Effeciently machining high temperature alloys

Large CNC vertical lathe

Inconel, Waspaloy, Hastaloy and other high nickel alloys require very low surface footages and thus machine very slow. Many machining practices can be applied to ease their cutting ability. Increasing insert life, running the highest possible surface footage, depth of cut and immense coolant flow for the removal of heat in combination will greatly increase your productivity. Try some of these tips and apply the ones that best fit your applications and improve your cycle times.

The main focus should be right where the rubber meets the road, type, grade and geometry of the cutting insert. CNMG’s are very common and are usually utilized in every possible citation due to the fact that they can turn and face eliminating a tool change. If you have turned inconel with this insert you notice after a short while a burr begins to build in front of the cut. This material is work hardened and is very difficult to cut. It will eventually break the insert and the build up will have to be removed before cutting can continue. The fix for this is choosing a geometry that leads into the material such as a SNMG at 45 degrees. This keeps the lip from building up and hardening. Another economical factor relating to this geometry is that you have eight cutting edges as opposed to four on a CNMG. Use this geometry for roughing. If you must meet in a corner (i.e. the cut does not pass all the way through the material) then change tools and then eat the corners out with a CNMG. Normally, changing tools is not productive and you would never think this way but due to the long cycle times in cutting these materials a new mind-set is necessary.

Ceramic offers great possibilities if the application is correct. Usually this is a finishing operation due to depth of cut. These inserts do not work well with over-lay type materials due to inconsistencies in the welding. Ceramics have come a long way and a new type of ceramic that cuts well with the use of coolant keeping the part cool is called a whisper. Yes, ceramic with coolant. You want to choose the strongest geometry possible and that is in the form of a button. There is no cutting tip to break off and a circle is just inherently strong. You can see cycle time improvements as great as ten times over that of carbide.

“They are just not built like they use too” referring to the stability and rigidity of machine tools directly influences your ability to machine at high metal removal rates. Back to the rubber and the road analogy, an insert is going to wear at the tip faster than anywhere else no matter what your depth of cut is. If your machine has the rigidity it is far more effective to take a large cut. Choose the biggest insert possible, mainly because this insert will be thicker and will resist breaking.

The most detrimental factor in machining high temperature alloys is the accumulation of heat. Coolant flow and pressure is of utmost importance. Getting the cooling fluid down to where the cutting is actually happening is paramount. The physics of metal cutting is at a molecular level and the cutting fluid must have the minute size to reach this level. A small molecule has this ability with enough pressure. The addition of large molecules in the form of antifoaming and antibacterial will hinder the coolants ability to effectively reach this macro level.

As in any machining process a multitude of variables effect how a part is going to run. The only effective way to find the best practice is trail and error. What works best on one machine may not be the fix for its neighbor.