Product category:
Special purpose and multi-function tooling, broaching, etc.
News Release from: Horn Cutting Tools | Subject: Horn Type 382 grooving/slotting cutter
Edited by the Manufacturingtalk Editorial
Team on 24 January 2003
Insert grooving tools halve machining
time
Substitution of a machining process using an insert type grooving/slotting cutter has reduced machining time on highly alloyed aerospace components from around 100 hours to 44 hours.
Substitution of a machining process using a Horn Type 382 grooving/slotting cutter with Type 314 grooving inserts has reduced machining time on certain components from around 100 hours to 44 hours at PWA International, Rathcoole, near Dublin The cutter is used to machine internal slots at the third and fourth stage positions on low pressure turbine casing repair sections manufactured in Inconel 901, Inconel 718 or Waspalloy
This article was originally published on Manufacturingtalk on 27 Apr 2004 at 8.00am (UK)
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On a prior operation within the same cell, which is carried out on a vertical boring machine, application of Horn 312 type grooving inserts has improved cycle times, on reprofiling of re-metalled features, by about 50 per cent.
This has been achieved through improved wear resistance of the Horn inserts, allowing sustained use of much higher speeds than the previous tooling regime.
PWA International is a leading specialist in the field of reconditioning major jet engine components produced by parent company Pratt and Whitney for use on civil airliners.
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Grooving tooling and applications engineering has helped a transmissions manufacturer to make considerable savings in machining times, tool life and solve swarf management problems.
Low pressure turbine casings vary in size up to around 70in maximum diameter and are not unlike a large metal bowl in shape.
These are constructed by welding a number of rings together.
On the inner surface there are a large number of annular ribs; these stiffen the main structure but their primary purpose, once they are machined with slots and holes, is to provide the means of locating internal engine components such as nozzle and stator vanes.
Hugh Kavanagh, PWA product support engineer explains.
"In service the inside of the engine is subject to high temperatures and the passage of corrosive gases while the cycle of expansion and contraction when the engine is running and idle causes fatigue.
Over time this causes deterioration of the internal features and all engine manufacturers specify periodic service intervals when major overhaul becomes necessary.
Our responsibility is overhaul of the case, which is subjected to very thorough inspection to determine wear, presence of cracking and shrinkage prior to remedial action being taken to return it to 'as new' condition." A wide range of repair procedures are available to PWA, in accordance with the manufacturer's manual for the engine.
In some cases a patch repair can be welded on.
In many cases a complete ring section is cut out and an entire new section is welded in using electron beam welding.
Another procedure is to rebuild worn sections by plasma spray application of new metal.
In all cases the repaired area is stress relieved to bring the assembly to a consistent metallurgical condition.
The case is then re-machined before being returned to the engine rebuilder for assembly.
Mr Kavanagh noted.
"Like any other business we are in a competitive market so it is important to develop processes that combine quality with maximum rates of productivity.
The parts that we recondition are worth hundreds of thousands of Euros so our customers tend not to hold stocks; therefore they need us to turn them round to schedule.
Tooling development is an important aspect of our activities as it allows us to maximise the performance of our machine tools." The machining process is complicated by the fact that the materials being machined are at the exotic end of the range while the components, though large, are also fairly delicate.
On the slotting operation, which is carried out on a rotary indexing table mounted on a large horizontal boring machine, dozens of slots up to around one inch deep need to be machined in the annular ribs.
"We used to machine all of these using an alternative make of cutter, " said Mr Kavanagh.
"Although this was satisfactory from the standpoint of accuracy the operation took a very long time - typically 100 hours.
Moreover around 95 per cent of casings that we handle need this operation so it was identifiable as a major bottleneck in the reconditioning process." The solution was provided by Horn UK, who were brought in by Dublin-based Flatley Engineering, distributors for Horn tooling in Ireland.
Horn applications engineering personnel worked with PWA to develop optimum feeds and speeds for the process.
It uses a Type 382 disc-type groove milling cutter of 160mm diameter having a double row of eight inserts to give 15.5mm overall width with 16 cutting edges.
These are provided by Horn 314 grooving inserts, each of which has three indexable cutting edges.
The diameter of the tool allows relatively high machining speeds to be achieved, while the Horn insert/toolholder combination allows much higher feeds and speeds to be sustained, providing much higher rates of stock removal than could be achieved previously.
"The Horn tooling has made a major impact on the slotting milling operation and the applicable costs." Kavanagh reports.
"Our capacity to complete slot machining has effectively been doubled by a relatively straightforward alteration to the machining route.
Throughput of these components is now much quicker as the bottleneck has been unplugged.
Indeed the success of this exercise led us to examine where else we could achieve savings using Horn tooling." The next candidate application turned out to be a close tolerance vertical boring operation within the same cell as the slotting application.
The principal activity on the vertical machines is re-machining of internal lips and grooves following welding repair to build up wear areas.
This is close tolerance work with lip thickness, groove width and groove depth needing to be held to 0.004in.
Moreover when the existing features have been re-metalled the ribs are already slotted so there is a high proportion of interrupted cut work.
"The latest cases are manufactured from Waspalloy which is exceptionally difficult to machine." Kavanagh added.
"Material hardness is around HRc 43/46 on the case and HRc 30 on the weld metal.
With the old tooling machining performance was poor as both speed and depth of cut were low and insert breakage was common." Tooling development work was completed by Flatley, working with PWA personnel.
In this instance Horn 312 inserts offered a straight swap from the previous tooling, allowing continued use of existing cartridge-type tool holders.
"Performance is much improved," Kavanagh confirmed.
"In addition tooling costs have reduced due to it not being necessary to replace the tips with the same frequency.
Depending on the extent of the repairs carried out to an individual casing we can be looking at between 16 and 30 hours of machining time on the VTLs.
Use of Horn tooling means this is around half the time that we needed previously.
Moreover the cycle time is predictable - which it wasn't before - so we can plan our machining throughput with much more confidence .
(This was Manufacturingtalk's Top Story on 23 January 2003).
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