Projects #3 for DEC3_MAR3 from Jason: 2.9L clone manifold.

[Jason]

VW has a 2.8L 12v VR6 motor and in germany they had a 2.9L of the same motor but the manifolds on the 2.9 had a bigger plenum. Since I have done a port and polish on my head and installed cams with a higher lift and enlarged the size of the valves, I decided that I need to incorporate the larger plenum and the best way is to make something similar to the 2.9L manifold.

The manifold in 2.8L form looks like the following image.


The 2.9L encloses the entire bottom section and is hollowed out as the plenum.
I began cutting out the manifold to hollow this section


Almost done


Once I cut the majority out, I then switched to using a flapper disk to smooth the ribs out of the manifold where I cut the supports out.

The material I am using to fill the bottom in is 1/4" 6061 Aluminum plate


I cut out a piece to fit


If you notice, I ground down the sides to make the plate sit flush with the bottom of the manifold. This pretty much placed it as if it was a piece built into the casting.

When welding, I had an issue where the weld kept cracking in only this spot. This was after welding it 3 times...


I solved it by welding the rest of the of the plate and then doing this.


This is the other half of the seam that was cracking.. For some reason this section of it welded fine.


and done. The bottom of this pic where the neck is located wanted to eat up the heat and blow away the plate. I had to sit on the manifold to form a puddle and pull it into the plate so not to burn a hole in the plate.


This was a rushed project and I used a 4 1/2" grinder and PP256 in TIG for this project. This was done with 3/32 tungsten and filler at ~180A

[jakeru]

Looks like a fun project. Maybe one of these days, I'll get to do one.

Interested in hearing some tips? I came up with some likely reasons for the cracking:
1. The alloy of the solidifying puddle is crack sensitive (when 6061 parent metals are involved, this is a common problem, and almost expected.) This kind of cracking (called "hot cracking") can occur before any strength even develops in the cooling weld bead. (There can be a hairline crack form right through the weld bead before you even flip your helmet up.)

The way to fix this is: don't weld thick 6061 aluminum with a closed corner joint configuration or with a non-grooved butt joint configuration. Instead, prepare a chamfer in the front surface of at least one of the two pieces of material for the butt joint (preferably extending at least 1/2 of the way deep into the thickness of the material or even deeper, preferably.) For the corner joints, alter the closed corner joint configuration into open corners. The void created by the opened corner or groove, gives a place for your filler rod to flow. That changes the metallurgy of the weld bead and often fixes hot cracking problems.

Sometimes, you can also change the filler rod alloy selection to change the metallurgy to a less crack sensitive weld bead as well. (the alotec filler rod selection chart rates the crack sensitivity of various parent metals and filler rods and displays the result as the attribute "W" (for "weldability")) Although I assume you were using 4043, which would be a good choice for this.

2. Lack of penetration (if you prepare a tight fitting butt joint without a chamfer or a "closed corner joint" and don't use enough current to penetrate deeply, then the thickness of the weld can be very thin compared to the rest of the metal, and also a stress riser.)

You can fix this by either using more current or going for "higher penetrating" arc settings (and/or slowing down the travel speed), or changing the joint type to one that is more encouraging of fusion at the root with less current (e.g., open corner instead of closed corner, or chamfered butt instead of unchamfered butt). With a crack sensitive parent alloy such as 6061, simply piling more current is a bad solution, because it will just melt that much more parent metals into your weld bead. You can pile the weld bead up high for additional strength, when its looks aren't objectionable. So the best solution comes back to chamfering your butt joints, and opening your corner joints.

Oh I almost forgot - welding the back side in addition to the front aids penetration tremendously. (However, it is not helpful however for projects like this with inaccessible backsides.)

3. Possibly contamination such as oils on the back side of the weld joint (the hydrogen causes porosity in the weld bead) - you can clean this off mechanically, with solvents, or with heat (hot enough so that starts smoking, and then keep it at that temperature until it stop smoking). It does look difficult to get in there. I probably would have gone with solvents on the back side, and flap wheel or aluminum grinding wheel on the front side, (like you did.) Maybe heating the part up until smoking (propane torch) if you really wanted it clean. Looking at what you started out with, it looks like a very dirty, oil soaked casting and I'm sure there was all kinds of junk all over any of its oxidized surfaces; challenging to clean for aluminum welding. Sometimes you can use the TIG torch to clean, or to "check cleanliness".

4. Forces caused by uneven heating and cooling during welding. You can't eliminate it, but you can reduce it by changing your weld sequencing, pre-heating the part (it's a good bit of work, so I rarely to it if I don't have to), or perhaps more easily, finding a "sweet spot" in current and travel speed that is not too slow but also not too fast. At the end of a weld especially, it is helpful to gradually taper off the current to let the root of the bead gain strength and avoid making a cooling crater. Welding too "hot and fast" *can* cause cracking problems, but you have to be going really fast to run into it, IME. Given your Although I don't think that was your problem given your settings gas (pure argon) and material thickness.

[Jason]

Thanks.. That all makes sense to me and I thought about a chamfer but decided I didn't need it but maybe it would have been a good idea. I think that putting down a wide weld over that section that was cracking made me move slower over that area and put more heat into it. You are right that I was using 4043 filler and that manifold was rather dirty. I think I used a 40Grit flapper wheel on this but may have been a 60. I had to take the guard off my grinder to get inside there.