Hello all!

I have been working on an electric press brake design for a couple months now and am just about to complete the assembly of a prototype I will be using to get the software developed and functioning correctly. My prototype is very small, only an 18 inch bend width, but this will allow me to rapidly prototype various software/control ideas at the comfort of my desk, or give me the ability to move the machine around very easily to test various criteria as required.

While the small prototype is great for testing, it does not accomplish what I set out to achieve. My goal is to create an economically priced servo press brake that can bend up to 4 feet wide material, and can create 40 tons of force. So while I have made excellent progress on my small prototype machine, I have struggled quite a bit on the larger design, specifically with the motion components as well as some of the general approaches to creating each part.

Here are some notes on my current design approach:
-Split the 40 ton force requirement across 2 separate servo motor/ball screw assemblies
-Secure the ram to the machine frame using square linear rails, this will also eliminate any radial force that I do not want transmitted to the ball screw.
-Based off my math I require 360Nm of torque applied to a ball screw with a 5mm thread pitch, using these numbers I can calculate a generated force of 86000 pounds. (More accurately, 2 ball screw assemblies applying 43000 pounds of force in tandem)
-I plan to achieve this force using 1.8KW DMM servo's attached to a 10:1 planetary gearbox that gets direct mounted to a ball screw attached to the ram of the machine.

My struggles begin with sourcing the motion components, here are some of my questions I am hoping some of the forum members might be able to assist me with:
1. I plan to use C7 ball screws, I cannot see the advantage of a ground ball screw is this application, but I am hoping some ball screw experts might be able to shed light on accuracy requirements when this much force is being applied.
2. I have been pleasantly surprised at the fair price of Thomson rolled ball screws, well within my target budget for the machine. I am wondering if anyone can suggest a better/alternate source for large diameter rolled ball screws? I am not too interested in ordering/working with companies based in China, I am willing to pay more to support North American manufacturing.
3. A big point of struggle I am having is choosing the correct ball screw diameter, based off my torsion calculations I will be ok with approx 1inch root diameter, but this seems very small and does not include a safety factor. I am really having a tough time trying to wade through this problem, I place a high degree of importance on this decision as it has to do with operator safety and overall machine performance so I am hoping to get some opinions on this. Any input would be greatly appreciated.

Please let me know if I can provide any more info or other details.

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