What is machining difficult-to-machine materials? This article explains why machining these materials is difficult, how to address the challenges, and tips for ensuring accuracy.

When designing high-performance machine parts, materials with excellent properties such as heat resistance, wear resistance, and corrosion resistance are required. Many of the materials that achieve these properties are difficult to process and are called "hard-to-machine materials."

While difficult-to-machine materials enhance product performance, they can also lead to problems during the machining process, such as reduced tool life, variations in dimensional accuracy, and increased cutting heat.Therefore, it is important to understand the material properties and then implement appropriate processing techniques and process designs.

This article summarizes the basic characteristics of difficult-to-machine materials and the reasons why they are difficult to process.This article explains the challenges and processing solutions for typical materials, as well as key points for ensuring accuracy.

What are difficult-to-cut materials?

Difficult-to-machine materials are a general term for materials that are extremely difficult to cut compared to common materials such as carbon steel and aluminum alloys.There is no clear numerical definition; it refers to materials that are judged to be relatively "difficult to machine" based on factors such as on-site processing experience and the degree of tool wear.

Typical examples include titanium alloys, nickel-based alloys (such as Inconel), and stainless steel.

While difficult-to-machine materials are challenging to process, they possess excellent mechanical and chemical properties such as high strength, heat resistance, and corrosion resistance. Therefore, they are indispensable materials in industrial sectors where extremely high reliability and durability are required.

Specifically, high-temperature components around automobile engines, jet engine components in the aerospace industry, and medical devices where biocompatibility is important (such as implants and artificial joints),It is widely used in semiconductor manufacturing equipment and other applications requiring extremely high precision.

While it offers excellent functionality, it places a very heavy load on the tool during cutting.

Therefore, when machining difficult-to-cut materials, it is important to select the optimal cutting tool and adjust the machining conditions according to the material properties, rather than using the same approach as for general metals.

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How to deal with difficult-to-cut materials in cutting processes? Issues and processing techniques for each material

What is cutting? A thorough explanation of the types, characteristics, and typical parts that can be produced.

Six reasons why machining difficult-to-cut materials is considered challenging.

Difficult-to-machine materials are not simply "hard"; their unique physical and chemical properties significantly increase the difficulty of processing them.

Here, we will outline six typical reasons why machining difficult-to-cut materials is challenging, along with specific problems that occur on-site.

1. When the hardness is high and tool wear is severe
2. When the thermal conductivity is low and cutting heat tends to concentrate at the cutting edge.
3. When there is insufficient processing experience and the machinability is difficult to predict.
4. When the viscosity is high and the chips are difficult to process.
5. When the chemical affinity between the material and the tool is high
6. If there is a possibility of ignition or fire during processing

1. When the hardness is high and tool wear is severe.

Many difficult-to-machine materials have high hardness and strength even at room temperature, which places an extremely large physical load (cutting resistance) on the cutting edge of the cutting tool.As a result, tool wear progresses faster than with normal materials, making it more prone to problems such as "chipping," where the cutting edge breaks off.

Tool deterioration directly leads to a decrease in machining accuracy and surface roughness (smoothness of the machined surface).

Therefore, when machining hard-to-cut materials with high hardness, it is important to appropriately select tool materials with excellent wear resistance, such as cemented carbide or CBN (cubic boron nitride), or tools with special coatings.

2. When the thermal conductivity is low and cutting heat tends to concentrate at the cutting edge.

Difficult-to-machine materials such as titanium alloys and Inconel have the characteristic of having "low thermal conductivity (they do not dissipate heat well)."Normally, the frictional heat generated during cutting is expelled along with the chips (metal shavings), but in the case of difficult-to-cut materials, the heat does not dissipate and concentrates at the cutting edge of the tool.

When the cutting edge reaches abnormally high temperatures (sometimes exceeding 1000°C), tool wear accelerates rapidly. Furthermore, thermal expansion of the tool and workpiece can cause variations in dimensional accuracy, and heat damage may remain on the machined surface.

