CNC Tube Bender

Hi All,

I'm starting a new project, I want to build my own CNC Tube bender.
The idea is to build the machine fully controlled by servomotor and everything controlled with Arduino.
I would like to be able to bend steel tube with an OD up to 2.5" with wall thickness of 3-4mm.

For the first version I will use the dies of my manual bender.

For the bending part I will need a servomotor with pretty high torque and it will be direct drive.

This is where I need help,
I have no clue about what would be the required torque?
and what brand/models exist on the market and what is good or not?

I found some brands like Yaskawa on google that seems to have a pretty high torque but once again, I have no clue if it's enough or not and what alternative could also work?
I also have no idea about the price range of a such servomotor so any indications would be appreciable.

Thank you very much.

Let's start with your manual bender. What type is it? Linear or rotary? Mechanical or hydraulic? Then how much pull or push is required on the handle to bend the largest tube? You can calculate the required torque from this information. Maybe a picture or a link to a picture would be helpful.

It's a CNC rotary bender (mandrel) that I want to do, I start with the bending part and later I will do the axis positioner, and of course the whole actioned by servomotor to achieve accuracy and repeatablity.
the manual bender is a chinese copy of the Baileigh RDB 100.

But be aware that the dies of my bender is just a temporary solution, it's more to do some servomotor test, I will later make my own dies later, I know a shop that have the equipment to do it.

I found some article that was mentioning a required torque of 350-400Nm but once again I have no clue.

Just to put this in perspective, first concider that 400 Nm is about the torque output of a mid-sized auto engine, and that number seems pretty reasonable for a direct drive tube bender. That would be a huge servo motor.

But not very practical in this application. First you don't need to turn the tube bender at 2500 RPM, more like maybe 2 RPM. A much smaller servo motor and a massive gear reduction would be practical. Maybe a gear reduction of about 1000:1. The gearbox is going to be more expensive than the servo motor. The motor torque is multiplied by the gear ratio. I would be looking for a planetary gearbox in the 500 to 1000 : 1 range, then choose a servo motor to match.

As nice as direct-drive servos are; I'd give some thought to using a hydraulic drive; an encoder; and a solenoid valve. I'm suspecting that it may turn out to be lower cost...

Interesting project, an acquaintance used to pay occasional visits to a company that bent car exhausts.The machine had the facility to feed the tube along to the next bend location and then rotate it before adding the desired bend so that the finished article just needed an end flange added.Do you intend to build a machine with this sort of capability?

Quote:

---

Originally Posted by Jim Dawson

Just to put this in perspective, first concider that 400 Nm is about the torque output of a mid-sized auto engine, and that number seems pretty reasonable for a direct drive tube bender. That would be a huge servo motor.

But not very practical in this application. First you don't need to turn the tube bender at 2500 RPM, more like maybe 2 RPM. A much smaller servo motor and a massive gear reduction would be practical. Maybe a gear reduction of about 1000:1. The gearbox is going to be more expensive than the servo motor. The motor torque is multiplied by the gear ratio. I would be looking for a planetary gearbox in the 500 to 1000 : 1 range, then choose a servo motor to match.

---

I don't think it require a gear box as the speed of a servo can be controlled, and you are right it's going to be more around 2-3rpm.
I want it to remain quite compact and using a gear box is not going to be compact.
If you look at the CNC Tube Bending machine on the market, many seems to be direct drive with a big servo with a size of around 15cm X 15cm X 30 cm.

Quote:

---

Originally Posted by routalot

Interesting project, an acquaintance used to pay occasional visits to a company that bent car exhausts.The machine had the facility to feed the tube along to the next bend location and then rotate it before adding the desired bend so that the finished article just needed an end flange added.Do you intend to build a machine with this sort of capability?

---

Yes it's correct I'm looking to build a real CNC as I explained in first post, so after the bend part solved, I will build an axis positioner that will push and rotate the tube to the next bend position.

