Keywords
Citation
(2003), "Cranfield team achieve breakthroughs in aerospace machining times, accuracy and surface finish using Holroyd Edgetek machines", Assembly Automation, Vol. 23 No. 1. https://doi.org/10.1108/aa.2003.03323aaf.003
Publisher
:Emerald Group Publishing Limited
Copyright © 2003, MCB UP Limited
Cranfield team achieve breakthroughs in aerospace machining times, accuracy and surface finish using Holroyd Edgetek machines
Cranfield team achieve breakthroughs in aerospace machining times, accuracy and surface finish using Holroyd Edgetek machines
Keywords: Cranfield University, Aerospace
A research project undertaken by a team at Cranfield University's School of Industrial and Manufacturing Science has employed Holroyd's superabrasive Edgetek machines to achieve significant breakthroughs when machining Nickel-based superalloys; materials which are notoriously difficult to work. The breakthroughs, in terms of reduced cycle times, better surface finish and improved accuracy, have been achieved using the latest high efficiency deep grinding (HEDG) techniques. They are likely to have a profound influence on the way that superalloys are machined in the future within the aerospace industry.
The Cranfield team, led by Professor David Stephenson, carried out lengthy "Burn Threshold Studies" on Inconel 718 - a superalloy commonly employed for gas turbine components, using Holroyd's "Edgetek" Superabrasive Machining process. Manufactured at Holroyd's UK factory in Rochdale, the multi-axis, CNC controlled Edgetek machines deploy proven HEDG techniques, using Cubic Boron Nitride (CBN) wheels at surface speeds of up to 200 m/s. This enables them to achieve high depths of cut and optimised metal removal rates far exceeding those of more conventional machines, such as CNC lathes, milling and machining centres and grinders (Plate 3).
Plate 3 Holroyd's superabrasive Edgetek machine
An Edgetek machine (a five-axis unit) was specified for the Cranfield research project due to its ability to machine Nickel-based superalloys such as Iconel 718, which are extremely difficult to work. The ability of these alloys to retain much of their strength at elevated temperatures means that wear rate on conventional tooling is rapid, even when cutting at low speeds. In addition, problems such as work-piece burn and poor surface integrity are common, due to the alloys" low thermal conductivity. Over the last 30 years developments in creep feed grinding techniques have addressed some of these problems, notably in achieving higher rates of metal removal, but economic pressures to reduce manufacturing costs further, and to improve productivity, still remain.
As a direct result of these pressures, a growing interest in HEDG has developed, which can be considered as a combination of creep feed grinding and high speed grinding, using high wheel speeds often in excess of 200 m/s. A main area of research has been to attempt to prove a commonly held HEDG theory that very high stock removal rates are associated with low work-piece temperatures. Key to this, were the grinding trials carried out at Cranfield University.
The trials were undertaken on blocks of Inconel 718 measuring 40 × 40 × 40 mm, using a "down grinding" mode and grinding parameters were varied over the following range: depth of cut: 0.05-1.5 mm, work speed: 0.05-55 mm/s and wheel speed: 50-150 m/s. For each test a series of 15 mm wide cuts was taken and resultant forces were measured using a three-axis dynamometer.
Although the results of the trials are naturally very detailed, the general trend shows a reduction in specific grinding energy as specific stock removal rates increase. Commenting upon this, Professor Stephenson said, "The thermal modelling results correlate well with experimental observations of grinding burn. Modelling indicates the potential benefits associated with HEDG, using high work speeds and large depth of cut to minimise the finished surface temperature. Thermal modelling also highlighted the significant contribution that CBN abrasives can make to heat removal."
These results, highlighting the large depths of cut and accompanying lower temperature work-piece characteristic of HEDG, have significant practical relevance in terms of aerospace manufacturing processes, in that the two promote dramatically improved productivity, less surface deformation, improved accuracy and better surface finish.
For further information, please contact: Paul Hannah, Sales Director (Machine Tools and Rotors), Holroyd, Harbour Lane North, Milnrow, Rochdale, OL16 3LQ, England. Tel: +44 (0) 1706 526590; Fax: +44 (0) 1706 353350;E-mail: phannah@holroyd.renold.com; Web site: www.holroyd.com