Stainless Steel CNC Machining

CNC machining is a way of using a numerically controlled machine tool for processing. First, a program is generated by CAD/CAM software and then transmitted to the machine tool. The machine tool automatically controls the relative movement between the tool and the workpiece according to the program, enabling a variety of machining operations. It has advantages such as high precision and high efficiency, and is widely used in many industries.

This article will introduce the CNC machining of stainless steel from multiple aspects, including the commonly used stainless steel grades in machining, various machining processes of stainless steel, the advantages, and challenges of stainless steel machining.

Can Stainless Steel be Machined?

Stainless steel can be CNC machined and can be processed through various processes.
In fact, many grades of stainless steel have good machinability. Although some stainless steels are difficult to machine, with the right choice of tools and processes, precise machining can be achieved.

Machining Processes of Stainless Steel

The CNC machining of stainless steel includes a variety of processes, which meet the requirements of different shapes, precisions, and surface qualities:

Turning

Turning is often used for machining rotational parts, such as shaft parts and disk parts. It can machine different features like outer circles, inner holes, conical surfaces, and threads.
Through turning, the diameter, length, and surface roughness of a stainless steel shaft can be precisely controlled to ensure the fitting accuracy between the shaft and other parts.

Milling

When machining the cavity of a stainless steel mold by milling, different types of milling cutters, such as end mills and ball nose mills, can be used to achieve rough and finish machining of the cavity, ensuring the dimensional accuracy and surface quality of the cavity.

Drilling

Drilling can be used to create various mounting holes, connection holes, etc. There is a large demand for drilling in fields such as mechanical manufacturing and electronic equipment.
To fix a part on a stainless steel plate, mounting holes are machined on the stainless steel plate through drilling.
Since stainless steel has relatively high hardness and toughness, when drilling, it is necessary to select the appropriate drill bit material and cutting parameters to ensure the accuracy and surface quality of the holes.

Boring

Boring is often used for machining high-precision holes, such as the cylinder holes of engine blocks and the bearing holes of machine tool headstocks.
Boring the bearing holes on stainless steel parts can ensure the roundness, cylindricity, and surface roughness of the holes, allowing the bearings to be installed accurately and ensuring the normal operation of the equipment.

Tapping

It is used for manufacturing parts that require threaded connections, such as bolt holes and nuts.
Internal threads are machined on stainless steel parts to connect with bolts, achieving the fastening and assembly between parts.

Grinding

Grinding is often used for machining parts with high requirements for surface roughness and dimensional accuracy, such as the forming surfaces of precision molds and the measuring surfaces of measuring tools.
Grinding the cutting edges of stainless steel tools can improve the sharpness and cutting performance of the tools, ensuring the service life of the tools and the machining quality.

Different Types of Stainless Steel for CNC Machining

304 Stainless Steel

304 has good corrosion resistance, heat resistance, low-temperature strength, and mechanical properties. It has good machinability, excellent welding performance, and a relatively moderate price. It is a highly versatile stainless steel material.
Many kitchen utensils, sinks, decorative railings and handrails in buildings, as well as some food processing equipment and medical instruments with high requirements for corrosion resistance and hygiene, are made of 304 stainless steel through CNC machining.

316 Stainless Steel

316 is made by adding molybdenum to 304 stainless steel, which significantly improves its corrosion resistance, especially pitting corrosion resistance and crevice corrosion resistance. It also has better high-temperature strength and oxidation resistance. However, its price is relatively higher than that of 304 stainless steel.
Components of ships, seawater desalination equipment, chemical pipelines and reactors, and some key components of pharmaceutical equipment often use 316 stainless steel for CNC machining to ensure that the equipment can operate stably for a long time in harsh working environments.

