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Practical TIG Welding: Stainless Exhaust Worked Example

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Stainless Exhaust Worked Example


00:00 - In this worked example, we're going to be applying the HPA 6 step TIG welding process to the fabrication of a section of exhaust for our Toyota 86 race car.
00:10 This is an existing exhaust system that's required some modifications in order to clear a new flat floor as well as to relocate a flexible stainless joint that allows the engine to move relative to the exhaust system.
00:23 In this case, the required section of exhaust is relatively small and starts from the flexible joint at the rear, including a V band flange to allow easy removal and installation and then continues forward to the base of the existing turbo dump pipe.
00:38 The material being used is 304 stainless with a 1.6 mm wall thickness and it's 3 inches in diameter.
00:47 Due to the compound angles involved with mating the two parts of the exhaust system together, pie cuts were utilised here.
00:54 This gives a little more flexibility in terms of achieving compound angles and a tight radius.
01:00 As usual, our welding process begins with the preparation of our raw materials and this actually starts with our part fit up.
01:08 However we are using commercial pie cuts here rather than making our own and hence the ends are nice and square and this guarantees a proper gap free fit up.
01:19 Part preparation continues by cleaning the surface of each side of the weld area using scotch brite, followed by some acetone on a clean rag to remove any surface contaminants.
01:29 It's just as important to focus our efforts on cleaning the inside of the tube as it is on the outside in order to avoid the contaminants being drawn into the weld pool.
01:39 Before we can tack the various parts together, we also need a way of holding them in place, and for this purpose we've found Kapton tape to work exceptionally well.
01:48 This tape is strong enough to hold the parts together so that the fit up can be confirmed and it's also sufficiently heat resistant to not be affected during the tack welding process.
01:58 We're using a wider half inch Kapton tape here to provide a little more strength and it's important to leave gaps or areas where we will be able to tack weld between adjacent pieces of the tape.
02:11 On any sections of cut tube, we need to ensure that the ends are square and the flat bed of the linisher is a good way to achieve this.
02:19 Of course any material removal like this will potentially require deburring as well as a final wipe down with acetone prior to welding.
02:27 At this stage, our new section of exhaust is fitting nicely in place, it's cleaned and it's ready to weld, so we can move on and consider our welder setup.
02:36 As we already know, stainless is a very reactive material so gas coverage is critical to achieving a strong and attractive high quality weld.
02:45 In order to achieve this, we're using a Furick BBW19 pyrex cup.
02:51 As we discussed in the body of the course, typically with the specialist cups like this one, the manufacturer will provide a recommendation for gas flow which in this case is 15 litres per minute.
03:02 We're using a red 2% thoriated tungsten in 2.4 mm diameter that's been sharpened to a 30° angle and we can set our stick out to approximately the same as the cup diameter.
03:13 It's important to mention here that while we are using the thoriated red tungsten, multi mix would also be a suitable choice for welding stainless.
03:23 While the gas lens can allow for additional stick out, in this instance, there's no tricky areas that limit access so additional stick out over and above our normal recommendation of the cup diameter isn't required.
03:36 The filler rod that we'll be using here is ER308L in a 1 mm diameter and as usual, we want to cut the full length of filler rod in half and ensure that it's been given a good wipe down with acetone and a clean rag prior to getting started.
03:52 Next we can adjust our welder settings to suit our application.
03:55 This starts of course with ensuring our welder is set to DC operation.
04:00 We're using high frequency start as normal and we've set the machine to use the remote foot pedal to allow for more precise amp control.
04:08 This is not strictly essential with stainless steel so if you don't have a foot pedal, you can simply rely on the button on your torch and select 2T or 4T operation depending on your own personal preference.
04:20 We're going to use a shielding gas pre flow of 0.7 seconds and a post flow of 6 seconds.
04:27 You'll note that the pre flow is slightly reduced from our baseline recommendation for stainless steel of 1 second and this is due to the fact that we're not running any additional stick out from the cup so the additional gas coverage isn't essential in this application.
04:42 Over the course of a lot of welding, this relatively small reduction in our gas pre flow can also end up saving us a little gas use in the long run too.
04:52 Finally, we can set the amps and from our material specific reference sheet, we know that we want to start with a recommendation of 35 amps per millimetre of material.
05:01 In this case, 35 multiplied by the 1.6 mm wall thickness, gives us 56 amps peak.
05:08 This is only a starting point of course and some test welds will let you fine tune this to suit.
05:14 Given the fact that we're using a foot pedal here, this gives us the ability to alter the amps mid weld, we've bumped this up slightly to 60 amps.
05:23 For our tack welds, we won't be using the pulse function, however we will be making use of pulse welding when it comes to completely welding the joins.
05:32 For this function, we're using a frequency or pulse per second of 1.3 Hz, a peak time of 50% and a background amps of 25%.
05:42 As usual, all of these settings can be testing and optimised on some test welds on scrap material prior to committing to your actual workpiece.
05:51 Next we can set ourselves up with our PPE.
05:54 This of course begins with our welding mask and prior to getting started with your first tack weld, it's important to just check that you have in fact turned it on.
06:02 Next we have our TIG welding gloves which are going to protect our hands from the heat as well as protecting our skin from the UV light emitted while welding.
06:11 Typically we'd also recommend wearing a long sleeve top or overalls to protect your forearms from UV light.
06:19 In this example, given that it was a hot day and the fact that from the seated welding position there's little chance of UV emitted from the arc reaching exposed skin, our fabricator Jimmy has chosen to wear a short sleeve tee instead.
06:32 This is something to keep in the back of your mind however, because often as you change your welding position, previously shielded skin on your forearms can become exposed to the arc without you realising.
