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Practical TIG Welding: Fuel Tank Worked Example

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Fuel Tank Worked Example


00:00 - In this worked example, we're going to be using the HPA 6 step TIG welding process in order to complete the welding on a custom aluminium fuel tank that's designed for an off road truck.
00:11 There's several elements that go into the construction of this fuel tank and we chose to have these laser cut out of 3 mm alloy sheet.
00:19 Internally, we've also incorporated some vertical walls with holes cut though them to provide some stability and strength as well as some anti surge effect.
00:28 To further eliminate fuel surge, the tank is designed to fit a Radium universal fuel cell surge tank which is a neat way of incorporating a lift pump, a surge tank, a high pressure fuel pump and a fuel level sender in one compact unit.
00:42 This surge tank also uses the industry standard 6 x 10, 24 bolt fill plate bolt pattern so it's compatible with most fuel cells.
00:51 In our case we designed the fuel tank using Fusion 360 so that we could confirm the design and fitment before having the individual alloy panels laser cut by a local sheet metal working company.
01:03 This saved time over cutting the parts by hand and provided a more accurate finished product.
01:08 We will be focusing in this worked example exclusively on the welding aspect of the fabrication, however if you want a more thorough look at the rest of the design, planning and construction process of this fuel tank, then we cover this as a worked example in our Fabrication Fundamentals course and you can check it out there.
01:26 Now that we know what we're welding, we can get stuck into the parts preparation.
01:32 We need to begin by cleaning up the raw edges from the laser cutting process and an efficient way of doing this without introducing any contaminants to the material is with a hand file.
01:42 By clamping each individual part onto our work bench and running the file along the cut edge, we can quickly get back to clean aluminium.
01:50 This filing process is followed up by running a deburring tool along the edges which removes any burrs that might remain after the filing is complete.
01:58 Following the deburring process, we can then use a fresh scotch brite pad to clean up the prepared edge on both sides of the material.
02:06 Lastly we can use acetone and a clean rag to wipe down all of the surfaces that we've just prepared.
02:12 With our parts ready to weld, we now need to assemble the fuel tank components in place.
02:17 Obviously being non ferrous, magnetic clamping aids aren't much help to us with alloy, however due to the design of the tank, the individual parts fit together quite nicely and reuqire little support.
02:29 The exception to this is the in fill panel that welds to the body of the tank at an angle.
02:35 In order to support this during the tack welding phase, we used kapton tape.
02:39 The end pane also required a little support, in particular ensuring that the remainder of the tank was properly aligned prior to welding so that the panels align nicely with no gaps.
02:50 To achieve this, we made use of a pair of clamps.
02:53 This is one of those normal situations where a variety of techniques can be applied to get the results that you're looking for.
02:59 Fortunately, due to the accuracy of the laser cut sheets and the fact that the part was modelled in CAD, the fitment was guaranteed to be good which makes the job easier when we come to setting everything up.
03:12 As you'll be able to see through this worked example, there is a little bit of back and forth between the various steps here.
03:18 Specifically between tack welding the parts and then clamping and this is normal for any job consisting of multiple parts like our fuel tank.
03:26 We can now move on and look at our welder setup.
03:29 Starting with the tungsten, we're using a white zirconiated tungsten in 2.4 mm diameter but multi mix would also be acceptable here.
03:38 We've sharpened the tungsten to a 40° angle and the last half mm or so has been flattened off.
03:44 Remember that the end of the tungsten will tend to ball up a little once we start welding alloy and this is absolutely fine.
03:52 We're using a number 7 cup and the stick out needs to be set at half of the cup diameter which in this case is about 6 mm.
04:00 We're using 100% argon as our shielding gas and the flow rate has been adjusted to 8 - 9 litres per minute.
04:07 A slight increase over our recommended baseline settings can be useful when we're welding a lot of external corners as we are in this example.
04:15 The filler rod that we'll be using for the fuel tank is 5356 alloy in a 2.4 mm diameter.
04:22 Remember that cutting the full length of the filler rod in half can make it easier to manage and we always want to give the filler rod a wipe down with acetone prior to use.
04:33 This particular job is going to burn through quite a lot of filler rod so we want to make sure that we've got plenty on hand and prepared before we get started.
