24 Questions
What is the primary difference between thermoplastics and thermosets in terms of processing?
Thermoplastics can be remolded while thermosets cannot
Which process is commonly used to produce complex parts with fiber-filled thermoplastics?
Injection molding
What is a key advantage of injection molding over other molding processes?
It offers tight dimensional control
Which of the following materials is NOT typically used in injection molding?
Wood fibers
What is a common application of unreinforced thermoplastics?
Household items
Which process is used to produce composite parts with complex shapes?
Injection molding
What is a key disadvantage of thermoplastics compared to thermosets?
They lack tackiness
What is the typical process cycle time for injection molding?
20-60 s
What is a major advantage of the extrusion process?
Low cost
What is the primary industry that utilizes compression molding for thermoplastic structural parts?
Automotive
What is the typical fiber volume fraction for compression molding?
20 to 30%
What is the material used in thermoplastic compression molding?
Polypropylene
What is the primary advantage of compression molding over other manufacturing techniques?
Fast production rate
What is the primary limitation of compression molding?
High capital investment
What is the purpose of tape winding in composite part production?
To consolidate the thermoplastic tape
What is the common material used in tape winding?
Thermoplastic prepreg tape
What type of voids are formed during helical winding?
Voids and porosities
What is a disadvantage of tape winding compared to wet filament winding?
Higher raw materials cost
What is the purpose of a heating station in thermoforming?
To soften the material
What is the name of the tool used in thermoforming to press the material into shape?
Positive and negative stamp
What is a characteristic of the thermoforming process?
Very short production times with high reproducibility
What is the purpose of a fixation device in thermoforming?
To prevent sagging
What type of materials are often used in thermoforming?
Fibre-reinforced materials
What is the final step in the thermoforming process?
Machining the workpiece
Study Notes
Thermoplastics vs Thermosets
- Thermoplastics do not require refrigeration and can be remolded, with any scrap being recycled.
- Thermoplastics have better toughness and impact resistance than thermosets.
- Thermoplastics are stiff and boardy, lacking the tackiness of partially cured epoxies.
Injection Molding (IM)
- Injection molding is the predominant process for producing thermoplastics into finished forms.
- It is a highly automated process with a process cycle time of 20-60 seconds.
- Materials used include resins (PP, nylon, PET, polyester) and fibers (glass, carbon, Kevlar).
- Typical applications include household items, equipment housing, sprockets, computer parts, and automotive parts.
Advantages of IM
- Allows production of complex shapes in one shot.
- Offers tight dimensional control (±0.002 in or ±0.05 mm).
- Part repeatability is better than other molding processes.
Extrusion
- Is a low-cost process with flexibility and post-extrusion alterations possible.
- Has disadvantages including variations in product size and limitations due to only one type of cross-section being obtained at a time.
- Has a high initial cost setup.
Compression Molding (CM)
- Uses Glass Mat Reinforced Thermoplastics (GMT) for high-volume parts.
- Primarily used in the automotive industry for making structural parts.
- Materials used include resins (primarily polypropylene) and fibers (continuous but randomly oriented glass fibers).
- Typical applications include bumper beams, dashboards, and kneebolsters.
Advantages of CM
- Is one of the fastest techniques for making composite structural parts.
- Has higher productivity, requiring fewer tools and less labor.
Disadvantages of CM
- Requires high capital investment.
- Limited to high production volume environments.
- Fiber volume fraction is limited to 20-30% due to high resin viscosity.
- Surface finish on the part is intermediate.
Tape Winding
- Uses thermoplastic prepreg tape wound over a mandrel.
- Voids and porosities are formed at the intersection of consolidated tapes.
- Has a high raw materials cost compared to wet filament winding.
Thermoforming
- Is a process using fibre-reinforced materials differentiated as foils or laminates.
- Involves heating the material, then molding it into a shape using a clamping frame and a forming tool.
- Has short production times of up to less than one minute per component with high reproducibility.
- Is easy to automate, making it suitable for large quantities.
This quiz covers the manufacturing methods of thermoplastic matrix composites, including injection molding, extrusion, compression molding, and more. It compares thermoplastics and thermosets, and discusses their advantages and disadvantages.
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