06:44 Given the small size of the exhaust section that we're working on here, it's possible for all of the welding to be completed at our welding bench from a seated position which aids comfort and allows better control over the torch and filler rod.
06:57 You may also benefit from having a variety of different sized blocks available that you can use to support your wrists while you go through the welding process.
07:06 Supporting your wrists in this way can help improve the stability of the torch and in turn the quality of your finished weld.
07:13 We can now actually get started with the welding process and this begins with tack welding our exhaust components together.
07:20 We don't need to purge the part in order to tack weld it and with good fit up like we have here, there should be no issue tacking the parts together using the fusion welding technique.
07:30 This means of course that we don't require filler rod.
07:34 It's important with all aspects of stainless welding to ensure that we retain the torch position when we terminate the weld to allow the post flow of gas to shield the heat affected area until it's cooled sufficiently.
07:47 With tubular components like this exhaust, we want to tack each join in multiple locations spaced evenly around the tube's circumference.
07:55 This will ensure that the parts don't move or pull when they're fully welded which will help ensure correct fitment of the exhaust.
08:03 With our section of exhaust tacked together, we can then get it assembled in place on the car and tack it to the rest of the exhaust.
08:10 Again we can use Kapton tape to support the parts prior to tack welding.
08:15 Beginning with the rear V band flange, we can tack this to the exhaust tube.
08:19 In this case, the V band flange provides a little bit too much gap for us to be able to use the fusion welding process so adding filler rod is necessary.
08:29 Rather than tack the section that we've just made to the front pipe now and create a large and awkward section to work with while we're completing all of our full welds, we can fully weld the new part that we've just made first.
08:42 Before fully welding this section, we do need to purge it of course.
08:46 In our case we're using silicon plugs designed for this purpose but of course there's a variety of other options that we have covered in the course that you can utilise instead.
08:57 We want to be mindful though of the V band flange since we're welding very close to where the silicon plug will fit and this could end up damaging the plug from the heat created.
09:07 A simply solution is to temporarily attach the opposite side of the V band flange and clamp it in place and then fit the silicon plug to this point and this removes the silicon plug further away from our heat source during welding.
09:21 We can now insert our argon supply and we're using a support on our welding bench to arrange the part so that the argon is entering at the lowest point and is being vented from the highest point.
09:31 We want to use approximately the same flow rate for our argon as we're using for our torch which you already know is 15 litres per minute and we need to allow it to run for around 30 seconds in order to purge the atmospheric gases out of the part prior to welding.
09:47 Before we start welding, we need to remember to switch the welder across to pulse mode with the settings that we mentioned earlier.
09:53 Now we can get started with our welding.
09:56 As usual, we want to start with a dry run to ensure that we can reach the entire length of the area we're intending to weld.
10:02 From here, we can strike an arc and lay down our first weld.
10:06 We want to concentrate here on maintaining the correct torch angle and a consistent arc length as we travel along the weld.
10:14 The pulse settings will allow you to time the inclusion of the filler rod with the point where the amps step up to the peak setting.
10:22 Once you've mastered this timing it can result in a nice uniform looking weld bead.
10:26 Initially you may find a slightly lower pulse frequency is helpful in order to get the welding action timed correctly, however as you gain experience you'll be able to increase this a little.
10:37 It's now simply a case of repeating the process for the remaining sections.
10:41 In this case, we're working along the visible sections of each join before rotating the tube to reveal the next sections to weld but really this is a personal preference.
10:51 When it comes to welding the V band flange to our tube, this flange is obviously thicker than the tube itself and this can benefit from a small increase in our amps as well as careful focus of the arc so that sufficient heat is input into the flange without overheating the stainless tubing itself.
11:09 We can now inspect our welds inside and out.
11:12 A good quality weld should be shiny with slight discolouration visible.
11:16 Predominantly this should be a straw colour however some light blue and purple colours may be visible as we can see here.
11:24 We want to take the time to ensure we haven't missed any sections of weld as well as making sure there are no areas of porosity or contamination visible.
11:33 The inside of our welded section should show a similar finish to the outside with a nice smooth weld bead and no sign of contamination or porosity.
11:42 With a new section of exhaust fully welded, we still need to weld this to the front pipe.
11:46 We can get the section back on the car and reinstall the V band clamp to hold the back end.
11:52 Once we've got the alignment correct with the front pipe, we can use a clamp to hold the two pieces in place before tack welding them together.
11:59 While access is a little tricky here, it's important to add at least a few tacks around the circumference to ensure that nothing moves prior to welding.
12:07 We need to purge this part prior to welding just like we've already done, and this time we have the wastegate dump pipe and the oxygen sensor boss to blank off too.
12:14 Using adhesive backed aluminium tape is a quick and effective solution to achieve this.
12:20 Given that the existing front pipe has been running on the car for some time, it's important to thoroughly clean the weld area inside and out.
12:29 We removed any surface contamination in an area about 25 mm back from the weld using a combination of the hand linisher, scotch brite and finally acetone.
12:39 The scotch brite and acetone treatment should be applied to the inside of this tube as well.
12:44 From here, it's a case of flooding the part with argon and completing the weld in the same way as our other sections.
12:50 With our part completely welded, we can then install it for the final time to confirm fitment.
12:56 Externally, we've got a great looking part with high quality, attractive welds and the extra work involved with purging the inside with argon will mean that the welds will be strong and reliable in a race application.
13:08 If you do have any questions on this worked example, please ask these in the forum and we'll be happy to help you out there.

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