Thermally assisted machining

Thermally assisted machining (TAM) of Ti6Al4V alloy for JSF program

The challenge

Build a TAM Prototype system for industry to use
The TAM prototype system involving laser optics integrated into the milling head will allow Australian machine houses to get interested in applying this technology for aerospace application potentially enable to be globally competitive.  Due to thermo-physical properties of titanium alloys the machining of these alloys is very slow and with growing demands for titanium parts in aerospace application machine houses can not maintain the productivity as demanded by aerospace industry.  The TAM process provides a technology and system that allows high speed machining for titanium alloys.  TAM working principle requires high power laser beam in the form of a line appropriately placed ahead of the cutting tool of a milling machine, and no coolant is used in the milling process.  Basic data such as level of laser power, laser head position ahead of the cutting tool, appropriate cutting depth and speed are essential to develop a prototype model.

CSIRO's fiber delivery laser. Lazer facing donward onto metal plate. Several wiers feeding into the laser

CSIRO 4 kW fibre delivery laser system and 3 axis Bridgeport milling machine used to develop working parameters.

Our response

Thermally assisted machining provides solution to machine Ti6Al4V alloy at high speed.
A high power laser beam in the shape of a line was used ahead of the milling cutter to locally preheat and soften the surface of the workpiece to the cutting depth without affecting the bulk of the workpiece.  A three axis milling machine was used along with a laser optics secured into the milling head.  Laser beam was delivered to the workpiece via optical fibre through the optics. Thermocouples were implanted into the workpiece and temperatures were recorded as a function of laser beam power, and feed speed utilising high speed data recorder.  Cutting forces were measured utilising force dynamometer to establish the boundary conditions at which the lowest cutting force is achieved.  Cutting tool requires cooling to prevent the formation of built-up-edge (BUE) at the insert edge and prolong tool life in dry milling operation.  The basic data were tested and validated at Ferra Engineering in 5 axis Vortex Mazak milling machine.  This project was partially funded by DMO and Lockheed Martin and has recently been completed in collaboration with RMIT University.

Drawing of Bridgeport milling machine. Includes bench top with overhanging device containing downward facing cylinder plus laser attachment both pointing to rectangular facing box

A schematic illustration of TAM model.

Drawing indicating insertion of chilled air through one nozzle and lazer beam through attached rectangular box like object.

High pressure chilled air is directed at the interface between insert and swarf. This reduces BUE formation and enhances tool life.

The results

This investigation revealed that a reduction of 30% cutting force can be achieved in high speed machining of Ti6Al4V using this technology.  To prevent BUE and increase tool life high pressure chilled air was directed at the interface between insert and swarf.  Cutting speed up to 200-220 m/min was utilised in this investigation and this is about in the order of 5 times that is conventionally used to machine titanium alloys.  All basic parameters including laser power, position ahead of the cutting tool, feed speed, and depth of cut have been established for prototype development.

Cylinder like object with groove inside of it.

Built up edge (BUE) formation at the tip of the insert during milling process. High friction temperature promotes welding between insert and swarf. This BUE reduces tool life substantially.