Improving the fatigue strength of high performance gears
Improving the fatigue strength of high performance gears
Keywords: Fatigue, Gears, Surface finishing
Recent development work undertaken by USF Surface Preparation Group sister companies, Impact Finishers and Vacu-Blast International, on improving the fatigue strength of the high performance automotive gears and transmission systems used in motor racing and rallying is said to have achieved remarkable results.
Employing a combination of controlled shot peening and vibratory "superfinishing"to process critical transmission parts has reportedly resulted in the fatigue life of carburised steel gears being increased by more than 50 per cent. The process has also proved effective on components produced in titanium, Inconel and other special alloys (Plate 1).
Explained Franck Petit-Renaud of the Shot Peening Division of USF Impact Finishers, who headed the development project, "The increase in fatigue strength equates to an improved torque performance in the region of 30 per cent,with obvious major benefits for parts operating in arduous and competitive racing situations. An added bonus of the process is that surface lubricity and cosmetic appearance are also significantly enhanced."
The new combined process involves precision shot peening of the parts in a programmable peening machine, drawing on technology developed originally by USF Vacu-Blast for the controlled peening of aero-engine components, followed by superfinishing in a vibratory bowl machine (supplied by USF Walther Trowal) with a wet non-abrasive ceramic media to which a special chemical accelerator (known as "REM FML575 IFP") is added.
Plate 1 These transmission parts have been processed by the Shot-Peening Division of USF Impact Finishers using the new combined peening and "superfinishing" technique (courtesy of Hewland Engineering)
According to Impact Finishers the initial controlled peening process achieves the uplift in fatigue strength by inducing a residual compressive stress on the surface layers of the part. Superfinishing then gently removes any remaining surface roughness, to produce an extremely flat, very smooth and shiny, high quality surface. There is stated to be no alteration in the original geometry of the part and the chemical element of the superfinishing media prevents subsequent oxidation.
Impact Finishers has produced a detailed technical description of the process, which is available to genuine enquirers on request from the company.
Details available from: USF Vacu-Blast International. Tel: +44 (0)1753 526511, Fax. +44 (0)1753 538093; E-mail: info@vacu-blast.co.uk; Web site: www.surfacepreparation.com
