Mi 231 manufacturing technology – i 1-15
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Mi 231 manufacturing technology – i 1-15 Mi 231 manufacturing technology – i 1-15 Document Transcript

  • Manufacturing Technology – I Manufacturing Technology – I MI 231 MI 231 Relative Weightage of Marks Class Work Sessional (CWS): 15% Practical Sessional (PRS): 15% Instructor – Dr. Akshay Dvivedi Mid Term Examination (MTE): 30% End Term Examination (ETE): 40% Objective: To impart knowledge about the process principles, equipment, and applications of different Autumn 2011-2012 forming processes, machining operations, and grinding processes. COURSE CONTENT COURSE CONTENT S. Contents Contact No Hours S. Contents Contact 1 Introduction: Classification of different manufacturing 2 No Hours processes, application areas and limitations, selection of a 4 Grinding: Operations and applications of surface, cylindrical 4 manufacturing process. and centreless grinding processes, dressing, truing and balancing of grinding wheels, grading and selection of grinding 2 Press Working of Sheet Metal: Types of presses, drives and 11 wheels. feed mechanisms; Operations: Shearing, bending, spinning, embossing, blanking, coining and deep drawing; Die materials, Total 28 stock layout, compound and progressive dies and punches, construction details of die set, auxiliary equipment, safety devices. 3 Machine Tools and Operations: Classification of machining 11 processes and machine tools, cutting tool materials, different types of cutting tools, nomenclature of single point and multi point cutting tools, concept of cutting speed, feed and depth of cut, use of coolants, constructional details including accessories and attachment, operations, setting and tooling for capstan and turret lathes, drilling, boring and broaching machines, milling operations. Suggested Books Different Components…Different Aspects Simple SmallS. No. Name of Authors /Books /Publisher Year of Pub. 1. DeGarmo, E. P., Black, J.T., and Kohser, R.A., “Materials and 1997 Processes in Manufacturing”, Prentice-Hall of India 23 feet, 6 tonnes , 2. Kalpakjian, S., and Schmid, S.R., “Manufacturing Engineering 2000 99.72% iron, and Technology”, Pearson Education No rust since 5th 3. Groover, M.P., “Fundamentals of Modern Manufacturing”, John 2002 century AD Wiley & Sons Big Complex 4. Lindberg, R.A., “Processes and Materials of Manufacture”, 1990 Prentice-Hall of India 5. Rao, P.N., “Manufacturing Technology”, (Vol. 2), Tata 1998 Iron pillar McGraw-Hill 1
  • Manufacturing – Need and concept Manufacturing – Need and concept• Manufacturing - Value addition processes by which raw Production Engineering covers two domains: materials (low utility and value due to inadequate material – Production or Manufacturing Processes properties and poor or irregular size, shape and finish) are – Production Management converted into valued products (high utility due to definite • Manufacturing Processes - science and technology of dimensions and finish manufacturing products effectively, efficiently, economically imparting functional ability. and environment-friendly through: – Application of any existing manufacturing process and system – Proper selection of input materials, tools, machines and environments. – Improvement of the existing materials and processes – Development of new materials, systems, processes and Value addition by manufacturing. techniques Manufacturing – Need and concept Manufacturing – Need and conceptProduction Engineering covers two domains: – Production or Manufacturing Processes – Production Management• Production Management - planning, coordination and control of the entire manufacturing in most profitable way with maximum satisfaction to the customers by best utilization of the man, machine, materials and money. Goal in manufacturing requires fulfillment of one or more of the following objectives: – Reduction of manufacturing time – Increase of productivity – Reduction of manufacturing cost – Increase in profit or profit rate Manufacturing – Need and concept Manufacturing – Need and concept A manufacturing process normally consists of a series of basic processes, which constitute the structure of the material flow. • Basic processes can be divided into three typical phases: – Phase 1 (material into a suitable state/geometry like heating, melting,Material flow is of three main types: sawing etc.)• Through flow, corresponding to mass-conserving processes – Phase 2 (desired geometry and/or change in properties) (change in material properties without change in geometry) – Phase 3 (component into the specified end state (solidification, cooling, deburring etc.)• Diverging flow, corresponding to mass-reducing processes• Converging flow, corresponding to assembly or joining processes 2
  • Engineering Manufacturing Processes Engineering Manufacturing Processes(a) Shaping or forming Manufacturing a solid product of (d) Regenerative manufacturing definite size and shape from a given material taken in • Production of solid products in layer by layer from raw materials in different form: three possible states: – Liquid – e.g., stereo lithography – Solid state – e.g., forging rolling, extrusion, drawing etc. – Powder – e.g., selective sintering – Liquid or semi-liquid state – e.g., casting, injection molding – Sheet – e.g., LOM (laminated object manufacturing) etc. – Wire – e.g., FDM. (Fused Deposition Modeling) – Powder form – e.g., powder metallurgical process.(b) Joining process – Welding, brazing, soldering etc.(c) Removal process – Machining (Traditional or Non-traditional), Grinding etc. Engineering Manufacturing Processes Engineering Manufacturing Processes N Engineering Manufacturing ProcessesFactors affecting the selection of manufacturing processes• Cost (material, manufacturing, operating and replacement cost)• Material (specified by design)• Quantity (determines economics of manufacturing process)• Machine or equipment availability (Machines and operators)• Quality (Surface finish, Accuracy (geometrical, dimensional)• Geometry (Cylindrical, conical, threads – Lathe) (Plane surface, slots – shaping, planning, milling) (Complex Shapes – Casting, Forging) 3
