Case Studies: Polymers

Machining of Polymers: Variables Affecting Surface Finish

Material Variables

  • Glass Transition Temperature (Tg)
  • Melt Temperature (Tm)
  • Viscosity
  • Molecular Weight

Machining Variables

  • Cutting Speed (relaxation rate)
  • Cutting Edge Radius
  • Tool Angles (Rake/Clearance)
  • Feedrate
  • Tool surface tribological properties

Representative Temperature Sweep for Thermoplastic Polymers

Representative Temperature Sweep for Thermoplastic Polymers

Rationale Behind Temperature Control (Tg < Room Temperature)

Rationale for temperature controlled cryo machining - Tg below room temperature

Rationale Behind Temperature Control (Tg > Room Temperature)

Rationale for temperature controlled cryo machining - Tg above room temperature

PEEK Machining Demonstration

Objective(s): 

  • To investigate the impact of various cryo gas temperatures on burr formation.
  • To compare surface characteristics of hydroxyapatite filled PEEK when machined dry and cryogenically.

Materials:

  • Unfilled PEEK, hydroxyapatite filled PEEK.

Machining conditions:

  • Tooling and machining standards per publicized guidelines (constant for dry and cryo machined samples).
  • Cooling:

– Compressed air

– Various cryogenic cooling conditions:

+ Liquid nitrogen, Cryo gas at -250°F, -150°F, -100°F and -50°F.

+ Cryo brushing at -250°F.

Analytical information:

  • Light microscopy, SEM, EDS analysis.

Note: Cryo gas temperature measured at End-of-Line (EOL) box prior to nozzle.

 

Dry Machining vs. Cryo-machining Results

Dry machining and cryo machining images

       Dry machining +                                Cryo machining                                Cryo machining + Cryo        compressed air                                  (-250°F cryo gas)                         brushing (-250°F cryo gas)

 

Dry machining and cryo machining examples

Comparison of Surface Profiles (Dry Cutting Vs. ICEFLY)

Burr formation in dry and ICEFLY-machined PEEK samples (slots)

Burr formation in dry and ICEFLY-machined PEEK samples (milled profile)