What Is The Best Way To Automatically Cut Aluminum?

Discussion in 'Metal Boat Building' started by John Stream, Feb 28, 2014.

  1. Barry
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    Barry Senior Member

    Most boat builders use plasma tables as they are cheaper to buy and run than waterjets or lasers. You have to clean up the edge with a small flapper disc to knock some of the dross off, but this is extremely fast. You can probably do 15 feet per minute on 1/4 inch.


    While plasmas will affect the temper at the cut, so will lasers, and as pretty much all of the edges will be welded, the welding heat will affect the joint even more in the HAZ area and take the strength down close to a 0 temper. Prox of course.
    The cutting rate in inches per minute is so fast that there is little distortion on sheet up to 1/4.

    I know of a couple of boat builders who use water jets, ( we used a High Definition plasma table)

    Someone suggested that you have to remove the oxide just prior to welding. Certainly you can do this manually but I do not know of a boat builder who would do this as when you are doing say a butt joint, you will have spent considerable time fitting and tacking the plates together prior to welding, perhaps days prior to welding and it is impossible to manually remove the oxide. The weld arc will remove the oxide, and the gas which shields the weld from the atmosphere will protect oxide inclusion in the weld.

    If you are considering a 50 footer, are you designing this yourself, which will mean a very difficult process to get a set of CAD programs for the various sheets.

    Many plan suppliers are able to supply CAD programs for their plans and the cost of getting the CAD programs put together is then split over many boats which makes the programs cheaper.

    Re the comment on welding aluminum for boat building, it is trickier than steel and processes like back cutting butt welds before welding the back side and hull welding sequences, crevice cracks that occur at the end of a welding pass need to be ground out before continuing. direction of the passes, to minimize distortion all come into play.

    There are a few good books, not sure if they are in print, by Pollard, and one by Colvin that have very detailed information on aluminum boat building.

    One is called Boatbuilding with Aluminum, if you go to Amazon books and type this in, often the site will put up other recommended books as there are others.

    Are you getting someone to design this or are you doing this yourself?
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Firstly you must consider that the oxide of aluminium has a melting point around 2050c. The oxide is also heavier than the weld pool and as such can be left behind and form inclusions. To eliminate this, simple wire brushing is done. And yes, this is done just prior to welding up the butts and seams once the plates have been fitted. Tedious, yes, essential, yes.

    In addition, when welding one side of a plate that has not had its oxide layer removed the opposite side is equally prone to failure as shown here:

    cleaning-edge-penetration.jpg

    The left hand image shows that the oxide layer prevented the weld pool mixing properly and thus cracks formed. The image on the right was with the oxide layer removed. So apart from inclusions, which are unwanted as they are sites of crack initiation, the oxide layer can promote cracking of the weld pool.

    But to also make matters worse, even if the inclusions are somehow removed and mixing of the weld pools occurs, you still get classic lack of fusion. Since the oxide has a melting point twice that of the weld pool and thus doesn't melt. If the layer is thick enough you will get lack of fusion, as shown here with a test piece that was welded deliberately with no oxide removed.

    xrayA32-DH_Redacted.jpg

    Thus I can only surmise that the boat builders you are referring to are not fabricating to Class rules and thus not weld using the correct procedures and highest QA standards to pass Class x-rays and other NDT testing.
     
  3. pdwiley
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    pdwiley Senior Member

    The only Colvin one I know of is the second half of 'Boatbuilding with Steel' by Gil Klingel ISBN 0-87742-029-7.

    Long out of print but copies seem readily available on the used book market. I have 2 copies, used to have 3 but gave one away. Well worth a read.

    It's interesting to note that what Tom says about using scraps and offcuts of aluminium here, there & everywhere due to their ease of cutting compared with steel has, in my opinion, been superceded by the ready availability of cheap plasma cutters. I saved nearly 2 full sheets out of the 16 I worked out that I needed by building a scale model and peeling templates off of it, mainly by re-using and re-cutting plate offcuts. Stainless was little more trouble, just reduced thickness ability with my Chinese made 50A plasma cutter.

