Plastics : Blow Molding and Thermoforming processes Simply explained

Blow Molding process:

The below describes the elements in the above diagram:

Parison Formation:

• Tube extrusion
• Wall thickness
• Length control

Mold Closing:

• Parison capture
• Pinch-off
• Seal formation

Air Injection:

• Pressure control
• Expansion
• Shape forming

Cooling:

• Wall setting
• Temperature control
• Time management

Ejection:

• Part removal
• Trim handling
• Quality check

Main role of blow molding:

• Creates hollow plastic items
• Makes containers and bottles
• Works like blowing up a balloon inside a mold

Best Used For:

 
Containers:

• Water bottles
• Soda bottles
• Shampoo bottles
• Milk jugs
• Chemical containers

Large Items:

• Fuel tanks
• Storage drums
• Industrial containers
• Large water tanks

Characteristics:

• Hollow inside
• Even wall thickness
• Strong construction
• Good for liquids

 Process Benefits:

• Production:
• Fast production
• Consistent quality
• High volume possible
• Cost-effective

 Design:

• Complex shapes possible
• Built-in handles
• Various sizes
• Good strength

Remark:

 
A parison is a hollow, tube-shaped piece of molten plastic that's extruded before blow molding. 

Think of it like a hot plastic tube that will become a bottle or container.

Thermoforming process:

The below describes the elements in the above diagram:

Sheet Heating:

• Temperature control
• Heat distribution
• Sag control

Sheet Formation:

• Mold contact
• Pre-stretch
• Material distribution

Vacuum/Pressure:

• Shape forming
• Detail reproduction
• Wall thickness

Cooling:

• Shape setting
• Temperature control
• Cycle time

Trimming:

• Edge removal
• Part separation
• Scrap handling

Main Role:

• Creates shaped plastic items from sheets
• Makes packaging and trays
• Works like vacuum-sealing plastic over a mold

Best Used For:

 
Packaging:

• Food containers
• Blister packs
• Electronics packaging
• Medical trays
• Product displays

Large Panels:

• Vehicle parts
• Refrigerator liners
• Shower units
• Signs
• Machine covers

Characteristics:

• One-sided detail
• Thin walls
• Large surface areas
• Uniform thickness

Process Benefits:

Production:

• Lower tooling costs
• Quick setup
• Large parts possible
• Good for small runs

Design:

• Fine detail possible
• Large surfaces
• Clear products
• Texture options

Quick Comparison:

 
Blow Molding:

• Makes       :  Hollow items
• Best for     :  Bottles and containers
• Strengths  :  Liquid containers
• Cost           :  Higher setup, lower per piece

Thermoforming:

• Makes       :  Shaped sheets
• Best for     :  Packaging and trays
• Strengths :  Large, detailed surfaces
• Cost           :  Lower setup, higher per piece