Mechanical Engineers Data Handbook Episode 9 ppsx

190 MECHANICAL ENGINEER’S DATA HANDBOOK 1.6.6 Characteristics of steel tools Carboo steels (for softer metals and wood; poor perfomace above 250°C) Composition Plain carbon steel, O.Z%Mn, water hardening 0.7-0.8%c 0.9%c Carbon steel + vanadium 0.8-1 .O%C, 0.2%Mn, 0.2%Va Chrome steel 0.9%C, 0.2%Mn, O.S%Cr High manganese steel OSM.8%C, 0.6-0.8Y0Mn Characteristics Applications High toughness, low hardness Shear blades, chisels, turning mandrels General purpose. Best combination of toughness and hardness High hardness, keen edge, low shock resistance Large taps and reamers Taps, screw dies, twist drills, mills for soft metals, files Water hardening, takes keen edge, more shock resistant than plain carbon steel Screw taps and dies, twist drills, reamers, broaches Water hardening, good abrasion Drawing dies, wood planes, chisels resistance, takes high compression Oil hardening, tougher but less Bending form dies, hammers, tool hard, high shock resistance shanks High-speed steels Composition (%) C W Cr Va Co Mo Characteristics Super ~ - ~- ~~ 0.8 18/22 4.5 1.5 10112 - Highest temperature of HSS. Very hard but not so tough. Most expensive. For materials with tensile strength =- 1225 MPa General purpose 0.75 18 4.15 1.2 - - Tougher than super and cheaper, for materials over 1225 MPa tensile strength than general purpose HSS. High wear resistance General purpose 1.25 7 4.3 2.8 6 5.5 Better impact resistance and cheaper tungsten/molybdenum High vanadium 1.55 12.5 4.75 5.0 5 - Best abrasion resistance. Used for hinhlv abrasive materials HSS, high-speed steels. MANUFACTURING TECHNOLOGY 191 5.6.7 Carbide and ceramic tools Carbides are graded according to series (see table) and by a number from 01 (hardest) to 50 (toughest), e.g. Po1 and K40. Series ~~ Material machined ~~ Carbides P Steel, steel castings M Cast iron, non-ferrous, plastic W with Co binder K Heat resistant steels, stainless steels W with Co binder W, Ta, Tt, Ni with Co binder SI&ered carbide tools - eollrdiriolllil ud poeitive rake Cutting speed (mmin-') Top rake (") Clean Rough scaly Material being cut Rough Fine metal metal Steel: Low-medium carbon Medium-high carbon Nickel chrome Cast iron: 200 Brinell hardness White heart Copper Brass Bronze and gun metal Aluminium alloy Plastics Glass 75 60 30 45-60 3-6 150-240 120-240 120-180 90-150 120-180 9-15 120-210 90-180 75-120 90-120 6-4 240-360 240-360 240-300 180-225 240-300 15-21 8 0-4 4 0-3 0.4 0 3.5-8 0 13-16 0-3.5 0-3.5 13-16 0 3.5 Ceramic tools (sinted ahminiurn oxide witb grain nlslersulbio&r) Material being cut Cutting speed (m min- ') Cast iron Steel Aluminium 60-610 w50 >610 192 MECHANICAL ENGINEER'S DATA HANDBOOK 5.7 General information on metal cutting 5.7. I Cutting speeds and feed rates Material of workpiece Mild steel Cast steel Stainless steel Grey cast iron Aluminium Brass Phosphor bronze Cutting speed (m s- ') High-speed steel 3 .O 27 3.5 90 50 15 72 75 100 18 60 18 36 4.5 13 180 270 120 180 75 33 25 45 180 150 50 - Feed rate (mmrev ') Rough Fine 0.625-2.0 0.1254.75 0.5-1.25 0.1254.50 0.5-1.00 0.075-0.175 0.4-2.5 0.20-1 .00 0.1-0.5 0.0754.25 0.375-2.0 0.20-1.25 0.3754.75 0.125-0.50 R, rough; F, fine; R & T, reaming and threading; D, drilling. 2.7.2 Power used and volume removed in metal cutting Symbols used: P=power (kW) d = depth of cut (mm) f= feed (mm rev I) o=cutting speed (mmin-') T= torque (N-m) D = drill diameter (mm) N = rotational speed (rev. min- ') w = width of cut (mm) f, = milling machine table feed (mm min- l) V= volume of metal removed (cm3 min- ') Material k, kD kM Material k, kD kM Aluminium 700 0.1 1 0.9 Mild steel 1200 0.36 2.7 Brass 1250 0.084 1.6 Tool steel 3000 0.40 7.0 Cast iron 900 0.07 1.9 MANUFACTURING TECHNOLOGY 193 Power kdfv Turning: P=- moo0 Drilling: T= k,fo.75D1.8 2nN T p=- 6ooo0 Milling: P = - kMdwfm 60 Volume of metal removed Turning: V = dfv ZD2j7V Drilling: V=- 4Ooo wdfM Milling: V=- lo00 5.7.3 Surface finish Different processes