What to Consider When Selecting a Servo Feeder for Your Roll Forming Operation

Hello everyone. I’m Brian Kopack from Formtek and welcome to Formtek Talks. In today’s podcast, I’m joined by Kevin Enos and Charlie Burgess, and our discussion focuses on servo feeders. Specifically how they function with press strokes and cycle rates and the various things you need to consider when deciding how to select them for your roll forming process. Thanks again for joining us.

I think I’m going to start off. Servo feeders when it comes to a roll forming application, is typically used when we have to do pre notching or pre-cutting type operation. Based on that Kevin, tell us a little bit about some of the advantages or features of various servo feeders and why you want them. There’s lots of things to consider when you’re talking about a servo feeder. Let’s just start with the basics. What are the basics things you guys need to know when somebody comes to you with a servo feeder type application?

The biggest things are going to be for sizing the unit first and foremost, the material thickness, the line speed, feed progressions or feed lengths, and that’s all that’s going to go into considering and being able to size the motors and the roll diameters and things of that nature. The backing up a bit, servo feeders ultimately are the replacement for mechanical feeders, gripper feeders, things of that nature rack pinion, more chance for marring the material, the way you have to transfer it far more limitations on making changes to those feed lengths, things of that nature set up by the operator or maintenance personnel. The mechanical or cam driven, that’s a very difficult process. When you have to be precise in the feed lengths, that is very difficult to dial that in.

A gripper feed is not ideal for applications where you can have scratching or marring on the material where basically you’re grabbing the material or pinching it on the sides, or possibly the middle dragging at a fixed distance, and then letting go and rotating back to position. A servo feeder by far and away is the simplest, easiest and most accurate way to convey material from point A to point B. You can make adjustments to a feed length in process at one thousands. You can plus or minus if going back to your hole location. If you’re missing by just a bit, you can adjust that while the machine’s running plus or minus one thousands at a time in putting in job numbers, which you can’t do with any of the four mentioned ways of feeding material from point A to point B.

Roll finishes, again, are a factor for the pin rolls. If you’ve got surface critical painted pre paint material, the roll finish is going to be critical to ensuring that, that material does not get marred or scratched. Repeatability of the unit, and we tend to get into roll repeatability versus part repeatability. The distinction is on the accuracy of the unit is plus or minus two thousands. If you were describe a line on your upper and bottom pin roll, you put in a specific feed length, those based on the circumference of the rolls, then you should have those two points meet back up after a full rotation. On a gripper style or cam style, there’s no way to achieve that level of accuracy.

The reason that we say roll repeatability versus part repeatability is there are other things, if there’s other coil conditions, for example, other than coil set in the material, the chance that you are going to be able to repeat that fee length each and every time is less achievable, not because the machine is incapable, but because of inherent conditions in the material. Those would be the biggest factors. Roll lift would certainly be another factor. The various types as was discussed in a different episode, where we talked about feeders with pulse through straighteners. There’s different configurations that you can utilize. And then finally, with a servo feed, you could do a two roll or a four roll servo feed. Again, that’s going to be application driven based on a four roll feed. You have twice the amount of surface contact with half the amount of air pressure, thereby mitigating the chances you’re going to scratch or damage the surface critical material you’re trying to feed into a roll form or a press.

Is a four roll feeder, more precise in terms of your feet length than accuracy, because you have that dual grip on the material?

It can be. It does decrease the chance for slippage by design. It’s not any more accurate than a two roll feeder. The accuracy, the roll repeatability is the same. The difference is by utilizing half the air pressure, you are pulling up that weight. There’s less chance you’re going to have roll slippage as a result versus a two roll where you have to have more pressure with just two rolls, carrying that material from point A to point B.

And tell us a little bit about … We were speaking offline and we were talking about cabinets versus mounting the servo feeder directly to the press with a shelf. Why would a customer choose one over the other? Obviously, if their press had nowhere to mount the shelf, that could be a determining factor, but is there a benefit to mounting the server feeder on its own cabinet?

There’s not a whole lot. It’s more customer driven and customer preferences as to being a cabinet mounted, which would be a standalone unit or mounted to the press itself. The biggest advantages of having a standalone unit, is you’re not subject to any vibration from the press itself. That vibration could translate into miss feeds, inconsistent feed lengths, things of that nature, accessibility to the press window would be another detriment of having a press mounted unit. Most customers nowadays opt for a cabinet mounted unit. You’re not subject to the same vibration. We do tie bar to the press to ensure at least in a press application, you’re going to have some inherent movement of that press. The feeder we need to be able to follow that inherent movement of inertia in the press that allows to maintain a consistent feed length and accuracy of that feed length.

