My interest is 1930’s steel framed aircraft using tubular steel construction with steel plate gussets/fish plates, eg Hawker Hind – Hurricane. CAD drafting, 3D laser scanning and laser cutting are wonderful productivity tools that allow the recreation of small runs of antique steel fuselage members. This would have been cost prohibitive or impossible to imagine ten years ago. These tools allow the recreation of wonderful aircraft. Anecdotally , I have acquired an impression that laser cut parts are not accepted in aviation circles. At core, I surmise that heat affected zones at laser cut boundaries are considered to render such parts unacceptable.
In the course of other engineering work I conduct business with laser cutters producing work for racing teams using 4130 tubes. I would accept that the forces that racing car bodies are subjected to may be equal or in excess to those that aircraft are subjected to. Laser cutters report no issue with the supply of laser cut 4130 components into the car racing industry.
I can understand that new technologies can be too complex for some to assimilate, and that a defensive response is to ride on the wings of hard earned credibility to dismiss an approach that requires you to launch a boat on unknown seas. This is OK, as long as it does not disadvantage or discourage progress. I can understand that the laser cutting technology of 2000 may have been cumbersome, and may have adversely affected materials, but I see the laser cutting technology of 2013 as entirely different.
Putting on my Spock ears, the only way I can pecieve that laser cutting may affect a material is via heat. In the case of a high tensile steel, this may soften the material in the heat affected zone. So what ? ( I am not a metallurgist, so this is where a metallurgist can sit me on my behind and put me right ).
In order to understand where a thought has come from, I try to go to the source. I figure most aeronautical engineers are afraid of things cracking up. Steve Austin, astronaut, a man barely alive. Challenger. Sally Ride. De Havilland Comet, lots of things falling after fluttering wings. I figure that cracks are what keep the engineer awake at night.
I figure stress cracking, or more realistically corrosion/stress cracking is the issue. The segue to laser cutting is the creation of weakened boundary zones on laser cut parts that allow stress cracking to originate. My gut feel is that a soft boundary zone may actually mitigate against the birthing of cracks in fishplates.
I have before me “Ferrous Metallurgy in Aeronautics – A complete survey of the qualities and characteristics of modern steels for Aero Work” by WH Hatfield, Aircraft Engineering May 1935. Relax, I also have a beer. Hatfield was the dude from England’s Vicker’s steel that I guess most influenced ferrous material selection for things like the Hawker Hurricane, which had high tensile stainless fish plates rivetted to a high tensile steel tube construction. I figure that this stuff was absolutely cutting edge in the 1930’s, requiring imaginative and open minded engineers exploring all the possibilities of fascinating new materials and processes. But their virgin, firework thoughts have now become the ossified dogma of the staus quo. I think Hatfield would have been driven to poetry by laser cutting and its possibilities.
I figure the fear of cracking really started with the move from timber based aircraft to metal based aircraft. In the opera citare Hatfield writes about the stresses created by punching and shearing metal parts. The staus quo accepts punched and sheared parts as being OK. The staus quo is comfortable with the creation of expensive punching and shearing tooling by vanishing artists, which, by its cost, holds back aircraft restoration. But the author of the staus quo warns : “there are a number of processes employed in fabrication, particularly with sheet materials, which are liable to leave the parts concerned in a state of internal stress. Any cold pressing or cold forming operation is liable to do so….it should be remembered that stresses of this kind are additional to the service stress, and they are apt to be ignored in calculations when designing.”
Put with colour, hidden microscopic stress zones created on material boundaries by punching or shearing operations affected by corrosion develop into microscopic cracks that open up on a sunny day and cause your wings to fall off above a preschool. So perhaps laser cutting may prevent this? Hatfield writes about how they tested for this in 1935 : ” Two pieces of 2.5 inch square were cut from high tensile stainless steel strip of two different qualities. Erichsen impressions (The depth of impression in millimeters required to fracture a cupped sheet metal supported on a ring and deformed at the center by a spherically shaped tool) were put on these four samples and, recognising that this left the samples in a state of internal stress, they were placed in a solution designed to cause accelerated corrosion. The solution was 50% HCl cold, and the pieces were left overnight. Numerous small cracks developed in two of the samples.”
So perhaps the thing to do is to crop some samples of high tensile steel in a sharp guillotine, a blunt guillotine and via laser cutter, and test them for corrosion cracking on their boundaries as described above. I will bet a six pack of Coopers stout that there will be more stress cracking in the guillotined samples. I would be interested in what anyone knows or thinks.