  • 4
  • Secondary Metal Shaping Selecting materials for manufacturing • Mechanical properties of materials – Strength, toughness, ductility, hardness, elasticity, fatigues, creep, … • Physical properties of materials – density, specific heat, thermal expansion and conductivity, melting point, and electrical and magnetic properties, …… • Chemical properties, environmental resistance and wear – corrosion, toxicity, flammability, …… • Strength : ability to bear load before fracture Material-Based Selection of Manufacturing • Toughness: resistance to both elastic and plastic deformation Processes • Ductility: extent of permanent or plastic deformation that a material undergoes before fracture (% elongation, % reduction Forming Deforming Removing Joining Modifying in area • Hardness: resistance to plastic deformation which includes Metals XX XX XX XX XX indentation, scratching, or marking Materials • Elasticity: ability to restore to original shape and size after Ceramics XX -- X -- -- removal of external deforming loads • Fatigue : permanent deformation and/or failure of a component Polymers XX X X X -- when subjected to fluctuating (both in magnitude and direction) loads Composites XX -- X X -- • Creep : permanent deformation and/or failure of a component XX - Widely Used when subjected to high stresses at high temperature X - Seldom Used • Stiffness: resistance to elastic deformation -- - Not Used . • Fracture : splitting of a component into atleast two halvesApplication Range of Manufacturing Processes According to Melting Temperature of the Material and Batch Size [G. Chryssolouris, 1991] 5
  • Classification of Deformation Processes• Deformation processes have been designed to exploit the • Bulk deforming processes can be classified as primary or secondary processes plasticity of engineering materials – Primary processes reduce a cast material into slabs, plates,• Plasticity is the ability of a material to flow as a solid without and billets deterioration of properties – Secondary processes reduce shapes into finished or semi finished products• Deformation processes require a large amount of force • Bulk deformation processes are those processes where the• Processes include bulk flow, simple shearing, or compound thickness or cross sections are reduced • Sheet-forming operations involve the deformation of materials bending whose thickness and cross section remain relatively constant Bulk Deformation ProcessesClassification of States of Stress • Rolling • Forging • Extrusion • Wire, rod, and tube drawing • Piercing • Squeezing processes Sheet-forming Operations Classification of Presses• Sheet - thickness < 5 mm• Sheet metal processes involve plane stress loadings and lower • Primary tool for sheet metal working is some form of press forces than bulk forming and successful manufacture depends on using right kind of• Almost all sheet metal forming is considered to be secondary equipment processing Stress Induced Operations – Capacity required Shearing Shearing, Blanking, Piercing, – Type of power (manual, mechanical, or hydraulic) or drive Trimming, Shaving, Notching, Nibbling – Number of slides or drives Tension Stretch-Forming – Type of frame Compression Ironing, Coining, Sizing, Hobbing – Speed of operation Tension and Drawing, Spinning, Bending, Compression Embossing, Forming 6
  • Classification of Presses – Drive Mechanism • Very light work - manually operated presses (foot operated or kick presses) • Heavier work – mechanical drives • Fast motion and positive control of displacement • Limited flexibility (length of stroke is set by design of drive) • Force varies with position • Preferred for operations like cutting, up to 10 cm drawing (maximum pressure near bottom of stroke) • Capacity – 9000 metric tons Press drive mechanisms Classification of Presses – Drive Mechanism Classification of Presses – Drive Mechanism • Mechanical drives types: • Mechanical drives types: – Crank-driven – Toggle mechnism • Simple • Drawing • Piercing, blanking, drawing – Screw-type drives • Double crank (multiple action dies) • Mechanical action resembling drop hammer – Eccentric or cam drives • Used for smaller ram stroke • Dwell at bottom of stroke • Deep drawing – Knuckle-joint drives • High mechanical advantage alongwith fast action • Coining Classification of Presses – Drive Mechanism Classification of Presses – Drive Mechanism• Hydraulic presses • Hydraulic presses – Reproducibility of position will have greater variation than a – Motion as a result of piston movement mechanical press – Stroke can be programmed (2.5 m) – Capacity - exceeding 50,000 metric tons – Preferred for operations – Accurate controlled on forces and pressure • requiring a steady pressure throughout a substantial stroke (deep drawing) – Availability of full pressure throughout the stroke • requiring wide variation in stroke length – Speeds can be programmed to either vary or remain constant • requiring high or widely variable forces. – Slower than mechanical presses in general (exception – 600 strokes per minute for high speed blanking) 7
