Introduction

Stainless Steel CNC Machining can be summarized as an art of precise and resistant parts manufacturing, which happen to be resistant to corrosion as well. The process is very advanced starting with a CAD/CAM software to design the part geometry and CAM software that line-up the design with G-codes and M-codes for CNC machines. 

The article goes into details on various machining techniques comprising CNC milling, CNC turning, and even the advanced methods through the use of laser cutting and EDM. Additionally, machines are elaborated additional on staining steel grades utilized inside the machine shop and the properties, uses, and machining challenges occurred in them. 

Consequently, a thorough review emphasizes the value of selecting an appropriate stainless steel grade in the overall machining process for a superior performance and successful project.

Metal CNC Turning Service
Stainless Steel CNC Machining-RALLY

What is Stainless Steel CNC Machining?

It is the most precise method of manufacturing corrosion-resistant and long lasting SS parts using computer numerical control machines.

Initially, the parts geometry is designed with the help of CAE/CAD software. After that, CAM software transforms the design into machine-readable code (G-codes and M-codes). Analyzing the code further, the CNC machine moves the cutting tool precisely and removes the material from the stainless workpiece.

Stainless Steel Machining Processes:

  • CNC Milling and Threading:

Milling is a primary process for stainless steel. It employs rotating tools to cut a stationary workpiece. The choice of tool and speed is crucial to avoid rapid wear. Threading allows for the creation of screw mounts and fasteners on steel parts, essential for pipes and tubes.

  • CNC Turning:

In turning, a stationary tool shapes a rotating workpiece. This method is prevalent for austenitic stainless steel, emphasizing minimal tool overhang to enhance machining efficiency.

  •  CNC Drilling:

Drilling, often combined with other techniques, creates holes in the workpiece. It's fundamental for adding screw holes or for assembly purposes, especially in stainless steel.

  • Laser Cutting:

Laser cutting melts and removes metal using an amplified light beam. It is suitable for thin stainless steel sheets. This process prevents tool wear but is costly and demands skilled operators.

  • Electrical Discharge Machining (EDM):

EDM uses electrical discharge to melt metal with high voltage and frequency. It's a specialized method limited by the thickness of stainless steel it can process.

  • Water jet Cutting:

This method uses high-pressure water to erode and cut through thick stainless steel sheets. While effective, it's less suitable for grades with low corrosion resistance due to potential adverse effects.

Check out our related blog post to learn more about the tooling process.

Related: What is CNC Machining?

Stainless Steel Types Used in CNC Machining:

Stainless Steel is not a single alloy, as it features over 150 grades. The grades fall under several classes, and each class presents distinctive properties and applicable traits. Let us walk through four common types that are frequently adopted in CNC machining.

1. Austenitic Stainless Steels:

The class (303, 304, 316, 310 and 321 grades) exhibits high corrosive resistance and toughness but it is not capable of hardening by heat treatment. Non-magnetic feature is due to components including nickel and manganese. The weldability of austenitic steels is high and they are ductile, with chromium levels up to 18 %.

Properties:

  • Corrosion Resistance: Very high
  • Heat Treatable: No
  • Magnetic: Non-magnetic
  • Toughness: Very high
  • Ductility: Very high
  • Welding Ability: High
  • Chromium Content: 18% on average
  • Nickel Content: 8% to 12%

Applications:

  • Household products (e.g., washing machines, dishwashers)
  • Automobiles
  • Aerospace components
  • Architectural structures

Challenges:

  • Low resistance to stress corrosion cracking

2. Ferritic Stainless Steels:

Ferritics are magnetic and chemically resistant family of metals, from which a number of grades including 409, 430, 430LI, 434, 439, 442, and 444 represent a few examples. They have the worst weldability but they have a good anti-stress cracking property because of the presence of chromium..

Properties:

  • Corrosion Resistance: Very high
  • Heat Treatable: No
  • Magnetic: Magnetic
  • Toughness: Medium
  • Ductility: Medium
  • Welding Ability: Low
  • Chromium Content: 10.5% to 30%
  • Nickel Content: Usually nickel-free

Applications:

  • Kitchenware
  • Automotive parts
  • Industrial tools

Challenges:

  • Limited weldability
  • Moderate toughness and ductility

3. Duplex Stainless Steels:

Combining the features of both austenitic and ferritic steels, duplex grades (2101 LDX, DX2202, 2304, 2205, 2507, and Zeron 100) types present a high corrosion resistance and are also heat-treatable. They are magnetic in their structure, have high toughness and medium to high ductility.

Properties:

  • Corrosion Resistance: Good to very high
  • Heat Treatable: Yes
  • Magnetic: Magnetic (due to ferritic structure)
  • Toughness: High
  • Ductility: Medium to high
  • Welding Ability: High (with nitrogen)
  • Chromium Content: 18 % to 30 %
  • Nickel Content: 1 % to 9.5 %

Applications:

  • Heat exchangers
  • Piping systems
  • Commercial equipment

Challenges:

  • Requires careful handling during welding to maintain properties

4. Precipitation-Hardened Stainless Steels:

The age-hardening process results in a substantial increase in the yield strength of the PH stainless steels (martensitic PH, semi-austenitic PH, and austenitic PH), which can be four times higher than those of the austenitic grades. Their special structure facilitates a variety of features and usages, which makes them very flexible in rigorous settings.