By: powerandpassion - 28th January 2013 at 12:28
EDM, be it plunge or wire cut, produces a recast edge (15-20thou thick) which needs to be removed from a highly stressed part.
Power&Passion
The suggestion that the existence recast edge produced by laser or EDM is “anecdotal” is stupid considering even a very elementary understanding of the process. Just try googling the subject and you find a good number of technical description of it and its detrimental performance on the material properties.Not wanting to look like a fool myself I will not argue with one.
VegaECM, I respect your knowledge. You have provided the most detailed, logical and considered flight over a topography I want to learn about, I appreciate it.
But play the ball, not the man, otherwise I will find you, marry your daughter, then you and I will sit and glare at each other over the Christmas turkey for the next 28 years while I, mouth full, cutlery waving, hand on daughter’s leg, make bold announcements over things I know nuthin’ about !
Anecdotal refers to conversations, posts, experiences I have come across. I would love to have some links to scientific papers which may provide more detail as part of a discourse. Until I get this wrapped in a rock and thrown through the window even Vega ECM is anecdotal !
Last week I was quoted $3,000 Australian dollars, enough to buy a dinner with Bill Clinton, to make up a press tool for a short run antique aircraft part. I have been sufficiently impressed with my public picking of fluff out of my belly button on this laser cutting topic to consider making up the same press tool out of 1mm high tensile steel in the ‘sliced crim’ method previously described. Sliced crim was the guy in America who volunteered after execution to be cryogenically frozen then sliced on a ham slicer, each slice being photograped to allow some interesting time lapse video to be made 15 odd years ago. I have not eaten ham in the US after this. I will find out his name and call this proposed tool making process after him. I really hadn’t thought about ham dude for 15 years until this stream of conciousness about laser cutting, and I appreciate folk have been very indulgent of me as I work the potter’s wheel, thank you.
Understanding, anecdotally, that laser will recast an edge from 5 thou to 15-20 thou on high tensile steel, starting from a CAD model, I will make up a press tool 150mm wide out of 150 slices of 1mm sheet bolted together through laser cut bolt holes. If the slices make an impression on the work, I will experiment with rubbing two pack car body filler over the working face, but I do not think I will need to do so. My hypothesis is that I will do this in one day, not the 4 weeks proposed by the toolmaker and at less cost than $3,000 quoted, using a cheapo laser located at the back of a take away food shop. I will let you know how much it costs, and I will run myself at parliamentary rates. Good people may be shaking their heads at me, but if I can make a short run stamping tool at a fraction of the cost then a lot of possibilities will open up.
I have also been struggling with the idea of turning up a sequence of strip forming wheels in a roll former to develop the flower of a profile, where material springback is an unknown factor. Now I think I might laser cut a 25mm wide wheel out of 1mm thick laser cut discs, and bolt them together. If I need more or less bias on a particular wheel then I can just change some discs rather than throw a whole turned piece away. It will be like Lego. At least I hope I will resolve a working set that can then inform a conventional turned up set at a fraction of the cost.
In respect of EDM I have been sufficiently excited to go and look at a second hand one left in the corner of a shed, just to play around with. I will see what it can and isn’t supposed to do. EDM is all new to me, I feel like I am about to go on a date with a really hot sparkin’ babe. Love it !
In the end, for the beer, I will lay identical test pieces together, calculate cutting cost per cubic mm, spread some anecdotal jam over the top, and move off to perplex on other issues. No one has yet complained over the choice of Coopers Stout for the beer competition, which means no one has tasted this elixir of youth that can double as boot polish. If we had a forum where people could feel safe to say ‘I do not know’ then I would twist the tops of more beer and say ‘try this’, as I too might be given a lesson in hoppy American cheerleader beer or something British strained through a grandmother’s overcoat.
By: Vega ECM - 27th January 2013 at 11:52
EDM, be it plunge or wire cut, produces a recast edge (15-20thou thick) which needs to be removed from a highly stressed part.
Power&Passion
The suggestion that the existence recast edge produced by laser or EDM is “anecdotal” is stupid considering even a very elementary understanding of the process. Just try googling the subject and you find a good number of technical description of it and its detrimental performance on the material properties.
Not wanting to look like a fool myself I will not argue with one.
By: dko - 27th January 2013 at 10:31
The wire EDM machines most known are: Agie, Makino, Fanuc, etc.. The average limit of these machines is that they have strokes: x = 35 inches, Y = 25 inches. The advantage of these machines for cutting plan is that you can cut several pieces in pack with a gain of time running and better repeatability in size. The cutting accuracy is very high and geometrically precise, finally no thermal shock because the workpiece remains immersed in the dielectric fluid during machining.