  • Classification of Presses – Frame • Considerations – capacity, accessibility and stiffness – limitations on size and type of work that can be accommodated – Work loading and unloading – Press setup time e.g., time required for changing dies • Arch-frame – Screw-drives for coining – Seldom used • Gap-frame (C shaped) – Versatile – Good accesability from three directions – Permit large workpieces – 1 metric ton to 300 metric tons Classification of Presses – Frame Classification of Presses – Frame• Inclinable press • Straight-sided press – Tilted – Accesibility from front and rear (from sides as well) – Ejection can be assited by gravity or compressed air jet• Open-back presses – Opening in back – Easy ejection of products/scraps Inclinable gap-frame press• Turret press – Multiple holes/slots with varying shaps/size – Upper and lower turret (muliple punches and dies)• Horn press – Cylindrical shaft (horn) in place of bed – Curved workpieces – Seaming, punching, riveting A 200-ton straight-sided press. Horn press Sheet Metalworking Sheet and Plate Metal Products 1. Cutting Operations • Sheet and plate metal parts for consumer and 2. Bending Operations industrial products such as 3. Drawing – Automobiles and trucks – Airplanes 4. Other Sheet Metal Forming Operations – Railway cars and locomotives – Farm and construction equipment – Small and large appliances – Office furniture – Computers and office equipment 8
  • Advantages of Sheet Metal Parts Sheet Metalworking Terminology• High strength • Punch-and-die - tooling to perform cutting, bending, and• Good dimensional accuracy drawing• Good surface finish • Stamping press - machine tool that performs most sheet metal operations• Relatively low cost • Stampings - sheet metal products• Economical mass production for large quantities Basic Types of Sheet Metal Processes Shearing, Blanking, and Punching1. Cutting – Shearing (simple shearing) to separate large sheets Principal operations in pressworking that cut sheet metal: – Blanking to cut part perimeters out of sheet metal • Shearing – Punching/ Piercing to make holes in sheet metal • Blanking – Slitting • Punching2. Bending • Piercing – Straining sheet around a straight axis3. Drawing – Forming of sheet into convex or concave shapes Shearing Shearing• Shearing is a process for cutting sheet metal to size out of a • Fracture and tearing begin at the weakest point and proceed larger stock such as roll stock. progressively or intermittently to the next-weakest location – Results in a rough and ragged edge• Shears are used as the preliminary step in preparing stock for • Punch and die must have proper alignment and clearance stamping processes, or smaller blanks for CNC presses • Sheared edges can be produced that require no further finishing• The shearing process produces a shear edge burr, which can be minimized to less than 10% of the material thickness. The burr is a function of clearance between the punch and the die, and the sharpness of the punch and the die. 9
  • Sheet Metal Cutting - Shearing Sheet Metal Cutting - Shearing Shearing of sheet metal between two cutting edges:Shearing of sheet metal between two cutting edges: (3) punch compresses and penetrates into work causing a smooth cut surface;(1) just before the punch contacts work; (4) fracture is initiated at the opposing cutting edges which(2) punch begins to push into work, causing plastic deformation; separates the sheet. Smooth shearing a rod by putting it into compression during shearing Conventionally sheared surface Slitting - Power shear for 6.5 mm steel Fineblanked surface Shearing Shearing (Press Operations) Sheet metal cutting operation along a straight line between two cutting edges • Typically used to cut large sheets Shearing operation: (a) side view of the shearing operation; (b) front view of power shears equipped with inclined upper cutting blade. 10
  • Blanking and Punching Shearing• Shearing (simple/square) Blanking - sheet metal cutting to separate piece (called a blank) from surrounding stock – Both cutting blades are straight Punching - similar to blanking except cut piece is scrap, called a• Curved blades to produce different shapes slug – Blanking – Punching – Piercing – Notching – Trimming Blanking Punching Blanking and Punching Punching Blanking - sheet metal cutting to separate piece (called a blank) from surrounding stock • Punching is a metal fabricating process that removes a scrap Punching - similar to blanking except cut piece is scrap, called a slug from the metal workpiece each time a punch enters the slug punching die. This process leaves a hole in the metal workpiece Characteristics: • Ability to produce holes in both strip and sheet metal during medium or high production processes. • The ability to produce holes of varying shapes - quickly Punching Punching • The punching process forces a steel punch, made of hardened steel, into and through a workpiece. • The punch diameter determines the size of the hole created in the workpiece • Punching is often the cheapest method for creating holes in sheet metal in medium to high production. 11
