CNC machining materials

We machine these metals by CNC milling and turning. We also cut and bend sheet metal in aluminum, stainless steel, mild steel, brass and copper. The exact grade is confirmed in your quote.

The CNC milling and CNC turning pages explain how each process handles these metals.

Each metal family has its own numbering system, kept by a standards body. Reading the first digits tells you what the alloy is made of and how it behaves.

1. 01

   Aluminum: the Aluminum Association series

   The four-digit wrought aluminum system was adopted in 1954 and is maintained by the Aluminum Association. The first digit gives the main alloying element.

   Series	Main alloying element	Heat-treatable?
   1xxx	Commercially pure aluminum (99% or more)	No
   2xxx	Copper	Yes
   3xxx	Manganese	No
   4xxx	Silicon	Some alloys
   5xxx	Magnesium	No
   6xxx	Magnesium and silicon	Yes
   7xxx	Zinc	Yes
   8xxx	Other elements, including lithium	Varies

   The 2xxx and 7xxx series reach the highest strengths, 6xxx is easy to extrude and machine, and 5xxx welds well (ASM International).

2. 02

   Carbon steel: the SAE and AISI four-digit system

   Mild steels follow the SAE system, set out in SAE J403 (SAE International). The last two digits give the carbon content in hundredths of a percent (PMPA).

   • 10xx: plain carbon steel.
   • 11xx: resulfurized, with sulfur added for easier machining.
   • 12xx: resulfurized and rephosphorized, for free machining.
3. 03

   Stainless steel: the AISI series

   Stainless grades are grouped by their structure (SSINA):

   • 200 and 300 series (austenitic): excellent corrosion resistance, non-magnetic when annealed, not hardened by heat treatment.
   • 400 series (ferritic and martensitic): magnetic; the martensitic grades can be hardened.
   • Precipitation-hardening (PH) grades: strengthened by aging, used for parts such as valves and gears.
4. 04

   Tool steel: the AISI letter groups

   Tool steels are grouped by letter, by how they harden or what they’re for (ASM International):

   Group	Meaning	Typical use
   A	Air-hardening, cold work	Dies, punches, gauges
   D	High-carbon, high-chromium	Wear-resistant tooling
   H	Hot work	Tools that run hot
   M	Molybdenum high-speed	Cutting tools
   O	Oil-hardening, cold work	General tooling
   S	Shock-resisting	Tools under impact
   W	Water-hardening	Simple, low-cost tooling

5. 05

   Titanium: ASTM grades

   ASTM B348 covers titanium bar (ASTM International). Grades 1 to 4 are commercially pure titanium, and Grade 5 is the Ti-6Al-4V alloy.

6. 06

   Copper and brass: UNS numbers

   The Copper Development Association keeps the UNS copper numbers: coppers run from C10100 to C15999, and brasses from C20000 to C49999 (CDA). C2xxxx are copper-zinc brasses and C3xxxx are leaded brasses for easier machining (CDA brasses).

This table gives a quick, sourced comparison. Use it to narrow the choice, then let the drawing and the quote settle the grade.

Brass and aluminum are generally the easiest metals to machine, and stainless steel and titanium among the hardest. Published machinability ratings can look contradictory, because they use two different baselines. For steels, the baseline is a free-machining carbon steel. For copper alloys, C36000 brass is rated 100 (CDA). A “100” on one scale isn’t the same as on the other.

Free-machining grades, such as leaded brass or resulfurized steel, cut faster but give something up in return. Our CNC turning page explains those trade-offs.

Start from what the part has to do:

• Light and stiff, with a good finish: aluminum, usually 6xxx; 7xxx where strength matters more.
• Exposed to water, chemicals or washdown: 300-series stainless steel.
• Low cost, welded or painted: mild steel.
• Wear, impact or heat in service: tool steel, hardened after machining.
• Highest strength for its weight: titanium.
• Threaded fittings and fine detail: brass.
• Carries current or heat: copper.

Not sure? Send the drawing with the part’s job described, and our engineers will suggest a metal in the DFM notes.

Not every finish suits every metal. These are the matches that matter most:

Our full list of finishes:

• As-machined
• Bead blasting
• Anodizing Type II
• Anodizing Type III (hard anodizing)
• Powder coating
• Brushing
• Passivation
• Electroplating (nickel, chrome, zinc)
• Painting

Put the material, the series or grade, and the temper or condition in the title block, for example “Aluminum 6061-T6” or “Stainless steel 316”. If a standard applies, such as ASTM B348 for titanium bar, name it. If you can accept an equivalent grade, say so, and we’ll confirm the exact grade in the quote.

Every order comes with a material certificate (mill cert) that traces the metal to the batch it came from, along with standard QC inspection and ISO 9001 documentation:

• Standard QC inspection
• Material certification (mill certs)
• ISO 9001 documentation