Drilled Manifolds (Podcast)

President and Principal Engineer Tom Rohlfs looks at the pros and cons of drilled manifolds. He explains the production process and outlines designs that are ideal for drilled production methods.


John Maher: Hi, I'm John Maher. I'm here today with Tom Rohlfs, President and Principal Engineer at Controlled Fluidics, a plastics machining company specializing in precision manifolds. Our topic today is drilled manifolds. What is a drilled manifold as opposed to other types of manifolds?

What Is a Drilled Manifold?

Tom Rohlfs: A drilled manifold is kind of the classic way to produce a manifold. Simply, it uses machining operations, drilling typically, as described, to create internal passageways and control fluid flow, be it gasses or liquids.

How Do You Make Drilled Manifolds?

John: And how are drilled manifolds made versus the other ways of making manifolds, which we've talked about in the past about multi-layered bonded manifolds? How are drilled manifolds different?

Tom: Drilled manifolds are the simplest of the manifolds. You could do quite complex configurations with drilled manifolds. Drilled manifolds generally require plugging, which means you're going to drill a lot of cross intersecting holes, and then you plug openings to create the pattern that you wish.

Obviously, if you didn't plug the holes, the manifold would just leak all over the place, so what you do is to create an internal network of channels. You essentially cross-drill as much as you need to and then plug off different ports to create basically a complete internal channel that has just your desired inputs and outputs, but generally it requires other holes to connect. Let me see if I can make up, say, an example here.

If you drill from up two sides of a manifold but spaced apart and you want to connect them, you actually have to drill, I guess it's a little confusing, you have to drill from another axis. If you drill in one axis, you need to drill other axes in order to connect it. And then that final axis is generally closed off so that the first original two inputs and outputs connect. I guess if you're attempting to make a shape like a Z, it would require cross drilling and plugging, so that's fine.

The nice thing about drilled manifolds, one of the big advantages, is you can use any type of material, be it metal, be it plastic, every stock shape and plastic could be used potentially as a manifold as well as metal. Very common: aluminum manifolds, steel manifolds, as well as Delrin, Teflon, PEEK. All materials that we generally don't bond can be used to have a manifold.

Drilled manifolds are limited by our ability to drill long holes. Typically speaking, we can drill a length of diameter ratio about 50 to one. If you took the diameter of your drill and multiplied it by 50, that's about as deep as we can go. Much beyond that becomes increasingly difficult. We have done some applications where it's up to 80 to one, but it's very difficult to drill a straight hole.

You can imagine these drills tend to wander. They don't necessarily go straight through your material as you're drilling them. You try to meet up with another hole, and if that drill starts to wander, even though you can make the hole, if it doesn't intersect with the hole that you want, you have a bad manifold. There's a drill length limitation to these manifolds. And that's really where you see the positives of a bonded manifold because that type of scenario is eliminated.

You could machine a channel as long as you want a bonded manifold, it doesn't matter. The drilled manifolds have their place. The nice thing about them is, as I was mentioning, is any type of material. In the world, you have a great material flexibility. They're also very inexpensive. A bonded manifold, in effect, you're machining three pieces, two layers, and then the final piece, whereas with a drilled manifold, you only have a single piece, you're machining it, and you're done.

Those are the two big advantages: cost and material choice on a drilled manifold. There's a lot of applications out there, especially on the simpler manifold sides where they make a lot of sense.

Types of Plastics Used for Drilled Manifolds

John: Yeah. You said that there's pretty much no limit to the types of materials that you can use, and so there's no types of plastics that really won't hold up to a drill or anything like that, and in fact, there are certain types of plastics that you can't use for multilayered bonding processes, but you can do with a drilled manifold.

Tom: Exactly. If you can drill it, you can turn it into a manifold. In the world of plastics, the number of plastics that are really successfully bonded is roughly five. You can bond about five plastics, but in the world of availability, there's probably 30, 40 different types of plastics, so really a small amount can be successfully bonded, but most of them, actually all of them, can be a drilled manifold.

Plugging Drilled Manifolds

Tom: I did want to touch a little bit about plugging. Oftentimes this is a question that comes up. A customer reaches out to me and says, "Hey, I have this drilled manifold, and I see here that I have to plug these ports in order to be a successful manifold. How do I do that? What do I do to plug off the port so that my manifold works out for me?" There's a couple of ways to do it.

One: you can simply press a pin in. If we had a PEEK manifold and you wanted to plug off a port, we'd make a PEEK pin and just using pressure, shove it into the hole. It's a good way. It works. That works well for materials that can take that type of stress. What's interesting about plastic materials is there's some that are very stress sensitive.

I don't know that we want to talk about that now, but we could if you'd like. And then other materials that are quite tough, that you could hit with a hammer and wouldn't bother them. With those types of tougher plastics, we can just press pins in and that's a good way to plug a hole.

