Highlights of the DARPA Advanced Machining Research Program

Abstract

Results of a four-year Advanced Machining Research Program (AMRP) to provide a science base for faster metal removal through high-speed machining (HSM), high-throughput machining (HTM) and laser-assisted machining (LAM) are presented. Emphasis was placed on turning and milling of aluminum-, nickel-base-, titanium-, and ferrous alloys. Experimental cutting speeds ranged from 0.0013 smm (0.004 sfpm) to 24,500 smm (80,000 sfpm). Chip formation in HSM is found to be associated with the formation of either a continuous, ribbon-like chip or a segmental (or shear-localized) chip. The former is favored by good thermal properties, low hardness, and fcc/bcc crystal structures, e.g., aluminum alloys and soft carbon steels, while the latter is favored by poor thermal properties, hcp structure, and high hardness, e.g., titanium alloys, nickel base superalloys, and hardened alloy steels. Mathematical models were developed to describe the primary features of chip formation in HSM. At ultra-high speed machining (UHSM) speeds, chip type does not change with speed nor does tool wear. However, at even moderately high speeds, tool wear is still the limiting factor when machining titanium alloys, superalloys, and special steels. Tool life and productivity can be increased significantly for special applications using two novel cutting tool concepts – ledge and rotary. With ledge inserts, titanium alloys can be machined (turning and face milling) five times faster than conventional, with long tool life (~ 30 min) and cost savings up to 78 percent. A stiffened rotary tool has yielded a tool life improvement of twenty times in turning Inconel 718 and about six times when machining titanium 6A1-4V. Significantly increased metal removal rates (up to 50 in.3/min on Inconel 718 and Ti 6A1-4V) have been achieved on a rigid, high-power precision lathe. Continuous wave CO2 LAM, though conceptually feasible, limits the opportunities to manufacture DOD components due to poor adsorption (~ 10 percent) together with high capital equipment and operating costs. Pulse LAM shows greater promise, especially if new laser source concepts such as face pump lasers are considered. Economic modeling has enabled assessment of HSM and LAM developments. Aluminum HSM has been demonstrated in a production environment and substantial payoffs are indicated in airframe applications.

Heat-Assisted Machining

“…Komenduri et al (39) conducted research on LAM of Ti-6Al-4V and Inconel 718 using an Nd-YAG pulse laser, which has the advantage of providing higher absorptivity for metals due to its shorter wavelength. To overcome the intermittent energy problem, two different techniques were applied.…”

The role of modeling in the development of advanced processes for metallic aerospace alloys

“…Following research in the early 1980s [7], hog-out of tita nium billet and plate via high-speed machining (HSM) has been investigated as a cost-effective alternative to produce aerospace parts, particularly when the lot size is small; i.e., for cases in which the high cost of forging dies or casting molds can not be justified. However, the high strength, low thermal conductivity, and reactivity of titanium and its alloys result in substantial machining challenges.…”

“…These include novel selective heat treatments to impart a graded micro structure in a component and rapid recrystallization heat treatment to produce a fine grain size [4,5]. Various machin ing techniques to reduce part distortion or to remove metal at high rates [6,7] are especially valuable to minimize scrap or rapidly produce parts via 'hog-out' techniques, respectively, and thus provide economic advantages or useful alternatives for high-cost materials and high value-added manufacturing sequences.…”

Cutting performance and coated tool wear mechanisms in laser-assisted milling K24 nickel-based superalloy

“…The associated manufacturing cost is very high due to low-material removal rates and rapid tool wear. Recent work on LAM has demonstrated its potential for machining Ni-based alloys [6][7][8]. However, a key limitation of the process today is the lack of affordable cutting tool materials that can withstand the high temperatures experienced in LAM and also possess reasonable tool life.…”