By: powerandpassion - 27th January 2013 at 01:05
….. back on the workpiece!
Powerandpassion :
Yes with wire EDM you can cut flat plate,
the cost is approx. 1 cent/euro X 1 sqare millimeter !
Dko, thank you for the price, let’s us compare apples with apples.
I suspect most EDM folk in the antipodes will look confused if I talk about flat plate cutting, can you give me direction on what brand/type/year of machine & settings will accomplish this, so I can walk in and ask the right stupid questions.
Qldspitty, had to put plastic over the keyboard, tears were squirting out !
Things I have learnt so far :
1) No body really knows, across a range of fora. Waterjet seems to be accepted in the same way that everybody accepts the earth orbits the sun and quantitive easing means someone is actually in control of the global economy. The whole thing is a grey area. I think in 1992 there were problems with effective laser cutting of material like aluminium that rapidly absorbed heat, perhaps resulting in rough, melting edges with the lasers of the time. So it may have been written off by chaps who played croquet with Geoffrey De Havilland.
There is a side story to this, which is the rising tide of engineers who came with the war effort, and carried through to the 90’s. To anyone younger than 60, these were Gods. Now that the tide has receded, we are still playing their LP records in the form of The Knowledge (most worthwhile) while youth struts its stuff with iphones, no doubt in a few years with direct brain implants of wireless devices on 24 month payment plans. I reckon there is something to be got from both tables. Anyway :
2) Laser cutting creates the anecdotal phenomena of edge hardening. Perhaps this can be utilised to make rapid, low cost press tools, strip forming tools for low runs of antique metal work. Eg, create 3D model (3D scan?), slice into 3mm slices (like that frozen crim in the US sliced for science), laser cut slices with common locating holes, bolt assembly together to make press tool/froming wheel with intrinsic hardfacing. You could also make quick, ‘hardfaced’ custom tools like spanners for disassembling Japanese engines copied from British and made in metric etc
3) I didn’t know that you could program into laser a cutting run followed by a defocused beam ‘heat treating’ run while the work was still in position. This might help in ‘single process’ making up of things like high tensile springs in the contact breaker assembly of a magneto, maybe the intricates in a turn and bank indicator, CC interrupter gears, crankshaft shims etc. I think the precise control over the laser beam offers possibilities.
4) I know lots of laser cutters and can reach one as easily as opening a fridge. I have to search for waterjet cutters and they say things like, ‘ join the queue.’ Therefore I think the competitive pressures on the laser industry will drive costs down and innovation up more readily than waterjet. Waterjet is a Japanese tea ceremony and laser is Coca Cola. Maybe it is more appropriate to use the geisha, I would like to discover some things about it and other processes.
At the moment I am trying to get an origianal part, a laser/water/EDM cut equivalent from original equivalent material, then convince the uni down the road to put them under their microscope, upload the photos and ask you to indentify which is which for phase one of the beer competition. It will be a trick question, so beware !
By: pat1968 - 24th January 2013 at 21:08
All I can add is this….
http://www.youtube.com/watch?v=9pe0rNieL-Q
that can’t be me too much hair!;)
By: dko - 24th January 2013 at 18:07
….. back on the workpiece!
Powerandpassion :
Yes with wire EDM you can cut flat plate,
the cost is approx. 1 cent/euro X 1 sqare millimeter !
By: QldSpitty - 24th January 2013 at 01:03
All I can add is this….
http://www.youtube.com/watch?v=9pe0rNieL-Q
By: David Burke - 23rd January 2013 at 21:53
I think it had as from midday yesterday there was no discussion about lazer cutting at all. Its very easy to glean the information you want from this thread -there is hardly any thread drift at all and the information about lazer cutting is easy to find and concise. If you find that this thread is a clear example of where moderation should take place I should steer clear of the rest of the forum !
As for your professional interest – I am sure your aware that lazer cutting isn’t something your ever likely to encounter in the manufacture of aircraft parts in the U.K. There is no requirement to do so and the existing methods of manufacture are more than adequate. But as you already manufacture parts your aware of that .
As for your moderation -clearly the thread hasn’t been moderated -why don’t you start your own thread so you can get exactly the information you want without any deviation? I see no need for any kind of moderation on a thread that has lasted over six days with no input from yourself so far except for expresssing your displeasure !
