Why Material Selection Drives 35–60% of Your Total Cost
In real production, material choice alone influences up to 35–60% of total manufacturing cost and machining cycle time. It is not a spec-sheet tick-box exercise — your material dictates machinability, tool life, tolerance stability, finish compatibility, and lead time all at once.
Before locking in any material, every engineer should answer four questions:
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Will the part see mechanical stress, impact, or fatigue? If yes, yield strength and fatigue limit move to the top of the priority list.
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What is the operating environment? Temperature range, chemical exposure, UV, humidity, and salt spray all narrow your options fast.
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What tolerance and surface finish are functionally required? Don't over-specify — every extra decimal place of tolerance can add 20–40% to cost.
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What is the budget and lead-time window? Some materials (titanium, Inconel, PEEK) carry 200–400% cost premiums and extended mill lead times.
Material Quick-Reference Matrix
The table below compiles production machining data across the most commonly specified CNC materials. Machinability is rated 1–10 (10 = fastest, easiest to cut). Anything scoring below 4 carries a significant cost and cycle-time penalty.
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Material
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Tensile Strength
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Machinability
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Corrosion Resistance
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Relative Cost
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Best For
|
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Aluminium 6061-T6
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310 MPa
|
9/10
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Good
|
£
|
General purpose, enclosures, frames
|
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Aluminium 7075-T6
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572 MPa
|
8/10
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Moderate
|
££
|
Aerospace, high-stress brackets
|
|
Stainless 303
|
620 MPa
|
8/10
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Excellent
|
££
|
Shafts, fasteners, high-volume fittings
|
|
Stainless 304
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515 MPa
|
6/10
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Excellent
|
££
|
Food equipment, medical devices, welded assemblies
|
|
Stainless 316
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579 MPa
|
5/10
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Superior
|
£££
|
Marine, chemical, pharmaceutical
|
|
Stainless 17-4 PH
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1170 MPa
|
5/10
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Good
|
£££
|
Aerospace, oil & gas, high-load components
|
|
Titanium Grade 2
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344 MPa
|
3/10
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Excellent
|
££££
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Medical implants, chemical processing
|
|
Titanium Ti-6Al-4V (Grade 5)
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950 MPa
|
2/10
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Excellent
|
££££
|
Aerospace structures, surgical instruments
|
|
Brass C360
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385 MPa
|
10/10
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Good
|
££
|
Valves, connectors, decorative parts
|
|
Copper C110
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220 MPa
|
9/10
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Good
|
£££
|
Bus bars, heat sinks
|
|
PEEK
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100 MPa
|
6/10
|
Excellent
|
£££££
|
Medical, extreme-temp, chemical
|
|
Delrin (POM)
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70 MPa
|
9/10
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Good
|
££
|
Gears, bearings, bushings
|
|
Nylon (PA6/66)
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80 MPa
|
8/10
|
Good
|
£
|
Wear parts, housings
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Note: On broader machinability indices, materials scoring below 40/100 (titanium, Inconel, precipitation-hardening steels) typically incur a +75–150% cost premium over free-machining grades. Factor this in at the quoting stage, not after PO placement.
Material-by-Material Guidance
Aluminium Alloys — The Lightweight Workhorse
Aluminium is the most widely specified CNC material in the UK: light, highly machinable, and naturally corrosion-resistant to a useful degree. Off the machine, aluminium parts typically hold ±0.01–0.02 mm tolerances and achieve Ra 0.8–1.6 µm as-machined. Cycle times run 30–50% faster than steel for comparable geometries.
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6061-T6 — The default general-purpose alloy. Excellent weldability, strong anodising response, and the best all-round balance of strength, cost, and machinability. First choice for enclosures, brackets, drone frames, and automation components.
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7075-T6 — Nearly double the tensile strength of 6061. The aerospace standard. Not weldable without specialist techniques, costs 30–50% more, and anodises to a duller, streaky finish due to its zinc content. Use when strength-to-weight is critical.
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5052 — Superior corrosion resistance, especially in marine environments. Lower strength makes it better suited to formed sheet or lightly loaded brackets than high-stress structural parts.
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2024-T4 — High fatigue resistance, widely used in aircraft fuselage skins. Poor corrosion resistance (typically clad or anodised). Rarely specified outside aerospace.
Stainless Steel — Strength and Corrosion, at a Machinability Cost
Stainless is the toughest challenge in CNC machining. High toughness causes work hardening during cutting, and poor thermal conductivity traps heat at the tool tip. Tool wear runs 2–3× higher than aluminium, cutting speeds must drop 40–60%, and cycle times stretch accordingly.
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303 — Free-machining grade with added sulphur. The easiest stainless to machine (8/10). Ideal for high-volume shafts, fasteners, and turned parts.
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304 — The most common general-purpose stainless. Excellent corrosion resistance. Standard for food equipment, medical housings, and architectural trim.
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316 — Added molybdenum delivers superior pitting and crevice corrosion resistance against chlorides. Mandatory for marine, chemical processing, pharmaceutical, and any implant-adjacent application.
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17-4 PH — Precipitation-hardening stainless reaching 1170 MPa tensile. Machine in Condition A (soft), then age-harden to H900–H1150. Widely used in aerospace and oil & gas.
DFM warning: Stainless threads are prone to galling if assembled dry. Always specify anti-seize compound or insert requirements on the drawing. This single note prevents more returned parts than almost any other.