produce different degrees of finish on machined surfaces. These are graded from N1 with an average height of roughness of 0.025 pm, up to N12 roughness 50pm. The manner in which a machined surface is indicated is shown. a+b+c+. . . L Average height of roughness, h, = -where a, b, c, etc. =area on graph, and L =length of surface. Roughness grade N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 h,(pm) 0.025 0.05 0.1 0.2 0.4 0.8 1.6 3.2 6.3 12.3 25 50 Finishing processes Surface indication Mill Ream Bore Broach Turn Lap Grind Hone, etc. 5.7.4 Merchants circle for tool forces ‘Merchant’s circle’ is a well-known construction for the analysis of cutting forces for a single-point tool. If the cutting and feed forces, the initial and final chip thickness and the tool rake angle are known, then the other forces, friction and shear angles can be found. Known: F, =cutting force F,=feed force t, =initial chip thickness t, =final chip thickness a = tool rake angle The diagram can be drawn to give: F, =shear force F, = resultant force F=friction force on tool face F,, = force normal to shear force F, =force normal to F p =coefficient of friction = F/F, 6 =friction angle = tan - p 4 = shear angle 194 MECHANICAL ENGINEER'S DATA HANDBOOK 5.7.5 Machining properties of thermoplastics Turning D r i 11 in g Milling Rake Clearance Cutting Cutting Cutting angle angle speed Feed speed Feed speed Feed Material ("1 ("1 (ms-') (mmrev ') (ms-') (mmrev ') (ms-') (mms-') Nylon 01-10 20130 2.1-5.0 0.1-0.25 2.0-5.0 0.1-0.38 5 <4 PTFE 01-5 20130 1.0-2.5 0.05-0.25 1.25-5.0 0.1-0.38 5 <4 Polystyrene Of - 5 20130 1.5-5.0 0.05-0.25 0.5-10 0.1-0.38 5 94 Rigid PVC 01-10 20130 1.5-5.0 0.25-0.75 2.5-30 0.05-0.13 5 <4 5.7.6 Negative rake cutting Roughing speed Finishing speed Feeds Material being cut (m min- ') (mmin-I) (mmftoot h) Steel 0.15%c 0.4%c O.8%C Steel castings Phosphor bronze and gun metal Copper Brass Aluminium and allovs 230 160 1 20 90 300 450 600 900 Milling: 0.2-0.4 300 210 135 105 420 Turning: 0.25-0.5 540 900 1200 MANUFACTURING TECHNOLOGY 195 5.7.7 Calculation of machining cost The ‘total-time cost per workpiece’ is made up of ‘machine-time cost’, ‘non-productive-time cost’ and ‘tool cost’. ‘Machining-time cost’ is for actual machin- ing and includes overheads and wages. ‘Non-produc- tive-time cost’ covers ‘setting-up’ and ‘loading- and unloading-time cost’. ‘Tool cost’ combines ‘tool- change-time cost’ and actual ‘tool cost’. The former is the cost of changing the cutting edge, the latter is the cost of the cutting plus resharpening. When ‘total cost’ is plotted against ‘cutting speed’ an optimum speed for minimum cost is found. Let: C, = machining-time cost per workpiece C, = non-productive-time cost per workpiece C, = tool-change-time cost per workpiece C, = tool cost per workpiece 8 2i 1 8 Cutting speed rnirnin - tR c =E “60 c,= t,+J - C,==- ( 3: t tR at. Total cost of machining C,,, = C, + C, + C, + C, (Elworkpiece) ctt + tshtmR C,=- Total tool cost per workpiece C,, = C, + C, l+n, at, Let : t, = machining time per workpiece (min) 5.7.8 Cutting fluids t, =loading and unloading time per workpiece (min) t,=setting time per batch (min) t, = tool life (min) t, = tool change time (min) t,, = tool sharpening time (min) R =cost rate per hour (E) nb = number per batch n, = number of resharpenings It is necessary when machining to use some form of fluid which acts as a coolant and lubricant, resulting in a better finish and longer tool life. The fluid also acts as a rust preventative and assists in swarf removal. The following table lists various fluids and their advan- tages. Group Description Advantages Soluble oil ~ ~~~~~ Oil, emulsifier and 2-10% water Good coolant. Poor lubricant Clear soluble oil As above, with more emulsifier Good coolant. Poor lubricant Water based fluids Solution of sodium nitride and Good coolant. Poor lubricant triethanolamine EP soluble oils Soluble oils with EP additives, e.g. Fairly good lubricant sulphur and/or