Not another CNC bender build

[wes_mcgee]

OK, sort of but instead a robotically assisted rotary draw unit. So I am currently moving into the second version of a robotically assisted bender. Eaton leonard makes a similar (smaller) product called roboflex.

Our initial version was quite small, using a nema 34 with a 100:1 gear head direct driving a rod bender modeled after a diacro. VErsion two is a bit more robust, using a servo driven 185:1 gear with 4250 Nm peak torque. I am assuming that will be good for something exciting!

My engineering degree helps a little, but I have a couple of holes in my design. Early in the process I made some assumptions. I saw some exploded axon views of a pines #2 and the only thing I could really size from it was they were using ANSI #100 to connect the hydraulic ram to the main gear. That helps, as it gave me a ultimate strength of approx 25k lb. So I sized a servo/gear that could output that with a 6" pitch diameter gear. Well I think I oversized that servo, as now I have read that chain drives have 5-10 safety factors, as the yield strength alone is 65% of the ultimate, and stretch is bad.

I am dealing with really low chain speeds and limited shock loads, I think as a bender engages that is a pretty smooth load curve. But I want to upsize my chain to at least match the motor power a bit more. Of course I can use current limiting, but I also want to be able to use the full capacity if I get up to that point. Part of this was due to not really ahve a good grasp on how much force you need to bend "X" tube.

So lets resize that chain. I still think in imperial, so lets use 3130 ft-lb as peak torque. I am thinking a bigger sprocket is a good idea, so lets say 8" pitch diameter, giving 10000 lb in the chain. 5:1 safety gives us a need for either #140 chain or duplex #100.

Let's back up on that though. If I use a chain selection chart, and put in my rpm and torque values, I come up with a very high design horsepower, something like 12-15. This would call for something like ANSI #200 chain or bigger. I have to assume that is wrong, as even this biggest benders only use duplex #160, and I don't think we are that big? Or at least we don't need to be, realistically I only wanted to bend 1.5"x.125wall. But I will take more if I can engineer it to work.

While I am going on about this, lets talk about dies. I am designing this to mimic typical rotary draw sets with clamp, forming, and pressure dies. I made my first set on a cnc mill out of chromoly. But I would prefer to just design it to fit something standard, and buy some used ones.

Question #1 anyone want to sell some used dies. I had a tooling company price making dies, and I was a little surprised, as one pretty standard set of the three parts was 3000$. Maybe that is typical, I know tooling is expensive. Maybe these were really nice.

Once I size the chain, I can get the sprockets, size the main shaft/spindle and start putting things together. Need to design the hydraulics for clamp and pressure. I am using an off the shelf hydraulic collet closer for my end of arm tooling. If you are curious basically we use a 7 axis kuka robot to control the plane and dist between bends, in addition the external servo the "bends" the material is also an external kuka axis, so it is directly driven in teh robot control at real time(allowing the robot to feed the material correctly as it is drawn in.)

Thanks in advance.

[wes_mcgee]

http://www.flickr.com/photos/wesmcgee/5556468943/

Here is a schematic of the original version of the bender, I am trying to put up a video as well on youtube

[TFGC]

What material do you need the dies machined from? Would brass or aluminum work? I also have a desire for a small benchtop bender for my CNC machining company; something like Pines CNC 15.