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Motorsport Fabrication Fundamentals: Penetration

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00:00 - Strength in motorsport fabrication is and always will be a huge priority.
00:05 Just how good our fabrication skills and processes are will be tested each and every time we put the finished product through its paces.
00:12 Because quality welds are crucial to the strength and safety of our vehicles, we need to be sure that our welding technique is producing results at a high standard.
00:21 A poorly performed weld can have severe consequences in motorsport so we need to be sure that we can test the number one aspect of a weld's strength, which is the depth of weld fusion, commonly known as penetration.
00:33 Penetration is the distance that the fusion extends into the base metal from the welding process.
00:39 There are a few variables in the welding process that'll affect this.
00:43 The one that has the greatest effect on the degree of weld penetration is current which is measured in amperage.
00:49 As the welding amps are increased, so is our weld penetration.
00:52 Of course as we decrease the amps, our weld penetration is also reduced.
00:57 Another variable is how fast we travel along the weld.
01:01 As travel speed increases, the amount of time that the arc is over the particular point on the weld reduces and the resulting heat and level of penetration is decreased.
01:11 Conversely, the slower the speed, the higher the level of heat and penetration we're going to see.
01:16 If we have our weld speed and amperage correct in both MIG and TIG and keep our torch angle directed evenly to both parts of the workpiece, then our weld penetration should be close to what we want.
01:28 A common problem with shallow penetrtion and bad welds is that often these may be ground back to improve the surface appearance.
01:35 Unfortunately if a weld hasn't penetrated sufficiently into the base metal, then the strength will lie solely in the weld bead itself and now by grinding this back we make a bad weld even worse and risk imminent failure in this area.
01:48 The reality is the only way to repair a bad weld is to cut it out and to start again.
01:54 But how do we know if our weld is in fact penetrating sufficiently into the parent metal? Unfortunately just looking at a weld's appearance won't tell us what we need to know about what's going on underneath.
02:05 We're going to need to do some testing, at least while we're learning and building up an understanding of the correct settings and technique.
02:13 When learning to weld, it helps to test to find out how your machine's settings, as well as aspects such as the angle of the torch and weld speed affects the finished weld on a variety of test pieces.
02:25 To test a weld joint we can make a cut though the weld and then polish the face of this cut.
02:30 Once this surface is smooth, we can then immerse the test piece into hydrochloric acid for a few minutes which will etch into the steel and reveal the weld area.
02:39 This area and the inclusion into the parent metal should be uniform and completely fill the root of the material.
02:46 If you have a gap, it may be from the amperage setting being too low or your travel speed being too fast.
02:52 The angle of the weld torch will be clearly noticeable in the cross sectional area as well.
02:56 We're looking for a uniform amount of penetration into the walls on each side of the weld that clearly shows that your torch angle hasn't favoured one side over the other.
03:06 When welding thin sheet metals we don't have the option to do this kind of testing.
03:11 Instead, we want the weld area on the back of the sheet metal to be heat affected but not completely molten.
03:16 This will let us know that we have sufficient penetration into the material.
03:20 Looking at your weld and understanding what lies beneath will give you a greater understanding of penetration and the effect this has on the strength of your weld.
03:28 Even if you've got some experience under your belt, spending a little time before a large project to do this cutaway penetration test first could save you a lot of headaches further down the track.
03:38 To sum this module up, the key to a strong weld is its penetration into the base material.
03:43 The amount of penetration we see is dependant on a few different factors.
03:47 Most crucially is the current setting but the speed at which we travel as we weld also plays its part.
03:53 If a weld suffers from poor penetration it will be inherently weak and unfortunately the only fix is to cut it out and start again.
04:00 So it pays to get it right the first time.
04:03 This takes practice and testing and as the testing process requires destroying the weld, it's important to get everything dialled in first on some practice pieces before committing to our final weld.

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