  • Punching and Piercing Piercing & blanking -Tools and Dies• A slug (the material punched out) is produced in punching operations but not in piercing work • Basic components of a piercing and blanking die• Piercing is “forming a hole in sheet metal with a pointed punch set are: punch, die, and with no metal fallout (slug).” stripper plate• In this case, a significant burr or deformed sharp edge is created • Punches are normally made on the bottom side of the material being pierced. from low-distortion or air- hardenable tool steel so that they can be hardened after machining PIERCE PUNCHES Piercing & blanking -Tools and Dies Piercing & blanking -Tools and Dies• Theoretically, punch should fit in die with a uniform • Punch tilted slightly to clearance approaches zero (practically- 5-7% of stock reduce cutting force (shear thickness) angle)• Uniform clearance should be maintained around the entire • Shear angle – reduces force periphery – increases stroke length• Theoretically, punch should not enter die, but should stop as its base aligns with top surface of die (practically- punch enters slightly in die) Piercing & blanking -Tools and Dies Piercing & blanking -Tools and Dies• Subpress dies (modular tooling) – assembled and combined on •Dies bed of press to pierce or blank large parts – single piece – component sections (that can be assembled) •simplifies production •simplifies replacement •flexibility of design changes •standard die components 12
  • Piercing & blanking -Tools and Dies Piercing & blanking -Tools and Dies Progressive die sets • First operationParts requiring multiple cutting type operation – strip stock is fed in first die,• Progressive die sets- two or more sets of punches and dies where a hole is pierced and mounted in line (one behind another, all facing in the same ram descends direction) • Second Operation• Transfer dies move individual parts from operation to – ram retracts and strip operation within a single press advances, the pilot on• Compound dies combine processes sequentially during a blanking punch aligns with single stroke of the ram pierced hole Progressive piercing and blanking die for making a – further descent of punch square washer blanks the completed washer-pieces – At same time, first punch pierces the hole for next washer Piercing & blanking -Tools and Dies Piercing & blanking -Tools and DiesProgressive die sets Progressive die sets • Used for multiple combinations of piercing, blanking, forming, drawing etc. • Quick and accurate position of work material • Simple construction • Economical to maintain and repair • Require final cut-off operationEleven station progressive die stages Piercing & blanking -Tools and Dies Piercing & blanking -Tools and Dies Compound die setsTransfer die sets • Piercing and blanking (or other combinations) occur• Part handling must operate in harmony with press motions sequentially during a single stroke of ram to move, orient and position the pieces as they travel through the die Part is blanked and subsequently pierced in the same stroke The blanking punch contains the die for piercing. 13
  • Piercing & blanking -Tools and Dies Nibbling Compound die sets • Contour is progressively cut by producing a series of overlapping notches (removing the material in small • More complex increments) • More breakage • Simple tools for complex shapes • More expensive • Nibbling is used when the contour is long and a separate • Precise alignment punch is impractical and uneconomical • Edge smoothness – determined by shape of tooling and degree of overlap in successive cuts Lancing Trimming • Metal cutting operation in which the metal is sliced or slit to • Removal or Trimming of the Flash free up metal without separating it from the original sheet. • Does not create a slug • Save material and eliminate the need for scrap removal • Done in progressive dies Shaving Notching • Cutting a specified small portion of material towards the edge• Finishing operation of the material stock• Removal of the burrs left on product during the blanking or punching/piercing operation• Greater dimensional accuracy• Close tolerance work 14
  • Cutoff Dinking• Separate a stamping or other product from a • Used to blank shapes from low strength strip or stock materials (rubber, fiber, cloth etc.)• Produces the periphery counter to the (Hammer or mechanical press workpiece acts on shank) Design for Piercing and Blanking Bending• Design rules • Bending is the plastic deformation of metals about a linear axis with – Diameters of pierced holes should not be less than the little or no change in the surface thickness of the metal (minimum 0.3 mm) area • Forming- multiple bends are made – Minimum distance between holes or the edge of the stock with a single die should be at least equal to the metal thickness • Spring-back is the “unbending” that occurs after a metal has been – The width of any projection or slot should be at least 1 deformed times the metal thickness (never less than 2.5 mm) – Keep tolerances as large as possible Bending BendingBend Allowance is length of neutral axis in bend Lb = α (R + kT)Where,α is bend angle (rad),T is sheet thickness,R is bend radius,k is constant (from (0.33 for R<2T) to 0.5 (for R>2T))Ideal case k = 0.5 (a) bending (b) rolling (c) Bending 90o 15
  • Bending Bending Minimum Bend Radius - the ratio at which a crack appears on outer surface of bend Expressed in terms of thickness (2T, 3T, 4T etc.) R = T(50/(r-1)) Where, R is bend radius, T is sheet thickness, r is tensile reduction of area of sheet metal 50% tensile reduction of area can be bent over itself R/T Ratio versus % Area Reduction Angle Bending (Bar Folder and Press Brake) BendingBending Force• Simple bending of a rectangular beam • Bar folders make angle bends up to 150 degrees under 1.5 mm• Bending force is function of : sheet metal – strength of material • Press brakes make bends in heavier sheets or more complex – length of bend (L) bends in thin material – thickness of sheet (T) – size of die opening (W)• Maximum bending force is P = kYLT2 / WWhere, T is sheet thickness, R is bend radius,k is 0.3 – 1.3, Y is yield stress Press Brake• Heavier sheet and/or complex bends Press Brake• Mechanical/Hydraulic with narrow/long bed and short strokes• Optional operations - Seaming, embossing, punching etc.• 7 m long sheets• Die material Roll Bead Formed – hardwood (low strength materials) – Carbon steels, gray-iron (a) Bead forming with a single die (b) Bead forming with two dies, in a press brake 16