To prevent this problem, process design that effectively dissipates cutting heat, such as optimizing the cooling method using high-pressure coolant (cutting fluid), is essential.

3. When there is insufficient processing experience and the machinability is difficult to predict.

Difficult-to-machine materials used for special applications tend to be less readily available on the market compared to general steel and aluminum materials, resulting in limited processing experience and data.In many cases, the optimal machining conditions—such as "which tool to use and at what speed"—have not yet been established.

Proceeding with processing without sufficient information increases the risk of sudden tool breakage and the production of defective products.

Therefore, the time and cost involved in designing the process through trial and error, carefully checking cutting conditions and tool life through prior test machining (test cutting), is one of the reasons why this type of machining is considered difficult.

4. When the viscosity is high and the chips are difficult to process.

Materials such as austenitic stainless steel are not only hard, but also have high "toughness (viscosity)" and are prone to work hardening (the phenomenon where the part that is machined becomes hard).Furthermore, during cutting, the chips tend to be generated in long, connected pieces rather than being finely broken down.

These long, extended chips can easily get tangled in tools and workpieces, causing scratches (tears) on the workpiece surface, and in the worst case, leading to machine shutdown or tool damage.

Therefore, when machining highly viscous, difficult-to-machine materials, it is essential to select a chip breaker (tool groove shape) that finely breaks up the chips and to adjust the machining conditions to improve chip evacuation.

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5. When the chemical affinity between the material and the tool is high.

Some difficult-to-machine materials have a high chemical affinity with tool materials such as cemented carbide, and tend to melt and adhere to the cutting edge under the high temperature and pressure conditions during cutting.This phenomenon is called "welding," and it causes a troublesome problem called "built-up edge," where material sticks to the cutting edge.

When built-up edge occurs, the original cutting edge shape changes, which not only reduces machining accuracy, but also significantly shortens tool life because the attached material peels off along with the cutting edge of the tool.

To prevent this problem,Using tools with a smooth coating that prevents material from adhering easily, and selecting the appropriate cutting fluid are important.

6. When there is a possibility of ignition or flammability during processing.

Materials such as magnesium and titanium have the dangerous property that the fine chips and dust generated during processing are highly flammable.In particular, if water-soluble cutting fluid reacts with magnesium to generate hydrogen gas, or if the temperature of the chips rises during high-speed machining or dry machining (machining without cutting fluid), it could lead to a serious fire.

In the machining process, strict safety measures are essential, even more so than machining techniques themselves. These measures include using appropriate cutting fluids (such as water-insoluble coolants) to prevent ignition, meticulously cleaning and managing chips, and preparing dedicated fire extinguishing equipment.

Typical types of difficult-to-machine materials and their processing challenges

There are various types of materials that are difficult to machine, and each has a different reason why it is difficult to cut.

Here, we will discuss some typical difficult-to-machine materials that are frequently handled in machining environments.This article explains its characteristics, applications, and specific points for successful processing.

1. Stainless steel (SUS material)
2. Titanium and titanium alloys
3. Inconel (nickel-based superalloy)
4. magnesium alloy

Stainless steel (SUS material)

Stainless steel is a familiar material widely used in everything from household goods to industrial machinery and medical equipment because it is rust-resistant (corrosion-resistant) and aesthetically pleasing.However, it is actually known as one of the most difficult materials to machine.

Austenitic stainless steels, such as "SUS304," are particularly tough and prone to "work hardening," where the surface hardens during machining.Furthermore, due to its low thermal conductivity, heat cannot escape, leading to rapid tool wear.

Processing points
To avoid damaging the work-hardened layer, it is important to select a sharp tool (with a large rake angle) and remove the material in one swift motion while maintaining the appropriate depth of cut.