Properties:

  • Corrosion Resistance: Variable
  • Heat Treatable: Yes
  • Magnetic: Variable
  • Toughness: High (after hardening)
  • Ductility: Variable
  • Welding Ability: Specific to alloy
  • Unique Additions: Elements like titanium, copper

Applications:

  • Marine constructions
  • Aircraft components
  • Nuclear plants
  • Chemical industry

Challenges:

  • Complex heat treatment process to achieve desired properties

Selecting the Right Grade of Stainless Steel for Machining

Selection of the most suitable grade of stainless steel for CNC machining is a basic aspect that defines the success of any project. The grade directly influences the entire machining process, the resultant performance of parts, and durability. The starting point in making an informed choice thus starts with the understanding of the distinct attributes of any class of stainless steel.

Think of corrosion resistance, strength, and the environment that is to be used in the grade of stainless steel. Austenitic steels are much liked due to their combination of ductility and weldability for their use in such parts that need high corrosion resistance. Ferritic steels offer good resistance and have magnetic properties, and they are appropriate in applications where such features are beneficial.

At the same time, duplex stainless steels combine the properties of both austenitic and ferritic grades in the material, thus providing a balanced solution for high strength and corrosion resistance. While precipitation-hardened steels offer higher yield strengths if applications require high strength and, therefore, can be applied in areas with high stress.

Hence, decision-making comprises evaluating the component application, its environmental conditions where the component is to be used, and the desired longevity that is being questioned. Once this is done, the matching of these requirements with the properties of the grade of stainless steel ensures the performance and life of the component.

Rally Precision has expertise in CNC machining. We understand the importance of material selection. We assist clients in choosing the right stainless steel grade. By considering all critical factors, we ensure the project's success.

Grade of Stainless Steel for Machining

Stainless Steel CNC Machining vs Aluminum CNC Machining

Both materials are used in a range of industries to develop durable parts. Stainless steel is an alloy of iron and carbon, but chromium, nickel, and molybdenum improve its properties. However, aluminum alloys with magnesium, zinc, and copper have different properties for specific uses.

Property

Stainless Steel

Aluminum

Elemental Composition

Iron, Carbon, Chromium, Nickel

Magnesium, Zinc, Copper

Corrosion Resistance

Excellent

Excellent

Electrical Conductivity

Low (<5%)

High (61%)

Material Hardness

80 to 700 (Brinell)

Less than 20 (Brinell)

Thermal Conductivity

Lower, but stable at high temps

Higher, but decreases at high temps

Weight

Heavier (8.0 g/cm3)

Lighter (2.7 g/cm3)

Durability

Higher

Lower

Machinability

More challenging

Easier

Weldability

Good

Requires expertise

Tensile Strength

Higher

Lower

Table 1. Comparison Between Stainless Steel and Aluminum

Related: CNC Machining Aluminum: Comprehensive Guide & Expert Tips

Custom Stainless Steel Parts
CNC Machining Aluminum Prototyping

Benefits of Stainless Steel in CNC Machining

·       High Tensile Strength

Superior tensile strength is found in stainless steel over mild steel, brass, and aluminum alloys. Heavy-load parts need tensile strength, the maximum stress a material can withstand before breaking. Stainless steel component strength allows for significant bending and rolling without failure, making it ideal for critical structural applications.

·       High Corrosion Resistance

The corrosion resistance of stainless steel is a major benefit. Chrome forms a protective layer on steel when exposed to oxygen, causing this resistance. Applications exposed to harsh environments benefit from this trait.

·       Cryogenic Resistance

At very low temperatures, some stainless steel grades remain stable and mechanical. Austenitic stainless steel is tough and tensile in sub-zero temperatures.

·       Biocompatibility

Biocompatibility makes stainless steel safe for medical use. Its inertness and corrosion resistance prevent tissue damage. It is used for surgical implants, medical devices, and instruments.

What are the Recommended Surface Finishes?

Getting the desired finish for your machined component is not only important for aesthetic purposes but also for the proper functioning. The benefits of each method vary by aesthetic preference and application.

·       Polishing

Polishing stainless steel parts gives them a high-gloss finish, from #3 or #4 to #8 mirror. Mirror finishes are popular because they reflect light and make parts shine. For applications that value aesthetics, this finish enhances the material's natural beauty.

·       Pickling and Bead Blasting

Bead blasting and pickling create a matte finish. The procedure entails bead blasting to roughen the surface before chemical cleaning in a passivation tank, which serves to eliminate surface contaminants and improve corrosion resistance. The result is a modern and industrial finish that is ideal for marine applications or harsh environments.

·       Brushing

Brushing gives steel a satin-like sheen and reveals its silver-gray undertone. Brushing diffuses light, making it look muted compared to polished finishes. Many designers prefer this finish because it softens the metal's look while retaining its texture and color.

Stainless Steel polishing
Stainless Steel Bead Blasting
Metal Surface Finishing: stainless steel brushing-finish

Conclusion

Making durable parts requires mastering stainless steel CNC machining. This guide covers stainless steel grades, processes, types, and machining challenges and benefits. Manufacturers can use stainless steel's properties for various applications with the right knowledge, tools, and methods. In today's competitive manufacturing environment, understanding stainless steel machining is crucial for precise finishes and part longevity.

Rally Precision leads CNC machining in stainless steel to produce high-quality, durable parts. Our experts use advanced technology and industry knowledge to tackle stainless steel machining problems with years of experience.

Contact Rally Precision now. Discuss how we can make your next project precise, durable, and excellent.

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