Lightening Holes - How Many?

I need to add hole to lighten a piece of sheet metal - titanium, actually - that is .028 thick, 1 inch wide and about a foot long. I need to lighten extensively but still keeping adequate strength.

I was thinking along the lines of 3/4 inch holes on 1/2 inch centers, then adding something like a 3/8 hole in between each 3/4 hole, top and bottom, say 1/4 inch from the long edge of the metal.

Am I on the right track? Again, I need to significantly reduce the weight but still have some strength - these are stiffening pieces for a larger flat panel.

 

How much can you lighten a piece that small? Is it all flat or does it have a crown, or a bent or rolled edge? Use a dimple die on the holes, that will put some integrity back into it after you drill holes.

 

Your piece of titanium weights 0.055 pounds. How much do you expect to save by cutting holes in it?

"still keeping adequate strength" is very relative. You need to tell us how it is loaded before we can make recommendations. Tension, compression, bending, what?

 

You said in another thread that this was OT. What the heck is it that lightening something that already weighs 0.550 lbs. is necessary?

 

It's actually a folded up piece. The pan will be 6" x 12" and this is a 1 inch high lip folded up on each side along long dimension of the pan. I want to prevent the pan from getting all flexible flier, and the pan will have many lightening holes drilled in it as well. Overall I want the completed thing to be rigid front to rear.

 

In response to those asking why the heck I am trying to lighten something already pretty light, it is because I am down to grams on a weight limit.

My kid is building a robot for a school competition. He is taking a traditional hot rod approach: big tires, wheels, motors and batteries. But there is an overall weight limit so we have to shave everywhere else to make it. That's why we are using titanium - it saved us some over sheet metal.

 

Way cool! I knew it had to be something interesting. I believe that you'd be on the right track with what you stated in the first post, unless it is one of them fightin' robots.

 

Holes are really a terrible way to save weight, unless they are a part of the original design.

Some quick numbers: The original 12" long rib weights 25 grams. Each 3/4" hole you cut is worth 0.23 grams. Cut 10 of those and you have saved 2.3 grams, less than 10%.

Go with a 1/4" lip, and glue 2 more 1/4" ribs diagonally down the center of the pan so they make an X shape. Less than half the weight and way stiffer than the original idea.

(i edited my first post because I missed a zero. The the number is 0.055 pounds, not 0.550 pounds)

 

I believe he meant 1/2" between the holes, otherwise they'd overlap.

 

Well, it kinda is, but the opponent has the same weight limitation so it is a pretty level playing field.

 

Yes, I was talking about the material remaining between the edges of the holes.

 

He might be able to go with a shorter rib. The X won't work, though, because of all the stuff that gets mounted to the pan.

Can you spot weld titanium with a conventional pinch-type spot welder?

 

Theoretically, yes. Practically, maybe. Titanium melts at 3135F, compared to Steel at about 2000F. If you can get the heat, it will weld.

The deal with Titanium is keeping the weld free free from contamination while the metal is molten, hence the inert atmosphere comments.

A spot weld is somewhat protected from the atmosphere by the mechanical nature of the process. Still, it is hard to say.

Try it. Cut a couple of small squares and spot weld them together. Let it cool off and then try to pry the pieces apart. Bust out the hammer and chisel and see just how much force it takes to get them apart.

This is not going into air combat, or to the bottom of the sea. Strong enough is strong enough.

 

I tried doing ACSII art to give a picture of what I meant but that didn't work. Here is a Paint image, however not to scale:

View attachment Frame.bmp

 

Thanks, good idea. Could maybe wash argon over the weld from the Mig while spot welding it. The spot welder my son can use at school is pretty heavy duty, so perhaps it can get this thin stock hot enough. Does titanium change color when heated?

 

Before you mentioned your robot project and all, I was trying to envision lightening a race car by grams! Holy cow, what a strict class THAT is!

 

Heres a jpeg

 

Is it possible to roll stiffening beads into a titanium sheet?

 

LOL - I'll bet that F1 parts get down to that level.

The rules my son is building for are intentionally challenging. He is learning a lot about design and engineering decisions as everything is a trade off.

 

Yes Titanium can be spot (resistance) welded without any gas coverage.
It will turn sort of black and blue with some redish hue. We used to resistance titanium jet engine parts without gas coverage all the time.

 

Thanks! Every spot weld replaces a machine screw or rivet, cutting more weight.

 

LOL. Now you know that's not what I meant.

Can you redraw to scale, using the layout I posted as a guide?

Let's see if we can distill this down into the actual layout I can use on this 1" wide strip. Every gram helps.