By: bloodnok - 23rd January 2013 at 21:15
Bloodnok – Seeing as you have had since the 17th of January to express whatever opinion you liked in this thread but have chosen not and the last comments were posted at midnight – it seems rather strange that you should choose to tell people what to do when the sage brush is clearly blowing through the thread!
I hardly think the tumbleweed was blowing through the thread when it was still on the front page!
Do you really think your petty squabbling about who knows the most about Hawker biplanes is really relevant to this thread?
I have a professional interest in this thread as my job often involves manufacturing aircraft components as it’s what I do for a day job. Reading this thread it’s not made clear whether either of you have actually ever had any hands on experience of working on any aircraft, you both just dance around what experience you both have, from which, in my experience can only lead me to one conclusion!
Usually I’m not in favour of moderation on forums, but if it was ever needed then this thread is a prime example.
By: pat1968 - 23rd January 2013 at 19:51
David I with you agree 100%
By: David Burke - 23rd January 2013 at 19:04
Maybe he has or maybe the idea of lazer cutting was discounted by many a long time ago and it became a debate on the cost of rebuilding Hawker biplanes . As for your ideas on petty squabling -until we take the ultimate steps of censoring anything what we don’t like -the internet remains as free as it can be so I would much rather have a lively debate on a subject rather than some watered down drivel where everyone agrees !
By: |RLWP - 23rd January 2013 at 19:01
Maybe Bloodnock has done what I have just done – ignored this thread for a while, then dipped in to it to find a nicely argued discussion on laser cutting, followed by a long tail of petty squabbling
Richard
By: David Burke - 23rd January 2013 at 18:50
Bloodnok – Seeing as you have had since the 17th of January to express whatever opinion you liked in this thread but have chosen not and the last comments were posted at midnight – it seems rather strange that you should choose to tell people what to do when the sage brush is clearly blowing through the thread!
By: bloodnok - 23rd January 2013 at 18:04
Why don’t you two take your petty point scoring somewhere else or carry it on by PM. 😡
By: pat1968 - 23rd January 2013 at 00:07
David i have never said that restoring aircraft is cheap. Least of all Hawker Biplanes. What i said was that your sweeping assumptions are exactly that assumptions. If you want to tell me what you do for a living be my guest but an assumption is still an assumption.
here are a couple of examples
I should imagine
but I guess
imagine away and i am sure if you say it enough times people will believe its a fact. As for engineering that’s a science so no room for assumptions!
By: David Burke - 22nd January 2013 at 23:45
Yet again you cannot help yourself but bite ! You cannot understand that beig told the price of a restoration actually means that the information is truthful and that by asking something like 1.4 million for an aircraft at auction might well be an indication that the owner would like to get his money back as opposed to making a huge profit. As for your beloved Afghan wrecks -they are wrecks like any number of other wrecks than have been recovered -seeing them doesn’t make you in any way more gifted than anyone else who hasn’t. They are an egineering job just like any number of other machines that have been recreated.
Again you don’t know what I do for a living but your more than capable of presuming ! Good luck getting a Hawker biplane flying on six pence!
By: pat1968 - 22nd January 2013 at 22:36
I take it all back clearly not having been involved in the restoration and not having seen the Hinds recovered from Afghanistan you are clearly a genius! As Churchill once said or was Sir Sidney Camm?
“Never in the field of aircraft restoration has so much been deduced from so little, from an armchair”
I take my hat off too you sir. Maybe you should nip out to Myanmar and get your deductive juices flowing they clearly need your amazing abilities.
By: David Burke - 22nd January 2013 at 18:48
Ahh -I knew I would get your ‘stock’ armchair critic reply that seems to be aimed at anyone who has an opinion that differs from yourself !
As for the Afghan Hinds -I have not seen them but I saw the Demon pretty much from start to finish and I should imagine that the process is damn near identical but I guess you will now tell me I am wrong yet again!
By: pat1968 - 22nd January 2013 at 17:47
‘Their condition is self evident’ so have you actually seen the Hinds that have been recovered or just looked at some pictures and now you are an expert? That is pretty much what I expected. You are a typical armchair critic.
By: David Burke - 22nd January 2013 at 17:27
Pat -you have the link on your page to the Afghan Hinds recovered in the last batch. Various others have been recovered over the years by various parties.The condition of the latest batch is self evident.
As for Spitfires -people choose what they are interested in -witness the number of posts about Spitfires that might exist in comparison to how many people are interested in Hawker metalwork.
Yet again I will refrain from insulting you -your welcome to carry on with your insults if you feel that is the best way of getting your point across.
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January 17, 2013 at 12:40 pm