I had been approached by a student in his final year at Cambridge University. He had modeled up exactly what was required, I had all the drawings and even flat layout patterns for the cones and wraps. So a bit spoilt on this one really but, apparently no one else would take this on in 1mm aluminium. I relished the challenge.
Duly parts were laser cut where possible and I started some real sheet metal work shaping with rolls, planishing hammers and stakes to form up the panel work to suit.
A lot of work went into this as all the joints had to match up spot on as I was going to need to purge the welds to leave a nice smooth bead of penetration on the inside.
As the material was only 1mm thick heat input was difficult to control as with aluminium heat is sucked away from the weld pool area. However, with the material being so thin once a weld pool was formed if I didn`t feed filler wire in immediately them it would drop through and leave a hole in the joint. Careful control with a foot pedal was needed to keep the welded joint from “blowing away”.
Fabrication of the main plenum had been analysed by the final year students to allow good airflow in conjunction with the rules and regulations under which they was going to be racing this single seater car. All parts had to be fabricated and welded together by the TIG welding process, other parts included cnc machined bell mouths and laser cut panels and flange. I also had to machine up a couple of bosses to incorporate sensors into the plenum.
The most difficult thing about this job was the simple fact that the drawings allowed little or no material from the bell mouths to the edge of the back plate, When welding such thick cnc machined parts to such thin sheet material the difficulty is always getting enough heat in the thicker part without melting away the thinner part. This was accomplished in a couple of ways. Firstly the back plate was sat on an aluminium heat sink block which helped drag some of the heat away from the thin material whilst directing the arc at the thicker bell mouth part. In future it would be advisable to leave a “land” if possible in order to reduce the chance of blowing away the thin sheet before sufficient heat build up was gained in the machined bell mouths.
Purging the inside of the plenum during welding with argon reduces the chance of atmospheric attack on the inside as weld penetration comes through the joint. This also helps in maintaining a nice smooth bead around the inside which will not disturb the airflow as much as if we hadn’t purged the joints. If I didn’t bother purging when welding the inside penetration bead would have been rough and inconsistent and possibly even hang through like “grapes” as we in the know call it. This would have been unacceptable for the job in hand.
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