Need suggestions on die material for pvc.

I am quoting a new die that will punching 1/8" pvc square tube stock. The die will be 3.5" square. Rigidity is paramount because 8" of the die will be inside the tube with only 3" of it at the rear for mounting. The current die they are using is dead soft and flexes horribly. I have not made a die with such a long section unsupported so I'd like to get some opinions.

Thanks.

Hardness is not going to affect deflection, unfortunately, and practically all alloys of steel have essentially the same modulus of elasticity (rigidity).

I'm assuming this is a horn press, so the answer to the following question is probably "no", but I'll ask if you can back up the PVC stock from below (outside). If so, you might be able to do something where the die expands (like an adjustable parallel maybe?) to fill the PVC stock, so you can transfer some of the load to a deeper supporting member below the stock.

I appreciate the thoughts. I like the support idea from below. I have a meeting with the customer on Friday so hopefully we can come up with a solution. My first thought was to reshape the punch to try and reduce the force needed and reduce deflection that way. The current problem is their die is deflecting downward .190" and cracking the pvc in the corner radii. They currently have the punch ground .070" shorter to cheat the deflection but it's still cracking. It's a really screwed up hack job by whoever made this thing.

0.190" inch deflection!?! They are lucky this thing hasn't busted off in the middle of a cycle and hurt somebody. I was expecting "flexes horribly" to mean something more like 0.025"!

OK, other suggestions. 1) Grind lots of shear into the punch, if the material will allow it; you might be able to reduce press forces to a fraction of the current value if the punch and die are currently both flat faced. 1/8" thick PVC, try 3/8" or even 1/2" of total shear. 2) Do this as multiple operations (more than one punch/die set). First punch out (or even drill) a couple of holes at the corners or ends of the shape to be removed. If you reduce the cutting perimeter by 50%, then you've also reduced the press force by 50%. In the second op, knock out what's left of the scrap.

I was dumbfounded when I saw it. Putting shear into the punch is exactly what I'm going to do. I cannot think of any other way to go about reducing the flex except multiple steps like you mentioned but they won't go for that. Thanks for the opinion. I just needed to hear it from someone else. Lol.

One last thought. Is the blank short enough that an outrigger support count be moved into the free end of the blank to help support the cantilevered end of the die? If they are punching on the ends of 6' blanks, then no. But if the blanks are 1.5 - 2' long, and if the support can be synchronized with blank loading/unloading, that's a possibility.

Maybe I'm imagining it wrong but are you sure the die needs to be changed and not whatever is holding onto it?