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Injection Molding vs. CNC Machining vs. Sheet Metal: Which Process Fits Your Custom Part?

Created on 05.21

Meta Description: A detailed comparison of injection molding, CNC machining, and sheet metal fabrication, helping you choose the most cost-effective process for your custom part based on design, volume, and performance needs.

When developing custom parts, many customers struggle to choose between injection molding, CNC machining, and sheet metal fabrication. Each process has unique strengths, limitations, and ideal applications—choosing the wrong process leads to unnecessary high costs, delayed deliveries, and parts that don’t meet your performance needs. As an OEM manufacturer offering multiple processes, we’ve compiled this comparison to help you make the right choice.

Key Process Differences: Overview

•	Injection Molding:	A “molding” process—molten plastic is injected into a mold cavity to create complex, uniform parts. Ideal for high-volume production of plastic parts.

•	CNC Machining:	A “subtractive” process—material is removed from a solid block (plastic or metal) to create complex, high-precision parts. Ideal for low-volume production or complex geometries.

• Sheet Metal Fabrication: A “forming” process—thin metal sheets are cut, bent, and welded to create lightweight, structural parts. Ideal for metal parts with simple 3D shapes.

When to Choose Injection Molding

Injection molding is the best choice for parts that meet the following criteria:

• Plastic Material: Parts made of plastic (PP, ABS, PC, etc.)—injection molding is the most cost-effective process for plastic parts.

• High-Volume Production: 500+ pieces—mold setup costs are spread across high volumes, reducing per-unit cost.

• Complex Geometries: Parts with complex shapes, internal features, or uniform wall thickness (e.g., enclosures, gears, medical devices).

• Uniformity: Parts requiring consistent dimensions and appearance across batches.

Ideal Applications: Consumer electronics enclosures, medical devices, automotive components, plastic gears, and packaging.

When to Choose CNC Machining

CNC machining is the best choice for parts that meet the following criteria:

• Low-Volume Production: 1-500 pieces—no mold setup cost, ideal for prototypes or small batches.

• High Precision: Parts requiring tight tolerances (±0.005-0.01mm)—CNC machining offers higher precision than injection molding or sheet metal.

• Complex Geometries: Parts with curved surfaces, deep cavities, or non-uniform shapes (e.g., custom fasteners, tooling, metal components).

• Metal or Plastic: Works for both metal (steel, aluminum, titanium) and plastic parts—ideal for mixed-material projects.

Ideal Applications: Prototypes, custom tooling, medical implants, aerospace components, and complex metal parts.

When to Choose Sheet Metal Fabrication

Sheet metal fabrication is the best choice for parts that meet the following criteria:

• Metal Material: Parts made of thin metal sheets (0.5-10mm thick, up to 20mm for heavy-duty applications)—steel, aluminum, stainless steel.

• Simple 3D Shapes: Parts made by bending, cutting, or welding thin metal (e.g., enclosures, brackets, panels).

• Lightweight & Structural: Parts requiring strength and lightweight (e.g., automotive body parts, industrial frames).

• High-Volume Production: 100+ pieces—fast production and low per-unit cost for simple metal parts.

Ideal Applications: Industrial enclosures, electrical panels, automotive brackets, outdoor metal structures, and sheet metal frames.

Cost & Lead Time Comparison

Process	Setup Cost	Per-Unit Cost (High Volume)	Lead Time (Prototype)	Lead Time (High Volume)
Injection Molding	High (mold cost: $5k-$150k+)	Low ($0.10-$1.00/piece)	7-14 days (mold + sample)	3-7 days
Injection Molding	High (mold cost)	Low	7-14 days (mold + sample)	3-7 days
CNC Machining	Low (no mold: $200-$500)	High ($5.00-$50.00/piece)	1-3 days	5-10 days
Sheet Metal Fabrication	Low (no mold: $100-$300)	Medium ($1.00-$5.00/piece)	1-2 days	3-5 days

The right process depends on your part’s material, design, volume, and performance needs. In some cases, a combination of processes (e.g., injection-molded plastic parts with CNC-machined metal inserts) is ideal. Our team can evaluate your design and recommend the most cost-effective process for your project.