Engineering Materials for CNC Machining Services
We machine a wide range of engineering materials for precision CNC components used in automation, semiconductor, medical, optical and industrial applications. The grade you write on the drawing is not a detail — it sets the cutting speed, the number of setups, the inspection method and the price, in that order.
Why material selection decides the quotation
Material selection is a critical factor in CNC machining performance, cost and product reliability. Change the grade on an unchanged drawing and the cutting speed can move by a factor of fifteen, tool life by a factor of ten, and the quotation by two to four times. That is why the material decision is not a line on a spec sheet — it is the first thing a process plan has to settle, and the reason a quotation at XS Precision comes with a recommendation rather than only a price.
Six material families we machine every week
Each family below has its own page, and each page is written the same way: grades, what the family is genuinely good at, where it typically ends up, and the point where it fights back. The table is a starting point; the rows after it are the honest version. All six families are machined in-house at Shenzhen XS Precision, on the same floor as the inspection equipment.
| Material | Common grades | Typical use | Page |
|---|---|---|---|
| Aluminum Alloys | 6061 · 6082 · 7075 | Automation components, structural parts, electronic housings | go → |
| Stainless Steel | 303 · 304 · 316 · 17-4PH | Medical devices, industrial equipment, marine components | go → |
| Carbon Steel | C45 · alloy steel | Mechanical structures, load-bearing parts | go → |
| Brass & Copper | CuZn39Pb3 · C11000 | Electrical components, precision fittings, conductive parts | go → |
| Titanium | Ti-6Al-4V (Grade 5) · Grade 2 | Medical implants, aerospace components, high-performance parts | go → |
| Engineering Plastics | POM · PEEK · PTFE · PA (Nylon) | Insulating parts, wear components, precision mechanical systems | go → |
Aluminum Alloys
The default choice for anything that has to be light, stiff enough and cheap to produce in volume. 6061-T6 is the workhorse; 6082 is the European equivalent with slightly better strength; 7075 is the aerospace grade and the one that punishes you for the extra zinc.
Stainless Steel
Chosen for corrosion resistance and cleanliness rather than for strength alone. 303 is the free-machining grade and the only one that behaves like a normal material; 304 and 316 are the ones customers ask for and the ones that work-harden in front of you.
Carbon Steel
Where stiffness, mass and cost matter more than corrosion resistance. C45 and alloy steels take a heat treatment and hold it, which is why machine frames, shafts and load paths are still made from them.
Brass & Copper
The easiest family on this list to machine and the one that carries current. Free-cutting brass produces short chips, takes a mirror finish and holds tight tolerances on a lathe all day.
Titanium
Bought for the ratio, not the number: about 60% of steel’s weight with comparable strength, and a stable oxide layer that survives seawater and body fluid. It is also the most expensive material on this page to cut.
Engineering Plastics
POM, PEEK, PTFE and PA replace metal where the part has to insulate, resist a chemical, run without lubrication or stay light. Tolerances are achievable, but they only mean something if the measurement conditions are stated.
How each material behaves at the cutting edge
Every material behaves differently during CNC machining. Aluminum allows high-speed machining with excellent precision; stainless steel needs work-hardening control; titanium makes heat management critical; plastics need deformation control. This is the part of the page worth reading twice, because it is the difference between a quotation and a guess. It is also why XS Precision quotes a cutting strategy rather than an hourly rate.
Surface finishes and what they do to your tolerance
Surface finish is specified for a reason — wear, corrosion, appearance, or a sealing face — and almost every finish changes the part after the last machining cut. Anodizing and plating grow the workpiece; electropolishing removes material; black oxide barely moves anything but introduces hydrogen that has to be driven out. The finishing operation belongs in the tolerance chain, and the drawing should carry the pre-finish size, and that line is written on every XS Precision process plan before the part is scheduled.