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What is stainless steel? A detailed explanation of its characteristics, types, and why it's rust-resistant

Titanium and titanium alloys

Titanium is a high-performance material that boasts three key features: lightness, strength, and rust resistance.Due to its high biocompatibility, it is widely used in aerospace components and medical implants such as artificial bones.

As a difficult-to-machine material, it is troublesome because it has extremely low thermal conductivity, causing cutting heat to concentrate at the cutting edge, and it readily reacts chemically with tool materials (such as cemented carbide), leading to "welding" where chips stick to the cutting edge.

Furthermore, because it has high elasticity (it bends easily), "chatter" (vibration) is likely to occur during thin-wall machining, making it difficult to achieve dimensional accuracy.

Processing points
It is essential to reduce the cutting speed and strongly cool and lubricate the cutting edge with high-pressure coolant. Furthermore, vibration countermeasures, such as using highly rigid machine tools and tools to prevent deformation, are necessary.

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Is titanium, a difficult-to-cut material, difficult to process? A thorough explanation of typical issues and solutions

Inconel (nickel-based superalloy)

Inconel is a superalloy primarily composed of nickel (Ni), with added elements such as chromium (Cr) and molybdenum (Mo).Because its strength and oxidation resistance do not deteriorate even in high-temperature environments, it is indispensable for aircraft jet engines and gas turbine components, but it is also feared within the industry as "the most difficult material to machine."

It is hard even at room temperature and undergoes significant work hardening; it does not soften even at high temperatures, resulting in tremendous load (cutting resistance) being placed on the tool during cutting.This material is also prone to "boundary wear," where only specific areas of the blade tip are worn away in a gouging fashion.

Processing points
Conventional carbide tools quickly become dull, so it is necessary to select special coated tools or ceramic tools that are highly heat-resistant and wear-resistant, and to set the machining conditions with extreme care.

magnesium alloy

Magnesium is the lightest of all practical metals and is used in automotive parts and lightweight laptop casings.In fact, magnesium itself is soft and has low cutting resistance, making it a "very easy material to machine."

However, it is treated as a difficult-to-machine material (a material that requires careful handling) for a completely different reason: the risk of ignition. The fine chips and dust generated during cutting easily combine with oxygen,Even a small amount of frictional heat can cause a violent combustion and explosion.

Processing points
Magnesium reacts with water to produce flammable hydrogen gas, therefore, the use of water-soluble coolants (cutting fluids) is strictly prohibited. Using water-insoluble (oil-based) coolants or implementing strict chip management and dedicated fire extinguishing equipment is absolutely essential for machining.

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Machining techniques and tips for ensuring precision when machining difficult-to-cut materials.

When machining difficult-to-cut materials, it's not just about whether the material can be cut, but also about designing the process with a view to how to extend tool life, how to maintain machining accuracy, and how to ensure consistent quality during mass production.

Here, we will explain four important measures and tips for overcoming the hurdles of machining difficult-to-cut materials and consistently achieving high-precision machining.

1. Selection of the optimal cutting tool (material and coating)
2. Optimization of cutting conditions (machining conditions)
3. Thorough cooling and lubrication (coolant) to dissipate cutting heat.
4. Use of highly rigid machine tools and jigs

Selection of the optimal cutting tool (material and coating)

It's no exaggeration to say that 8% of the success or failure of machining difficult-to-cut materials depends on the choice of tools.The first step is to select tools with excellent wear resistance and heat resistance, tailored to the characteristics of the material (whether it is hard, generates heat, or is viscous).

1. Choosing the right tool material
In addition to general cemented carbide, we select specialized tools from the base material stage, such as "ceramic tools" for high heat-resistant alloys like Inconel, and "CBN (cubic boron nitride) tools" for high-hardness materials.

2. Effects of the coating
To prevent "welding" (chip adhesion) in titanium alloys and stainless steel, using tools coated with a special coating (such as TiAlN) that offers excellent heat resistance and lubricity can dramatically extend tool life.

