Other questions

Question 1

Residual stresses in injection molding

Answer 1

• Temperature difference between the inner and outer layers of the part. Non-uniform cooling and the development of residual stresses.
• Non-uniform shrinkage.
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• if the stresses exceed the material’s strength or if they are concentrated in certain regions, they can lead to warpage, distortion, or even cracking of the part over time
• Mitigation: cooling rate and injection pressure, ribs or fillets.

Question 2

Which size of the machine would you select for a selected part? (calculation problems, closing force)

Question 3

Classification of fluids and viscosity diagram

Answer 3

• Newtonian fluid.
• Intrinsical or structural flow (pseudoplastic fluids), orientation of the polymer molecules in the direction of flow with increasing shear stress. Viscosity: describes the internal friction of the material.
• Thermoplastics have a much higher viscosity than thermosets, a lot of pressure is needed to push the polymer to the mold

Question 4

Viscosity diagrams

Answer 4

THERMOSETS: Process time is determined by reaction kinetics. Liquids (like water), then the curing starts and the viscocity increases (solid).
THERMOPLASTICS: Heating / Cooling capacity. Starts solid and ends solid.

Question 5

1) Clamping force

Answer 5

Flow path length / thickness > 100: injection pressure / speed influenced part. Flow path from the separation of the runners to the end of the part.
Otherwise:
holding pressure dependent
* 2 cavity mold: complete holding pressure is the influence of both projected areas (projection in the injection direction)
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Clamping force:
- direct proportion: A_projected, ratio (flow_path_length / thickness)

Question 6

2) Cooling time temperature calculations

Answer 6

Cooling time:
- direct proportion: thickness
- indirect proportion: effective temperature diffusivity

Question 7

3) Calculation of averaged residence time tv

Answer 7

Residence time:
- direct proportion: cycle_time, screw_size
- indirect proportion: total_part_volume

Question 8

Organo sheets description

Question 9

Cycle times

Answer 9

t_injection, t_cooling, t_secondary (direct proportion to closing force)

Question 10

a) Please describe the procedure for a cold pressing process with a thermoplastic.

Question 11

What are the advantages and disadvantages, if you use a thermoplastic material for producing a fibre reinforced part?

Answer 11

ADVANTAGES:
* Weldability and repairability: Thermoplastics can be easily welded together. Thermosets require adhesive bonding or mechanical fastening.
* Impact resistance: Thermoplastics generally exhibit better impact resistance compared to thermosets. Higher toughness, can absorb more energy during impacts.
* Shorter processing cycles: Thermoplastics have faster processing cycles (no curing stage like thermosets).
DISADVANTAGES:
* Higher temperature resistance: Thermoset materials can withstand higher temperatures without significant degradation.
* Superior chemical resistance.
* Higher mechanical strength: Load-bearing applications.