CNC machining of stainless and acid-resistant steel requires significantly greater process control than working with standard structural steels. These materials are commonly used in environments requiring high corrosion resistance, yet they present many technological challenges during machining.
We describe the basics of CNC machining technology for ‘standard’ steel in a separate article, whereas stainless and acid-resistant steels require a different approach to cutting parameters and process stability.
Process stability is key: tool selection, temperature control and minimising work hardening. Even minor parameter errors can degrade surface quality and shorten tool life.
At SIM Gdynia, we carry out projects requiring precision CNC machining of stainless steel for the medical, energy and marine sectors. In this article, we share our experience and highlight the key challenges associated with machining these materials.
Why CNC machining of stainless steel is challenging
Stainless steels have properties that can cause technical difficulties during machining. Understanding these phenomena is the basis for proper production planning.
Stainless steels are one of the most commonly machined groups of materials in industry – we describe this in more detail in our article on the most commonly used materials in CNC machining.
Low thermal conductivity
Stainless steels dissipate heat much less efficiently than aluminium or structural steels. As a result, a large proportion of the energy generated during machining remains in the tool and the chips.
If the machining parameters are incorrectly selected, the cutting edge quickly overheats, leading to blade deformation and a reduction in tool life.
An additional challenge is the hardening of the material during machining, which can hinder further cutting and accelerate tool wear.
Build-up on the cutting edge
Austenitic steels are ductile materials. During machining, small fragments of material can adhere to the tool’s cutting edge, forming what is known as build-up.
This alters the geometry of the cutting edge, which negatively affects surface roughness and the maintenance of dimensional tolerances.
The properties of austenitic steels, such as low thermal conductivity, a tendency towards work hardening and the formation of built-up edges on the cutting edge, significantly complicate the machining process. Understanding these phenomena allows for the correct selection of tools and CNC machining parameters, thereby reducing the risk of process instability.
Strategies for machining stainless steel
Stable CNC machining of stainless steels requires the use of appropriate tools, cooling and cutting parameters.
Tool coatings
When machining AISI 304 and 316 steel, tools coated with AlTiN or TiAlN are often used, as these coatings offer high temperature resistance.
These coatings form a protective layer of aluminium oxide, which acts as a thermal insulator and protects the cemented carbide from degradation.
High-pressure cooling
During deep milling, standard cooling may not reach the cutting zone directly. The use of high-pressure spindle cooling enables effective chip removal and temperature stabilisation.
Cutting parameters
The selection of cutting parameters for stainless steel differs significantly from those used for structural steels.
| Machining parameter | Carbon steel (e.g. S235) | Stainless steel / acid-resistant steel |
| Cutting speed (Vc) | 200–300 m/min | 60–120 m/min |
| Feed per tooth (fz) | higher | moderate and stable |
| Process stability | high | crucial for quality |
Lower cutting speeds are necessary to limit tool overheating and ensure process stability.
Stable CNC machining of stainless steels requires the right choice of tools, effective cooling and appropriate cutting parameters. Only the combination of these elements allows for tool life and consistent part quality.
Control of material chemical composition
In projects carried out for the energy or medical sectors, material documentation alone does not always provide full certainty regarding the material’s composition.
That is why at SIM Gdynia we verify the steel grade using a spectrometer, which allows us to quickly determine the content of key elements such as chromium, nickel and molybdenum.
One of the differences between these steel grades is the presence of molybdenum in the latter, which significantly increases corrosion resistance in a chloride environment.
We discuss this method of material testing in more detail in our article on analysing the chemical composition of materials using a spectrometer.
The use of stainless steels in demanding industries
High corrosion resistance and good mechanical properties mean that stainless steels are widely used in many demanding industrial sectors.
Medical industry
In the manufacture of surgical instruments and medical equipment components, surface quality is crucial. Very low roughness values are often required to enable subsequent finishing processes.
Marine and energy industries
In a marine environment, components made of stainless steel are exposed to chlorides, which can cause pitting corrosion (a type of corrosion in which the metal is destroyed locally, forming small, deep holes rather than uniform wear across the entire surface).
Therefore, when machining components for the marine and energy industries, we pay particular attention to surface integrity, cutting parameter stability and material quality control.
Their high corrosion resistance and stable mechanical properties mean that stainless steels are widely used in the medical, marine and energy sectors. In these sectors, surface quality and the stability of the CNC machining process have a direct impact on the operational safety of components.
Summary
CNC machining of stainless and acid-resistant steels requires appropriate technological preparation, stable cutting parameters and material control.
These materials are commonly used in the medical, energy and marine industries, where even minor deviations in quality can lead to serious operational problems.
That is why at SIM Gdynia we place great emphasis on both CNC machining technology and the control of materials and finishing processes, which ensure the durability and reliability of the components we produce.
Does your project involve stainless steel or acid-resistant steel components?
Please contact our technical team.