04:40 Now we can move onto dialling in our welder settings and most obviously here we need to ensure we've selected AC mode since we're welding alloy.
04:49 This is one of those settings that's absolutely obvious yet we can guarantee you'll still overlook it every now and then, particularly if you're back and forth frequently between ferrous and non ferrous materials.
05:03 In this instance, we're going to be using a foot pedal to give us a little more control over the weld amps as the weld progresses and the material heats up.
05:11 This works of course in conjunction with our amps setting and we can start here by using our rule of thumb of 40 amps per millimetre.
05:19 With 3 mm thick material of course this gives us a recommendation of 120 amps however the foot pedal gives us a little more control here and we often end up purposefully setting the amps a little higher than our rule of thumb would suggest.
05:34 This does also come down to the specific material and the skill and experience of the operator.
05:40 As you become more proficient and confident welding alloy, you can usually increase your travel speed which means that you can then use a slightly higher amperage.
05:49 In this case, we've settled on 132 amps.
05:52 Given that we're using a foot pedal, the start amps, up slope and down slope are all manually controlled by our foot position on the pedal.
05:59 Our AC balance for this job is set to 70% and the AC frequency is 100 Hz and this is a pretty typical starting point for clean aluminium sheet like we're working with here.
06:11 We're also using 1 second of pre flow and 5 seconds of post gas flow in order to keep our tungsten free of oxides.
06:18 We've increased the post flow a little over our baseline recommendations here which is predominantly due to the long weld runs for this particular job.
06:26 As usual, it's always advisable to test your settings on some scrap material of the same thickness to ensure that you're getting the desired finish as you may find some fine tuning is required.
06:38 Before we get stuck into the welding, we also need to make sure that we've got ourselves set up and ready to go.
06:43 This includes our PPE of course and starting with our mask, it's always important to ensure it's been turned on to avoid arc eye.
06:51 We also want to ensure we're wearing a long sleeve top to provide protection from UV light.
06:56 A good quality pair of TIG welding gloves are also essential to protect from UV light as well as heat during the welding process.
07:03 The important aspect here is to make sure that no skin is exposed to the arc during welding.
07:09 Since the fuel tank is easy enough to move around, we have the benefit of being able to complete the welding while seated comfortably at our welding bench.
07:17 Given the location of some of the welds and your personal preference, it can be beneficial to utilise blocks of various heights in order to provide support for your wrists while welding.
07:28 A fabrication apron is also an optional extra and this can provide a convenient place to store your consumables such as spare tungstens.
07:36 It also provides a little more protection during the preparation steps, however in our case, we're not using any power tools so the added protection is not quite so critical.
07:46 Now we're at a point where we can actually begin the welding process and if everything has been completed correctly up to this point, we should be able to relax and concentrate on the job of laying down a quality and consistent weld.
07:58 With a job like this with a number of parts, the welding process is a little more involved and requires us to move back and forth between tacking the parts together and clamping and supporting the parts that we're about to weld or tack.
08:11 As usual, we always want to perform a dry run or test run just to make sure that we've got the ability to comfortably complete the weld as we expect.
08:20 The fuel tank is not too tricky here since it involves a lot of long straight welds where access is not too difficult.
08:26 We started by assembling and tacking the bottom section of the tank which also includes the internal baffle plates.
08:33 Initially all we want to do is apply a small tack into the corners while we confirm fitment.
08:37 We want to make sure that the parts are aligned correctly so that we end up with a nice 90° edge between the panels that we're welding up.
08:46 This gives us a nice valley that we can then fill with our weld bead.
08:50 With the base of the tank tacked together, we can then tack the angled in fill panel onto the rest of the fuel tank base.
08:57 Next we can flip the tank over and tack the end panel in place, ensuring that we manage the alignment of the various panels as we go.
09:05 At this stage, the top of the tank is just being held in place temporarily to aid alignment and we don't want to tack this in just yet.
09:13 We've now got the majority of the tank tacked together and we've gone through and added some additional tack welds about every 200 mm which will help ensure nothing moves or pulls with the heat when we perform the full welds.
09:26 Remember though that we want to keep our tack welds small and uniform so that we can weld over the top of them without them being obvious.
09:34 Before we add the top to the tank we need to take the opportunity to stitch the internal baffle plates to each other as well as to the outside of the tank.