I have build a bike frame with the manual bender and it has been very annoying to do the mirror part so I looked at CNC Tube bending and obviously the cost of those machine is huge so I thought why not building one as it doesn't seems to be unreachable ;)

Quote:

---

Originally Posted by garthos

I don't think it require a gear box as the speed of a servo can be controlled, and you are right it's going to be more around 2-3rpm.
I want it to remain quite compact and using a gear box is not going to be compact.
If you look at the CNC Tube Bending machine on the market, many seems to be direct drive with a big servo with a size of around 15cm X 15cm X 30 cm.

---

To get a servo motor with that much torque for direct drive you are going to need one in the 75KW range. There are some lower power, low speed, very high torque servo motors available, but it would be less expensive just to buy a CNC tube bender.

I looked at a number of electric servo tube benders on the net, and all of them had a gear box on the bending mandrel drive. I agree that the servos are about 30 cm long, but about 15 cm of that length is gearbox.

The commercial tube benders I have retrofitted have used hydraulics and servo valves for the bending process.
Al.

I was looking a CNC like that:
https://www.youtube.com/watch?v=Ux1GB1gpXDw

I'm not 100% sure but this kind of CNC seems to use Servomotor, and I'm not sure it's really relevant to speak of kilowatt, the important point is the torque.

from what I see there is 3 possibilities for the bend:

- a electric induction motor (like an industrial 2 hp motor from Mitsubishi for example), a gearbox, and then control the rotation angle with a sensor
- a hydraulic actuator , with also an angle sensor
- a servomotor

I looked many model of CNC bender and the one that uses hydraulic actuator always have visible hydraulic pipe.
the smaller bender (Not CNC) but electric, seems to use the first option but many CNC seems to be using servomotor for the bend as well.

So before to eliminate the Servomotor option, I would like to see some reference of servomotor that have a sufficient torque (eg: 400Nm) and see how much space it take and how much it costs.

The reason I would prefer using a servomotor is also for high accuracy.

By the way, it doesnt matter if the servo have an integrated gearbox, as long as it comes with the servomotor and it's accurate that's fine, any reference of such servo to share?

In addition, I found this article that tend to confirm my thought:
https://www.thefabricator.com/tubepi...ectric-machine

the bend can be ensure by a servomotor, the question is more then what reference is suitable, any of you have experience with the Yaskawa or any other brands that have very high torque?
My domain is IT and electronics, no issue for me to do the programming part but I have no clue how to calculate the required torque, any suitable servomotor reference will allow me to make some progress :)

if I look the machine proposed here, they claim that there is no hydraulics component and that it consumes less than 5kW:
https://www.blmgroup.com/en/tube-bending
so the 75KW servomotor mentioned earlier seems to be way oversized.

I also found this Servo with geared mounted on it that seems suitable:
https://precision.nabtesco.com/en/products/detail/AF-N
Is anyone know those servos?

Quote:

---

Originally Posted by garthos

So before to eliminate the Servomotor option, I would like to see some reference of servomotor that have a sufficient torque (eg: 400Nm) and see how much space it take and how much it costs.

The reason I would prefer using a servomotor is also for high accuracy.

By the way, it doesnt matter if the servo have an integrated gearbox, as long as it comes with the servomotor and it's accurate that's fine, any reference of such servo to share?

---

A servo motor drive is a good option, but it needs a gearbox.

One option of a slow speed, high torque servo is the Mitsubishi TM-RFM series, for the torque required you would want the TM-RFM240J10 motor https://www.yumpu.com/en/document/re...-j3-b-rj080w/5

These are only about $35,000. https://www.powermotionstore.com/products/TM-RFM240J10 And that does not include the drive for it. The drive for the motor is pretty reasonable at only $3400 https://www.powermotionstore.com/products/MR-J4-500A-RJ So for about $39,000 you could have exactly what you are looking for. There are other brands available, but all are around the same price.

Now for a more standard servo motor, the Mitsubishi HA-LP50K1M4 is rated at 318 Nm and a peak torque of 792 Nm. A bargain at only $54,195 not including the drive. https://shop.gibsonengineering.com/products/HA-LP50K1M4 Of course this is only a 50 KW motor so does not quite have the rated torque required. But I got tired of looking at motor specs. But it would probably direct drive your machine, if you have about 400 amps of 400V, 3 phase power available.

