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Metal Forming (Extrusion # (Types of extrusion (Tube Extrusion…

- - - - Hollow Ram
    - - Fixed Mandrel
        
        Hot piercing (oxide at surface, dirty layer)
        
        concentricity lost if diameter of billet < container
      - Retractable mandrel
        
        for soft billets
        
        piercing in situ, no issue of alignment
        
        Chop off the solid region at beginning
        
        doesn't buckle because it's supported
        
        "Seamless tubes"
    - - Forward
        
        Thin walled tubes eg: toothpaste
      - Backward
        
        Severe tests of ductility!
    - - Soft, easily weldable materials
        
        Split into four streams, them make them merge
    - - 2 barrel shaped rolls
      - Singular Advantage :explode: diameter of tube can be larger than billet
  - - - Temperature
      - Ram Speed \( \dot{\epsilon} \)
      - Type of extrusion (Forward, Backward)
    - - Cu based alloys
        
        Graphite suspension in mineral oil/grease
        
        MolyKoat
      - SS, Fe alloys, Ni SA's
        
        Phosphating (generic term) (Zn)
        
        Tenacious coating to carry lubricant
        
        Can have additional lubricant in the holes
        
        Excellent finish
        
        Cu/Fe Phosphate/Oxalate/Sulphate
      - Hot extrusion
        
        Glass is lubricant!
        
        Ugine-sejourmet process! but glass coating!
        
        Glass needs to be machined off
  - - - Vertical
        
        Self Aligning :check:
        
        Uniformity of temperature :check:
        
        Basement/Headroom needed :red_cross:
        
        Small extrusion rations :red_cross:
      - Horizontal
        
        Heavy Duty :check:
        
        No homogeneity in temp :red_cross:
        
        Thin walled not possible
        
        Needs floor space
  - - - A ring formed due to oxides coming in (after 75%)
      - Scalping operation by using a diameter of ram smaller than that of container
    - - Break symmetry by tilting or shifting ram
    - - V shaped pattern
      - Lot of flow at periphery, less at centre
- - - - Cold Working
      - Warm Working
      - Hot Working
    - - Sheet Metal Forming
      - Rod Drawing
      - Billet/Bloom mill
    - - Simple
      - Compound
    - - Tension
      - Shear
      - Torsion
      - Compression
      - Type of Stress
        
        Squeezing # #
        
        Only compressive loads
        
        Large Deformations (depending on strength of tools) #
        
        Cross section and shape changes
        
        Primary operation! Quick reduction of diameter!
        
        Forging; Extrusion; Rolling :star:
        
        Drawing #
        
        At least one tensile load
        
        Extent of deformation low
        
        Compression to Tension ratio (C/T) :warning:
        
        If high (4-7), Shape change & CS change
        
        Wire Drawing :star:
        
        If low, Shape change only
        
        Sheet Metal Working :star:
        
        Bending #
        
        Stress/Strain Gradients
        
        Moments applied
        
        Shape change only
        
        Fracture occurs before necking
        
        Cutting
        
        Separation into parts
        
        One or limited no. of strokes
        
        Shearing operation #
        
        Incremental
        
        Fracture Important! :red_flag:
        
        More ductile, bad!
        
        Ductility proportional to chip size
  - - - Compressive Loading
      - Slenderness Ratio (L/D) :warning:
        
        Instantaneous! :red_cross:
        
        Rough limit = 2.5 (unsupported)
      - Rubber Sleeve - "supports"
    - - Tensile Loading
      - Superposing hydrostatic pressure may even make drawing squeezing!
    - - Triaxial Stress State
      - Lower strain hardening better!
      - Hot working helps! :check: #
  - - - Strength :check:: (strain hardening)
      - (Strength/Weight) :check::
      - Grain Size :arrow_down:
        
        Strength, Toughness :check:
        
        Fatigue :check:
        
        Creep :red_cross:
    - - Fatigue :check:
      - Wear resistance :check:
    - - Chemical Inhomogeneity
        
        Inclusions/P and S stringers
        
        Cannot be removed
        
        Primary Banding
      - Physical Inhomogeneity
        
        Secondary Banding
        
        Heat Treatment
        
        Can be removed
      - Elimination Methods
        
        Vacuum Arc Remelting for heavy inclusions
        
        Vacuum Induction Melting for lighter inclusions
        
        Electro-slag refining
        
        Modify Shape (CeS)
- - - - Iso-stress process
      - Softening Processes # #
        
        Dynamic Recovery (DRV) :star2:
        
        Dynamic Recystallisation (DRX) :star2:
      - Delta T Adiabatic :warning: #
        
        Function of strain rate (:arrow_up:)
      - Anisotropy in final product (fibering/banding)
      - No net work hardening
    - - Small Loads, Large Deformations
      - Casting defects closed
      - Cast microstructure broken down
      - Chemical Inhomogeneity (:arrow_down: ; diffusion)
    - - Surface Reactions
        
        S pickup :arrow_right: Hot Shortness :red_cross:
      - Oxidation
        
        Additional Steps! Due to scaling
        
        Rolled in/forged in oxides
      - Reactive Metals
        
        Expensive!
      - Decarburisation increases
      - Non uniform structure
        
        Surface fine grained
        
        Interior coarse grained
      - Large dimensional tolerances
    - - Upper Limit
        
        Melting point of metal
        
        Grain Growth
        
        Oxidation
        
        Hot Shortness
        
        Burning (oxides between grains)
      - Lower Limit
        
        DRX and DRV needed
        
        Purity :arrow_up: Lower limit :arrow_up:
        
        Degree of working :arrow_up: Lower Limit :arrow_down:
    - - At given P, as T :arrow_up:, def :arrow_up:
      - At given T, as P :arrow_up:, def :arrow_up:
      - As strain rate :arrow_up:, Preheat temp :arrow_down:
    - - Forging
      - Rolling
      - Extrusion
      - Hot Swaging/Hot Spinning
  - - - Work Hardening takes place
        
        Softening mechanisms absent/minor
      - Region I preferred for CW-A cycles
        
        Region II has drastic changes in properties
        
        Region III has partial softening
      - Cold work - Anneal (CW-A) cycles required
        
        Final product properties can be regulated
      - Grain Fragmentation
        
        Grain size :arrow_down:
        
        Hall Petch
    - - Desired Strength Possible #
      - Smaller Tolerance! opposite
      - Surface Finish possible
        
        Mirror finish with light lubricants
        
        Matte finish with viscous lubricants
        
        No scaling/Oxidation opposite
      - Residual Stresses controlled
        
        Bad if surface worked less! :warning: (tensile)
        
        Great if surface worked more! :star2:
      - Easy inspection and testing
      - High temperature furnace not needed
    - - High loads necessary
        
        Heavy duty equipment
      - High quality tools
      - Needs annealing and stress relieving
      - Material purity needed
    - - Cottrell atomosphere moves faster
      - Dislocations also move with it
      - Catch-break; catch-break
    - - Forging
      - Extrusion
      - Rolling
      - Drawing
      - Sheet Metal Working
  - - - Product Oriented
      - Formability Required
      - Product precision
      - Lubricant effectiveness
    - - Over HW #
        
        Less oxidation, scaling, surface reaction
        
        Better dimensional control
        
        Heating costs reduced
        
        Better uniformity
      - Over CW #
        
        Less power required
        
        Tool costs reduced
        
        Greater formability (No need of CW-A)