09:43 There's no requirement here for strength but rather we're just preventing them from moving relative to each other in use so a few short stitch welds is more than sufficient.
09:53 This is also our last opportunity to access the inside of the tank easily so it's a good opportunity to give it one last clean out.
10:01 Now we can prep the top of the tank and this requires a threaded machined adaptor plate to be welded to what will be the inside of the tank lid.
10:08 This is threaded for the fasteners that will attach the surge tank to it.
10:12 This part doesn't actually need to seal fuel though so it just needs to be securely tacked rather than fully welded.
10:20 We do want to ensure that the threaded holes align with the holes in the lid so before welding, this is temporarily bolted in place.
10:27 The tricky part here is that this machined piece of alloy acts as a great heat sink due to its thickness which is going to make it harder for us to weld.
10:35 We'll require a lot more amps in order to form the molten weld pool normally so to help us out, we're using a butane torch to pre heat the thick section of alloy.
10:44 Pre heating like this can be worthwhile if you're finding it difficult or slow to form a molten weld pool.
10:51 A butane torch should be directed predominantly at the thick section of alloy and just 20 to 30 seconds is usually enough to raise the temperature sufficiently to make welding much easier.
11:01 We've also supported the workpiece off the welded bench so that heat isn't conducted away from where we need it during the weld.
11:09 We're just going to stitch weld this component to the tank lid in 4 places evenly spaced around the perimeter.
11:15 We can also benefit from temporarily increasing our peak amps and we want to focus our arc predominantly on the thick section of material and less so on the thinner, flat panel.
11:25 Once its welded, we can then remove the bolts and assemble the lid into location.
11:30 The internal baffles locate into slots that are laser cut into the tank lid so a little gentle force is required here to positively locate everything into place.
11:39 Now it's a case of tack welding the lid into place, initially at the corners before placing tacks every 150 to 200 mm along the edges.
11:48 Next we can weld the baffles to the lid along each of the slots.
11:53 Given the fact we're dealing with clean aluminium that's relatively thick, this should weld very easily and it should be simple to produce a quality, shiny weld bead.
12:01 This is also a good opportunity to dial in your technique before committing to the more visible external welds on the tank.
12:09 You can see the technique in action here which we've sped up and the important aspects to concentrate on are the angle of the torch, the distance between the tungsten and the work piece, the speed of travel and of course the consistency of your filler rod inclusion.
12:25 The finished result should be a shiny weld bead with a consistent bead profile like we can see here.
12:31 Now it's time to commit to the external welds on each edge of the tank.
12:35 There's around 6 metres of total weld length in this tank so sufficed to say, there is a lot of time spent on the torch.
12:42 With such long weld runs in places, it's not possible to complete the full weld in a single pass so we need to be mindful of setting ourselves up correctly and performing a dry run to make sure that we can complete the section we're about to attack in one go.
12:56 When welding the edges of the tank we essentially have a small 90° fillet weld that we're completing so it's important to hold the torch so as to evenly distribute heat into both sides of the weld.
13:08 Good visibility is also important to help you track the length of the weld in a straight line.
13:13 One of the issues with so many welds on a thermally conductive material such as aluminium is controlling the heat between the welds and cooling it back down.
13:22 Waiting and allowing the parts to cool naturally is going to take a long time with aluminium so between welds, we used a fan to help circulate air through and around the tank and speed up this cooling process.
13:34 The fan we're using has a large shroud around it and this was big enough to support the whole tank so by simply sitting the tank on the fan for a few minutes, this was enough to cool the tank back down to a manageable level.
13:45 This of course also means that care is required any time we're handling the tank to reposition it as the heat from the weld will be conducted through the rest of the tank very quickly and even areas that are quite a distance from the location you've just welded can be much hotter than you'd expect.
14:02 Our TIG welding gloves however should offer sufficient protection to allow the tank to be handled between welds.
14:08 So at this point we've got a completely welded fuel tank that's ready for pressure testing.
14:13 It's always a good idea on a job of this size to take a final look over each and every one of your welds, looking for any potential imperfections or impurities that may need to be addressed.
14:25 Any pin holes or porosity for example will be a potential leak and will therefore need to be addressed and rectified by grinding out the weld and rewelding.
14:33 If you have any questions on this worked example, please ask those in the forum and we'll be happy to help you out there.

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