  • BendingSpringback • Springback Ri/ Rf = 4(RiY/ET)3 - 3(RiY/ET) + 1 Q. A 5 mm sheet is bent to a radius of 10 mm. Calculate theWhere, Y is yield stress, E is elastic modulus radius of part after it is bent• Spring back increases with decrease of E and increase of R/T (Yield stress = 205 MPa, E = 190 Gpa) and Y Ri / Rf = 4(RiY/ET)3 - 3(RiY/ET) + 1 (overbend or springback allowance) RiY / Et = (10 x 205 * 106) / (190 x 109 x 5) = 0.00216 Ri / Rf = 4 (0.00216)3 – 3 (0.00216) +1 = .993 Bending BendingSpringback Springback• Remove the bent piece at stage (b) – positive spring back• Upon unloading at stage (d) – negative spring back (inwardly) because it is being unbent from stage c• The amount of this inward (negative) spring back can be greater than the amount of positive spring back Design for Bending BendingSpringback • Several factors are important in specifying a bending operation – Determine the smallest bend radius (R/T = (50/(r-1))) that can be formed without cracking the metal – Metal ductility (reduction in area in uniaxial tensile test) – Thickness of material Relationship between the minimum bend radius (relative to thickness) and the ductility 17
  • Considerations for Bending Considerations for Bending• If the punch radius is large and the bend angle is shallow, large amounts of spring back are often encountered • The minimum inner radius should be at least 1 material thickness• The sharper the bend, the more likely the surfaces will be • Minimum flange width should be at least 4 times the stock stressed beyond the yield point thickness plus the bending radius (damage to tooling or operator)• Parts with multiple bends should be designed with most of them at same bend radius (less setup time and tooling cost)• Bends should be made with the bend axis perpendicular to the rolling direction (fracture in hard material) • Tolerance should not be less than 0.8mm Considerations for Bending Air-Bend, Bottoming, and Coining Dies • Forming Near Holes – When a bend is made too close to a hole, the hole may become deformed (teardrop) • Bottoming dies contact and – For a hole < 1" in diameter the minimum distance "D" = 2T + R compress the full area – For a slot or hole > 1" diameter then the minimum distance "D" = within the tooling 2.5T + R – Angle of the bend is set by the geometry of the tooling • Air bend dies produce the desired geometry by simple three-point bending • If bottoming dies go beyond Air-bend (left) and bottoming (right) the full-contact position, the press brake dies operation is similar to A. Teardrop B. hole < 1” C. hole > 1” coining Roll Forming Roll Forming • Progressive bending• Roll forming is a process of metal strips as it by which a metal strip is passes through series progressively bent as it of forming rolls passes through a series of (80m.min) forming rolls• Only bending takes place • Any material that can during this process, and be bent can be rolled all bends are parallel to one another• A wide variety of shapes can be produced, but changeover, setup, and adjustment may take several hours Eight-roll sequence for the roll forming of a box channel 18
  • Roll Bending Draw Bending, Compression Bending, and Press Bending • Roll bending is a continuous form of three-point bending – Plates, sheets, beams, pipes – Lower rolls – driven – Upper roll – controls degree of curvature Forming Rolls (a) Draw bending, in which the form block rotates (b) moving tool compresses the workpiece against a stationary form (c) press bending, where the press ram moves the bending form. Tube Bending Tube Bending • Wet Sand • Flexible mandrels • Pressure bulging • Key parameters: outer diameter of the tube, wall thickness, and radius of the bend Production of fittings for plumbing (expanding tubular blanks) Seaming and Flanging Straightening • Opposite of bending• Seaming is a bending operation that can be used to join the • Done before subsequent forming to ensure the use of flat or ends of sheet metal in some form of mechanical interlock straight material• Common products include cans, pails, drums, and containers • Various methods to straighten material• Flanges can be rolled on sheet metal in a similar manner as – Roll straightening (Roller levering) seams – Stretcher leveling- material is mechanically gripped and stretch until it reaches the desired flatness Various types of seams used on sheet metal. Method of straightening rod or sheet by passing it through a set of straightening rolls 19
  • Drawing and Stretching Processes Deep Drawing and Shallow Drawing • Deep drawing is typically used to form solid-bottom• Drawing refers to the family of operations cylindrical or rectangular where plastic flow occurs over a curved axis containers from sheet metal and the flat sheet is formed into a three- • Shallow drawing - depth is dimensional part less than diameter Deep Drawing and Shallow Drawing• Key variables: – Blank and punch diameter – Punch and die radius – Clearance – Thickness of the blank – Lubrication – Hold-down pressure Limitations of Deep Drawing Limitations of Deep Drawing• Typical limits to drawing operations • Shallow Drawing – little change in circumference and small – Wrinkling (movement of blank into die cavity induce area is confined by blankholder compressive stresses in flange) • Deep Drawing – more change in circumference – Tearing (walls elongates and tend to thin) • More wrinkle and tear -Thin material – Earing (Edges of cups may become wavy) 20