Those would be the biggest advantages of one over another. In both cases, I would recommend having adjustability of those units, so you could adjust your pass line height. A lot of folks do not have consistency in their dyes where you’re in the press itself. So you would have to modify the pass line location to accommodate for various die heights, feeding into a roll forming application certainly having that mounted on a shelf directly to the roll form. You’re not dealing with a lot of those same issues you’re dealing with a press. You’re also typically dealing with narrower widths with a roll forming machine than you can get into on a feeder, or I’m sorry, on a press.

On the note of accuracy and roll movement you can definitely control and you’re down into the thousands. When a customer says, hey, I absolutely have to have my holes lined up to a thou less. I know there’s such a thing as like a pilot hole reference and opening and closing of the servo feeder so that you can let the strip move with respect to the additional pilot hole. That’s in the dye. You obviously have that option, but is there some things that you’re doing special there to accomplish that?

It’s nothing special. It is, as you said, being able to, whether it’s in a piloting and a dye, for example, we have to be able to open those pin rolls to allow that material to settle into a location. That’s going to ensure the repeatability from the hole to hole location. And that’s done of course, typically via an encoder on the wheels or the rolls themselves to denote the location. It does have the ability to move quote unquote forward or backwards to accommodate for localizing that specific hole location.

And that’s probably the most accurate style that you could get, right?

Absolutely.

That’s a feature that a customer could add provided that they have the correct accommodations in the dye itself that they could utilize.

The pilot is the most accurate?

I think the pilot is the most accurate.

Yes.

I think there’s other ways to get close to that. And I know we have used where we actually put it encoder on the material, and we’re looking at the revolutions of the servo feeder, and we’re comparing the two. And obviously we’re trying to see if there’s slip. We use the encoder on the material as a pseudo closed loop situation where it’s the master. And we’re looking at what the servo feeder is saying it should have moved and we’re comparing the two. And if it gets way out of whack, we can either throw an error code or let somebody know that something’s just not right, but we can still follow what the encoder on the material is doing.

Correct.

You see, because in my mind, when you open up the feeder roll, it kind of loses its relationship to the strip, because you’re now you’re allowing the pilot to move the strip wherever it needs to be in order to get the accuracy on your holes. But the feeder, I know you’re just opening and closing, but if that strip does move now, it’s moved relative to where that feeder thought the strip was. And that’s why I always thought that was not a great application.

I think when the servo feeder closes and correct me, if I’m wrong, Kevin. When the servo feeder closes back down on that material, it essentially is re zeroing its movement from that point.

That’s correct.

It says it moves another five inches or eight inches or whatever the length is. And then it’s going to wait for the dye to kind of close and start grabbing the material and then let go of it, so it can move to where it needs to.

That exactly correct. And I would add to that to Charlie’s point. The reason it doesn’t lose the accuracy is the fact that you are doing the measurement. The critical measurement is from hole to hole and not necessarily on the feed length at that point. The reason for opening those rolls and re zeroing is what’s going to ensure we’re going to feed the specific amount, but the piloting is what’s going to ensure that the hole location, again, you could have other coil conditions where the feeder is showing it moved that material exactly where it was supposed to at the orientation from hole to hole could still be off as a result of some other material problem.

The other thing to Brian’s question would be what we call batching and gagging. It’s not necessarily hole to hole, but you may have an application, whether it’s punching on a roll form or some other application where going to move the material and increments of two inches and then two inches, and then your next couple of punches or movements may be three inches. There’s going to be a pattern or a grouping of movements that have to follow. Again going two, two, two and then you have a couple of three inch movements and then you repeat that process all over again. Another advantage with the servo feed is the flexibility to provide that type of capability that is not the case with the more mechanical type of feeders.

Hitting on that a little bit, there’s a feature that is always offered on the servo feeders called programmable pattern control. And that is, I think when you get kind of the indexing you’re talking about where it varies a lot through the length of a single part, but where is that cutoff where you need programmable pattern control as opposed to not having it?

That’s customer driven. Every application being different, some are going to require that type of movement and that type of a pattern versus other applications that do not, they’re facilitating a fixed distance or feed length each time and not an inconsistent grouping of feed length. It’s really more application driven than it is anything as far as what we would offer or not offer. Inherent is our ability to provide it, but not every customer has a utilization for it.

Anytime you have an any non-consistent pattern, you have to have programmable pattern control, as long as you’re hitting the same distance on the same hole throughout the length of the part, you don’t need it. But if you have any kind of variation and hole spacing, then you need to have that feature?

That’s an inconsistent pattern that in and of itself is a pattern. Yes.

Okay. Right.

I’m going to throw out a question that I get asked all the time is, why do we put a servo feeder on the entry side of the press where some people will put it on the exit side of a press? It’s, on the entry side, you’re pushing material in on the exit side, you’re pulling material in. In my mind, in theory, not be a difference to the servo feeder if it’s pulling or pushing. But if you’re applying dye lube on the material, in your punching process, I could see that being harmful to the servo feeder rolls in its grip on the material if it’s on the exit side of the press, because it’s pulling this material and there’s lube on it, it could increase the chances of slip. Can you think of any other reasons? Is it beyond that? Is it really just customer preference or is there a technical reason?