| Process | Alu | Stainless | Steel | Brass | Ti | Plastics | Effect on size |
|---|---|---|---|---|---|---|---|
| Anodizing, sulfuric | ● | ○ | ○ | ● | ● | ○ | Adds 5–25 µm per surface; dielectric, so mask any earth path |
| Hard anodizing | ● | ○ | ○ | ○ | ● | ○ | Adds 25–50 µm per surface, grows inward and outward; 7075 goes grey-brown |
| Electropolishing | ● | ● | ● | ○ | ● | ○ | Removes 5–20 µm; deburrs and passivates at the same time |
| Passivation, ASTM A967 | ○ | ● | ○ | ○ | ● | ○ | No dimensional change; removes free iron from the surface |
| Nickel plating, electroless | ● | ● | ● | ● | ● | ○ | Adds 5–25 µm per surface, uniform on internal bores |
| Black oxide | ○ | ● | ● | ● | ○ | ○ | Adds about 1–2 µm; must be de-embrittled after pickling |
| Bead blasting | ● | ● | ● | ● | ● | ● | Removes nothing measurable but raises Ra, typically 1.6 to 3.2 µm |
| Polishing / buffing | ● | ● | ● | ● | ● | ● | Hand operation; removes material at edges more than on faces |
| PVD / DLC coating | ● | ● | ● | ○ | ● | ○ | Adds 1–5 µm; needs a mirror substrate to look right |
Where each material ends up, and what tends to bite
Materials are widely used across automation systems, semiconductor equipment, medical devices, optical systems, robotics and industrial machinery — and the same grade causes different trouble in each of them. The four problems below are the material-related machining issues we see most often, and every one of them is cheaper to catch in the review than at first article — which is why the review at XS Precision happens before the quotation, not after it.
Questions we get asked before a materials decision
Short answers from the Material Expertise desk to the questions that come up most often when a drawing first arrives. If the question you have is not here, it is usually answered on the material page or in the selection guide — and if it is not, ask it in the quotation and we will answer it in writing.
Which material is best for CNC machining?
It depends on the application, the strength requirement and the cost target, and those three usually disagree. The honest answer is that no material is best in general: aluminum is best for low weight and fast production, stainless for corrosion and cleanability, carbon steel for stiffness per unit cost, brass for conductivity and easy cutting, titanium for strength-to-weight and body compatibility, and engineering plastics for insulation and chemical resistance. Send the drawing and the service conditions and we will tell you which family wins on your part.
Do you help with material selection?
Yes. Material selection is part of the quotation, not an extra service: before we price a part we check the grade against the loads, the environment, the finishing operation and the inspection method, and we tell you if the grade on the drawing is going to cost you more than it needs to. If a substitution would work, you get the reason and the saving in the same message.
Can you machine PEEK and titanium?
Yes, both. PEEK and the other engineering plastics are machined on the same machines with dedicated tooling and controlled clamping; titanium is machined with high-pressure coolant and a tool life budget agreed before the run. Both materials cost more in time than in stock, so the quotation shows which one is driving the price.
Should I specify the grade or leave it to you?
Specify the grade if the part is regulated, qualified or already in service, because the change has to go through your own approval. Leave it open if the only requirement is functional — a drawing that says “stainless” instead of “316L” often means the customer has not decided, and that is a good moment to ask the question.
Why does a material change move the price so much?
Because it changes the cutting speed, the tool life and the number of operations. Titanium at 20–40 m/min against aluminum at 300–600 m/min is machine time before anything else, and materials that work-harden also add tool changes and sometimes an extra finishing pass.
Can you supply the material certificate?
Yes. Material is booked in with its heat lot and certified to EN 10204 3.1, and the lot follows the batch through the shop. Heat treatment, anodizing, plating and passivation each add their own process certificate, so the documentation package matches the parts months later.
What if the material on my drawing is wrong?
We say so before quoting rather than after delivering. The common cases are a free-cutting brass specified for a wet environment, 304 specified where 316L is needed, or an aluminum wall that is too thin for the tolerance called out. Each of those is cheaper to fix on the drawing than on the shop floor.
Need help choosing the right material?
Upload your drawing and the XS Precision engineering team will recommend the best material based on performance, cost and manufacturability. If the grade on the drawing is already right, we will say so and quote it; if a different one would serve you better, you will get the reason with the price.