What is precision machining of SUS304? Explanation of machining characteristics, accuracy limits, and design considerations.

SUS304 is known as a representative stainless steel material that offers an excellent balance between corrosion resistance and workability.It is used in a wide range of applications, including food processing machinery, medical equipment, semiconductor equipment, and industrial machinery, and is often adopted in fields where high reliability is required in corrosive environments.

On the other hand, when using SUS304 as a precision component, design that takes into account issues such as work hardening and wear resistance is essential.Therefore, it is important to understand the relationship between material properties and processing steps, and then consider appropriate processing methods and specifications.

This article will cover everything from the basic characteristics of SUS304 to the challenges in precision machining, design considerations, and actual machining examples.This section explains the information that serves as a basis for decision-making in the design of precision parts.

Characteristics of SUS304 and why it is used in precision parts

SUS304 is one of the most commonly used stainless steel materials. It offers an excellent balance of corrosion resistance, workability, and cost, and is used in a wide range of industrial fields.

Here, we will summarize the reasons why SUS304 is chosen for precision parts from the perspective of its material properties.

1. SUS304 is a representative grade of austenitic stainless steel.
2. SUS304 is often used in corrosive environments and for high-precision applications.
3. Mechanical properties and physical characteristics of SUS304

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SUS304 is a representative grade of austenitic stainless steel.

SUS304 is classified as an austenitic stainless steel, primarily composed of chromium (Cr) and nickel (Ni). Because its typical composition is approximately 18% chromium and 8% nickel, it is sometimes referred to as "18-8 stainless steel."

The chemical composition of SUS304 is as follows:

SUS304 is often used in corrosive environments and high-precision applications.

SUS304 is a material with excellent corrosion resistance and heat resistance, making it resistant to corrosion.Even when in contact with moisture, chemicals, or food components, it is less prone to dimensional changes or performance degradation due to corrosion.

Furthermore, because it is basically non-magnetic, it is sometimes used in applications where magnetic influences must be avoided, such as around electromagnetic equipment and sensors. However, it is more expensive than SUS430, and it is important to note that it becomes magnetic as work hardening progresses through cold working.

Furthermore, SUS304 is prone to work hardening and has low thermal conductivity, which means that cutting heat tends to concentrate on the tool. Therefore, although it has high cutting resistance, it is a material that is easily plastically deformed and suitable for machining complex shapes.

For this reason, it is widely used as a rotating part or sliding part, such as a shaft, rod, or screw.

Mechanical properties and physical characteristics of SUS304

The typical characteristics of SUS304 are as follows:

SUS304 has moderate strength and a good balance with corrosion resistance,Its wear resistance is not very high. Caution is required when using it in sliding parts or areas where wear occurs.

Furthermore, since SUS304 cannot be hardened by heat treatment, other methods such as cold working or surface treatment must be considered to increase its strength and hardness.

Reasons why precision machining of SUS304 is said to be difficult

To successfully perform precision machining of SUS304, it is necessary to understand the inherent properties of the material and optimize the cutting conditions and tool material accordingly.
Especially in continuous machining, process-related measures such as managing the accumulation of machining heat and fine-tuning the cutting speed are essential.

From here, we will summarize the main reasons why SUS304 is treated as a "difficult-to-machine material" in manufacturing and is considered to be highly challenging to process for precision.

1. Work hardening can easily cause cutting problems.
2. It is difficult to achieve precision with grinding finishes.
3. SUS304 is unsuitable for heat treatment.

Work hardening can easily cause cutting problems.

The biggest challenge with SUS304 in precision machining is a phenomenon called "work hardening," in which the localized hardness of the material increases sharply when it deforms.

When the cutting edge touches the material during cutting, plastic deformation occurs, significantly increasing the surface strength of the machined area. When the next cutting edge then cuts through this hardened layer, excessive load is placed on the tool, leading to chipping (breakage of the cutting edge) and rapid wear.

Tool deterioration directly leads to a deterioration in surface roughness and variations in dimensional accuracy,The selection of a sharp cutting edge to suppress work hardening and the setting of an appropriate cutting depth to remove the hardened layer in one go are strongly required.

It is difficult to achieve precision with grinding finishes.

In precision machining, grinding is often performed after cutting to ensure final dimensional accuracy.However, because SUS304 is a relatively tough material, controlling the grinding process tends to be complex.

When grinding wheels become clogged or burned during grinding, it can lead to a deterioration in surface roughness and roundness.The selection of grinding wheels, dressing conditions, grinding speed settings, and consideration of additional finishing processes are all important.

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SUS304 is unsuitable for heat treatment.

While "heat treatment" is a common method for increasing wear resistance and strength in precision parts,SUS304 is classified as an "austenitic stainless steel," meaning its hardness cannot be increased through heat treatment.

Unlike carbon steel or martensitic stainless steel, its structure cannot be hardened by heating and rapid cooling, which limits its application to sliding parts and areas subject to heavy wear.

If you want to enhance the strength while taking advantage of the corrosion resistance of SUS304, you should consider changing the material to martensitic stainless steel (such as SUS440C) or hardening it through surface treatment.

Since incorrect material selection directly impacts product lifespan, it's crucial to correctly understand the thermal properties of SUS304 during the design phase.

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Key design points for precision machining of SUS304.

When using SUS304 as a precision component, designing with material properties in mind is crucial.Here, we'll summarize the key points to keep in mind during the design phase.

1. It has high corrosion resistance but is weak against wear.
2. Cold working may cause the material to become magnetic.

It has high corrosion resistance but is weak against wear.