I'll look up a motor gearbox combination tomorrow, it's past my bedtime now. But about a 1 KW servo motor and a 500:1 gearbox would be about the right combination for your needs, and not expensive. You normally buy the gearbox and motor as separate pieces, but the motor just attaches to the gearbox, looks like all one unit when assembled.

anyone has an idea about it?

Quote:

---

Originally Posted by garthos

so the 75KW servomotor mentioned earlier seems to be way oversized.

I also found this Servo with geared mounted on it that seems suitable:
https://precision.nabtesco.com/en/products/detail/AF-N
Is anyone know those servos?

---

You were the one that insisted that a gearbox was not acceptable and must be direct drive. A 50 KW servo would almost do what you want. Of course a 75 or 50 KW servo is ridiculous. You can find one of these if the $50,000 range.

The servo in the link above would work. But my guess is those are expensive.

Quote:

---

Originally Posted by Jim Dawson

I'll look up a motor gearbox combination tomorrow, it's past my bedtime now. But about a 1 KW servo motor and a 500:1 gearbox would be about the right combination for your needs, and not expensive. You normally buy the gearbox and motor as separate pieces, but the motor just attaches to the gearbox, looks like all one unit when assembled.

---

Totally missed that point, I didn't read properly ;)
Seems to be a more reasonable solution :)

Do you have any references to recommend?

Well it looks like this thread is alive again. I'll look into this later.

Quote:

---

Originally Posted by Jim Dawson

Well it looks like this thread is alive again. I'll look into this later.

---

Yes it's still, I have been a bit busy with some other stuff, and for some reason I don't get notification, so I didn't noticed I was getting response ;) thanks for your help

Hi Gath - The benders I have been involved with used a hydraulic ram and a chain. The chain runs around a sprocket on the bending lever. The chain runs to a spring for the return or another ram. On the CNC ones there is an encoder on the axis. Even if the machine is fully CNC you will still muck up the forst couple getting them symmetric. Springback and tube tolerances are always different tube batch to batch. Cheers Peter

Quote:

---

Originally Posted by peteeng

Hi Gath - The benders I have been involved with used a hydraulic ram and a chain. The chain runs around a sprocket on the bending lever. The chain runs to a spring for the return or another ram. On the CNC ones there is an encoder on the axis. Even if the machine is fully CNC you will still muck up the forst couple getting them symmetric. Springback and tube tolerances are always different tube batch to batch. Cheers Peter

---

I also saw those solution but I would prefer to go full servo drive, I should have been maybe more accurate but what I'm building is a mandrel cnc bender.

I already solved the problem of feeding part (Z-axis) that is going to be ensured by a rack and pinion and 2 guide way from Hiwin, and the rotation of the tube, it's basically a rotary chuck that have 2 servos, one to control the opening and closing of the chuck and one to control the rotation of the tube.

now I'm starting the bending part, the bending will be a bending arm bolted on the geared servo motor, and the clamping system will be on this arm made of a linear actuator using a servo that will push the clamping die.
Then will come the controlling part and it's gonna use some Arduino based PLC.

That's the idea :)

After a lot of research, I found this actuator reference from Nabtesco:
https://precision.nabtesco.com/en/products/detail/AF-N

So it's a geared servo motor, they even mention the Tube bender use case in the doc so I guess it should work.
So I asked a quotation for the following 2 models:
- AF042N126 (A6_1kW) with a rated torque of 412N and speed of 15rpm
- AF080N129 (A6_2kW) with a rated torque of 784N and speed of 15rpm
The problem is I don't know yet the price but I already know that I will have to wait 1 or 2 months as the local distributor doesn't have it in stock.

So I would be very interested to have a plan B, like maybe with a gear and servo separated.
Like a Mitsubishi one for the Servomotor as it seems easier to find where I am, but then come the gearbox where I don't know much about it...
I guess there is the formula to calculated the rated torque of a servo + gear reducer?
Or if anyone know some suitable references, I would be very interested.

