CNC Machining Materials — How to Choose the Right Metal for Your Part
Selecting the right cnc machining materials before you send a CAD file saves time, cuts cost, and avoids production surprises. At QDJ-PROTOTYPE, we machine thousands of parts every month — from one-off prototypes to low-volume production runs — and the single most common question from engineers is: “What material should I use?”
This guide is not a generic textbook. It is what we actually stock, machine, and recommend on our shop floor in Dongguan. You will also see where spending a little extra on material makes sense, and where a standard grade gets the job done.
What CNC Machining Materials We Stock and Machine Every Day
We keep raw stock of the grades most requested by our hardware, medical device, and robotics customers. This is not a distributor catalogue — these are the cnc machining materials we pull from our rack every morning:
- Aluminum 6061-T6 — general-purpose, good strength-to-weight, anodizes well
- Aluminum 7075-T6 — aircraft-grade, higher strength, less corrosion resistance
- Stainless Steel 304 — food-grade, excellent corrosion resistance, non-magnetic
- Stainless Steel 316 — marine-grade, better pitting resistance than 304
- PEEK — high-performance thermoplastic, replaces metal in high-temp applications
- Delrin (POM) — tight-tolerance acetal, excellent for gears and sliding parts
We also source brass C360, titanium Grade 5, and PTFE on demand for repeat customers — but we do not pretend to “stock everything.”
Aluminum: The Workhorse (and When to Upgrade)
At least 70% of our CNC work is aluminum. It machines fast, holds tolerances well, and anodizes into a clean professional finish. For brackets, housings, heat sinks, and most general-purpose parts, 6061 is hard to beat at about $3–5/kg.
But here is what most online guides will not tell you: if your part is thin-walled (under 2 mm) and needs tapped holes, 6061 can gall during machining. We have seen it. For those jobs, we often suggest 7075 — about 50% more expensive but noticeably easier to machine cleanly at thin sections.
When to pick 7075 over 6061: thin walls under 2 mm, tapped holes M3 or smaller, or applications where a few extra grams of weight savings matter. Our free DFM review flags these material risks before we cut anything.
Stainless Steel: When Corrosion and Cleanliness Matter
We machine 304 and 316 regularly for medical device prototypes, food-processing components, and marine hardware. Compared to aluminum, stainless runs slower, costs about 3× more in raw material, and requires sharper tooling — but the pay-off is real corrosion resistance and a premium surface finish.
Rule of thumb: use 304 for indoor or food-contact parts; use 316 if saltwater, sterilisation chemicals, or implant-grade cleanliness are involved.
Engineering Plastics: Not “Just Plastic”
PEEK and Delrin are cnc machining materials we treat with as much care as aluminum. PEEK replaces metal in high-temperature, chemical-resistant, or electrically insulating applications. It costs roughly $80–120/kg and requires annealing after machining to relieve internal stress — if your supplier skips this step, the part will warp later.
Delrin is our go-to for gears, bushings, and sliding mechanisms. It holds tolerances as tight as ±0.02 mm and does not absorb moisture like nylon — meaning dimensions stay stable from our shop floor to your assembly line.
How We Help You Choose (Before You Commit)
Every part we quote gets a free 5-point DFM review. One of those five points is material assessment: is your selected grade available in the stock size you need? Can we hold your specified tolerance in that material? Is there a more cost-effective option that meets the same functional requirement?
You do not need to be a materials engineer to get a good result. You just need a CAD file and a quick conversation with our team.
Send Us Your CAD — We’ll Handle the Material Decision
Upload your STEP or IGES file through our Request a Quote page, or email us at info@qdj-prototype.com. We will return a free DFM review covering material, tolerances, and tool access — typically within one business day.
QDJ-PROTOTYPE is the CNC machining brand of Dongguan Qindejing. ISO 9001:2015 certified. 3/4/5-axis. Free DFM. Real shop floor, real materials, real people.
