What’s the cost difference between milling plastic and metal?
What’s the Cost Difference Between Milling Plastic and Metal?
Plastic CNC milling is often less expensive than metal CNC milling for accessible, lightly loaded parts, but there is no reliable universal percentage. The cost difference depends on the exact material grade, stock form, geometry, tolerance, quantity, finishing, and inspection plan. ABS or POM can reduce cutting time and tool cost on a simple prototype, while PEEK, filled polymers, unstable thin walls, optical surfaces, or certified stock can cost more than a straightforward aluminum part. Buyers should compare the same drawing revision and acceptance requirements in both materials, then select the option that meets service conditions with the lowest total validation and rework risk.
Cost Drivers to Put on the Same Basis
Factor | Plastic Milling | Metal Milling |
|---|---|---|
Material Cost | ABS, POM, or PC stock may cost less, while PEEK, PTFE, filled grades, certificates, color control, and stress-relieved stock can reverse that advantage. | Aluminum can be cost-efficient; stainless steel, titanium, and nickel alloys add purchase cost, cutting difficulty, or both. |
Machining Time | Cycle time can be shorter for open, rigid features, but heat-sensitive surfaces and flexible walls may require light cuts, extra setups, or stabilization time. | Higher strength or work-hardening behavior can slow roughing and finishing, although a stable metal part may need fewer corrective trials. |
Tool Wear | Unfilled plastics are often gentle on cutters; glass- or carbon-filled polymers can be abrasive and raise tool replacement and inspection frequency. | Stainless steel, hardened steel, titanium, and nickel alloys can consume tools quickly, so tool life and change time belong in the quoted machining rate. |
Surface Finish | Burrs, melting, whitening, clamp marks, optical polishing, or coating preparation can add manual work even when the cutting cycle is short. | Bead blasting, anodizing, passivation, polishing, or coating may outweigh the initial cutting difference and can change inspection timing. |
Setup/Fixturing | Lower clamping force suits simple stock, but a weak datum scheme can allow distortion during cutting or movement after release. | Rigid workholding can cost more to prepare, while material stiffness may preserve datum relationships through repeat setups and inspection. |
Illustrative Cost Screen: 100 × 80 × 10 mm Bracket
Material | Machining Time | Tool Cost Impact | Relative Cost Decision |
|---|---|---|---|
ABS Plastic | Potentially shortest when pockets are shallow, walls are supported, and cosmetic faces need only controlled deburring. | Low for unfilled ABS; risk shifts to clamp marks, burrs, heat smear, and dimensional movement after unclamping. | Lowest only when stiffness, threads, heat exposure, and inspection requirements remain within the selected grade’s validated limits. |
Aluminum 6061 | Moderate in this screen; cutting force is higher than for ABS, but predictable machining can reduce trial adjustments. | Medium; tool wear is usually controllable for accessible bracket, plate, and housing features with a stable setup. | Can be the better value when the part needs stiffness, durable threads, anodizing, or repeatable assembly dimensions. |
Stainless 304 | Usually longest in this three-material screen because work hardening, heat, and tool engagement demand tighter process control. | High; cutter wear and deburring can increase around small slots, internal corners, interrupted cuts, and thin edges. | Higher machining cost may be justified when corrosion resistance, strength, and service temperature prevent later replacement or redesign. |
This bracket table is a screening scenario, not a time or price quotation; feature depth, stock removal, setups, batch size, inspection, and supplier rates remain unspecified. Plastics like ABS or POM can reduce cycle time when the design avoids slender unsupported walls, deep narrow pockets, aggressive thread loads, and heat-sensitive finishes. Metals like aluminum can offer better project value when stiffness, thread strength, or anodizing prevents additional inserts, redesign, or rejection. A comparable RFQ should state quantity, stock form, minimum wall and unsupported span, critical tolerances, surface finish, insert or thread loads, operating temperature, and first-article inspection requirements.
When Higher Machining Cost Lowers Total Project Cost
Metal can be more cost-effective when its higher machining price prevents later failure, redesign, or inspection rejection. A plastic version may look cheaper at quotation, then lose that advantage if the part creeps under load, moves after unclamping, cracks around inserts, changes with moisture, or fails the operating temperature. Aluminum or stainless steel may therefore reduce total project cost even when the unit machining line is higher.
Tighter tolerances and thermal stability matter when datum relationships, bearing seats, or mating faces must remain stable after machining, storage, assembly, and temperature change.
Mechanical strength for load-bearing functions can favor metal if plastic would need thicker walls, metal inserts, repeated samples, or a major geometry compromise.
Surface treatments can change the comparison: direct anodizing requires a suitable metal, while plating on plastic needs a separate activation and conductive-layer route that adds qualification work.
Plastic remains attractive for prototype covers, fixture details, electrical insulators, lightweight housings, and low-load components when the selected grade meets the actual environment. Metal becomes the better economic choice when durability, dimensional stability, threaded interfaces, finishing options, or validation risk outweigh lower plastic cutting loads. A side-by-side quote is meaningful only when both options use the same drawing revision, quantity, tolerance interpretation, finish note, inspection plan, and operating conditions.
RFQ Inputs for a Comparable Plastic-versus-Metal Quote
Neway provides CNC machining services for both plastics and metals, including ABS, POM, aluminum 6061, and stainless steel 304. Submit the 2D drawing and 3D model, target quantity, approved material grade and stock form, operating loads and temperature, visible surfaces, tolerance and datum notes, threads or inserts, finishing, certificates, and inspection expectations. Ask the supplier to separate material, setup, cycle time, tooling, finishing, inspection, and non-recurring qualification where practical. The useful decision is not the lowest line-item price; it is the material and process route most likely to pass assembly, service, and validation without rework.
