Wrong grade or temper
Strength, corrosion, or weldability miss the function — first articles fail or field life shortens when only a family name (e.g. “aluminum”) was quoted.
CNC Materials Guide for Machined Parts
Choose a material specification from load, environment, life and dimensional needs. Compare material families here, then confirm the exact grade, condition, stock and process fit for the drawing.
When this guide applies
Use this CNC materials guide when the material is not yet fully specified. Start with what the part must withstand: load and stiffness, temperature, medium, wear, mass, electrical or thermal behavior, and the required service life. Define those conditions before selecting a familiar grade.
Compare candidate materials across the whole route: available stock form, machining, heat treatment, finish, inspection and required records. A material that is easy to machine is not necessarily suitable for the environment, and a listed family does not imply current stock or a verified regulated-use grade.
After selection, pass the exact grade and condition to purchasing. Substitutions need the drawing owner’s agreement. Use the material machining pages below to check supplier and process fit; use functional tolerances and GD&T for acceptance requirements.
Selection example: a humid sliding fit. PA6/PA66 moisture uptake can change finished dimensions. Compare the selected nylon grade and conditioning state with an appropriate POM candidate using grade-specific moisture, wear and compatibility data. Ensinger's dimensional-stability guidance explains why nylon moisture uptake matters. A candidate with lower moisture uptake still needs load, temperature and mating-material checks.
Selection example: machining followed by welding. The strength of 6061-T6 starting stock is not automatically retained in the weld region. Hydro's 6061 alloy data identifies that condition change. If welding follows machining, state the required final material condition and review the welded assembly's design basis rather than carrying the starting-stock property into the final-part specification.
For each candidate, record the grade/condition, property source and test condition, limiting service condition, necessary secondary operations and reason for keeping or rejecting it. Compare confirmed total-route quotations after that screening; a material price alone cannot establish finished-part cost.
Machining by material
Aluminum CNC machining
6061, 7075, and related alloys for structural and enclosure parts.
Steel CNC machining
Carbon, alloy, stainless, and tool steels with process planning for hardness.
Copper CNC machining
Copper, brass, and bronze for conductivity and thermal parts.
Plastic CNC machining
POM, PEEK, PTFE, nylon, and other engineering polymers.
Metals and plastics at a glance
| Family | Functional questions | Specification to resolve | Machining / finish interaction | Evidence to request |
|---|---|---|---|---|
| Aluminum | Required stiffness, load, mass and environment | Alloy, temper and stock form | Stress release, thin-wall stability, clamping and finish response | Specified material records, final-fit and appearance requirements |
| Carbon / alloy steel | Load, hardness, wear and corrosion protection | Grade, supplied condition and heat-treatment state | Sequence, movement and final machining / grinding allowance | Material identity and treatment or hardness records where required |
| Stainless steel | Medium, concentration, temperature, cleaning and load | Exact grade and supplied condition | Work-hardening, burrs, passivation or other specified finish | Requested material and finish documentation; suitability confirmed for the use |
| Copper / brass / bronze | Conductivity, thermal duty, contact, wear or elastic function | Exact alloy and condition, including oxygen-free or composition requirements if applicable | Soft-face protection, burr control and plating | Material records and any specified conductivity or composition evidence |
| Engineering plastics | Load, temperature, humidity, medium, wear and insulation | Manufacturer grade, fillers, stock and conditioning | Clamping, movement, tool heat and measurement state | Grade-specific data and requested lot / conformity documentation |
| Specialty alloys | Requirements that the common families cannot meet | Exact specification, condition and supply evidence | Part-specific feasibility and secondary operations | Availability, documented properties and inspection scope confirmed before ordering |
Note
This is a qualitative selection framework. Property values depend on grade, temper, filler, product form, test method and environment. Obtain the applicable supplier data or material specification before using a value in design.
Choosing engineering plastics
| Family | Duty to define | Condition affecting selection | Dimensional / process questions | Before specifying |
|---|---|---|---|---|
| POM / acetal | Load, sliding wear, stiffness and environment | Manufacturer grade and operating temperature | Wall stiffness, edge quality and the required measurement state | Confirm compatibility and grade data for the actual duty |
| PTFE | Medium, sealing, friction, pressure and temperature | Virgin or filled grade and load over time | Clamping deformation, recovery and supported/free state | Verify the specific grade and functional limits |
| PPS / PEEK | Temperature, load, chemical exposure, wear and electrical needs | Manufacturer grade, fillers and duration of duty | Stress, workholding, annealing if agreed and final measurement | Use grade-specific data rather than a universal maximum temperature |
| Nylon PA6 / PA66 | Impact, wear, humidity and water exposure | Grade and moisture conditioning | Movement between machining, measurement and service | Agree the conditioning state and fit requirements |
| ABS / PC / acrylic / UHMWPE | Prototype, impact, appearance, transparency or wear needs | Exact material and grade; availability and route reviewed | Edges, stress, finish and geometry affect suitability | Confirm the selected grade and required documents before release |
Note
A family name is insufficient to set tensile strength or service temperature. Define the applicable test conditions, exposure duration and safety/design margins through the responsible engineering process. About ±0.05 mm is an existing plastic machining planning reference that still needs feature-specific DFM confirmation.
Selection by project priority
| Priority | Define first | Compare next |
|---|---|---|
| Weight and stiffness | Loads, allowable movement, space and joining method | Material properties together with geometry and stock form |
| Wear and motion | Contact, speed, load, lubrication, medium and life | Material grade, treatment, surface and replaceability |
| Corrosion or chemical exposure | Medium, concentration, temperature, time and cleaning | Grade-specific compatibility and any finish requirements |
| High temperature | Continuous / peak exposure, duration and load | Grade-specific data, expansion and the whole assembly |
| Electrical or thermal function | Required behavior and the relevant test or specification | Alloy/polymer grade, contact geometry, finish and records |
| Controlled or regulated application | The actual standard, material specification and evidence required | Grade and supply-chain documents reviewed for that stated scope |
| Cost and delivery | Quantity, finish, inspection, documentation and needed date | Complete route and confirmed availability, rather than stock price alone |
What goes wrong with an incomplete material spec
Metal tolerances on plastics
Feature geometry, material grade, temperature, moisture and restraint affect the achievable limit. Confirm plastic requirements through DFM instead of copying a metal tolerance.
Missing certs and lot linkage
MTR, CoC, or heat-lot paperwork requested after cut stock arrives adds delay. State required documentation on the RFQ.
Finish and substrate mismatch
Specify finish together with the actual substrate, protected surfaces and final dimensions. Review compatibility before quotation and agree any change with the drawing owner.
What to include in your material RFQ
- Function and environment: load, temperature, medium, humidity, wear and any relevant electrical or thermal requirement.
- Selected specification: exact grade, temper / condition, fillers and manufacturer grade for polymers; stock form or supply restrictions when needed.
- Drawing and acceptance: current revision and units, functional features, individual/general requirements and the state after heat treatment or finish.
- Supply and records: quantity, target delivery and requested material, traceability, conformity, finish or inspection documents. Confirm each document’s scope rather than treating a material name as a certification.
- Open decisions: candidate alternatives, missing data and the person authorized to approve a substitution or drawing change.
STEP and a marked PDF are recommended when available. Technical details and attachments are optional RFQ fields. See quote preparation and upload formats, then Upload CAD for DFM Review. With a complete RFQ, we typically respond within one business day; complex multi-process projects may take 1–2 business days.
Need a material recommendation with your quote?
Share the functional requirements, candidate material specifications and open questions so material and process fit can be reviewed together.