230516 - Polymer technology

Question 1

influence of sprue shape

Answer 1

Linear sprue promotes a better flow of the material, point sprue will not promote a uniform flow

Question 2

Metal inserts

Answer 2

Metal inserts:
* security against twisting and tearing out
* Heat insert to expand, if inserted cold, the polymer is hot and the insert will expand and crack the plastic

Question 3

Holes

Answer 3

Reduce notch effect by adding a pestañita around the hole
keep the thickness constant

Question 4

Threads

Answer 4

• External: best. The thread would be unmolded with core and cavity.
• Internal: unfavorable. Favorable if a socket is inserted outside the boss to prevent crack formation or creep of the plastic. The mold would need to “screw out” of the internal thread.

Question 5

Design variables of composite materials

Answer 5

• Type of fiber, carbon and glass fiber together for example (cost-effective). aramyd or PE and carbon (impact strength improves).
• length
• fiber volume. High fiber content increases risk of fiber to fiber contact and not bonded fibers.
• orientation of layers and shift sequence

Question 6

Design rules composite

Answer 6

• first and last layer 45deg
• Neighboring layers should not differ more than 60deg. High shear, delamination, or warping. (mechanical properties of the composite are smaller in transverse direction to the fiber)
  *Avoid sharp corners: not an appropriate positioning of the laminates. (tool made or hand made).

Question 7

Crack stoppers

Answer 7

• Bad: thick laminates
• Good: thin laminates with a variation in the fiber orientation stacked, will stop the propagation of the cracks. Variations in fiber: improves resistance to shear stresses.

Question 8

Stiffeners

Answer 8

• ribs
• double shell structures.
• sandwiches panels

Question 9

What is cold pressing?

Answer 9

1. Cold tool (60deg).
2. preimpregnated thermoplastic material GMT (glass mat reinforced thermoplastic), LFT (long fiber reinforced thermoplastics). preheating.
3. close tool.
4. pressure.

Long fiber. injection molded: short fiber.

Question 10

Comparison between long fiber and short fiber

Answer 10

• Long fiber composites: pultrusion or injection molding. Higher mechanical properties compared to short fiber. Expensive.
• Short fiber composites: compression molding, injection molding, or extrusion. Greater manufacturing flexibility: shape complexity and moldability. Distribute impact energy more effectively

Question 11

Effects on organo sheets on corners

Answer 11

• Organo sheets: High-performance, semifinished materials with carbon, glass, or aramid fiber fabrics embedded in a thermoplastic matrix.
• It may be necessary to clamp the organo sheet on the corners to avoid distortion of the fibers.
• A further injection molding process can be included to mold snap fits or other features.

Question 12

Differences between metal and silicone stamps

Answer 12

special silicone, not a high complexity.

Question 13

What is thermoplastic winding?

Answer 13

• Winding continuous thermoplastic filaments or tapes around a mandrel or core (heated by radiation). Fibers or tapes impregnated with molten thermoplastic resin.
• High-strength, lightweight, and corrosion-resistant products. Pipes, tanks, pressure vessels, and tubes.
• More fiber volume content.

Question 14

parameters of thermoplastic winding

Answer 14

• Winding speed.
• Fiber Tension: avoiding wrinkles or voids.
• Consolidation Pressure and Time: achieve proper interlayer adhesion without causing excessive deformation

Question 15

advantages / disadvantages of thermoplastic winding

Answer 15

ADV:
* high laminate quality
* large components
DIS:
* long time cycles
* concave curved surfaces (gaps will be produced)

Question 16

UD tape filling

Answer 16

• UD stands for “unidirectional”, exceptional strength and stiffness along the length of the tape.
• The tape used in UD tape filling is typically made of high-strength carbon or glass fibers impregnated with a polymer resin, such as epoxy.
• fiber enriched tape is applied to the shape with a hot roller.
• Local reinforcers: lightweight, strong, and stiff structures are required, such as aircraft components, automotive parts, sporting goods, and wind turbine blades.

Question 17

Disadvantages of UD tape filling

Answer 17

• Limited mechanical properties in transverse direction.
• Delamination risk.
• Manufacturing time and labor-intensive.
• Cost.

Question 18

Hand lamination

Answer 18

• Manually applied to a tool mould, impregnated with a laminating resin.
• Small batches and prototypes.
  1. Mold separation.
  2. gelcoat, appearance layer, top layer resin.
  3. layer application
  4. application of auxiliary materials.peel ply WHAT FOR?
  5. curing.
  6. demolding

Question 19

release agent

Answer 19

• Wax-based release agents
• Semi-permanent release agents (silicone based)
• PVA (Polyvinyl alcohol) release agents

Question 20

gelcoat

Answer 20

• Fiberglass-reinforced plastics (FRP) and composite molds.
• Pigmented resinous material that serves as both a protective layer and an aesthetic finish for composite surfaces.
• Gelcoat is typically applied to the mold before the reinforcement material is added, forming the outermost layer of the finished composite part

Question 21

Advantages of gel coat

Answer 21

• Easy demolding and repairability
• Aesthetic finish: smooth and glossy finish to composite parts.
• Surface imperfection coverage.
• Protection from UV radiation, moisture, and abrasion.