There, it is not in that case, predominantly not a customer per reference, the reason for it. And again, as I’ll use a press as an example, the reason it’s located on the entry side in most instances is the fact that you are facilitating that material into a dye. Whatever that dye pattern is, punching a hole, making a part, once it does that process, there’s less material to work with on the other side or the exit side, then you get into things like lube. There could be vinyl application, any number of reasons. The vast majority of the applications have the feeder on the entry side of the product, because you are having other processes done on the other side of those rolls if you look at it that way, conversely, if we were located on the exit end, we would be feeding out a skeleton of material.

And what you’re going to get as a result of that is different than what’s on the inside. Plus if you have any issues in the dye itself, that could create problems on the exit side feeder versus one you wouldn’t experience on the entry side of the feeder. It is more driven by the fact that there’s something occurring after the feed rolls, where the precision required is induced at the entry side and not on the exit side. Now that being said, there are applications that do require the material to be pushed or pulled from the exit side to another, a secondary operation. There is what’s called a push pull feed where you’re bringing that material in via a feed on the entry side, but then also require a powered feed on the exit side to get that material through the dye out to. Again, you’re the skeleton to another operation rewinding or otherwise.

Okay. And tell me a little bit about the servo feeders that essentially have touch screen control versus non-touch screen. Is it something that the operator can just work directly at the machine and do the programming versus doing the programming on a computer and downloading that?

All the feeders today have an HMI and that’s because they can be operated independently or as part of the entire line. And there would be opportunity to set up a job number, for example, at the feeder, which you cannot do at the straightener end. Conversely, there again, the micro adjustment of plus or minus a thousands, for example, typically that’s done at the feed end because you’re close to the die or close to the roll former. You can see the impact to that and the adjustments that are made. Unfortunately in today’s market with the result of fewer employees, the automation factor becomes of greater need.

The ability at the front end of a line at the straightener or the leveler, for example, being able to set it up by job number where everything is done at the feed control and transfer it down to the servo. There’s various levels of integration and automation that can be done, but almost all of them now are done at the feeder via a part number could be a barcode scanner, again, a various amount of methods to accomplish that. But the benefit of being able to do it right there at the feeder is certainly advantageous as you can get into some pretty good distances from one piece of equipment to another, on a larger line.

Tell us a little bit about the maintenance servo feeders. Obviously the roll diameter should in theory, never change. That would keep your accuracy at a certain level. But obviously if it’s always moving material it’s wearing. Is there a way to recalibrate a servo feeder after the roll have worn so much? Or is your basic recommendation just to put new rolls on the servo feeder?

Ideally new roll because typically there’s a finish associated with that roll. And the portion that wears out is going to be associated with that finish. As I cited earlier, the example of scribing the two lines top and bottom, that being the quickest way to be able to determine if there is variation from the time that machine was originally purchased to how it may be operating today, the rolls could be reground and recoded and you’re back to square one. The chances that you’re going to duplicate the original drawing, you may be off slightly. And again via the machine controls you can adapt to what that variance may be, do see customers that have no matter what experience slippage they may over or underset the feed lengths to accommodate for that as well. There’s a couple of ways that people do it ideally to replace the rolls that would also then afford you less downtime and having a spare set of rolls. When that has to be done again in the future, it would not impact negatively the production timeline on a project or a process having to wait for rolls to come back.

So there’s an offset feature in the controls that you can use to just for the wear?

That’s correct.

Now, how does somebody know other than just making the rolls that they’ve worn is that’s basically what they have to do?

That’s going to give you your best determination. They would typically notice plus or minus variation. Normally you would see if there’s an issue with the feeder, you’re going to see a plus plus plus plus variation. If you’ve got roll diameter changes, you may see plus and minus, and that’s going to be a good indication just visually, even of determining whether or not you’re seeing a problem there to start investigating, but marking the rolls is I is the best way to determine whether or not there’s been a change to that diameter. The roll finishes I mentioned before, being an example and we tend to talk about that is RMA, which are peaks and valleys on the pin rolls themselves. And that’s what gives you the grip on the material that will, as you think of it in the terms of peaks and valleys, that will degrade over time. I think in most instances, those pin rolls will last, the feed rolls will last quite a long time, but over a year or two or three, certainly then you may have to look at replacing those or again have them reground and refinished.

What about roll pressure? Do you ever have the need to adjust that for not just wear, but for production purposes?