    Tom Colvin was the person who advised me not to build out of aluminium.... it was very good advice in retrospect so I'm glad I followed it.

    PDW
     
  4. Barry
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    Barry Senior Member

    Aluminum Boatbuilding by Earnest Sims

    Boatbuilding with Aluminum Stephen Pollard

    As you mentioned, these are the back sides of welds on butt welds

    The picture on the left with the associated cracks are due to an excessive amount of heat and penetration, and hence the cracking caused by contraction of the weld upon cooling. This is a poor weld. With proper welding heat, the back side of the weld should look just slightly impacted from the weld bead from the other side, after one side is done, you have to back cut the weld back to a depth that any voids caused by the varying depth of penetration until you are back into sound material, and then reweld.
    Without knowing the thickness of the plate, I would venture a guess that it is very thin as you can see concentric penetration which normally means that the welding is cycling his gun (not pulse arc) which is causing this intense cracking of the weldment. I would not get into this boat.

    The picture on the right is only slightly lower in heat but way above a good weld heat due to the excessive penetration and again the welder cycled his gun as shown by the round shape of the imprint of the weld.


    Regarding the last picture, without knowing the thickness, weld settings, alloys etc, at first glance, this piece appears to be lacking in heat as there should be some imprint coming through if the heat was correct

    It is imperative to weld both sides of the plate when butt welding and if you are welding say an angle onto a plate, weld on both sides of the angle at the same but opposite bead location.
    Aluminum work hardens very quickly when stresses approach the yield strength and inclusions and or cracks will cause stress concentrations at stress values much below the yield strength
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    I got the image from this site ( http://www.mig-welding.co.uk/aluminium-welding.htm ) which indicates the presence of the oxide layer which I mentioned. I didn't have any images immediately to hand thus used their image.:

    6mm plate, 5083-O, 20.5V, 97Amps, 5.9 mm/s wire speed.

    Visually, apart from the dirty oxide layer and the splatter caused by it, the weld looked like any other. But clearly exhibiting lack of fusion. Not a heat issue at all. I have many more images like this, made with oxide layer intact.

    I conducted a series tests of with and without oxide layer. Both test pieces identical in every way, as was the welder and welding set etc. It was clear, leaving the oxide layer, no matter what one thinks, is extremely deleterious to the quality of the joint when inspected via NDT. Yet visually almost all were acceptable. Those with the oxide layer removed, all acceptable and passed x-ray NDT.

    All depends upon your procedures.

    We only weld one sided using ceramic backing, such as these. Never have any problems:

    cermic backing.jpg
    http://www.weldmyworld.com/blog/2011/06/welding-with-backing-tape.html
    http://www.thermindo.com/b/756-ceramic-baking.html
     
  6. rwatson
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    rwatson Senior Member

    Oxide is a problem according to the experts

    "06
    .....
    Should aluminium oxide (AI2O3) on the surface be removed?
    To make welding easier and prevent defects in the weld,
    aluminium oxide close to the weld is usually removed. The
    reasons for this are:

    — Al2O3 has a considerably higher melting point (app. 2050°C)
    than aluminium (about 500°C – 600°C, depending on the alloy)
    —Al2O3 is heavier than aluminium and can lead to inclusions
    —Al2O3 is hygroscopic and binds to moisture, which leads to the formation of pores"

    BUT - there are other considerations too - ending in this summary

    "However, if no aluminium oxide or hardly any is detected in the weld, this is basically due to the cleaning effect of the electrical
    current. This incidentally occurs in MIG as well as TIG welding. Whether the aluminium oxide skin should be removed in the weld region and if so, to what extent, depends on the circumstances of each case. A lack of oxide can make the arc behave erratically, creating atmospheric humidity and eddying, leading to the formation of pores. Compromise, therefore, is often needed. Pores can also occur if the weld area still shows
    signs of moisture. Simply drying the area, using a neutral oxy-acetylene flame, is often the solution. At the same time, the weld is preheated"



    http://www.boc-gas.com.au/internet....sShielding_Arc_Welding_AUS_LR_FA351_83410.pdf
     
    Last edited: Mar 17, 2014
  7. CDBarry
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    CDBarry Senior Member

    I was chief NA at a yard that built lots of aluminum boats up to about 85 feet.

