Material selection is not a formality at the bottom of the drawing. The material affects the price, the machining time, the tolerances, the durability of the part, the corrosion risk and the availability of stock. The same shape made from C45, stainless steel and aluminium can have a completely different process and a completely different price.
The best decision starts with the function of the part: what it has to transmit, in what environment it works, whether weight matters, whether it will run against a bearing, whether it must resist moisture, chemicals or temperature.
Three common material choices
C45 steel
C45 is a popular structural steel for machine parts. It works well for shafts, sleeves, pins, spacers, clamping elements and parts that have to carry mechanical loads. It can be machined by CNC turning and CNC milling, and if needed it can undergo further heat treatment.
It is not a corrosion-resistant material. If the part works in moisture or in an aggressive environment, a surface protection or a different material must be considered.
Stainless steel
Stainless steel makes sense when corrosion would be a problem: the food industry, chemicals, humid environments, washdown, outdoor components, parts working close to water. It is more expensive and usually harder to machine than C45, but it can save on servicing and part replacement costs.
With stainless steel the grade selection needs care. A decorative part has different requirements than a component in contact with food, and different again from a part exposed to chemicals.
Aluminium
Aluminium is chosen where weight, good machinability, thermal conductivity, appearance or anodising matter. It is a common material for housings, plates, adapters, holders, covers and prototype parts.
It is not always automatically "cheap". With thin walls it can distort, and visual requirements or anodising can add cost.
Practical comparison
| Criterion | C45 | Stainless steel | Aluminium |
|---|---|---|---|
| Mechanical strength | Good | Good, grade-dependent | Lower than steel, but sufficient in many housings |
| Corrosion resistance | Low without protection | High | Good, especially with anodising |
| Weight | High | High | Low |
| Machinability | Good | More difficult | Very good, but watch for distortion |
| Material cost | Usually moderate | Higher | Variable, often higher than plain steel |
| Typical applications | Shafts, sleeves, pins | Food industry, chemicals, moisture | Housings, adapters, plates, prototypes |
Material vs the price of a CNC part
The material affects the price in four places:
- the purchase cost of the stock material,
- the cutting time,
- tool wear,
- the dimensional risk and inspection.
For a single piece the material difference may be less visible than the setup cost. For a series, the material and the cycle time start to dominate. More about the price structure in how much does a CNC part cost.
Decision framework: how to choose?
| If the priority is... | Consider first |
|---|---|
| Strength at a reasonable cost | C45 |
| Corrosion resistance | Stainless steel |
| Low weight | Aluminium |
| A machine part working in dry conditions | C45 or an alloy steel |
| A component that is washed or exposed to moisture | Stainless steel |
| A prototype with quick design changes | Aluminium or an easily available material |
What to include in the enquiry?
If the material is known, state the specific grade. If not, describe the requirements:
- the load,
- the working environment,
- contact with water, chemicals or food,
- weight requirements,
- the expected service life,
- whether a substitute is acceptable.
If in doubt, it is worth sending the documentation for a consultation. Nomatec can help assess whether the material matches the function, or whether it requires a change of geometry or a different machining technology.
Summary
C45, stainless steel and aluminium do not compete on price alone. Each material solves a different problem. C45 is universal for many machine parts, stainless steel protects against corrosion, and aluminium reduces weight and makes rapid prototyping easier. A good material choice shortens the quoting process and reduces the risk of changes in production.
If you have a part but are not sure about the material, send the design for a review. It is better to settle this before production than after the first failed batch.
FAQ
Is C45 a good material for machine parts?
Yes, C45 is a common choice for shafts, sleeves, pins and loaded components, as long as the corrosion resistance of stainless steel is not required.
When is stainless steel worth choosing?
When the part works in moisture, in contact with chemicals, in a food environment or wherever corrosion would be a risk for the process or for hygiene.
Is aluminium always the cheapest to machine?
Not always. Aluminium often machines quickly, but the material price, surface requirements, anodising and the risk of distortion can change the cost.
Does the material affect tolerances?
Yes. The material affects dimensional stability, stresses, distortion of thin walls and the choice of machining parameters.
What should I do if I do not know which material to choose?
The best approach is to describe the function of the part, the loads, the working environment and the budget. On that basis the material can be selected or alternatives proposed.
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