Very rarely. The roll pressures are a factor, but less so overall compared to other parts of the machine, the biggest issue is having balance pressure from one side to the other. The material isn’t being skewed one direction or another, and then there’s also the roll finished type materials. For example, there’d be some applications where instead of two steel rolls, you may have a steel bottom roll and an upper roll of a different material, a hard rubber, for example. You may see less of an impact to air pressure on a rubber roll than you would with two steel rolls. You would tend to see the pressure adjustments more associated with a more formable roll, a softer roll than you would with the harder materials.

So you might use rubber like in a prepaid application?

Correct.

But then that would probably also have a higher wear rate. I would assume.

Than thin steel. Absolutely.

You’d better keep your eye on it. If you’re in a rubber roll type application.

That’s correct. And they do make different types of materials based on hardness. There’s 50 different types of rubber roll as well. It sounds simple in theory, but if somebody orders the wrong material, they’re going to see an impact to that right away. And that’s where you may get into adjusting, having to adjust air pressures, to accommodate for a softer or harder material. You would also see more wear and tear if you’ve got burs, for example, on the steel that are going to cut into that rubber material versus not being the case with hard steel.

Interesting you brought that up. I’ve also heard that because you run a multitude of widths of strips that there’s strategies for wear on rolls, on how you run the material through as far as … If you always run a bunch of narrow material, that area on other roll is going to wear. And then if you run a wider material, you’re in a area of the roll that saw little work that you can sometimes have problems there?

You can, and you literally have to be running, we’ll just say for a conversation, two inch material, 80% of the time to notice a difference. Would that being said, it still shouldn’t impact the overall performance because on the wider material, the surface contact area is not going to see the same wear as that two strip area, a two inch strip area would be running on a normal basis. I think kind of related to that problem is really more with where you’re running the material. All the materials should be run through the center line of the machine and not off to one side or another, because that will impact the balance if you will. It does afford the opportunity to skew that material to one side or another. And your issue or your question about the roll pressures then also become a factor. You have a specific thickness of material on one side and no thickness of material on the other. It definitely presents more opportunities for problems than almost any other anything else.

Okay. Well, one last question that I have, and that’s going to be based on or directed towards the performance of the servo feeder specifically your feed length, how fast you can move the feed length through the dye and the cycling of the press. When I’ve looked at various charts in the past, it seems like it’s dependent on the engagement of the dye versus the rotation of the ram where it’s at, in a certain degrees and how fast you can go. Talk a little bit about that. Do you have a lot of customers that get into that level of detail? I know in the roll forming world, sometimes we do. Because we’re really trying to push the limits of how fast we’re moving material through. And if we’re doing really long feed rates or things like that, tell us a little bit about that.

In simple terms, the accel and the decel rate is what we’re referring to. The answer, your first question, we do not have a lot of customers historically, where that’s been an issue or an area requiring adjustment. Anything for every action, there’s an equal, but opposite reaction, changing the accel and decel can have a detrimental effect as well as a beneficial one. It’s something that very few customers mess with because they don’t want to have a negative impact on other aspects of how the machine operates. That being said, the advent of servo presses has really brought that to the forefront where historically had kind of been on the back burner for most folks, for the reasons I mentioned. With a servo press, that window is far more flexible and you’re no longer dealing with simply 360 degrees.

Without getting too far ahead of myself, the accel and decel, will impact how quickly you can move the material and how quickly you can slow the movement of that material, based on the degrees available for not only feeding the material into that point, but also getting the tooling engaged, getting the tooling removed before you have that next movement. With a servo press what’s increased greatly there, is the accel and decel effect on it because you’re no longer dealing with a 360 degree window. You could be dealing strictly with 180 degree window and the pendulum mode, they’re only running basically at the bottom of that circle. You’re only running basically half of that rotation instead of a full rotation. The time afforded you to make a movement with the feeder then becomes directly tied to that acceleration and deceleration rate. It is something that is growing in adjustability for customers as they gravitate more towards servo presses than the mechanical presses of yesteryear.

Yeah. I had an application which you’re referring to and I think the term was press angle?

Yes.

Was the amount of stroke that you have available for you to move the material. And then had a very fast application, was a 24 inch feet at 200 feet a minute. And we had tried to explore all the avenues of maximizing the press angle, which as you said, 180 is pretty safe, but then we were getting into the 270 range. And then we were also playing with trying to get the acceleration rate of the servo feeder to maximize. And it just became so dangerous because you were at the max max of every aspect of feeding that we ended up just abandoning the whole idea. It was just too risky.

And conversely you have a similar issue. If you are doing a cut the length line as an example, where you might be accelerating and decelerating a feed length of 240 inches. We tend to think of speed as it pertains to the shorter feed lengths and the faster strokes per minute versus a longer continuous feed length. There is again, a benefit on both ends of that spectrum.

Well, thank you too. I appreciate all the information that you’ve shared with us today on behalf of Charlie and Kevin, I’m Brian Kopack. And thank you for tuning in to today’s Formtek Talk. See you next time.