    We had our metal plasma cut by a subcontractor, and basically didn't do anything to it afterwards, and had no problem, but we had good weldors and kept the shop clean.

    Some firms will cut it for free if you buy the aluminum from them, by the way.

    Don't worry, be happy.
     
  8. FishStretcher
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    FishStretcher Junior Member

    I used to program a sheet metal cutting laser. (at least for the one I used, they might be better now)The beam is hourglass shaped, typically with 20mm beam diameter focused down to 0.2mm at the narrowest. The reason being that the power/ area is too much for a mirror at the focused spot size. Generally, you use oxygen or shop air assist to oxidize your way through. So there is slag. And there will be some HAZ. I cut tons and tons of 5052. And TIG welded literally tons of it too.

    I am not certified to weld anything. But I got paid to do it, and have TIG welded 1mm sheet with open corners and MIG welded 10mm fire truck bodies. And a lot in between. And the constant though all of this is that cleanliness is key. We used wire brushes and sometimes ispropanol to degrease, or other cleaning agents. The brushes were segregated by which material they could be used to clean. And this was just at a run of the mill sheet metal shop.

    I have never seen or experienced a TIG process cleaning aluminum on its own. Maybe it does, but it certainly isn't anything I would rely on.

    And if you are welding a non-heat treatable ally that retains decent strength after welding, make sure you use the correct filler rod. Otherwise the strength of the parent material is a huge waste.

    Personally, I would go for water jet cutting. You could also CNC punch it, if a nibbled edge is OK. Often times you want open corners anyway, so that might help. If they can punch that alloy. The toughness of 5083 might be problematic in a punch press.
     
  9. yofish

    yofish Previous Member

    I have engaged two of the methods, plaz and router: I say router, if you can afford it.
     
  10. JJO
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    JJO Junior Member

    Waterjet will produce a cut with the least amount of contaminated material to be removed prior to welding (besides cutting with a blade or bit).

    Laser be next as far as amount of contaminated material that would need to be removed prior to welding, Depending on the source/vendor this can vary per laser power, type, and skill level. Laser is also a the highest cost initial investment of the options listed. So, one might think it is possible the vendor may have higher cost to do the work.

    Plasma would produce the most waste in kirf, and material to be removed prior to welding. But would be a lower cost option for your vendors investment. Again one might think your cost should reflect this.

    CNC routing process, the aluminum would come to you ready to weld with the exception of having to remove the AL oxide. Witch you would do with any of these processes.

    If you have probably vendors for all options I would have all methods quoted then re-evaluate based on work you will have to do after your geometry is cut based on your cost, and your production time requirements

    Also testimony of people/companies in your area on the skill level of probably vendors is something else I would personally look into...
     
  11. JJO
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    JJO Junior Member

    If aluminum oxides and cut kirf contaminants are not removed from the weld joint prior to welding, you will most certainly have discontinuities if not defects in your welds.

    So, you then must ask yourself, am I OK with discontinuities, and or defects in the welds on my boat/boats.

    I have been to a large AL yacht yard (yachts that have heli landing pads on them) before where the above cleaning was not done, the welds looked to be poor quality. When I asked the welder foreman about it, he told me it is ok for one or two welds to fail on boats this size.

    My thoughts... I don’t thinks so.
     
  12. CDBarry
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    CDBarry Senior Member

    I understand that water jet and router may be a bit better, but we never had a problem with generic plasma arc for either aluminum or steel.
     
  13. JJO
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    JJO Junior Member

    I agree that plasma cuts both, and will work. My preference would be to remove some contaminants from plasma edges before welding.
     

