Need to bend stainless plate. This technique look ok?

[David916]

I was thinking more like 60-75 ton OBI. Preferably back geared.

If you're making a punch press tool, make it to do the job in one hit. Make it idiot proof so you can practically throw the part in the tool and it comes out perfect.

75 ton would be nice -I'll look into finding one for sale that isn't too far away from me.

Quick question, do my calculations seem correct? I'm coming up with 4 tons are required to do a 90* bend on 0.1875" thick x 6" wide 304 stainless if I were to use a 3" wide die opening. Does that seem right?

 

[David916]

If the calculations are right, I'd love to use my 5 ton obi press for the time being.

 

[Garwood]

75 ton would be nice -I'll look into finding one for sale that isn't too far away from me.

Quick question, do my calculations seem correct? I'm coming up with 4 tons are required to do a 90* bend on 0.1875" thick x 6" wide 304 stainless if I were to use a 3" wide die opening. Does that seem right?

Technically it kinda is, but no, you won't make a nice bend in 3/16 304 that wide with 5 tons.

OBI tonnage is peak force a small amount above stroke BDC. Non-geared presses have very peaky tonnage. They are better for punching. Back geared presses have a wider crank angle where they can do work so are better for tough forming and drawing work.

Hydraulic is fine, just realize that you're gonna have to build something with some substance (lots of steel) to get a nice, repeatable part.

You also have the safety aspect. A modern OBI is osha friendly. Your homemade thing, not so much.

I recommend OBI's because they're cheaper than a press brake and work great for products where they just live setup for one job forever. Big ones are cheap. I bought a creampuff C45 Bliss made in the 80's recently for $2000. Then I watched a C60 Bliss sell on Ebay for $300 500 miles away. Then a pair of 150 ton Bliss's went for $500 also on Ebay and within driving distance. Shouldn't be hard to find something ready to run, safe and nice shape.

 

[David916]

Technically it kinda is, but no, you won't make a nice bend in 3/16 304 that wide with 5 tons.

OBI tonnage is peak force a small amount above stroke BDC. Non-geared presses have very peaky tonnage. They are better for punching. Back geared presses have a wider crank angle where they can do work so are better for tough forming and drawing work.

Hydraulic is fine, just realize that you're gonna have to build something with some substance (lots of steel) to get a nice, repeatable part.

You also have the safety aspect. A modern OBI is osha friendly. Your homemade thing, not so much.

I recommend OBI's because they're cheaper than a press brake and work great for products where they just live setup for one job forever. Big ones are cheap. I bought a creampuff C45 Bliss made in the 80's recently for $2000. Then I watched a C60 Bliss sell on Ebay for $300 500 miles away. Then a pair of 150 ton Bliss's went for $500 also on Ebay and within driving distance. Shouldn't be hard to find something ready to run, safe and nice shape.

Ah, very good. It all makes sense now and thank you for breaking it down. Bought two 5 ton obi presses last week for $100 each and haven't used them yet and didn't know about geared vs non-geared, so thank you.

Ok, I now know what I need to do. Will report back in a few days with my build for some feedback.

Thanks to everyone who took time out of their day to respond to me. Really appreciate it.

 

[Garwood]

Ah, very good. It all makes sense now and thank you for breaking it down. Bought two 5 ton obi presses last week for $100 each and haven't used them yet and didn't know about geared vs non-geared, so thank you.

Ok, I now know what I need to do. Will report back in a few days with my build for some feedback.

Thanks to everyone who took time out of their day to respond to me. Really appreciate it.

In my experience, it's easier to find a bigger non-geared OBI than you need than finding a backed geared OBI of the size you need. I just mentioned it because there is a distinction between the two and it's important to note when you are planning to form thicker materials with an OBI.

 

[metalpyro]

I'm on the press brake band wagon. A couple of remarks above unlocked the secrets key to your success.

In order to get a consistent measurement between the flanges, you must gauge off of one end, whether it be with a CNC back gauge or fixed gauges. The CNC would be easier to set up and fine tune, but either will suffice. Besides the benefit of being able to fine tune the gauge dimension between the bends, you will be able to compensate for the difference in the blank size (which hasn't been discussed yet). By compensate, I am saying you can control where any differences plus or minus from your developed length end up. What I mean is one of the unequal flanges better suited to put the difference?

The other comments regarding the variable thickness you will be dealing with is high on the list of concerns. As was previously mentioned, you will have different thickness of parts from the same sheet or bar. You will have different results from the "with the grain" or "against the grain" even if the thickness is exactly the same. Again, this is where a CNC brake would shine. You would be able to fine tune the depth of the ram to compensate for the thickness difference of the blanks.

Trying to hit a perfect 90* in a single hit is like aiming at a moving target. You're not going to hit it every time. I always try to over bend the part slightly. It is way easier to unbend to 90 than it is to add more to the bend.

What is the source for the blank? Flatbar or sheet?

Wouldn't the OBI press hit at a high rate of speed?

 

[Garwood]

Wouldn't the OBI press hit at a high rate of speed?

OBI's are generally faster than press brakes, atleast older ones.

Steel's max forming speed is 80 feet per minute. Depends on stroke obviously, but a typical 3" stroke press could run 200+ strokes per minute and be well under steel's maximum forming speed.

Here's the thing- To a press brake guy that's a press brake job. To a product guy that's a stamping press job.

In what I would consider a small-mid size stamping press (one that you can easily move with a 10K forklift) you can make that part in a simple tool in one hit and it will be perfect.

