MK3 VW GOLF ALLOY HEADER TANK FABRICATION

MK3 VW GOLF ALLOY HEADER TANK FABRICATION

A new job this week was to make an alloy header tank for a GOLF MK3.

This was made to customer specification for fitting by the customer. The tank itself is to be mounted where the coil pack normally resides and so this needs to be relocated.

Initially I considered making the tank form 2mm thick NS4 Aluminium however upon measuring out some sizes soon realised this was a baby tank and could easily be manufactured from 1.5mm thick NS4 Aluminium.

Image below shows sketch I was working to –

The header tank was to include a CNC machined pressure cap and weld in neck, 15mm bottom outlet and return 6mm stub.

Return Pipe stub was machined on a CNC lathe and is a standard item we keep on the shelf.

The 15mm outlet pipe stub was machined by hand on a manual lathe with a ridge around the end, this is to reduce the chance of the pipe slipping off the stub and is a standard method we use instead of just a straight piece of tube. No one likes pipes blowing off stubs – there is always someone to take the proverbial when things go wrong.

Below is all the parts and sheet pressings ready for tacking up.

Set up on this job is critical, with the tank being so small and made from aluminium heat transfer through the material will quickly saturate through the job, this will lead to welds “flooding” out as the material becomes so hot that it has the effect of welding with too high an amperage. Heat input and heat “management” then is critical to even, regular welds.

If joints are misaligned then a nice even fillet will not be achieved easily, this could mean the weld fillet will be lopsided and penetration in the joint may be affected.

Weld joint set up above is good and literally the inside corners of the material are tacked up touching each other, this is ideal for this type of tank made from thin aluminium material. Even a gap in the joint in material this thin is going to make welding this difficult as if not careful the material will melt away before filler can be added. I like to weld thin gauge aluminium outside corner joints with no gap so that as the welding arc heats up the material a small “tear-drop” appears, I then know that a good penetration bead will be achieved. This in turn helps me achieve a good “sealing” weld. I used TIG welding to complete this tank for looks and neatness.

So once all panels are tacked up I will proceed to fully TIG weld the main body, again ensuring that I manage the heat input to reduce the chance of the material becoming saturated with heat and the weld “growing” in width. We want all welds to be the same fillet profile thus ensuring a nice even looking job. On this one I actually had one joint with a gap in as I had mistakenly taken off a mm when allowing for bending allowance, I should have added it on (DOH). So I had to really turn down my welding plant, concentrate my welding arc to ensure that both edges melt evenly and add filler wire as soon as possible before the edges “blew” away.

When the main body was completely welded, after inspection; I continued to tack in place all fittings, ensuring alignment and welded them in one at a time.

The resulting tank is shown below

You will notice that the pictures show flat mounting brackets either side of the tank, these will be drilled by customer upon fitting to allow the tank to be fixed in position using 3 bolts. The tank needed to be pressure tested before and after these mounting brackets were welded on. This ensured that the tank is leak free before adding these mountings and also after welding them in position. With a clean and using a bit of “chrome” polish the tank is ready to pack up and despatch to the customer.

We only generally offer custom made 1 off jobs but, welcome any enquiry and would willingly help and advise any customer with any project.

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Thanks for reading 🙂

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