  14. Oleboynow

    Oleboynow Previous Member

    the best way is with a saw with the foot taken off, you can cut quite curved shapes, even the outline of a yacht round build transom and cutting a long curved plate say 8m long, iis fast one m every 30 seconds
    I wrote a book on it all one, here is part of the chapter on welding
    If anyone wants a copy of building in alloy from me, it is free, I have 33 year exp in alloy and before this in steel
    I wrote this 15 years ago



    Welding

    This is one of the biggies

    I NOW have to fit 25 years of hands on boatbuild welding into one chapter.
    Welding in Al Al is different that of welding in steel, by one major factor and lots of smaller factors, and that is this, You can have a nice looking weld in Al Al, and it can be useless as a strong flawless weld when it is either tested by destruction method or by non destructive method. I have known personnel to come from mig welding steel, and having to be taught mig welding aluminum
    I found that in five years one become not only proficient in welding AL, but fairly adept at maintaining the gear, troubleshooting faults with gun and machine, knowing why a weld was not good, and generally not having to ask why and how, with weld preparation, testing, size of weld, spacing of weld etc, m not saying that if taught my someone with years of experience in the above, and astute keen man cant learn and produce in a shorter time, but by and large five years is what it usually takes

    Let us assume that you have never welded the metal before.
    First up make sure you are protected, because of the high amps and glare from the metal when welding, you can easily become badly burnt. Burns around the neck and upper chest can cause cancer. I discovered that the tiny third degree burns from spatter, cause your hair not to grow back, so wear a hat. Always wear gloves or your hands will look like parchment after a few years, mine do!

    Ok we will start from scratch. Get some metal off cuts, say 6mm plate and run up your machine to about 220 amps, adjust the volts til the arc is just on the point of spraying, the arc will almost hiss like a snake. Start about 24 volts and work from there Make sure the gas is at about 16l/min
    Wire brush or sand the area you are going to weld, and then tack two pieces into a T, so as to make a fillet weld. Now start to weld with the gun angle at about 30 degrees and pushing the weld pool, never drag the weld as some do in stick welding.
    At this stage do not get into the habit of “stirring” I will explain why later
    But run with the weld, with the wire slightly favoring the vertical plate the speed of travel will determine the size of the leg (g1) and the thickness of the throat, (a) which will determine the strength of the weld. T he first rule of welding is to be comfortable, if you are not then the weld cant be first rate. Get your head very close to the weld, so as you can see what is happening to the weld pool. Use about 10mm of stickout that is hold the nozzle about that far from the weld. Always use two hands, never try to weld single-handed, rest the left hand small finger on the work, or bench, if right handed and vicar versa if right handed. Now practice and practice til you have what you think is a reasonable weld.
    Throw you piece into a drum of water and take to the vice, now knock the pieces apart, you should at this stage have only welded one side, so a tap into the weld will break it apart. Now look at the root of the weld, has it penetrated into both pieces or is there a black sooty line? It is easy to see penetration Is there is now penetration you must increase your heat, up the amps, until you achieve penetration If there is penetration into the bottom plate and not the vertical one try pointing the arc center more to the vertical plate. Lack of penetration here, is sometimes called cold lap,

    If you come from a steel welding background the main difference is travel speed Al Al is done much much faster than in steel

    You must run with the weld, keep moving, Later you will see the table for leg and throat measurements

    Now try some fillets in the vertical position, once again you can hold your gun still without weaving or stirring, this applies to most seal welding, but where strength is required as in the frame to plate weld a slow weave will give you the required dimensions you will need to back off on the amps, on and volts on the verticals, to maintain weld form, If you are welding say 4mm plate to 5 mm framing then you can run straight up without weave. This is all about practice on the job, getting to know your machine Once you get the machine running right, and with time you will be able to set it up in any situation with any plate thickness
    The golden rule is never have the weld too cold, it must penetrate

    The time will arrive when you must decide about how you join the plates. Joints that run fore and aft are always called seams, although they are still butt welds, the joints that join the plates end on are called butts.

