Welcome to Part 3 of the 4 Part series which takes a look at the machining and considerations of titanium. In the first part Part 1 – the general handling considerations when working with titanium and in Part 2 we looked at how to machine titanium with turning which ‘turned’ out to be a relatively easy process if standard techniques and approaches were followed.
This part will focus on Milling and how titanium metal can be milled effectively. Milling involves removing metal by rotary cutting from a work piece in the direction of angle with the axis of tool. A milling machine is often called a mill which have involved into being automated machines with the introduction of CNC. Furthermore in recent times turning and machining equipment has been integrated to create “live tooling” and where multitasking machine perform both machining and turning.
But to take it back to basic milling, it is more difficult from turning and the relative ease with which turning is performed. What happens is that during milling chips tend to stick to the teeth and so cutting is only partly performed on a rotation. Further more when contact is made next, when the chip is dropped off the tooth is easily damaged.
This problems is quite serious and cannot be solved easily. It can be limited by using a climbing mill rather than the standard milling machine. With climbing milling the cutter only ever touches the part with the thinnest material and so reduces chip welding. When slabs are milled then it is important that the slap should be worked in the same direction of cutting teeth. When it comes to the slab and milling the face then the cutting teeth should emerge from the direction of workpiece feed.
Its common for chipping to be the cause if the cut edge fails during titanium milling. From experience high speed steel are far more effective than carbide tools and whilst the carbide tools can reach the higher speeds then they still dont prove as cost effective as high speed steels. In any case it is worth experimentation between the two types to understand the benefits and costs for individual jobs. Finally as with the case with milling we suggest that a coolant which is water based is preferred.
So to recap on the key points with milling titanium:
- Use climb milling to reduce chips and teeth damage
- Experiment with both carbide and high speed cutting tools – The carbide may give you slightly better results but at much higher costs
- Use water based coolants