Titanium is widely used in a variety of applications due to its versatility and strength. It has a very high strength-to-weight ratio, weighs about half as much as copper and only slightly more than half of stainless steel. It is much less dense and has high heat and corrosion resistance. It even has several properties for biomedical compatibility, making it great for medical use. Applications within aerospace engineering, military and biomedical fields, among others, use titanium and titanium alloys for their strength and various properties.
Despite its advantages, titanium can be stressful to work with, for both the machine operator and their tools. But with the right approach, you can make the process of cnc machining titanium much less painful.
Machining Process for Titanium
Titanium can be a complicated metal to work with. All of those properties that make it ideal for intense applications make it formidable to work with. Its heat resistance and reactivity can damage your tools, and by extension, your workpiece, if you aren’t careful. You’ll need to consider every aspect of the process when working with titanium.
1. Cutting Tool
Your choice of cutting tool can have a significant impact on the job. As you’ll see, working with titanium involves a lot of high heat, so you’ll need a tool that can stand up to the heat and the hardness of titanium itself. A coated high-speed steel tool is probably your best bet. These tools are made of a combination of tungsten, carbon and vanadium and can maintain hardness up to 600℃. This type of tool can allow you to make deeper cuts and cause fewer shocks within the workpiece, creating less of an opportunity for chipped edges to occur.
2. Tool Coating
Tool coating is another significant way to make your cutting simpler. A coating helps your tool better deal with the high temperatures generated during titanium cutting. For example, a coating can make a carbide tool a reliable option. Titanium aluminum nitride (TiAlN) is one coating option that is driven by heat. As the surface heats up, it forms a layer of aluminum oxide, which brings down heat transfer and chemical diffusion between the tool and the workpiece. This coating transfers heat to the chips as the tool generates them.
3. Stable Surface
The titanium also needs to be cut on a very stable surface. This metal can be prone to chattering, or heavy machine vibrations, because of its flexibility and the high forces involved with cutting it. While one option is to reduce power, this could be worse for your machine and the project. Increasing speeds can lead to fire risks with excessive heat. Too much heat can also cause strain hardening, which can make your cutting edges even stronger. This extra strength makes your tools work harder and degrade faster.
Some ways you can increase stability instead include using a larger core-diameter end mill and finding the shortest overhang between the spindle nose and the tooltip. You’ll also want to keep your titanium machining feeds and speeds consistent and keep your tool moving steadily. If it drags in a corner for too long, it can result in more chatter and heat, wearing down the tool.
4. Climb Milling
Climb milling is a useful strategy to keep your chips in check. In conventional milling, which is the traditional method, the chips created from your tool start thin and increase to larger widths. This thin-to-thick approach puts more heat into your piece and increases strain hardening. It also causes more rubbing, which can degrade your tool faster. By using climb milling, the chip width starts high and then decreases, increasing the likelihood of heat transfer to the chip instead of your workpiece. It also creates a cleaner shear and pulls chips behind the cutter, so they don’t get in the way of new cutting.
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If you keep some core principles in mind about the metal and your machinery, you should be able to cut titanium without too much headache. Some aspects are known to be difficult, so you’ll need to pay special attention to these factors.
1. Keep Temperatures Down
Since titanium doesn’t conduct heat well, most of the energy generated during the cutting process goes into the tool. This heat can have several adverse effects, the most notable of which is causing premature tool failure. It can dull your tool and cause rubbing, generating even more heat and continuing the cycle. Depending on the materials you’re using, this could also be a fire risk. The dulling of your tools can be expensive for you and damaging to the piece of work.
Poor heat dissipation can also lead to strain hardening, in which the edges of your workpiece harden and become tougher to cut. This hardening affects the speed at which you need to be cutting and can lead to faster tool degradation. Using a generous amount of coolant can help bring down temperatures.
2. Make Your Surface Stable
One effective way to put added strain on your tool is to expose it to shock and jarring changes in force. It is common for the tool to experience this when it enters and exits the material. Instead of inserting the tool directly into the metal, gently arc it inward to ease it into the cut. This arc lets you gradually increase the pressure and makes the entry less jarring on your tool and less likely to tear the material. This path should follow thick-to-thin milling, as well as move in the same direction, clockwise or counterclockwise, as the tool.
For a similar result at the end of your cut, consider a chamfer. A chamfer is a sloped groove in the material. It lets the tool lose depth gradually instead of abruptly, which helps ease the transition for the tool with less force.
3. Watch Your Tools
A sharp tool is necessary for efficient cutting, and titanium can wear your tools very quickly. Inspect them frequently and replace them if they start to wear. A dull tool will add heat and consequently wear out even faster.
4. Leave Your Tool a Lot of Room
By using a tool with a smaller diameter, you create more exposure to air and coolant. Doing this allows the cut edge to spend more time cooling down. It also isn’t exposed to the tool and its heat for as long. This method is an effective way to control the temperature by giving the metal time to breathe in between cuts.
5. Reduce Galling
Titanium alloys to other materials readily, which can cause galling and rewelding of the edges while cutting. Keeping the heat down, using sharp tools and using lubricant can help reduce this effect.
6. Control Chipping
Edge chips occur when the metal pieces being cut off compress and adhere to the edge of the cutting tool. As more pieces build up on the cutting tool, they negatively impact performance and can result in a more quickly damaged tool and a poor cut. Using a sharp tool and lubricant can help reduce chipping.