The flange-flange dimension is a non-issue. It's built into the tool.

To deal with material thickness variations you can add discreet or obvious features to coin the bend.

I'm probably getting way out there for 20 pcs a day, but this is how I do some of my stuff. I will spend a couple days building a simple soft tool and I'll run parts through it for a few hours once every few months or so.

I have a press brake. A close friend has 5 of them. I know how they work. When you have a long running part and can build a simple tool you can make hundreds, or thousands of parts in a short time with a stamping press VS the same parts over hours or days with a press brake.

Press brakes are versatile. Stamping presses are productive.

 

[metalpyro]

Press brakes are versatile. Stamping presses are productive.

Fair enough

 

[Strostkovy]

Just bring it to a job shop and pay the minimum to have it bent. It's maybe 5 minutes in setup and 10 seconds per part, without trying to be fast.

 

[Strostkovy]

I'm on the press brake band wagon. A couple of remarks above unlocked the secrets key to your success.

In order to get a consistent measurement between the flanges, you must gauge off of one end, whether it be with a CNC back gauge or fixed gauges. The CNC would be easier to set up and fine tune, but either will suffice. Besides the benefit of being able to fine tune the gauge dimension between the bends, you will be able to compensate for the difference in the blank size (which hasn't been discussed yet). By compensate, I am saying you can control where any differences plus or minus from your developed length end up. What I mean is one of the unequal flanges better suited to put the difference?

The other comments regarding the variable thickness you will be dealing with is high on the list of concerns. As was previously mentioned, you will have different thickness of parts from the same sheet or bar. You will have different results from the "with the grain" or "against the grain" even if the thickness is exactly the same. Again, this is where a CNC brake would shine. You would be able to fine tune the depth of the ram to compensate for the thickness difference of the blanks.

Trying to hit a perfect 90* in a single hit is like aiming at a moving target. You're not going to hit it every time. I always try to over bend the part slightly. It is way easier to unbend to 90 than it is to add more to the bend.

What is the source for the blank? Flatbar or sheet?

Wouldn't the OBI press hit at a high rate of speed?

It sounds like you are familiar with very old press brakes.

Gauging off of one end can be more convenient for forming, but also isn't really necessary. Get an accurate part by measuring the actual bend allowance once, and cutting your blank accordingly. Pushing the error to one side or the other is lazy, and gauging off of the flange only compensates for half of the error. ( I realize now the recommendation was to compensate for varying blank length, but I'm leaving what I typed because it is useful).

The worst variation we see within one sheet is 0.003", and usually much less. Between sheets can be more, but stack parts by heat number and grain orientation and you will have no issues keeping angles accurate and repeatable.

We generally see 0.3 degrees of random variation across like grained parts within the same mill batch of plate. This is from 10 gauge to 1/4" steel. Trying to compensate for more than the random variation will end up making your bends worse, as you amplify the error with each adjustment. I find it very easy to add a half of a degree to a bend in steel or stainless, and only have issues when using die film, where 1-2 degrees of overbend occur with a rehit to the same position.

 

[Scruffy887]

Please specify what your "mass production" part needs to look like. Need radius at all bends too. If you cannot define it, cannot get it made. Duh! Cannot get good advise for you either.
If you came into my shop with that I would most likely send you away. Prior experience!

 

[Strostkovy]

Please specify what your "mass production" part needs to look like. Need radius at all bends too. If you cannot define it, cannot get it made. Duh! Cannot get good advise for you either.
If you came into my shop with that I would most likely send you away. Prior experience!

Do you have the tooling for every radius a customer can come up with? If someone came in with some blanks and said I need these bent at these dimensions, I'd ask which two flange dimensions are critical and ask if the standard radius I'd use for a given material is okay or if they have special requirements.
Having worked at a job shop the was able to turn a profit off the lowest value walk ins, it's important to match your results with customer expectations, and to also not gate keep the little guys when they are first figuring something out because around 5% of them start placing some very large orders. For example, a roofing installer may know very little about sheet metal, but knows a lot about how the tool they want needs to work and look like. You make 5 of them for the shop minimum at $45, and then a few weeks later he comes back and places an order for 1000 pieces.
Granted, not everyone likes to work the piddly shit, and yhou may turn someone like him down on the basis of quantity alone. But not having hard numbers for features that don't matter is definitely not a concern for me.

 

[David916]

Please specify what your "mass production" part needs to look like. Need radius at all bends too. If you cannot define it, cannot get it made. Duh! Cannot get good advise for you either.
If you came into my shop with that I would most likely send you away. Prior experience!

That makes zero sense.
I never once said I make things for others.
I also said the radius "doesn't matter".
I manufacture a part in-house and this is for my shop.
With that said, might need a bit more "experience"...

 

[Scruffy887]

That makes zero sense.
I never once said I make things for others.
I also said the radius "doesn't matter".
I manufacture a part in-house and this is for my shop.
With that said, might need a bit more "experience"...

Advise given, advise rejected. Learn how to specify what you want, even ask how to specify your part.
Oh, air cylinder on your hold down is useless. Hydraulics will overpower it and your bend radius will grow.

 

[David916]

Advise given, advise rejected. Learn how to specify what you want, even ask how to specify your part.
Oh, air cylinder on your hold down is useless. Hydraulics will overpower it and your bend radius will grow.

HUH? you commented on radius, I said a long time ago radius doesn't matter. I don't know why you are still talking about it and said "you'd turn me away from your shop if I were to ever come in"

We've moved on from pneumatics...

Please don't reply to this post anymore. Thanks