Difficult-to-Machine Materials: Basic Knowledge and Types

This page explains the basic knowledge, types, and key points for processing difficult-to-machine materials.

What are Difficult-to-Machine Materials?

Difficult-to-machine materials refer to materials that are hard to process or handle. Due to their nature, processing these materials is more challenging, making it difficult to achieve the required dimensions or surface roughness. Additionally, the tools experience greater wear due to the increased load, which can lead to other issues.

The reasons why difficult-to-machine materials are difficult to process are mainly due to the following factors:

① High hardness / Strong elasticity (or softness)

Materials with high hardness or strong elasticity that are prone to deformation are difficult to machine, making it challenging to achieve high-precision dimensions. Additionally, due to their hardness or softness, these materials place a heavy burden on machining equipment, causing rapid wear. As a result, selecting the appropriate machining method is crucial. In some cases, a combination of polishing, cutting, and grinding methods may be necessary.

② Materials may weld onto cutting tools

When machining materials with low melting points, chips generated during cutting may melt and weld onto the cutting tool. In such cases, the welded chips may begin to machine the workpiece instead of the cutting edge, which can cause the tool to chip (damage) or result in a decrease in machining accuracy.

③ Materials are prone to deformation during machining

If the workpiece has high thermal conductivity, it is more likely to warp due to heat generated during machining. Conversely, if the workpiece has low thermal conductivity, heat may not dissipate easily, causing local temperature increases and leading to warping or other deformations.

④ Work hardening occurs easily

Work hardening refers to the phenomenon where a metal becomes harder when subjected to force and plastic deformation (permanent deformation). When the metal hardens, it becomes more brittle and more difficult to machine.

⑤ Cutting chips may catch fire

When machining difficult-to-machine materials, the cutting chips generated may catch fire due to the heat produced. If the chips catch fire, they may ignite the oils used in the machinery, so caution is necessary.

Types of Representative Difficult-to-Machine Materials

This section explains the characteristics of representative difficult-to-machine materials such as stainless steel, titanium, Inconel®, and tungsten.

Stainless Steel

Stainless steel is an alloy containing more than 50% iron and at least 10.5% chromium. Known as “stainless steel” in English, it is resistant to rust, as the name suggests. In addition to its resistance to corrosion, it also has excellent heat resistance and strength.

Stainless steel has low thermal conductivity, and when cutting, high temperatures at the machining site can cause the workpiece to melt and weld onto the tool. Additionally, issues such as work hardening, which can cause the workpiece to crack, and tool wear are also common challenges.

TDC Stainless Steel Machining Examples

Titanium

Titanium is a metal known for its high strength, corrosion resistance, and heat resistance, and is used in a variety of industrial and manufacturing sectors. It also exhibits low-temperature toughness, making it suitable for use in cold environments, including as a building material.

However, titanium has low thermal conductivity, which means that heat generated during machining doesn’t dissipate easily, leading to increased tool wear due to higher temperatures. Additionally, the chips produced can retain heat, potentially leading to ignition, which is why titanium is considered a difficult-to-machine material.

TDC Titanium Machining Examples

Inconel

Inconel is an alloy of nickel combined with iron, chromium, and carbon, known for its excellent heat and corrosion resistance. It maintains its strength even at high temperatures and is used extensively in the chemical industry due to its resistance to corrosion.

The reasons Inconel is difficult to machine include its high strength at elevated temperatures and low thermal conductivity. During machining, it retains its strength even at high temperatures, causing tools to wear quickly. Moreover, the heat generated during machining is slow to dissipate, so tools may suffer from thermal damage.

TDC Inconel Machining Examples

Tungsten

Tungsten, meaning “heavy stone” in Swedish, is a metal that is about 2.5 times denser than iron and has high hardness and a high melting point. These characteristics make it ideal for use in cutting tools, balance weights, and heat-resistant structural components.

However, due to its hardness and heat resistance, tungsten places significant strain on cutting tools during machining, making it extremely difficult to cut.

TDC Tungsten Machining Examples

Key Points for Machining Difficult-to-Machine Materials

Machining difficult-to-machine materials poses challenges such as achieving high precision and surface roughness, as well as significant wear on cutting tools.

However, these issues can be addressed through measures such as using rigid machining equipment, high-quality cutting tools, and optimizing machining speeds to suit the material properties.

For example, when machining stainless steel, using oil mist to cool the machining area can reduce tool wear and maintain machining accuracy. Other measures include lowering feed rates to minimize temperature rise and using wear-resistant tools to improve durability.

Consult TDC for Machining Difficult-to-Machine Materials

At TDC, we have a proven track record and know-how in machining a wide range of difficult-to-machine materials, including stainless steel. We cater to both prototype and mass production requests, so feel free to reach out to us with your requirements.

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