A major advantage of SUS304 is its corrosion resistance, and it is used in medical equipment, food processing machinery, semiconductor manufacturing equipment, etc.Due to its corrosion resistance and cleanliness, SUS304 is often adopted as a standard material.

On the other hand, attention must be paid to increased clearance and decreased precision due to wear. For sliding parts and areas where wear is expected, it may be necessary to design considering the friction conditions with the mating parts, as well as to consider surface treatment or alternative materials.

Cold working may cause the material to become magnetic.

Austenitic stainless steel is basically nonmagnetic,Cold working can alter the structure of a material, sometimes causing it to become magnetic.

This can be a problem in mechanisms susceptible to magnetic fields, such as sensors and electromagnetic devices. If maintaining non-magnetic properties is necessary, processing conditions and material selection must be carefully considered.

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Examples of high-precision parts machining using SUS304

In precision machining, the accuracy that can be achieved varies greatly depending not only on the material properties but also on the machining technology and equipment capabilities.Here, we introduce typical examples of precision parts being machined using SUS304.

1. Small diameter precision shaft
2. High-precision sliding screws
3. Rods for corrosion-resistant environments

Small diameter precision shaft

Small diameter shafts are components used in rotating mechanisms such as motors and actuators.For parts with a diameter of a few millimeters or less, roundness and surface roughness significantly affect the mechanical performance.

In small-diameter shafts made of SUS304 stainless steel, precision control at the sub-micron level is sometimes achieved through grinding. For example, achieving a roundness of 0.0001 mm makes it possible to construct a rotating mechanism that suppresses vibration and wear.

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High-precision sliding screws

A sliding screw is a mechanical component that converts rotational motion into linear motion.In precision equipment, it is essential to minimize backlash as much as possible.

In the case of sliding screws made of SUS304 stainless steel, high-precision thread shapes can be achieved through grinding, resulting in mechanisms with backlash of 2 μm or less. In precision positioning mechanisms, such high-precision machining is a crucial factor that affects the performance of the device.

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Rods for corrosion-resistant environments

In equipment used in chemical or high-humidity environments, SUS304 rods are sometimes used to prevent component deterioration due to corrosion.

In precision rods, straightness and surface roughness affect sliding performance. By stabilizing surface quality through grinding, stable operation can be achieved over a long period of time.

Frequently Asked Questions about Precision Machining of SUS304

SUS304 is chosen as a primary material for precision parts due to its excellent corrosion resistance and versatility, but it also has the characteristic of being difficult to machine. To successfully perform precision machining, it is essential to have a deep understanding of the unique material properties of SUS304 and to design an appropriate process.

This section answers frequently asked technical questions from designers and manufacturers considering precision machining of SUS304.

Q1. Is SUS304 a suitable material for precision machining?
Q2. What level of precision can be achieved with SUS304?
Q3. Which process is most important in precision machining of SUS304?

Q1. Is SUS304 a suitable material for precision machining?

SUS304 offers an excellent balance of corrosion resistance and strength, making it the most commonly used stainless steel for precision parts in medical equipment, semiconductor manufacturing equipment, food processing machinery, and other applications.

However, from the perspective of precision machining, it is important to note that this material is prone to "work hardening," where the surface hardens during machining, and therefore places a heavy load on the tools.

Furthermore, because stainless steel exhibits strong "toughness" during cutting, it is prone to burr formation and dimensional changes due to thermal expansion. Therefore, maintaining high precision requires setting processing conditions with high cooling efficiency and selecting tools specifically designed for stainless steel.

By entrusting the processing to manufacturers who are thoroughly familiar with these characteristics, SUS304 can be transformed into highly reliable precision parts.

Q2. What level of precision can be achieved with SUS304?

The precision achievable in precision machining of SUS304 depends heavily on the machining equipment and methods employed.

While there are limitations to general lathe machining alone, combining it with ultra-precision grinding can sometimes achieve extreme accuracy, such as an outer diameter tolerance of ±0.002 mm (2 microns) and roundness at the level of 0.0001 mm (0.1 microns).

In workshops specializing in ultra-precision grinding, thorough temperature control that takes into account the thermal expansion of the material, and the use of sub-micron level measurement technology are employed.Even though it's made of SUS304 stainless steel, it meets the stringent geometric tolerances required in the aerospace and medical fields.

Q3. Which process is most important in precision machining of SUS304?

In the manufacturing of precision parts using SUS304, the "finishing process (grinding)" plays the most important role in determining the final dimensional and geometric accuracy.

Work-hardened layers and internal stresses generated during the previous cutting (turning) process can cause product aging and distortion. In the finishing process, low-load, high-precision grinding can be performed to remove heat effects and burrs from cutting, making it possible to stabilize the outer diameter accuracy and smooth surface roughness according to the design drawings.

In particular, for shaft shapes with multiple mating parts, controlling the degree of coaxiality during the finishing process significantly impacts the overall performance of the product.Selecting the right grinding technology is key to improving quality.

Summary | Precision machining of SUS304 requires process design that understands the material properties.

SUS304 is a representative stainless steel material with excellent corrosion resistance, used in a wide range of industrial fields.However, there are unique challenges such as work hardening and wear resistance, so it is important to consider design and manufacturing processes that take into account the material properties.

Sanwa Needle Bearings is capable of manufacturing precision parts with sub-micron level accuracy control through its grinding technology, including its own proprietary equipment.We handle everything from prototyping to mass production in-house, and we also propose processing methods tailored to the application and material characteristics.

If you have any problems with precision parts machining, including SUS304, please feel free to contact us.