Straightening an aluminium plate

**Marc** · 11th January 2015, 05:26 PM

I have a couple of 15mm aluminium plates 160 x 230 with two 100x100x20 tenons welded in the center of the plate some 70 mm apart. The tenons have both a 26mm hole for a 25mm stainless steel pin that goes through them. They are anchoring points for a pontoon ramp.

I have to bolt them in a different point on the side of the pontoon. When I unbolted them I noticed they both have a significant bent most likely the result of the welding. With a straight edge on it there is a 10 mm deflection in the center.

If it was steel I would chuck them on the forge and bash them back in shape. What do I do with aluminium? I need them straight but don't want to compromise their integrity since they hold a good amount of weight. So much so that I thought in welding a third tenon since the pin is way longer and can accommodate a third.

So how do I make this straight again and keep it straight when welding the third tenon?

**scottyd** · 11th January 2015, 05:32 PM

Im not an engineer, but Id be making it again. Aluminium has really poor fatigue resistance, its not going to like being bent back and forth and if its going to be supporting a lot of weight, id be tending on the side of safety.

**Simplicity** · 11th January 2015, 05:52 PM

Can we see some pics if possible

**Karl Robbers** · 11th January 2015, 06:23 PM

Either press it straight or set it up on appropriate blocking and get at least a 12 pound hammer and straighten it. Think one or two big blows rather than tickling it.
The ally will be relatively soft in the weld zone and should straighten fairly easily. Do not apply heat.

**Marc** · 11th January 2015, 08:20 PM

Thank you for the answers. So big whack no heat. Got it.

**QC Inspector** · 11th January 2015, 09:03 PM

On aircraft parts machined from aluminium plate or forgings there are two ways that are used to straighten parts after machining. The application is controlled be the drawings and specifications for the part.

The first way is by "bumping". The part is put on a hydraulic press and pressure applied to bend it to shape. Bending back to correct over bending is not allowed. This is usually done for thick parts.

The second is by Shot Peen Straightening. The surface on the concave side is shot peened to stretch that surface until the needed flatness is achieved. This is usually done on thin parts.

For your application I would use a hydraulic press if you have access to one rather than beating it into submission.

Pete

**Marc** · 12th January 2015, 10:53 AM

I don't have a press but have a large vice, a few blocks and it should work just as well.

**Karl Robbers** · 13th January 2015, 08:44 PM

Originally Posted by Marc

I don't have a press but have a large vice, a few blocks and it should work just as well.

It'll be all good. Just remember that a heavy hammer pushes large areas and light hammers are for localised work, so get the heaviest flogging hammer that you have and let rip with a good solid blow.
Certainly not kosher for aeronautics etc, but to quote an old boss of mine, "we're not building Swiss watches here."
If you really, really had to, you could warm the plate with oxy, but I'd avoid it if at all possible. Placing your blocks wider apart can help if it doesn't want to move for you.

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