Troubleshooting Common Problems Milling Titanium
There are a number of different cutters, end mills and drilling tools you can use on titanium, but they all face the same issues. These are heat, chatter, and tool wear.
Titanium Low Heat Conductivity:
Heat is possibly the hardest factor to deal with when milling. Titanium has a very low thermal conductivity. This means, unlike working with steel or other metals, the block of titanium and the chips do not absorb much heat. Most of the heat generated by friction builds up in the tooling. When the tool gets hot, the edge softens and the tool becomes useless. This is called plastic deformation wear. When the tool dulls, it increases the cutting forces, which, if left unchecked, destroys the tool.
Check the speeds and feeds are correct for the tooling. Incorrect cutting speed can generate too much friction and an improper feed rate can overload the cutters. Keep the radial engagement low. With less of the tool’s surface cutting it has more time to cool. Use a tool with a higher number of flutes. The more flutes on the end mill, or cutting surfaces in general, the better the heat is dispersed. Ensure that the thick to thin chip method is being used. The thick chips at the start of a cut will carry away more heat and the thin chips at the end of a cut will be less likely to weld to the cutter. When milling small pockets, use tooling much smaller than the pocket itself. This means the tool is using less of its cutter area at any one time and can cool properly.
Chatter Problem When Milling Titanium:
Tool chatter can ruin an end mill in seconds. The vibration can shatter a tool, dull the cutting edges and damage the titanium being machined (milled). The violent vibration could also damage fixtures or spindles, which costs time and money to replace.
Start by arcing in. When arcing into titanium, the blade is not trying to cut using a full 180 degrees of its cutting surface. This ensures you get a smoother transition into the cut. Use a chamfer at the end of the cut. This allows tooling to ease out of the material. Rely on a secondary relief style tooling to help reduce forces.
Carbide Tool Wear Problem:
Tooling used incorrectly can wear faster and cause work hardening. This is often caused by working the same part of the tool for long periods or in the same way. It can also be caused by improper speed and feed settings.
Alter the axial depth when you are cutting. At the depth of cut, oxidisation and other reactions can actually damage the tooling. By altering the axial depth, the problem is spread so that no one piece needs to absorb all the punishment.