How Is Machining Titanium Different Than Other Materials?
One of the most significant factors of titanium that makes it a fierce contender in the world of metals is its strength. Titanium is great for intensive applications where only the highest-grade materials can withstand the heat and tension applied to them. It is often subject to great heat from extreme friction. It also performs well in highly corrosive environments. The next section covers more of the applications that make use of these properties in more detail.
A key detractor in using titanium is its cost, which is why many will opt for steel or aluminum if the application can handle it. Titanium can be quite expensive compared to the other two. These alternative options are cheaper and have comparative qualities. Depending on the application, sometimes they can be used instead of titanium to save money and cover more ground.
Machining Titanium vs Steel
Steel is an alloy. Carbon and iron typically make up steel, but it is often combined with other elements to achieve different characteristics. Titanium can be an alloy, or it can be used pure. Many machinists work with “Grade 5” titanium, or Ti 6Al-4V. This combination is the most common titanium alloy, and it makes up about half of all global titanium consumption.
The alloys that mix with steel give it a variety of characteristics. Stainless steel is readily weldable and pliable, allowing for use in many different ways. Its shiny surface makes it an excellent fit for household appliances and some furniture. Stainless steel is also very strong and is suitable for structural components and is resistant to corrosion.
One major consideration here is that stainless steel is much more susceptible to fatigue. Titanium is very strong, even in high and frequently changing heat, and has high tensile strength. Stainless steel is also much heavier, so engineers often use it where weight isn’t as much of a concern. The low density of titanium allows it to have the strength of steel without the weight.
Machining Titanium vs Aluminum
Titanium and aluminum share similar qualities, including a good strength-to-weight ratio and corrosion resistance. For less extreme applications, aluminum can sometimes do the job for a lot less. It is a much cheaper option since it is much more common and not as difficult to produce as titanium.
Aluminum is often used in large-volume projects, where titanium might be too expensive since aluminum is lightweight and can cover a lot of ground. However, it doesn’t have a very high tensile strength or heat resistance in comparison to titanium. Its electric conductivity is much better than titanium, and it has strong thermal conductivity. As far as actually cutting goes, aluminum is much easier to modify than titanium.
One more aspect to titanium that makes it worthwhile is its corrosion resistance. This resistance is due to an oxidizing process that forms a protective layer upon exposure to air. This layer can even repair itself.
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As you’ve probably gathered, titanium is incredibly versatile and sees usage in high-end applications. Engineers and designers choose it for a variety of purposes in intense conditions.
Titanium allows aircraft to withstand incredibly high speeds — and incredibly high friction — that other metals like aluminum and steel would melt from. Famously, the Lockheed SR-71 Blackbird was the first major use of titanium in aerospace engineering. It needed to be lightweight as it was designed to travel three times the speed of sound.
While the commercial airplanes use significant amounts of titanium, military aerospace is where much of the world’s titanium finds its use. Titanium’s low weight, high strength and high heat resistance make it ideal for such use. It is costly, however, so a military-sized budget doesn’t hurt. The lightness of the planes can reduce fuel costs, making it more efficient in that regard. Titanium can be used in the general frame as well as various parts, including components of the engine. The incredibly high temperatures from a jet engine make titanium a great fit.
Other common uses for titanium include applications in the following areas:
Military: In addition to the military aerospace applications, titanium is common in missiles and artillery. It can also provide coverage to submarines and ground vehicles with its excellent ballistic resistance.
Ships: Titanium also performs well in the ocean. Its corrosion resistance makes it perfect for combating the forces of seawater. Various shipbuilding components, such as propellers, ballast and piping systems are some of the uses for titanium. Along with the corrosion resistance, it also reduces weight and allows for a lighter ship.
Medical: Titanium even has a place inside the human body. It is used commonly in implant devices, such as hip joints, knee jones, bone plates and pacemakers, among others. Most implants use vanadium- and aluminum-free alloys based on Ti-6Al-4V. Physical properties of biocompatible materials include low electronic conductivity, high corrosion resistance and a thermodynamic state at physiological pH values, all of which are present in titanium. It also promotes osseointegration, or the connection between bone and another object, like an implant.
Dental: For similar reasons as medical applications, titanium is also frequently used in dentistry. Dental implants, along with bridges and crowns, are some of the common uses.
Sports: Some consumer goods making use of titanium include sporting equipment. Most get their benefit from the lightweight nature of the metal. Golf clubs, bike frames, baseball bats, tennis rackets and camping gear are just a few instances of titanium in sporting goods.
Jewelry: Even jewelry is using titanium — again, mostly for its weight, but also its attractive color. Watches, eyeglasses frames and wedding bands are popular accessories to use it, along with necklaces, bracelets and earrings.
Improve Your Titanium Machining Process Today
If you arm yourself with the tools and knowledge necessary to take on titanium cutting, it doesn’t have to be a difficult or expensive endeavor. Working with a sturdy machine and well-designed tools will keep heat risks low, while practices like climb milling and using sharp tools will help keep costs down. You can make life easier for your workers and yourself by investing in the proper tools for titanium cutting.
Astro Machine Works can help you develop and find those tools. Our friendly and passionate team members are there to help you optimize your setup for titanium cutting. Contact us today to find out how!
