High Efficiency Deep Grinding|
HEDG grew out creep feed grinding and if current news reports are any indicator it will be the technology of the future for grinding of new materials, particularly with applications of CBN for aerospace metals. In 2001, a collaborative program brought together researchers at Cranfield and Liverpool John Moores universities, UK, with 7 industrial partners in a program that validated the technology and developed methods to optimize this process with phenonmena material removal rates that halved traditional product cycle times. Recently Holroyd, parent company for Edgetek and its HEDG machine tools, reported a $1.2 Billion sale to a Chinese aerospace manufacturer for systems to manufacture compressor blades for jet engines. In the US Max-Tek LLC actively promotes its line of Superabrasive Machines using the technology.
Compared to more conventional creep feed grinding, HEDG has much higher specific removal rates, typically 50 – 2000mm3/mm/s compared to 0.1– 10mm3/mm/s. In addition, the lower finished surface temperature adds improvement to the quality of the finish. As this book and research shows, contrary to conventional wisdom, thermal damage drops dramatically at very high wheels speeds and grinding efficiency raises equally dramatically.
The scientific basis for HEDG technology can be found in this book by Taghi Tawakoli.
|AN EXCERPT FROM CHAPTER TWO...|
As the creep feed grinding technique has developed, and its areas of application widened, conventional machining methods, such as form milling and turning, can now be replaced to some extent.
Following the introduction of the process into industrial manufacturing, it took a long time for creep feed grinding to win general acceptance. Larger contact lengths, higher total energy conversion, and higher grinding forces led to the widely held view that creep feed grinding might cause thermal damage to the surface of the workpiece and the surface zone.
Scientific research succeeded in throwing light on the technological mechanisms, thus explaining the advantages of creep feed grinding compared with conventional reciprocating grinding. In particular it was the important finding that, in creep feed grinding, during the removal process the newly produced surface is exposed to a substantially lower thermal load than in reciprocating grinding, which led to the widespread adoption of the creep feed grinding method.
Research into creep feed grinding at higher stock removal rates could only be carried out with the introduction of new machines and grinding tools and the higher peripheral speeds possible with such tools. This research paved the way to the current use of high performance machines with modern CNC control systems for carrying out semi automated machining operations.
The further development of creep feed grinding at greater stock removal rates gave rise to the term 'high efficiency deep grinding'. The machines used for high efficiency deep grinding have a high spindle output and are fitted with a stepless speed control. At wheel speeds in excess of 100 m/s special grinding wheels must be used. Very few aluminiurn oxide wheels can be used at peripheral speeds as high as 125 m/s. The development of new abrasives, such as CBN (cubic boron nitride), has resulted in significant advances in the field of modern highefficiency grinding. Very high wheel speeds (v, > 100 m/s) are possible when CBN abrasives are used in specially made grinding wheels (for example, with a metal bond).