Plastics : Thermoforming Explained Simply

Simply put, you heat plastic until it's soft, then shape it over or into a mold.

Basic Steps:

1. Sheet Preparation:

• It starts with a flat plastic sheet
• Different thicknesses are used for different products
• The plastic sheet can be clear or colored

2. Heating:

• We heat the plastic sheet until it is soft
• It is like warming up cheese until it is stretchy
• The temperature should not be too hot as not to melt plastic or too cold for the sheet to remain stiff
• Heat must spead evenly across the sheet

3. Types of forming:

Vacuum Forming:

• Air is removed to pull plastic into shape
• Heated plastic sheet is stretched over a mold and then vacuum suction pulls it into shape.
• Most common method used

Pressure Forming:

• Uses pressure to push plastic into shape
• Affords better detail than vacuum forming

Twin-Sheet Forming:

• It is like making a sandwich with two buns
• Two sheets formed and joined together
• Used to make makes hollow parts

4. Cooling:

• We let the plastic cool and harden
• It is like letting jello set
• Plastic must stay in the mold until firm
• The cooling time affects quality

5. Trimming:

• It is used to cut away excess plastic
• It is like like trimming excess crust from a pie
• It is used to remove the unwanted parts
• It makes clean edges

Common Products Made:

Packaging:

• Used for food containers
• Blister packs
• Clamshells which are made from two hinged halves that close together like a clam's shell. 
• Drink cups

Large Parts:

• Refrigerator liners
• Shower units
• Car parts
• Advertisement signs

Consumer Goods:

• Plastic trays
• Storage containers
• Equipment covers
• Display items

Important Things to Know:

1. Material Choice:

Good materials:

• PET (for soda bottles)
• PS (for foam cups)
• PVC (for pipes)
• PE (for milk jugs)

2. Advantages:

• Thermoforming is cheaper than injection molding for big parts
• Good for large items
• Lower tool costs
• It is quick to start production

3. Limitations:

• Thermoforming is not good for complex shapes
• It can make limited details
• Has uneven thickness
• There is a material waste from trimming

Common Problems and Solutions:

1. Thin Spots:

Thin spots are areas in a plastic part where the material is thinner than intended, making these sections weaker and potentially causing product failure

Solution to the thinness issue:

• Better heating
• Proper material thickness
• Correct forming speed

2. Webbing:

Webbing in plastics refers to unwanted thin membranes or "webs" of plastic that form between parts or sections of a molded product

Solution:

• Adjust thetemperature
• Change the forming speed
• Modify the design

3. Poor Definition:

Solution:

• Use more vacuum or more pressure
• Use better temperature control
• Use proper material choice

Tips for Success:

1. Temperature Control:

• Use even heating
• Use the right temperature for material
• Use the proper heating time

2. Material Handling:

• Use clean sheets
• Use proper storage
• Careful loading

3. Mold Design:

• Must have good air flow
• Proper draft angles
• Smooth surfaces

Cost Considerations:

1. Setup Costs:

• Thermoforming molds are cheaper than injection molds
• Heating equipment
• Trimming tools

2. Running Costs:

• Material sheets
• Energy for heating
• Labor
• Trimming waste from removing unwanted edges

Thermoforming shouldbe be used:

• Large parts
• Simple shapes
• Low volume production
• Quick prototypes

Thermoforming should not be used for:

• Tiny parts
• Complex shapes
• High precision models with lot of details
• Thick walls

Quality Checks:

Visual:

• Check for even thickness
• Check for good detail
• check for bubbles
• for that the edges are clean

Physical:

• Must be of a proper fit
• Must have the right strength
• Must have the right thickness
• Must have the right dimensions

Environmental Considerations:

1. Material Use:

• Can use recycled material
• Ca use recyclable scraps
• Material selection is important

2. Waste Reduction:

• Try to minimize trim waste
• Try to reuse scraps
• Efficient nesting which is the process of arranging multiple parts or patterns on a sheet of material (like plastic) to minimize waste and maximize material usage

Safety Considerations:

1. Safety regarding operation:

• Hot surfaces
• Moving parts
• Sharp edges

2. Safety regarding the material used:

• Proper ventilation
• Material handling
• Protective equipment