Titanium — Reserved for When Nothing Else Works
Titanium (especially Grade 5 / Ti-6Al-4V) offers an unmatched strength-to-weight ratio and corrosion resistance, but it is the most expensive material to machine commercially. Four factors drive this:
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Very low thermal conductivity — heat concentrates at the cutting edge
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High chemical reactivity with carbide tooling
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Strong work-hardening tendency
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Significant springback after cutting
The result: tool wear 3–5× higher than aluminium, machining efficiency 40–70% slower, and a +200–400% cost premium over baseline materials. Reserve titanium for aerospace structural parts, medical implants, high-performance automotive, and defence applications where its properties are genuinely irreplaceable.
Brass, Copper & Engineering Plastics
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Brass C360 (machinability 10/10) — Perfect for high-precision turned parts, valve bodies, electrical connectors. Takes a bright, decorative finish straight off the lathe.
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Copper C110 — Extremely high electrical and thermal conductivity. Soft and gummy to machine; best for bus bars and heat sinks where conductivity trumps mechanical strength.
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PEEK — Outstanding chemical and high-temperature resistance (continuous use to 260°C). Medical and semiconductor applications dominate.
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Delrin (POM) — The most popular engineering plastic for CNC. Excellent dimensional stability, low friction, and machines cleanly like a soft metal. First choice for gears, bushings, and jig components.
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Nylon (PA6/66) — Good wear resistance and self-lubricating properties. Used for cable ties, wear pads, and low-load structural housings.
Surface Finish Selection — An Engineering Decision, Not an Afterthought
Surface finishing transforms a precision-machined blank into a component that survives its service environment. The right finish provides corrosion protection, wear resistance, controlled electrical conductivity, or a combination of all three. Choosing incorrectly — or omitting the finish specification entirely — leads to premature failure, costly field returns, or cosmetic rejection.
Surface Finish Quick-Reference Matrix
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Finish
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Base Material
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Thickness / Build-up
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Best Application
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Anodise Type II (Sulfuric)
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Aluminium
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8–25 µm
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Corrosion resistance, colour, general engineering
|
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Anodise Type III (Hardcoat)
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Aluminium
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25–75 µm (up to 100)
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Extreme wear resistance; hardness equivalent to 60–70 HRC
|
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Chromate conversion (Alodine / Chem Film)
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Aluminium
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< 1 µm
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EMI shielding, conductive surface, primer base
|
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Powder coat (Polyester)
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Steel, Aluminium
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60–100 µm
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Outdoor UV resistance, colour, corrosion protection
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Powder coat (Epoxy)
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Steel, Aluminium
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40–80 µm
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Indoor corrosion, chemical resistance
|
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Electroless nickel
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Steel, Al, Copper
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5–25 µm
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Uniform coverage on complex geometry, wear + moderate corrosion
|
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Electrolytic zinc plating
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Steel
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5–15 µm
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Mild corrosion, low cost, fasteners
|
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Hard chrome plating
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Steel, Cast iron
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5–500 µm
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Hydraulic rods, sliding contact surfaces
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Passivation
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Stainless steel
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No build-up
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Removes free iron, restores passive chromium oxide layer
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Black oxide
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Steel, Stainless
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< 2.5 µm
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Mild corrosion, anti-glare, aesthetic
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Electropolishing
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Stainless steel
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Material removed
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Surface smoothing, Ra reduction, biocompatibility
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How to Choose by Functional Requirement
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Corrosion protection → Anodising (aluminium), passivation (stainless), powder coating (steel/aluminium)
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Wear resistance → Type III hard anodise, hard chrome, electroless nickel, PVD coating
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Electrical conductivity → Alodine (conductive), gold/nickel plating (conductive), powder coat (insulating — specify clearly)
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Biocompatibility → Electropolishing + passivation per ASTM A967 for 300-series stainless
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Aesthetics/colour coding → Type II anodise (RAL-matched dyes), powder coat, brushing + clear lacquer
Industry-Specific Recommendations
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Industry
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Recommended Finishes
|
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Aerospace
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Type II/III anodise, chromate conversion, polyester powder coat. Note: 7075 parts often require hardcoat on wear surfaces.
|
|
Medical
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Passivation + electropolishing (ASTM A967) for all 300-series stainless; titanium benefits from PVD or nitriding.
|
|
Automotive
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Powder coat, zinc plating, anodise, wet paint — selected by under-bonnet vs exterior zone.
|
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Food & Beverage
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Passivation, electropolishing, food-grade epoxy powder coat.
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Electronics & RF
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Gold flash over nickel, Alodine (conductive), Type II anodise (dielectric).
|
|
Marine / Outdoor
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Polyester powder coat (UV-stable), 316 stainless + passivation, hard anodise on aluminium.
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Conclusion
Material and surface finish selection is not a late-stage afterthought — it is the foundation of a successful
CNC machining project. The most cost-effective part is not the one made from the cheapest material, but the one whose material and finish are matched precisely to its functional requirements from day one.
Engineers who invest 30 minutes upfront in material/finish planning typically save weeks of rework, hundreds of pounds in scrap, and the credibility cost of a missed delivery. Suppliers who contribute proactively at this stage — offering DFM feedback on material substitutions, finish feasibility, and tolerance stack-up — earn repeat business because they de-risk the entire programme.