  • Deep Drawing Deep Drawing• Deep Drawability (LDR) • Earing is caused by planer anisotropy of sheet (ΔR) – LDR = Do/Dp • ΔR = (R0 -2R45+R90)/2 – Where, Do – max. blank diameter, Dp – is punch diameter • at ΔR = 0, no ears are formed• Ability of a sheet metal for sucessful drawing operation is defined by normal anisotropy (R) R = Width strain / Thickness strain Cold rolled sheets have anisotropy in planer direction Rave = (R0+ 2R45+ R90)/4 Where angles are relative to rolling direction Limitations of Deep Drawing Limitations of Deep Drawing • Different techniques can be used to overcome these limitations • Forward redraw - material undergoes reverse bending as it – Simple shapes – Multiple operations flows into the die – Complex shapes - Draw beads • Reverse redrawing – starting cup is placed over a tubular die – Vertical projections and matching grooves in the die and and punch acts to turn it inside out] blankholder • Trimming may be used to reach final dimensions Ironing Draw beads • Process that thins the walls of a drawn cylinder by passing it between a punch and a die • Control flow of blank in die cavity • Die and Punch Set Used is Similar to that of Drawing Operation Except that the Clearance Between the Die and Punch is Smaller than that Used in the Drawing Operation. • The Material Gets Compressed Between Punch and Die which Reduces the Thickness and Increases the Height. • The Wall Thicknesses can be Reduced to as Much as 50% in a Single Ironing Operation. 21
  • Embossing • Press working process in which raised lettering or other designs are impressed in sheet material • Drawing and bending of the material • Die set consists of a die and punch with the desired contours, so that when the punch and die meet, the clearance between them is same as that of the sheet thickness • Providing dimples on sheets to increase their rigidity • Decorative sheet work used for panels Spinning Spinning• Produces rotationally symmetrical shapes – Spheres, hemispheres, cylinders, bells, and parabolas • After Proper Clamping, the Blank is Rotated to its Operating• Sheet metal is rotated and shaped over a male form and Speed. gradually moving force is applied (blank takes shape of form) • Spinning Speed Depends on the Blank Material, Thickness• Setup – Centre lathe and Complexity of the Desired Cup. – Head stock – hard wood form block (desired shape) • Then the Hard Wood or Roller Type Metallic Tool is Pressed – Tail stock – Blank ( freely rotating, hard wood or metal) and Moved Gradually on the Blank so that it Conforms to the Shape of the Form Block. • Spinning is Comparable to Drawing for Making Cylindrical Parts. Spinning Spinning Types• Spinnability – – as the ability of a metal to undergo shear spinning 1. Conventional spinning deformation without exceeding its tensile strength and – Conical and curvilinear shapes tearing – Related to tensile reduction of area – Normally at room temperature 22
  • Spinning Types Spinning Types2. Shear Spinning 3. Tube Spinning• Part diameter is maintained where as thickness is reduced • Thickness is reduced by spinning them on cylindrical mandrel• Considerable forces using rollers• Considerable heat • Reduction depends on tensile reduction of area of the material• Requires cooling • Both external or internal• Tooling – tool steels • Both forward or backward• No wastage of material• Balancing required COINING Tool and Die Materials• Closed–die forging operation (the flow of the material occurs only at the • High strength, impact toughness, wear resistance at room and top layers and not in the elevated temperatures entire volume)• Coining die consists of the punch and die which are engraved with the necessary details required on both sides of the final object.• The blank is compressed by the die with a very high pressure (5 to 6 times strength of material) is applied due to which very fine details are obtained on the surface. Tool and Die Materials Safety devices • Barrier guards• Shearing – Prevent operators exposure to nip points and pinch points – Cold D2, A2, A9, S2, S5, S7 – Fixed, adjustable or self-adjusting – Hot H11, H12, H13 – Mechanical, electric, hydraulic, and optical interlocks are• Press Working Zn alloys, 4140 steel, CI, Comp., A2, D2, O1 provided untill barrier guards are in place• Deep Drawing W1, O1, Ci, A2, D2• Coining W1, O1, A2, D2, D3, D4, H11, H12, H13 1. Spring-type interlock shuts off power to machine when guard door is opened 2. Guard can only be removed by removing the Plug Source : Triodyne , Inc. 23
  • Safety devices Safety devices• Dead-man Control: power is automatically • Maintenance – Zero mechanical state shut off in the event of operator passes out or • Locking out • Personal protective equipment ( goggles, face shields, ear dies – e.g. belt strap in elevated cranes plugs, helmets, gloves, aprons etc.)• Presence setting devices Machining Machining • Machining – A subtractive process used to get desired shape, size, and finish by removing surplus material in the form of chips by a cutting tool and by providing suitable relative motion between the workpiece and cutting tool – Process of finishing by which jobs are produced to the desired dimensions and surface finish by gradually removing the excess material from the preformed blank in the form of chips with the help of cutting tool (s) moved past the work surface (s). Machining Processes Using SINGLE-Point Using MULTI-Point Using ABRASIVES• Machining requirements Cutting Tools Cutting Tools as Cutting Tools  Turning  Milling  Grinding  Step Turning  Drilling  Honing  Taper Turning  Reaming  Lapping  Form Turning  Knurling  Polishing  Contour Turing  Sawing  Buffing  Facing  Necking  Parting-Off  Boring Unconventional Machining  Counter-Boring Processes  Counter-Sinking AJM, USM, WJM  Shaping ECM, ECG  Planing CHM IBM, PAM, EDM, LBM, PAM 24
