Compression Molding and Free Air Blowing

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Compression Molding and Free Air Blowing

• Presented by
• Joumana Zeid
• Adam Falk
• Santosh Iyer
• Rick Kruger
• Jaquelina Lee
• Diane ODonnell
• Brandon Cheney

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Presentation Overview

• Compression Molding
• Laboratory objectives
• Experimental operating conditions
• Compression molding process, background,
  methods
• Experimental results
• Free Air Molding
• Free air molding background
• Laboratory objectives
• Experimental operating conditions
• Experimental results
• Conclusion

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Compression Molding Background

• One of the oldest known molding processes.
• Widely used to produce articles from
  thermosetting materials.
• The plastic material is placed in a mold cavity
  and formed by heat pressure.
• Most compression-molding equipment is typically
  sold by the press or platen rating.
• A force of 2900psi is usually required for
  moldings up to 1inch (25 mm) thick. An added
  725psi should be provided for each 1inch (25 mm)
  increase.

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Compression Molding Laboratory Objectives

• Compression Blow mold two satisfactory flanges
  with compression-molding machine.
• Become familiar with controls and process of
  compression blow molding

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Compression Molding Laboratory Procedure

• Turn on heater switches and set temperature to
  360F
• Clean mold with compressed air and spray on mold
  release
• Pour phenolic powder into mold
• Close mold halves to pressure of 1700psi
• After 30sec open mold to release entrapped gasses
• Reapply pressure to 1700psi and hold for 10 min

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Compression Molding Laboratory Results

• Red and Black powder was used
• Both came out very good
• Mechanical deformation around flange holes are
  due to difficulty in removing the flange from the
  mold
• First run with red powder had one unformed
  section where powder had not melted
• This was due to low mold temperature

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Compression Molding Laboratory Discussion

• Three flanges were produced
• All three parts were high quality
• One part contained defects that were due to
  problems with the heating mechanism
• The flanges have a glossy exterior finish
• The dimensions of the flanges are extremely
  accurate

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Important Factors in Compression Molding

• The mold temperature must be high enough to
  completely melt the phenolic powder
• If the temperature is too low there will be
  unformed regions
• Once the powder melts the density increases and
  the volume of the powder decreases
• This results in a drop in the pressure on the
  mold which must be compensated for

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Thermoforming Background

• Thermoforming is an ancient technique
• Thermoforming was an early application when
  synthetic plastics became available.
• Nowadays, thermoformed items surround us,
  especially in packaging industry.

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Thermoforming Process

• Thermoforming processes are possible because
  thermoplastic sheets can be softened and
  reshaped, and the new shape is retained when the
  material is cooled.
• The force required to change a sheet into a
  desired product can be mechanical, air, or vacuum
  pressure.
• Tooling cost is low.
• Parts with large surface areas may be produced
  economically.

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Thermoforming Techniques

• Straight vacuum forming
• Air-slip forming
• Free-Blow Thermoforming (as shown on the right)

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Free Air Blow Forming Process
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Free Air Blow Forming Objective

• To blow form an object by using a precut
  template.
• Become familiar with controls and process of
  free-blow thermoforming.

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Free Air Blow FormingEquipment

• For this experiment we used a Thermoformer
• We also needed sheets of plastic (ABS and
  polystyrene), thermal gloves, two molds and a
  radiant heater

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Free Air Blow Forming Procedure

• Sheets of plastic were cut to appropriate size
• Place sheet on the platen with the yoke in the
  correct position centered
• Bring assembly up to the clamping frame to check
  the alignment
• Obtain a good seal between the wooden yoke,
  plastic sheet and plate

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Free Air Blow Forming Procedure

• Preheat plastic sheet using radiant heater
• Remove heater, bring assembly into contact with
  the frame and seal it
• Turn in pressure very slowly
• Wait till the plastic cools down then remove from
  thermoformer
• Trim part to produce final product

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Free Air Blow Forming Results

• Satisfactory samples were produced
• Results for ABS samples (all done with a circular
  mold)

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Free Air Blow Forming Results

• Note All ABS samples were heated for the same
  amount of time except for the first sample
• Results for Polystyrene samples (star shaped mold
  was used)
• 1. Sample burst due to applying air pressure too
  fast.
• 2. Second sample was done with good results

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Compression Molding Advantages and Disadvantages

• ADVANTAGES
• Little waste (no gates, sprues, or runners in
  many molds)
• Low tooling costs.
• Process may be automated or hand-operated
• Parts are true and round
• Material flow is short less chance of disturbing
  inserts, causing product stress, and/or eroding
  molds.
• DISADVANTAGES
• Hard to mold complex parts
• Inserts and ejector pins are easily damaged
• Long molding cycles may be needed.
• Unacceptable parts cannot be reprocessed
• Some part dimensions are controlled by material
  charge rather than tooling.

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Free Air Blow Forming Advantages and
Disadvantages

• Advantages
• Easy to update mold yokes
• Inexpensive production
• Disadvantages
• Poor reproducibility
• Cannot produce parts of any complexity
• Significant waste