The improvement of machinability during laser-assisted milling of Ti-6Al-4V alloy was investigated. The effects of laser processing and milling parameters on cutting forces and tool wear have been examined. It is found that local heating and softening of the workpiece by the laser beam in front of the cutting tool significantly reduced the cutting forces, especially the force in the feed direction during up-cut milling. Laser power, tool–beam distance, depth of cut and cutting speed are the parameters influencing the change of feed force during laser-assisted milling. Analysis of the workpiece temperature rise due to laser beam heating shows that the feed force is strongly dependent on the workpiece temperature in front of the cutting zone; significant reduction of feed force occurred when the temperature in front of thecutting zone was in the range 200–450°C. Edge chipping is found to be the tool failure mode for both conventional milling and laser-assisted milling. A significant improvement in tool life during laser-assisted milling was obtained when the workpiece temperature in front of the cutting zone was at an optimum value. Compressed air was used to remove the chip from the cutting tool, which made the milling process more effective. The optimum workpiece temperature in front of the cutting zone with compressed air delivered through the spindle is about 350°C, higher than that with compressed air delivered through a stationary nozzle (about 230°C). The maximum tool life in the former case is much longer than that in the latter case.

The current investigation evaluates laser assisted machining, which uses an external laser beam to heat and soften the material to be machined locally in front of the cutting tool and offers an alternative approach to improving the machinability of titanium alloys. By reducing the cutting resistance, the cutting tool sees less pressure and life is enhanced. This paper reports on the cutting forces and tool life during laser assisted milling of Ti6Al4V alloy. Cutting forces, especially the force in the feed direction, reduce dramatically with laser beam assistance. The reduction of feed force depends on the laser power, depth of cut and cutting speed. This paper also discusses the major tool failure mode observed during both conventional and laser assisted milling operations.

Removal rates for machining titanium alloys are an order of magnitude slower than those for aluminum. The high strength and hardness coupled with the relatively low elastic modulus and poor thermal conductivity of titanium contribute to the slow speeds and feeds that are required to machine titanium with acceptable tool life. Titanium has extremely attractive properties for air vehicles ranging from excellent corrosion resistance to good compatibility with graphite reinforced composites and very good damage tolerance characteristics. At current Buy to Fly ratios, the F-35 Program will consume as much as seven million pounds of titanium a year at rate production. This figure is nearly double that of the F-22 Program, which has a much higher titanium content. As much as 50% of the final cost of titanium parts can be attributed to machining. Specifically, in this task, we are working to improve the material removal rate of titanium to reduce cost. Lockheed Martin is evaluating the potential to use lasers to heat the material ahead of the tool to reduce its strength. Coupled with other technologies that can improve the tool life and prevent the titanium material from welding to the tool, there is hope for a practical solution using similar milling machines to those which exist today, if not a simple retro-fit option. This presentation will present the current progress of this project and its potential impact to the Joint Strike Fighter.

Titanium alloy (Ti–6Al–4V) is one of the materials extensively used in the aerospace industry due to its excellent properties of high specific strength and corrosion resistance, but it also presents problems wherein it is an extremely difficult material to machine. The cost associated with titanium machining is also high due to lower cutting speeds (<60m/min) and shorter tool life. Laser-assisted machining (LAM) and consequently hybrid machining is utilized to improve the tool life and the material removal rate. The effectiveness of the two processes is studied by varying the tool material and material removal temperature while measuring the cutting forces, specific cutting energy, surface roughness, microstructure and tool wear. Laser-assisted machining improved the machinability of titanium from low (60m/min) to medium-high (107m/min) cutting speeds; while hybrid machining improved the machinability from low to high (150–200m/min) cutting speeds. The optimum material removal temperature was established as 250°C. Two to three fold tool life improvement over conventional machining is achieved for hybrid machining up to cutting speeds of 200m/min with a TiAlN coated carbide cutting tool. Tool wear predictions based on 3-D FEM simulation show good agreement with experimental tool wear measurements. Post-machining microstructure and microhardness profiles showed no change from pre-machining conditions. An economic analysis, based on estimated tooling and labor costs, shows that LAM and the hybrid machining process with a TiAlN coated tool can yield an overall cost savings of ∼30% and ∼40%, respectively.

Titanium has extremely attractive properties for air vehicles ranging from excellent corrosion resistance to good compatibility with graphite reinforced composites and very good damage tolerance characteristics. At current Buy to Fly ratios, the F-35 Program will consume as much as seven million pounds of titanium a year at rate production. This figure is nearly double that of the F-22 Program, which has a much higher titanium content. Lockheed Martin has initiated “Project Black Ti” to reduce the cost of titanium parts by reducing the titanium consumption but not the quantity of titanium parts. Ultimately, we want to reduce the inherent waste in the current processing of titanium alloy products. The Kroll process, by which most titanium product is made today, is nearly 60 years old. Kroll himself predicted the process would be replaced within 15 years due to inherent inefficiencies – in 1950. Titanium is also mis-characterized as a precious metal, which it is not. It is the ninth most abundant element on the earth’s surface. Aluminum by comparison is the third most abundant but has a much more efficient method to convert it to a usable form. Until the turn of the 20th century, aluminum was considered to be as precious as platinum until the Bayer Process brought prices down from $1200/kg to $0.60/kg. Regarding titanium, one way to improve efficiency and buy less material to make the same parts is via Powder Metallurgy (PM). Until recently, titanium alloy powder was very expensive. However, new methods of producing titanium alloy have been developed which generate powder as an output versus massive ingots, which require multiple melts to achieve homogeneity. With powder, in theory, we should be able to get much closer to net shape and reduce the initial buy and reduce significant machining costs. These low cost titanium powders are becoming commercially available, which has the potential to initiate a paradigm shift in the applications of titanium. PM technologies and the consolidation of these new powders are now economically viable with the potential cost of the new powders running approximately an order of magnitude less than conventional PM grade powders. This paper will present the current status of “Project Black Ti” and its potential impact to the F-35 program.