  • Machine tool • A machine tool is a non-portable power operated and reasonably valued device or system of devices in which energy is expended to produce jobs of desired size, shape and surface finish by removing excess material from the preformed blanks in the form of chips with the help of cutting tools moved past the work surface (s) • Physical functions of a Machine Tool in machining are: – firmly holding the blank and the tool – transmit motions to the tool and the blank – provide power to the tool-work pair for the machining action – control of the machining parameters, i.e., speed, feed and depth of cut Basic Machine Tools Basic Machine Tools Centre lathes Centre lathes – Cylindrical shapes – Manual lathes or CNC External Internal Basic Machine Tools Basic Machine ToolsShaping machine Shaping machine• Ram: it holds and imparts cutting motion to the tool through • Power drive with speed and feed change mechanisms reciprocation • Shaping machines are generally used for producing flat surfaces,• Bed: it holds and imparts feed motions to the job (blank) grooving, splitting etc.• Housing with base: the basic structure and also accommodate the drive mechanisms 25
  • Basic Machine Tools Basic Machine Tools Drilling machinePlaning machine • Drilling (originating or enlarging cylindrical holes)• In planing the job reciprocates for cutting motion and the tool • Boring, counter boring, counter sinking etc. moves slowly for the feed motions unlike in shaping machine. • Cutting internal threads in parts like nuts using suitable• Planing machines are usually very large in size and used for attachment large jobs and heavy duty work. Basic Machine Tools Basic Machine Tools Milling machineDrilling machine • Flat surfaces• Column with base: it is the basic structure to hold the other • Slotting parts • Slitting • Grooving• Drilling head: this box type structure accommodates the power • Parting drive and the speed and feed gear boxes • Forming• Spindle: holds the drill and transmits rotation and axial translation to the tool for providing cutting motion and feed motion – both to the drillD• Pillar drill, column drill, radial drill, micro-drill etc. Classification of Machine Tools Classification of Machine Tools1. Direction of major axis 4. Degree of automation – horizontal center lathe, horizontal boring machine etc. – Manual – e.g. lathes, drilling machines etc. – vertical – vertical lathe, vertical axis milling machine etc. – Semi-automatic – e.g. turret lathe – inclined – special – Automatic – e.g., CNC Drill, CNC Mill, CNC lathe etc.2. Purpose of use 5. Type of automation – general purpose – e.g. lathes, milling, drilling machines etc. – fixed automation – e.g., single spindle and multispindle – single purpose – e.g. facing lathe, roll turning lathe etc. lathes – special purpose – for mass production – flexible automation – e.g., Machining Centers3. Number of spindles 6. Precision – single spindle – center lathes, milling machines etc. – Ordinary – multi-spindle – gang drilling machines etc. – High precision 26
  • Classification of Machine Tools Cutting Tool • Removes excess material through direct mechanical contact7. Size • Tool moves along the workpiece at a certain velocity (cutting speed – V) – Heavy duty – e.g., heavy duty lathes (e.g. ≥ 55 kW), boring and a depth of cut (to) to produce a chip just ahead of tool by shearing the mills, etc. material continuously along the shear plane – Medium duty – e.g., lathes (e.g. – 3.7 ~ 11 kW), column drilling machines etc. Tool material Selection depends on: – Small duty – e.g., table top lathes, drilling machines, • Work material (hardness, chemical and metallurgical state) milling machines. • Part features (geometry, accuracy, finish, surface-integrity) – Micro duty – e.g., micro-drilling machine etc. • Machine tool characteristics (rigidity, horsepower, speed, feed , precision) • Support system (Operator, sensors, controls, method of chip removal,6. Configuration lubrication, maintenance) – Stand alone type – most of the conventional machine tools. – Machining system – e.g., machining center, FMS etc. Cutting Tool Cutting Tool • Tool Material Characteristics – Hardness – Toughness – Wear Resistance – Chemical Inertness – Resistance to bulk deformation – Thermal Properties – High Stiffness – Geometry – Finish Tool Selection (material, geometry, cutting conditions) Toughness—resistance to breakage and chipping Cutting Tool Cutting Tool Hardness of cutting materials Wear resistance—resistance to abrasion and erosion Hardness—resistance to deforming and flattening 27
  • Cutting Tool Cutting Tool Cast-cobalt alloys (1915) Cutting Tool Cutting Tool • Tool steels • HSS • Coated HSS • Cast Cobalt Alloys • Carbides / Sintered Carbides • Coated Carbides • Ceramics • Cermets • Diamonds • Polycrystalline CBN’s – and many more………….. Cutting Tool Cutting ToolTool steels Tool steels• Carbon and low-/medium-alloy steels • With increase in carbon content, steel become lesser ductile• Steel is considered to be carbon steel: and melting point decrease – when no minimum content is specified or required for Cr, • Hardness loss at 200 0C Co, molybdenum, Ni, Ti, W, V or zirconium etc. • Mo and Cr increases hardenability – when the specified minimum for copper does not exceed • Mo and W improves wear resistance 0.40 percent; – when the maximum content specified is less than Mn - 1.65, • Applications Si - 0.60, Copper - 0.60. – Drills, Taps, Dies etc. – steel which is not stainless steel – Low speeds• 0.9 to 1.3% carbon• With increase in carbon content, steel become harder and stronger 28