Thank you very much

Maybe this one in a 160:1 ratio. Could be used with a 1 - 2 KW servo motor and give the needed torque. Harmonic gear reducer / hollow-shaft / high-precision / electrical for servo motors - RITM IndustryRITM Industry

You should make sure that you are sitting down when you receive the quote for a harmonic drive of the correct size. However, you can buy pre-owned examples from ebay dealers in South Korea and China. The prices are still significant but still quite a bit less than a new one.

Looks as if a 45 or 50 size drive would be required. https://www.harmonicdrive.net/produc...-units/shg-2uh

Most of these cnc benders use internal mandrels to stop the tube collapsing. Basing it on a basic Baileigh(?) machine doesn't sound like the greatest idea.

Quote:

---

Originally Posted by Muzzer

You should make sure that you are sitting down when you receive the quote for a harmonic drive of the correct size. However, you can buy pre-owned examples from ebay dealers in South Korea and China. The prices are still significant but still quite a bit less than a new one.

Looks as if a 45 or 50 size drive would be required. https://www.harmonicdrive.net/produc...-units/shg-2uh

Most of these cnc benders use internal mandrels to stop the tube collapsing. Basing it on a basic Baileigh(?) machine doesn't sound like the greatest idea.

---

at the begining I wanted to reuse the dies from my manual bender but no way it's not gonna be possible, so it's ok I will draw it and there is a workshop near my house that can machine it.

What I'm designing now is a CNC mandrel bender,

Quote:

---

I already solved the problem of feeding part (Z-axis) that is going to be ensured by a rack and pinion and 2 guide way from Hiwin, and the rotation of the tube, it's basically a rotary chuck that have 2 servos, one to control the opening and closing of the chuck and one to control the rotation of the tube.

now I'm starting the bending part, the bending will be a bending arm bolted on the geared servo motor, and the clamping system will be on this arm made of a linear actuator using a servo that will push the clamping die.
Then will come the controlling part and it's gonna use some Arduino based PLC.

---

So for now I think the most suitable i found is this geared servo from Nabtesco but as i was saying earlier I gonna have to wait 1 or 2 months once it will be ordered and i still didn't receive the price:
https://precision.nabtesco.com/en/products/detail/AF-N
So I'm looking for alternative :)

I also saw this:
http://www.apexdyna.co.th/index.php?...e&Id=539968170
but I'm not sure if it suitable, I'm trying to look at what is available here in Thailand, so there is principally Japanese, Taiwanese brand but I really have no clue about gears...

Quote:

---

Originally Posted by Muzzer

You should make sure that you are sitting down when you receive the quote for a harmonic drive of the correct size. However, you can buy pre-owned examples from ebay dealers in South Korea and China. The prices are still significant but still quite a bit less than a new one.

---

How much should I expect for such gear?
I'm expecting to pay around 1500$ for the bending servo and gear as it's the biggest one and it's about few hundreds dollars for the other axis servos, it's just a guess to be honest.

I'm close? or very far?

Did this CNC Bender ever happen?

Quote:

---

Originally Posted by Tinine

Did this CNC Bender ever happen?

---

Doubt it
You need hydraulics to generate the bending moment needed for pipe, using proportional control valves and encoders for feedback.
Not servo motors.

Quote:

---

Originally Posted by servtech

Doubt it
You need hydraulics to generate the bending moment needed for pipe, using proportional control valves and encoders for feedback.
Not servo motors.

---

My experience also, per post #10. ;)

United States Patent 5,862,697
Electric CNC Tube Bender. That's my name on it.

All the big-name CNC bender manufacturers now make 100% electric CNC benders. I started the whole thing but was never really a fan. Much prefer the hybrid approach.

There has been mention of proportional valves; not strictly necessary. Take a bang-bang (directional valve) with DC coils and PWM the coils. Horrendous deadband/hysteresis but if one has control of the PID, this is easily compensated for. When forming a tube, the bend-arm only needs to hit a target.

Distance Between Bends (DBB) is the Y axis
Plane Of Bend (POB) is the B axis
Degree OF Bend (DOB) is the C axis

And this is how a CNC tube bender is programmed - Lengths, Rotations, Angles. No G-Code involved.

It's a real shame that nothing came of this project :(

Regards,

Craig