    On the seams there are 3 ways to join and prep
    The first is after the plate has been fitted up to the one above or below, the plate is taken down, and the edge can be prepped off as in the fig 6,you may do this with 8mm plate leaving 1.5mm land and welding the inside first. You would then come from the outside with a skillsaw, a weld chaser is usually to thick in the blade for this, and just cut back to the inside weld. once again you can do a test piece. You may find that using the correct temperature from the inside will alleviate the need to cut back from the outside, try it, and then do a nick break test on the test piece. The nick break test is done like this,
    Your test piece is say two pieces 75x300 long, now they should have been prepped and welded as if that were the job itself, now just skim the meataxe, not the grinder over the welds, this will show surface irregularities like excess porosity. Cut a slice off a 60mm or so long and put a slight saw cut along the weld on the band saw, say a mm deep or so, now put the piece in the vice and break open using the nick as the break point You will see all now, lack of root fusion, porosity etc Different codes allow different levels of porosity A few gas bubbles are ok, after all I say this, do holes cut in hydraulic crane jibs compromise the structure? Most classifation societies are sensible about porosity, but now and again you will get some officious inspector who reads too much has no welder quals himself, who may be awkward What is NOT allowed is lack of root fusion, you will see this quite clearly as you break the weld
    Ok you can do many of your own mechanical tests, making up mandrels.
    Try to obtain a book, the British Standards for aluminum construction and welding will do just fine.
    The next weld prep for seams and butts is this, used for all thicknesses up to 6mm Cut a small bevel on both plates inside, which is called a sighting notch see fig 8, weld off nice and hot from the inside, run don’t stir. Then from the outside cut back to the root with the saw again, Weld from the outside using enough heat to penetrate the root but not enough to undercut the plate. Running again and not stirring running with the weld will not cause undercut where stirring often does. Once again test pieces first.
    Next method is an old method rarely used because it has either been forgotten or never learnt by most engineering and weld shops
    It is the temporary backing bar method it can save time but must be done properly; you only get one chance to get it right
    The drill is this. Where each seam is, cut a notch like this AT EACH SEAM CENTRE AND ON EACH FRAME, instead of a half hole. See fig 9. Then make up an 2400mm length of mild steel bar, 38mmx10mm or 1 and a half ins by three eighths of an inch, now grind or mill a groove into one surface 4mm wide and 3 deep. Don’t worry about the time and effort in making this bar up; you can use it for 20 years.
    Now with the plates in place leave a small gap 1-2mm. Slide the bar in and wedge with tapered wedges You will need 50 of these wedges hanging around the shop, they will be used for many things they should .be slow taper like Morse.






    To make the cutout in the frame, drill with 10mm drilling the corners and then finish cuts with a quality jig saw.
    With the bar wedged (dogged) into place, at each frame should be enough, although where there is not much curve along the bar, a wedge between frames may have to me dogged in
    Now weld from the outside using plenty of heat,(around 230 amps on 6mm) once again a test piece is a must what you should end up with when the bar is removed is a tidy bead in the inside. Which means full penetration. Short backing bars are often useful for the situations where it would be difficult or messy to two sides weld.
    Two sided full prep is nor advisable for welding plate under 6mm as it is easy to blow the plate apart.

    I have used this backing bar method on a mussel harvesting vessel. But putting the bar on the outside of the hull this boat had frames about 1200 centers with longitudinal The bottom was 10mm Pl. so we prepped out the inside and left a small gap with two mm land and poured the weld in from the inside, one pass, saved a huge amount of overhead welding Where each frame was we cut back from the outside and that was it.
    Ok great firms like Lincoln have written books 2 inches thick on welding and there is reams of data available on how to arrive at the size of welds, BUT that data assumes that one has arrived at the stresses, loads imposed on a weld, and in yachtuilding that is pie in the sky stuff, I’ll bet my last red cent that a scientist could waffle on and scrawl out formulae by the mile, and it would be of no use whatsoever to the practical yachtbilder, apart from the loads imposed on the chain plates, the resat is by “feel, and what works”
    Put it this way, I have never ever been advised as to the size, pattern, of welds by any Lloyds inspector, book, or guru, but have worked on what works, given that I have had to warranty my hulls for 5 years, and covering all manner of craft from fast planning boats to easy riding sailboats

