Polymer Extrusion & Injection Molding Process Comparison

Extrusion is widely used in various industries.

The screw in the extruder rotates and develops sufficient pressure to force material to go through a die and produce products with desired geometry. 

Injection molding is the most commonly used manufacturing process for the fabrication of plastic parts. A wide variety of products are manufactured using injection molding, which vary greatly in their size, complexity, and application. The injection molding process requires the use of an injection molding machine, raw plastic material, and a mold. The plastic is melted in the injection molding machine and then injected into the mold, where it cools and solidifies into the final part.
Polymer Extrusion
Property Name   Polymer Extrusion   Injection Molding
Shapes Flat, Thin-walled: Cylindrical, Thin-walled: Cubic, Solid: Cylindrical, Solid: Cubic Thin-walled: Cylindrical, Thin-walled: Cubic, Thin-walled: Complex

(Flat)

Part size Diameter: 0.04 – 6.0 in Envelope: 0.01 in³ – 80 ft³

Weight: 0.5 oz – 55 lb

Materials Thermoplastics

(Elastomer, Thermosets)

Thermoplastics

(Composites, Elastomer, Thermosets)

Surface finish – Ra (μin) 16 – 63

(8 – 75)

4 – 16

(1 – 32)

Tolerance (in.) ± 0.04

(± 0.01)

± 0.008

(± 0.002)

Max wall thickness 0.016 – 6.0

(0.0008 – 6.0)

0.03 – 0.25

(0.015 – 0.5)

Quantity 10000 – 1000000 10000 – 1000000

(1000 – 1000000)

Lead time Weeks Months

(Weeks)

Advantages Good surface finish, High production rate, Low labor cost, Little scrap generated Can form complex shapes and fine details, Excellent surrface finish, Good dimensional accuracy, High production rate, Low labor cost, Scrap can be recycled
Disadvantages Limited to uniform cross sections, High equipment cost, Long lead time possible Limited to thin walled parts, High tooling and equipment cost, Long lead time possible
Applications Rods, bars, tubing, sheet, cable, frames Housings, containers, caps, fittings
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