how to weld thin sheets of aluminium (t<1mm)? is there any special type tig welding or razing machine

 

There are plenty of TIG welding machines out there that are able to do the job.
I would, If viable, Jig the job and have the ability to deliver argon to the back of the weld too.
Other than that I would suggest employing a welding operative with a good eye an a steady hand.

 

Not knowing the exact application, the best and one of the most cost-efficient methods of welding aluminum sheet <1mm would be ultrasonic welding http://www.ultrasonics.org/Proceedings_2006_UIA/Devine_2006_UIA.pdf

 

is there any brazing methods??

 

Yes there is, although I've never used it. There is a video here.
http://www.aluminumrepair.com/video_new.asp
Later in the video it shows an aluminium drinks can being brazed with little or no distortion.

 

@JeffYates thanks for the video

@rbutschle I think, we cannot afford ultrasonic welding ,

 

Understood, again, not knowing application or scope, Jeff's suggestion sounds great for smaller quantities!

 

Thanks for sharing this amazing video!

 

this website helps http://www.mig-welding.co.uk/thin-metal.htm

 

tried TIG and MIG, but too much distortion