Stainless Steel CNC machining

There is a common misconception that products made from stainless steel don’t rust. However, stainless steel can indeed rust, although it is relatively resistant to rusting in ordinary environments. It has a thin and tightly adhering oxide layer on its surface, which acts as a protective film, preventing oxygen atoms and external corrosive factors from affecting the inner surface for a certain period. This maintains a state of relative resistance to oxidation and rust.

Nevertheless, when the protective film on the surface of stainless steel is continually damaged, oxygen atoms from the air or liquids can infiltrate, and iron atoms from the metal can leach out, leading to chemical reactions that form a loose, iron oxide layer (rust). Over time, this corrosion process results in rust on the surface of stainless steel. 

During the CNC machining of stainless steel, the surface may accumulate dust and particles of other metal elements or environmental contaminants. In a humid environment, this can lead to electrochemical reactions on the stainless steel surface, breaking down the original protective film. This is known as electrochemical corrosion and is one of the factors that cause stainless steel to rust.

If the environment in which stainless steel is machined, stored, or transported contains a significant amount of sulfides, chlorides, or other acidic ions and comes into contact with humid air or moisture, it can create an acidic liquid. Over time, this can also cause chemical corrosion of the stainless steel, leading to rust.

To prevent stainless steel from rusting, manufacturers and storage facilities should take effective preventive measures, which may include the following suggestions (for reference only):

During the machining of stainless steel, avoid using the same machining equipment for other metal materials to prevent contamination from metal dust.

Before surface treatment, clean the finished stainless steel products to remove dust, dirt, oil stains, and rust spots from the surface.

If there are rust spots or traces on the surface of stainless steel materials before machining, perform rust removal (recommended environmentally friendly rust remover that does not corrode the stainless steel surface, such as VCI-708 organic acid-based rust remover).

Ensure that the cutting fluids, mechanical oil, human sweat, and airborne dust on the stainless steel surface are thoroughly cleaned to avoid affecting subsequent surface treatments and maintain cleanliness for storage and transportation (recommended VCI-600E biodegradable and environmentally friendly cleaning agent, a water-based product with plant-based components, safe and effective for cleaning surfaces below 200μm).

For stainless steel storage and transportation, use rust-proof packaging and add desiccants inside the packaging. This helps prevent the formation of condensation on the stainless steel surface, reducing the risk of corrosion in a closed environment for an extended period (recommended VCI-2000 rust-proof bags and VCI desiccants).

Milling stainless steel typically requires a spindle speed ranging from 200 to 1000 RPM. In general, the specific required spindle speed typically depends on different materials ofcutting tool, the dimensions of the workpiece, and the machining requirements.

The feed rate for milling stainless steel should be between 0.05 to 0.2 mm per tooth of the cutter. The exact value depends on the required surface roughness, spindle speed, and the material of the cutting tool.

Characteristics of Milling Stainless Steel:

Stainless steel is a common material with a high level of machining difficulty. It has strong adhesion and melting characteristics, causing chips to adhere to the cutter’s teeth, which deteriorates the cutting conditions. During up-milling, cutter teeth initially slide on the hardened surface, increasing the tendency for work-hardening, leading to more significant impacts and vibrations during milling, making the cutter teeth more prone to wear.

Milling Stainless Steel Techniques:

When milling stainless steel using a machining center, the selected milling cutter’s blade should be extremely sharp to better withstand the impact forces generated during milling. Additionally, the chip groove of the milling cutter should be wide. When machining stainless steel, you can choose a vertical milling cutter, cylindrical milling cutter, or helical milling cutter. The helix angle of the cutter can be set to 45°. Moreover, the rake angle of the milling cutter should be adjusted to reach 27° or more.

CNC Machining Precautions:

When aligning the workpiece, use hand rotation of the chuck or low speed to align; avoid high-speed alignment.

When changing the spindle’s rotation direction, stop the spindle first before changing the direction suddenly.

When mounting or dismounting the chuck, only use hand rotation to drive the spindle’s rotation; do not forcibly loosen or tighten directly, and place a wooden block on the bed surface to prevent accidents.

Tool installation should not extend too far, and shims should be flat, with a width matching the cutter’s bottom width.

Do not use reverse turning of the spindle to brake during work.

The significant price difference between Stainless steel 304 and Stainless steel 201 can be attributed to three main factors:

Nickel Content: 304 stainless steel contains a higher proportion of nickel, typically ranging from 8% to 10.5%, whereas 201 stainless steel contains only 3.50% to 5.50% nickel. Nickel content directly affects a material’s corrosion resistance. Thus, 304 stainless steel exhibits superior corrosion resistance and oxidation resistance.

Ductility: 201 stainless steel has a higher carbon content, around 0.15%, while 304 stainless steel has a carbon content of approximately 0.07%. This makes 201 stainless steel relatively harder, while 304 stainless steel is more ductile. Scratches on 201 stainless steel surfaces tend to be more noticeable compared to 304 stainless steel.

Brightness: 201 stainless steel contains a higher manganese content, around 5.5% to 7.5%, while 304 stainless steel has lower manganese content, not exceeding 2%. In terms of appearance, 201 stainless steel tends to have a darker color, while 304 stainless steel is brighter. This difference in brightness is one of the factors contributing to the higher price of 304 stainless steel.

For improved machining performance, 303F stainless steel is a good choice. It offers excellent machining properties and can help address various machining challenges. If you are working with materials that are too hard or have poor machinability, it can lead to issues such as reduced product quality and increased costs. 303F stainless steel is the solution because it features a higher sulfur content, enhancing its machining performance. It reduces burrs and other issues during machining, leading to higher production efficiency and better product quality. Whether you’re machining bolts or nuts on automatic lathes, 303F stainless steel’s advantages will shine.

440C stainless steel is favored for its wide range of applications. It offers excellent dimensional stability at high temperatures, making it suitable for high-temperature bearing steel. Its excellent straightness, down to around 0.005mm, ensures precision and stability in products. Moreover, 440C stainless steel can be used to manufacture high-quality cutting tools, such as medical scalpels, scissors, nozzles, bearings, and more. It possesses good hardness and wear resistance, making it a reliable choice for various tasks.

430F stainless steel is an excellent choice for automatic lathe machining. It offers outstanding high-temperature dimensional stability and is ideal for machining bolts and nuts. With excellent straightness, it ensures high precision and surface finish. The 430F stainless steel’s machining performance is superb, making it a reliable choice for applications that demand high precision, straightness, and surface finish.

In engineering design, both 303 and 304 stainless steel, which belong to the austenitic stainless steel 300 series, are commonly used. However, there are significant differences between them. 303 stainless steel contains added sulfur, reducing its corrosion resistance. In terms of machinability, 303 stainless steel is favored for its excellent performance and is used in parts that require extensive machining. It has better machinability and is easier to work with. On the other hand, 304 stainless steel is more challenging to machine but offers superior overall mechanical properties. Thus, 304 stainless steel is more suitable for applications that demand high surface finish and cutting requirements. In terms of corrosion resistance, 304 stainless steel generally outperforms 303 stainless steel. Its lack of sulfur makes it more resistant to corrosion, especially in harsh environments like seawater and chloride exposure.