Optimization of cutting conditions (machining conditions)

Because difficult-to-machine materials have high cutting resistance (rebound force when cutting),If you machine using typical settings (cutting speed, feed rate, depth of cut), the tool will break very quickly.

1. Reduce the cutting speed.
To prevent the cutting edge from overheating, the general rule is to set the "cutting speed (rotational speed)" low.

2. Experimentation with feed rate and depth of cut
With materials that undergo "work hardening," such as stainless steel, gradually removing material is counterproductive as it only scrapes the hardened surface. Therefore, a program design is required that maintains the appropriate depth of cut and feed rate (cutting firmly without slipping) so that the cutting edge can accurately grip the area beneath the hardened layer.

Thorough cooling and lubrication (coolant) to dissipate cutting heat.

The biggest enemy in machining difficult-to-cut materials is heat.Difficult-to-machine materials with low thermal conductivity cause cutting heat to concentrate at the cutting edge, leading to tool wear and dimensional defects due to thermal expansion of the workpiece.

Utilization of high-pressure coolant
With conventional cutting fluid application methods, the heat at the cutting edge can cause the oil to evaporate, preventing it from reaching the crucial machining point (film boiling phenomenon).

Using a high-pressure coolant system, which precisely sprays high-pressure oil or liquid between the cutting edge and the chip, ensures reliable cooling and lubrication while simultaneously forcibly breaking up and removing the chip. This is key to stabilizing the machining process.

Use of highly rigid machine tools and jigs

In order to overcome the high cutting resistance of difficult-to-machine materials,Not only are the blades themselves important, but the "strength" of the machine that mounts them is also essential.

The importance of machine rigidity lies in the fact that using a machine with low rigidity (easily flexing) can cause "chatter" (fine vibrations), resulting in rough machined surfaces or chipped tools. Therefore, selecting an NC lathe or machining center with a robust spindle and bed is essential.

Clamping (fixing) using a jig
Even if a machine is robust, it's useless if it doesn't securely hold the workpiece. Designing and setting up specialized jigs that securely hold the workpiece and minimize vibrations during machining are also extremely important factors in achieving high-precision machining.

Sanwa Needle Bearing's Technology for Machining Difficult-to-Machine Materials

When machining difficult-to-cut materials, it's not just about whether the material can be cut, but also whether dimensional accuracy and machining quality can be consistently maintained even in mass production.
Sanwa Needle Bearing has established a stable processing system that combines precision machining technology and quality control for difficult-to-machine materials such as heat-resistant steel, titanium, and ceramics.

Here, we introduce some typical examples of machining difficult-to-cut materials that Sanwa Needle Bearings can handle.

1. Heat resistant steel
2. ceramic
3. Titanium
4. Other processed products

Heat resistant steel

Heat-resistant steel has low thermal conductivity, which means it does not easily release heat from the workpiece during machining.Sanwa Needle Bearings mass-produces heat-resistant steel parts, primarily for automotive parts manufacturers, allowing us to propose the most suitable processing method depending on the shape and application.

Another strength is our ability to provide consistent support from the initial prototype stage of development to the end of mass production.

Furthermore, compared to general stainless steel materials, it can be difficult to obtain materials of the required diameter. Processing from thicker materials increases processing costs and lead times, so material procurement that takes cost and lead time into consideration is essential.

We procure materials appropriately in cooperation with trading companies and have established an efficient processing system.

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Examples of Sanwa Needle Bearing's heat-resistant steel parts manufacturing can be found here.

ceramic

Ceramic parts are difficult to handle due to their high material hardness, making them prone to cracking and chipping, and it can be challenging to obtain parts with the desired shape and precision.

Because the materials are not only expensive but also their quality affects the final product after processing, it is important to discuss quantities and specifications in advance.

Sanwa Needle Bearing has extensive experience processing a wide range of ceramic materials, including silicon nitride, alumina, and zirconia, and can handle micron-level precision, especially for cylindrical components.