    Here is what works in practice/
    Fillets 6,8.10, pl. sections, leg 8-10mm
    Throat, 5-6mm, length of weld 80-100
    Fillets 3-5 plate, leg 5mm throat 4mm –5mm length 60mm
    I prefer the stitch pattern, that is welds same place each side of the frame, ok the weld will show more on the outside but a heavy sand does away with the lump at the weld point

    The welding would go like this
    At each floor forward of the main mast, fully weld that floor both sides. This is the area that will take the most pounding the most shocks in the hull of a sailboat at sea, falling off of waves this is the landing zone, if you have never been in mid ocean in a storm or full gale when it blows for 3 days, then you will not quite understand how it is, but if you have then you will have experienced the eerie silence as the boat comes over the top of a 30 foot wave and there is nothing but air under her forefoot, and then the sickening thump as she lands in the trough. Lloyds require that the floors in this area be fully welded both sides and It is quite plain to see why.
    Going up the rest of the bottom I chain weld 80 miss100, 80 miss hundred. Right up to the deck level.
    Working back through the boat the floors can then be chain welded, or staggered,
    Of course the
    Insides of water tanks will bed to be fully welded, keeping the weld smaller and hot, again run with the weld, don’t stir.
    Engine beds once again fully weld, this is because of the loads imposed upon them and because they are subject to vibration
    Under the deck where the deck meets the topside plates can either be stitched or fully welded, once again it is so simple and much tidier to run a full length bead
    At this stage I should point out that it is necessary to weld off the boat evenly each side should not get to far ahead of the other, I once knew one of these amateur professional guys I was taking about early in the book, who decides to build himself a boat. He built it in steel, and plonked the keel down and fully welded the keel to bottom on one side, result keel 3 inches out of plumb!
    I will talk more of this in the setting up stage.
    I never weld seams, butts on the job until all of the plating is finished
    Decks are different; you can make up large c hunks of deck on the floor, as long as you can get them up onto the structure

    It is a good idea to make up welding marker sticks, with the pattern of the weld spacing marked on in felt. This way all the welding will be of uniform appearance.
    It may seem like teaching your grand mother to suck eggs, but a welder shoulder have the following with him at all times
    Side cutters, 6 inch shifter, tip cleaners, a spare tip, wire brush, meat axe handy, there is nothing so maddening than when a wire stoppage occurs, or the a tip burns back, than to have to hunt around for these simple tools, it wastes time. Men should be taught to carry these articles, just as they should always have tape measure, pen, and felt tip to hand elsewhere on the job. As an employer nothing pleased me more than having a man who never had to spend half the day searching for
    This and that.

    Some simple tips for troubleshooting
    Weld arc starts to spray, means your voltage has stayed constant but the amps have dropped. This is caused by wire feed speed slowing which is in turn caused by swarf, or some other body in the liner, or buildup of alloy in the tip end, or one of the feed motors losing power. As I said earlier, keep your liner clean, observe the maintenance schedule. Keep a set of tip cleaners to hand.

    Make sure the gun cable does not have twists or tight turns, which will slow the feed rate

    Most all weld variation is caused by the above faults in a electronically controlled welding power source the machine will to a point compensate for these things until the weld becomes to cold and will not flow, or penetrate.

    The earth is very important; if it gets hot, then increase the size. Some copper weld cables corrode badly inside, this does not show at the ends of the cable, but hot cables are a sure sign of corrosion. I have encountered this problem where the welder seemed to over a period of time, need higher settings for the same power, and when the earth cable was changed, it was a different machine altogether.
    Much time can be save by going to a GOOD boatshop and getting a demonstration, offer to pay someone a hundred dollars for a couple of hours tuition

    Keep the weld area clean, contaminates in the weld can cause problems
    Do not get tempted into buying cheap wire, make sure the wire is certified 5456 grade

    In summery then being a crash hot A.SM.E9 welder will help, especially when it comes to understanding weld sequence, joint preparation.

    But there will still be much to learn about MIG in alloy boat building.

    Practice and practice. Do as many test pieces as you can before starting to weld on the structure.

    As we go through the build I will explain more about welding.
     
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