Bending steel tube with CNC Router MDF Jig in Hydraulic Press

JD Tek · Sep 22, 2020

I am curious if this idea is possible, I have never bent steel / made a hydraulic fixture before. I have read that you need to take kinking of the steel tubing into consideration. Ideally if this method works I may CNC machine the die / jig out of aluminum, but I have access to a bunch of MDF to prototype and think it may be cool to try. The tubing will be .75" with .0625 wall.

Jig / Forming Die Idea:

Part I want to make:

DDoug · Sep 22, 2020

JD Tek said:
I am curious if this idea is possible, I have never bent steel / made a hydraulic fixture before. I have read that you need to take kinking of the steel tubing into consideration. Ideally if this method works I may CNC machine the die / jig out of aluminum, but I have access to a bunch of MDF to prototype and think it may be cool to try. The tubing will be .75" with .0625 wall.

Jig / Forming Die Idea:
View attachment 299995

Part I want to make:
View attachment 299996

Go for it.

adh2000 · Sep 22, 2020

I cannot even imagine that working. The problems are so many where to start.

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Milland · Sep 22, 2020

adh2000 said:
I cannot even imagine that working. The problems are so many where to start.

But it will be educational...

Hardplates · Sep 22, 2020

Not a snowballs chance in hell

Limy Sami · Sep 22, 2020

Keep a safe distance when you try it

danil · Sep 22, 2020

Good concept, bad geometry for it's use. I was bending.some 3/3/4" stainless on a 2-1/2 radius yesterday on a cast plastic die 2.25" thick ..... It cracked after around 600 pcs. Then I made it the oreo with (2) plates of 1/4" flat stock(machined profile to match bend radius) and it held for another 50 pcs. which completed the current order. I will cut a new metal die before the next run.

For your application, you have a higher force concentration than I believe the material would handle with those tight radii.

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Garwood · Sep 22, 2020

danil said:
Good concept, bad geometry for it's use. I was bending.some 3/3/4" stainless on a 2-1/2 radius yesterday on a cast plastic die 2.25" thick ..... It cracked after around 600 pcs. Then I made it the oreo with (2) plates of 1/4" flat stock(machined profile to match bend radius) and it held for another 50 pcs. which completed the current order. I will cut a new metal die before the next run.

For your application, you have a higher force concentration than I believe the material would handle with those tight radii.

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The aluminum tube will just kink over and the MDF will blow apart.

The part is drawn with an inside radius smaller than it's diameter.

ChipSplitter · Sep 22, 2020

digger doug said:
Go for it.

Bondo · Sep 22, 2020

1 bend at a time

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JD Tek · Sep 22, 2020

Thanks everyone so far for the feedback, I watched a ton of YouTube videos after lol and I can now see the radius of the corner is way to small... I updated it a bit, and think using aluminum for the die will be better... and I will probably have to tweak this for one bend at a time although getting both would be cool.

Garwood · Sep 22, 2020

That will work fine for solid, but tubing you will have to do one bend at a time.

TDegenhart · Sep 22, 2020

To have any chance of success, the force and die will need to have a radius about the same as the tubing, particularly at the bend. Then fill the tubing with dry sand or one of the low melting point metals to help support the corners during the bend.

Tom

DDoug · Sep 22, 2020

ChipSplitter said:

Well the Op modelled it soooo nicely on CAD....it Just plain has to work...

L Vanice · Sep 22, 2020

TDegenhart said:
To have any chance of success, the force and die will need to have a radius about the same as the tubing, particularly at the bend. Then fill the tubing with dry sand or one of the low melting point metals to help support the corners during the bend.

Tom

One way to make tubing behave pretty much like solid rod when bent is to fill the straight tube with Cerrobend, a bismuth alloy that melts at 158 degrees F. The metal is expensive, but it can be easily melted out and reused. Similar alloy is available without the trade marked name on eBay.

Wood's metal - Wikipedia

Note that a sharp bend may cause the outside of the bend to crack, with or without a filler, and even a solid steel rod may crack in that circumstance. Red heat at the bend can prevent steel from cracking. That is how a blacksmith would do it, without the bismuth filler, of course.

In high volume professional bending, the tube can be put in tension as it is bent, which prevents kinking on the inside of the bend. It takes special equipment to do it that way.

Larry

Scruffy887 · Sep 22, 2020

MDF has very little strength to keep it from splitting. And your design does not wipe the material around the die. It should work by the third or forth version. But that depends if you can sort out what happened with the last version. Sometimes the problem gets moved upstream.

richard newman · Sep 23, 2020

Wind instruments are bent with ice inside rather than low temp alloy metal. Cheaper, and re-usable also. Gotta have a big freezer tho.

L Vanice · Sep 23, 2020

richard newman said:
Wind instruments are bent with ice inside rather than low temp alloy metal. Cheaper, and re-usable also. Gotta have a big freezer tho.

Yamaha kindly produced a documentary on how they make trumpets which someone posted on PM a while back. At 3'16" from the start, you will see them pouring metal into the tube before power bending.

Yamaha making Trumpets - with Jens Lindemann ( Part 1 ) - YouTube

Larry

kineticmx · Sep 23, 2020

Give us more info on intended application and quantity. Is this a production part or just a science experiment to make one bracket?

Google search compression bending. You will never get that arrangement to bend kink free regardless of the die material. The wiper die needs to be rotating along the axis of the bend so its tangental to the bend at all times. Hydraulic press isn’t really the right tool for this but if its powered you could use its pump to actuate a different cylinder.

I have a very similar part I produce and built a hydraulically actuated bender for it, if you are serious about building a production die set I can post up some more info.

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Mud · Sep 23, 2020

richard newman said:
Wind instruments are bent with ice inside rather than low temp alloy metal. Cheaper, and re-usable also. Gotta have a big freezer tho.

I saw that on How It's Made. I wonder if the temp is important, ice gets a lot harder to crush at lower temps, I'd think you'd be able to make it too hard to work properly.

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