Alternatively, some customers specify either a ceramic or stainless steel ball, and we'll buy balls that are slightly larger than the channel diameter and just push them in. And they work quite well. Lastly, we use an adhesive glue. We'll take a plug and we'll either use a solvent, depending on the material, or adhesive and bond a plugin. That works well for materials that are stress sensitive and might crack if we put too much pressure on them via the ball type approach.

Disadvantage of Drilled Manifolds

John: If you're plugging a certain hole that doesn't need to be used and it's long, do you end up with a point where you know could have some of the material that you're putting through the manifold get stuck in that extra side channel that you've plugged off? Is that one of the issues or disadvantages?

Tom: That's the downside to a drilled manifold. You have those nooks and crannies, those incomplete holes, those dead ends that can entrap the liquid or the gas that the customer's using for their working fluid. That is one of their disadvantages.

It is possible with careful application of the plug to actually make that relatively limited, meaning you can push the plug almost so that it creates a perfect corner. But, still, it never can be quite as good as we... It can't be as good as a bonded manifold where we're just machining that corner, and that corner is essentially flawless.

John: Do those plugs also create a failure point as well where that plug could actually come out? Or do you not really have that issue?

Tom: Ideally? No. But, yeah, for sure it can be a failure point. Ideally, if we've done our job right, no, it doesn't fail. But, the world of plastics, especially those that are bonded, one of the downsides of plastics in general is that some of them are very stress sensitive. And when I say stress sensitive, I think this is a topic we should probably touch on, stress sensitive plastics are generally the amorphous plastics.

And what happens is, be it chemical attack, mechanical stress, or thermal stress, or a combination of all three, the plastic starts to fail. And it fails in a way that it cracks. And so it's an issue with anything that ... Oftentimes, we like the amorphous plastics. And amorphous plastics are probably the number one choice for manifolds because you can see through them.

That's important to customers. Oftentimes, they want to see what's going on. They're clear, there's imaging potentially involved. And so a lot of times they want to use those amorphous plastics. They're clear. The downsides to them is that they are stress sensitive. And if they have a chemical attack, someone puts a solvent through them, they will crack and fail. That's their downside. With drilled manifolds allowing for other materials like PEEK or Teflon, highly chemical resistant, that gives the customer an opportunity to have a manifold that's not going to fail for them. And they can use very aggressive chemicals, not a problem.

Advantages of Drilled Manifolds

John: Okay. One advantage there of a drilled manifold would be being able to use a certain type of plastic that works better.

Tom: Much more chemical resistant.

John: Is chemically resistant, but that you couldn't do a bonded manifold with.

Tom: That's correct. That's where we see... so if a customer is running gas chromatography, uses a lot of Teflon because their chemicals tend to be very aggressive and the majority of the plastics will not tolerate them. And so they use a lot of Teflon. They end up with drilled manifolds and will do plugging or things like that. And that works for their application quite well, actually.

Drilled Manifolds Are Less Expensive

John: You mentioned that the drilled manifolds generally are less expensive as well. Do you tend to start with a drilled manifold if that's all that it takes for a customer to use, or do you just jump right to multi-layered bonded manifolds if a customer wants that?

Tom: No, no. We absolutely do start with a drill manifold, but generally speaking, it's pretty obvious fairly quickly. Drilled manifolds can be reasonably complex, but they don't tend to have a lot of use in the life science industry because people are concerned with carryover.

When they're going run-to-run, in life sciences, carryover is a big problem. Its cause is essentially cross contamination. As soon as you get to that point, it almost immediately eliminates drill manifolds. But, yeah, no, we're always for the lowest cost solution for our customers.

Oftentimes, it's not unusual that a customer will do manifold design, and they'll send it to us. And we haven't touched on this much, but not only do we do two layer manifolds, but we could do three, four, five layer manifolds. Depending on the complexity of the channel pattern, customers will send us a design that's three layers and we see a way to convert it to two layers, we're going to do that for them, right?

That just makes it easier for us to produce. It'll make it lower cost for them. It just makes for a better manifold. Yeah. We're always looking for those opportunities. If someone needs a simple manifold, we're going to start with drilled and work from there.

When Manifold Design Requires Drilling

John: Do you have anybody ever come to you and say, "Oh yeah, I want a multi-layered bonded manifold. This is the design," and you look at it and say, "Hey, that's pretty simple. I think we can just do this with a drilled manifold."?

Tom: You bet. Yeah. For sure. That's happened a number of times. And then the reverse happens. They'll send us a design where, and this is common, where they'll have designed a hole that's 125 to one, length to diameter. And I tell them, "I can't drill that. We got to turn this into a bonded manifold." Ultimately, they're happy because they're getting what they want, but, yeah, we have to redirect the conversation to talk about capabilities of drilling and what makes sense and what doesn't. That's a common misunderstanding point by engineers. They sometimes think you can drill forever. Obviously not.

John: Right. All right. Well, that's really great information, Tom. Thanks again for speaking with me today.

Tom: You're welcome.

To Learn More, Contact Controlled Fluidics

John: And for more information, visit the website at controlledfluidics.com or call 603-673-4323.