Straightening out bend in cast alluminium

[Zero-Five-Two]

After a bit of advice from anyone who knows better than I.

I've got a small issue with the cast aluminium radiator surround on the old Tanker.  It's had a bit of a dink on the off side that I would like to straighten out

 

 

Depending on which photo you look at is how bad it looks, but in the flesh and up close it looks awful, and the centre grill wont sit flat like it should.

Now if it was made of steel you would simply whack it back into shape with a suitable hammer and possibly a bit of heat.

But this is cast aluminium and I'm not sure how to treat it. I'm assuming if I give it a fourpenny one with a big hammer bits will just break off.

Anybody got any experience of such stuff?

[john1950]

Any blows It usually just goes crack, limited success heating and squeezing with G clamp and blocks of wood. Makes your eyes water more than the cracking.

[Ron]

If it is cast aluminium, I think the repair would be best done by a professional (MIG?) welder, by breaking/cutting out the damaged area and welding it back in straight. In which case, you would have nothing to loose by having a go at straightening it yourself.....After all it already bent without cracking. I would anneal the area by getting it sizzling  hot with a gas torch  (don't melt it though). Back up the area with a dolly/ heavy block and see if it taps back to shape. Ron

[Citroman]

A car restorer from a firm that makes aluminium bodies once told me a trick to form aluminium. That was clean it up first to bare. Then trace some lines on it with a bar of soap. Then slowly heating it with a torch from the other side till the soap lines get black. Then the aluminium is softened up enough to form. I don't know if this also works for cast aluminium. Good luck.

[ruxy]

Look at the evidence , impact it did not fracture .  Therefore  IMHO it is a grade of 'malleable' aluminium - someting like LM6 .   The problem is now localised stress that will need relieving with a low temp flame - then I would follow the already suggested method of timber blocks and G clamps.  Due to the value  and potential firther  £ loss - I would suggest you spend some time with the forming blocks , a series such that the re-alignment is gradually progressive.

Edited December 2, 2018 by ruxy
spelin

[No Signals]

I think you have had all the areas covered so I've nothing to add except to re-affirm what Citroman said about the rubbing with bar soap, it works on cast ally as well but be careful not to overheat it - just to the point of 'blacking'.  Then steady pressure with shaped blocks and clamps.  Re-heat as often as required but don't forget to resoap it.

[mogmaner]

You could try Metal shrinking, heat yousing soap as a temp gide the quench with cloth soaked in cold water on the out side,this will make the outer surface to shrink faster on outside than the inside ,slowly pulling the twist or dint over multiple heating and coolings ,worth trying on a piece of scrap material to gain a feel for how the metal moves.

[Zero-Five-Two]

Many thanks for the advice guys, I think I will have a go at the warming and straightening with clamps first. Photos to follow as it progresses

[MatchFuzee]

Posts 6 & 23 (same person) recommend annealing the aluminium but letting it cool before bending:-

https://www.practicalmachinist.com/vb/general/can-i-heat-straighten-cast-aluminum-195814/

[ruxy]

That pm.com  has a few good points , inc. the use of a  IR heat temp. detection gun.  Better than the older soap trick that may be iffy  ?   ,  the point being is that to succeed without damage - you need to enlarge the  'grain size'  to max. within the heat affected zone of the torch  (I think I would be using a 12mm propane nozzle and plumbers  soldering mats to envelope .  The nearer to the melting point - the bigger the grain and therefore the less risk.  From the application ,  vibration stress over many years and possibility of a knock on what is 'decoration' with a purpose,  LM6 is what I would guess at / select , I do have a materials book going back to my 1960's studies and it has always stood me in good stead - I need to find it.  Still good to use in. conj. with the internet.  So as not to have a rax-up - I don't think I would dare approach within 100C of the guestimate melting point.