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Polymer-process and Machining Fundamentals, Machining, . (Temperature) -…

- - - - (Movable) Cores of metal
      - Ejector pins
        
        (shrinkage is larger than in metals) to make sure the material can be removed
      - Cooling system for organized solidification
    - - Multi-component
        
        1st: first component injected
        
        Rotates
        
        2nd component is injected
      - Gas-assisted
        
        1: inject component into mold
        
        2: Gas is blown into mold, and makes component hollow
        
        Less material = needed
      - Foam
        
        While liquid lnjected, gas is also injected
        
        1: apply pressure
        
        2: loosen mold --> gas will spread
      - Reaction
        
        2 diff components
        
        1: cure diff components
        
        2: inject into mold
    - - Avoid undercut
        
        use draft angles: instead of 90* make 100* because shrinkage will occur
      - Scars will be visible
      - Uniform wall thickness
        
        Prevent: internal stress, sink marks, cavities, sharp corners
  - - - Heating material with screw
      - Continuous process
        
        no leftovers
      - Die design comparable to metals
      - Extruded plastic will swell after leaving die
    - - Plastic is fed through tube
        
        is clamped together on bottom
        
        Blown into shape
        
        Scar = visible, line on bottom of object
    - - air is blown in pre made part to give shape
        
        plastic bottles: small scar on bottom
        
        Coca cola bottle
  - - - Plug (sort of shape) pressed down on preheated sheet of plastic into mold
    - - Pre Heat sheet, apply outside pressure (by blowing on sheet)
      - Or Apply pressure by making a vacuum that pulls sheet into shape
  - - - Placed in mold
        
        Heated to melt and make material Viscous
        
        Rotated around 2 diff axis (for even division inside mold)
        
        Solidifies and becomes hollow product
    - - Not always uniform (depends on forces from rotational axis)
- - - - alfa + beta + gamma = 90*
        
        Gamma: Rake angle
        
        Alfa: Clearance angle
        
        Beta: Wedge angle
    - - Hear Angle Fi
        
        Smaller angle = higher forces needed to remove chip
  - - - Problem: chip becomes longer and longer --> can intertwine with tool
      - This type depends on material (aluminium has more chance)
    - - Breaks away easier
    - - Creates small particles
        
        Problem: break off makes small shocks that damage tool
- - - - f x n x z
        
        f = feed per tooth, n = number of revolutions, z =
    - - speed of tool at tip (circonfrence)
      - High speed = rough
      - pi x diameter x n
    - - Depends on:
        
        Workpiece Material (soft = less F)
        
        Rake angle
        
        Width of cut (big width = more F)
        
        Thickness of cut
  - - - (Thermal) hardness of tools
      - Friction Forces
    - - Flank wear (Vb(a))
        
        Between flank piece + work piece
      - Crater wear on rake face (Kt(b))
        
        Between chip and rake face
    - - Tool life (T) = Max operational life
  - - - No melt, break or having thermal cracks from heating up
    - - Withstand shocks from serrated chip
    - - Withstand differences in temp
    - - Particles no glue onto tool
        
        Creates rough surface finish
  - - - Better accuracy
    - - Smoother surface
    - - Mineral oils
      - Vegetable oils
    - - Emulsions
      - Aqueous solutions
- - - - Linear CH2's in a row
      - Branched CH2's in a row, with extra branches
        
        Held by Weak VDW forces
        
        Can Deform
        
        easy to work with
    - - Rigid (not flexible) 3D network covalent bonds
    - - Flexible 3D network with small crosslinks (Holds layers together)
  - - - Mobility between molecules
      - Plus low VDW-Forces that keep it together
    - - Heat = Liquification
      - Cool = Solidification
    - - Linear chain:
        
        Low Viscosity (like water)
        
        Crystallization (structured)
        
        Can withstand higher deformation
      - Branched chain:
        
        High Viscosity (Syrop)
        
        More force needed for deformation
        
        Amorphous (Chaotic)
        
        Ductile, soft and less heat resistant
    - - higher temperature, less deformation resistance
      - Less crystalized = more rubbery (once it starts heating up) After Tg (Templerature in solid state)
        
        Rubber state only in plastics
      - After Tm (Melt temp), no matter the crystalization: they all melt and become Viscous liquid
  - - - Cross link structure, 3D network
        
        From Vulcanization
        
        Don't soften with increase temp
    - - Mix 2 components, then they cure
    - - Heated and Shaped, over and over again Reusable
      - Vacuum Thermoforming
      - Cold deformation
      - Blow molding
      - Extrusion/Injection molding
      - Characteristics:
        
        High viscosity
        
        Bad heat conductor
        
        More Shrinkage in solid state than metals
  - - - Cool down time
- - - - Tool is worn out
  - - - n (= Exponent of Taylor): A measure for Temperature sensitivity
        
        n(Cemented Carbide) = 0.15 <--> 0.30
        
        n(Ceramics) = 0.25 <--> 1.00
        
        n(HSS) = 0.08 <--> 0.20
        
        Found In table
- - - - (Ex) HC-P 15
        
        15 = measure for mechanical stress resistance
        
        HC = main group, coated cemented carbide
        
        Workpiecematerial, P = steel
        
        K = Cast iron, non-ferrous
        
        M = Stainless steel