Product category:
Abrasive machining - manual and CNC machines
News Release from: Raysun Innovative Designs | Subject: Diati superabrasive high metal removal process
Edited by the Manufacturingtalk Editorial
Team on 12 July 2004
Grinding machines titanium faster than
milling
Capable of halving milling cycle times on titanium alloys, a superabrasive high metal removal rate grinding process will machine these difficult metals typically at 50mm3/mm of wheel width/sec.
Developed and patented world-wide by Raysun Innovative Design of Rugby, UK, the 'Diati' process uses an electroplated diamond grit regular or form profiled wheels operating at wheel speeds of 50-150m/s and under internal and external high pressure coolant, to remove a high volume of titanium alloy in a small space of time "It lends itself to the machining of non-ferrous alloys including titanium carbides, titanium alloys and ceramics," said Steve Ray, managing director of Raysun
This article was originally published on Manufacturingtalk on 26 Jan 2006 at 8.00am (UK)
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Raysun and Rolls Royce had originally developed the 'Viper' superabrasive grinding process, which uses open-structured abrasive wheels and high-pressure coolant to successfully replace milling when machining turbine and compressor blades in nickel-based alloys.
To-date, said Steve Ray, some 60 machine tools from Bridgeport Machines, UK (www.bpt.com) and Makino, Japan (www.makino,com) are being used by turbine manufacturers to 'Viper' grind components.
These same manufacturers wanted us to use the process for machining titanium alloys: "But it is no use grinding them," said Steve Ray.
"Titanium alloys are gummy, soft and ductile materials.
Titanium clogs up grinding wheels very quickly and the risk of 'burning' the alloy surface and changing the metallurgy locally (through burning and impingement of 'foreign' matter) is very high.
But the customers wanted to use grinding to acquire highly accurate blade root profiles," explained Steve Ray.
"Using single-point or form milling techniques is very expensive - so - we looked at titanium." Development work at Raysun began about two years ago, without any government or local authority help.
After much trialling and experimentation, the 'breakthrough' came on Christmas Eve (December 24), 2002.
"We found a set of parameters, the correct coolant system set-up, using a very small depth of cut and very high wheel speed to remove a high volume of material in a small space of time." The result is a process that can completely finish-machine a compressor blade from the as-forged condition in some 5min total cycle time: "Very typically in half the time it would take to mill one," said Steve Ray.
At the development stage, Raysun, with the support of Tyrolit (www.tyrolit.com), was basically looking at superabrasive grinding with the aim of developing a coolant system and wheel design that would keep the abrasive clear during cutting and would flush the fine swarf clear from the cutting area.
The process generates a lot of fume and smoke, so a fume evacuation system had also to be trialled.
Also, Raysun specified a full 5-axis machining centre to do the work.
The wheel design consists of a hard metal core that has a labyrinth of internal coolant passages.
The labyrinth is divided up into quadrants, one quadrant being used at a time.
Coolant pressure is 30bar.
Diamond abrasive grit is electroplated onto the wheel surface.
External coolant pressure is 80 bar.
The five-axis machining centre sought had to be stiff, with plenty of space around the spindle head.
Upon approaching Hermle, Germany (www.hermle.de), and after describing Raysun's intentions, the company said "We catch your vision" and a C40 machine was offered.
When asked why not the existing machining centre suppliers of the 'Viper' process, Steve Ray commented that, at the time, the UK company did not specialise in full 5-axis while the Japanese supplier would tend to keep the technology in Japan.
At first, silicon carbide wheels were tried, but wheel life proved to be low, while wheel particles tended to become embedded in the work surface.
Hence the choice of diamond grit.
Then came the problem of keeping the cutting zone cool enough.
It demanded a complete re-think on coolant delivery as well as taking the approach of taking light depth of cut at very high cutting speeds.
Along with the actual process development, the whole scenario - including process software, filtration and fume extraction, as well as automatic wheel-changing, and so on, was finalised ready for pre-production runs.
Once production trials are completed, then Raysun will be in a position to offer a complete 'package', which, depending on package options, will be in the region of EUR 400,000.
Geo.
Kingsbury (UK agent for Hermle, www.geok.com ) will deliver the machining centre, after-sales back-up, service and support.
Outside of the UK, the process package will probably be made available through Hermle agents.
Steve Ray made no hesitation in answering a question about consumable costs: "These are not yet fully optimised.
Certainly they can be double the milling consumable costs, but will do the work in half the time." He added that it also depended on the amount of stock removal.
Some companies have precision forged blade blanks; others machine a complete blade from a solid billet.
On reflection, Ray said that the whole development process of 'Diati' had involved the 10-man company in: "taking a 'whole heap' of known things in grinding and coolants and combining 'old tricks' into 'new tricks'." He said: "I reckon we fairly well got what we could get - maybe there is still some 'fine tuning' to be done.
The wheel design development was very arduous, as the materials used in the wheels are very important.
There is a labyrinth of channel holes and unless you get it right, the wheel can explode." the Diati idea was first presented to three key existing users of the 'Viper' process and two of them came in partnership to develop the process.
Raysun has applied for world-wide patents on all aspects of the Diati process.
As well as machining turbine blades and other engine components, the process may also be applicable to machining, for example, titanium alloy surgical implants.
(Mike Page).
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