410 Stainless Steel

410 belongs to martensitic stainless steel, which has high strength, hardness, and wear resistance, and also has a certain degree of corrosion resistance. After heat treatment, its mechanical properties can be further improved. But compared with austenitic stainless steel, its corrosion resistance is slightly worse.
Some high-performance tools are made of 410 stainless steel. The precise shape of the tool is machined by CNC, and then its hardness and wear resistance are improved through heat treatment to meet the requirements of cutting.

430 Stainless Steel

430 is a ferritic stainless steel with good corrosion resistance, thermal stability, and machinability, and it has a relatively low price. However, its strength and hardness are relatively lower than those of martensitic stainless steel, and its toughness is not as good as that of austenitic stainless steel.
The inner linings of refrigerators are usually formed by CNC machining of 430 stainless steel. Using its good corrosion resistance and machinability, it can meet the product’s usage requirements while reducing costs.

17-4PH Stainless Steel

17-4PH is a precipitation-hardening stainless steel that is also commonly used in machining. After appropriate heat treatment, 17-4PH stainless steel has high strength, high hardness, and good toughness. Its tensile strength can reach more than 1000MPa, and its yield strength can also reach about 700MPa. At the same time, it also has a certain elongation, which makes it perform well in the manufacturing of mechanical parts that bear large loads.

For some parts with extremely high requirements for dimensional accuracy, such as precision parts in the aerospace field and key components in high-end medical devices, the characteristics of 17-4PH stainless steel make it an ideal material choice, and high-precision dimensional control can be achieved through machining.

Advantages of Stainless Steel in CNC Machining

High Machining Precision

Stainless steel materials have good stability. During the CNC machining process, they are not likely to deform excessively due to factors such as cutting force and cutting heat, which can ensure the dimensional accuracy and shape accuracy of the parts. For example, when machining high-precision stainless steel molds, CNC machining can control the dimensional error within a very small range to meet the high-precision requirements of the molds.CNC machining equipment has high precision. Combined with the stability of stainless steel materials, it can achieve the machining of small dimensions. For example, in the machining of stainless steel watch movement parts, parts with dimensional accuracy reaching the micron level can be machined to ensure the accurate operation of the watch movement.

Good Surface Quality

Stainless steel itself has a uniform texture. After CNC machining, the surface roughness value is low, and a good surface quality can be obtained. The cutting parameters of CNC machining can be precisely controlled, and the cutting process is stable, reducing the generation of surface tool marks and burrs. For example, in the machining of stainless steel bathroom products, the surface after CNC machining is smooth and bright, and without excessive subsequent polishing treatment, it can meet the appearance requirements of the products.
CNC machining can achieve complex surface machining. For stainless steel sculptures, handicrafts, etc., it can precisely machine various surface shapes and maintain good surface quality, making the products have higher artistic value and ornamental value.

Good Machinability

Although the machining difficulty of stainless steel is relatively high, in CNC machining, these difficulties can be overcome by selecting the appropriate tools, cutting parameters, and machining processes. For example, using carbide tools, optimizing cutting speed, and feed rate parameters can effectively improve the machining efficiency and quality of stainless steel. Compared with some high-hardness and high-brittleness materials, stainless steel has better machinability in CNC machining and can achieve a variety of machining methods, such as milling, turning, drilling, and boring.
Stainless steel has good toughness and is not likely to crack or break during the machining process, making it suitable for machining parts with complex shapes. In CNC machining, various complex machining paths can be achieved through programming. For some stainless steel parts with complex structures, such as stainless steel impellers in aircraft engines, multiple machining processes can be completed at one time through CNC machining, improving production efficiency and machining accuracy.

Material Performance Advantages

Stainless steel has good corrosion resistance and oxidation resistance. After CNC machining, the surface performance of the parts will not be significantly affected by the machining process and can maintain good performance for a long time. This enables stainless steel parts to still work normally in some harsh working environments, such as wet, acid-base and other corrosive environments, and have a long service life. For example, in fields such as chemical equipment and food processing equipment, stainless steel parts after CNC machining can meet the requirements of the equipment for corrosion resistance and hygiene.

