材料選定は通常、CNC 部品のコスト、重量、被削性、最終性能に影響を与える最大の単一決定です。本ガイドは JLYPT が日々加工している材料と、それぞれの適用先 — 工場の現場視点で執筆 — を解説します。
How to think about material choice
Most material decisions can be reduced to four questions, in order:
- Mechanical requirements — yield strength, fatigue, stiffness, weight target, operating temperature.
- Environment — corrosion, chemicals, UV, food/medical contact, sterilisation cycles.
- Machinability and cost — how fast it cuts, how much the bar stock costs, what tooling wear to expect.
- Finishing and downstream processes — does it anodise, plate, weld, paint, glue?
Aluminium alloys — the workhorses
Aluminium dominates CNC work because it cuts fast, takes a beautiful surface, anodises in any colour, and weighs a third as much as steel. For most consumer and industrial parts, the question is which aluminium alloy, not whether to use aluminium.
| Alloy | Yield (MPa) | Best for | Trade-off |
|---|---|---|---|
| 6061-T6 | 276 | General-purpose: housings, brackets, fixtures | Moderate strength; most common |
| 6063-T5 | 215 | Extruded profiles, decorative anodised parts | Softer; slightly worse machined finish |
| 7075-T6 | 503 | Aerospace, motorsport, structural | Harder to machine, less corrosion resistant, anodises poorly |
| 2024-T351 | 345 | Aerospace skin, fatigue-loaded parts | Susceptible to stress corrosion; usually clad |
| 5052 | 193 | Marine, sheet-metal-style folded brackets | Lower strength but excellent corrosion resistance |
| MIC-6 / cast tool | 170 | Vacuum chucks, optical bases, tooling plates | Stable but heavy; rarely used for end-use parts |
Carbon and stainless steels
When strength, fatigue resistance or corrosion in aggressive environments matters, steel is the answer. Three families cover almost everything we machine:
Carbon & alloy steels
- 1018, 1045 — cheap, weldable, easy to machine. Good for shafts, jigs, low-stress brackets.
- 4140, 4340 — pre-hardened or heat-treatable to ~50 HRC. Used for gears, drive shafts, tool holders.
- Will rust without coating — plate, paint or oil.
Stainless steels
- 303 — free-machining, but worse corrosion resistance and not weldable.
- 304 — the default food/marine grade.
- 316L — superior corrosion resistance, medical-implant grade.
- 17-4PH — precipitation-hardened, ~40 HRC, aerospace and pumps.
- 15-5PH — similar to 17-4 with better transverse properties.
For surface treatment of steel parts, see our surface finishing services — passivation for stainless, black oxide for tool steel, electroless nickel for carbon steel.
Titanium and superalloys
Titanium and nickel superalloys are the answer when no other material works — typically aerospace, medical implants, downhole oil tools and high-end motorsport.
| Material | Strength | Density (g/cm³) | Typical use |
|---|---|---|---|
| Ti-6Al-4V (Grade 5) | 895 MPa | 4.43 | Aerospace structural, bicycle frames, surgical implants |
| CP Titanium (Grade 2) | 275 MPa | 4.51 | Chemical processing, marine |
| Inconel 718 | 1240 MPa | 8.19 | Jet engine hot section, downhole tools |
| Inconel 625 | 760 MPa | 8.44 | Marine seawater, chemical processing |
| Hastelloy C-276 | 690 MPa | 8.89 | Worst-case chemical environments |
| Monel 400 | 241 MPa | 8.80 | Seawater, hydrofluoric acid |
Brass, bronze and copper
Copper-based alloys are niche but indispensable for electrical, plumbing and decorative work.
- C360 brass (free-machining). Cuts like butter, ideal for valves, fittings, electrical components and decorative hardware.
- C932 bearing bronze. Self-lubricating; bushings, gears, marine fittings.
- C110 (oxygen-free copper). Best electrical and thermal conductivity; bus bars, heat sinks, RF.
- Beryllium copper (C17200). Springs, non-sparking tools, EMI gaskets — but requires careful handling due to dust hazards.