chlorine 196 MECHANICAL ENGINEER’S DATA HANDBOOK Cutting fluid applications (continued) Group Description Advantages Straight oils Mineral or fatty oils (lard, sperm, Good lubricant. Often unstable. olive, neat’s foot, rape, etc.) alone or compounded Sulphurized EP oils Straight oils with sulphur, zinc oxide or other additives (0.2-0.8%S) Mineral and fatty oil blends with sulphur and chlorine additives Average coolant. Good lubricant. Pressure resistant. Prevents welding More efficient than sulphurized oils. For most arduous conditions. Highly resistant to welding of chip of chip on tool Sulphochlorinated EP oils on tool Chlorinated materials Carbon tetrachloride and Very good EP fluid. Highly trichlorethylene alone or blended with oils dangerous to use Gases and vapours Air, oil mist, CO, Limited cooling power. Chip dispersed EP, extreme pressure. 5.8 Casting Casting is the forming of metal or plastic parts by introducing the liquid material to a suitably shaped cavity (mould), allowing it to solidify, and then removing it from the mould. Further processing is usually required. 5.8.1 Sand casting SAND CASTING In sand casting the mould is made in a ‘moulding box’ produced by inserting previously made ‘cores’ of baked sand. Molten metal is poured into runners until grinding and sandblasting. Practically any metal can be cast. using a special sand and a wooden ‘pattern’. Holes are it appears in risers. The casting is cleaned by chipping, Required casting Runner Risers Moulding box MANUFACTURING TECHNOLOGY 197 INVESTMENT CASTING Turbine biada 5.8.2 Shell moulding This is a form of sand casting done using a very fine sand mixed with synthetic resin. The pattern is made of machined and polished iron. The sand mixture is blown into a box containing the pattern which is heated to produce a hard, thin (6-10mm) mould which is split and removed from the pattern and then glued together. It is a high-speed process, producing highly accurate castings. 5.8.3 Investment artlng (lost wax casting) Wax patterns are made from a permanent metal mould. The wax patterns are coated with ceramic slurry which is hardened and baked so that the wax is melted out. The cavity is filled with molten metal to give a precision casting. Any metal can be cast using this process. Wax panern .ylil ofceramic Fan impeller 198 MECHANICAL ENGINEER’S DATA HANDBOOK 5.0.4 Die casting The mould is of steel in several parts dowelled together. Molten metal is fed by gravity or pressure and, when solid, is ejected by pins. Aluminium, copper, manganese and zinc alloy are suitable for casting by this method. DIE CASTING Ram ,Feed hol Valve body Shafl coupling pml 5.8.5 Centrifugal casting Cylindrical or circular components such as piston rings, cylinder liners, pipes, etc., may be cast in a rotating mould. Centrifugal pressure gives a fine grain casting. Any metal may be cast using this process. CENTRIFUGAL CASTING i Feed 4 w Vertical axis Gear wheel MANUFACTURING TECHNOLOGY 199 5.9 Metal forming processes 5.9. I ‘Forging’ is the forming of metal parts by hammering, pressing, or bending to the required shape, usually at red heat. ‘Hand forging’ involves the use of an anvil and special hammers, chisels and swages. A ‘drop forging machine’ uses pneumatic or hydraulic pressure to compress hot metal blanks between hard steel dies. Hand forlry Md drop hwng Fo@ngwithfiashnmwval [...]... 0.8 1.5 100-127 90 -100 2.5 3.0 75 -90 (C) 'd) -\ / - Leftward Rightward 60-75 4 O 4.8 Rightward 3-4 50-60 6.0 35-40 8.0 I I 208 MECHANICAL ENGINEER'SDATA HANDBOOK Gas welding - edge preparation, speed, and metal thickness (continued) Welding rod diameter (mm) Edge preparation 3-6.5 Speed (mmmin-') Method Metal thickness (mm) Rightward 30-35 22-25 9. 5 12.5 Rightward 19- 22 15-16 10-12 15.0 19. 0 25.0 3E 4... a,=yield stress + + I(: +) Initial length of strip Li = h - t -2r b - r - ) t 204 5 .9. 