Plastics : A comprehensive look at Thermoforming

Thermoforming is a manufacturing process where a plastic sheet is heated until pliable, then formed over or into a mold using vacuum, pressure, or mechanical force, and finally cooled to maintain the new shape.

How thermoforming works:

• Sheet heating until flexible
• Sheet forming using mold and pressure/vacuum
• Cooling is performed to retain shape
• Excess material is trimmed
• The finished part is removed

Advantages:

• Thermoforming has less tooling costs than injection molding
• Good for large parts
• Fast production cycles
• Low waste
• Simple tooling
• Ideal for prototype making
• Good for low to medium volumes

Injection molding is a manufacturing process where molten plastic material is forced under pressure into a mold cavity, where it cools and hardens to create a part with the desired shape. The process is widely used to produce everything from small components like bottle caps to large parts like car bumpers.

Disadvantages:

• Limited to sheet materials
• It has less complex parts than injection molding
• Limited material thickness
• May have thickness variations
• Produces only one finished surface
• It has material waste from trimming

Common applications:

• Food packaging
• Blister packs
• Vehicle dashboards
• Refrigerator liners
• Shower trays
• Signs
• Medical device packaging
• Aircraft interior panels
• Point-of-purchase displays
• Equipment covers

Types of thermoforming:

Vacuum forming:

• Uses vacuum to pull plastic onto mold
• It is the simplest method of thermoforming

Pressure forming:

• Uses pressure to push plastic into mold
• It produces better detail than vacuum forming

Twin-Sheet forming:

• Forms two sheets simultaneously
• It can create hollow parts

Drape forming:

• Sheet draped over positive mold
• Good for simple shapes

A positive mold is a solid form or shape around which material is formed or wrapped to create a hollow part or cavity, essentially creating the inner surface of the final product.

Key process parameters for thermoforming:

• Sheet temperature
• Heating time
• Cooling time
• Vacuum/pressure level
• Material thickness
• Mold temperature