DN Where D = Drill diameter, N represents spindle rev/min.  Feed Rate Fr= N f Where f is the feed.  The machining time in drilling Tm = d/Fr where d is the hole depth.  The rate of metal removal Rmr = D2Fr/4 48  Example  A gun-drilling operation is used to drill a 3.5-mm-diameter hole. It takes 3.5 min to perform the operation using high-pressure fluid delivery of coolant to the drill point. The current spindle speed = 3500 rev/min, and feed = 0.05 mm/rev. In order to improve surface finish in the hole, it has been decided to increase the speed by 20% and decrease the feed by 25%. How long will it take to perform the operation at the new cutting conditions? ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Example  A gun-drilling operation is used to drill a 3.5-mm-diameter hole. It takes 3.5 min to perform the operation using high-pressure fluid delivery of coolant to the drill point. The current spindle speed = 3500 rev/min, and feed = 0.05 mm/rev. In order to improve surface finish in the hole, it has been decided to increase the speed by 20% and decrease the feed by 25%. How long will it take to perform the operation at the new cutting conditions? Solution: fr = Nf = 3500 rev/min (0.05 mm/rev) = 175 mm/min Hole depth d = 3.5 min(175 mm/min) = 612.5 mm New speed v = 3500(1 + 0.20) = 4200 rev/min New feed f = 0.05(1  0.25) = 0.0375 mm/min New feed rate fr = 4200(0.0375) = 157.5 mm/min New drilling time Tm = (612.5 mm)/(157.5 mm/min) = 3.89 min ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Milling  Machining operation in which work is fed past a rotating tool with multiple cutting edges  Axis of tool rotation is perpendicular to feed direction  Cutting tool called a milling cutter  Cutting edges called teeth  Machine tool called a milling machine  Interrupted cutting operation  Basic milling operation creates a planar surface  Other geometries possible ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Two Forms of Milling (a) Peripheral milling and (b) face milling ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Peripheral Milling vs. Face Milling  Peripheral milling  Cutter axis parallel to surface being machined  Cutting edges on outside periphery of cutter  Face milling  Cutter axis perpendicular to surface being milled  Cutting edges on both the end and outside periphery of the cutter ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Types of Peripheral Milling (a) Slab milling, (b) slotting, (c) side milling, (e) straddle milling, and (e) form milling ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Types of Face Milling (a) Conventional face milling, (b) partial face milling, and (c) end milling ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Types of Face Milling (d) Profile milling, (e) pocket milling, and (f) surface contouring ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Knee-And-Column Milling Machines (a) Horizontal and (b) vertical knee-and-column milling machines ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e Summary of Milling Parameters and Formulas  Example  Peripheral milling is performed on the top surface of a rectangular work part that is 400 mm long by 50 mm wide. The milling cutter is 70 mm in diameter and has five teeth. It overhangs the width of the part on both sides. Cutting speed = 60 m/min, chip load = 0.25 mm/tooth, and depth of cut = 6.5 mm. Determine (a) machining time of the operation and (b) maximum material removal rate during the cut. ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Example  Peripheral milling is performed on the top surface of a rectangular work part that is 400 mm long by 50 mm wide. The milling cutter is 70 mm in diameter and has five teeth. It overhangs the width of the part on both sides. Cutting speed = 60 m/min, chip load = 0.25 mm/tooth, and depth of cut = 6.5 mm. Determine (a) machining time of the operation and (b) maximum material removal rate during the cut. Solution: (a) N = v/πD = 60(103) mm/70 = 273 rev/min fr = Nntf = 273(5)(0.25) = 341 mm/min A = (d(D-d))0.5 = (6.5(70-6.5))0.5 = 20.3 mm Tm = (400 + 20.3)/341 = 1.23 min (b) RMR = wdfr = 50(6.5)(341) = 110,825 mm3/min ©2013 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 5/e  Shaping and Planing  A straight, flat surface is created in both operations  Interrupted cutting operation  Subjects tool to impact loading when entering work  Typical tooling: single-point high-speed-steel tools  Low cutting speeds due to start‑and‑stop motion Similar operations, both use a single point cutting tool moved linearly relative to the work part ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Broaching  A multiple tooth cutting tool is moved linearly relative to work in direction of tool axis  Advantages:  Good surface finish  Close tolerances  Variety of work shapes possible  Cutting tool called a broach  Owing to complicated and usually custom‑shaped geometry, tooling is expensive ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  Sawing  Cuts narrow slit in work by a tool consisting of a series of narrowly spaced teeth  Tool called a saw blade  Typical functions:  Separate a work part into two pieces  Cut off unwanted portions of part  Cut outline of flat part (a) Power hacksaw, (b) band saw (vertical), and (c) circular saw ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e  High Speed Machining (HSM)  Cutting at speeds significantly higher than those used in conventional machining operations  Persistent trend throughout history of machining is higher and higher cutting speeds  Interest in HSM is due to potential for faster production rates, shorter lead times, and reduced costs ©2016 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 6e