8 MECHANICAL ENGINEER'SDATA HANDBOOK Rolled sections Rolled sections are made to British Standards BS 4: Part 1 and BS 4848: Part 4 Unequal angles D x B from 40mm x 25mm to 200mm x 150mm Universal beams D x B = 127mm x 76 mm to 91 4 mm x 4 19 mm t and T are of several sizes in each case Universal columns D x E = 152mm x...200 MECHANICALENGINEER’SDATA HANDBOOK Vehicle axle FORGINGS 5 .9. 2 Drawing process This is the forming of flat metal blanks into box and cup-like shapes by pressing them with a shaped punch into a die The process is used for cartridge cases, boxes, electrical fittings, etc First stage Second stage Deep drawing f-\ h Deep-drawn components A 20 1 MANUFACTURING TECHNOLOOY 5 .9. 3 Extrusion Hot... ~ ~ c t i o n s Billet Hot extrusion 5 .9. 4 Impact extrusion A metal which is plastic when cold may be extruded by the impact of a high-velocity punch The metal of the blank flows up the sides of the punch to produce a cylinder The process is used for manufacturing toothpaste tubes, ignition coil cans, etc Impact extrusion 202 5 .9. 5 MECHANICAL ENGINEER'S DATA HANDBOOK Rolling Press work A press is used... 182-21SoC), 60% tin and 40% lead (melting range 182-188°C) and 95 % tin and 5% antimony (melting range 238-243 "C).Solder is available in the This is an alloy of silver, copper and zinc with a melting point of about 700°C used mainly for joining brass and copper It is in strip form and is used with a flux powder 206 5.10.2 MECHANICALENGINEER'SDATA HANDBOOK Soldered joints I Single lap joint v M Gas-alr brazing... acid solution and hot water wash Copper Copper-silver low melting point rods 3.2 mm diameter White powder in paste with water Cleaning is with boiling water and by wire brushing 210 5 I I.5 MECHANICAL ENGINEER’SDATA HANDBOOK Flame cutting Steel plate over 300mm thick can be cut by this method, either manually or by automatic machine using templates for complicated shapes Thin plates may be stacked so... single or double V or U, or single and double bevel or J To avoid distortion, especially with thick plates, an unequal V weld may be used the smaller weld being made first @& Fillet wekls 212 MECHANICAL ENGINEER'S DATA HANDBOOK Resistance welding is used to produce spot welds and stud welding by passing an electric current through the two metal parts via electrodes In seam welding the electrodes are wheels... all the welding processes, together with recommendations for the use of a number of these (50)25(50) Intermittent 8 mm fillet welds, 25mm long, starting with 50mm space and 50mm gaps 2 14 MECHANICAL ENGINEER'S DATA HANDBOOK Recommended welding processes R R S S R R R R S Manual metal arc Submerged arc TIG MIG Flash welding Spot welding Oxyacetylene weldiing Furnace brazing Torch brazing R R S S R R... Uneaual double U Resistance spot welding Single bevel (SBBW) Double bevel (DBBW) Single J (SJBW) r Double J (DJBW) Resistance seam welding 213 MANUFACTURING TECHNOLOGY 5.12.4 Weld symbols weld symbok, (Bs 499 ) 6mm fillet weld on one side of joint 8 mm fillet weld all round on one side U butt weld on one side with sealing run 6mm fillet weld on both sides of joint \ V butt weld on one side 5 4 mm diameter... channel) 203 MANUFACTURING TECHNOLOGY Drawing process Jm Blank diameter D = Required force F = ndta, where: uu= ultimate tensile stress f L F-Cl Distance - D x P Shearing process Shearing force F = - 5 .9. 7 (3) Sheet metal work Allowance for right angle bend Lengths a and b are reduced by an ‘allowance’c, and where: h=the ‘shear’ c =r IF +t -a (r +;) When r=2t (as is often the case), c= 1.037t Allowance . 100-127 Leftward 100-127 90 -100 Leftward 75 -90 Rightward 60-75 Rightward 50-60 35-40 0.8 1.5 2.5 3.0 4 .O 4.8 6.0 8.0 208 MECHANICAL ENGINEER'S DATA HANDBOOK Gas welding. alloy Plastics Glass 75 60 30 45-60 3-6 150-240 120-240 120-180 90 -150 120-180 9- 15 120-210 90 -180 75-120 90 -120 6-4 240-360 240-360 240-300 180-225 240-300 15-21 8 0-4. speed (m min- ') Cast iron Steel Aluminium 60-610 w50 >610 192 MECHANICAL ENGINEER'S DATA HANDBOOK 5.7 General information on metal cutting 5.7. I Cutting speeds