Furthermore, we can manufacture ceramic parts with complex shapes using machining centers and other equipment. We have a system in place to handle everything from material procurement and shape design to precision requirements on a custom-made basis.

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Examples of ceramic parts manufactured by Sanwa Needle Bearing can be found here.

Titanium

Titanium is a material that can be made approximately 40% lighter compared to stainless steel (SUS).Sanwa Needle Bearing specializes in the custom manufacturing of titanium parts, providing high-quality products tailored to your specific requirements.

Our integrated production system allows us to handle everything from single prototypes to mass production of millions of units. Furthermore, in recent years, through collaboration with partner companies, we have also been able to offer near-net-shape machining using the lost-wax casting method.

To minimize surface damage and deformation, we combine cutting and grinding technologies to shorten delivery times, reduce costs, and stabilize quality.

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Examples of Sanwa Needle Bearing's titanium component manufacturing can be found here.

Other processed products

Sanwa Needle Bearings offers precision machining services for a wide range of materials, including difficult-to-machine materials.Even hard and brittle materials can be machined with high precision through grinding, and under certain conditions, it can handle fine shapes such as tip taper of φ0.02 or less.

Furthermore, since grinding of difficult-to-machine materials is handled with specialized machines, the quantity that can be processed may vary depending on the quantity, shape, and required precision. Our skilled technicians set up processing methods according to the application, enabling us to handle the processing of difficult-to-machine materials such as tungsten and silicon.

Furthermore, based on our extensive experience in processing a wide range of materials, we can also propose materials tailored to specific applications, such as corrosion resistance and magnetic properties, and provide support for component design.

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Examples of parts manufactured from other materials by Sanwa Needle Bearing can be found here.

Frequently asked questions about machining difficult-to-machine materials

This section introduces frequently asked questions and key points regarding the design and processing method development stages for machining difficult-to-machine materials.

Q1. Why is understanding material properties important when machining difficult-to-cut materials?
Q2. How can I determine if a difficult-to-machine material is suitable for a component?
Q3. If difficult-to-machine materials are used in mass production, is it necessary to process prototypes using the same material?

Q1. Why is understanding material properties important when machining difficult-to-cut materials?

Difficult-to-machine materials vary greatly in hardness, strength, thermal conductivity, and work hardening tendencies, resulting in different machinability.

For example, with materials that have low thermal conductivity, cutting heat can concentrate on the tool, leading to tool wear and a decrease in machining accuracy. Therefore, it is important to understand the material properties before selecting tools and setting machining conditions.

Q2. How can I determine if a difficult-to-machine material is suitable for a component?

Whether or not to use difficult-to-machine materials for components is determined by considering the balance between performance requirements such as heat resistance, wear resistance, and corrosion resistance, and machinability.

It is important to consider factors such as processing accuracy, stability during mass production, and cost, and to decide on material selection and processing methods together during the design phase.

Q3. If difficult-to-machine materials are used in mass production, is it necessary to process prototypes using the same material?

In most cases, it is considered desirable to create prototypes using the same materials as those used in mass production.

Because tool wear and machining accuracy vary greatly depending on the machining conditions for difficult-to-machine materials, it is important to confirm the machining conditions and processes using the actual material during the prototyping stage.

Summary | When machining difficult-to-cut materials, it is essential to consider machining methods that match the material's properties.

Difficult-to-machine materials possess excellent properties such as heat resistance, wear resistance, and corrosion resistance, but they are also materials that are difficult to process.Therefore, it is necessary to understand the material properties, optimize tool selection and machining conditions, and design an appropriate process.

Since difficult-to-machine materials are often used in precision parts, it is essential to consider both material properties and processing techniques to ensure accurate machining and stability during mass production.

Sanwa Needle Bearing also handles precision machining of parts using difficult-to-machine materials.If you are considering the optimal processing method based on material properties and applications, please feel free to contact us.