Quick Overview: Injection moulding vs compression moulding vs blow moulding vs extruion molding.

Injection molding, compression molding, blow molding, and extrusion each have distinct advantages, costs, and design constraints. Choosing the right process depends on part complexity, volume, tolerance, material, and production efficiency.

1. Injection Molding

Definition: Molten plastic is injected under high pressure into a precision mold.

• Design Complexity: High. Can produce thin walls (<0.5 mm), intricate undercuts, and multi-cavity molds.
• Typical Cycle Time: 10–60 seconds per part (varies with size, cooling, and material).
• Volume: Millions of parts/year feasible.
• Tooling Cost: $5k–$500k+ depending on mold complexity.
• Tolerance: ±0.05–0.3 mm (high precision).
• Material Wastage: 2–5% typical (sprues, runners, rejected parts).
• Applications: Automotive dashboards, medical devices, electronics, consumer goods.
• Pro Tip: Conformal cooling channels in molds reduce cycle time by 15–30%.

Visual Insight: Injection molding is ideal for 3D shapes with internal cavities, multi-cavity molds allow high-volume replication.

2. Compression Molding

Definition: Preheated thermoset is placed in an open mold and pressed under heat.

• Design Complexity: Low–medium. Best for flat or slightly curved parts.
• Typical Cycle Time: 1–5 minutes per part (longer than injection).
• Volume: Hundreds to tens of thousands per year.
• Tooling Cost: $2k–$50k.
• Tolerance: ±0.1–0.5 mm.
• Material Wastage: <5%, generally easy to trim flash.
• Applications: Brake pads, electrical switchgear, dinnerware.
• Pro Tip: Preheating material reduces voids and improves surface finish.

Visual Insight: Compression molding is simple, but slower and mostly for thermoset materials.

3. Blow Molding

Definition: Hollow shapes are formed by inflating a heated parison inside a mold.

• Design Complexity: Low. Limited to hollow, mostly symmetrical parts.
• Cycle Time: 15–60 seconds for bottles; up to several minutes for large tanks.
• Volume: High; millions of bottles/day possible.
• Tooling Cost: $5k–$100k.
• Tolerance: ±0.2–0.5 mm (depends on wall thickness).
• Material Wastage: 2–10%.
• Applications: Bottles, drums, automotive ducts.
• Pro Tip: Control parison thickness precisely; uneven thickness causes weak spots.

Visual Insight: Best suited for hollow containers, neck finish often requires injection blow molding.

4. Extrusion Molding

Definition: Plastic is melted and forced through a die to create continuous profiles or sheets.

• Design Complexity: Low. Only constant cross-sections possible.
• Typical Speed: 1–15 m/min depending on profile and material.
• Volume: Continuous, unlimited length production.
• Tooling Cost: $1k–$20k for dies.
• Tolerance: ±0.1–0.5 mm (depends on cooling and puller speed).
• Material Wastage: Minimal, can recycle trimmed edges.
• Applications: Pipes, tubing, rods, window profiles, films.
• Pro Tip: Cooling rate and die design are critical for dimensional stability.

Visual Insight: Extrusion is perfect for long, uniform profiles, can co-extrude multiple layers.

Comparative Table with Metrics

Special Insights for Designers

• Cycle Time vs Part Complexity: Injection molds are fast but expensive; compression is slower; blow molding speed depends on part size.
• Material Efficiency: Extrusion produces the least waste; injection and blow molding require sprues or parisons.
• Tolerance Trade-offs: Tightest tolerances with injection; extrusion and blow are looser.
• Simulation & Digital Twin: Use Moldflow, SolidWorks Plastics, or Autodesk Fusion simulation to predict warpage, shrinkage, or sink marks.
• Hybrid Solutions: Insert molding or co-extrusion allows combining processes to reduce cost and increase functionality.
• Sustainability Tip: Thermoplastics (injection, blow, extrusion) can incorporate recycled material; thermosets cannot.