Stainless steel also has high strength and hardness. The parts after CNC machining can bear large loads and are not easy to deform and damage. In the field of mechanical manufacturing, stainless steel parts are often used to manufacture some key load-bearing components, such as the crankshafts and connecting rods of automobile engines, which can ensure the reliability and stability of the components under high-speed operation and high load conditions.

Challenges in Stainless Steel CNC Machining

Severe Work Hardening

Stainless steel materials are prone to work hardening during the cutting process. This is because stainless steel has high toughness. Under the extrusion and friction of the tool, the hardness of the material surface layer will increase significantly, making subsequent cutting more difficult, accelerating tool wear, and reducing machining efficiency.
For example, when machining austenitic stainless steel, the hardness after work hardening may be 1-2 times higher than the original hardness, resulting in an increase in cutting force, and the tool is prone to problems such as chipping and excessive wear.

High Cutting Force

Stainless steel has relatively high strength and toughness, and a large cutting force is required during cutting. This not only puts forward high requirements for the power and rigidity of the machine tool but also easily causes the workpiece to deform. Especially when machining thin-walled stainless steel parts, the excessive cutting force may cause large elastic and plastic deformations of the workpiece, affecting the machining accuracy and surface quality.
For example, when milling stainless steel thin plates, problems such as uneven plate surfaces and burrs at the edges may occur.

Rapid Tool Wear

Due to the high hardness and good toughness of stainless steel, the friction between the tool and the workpiece is intense during the cutting process. Coupled with the influence of work hardening, the tool is prone to wear. Tool wear will cause the cutting edge to become blunt, further increasing the cutting force, reducing machining accuracy, and increasing the surface roughness value. Moreover, frequent tool replacement will increase the machining cost and auxiliary time, reducing production efficiency.
For example, when drilling stainless steel materials, ordinary high-speed steel drill bits wear out quickly and often need to be replaced frequently. Although using carbide drill bits can improve the tool life, the cost is relatively high.

Difficult Heat Dissipation

Stainless steel has a low thermal conductivity, and the heat generated during the cutting process is not easy to dissipate, which is likely to cause the temperature in the cutting area to rise. High temperature will reduce the hardness and strength of the tool, accelerate tool wear, and may also cause thermal deformation of the workpiece, affecting machining accuracy.
For example, when grinding stainless steel, due to the difficulty of dissipating grinding heat, defects such as burns and cracks are likely to occur on the workpiece surface.

Difficult Chip Breaking and Removal

Stainless steel has good toughness, and the chips are not easy to break during the cutting process, and are likely to form ribbon chips. Ribbon chips will wrap around the tool and the workpiece, affecting the smooth progress of the cutting process, and may also scratch the machined surface or even damage the tool. Especially in the automated machining process, if the problem of chip entanglement cannot be effectively solved, it will lead to the interruption of machining, reducing production efficiency and machining quality.
For example, when turning stainless steel shaft parts, appropriate chip-breaking measures need to be taken, such as selecting appropriate tool geometric parameters and optimizing cutting parameters, to ensure that the chips can be broken and removed smoothly.

Complex Machining Parameters

The machining parameters of stainless steel need to be precisely controlled, such as cutting speed, feed rate, and cutting depth, which increases the complexity of the process.

Finding the Ideal Stainless Steel Alloy for Each Project

Stainless steel comes in many different forms. It is crucial to determine which stainless steel material should be used for the product. If the product’s usage environment has a high requirement for corrosion resistance, martensitic stainless steel should be selected. If the product requires high strength, high pitting corrosion resistance, and corrosion resistance, duplex stainless steel may be the appropriate choice.
Easia has rich experience in stainless steel machining and can simplify the process of finding the suitable material that meets the unique requirements of the project.
Easia provides efficient customized stainless steel services. At every stage of the design and production of stainless steel products, we have experienced engineers to serve you, ensuring that our products meet the needs of customers in every aspect.