  • Cutting Tool Cutting ToolHSS TiN coated HSS• Good wear resistance, hardenability and hot hardness • Film thickness 0.00254 - 0.00508 mm• Good toughness and resistance to fracture • 10-20% higher cutting speeds than HSS• Good cutting at 400 0C • Gear cutters, drills, bandsaw, circular saw blades, form tools,• Easy fabrication inserts etc.• Types • Reduced tool wear – Molybdenum (M series) • High hardness • 10% Mo with Cr, V, W, Cr and Co • PVD • High abrasion resistance than t series • Less Distortion than T series • Cheaper than T series – Tungsten (T series) • 12-18% W, Cr, V and Co (18-4-1 W-Cr-V)• Used for complex tool geometries Cutting Tool Cutting ToolCast Cobalt Alloys Carbide or Sintered Carbides• Cobalt rich, chromium-tungsten-carbon cast alloys • Types:• Stellite tools (Deloro Stellite Company) – Tungsten carbide (WC bonded together in a cobalt matrix) • 1-5 µm WC particles are combined with cobalt in a mixer, then presses and• Non-magnetic and corrosion-resistant cobalt alloy sintered into the desired insert shapes.• W or Mo and a small amount of carbon • Cemented carbides Sintered Carbides• Retain hardness to much greater temperatures • With increase of Co – toughness increases but there is decrease in strength, hardness and wear resistance• 25 % higher cutting speeds than HSS • Machining steels, CI, nonferrous and nonmetals• Cast to shape – Titanium Carbide (TiC in Ni-Mo alloy matrix)• Used only for single point tools or saw blades • Higher wear resistance than WC • Lesser toughness than WC • Machining hard materials like steels, CI • Higher speeds than WC • Finishing and semifinishing ferrous alloys • Auto industry using Ni-Mo binder Cutting Tool Cutting ToolInserts• Individual cutting tools with several cutting points Inserts are clamped on tool shank with various locking• Sq inserts (8 cutting edges), triangular insert (6 cutting edges) mechanisms • (a) Clamping • (b) Wing lock pins • (c) Thread-less lock pins - secured with side • (d) Brazed on a tool shank 29
  • Cutting Tool Cutting ToolChip Breaker• Continuous chips are undesirable as they are a potential safety hazard Chip Breaker (a) tightly curled chip• Cutting at low speed may lead to welding of chips to tool face (b) chip hits workpiece and breaks• Ideal chip – Shape of letter “C” or number “9” and fits within 25 mm (c) continuous chip moving away from workpiece square block (d) chip hits tool shank and breaks off• Procedure used for breaking chips intermittently is with use of chip breaker Cutting Tool Cutting ToolChip Breaker Chip Breaker• Controlling chip flow • Chip breaking in softer materials like Al include machining at• Eliminating long chips small increments and then pausing.• Reducing vibration and heat • In shaping, milling or other such intermittent operations chip breakers are not required Cutting Tool Cutting Tool• American National Standards Institute (ANSI) – C-1 to C-8• ISO Standards – P, M and K ISO Classification of Carbide Cutting Tools According to Use Classification of Tungsten Carbides 30
  • Cutting Tool Cutting ToolCoated Carbide tools Coated Carbide tools• Coating increase tool life by 200-300 times • Single or multiple• Coating increase 50-100% in speed of the same tool life • Multiple coating provide stronger metallurgical bond between coating and substrate• 80-90 % of carbide tools are coated • For multiple coating:• Bulk tool material can be tough, shock resistant carbide that can withstand – Innermost layer should bond high temperature plastic deformation and resist breakage with substrate• Thin chemically stable, hard refractory coating of TiC, TiN, TiCN or – Outermost layer should resist Al2O3, Diamond, TiAlN, CrC, ZrN etc. wear – Intermediate layer should• Fine grained coatings bond well and be compatible• Free form binders and porosity with both layers• Low coeff. of friction for coating – non adherence of chips on rake face Cutting Tool Cutting Tool Ceramics (White or cold-presses ceramics) • 1950 • Pure Aluminium oxide, Al2O3, or SiC • Pressed into insert shapes under high pressure • TiC and ZrO may be added to improve toughness and resistance to thermal shock Cutting Tool Cutting ToolCeramics Cermets (Ceramics + Metal)• Particulates or whiskers • Black or hot-pressed ceramics• 2 to 3 times cutting speed than WC • Mix of 70% aluminium oxide and 30% TiC• High hardness and chemical inertness • Intermediate performance between ceramics and carbides• Hard and brittle – require rigid tool holders and machine tools• Less tendency to adhere to metals during machining – good SF• Used for high speed cutting/finishing of super-alloys and high strength steels• Not suitable for Al, Ti as they react with alumina based ceramics 31
  • Cutting Tool Cutting ToolPolycrystalline CBN Polycrystalline CBN• High hardness (Knoop 4700 at 20 oC 4000 at 1000 oC)• Low chemical reactivity• 0.5-1 mm layer of PCBN is bonded to a carbide substrate by sintering under pressure.• Carbide provides toughness – CBN provides high wear PCBN Tips resistance and cutting edge strength• Used for automotive industry Difficult-to-machine materials• Used for aerospace materials• Higher cost than ceramics tools or cemented carbides but tool life is 5-7 times that of a ceramic tool Solid PCBN Cutting Tool Tool GeometryDiamond• High Wear resistance, low tool-chip friction, sharp cutting edges• Used for fine surface finish and dimensional accuracy• Brittle - Light and uninterrupted finishing cuts• High speed machining and fine feeds• Single-crystal diamond tool – machining optical mirrors• Polishing is not required after machining• Polycrystalline diamond tools (compacts or industrial diamonds) – small synthetic crystals, fused by high pressure and temperature to a thickness of .5-1 mm and bonded to a carbide substrate 32