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Practical TIG Welding: Tack Welding

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Tack Welding


00:00 - Before we can actually lay down a weld in the first place, we're almost always going to need to start by tacking our components together.
00:06 Tack welding is simply the process of temporarily welding our work piece together in the correct orientation so that we can then go ahead and completely weld the part.
00:16 This serves a couple of purposes.
00:18 The first and most obvious is locating the parts in position so that we can weld them together.
00:23 However tack welding also allows the orientation of our parts to be confirmed and checked prior to committing to fully welding.
00:32 It's always a lot quicker and easier to cut through a few tack welds rather than cutting through a completed weld if you then find that the parts don't fit quite right.
00:42 This becomes increasinly important with complex parts like exhaust systems where you may have minimal clearance to other components in the car.
00:49 Strategic use of tack welds positioned around the circumference of your work piece can also help reduce or eliminate distortion of the part from heat when you do commit to fully welding the part.
01:01 If we compare tack welding using the MIG welding technique to TIG welding then there are some significant differences and MIG is substantially easier here since we can hold the part with one hand while tacking with the other.
01:13 TIG on the other hand requires both of our hands so that we can then add filler rod so we're very reliant on a good fit up and clamping aids to hold the parts in location while we tack them.
01:25 We want to make sure that our tack will hold but we also want it small enough so that we can lay a uniform looking weld over the top of it.
01:33 Essentially making it disappear when the part is fully welded.
01:36 A good fit up is critical to being able to produce a tack that's small in size but big on strength since the two parts of the component we're tacking need to be in contact with each other.
01:47 Having a freshly sharpened tungsten is also important here because this will aid in the precise control of the arc to minimise heat input and direct it into the location that we want to tack.
01:58 It's also possible to tack weld without using filler rod in a process called fusion tacking.
02:04 This is something that's done frequently with parts like stainless steel and titanium exhaust systems.
02:11 A fusion tack works in the same way as a regular tack but instead of using filler rod to join the two parts, we're essentially melting the two parts of our material together.
02:20 This creates a nice small tack that won't affect the shape of the finished weld like a lump of filler rod sitting on the surface can.
02:28 Again, a sharp tungsten and good fit up is the key here.
02:32 One other factor that will greatly improve this process is having a clean and uncontaminated sharp edge of the surface being welded.
02:40 If there are any contaminants on the edge of the surfaces we're trying to bridge then the results can be ugly and this can then be hard to come back from.
02:49 When tacking parts, it's also important for us to ensure that all areas of our part are held tightly.
02:55 This means that you may need multiple tacks around the perimeter of the work piece depending on its size.
03:01 When using multiple tacks like this, we want to place tacks on opposing sides of the work piece.
03:06 This ensures that our part is held in place by the opposing tack and this reduces the effect of expansion and contraction during the final weld.
03:15 It's common for some parts to be more difficult to tack than others and clamping them may be difficult or you may not have the right clamps.
03:23 An option that we've found to work really well in the HPA workshop is the use of Kapton tape to help support our parts prior to tacking.
03:31 This works very well on tubular structures such as exhaust systems but can be applied to just about anything.
03:38 Kapton tape is used in the wiring industry and is an insulating tape that's gold in colour.
03:44 The reason it works well for tack welding is that it has a high melting point and it also doesn't leave a sticky residue behind on our material.
03:52 This means that the kapton tape is not going to be affected by a tack weld placed near to it.
03:58 The process is to cut a small section of tape and apply this across the weld join to hold the parts together.
04:05 By leaving a small gap between subsequent sections of tape, we provide an area to complete the tack weld.
04:11 The kapton tape is also surprisingly strong and can still support exhaust pipes sufficiently well to confirm fit up prior to committing to a tack weld too so it's a worthwhile technique to try out in your own workshop.

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