Engineering plastics
CNC-machined plastics fill applications where metal is too heavy, too conductive or too expensive. Sheet stock and extruded rod are routinely turned and milled to ±0.05 mm tolerances.
| Material | Strengths | Watch out for |
|---|---|---|
| Delrin / POM | Low friction, dimensional stability, machines cleanly | Difficult to glue; weak in UV |
| Nylon (PA6, PA66) | Wear resistance, gears, bushings | Absorbs moisture and grows ~2% |
| PTFE (Teflon) | Chemical inert, very low friction, –200 to +260°C | Soft, creeps under load |
| Polycarbonate (PC) | Optical clarity, impact resistance | Scratches easily; chemical sensitive |
| Acrylic (PMMA) | Optical clarity, easy to polish | Brittle, not for impact |
| PEEK | Aerospace/medical, –60 to +250°C, autoclavable | Very expensive (~$300/kg bar stock) |
| UHMW-PE | Wear resistance, chemical inert, food-safe | Difficult to machine to tight tolerance |
For micro-features in plastics — sub-millimetre walls, optical surfaces — see our micro-machining services.
Materials at a glance
A condensed reference for selecting a starting material based on your top requirement:
| Top requirement | Start with | Upgrade path |
|---|---|---|
| Cheap and good enough | 6061 aluminium | 7075 → 17-4PH |
| Strength-to-weight | 7075 aluminium | Ti-6Al-4V |
| Corrosion resistance | 316L stainless | Hastelloy C-276 / Monel |
| Wear resistance, low friction | Hardened 4140 + DLC coat | Tool steel (D2, A2) |
| Heat resistance (>500°C) | Inconel 625 | Inconel 718, Waspaloy |
| Electrical conductivity | C110 copper | Silver-plated copper |
| Thermal conductivity (heat sinks) | 6061 aluminium | C110 copper |
| Optical clarity | Acrylic (PMMA) | Polycarbonate |
| Food contact / sterilisation | 316L stainless | PEEK for plastics |
| Magnetic permeability needed | 1018 carbon steel | 4140 hardened |
| Non-magnetic (MRI rooms) | 316L stainless or Ti | Beryllium copper |
Material × finish compatibility
The chosen surface finish often constrains the material. Always check both before locking the design:
| Finish | Compatible materials | Not compatible |
|---|---|---|
| Type-II anodising (decorative + protection) | 6061, 6063, 5052 | 7075 (poor cosmetic finish) |
| Type-III hard anodising | 6061, 7075, 2024 | 5xxx series (some grades) |
| Bead blasting | Most metals and plastics | Anything that must remain optical |
| Powder coating | Aluminium, steel, stainless | Plastics (heat-sensitive) |
| Electropolishing | Stainless 316L, 304 | Carbon steel |
| Black oxide | Carbon and tool steels | Stainless (only specific grades) |
| PVD coating | Stainless, tool steel, carbide | Aluminium (substrate softens at coating temp) |
Read more about specific finishes in surface finishing and PVD coating.
よくあるご質問
- アルミ 6061 が圧倒的。バー材が安価で、速く切削でき、あらゆる標準仕上げを受け入れます。JLYPT の産業用作業の約 70％ は 6061 です。
- ほとんどは可能ですが、異なる工具で。チタンとニッケル系スーパーアロイは遅い切削速度と鋭い工具が必要です。マグネシウムは特殊な消火対策が必要です。
- 実用上：Ti-6Al-4V は疲労を含めると 7075 アルミをわずかに上回ります。純粋な引張強度対重量では現代のカーボンファイバー複合材が勝ります。
- アルマイトの色は合金、浴の化学、時間に依存します。同一バッチ = 良好な一致。異なるバッチ = 若干の変動。クリティカルな作業は単一バッチで処理する必要があります。
- 部品が湿気、塩、化学物質に継続的に晒される場合はステンレス。乾燥した屋内環境では亜鉛メッキ／塗装炭素鋼が遥かに安価です。
- 多くの場合いいえ。3D プリントされた Ti-6Al-4V 部品は CNC 加工されたものとは異なる材料グレードです。認証された航空宇宙や医療作業では、別途認定なしには代替できません。CNC vs 3D プリント比較を参照してください。
- はい — 一般的な合金 (6061、7075、304、316L、Ti グレード 5、Delrin、PEEK) を在庫しており、完全な材料試験報告書 (MTR) と適合証明書と共に特殊材料を調達できます。
最も安価な CNC 加工材料は？
同じ機械ですべての材料を加工できますか？
最高の強度重量比を持つ材料は？
アルマイト処理アルミはバッチ間で色が揃いますか？
ステンレスかメッキ鋼か？
3D プリント材料は CNC 加工と互換性がありますか？
JLYPT は私のために材料を調達できますか？
著者について
JLYPT Engineering Team
Senior CNC Application Engineers
Our application engineering team brings 15+ years of combined experience producing precision components for aerospace, medical, robotics and industrial automation customers.
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