When machining titanium, feed rate and speed are not the only considerations. Titanium's heat conductivity is remarkably low, and a change in the feed rate only increases the temperature by 149oC (300oF). This makes it essential to use a cutting fluid to help reduce the forces of cutting and to carry the heat away. A sharp tool is also essential, and should be replaced as soon as the first sign of wear appears. While tool wear is not linear, a small amount of wear is often enough to cause tool failure.
CNC Machining For Titanium Parts
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High-speed steel tool
When it comes to machining titanium and its alloys, a high-speed steel tool (HSS) is essential for efficient cutting. Titanium has low strength compared to common alloys, and is also thin - only 0.022 inches thick - and brittle. Brittle materials have a restricted dislocation motion, which leads to plastic deformation and failure. In addition, a high-speed steel tool will also increase tool life because it can withstand higher cutting speeds.
High-speed steel is composed of a martensitic structure that contributes to its hardness and wear resistance. Martensite is formed by heating the steel to near-melting temperatures and then quenching it in a salt bath. The process produces a high amount of complex metallic carbides, which are responsible for the high-speed steel's hardness and wear resistance.
C-2 carbide tool
Choosing the right C-2 carbide tool for titanium and its alloys machining requires careful consideration of several factors. Firstly, the hardness of the tool must be selected based on the chemical composition of the material. Then, the cutting temperature should be suitable. The tool should be able to handle a cutting temperature of around 700-800 degrees Celsius and its pressure level should not exceed 1.5 GPa.
Cemented carbide tools are available in various coatings and grades. The two most common types are uncoated and coated. In a recent review of cemented carbide tools, Garcia et al. discussed the potential for tailoring the materials to meet the severe mechanical and thermal conditions. However, in order to design these materials, an extensive understanding of wear mechanisms is necessary.
Drilling
There are many aspects to consider when drilling when machining titanium and its alloys. First, cutting fluids must be properly selected to avoid affecting the mechanical properties of the metal. Chlorine ions have been found to cause stress-corrosion cracking of titanium alloys in laboratory testing. For this reason, chlorine was considered a suspect element in the past, regardless of concentration or specific conditions.
Wear rate is another important consideration. The wear of cutting tools is dependent on the amount of cutting fluid and the feed rate. When using a cutting fluid, the amount of heat emitted by the cutting tool should be kept to a minimum. Cutting tools should be replaced as soon as they show signs of wear. Wear is not linear in titanium, and even a small amount of wear can lead to complete tool failure.
Feeding into the stock
While there are many benefits to machining titanium, it's not without challenges. The material's high modulus of elasticity (modulus of springiness) and high hardness make it a challenging material to machine. Cutting speeds and feeds should be controlled carefully to avoid excessive wear and tear and increase tool life.
Machining titanium requires proper tools and techniques to minimize stress on the materials. When choosing tools, remember that tool wear does not occur linearly, but is typically a fraction of the initial wear. That is why you should avoid using dull tools. Instead, use tools with a radius of at least 70 percent of the minimum internal radius of the tool.
Tool life
Tool life is an important factor in the manufacturing process, especially if the machining requires a high-speed operation. However, machining titanium alloys poses specific challenges. This metal has high chemical reactivity and a low thermal conductivity, which increases the risk of premature tool failure. In addition, the metal's high elasticity increases friction, causing the edges of the tool to rub together instead of cutting.
The cutting tool geometry is another important factor that influences the life of the tool. Using varying rake and primary clearance angles increases tool life. Higher rake angles result in longer tool life than lower rake angles. For example, a 14-degree rake angle produces longer tool life than a ten-degree primary clearance angle.
Cutting forces
Cutting forces for titanium and its alloys vary with feed rate, but they are similar in general. The feed rate affects cutting speed only slightly. For most applications, the speed is set so that the cutting force is maintained for a long time. The cutting fluid helps to keep the tool cool, and it also carries heat and chip away, which reduces cutting forces. It is important to use sharp tools, and to replace them when they start to show signs of wear. Tool wear is not linear, and a small amount of wear can result in complete tool failure.
Titanium and its alloys are hard and durable metals. They are highly versatile and can be used in many applications. They can be found in aircraft parts, biomedical devices, and sporting equipment. Although they have excellent properties, titanium alloys are not the easiest metals to machine. This can lead to low cutting efficiency, fast tool wear, and poor quality.
