Table of Contents
- Machining Process for Titanium
- Titanium Machining Tips
- How is Machining Titanium Different Than Other Materials?
- Machining Titanium vs Steel
- Machining Titanium vs Aluminum
- Common Uses for Machining Titanium
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 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.
Titanium Machining Tips
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.