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.

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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

Source:https://www.sukoptfe.com/polymer-extrusion-injection-molding-process-comparison