This interview is with Rich Nielsen, Director of Engineering at IMS Buhrke-Olson, a metal stamping and assembly company. We discussed various aspects of stamping engineering. The interview is about 17.5 minutes long.
During the interview we discussed:
Rich Nielsen (left) and Mike Pfeifer
Mike P.: Good afternoon. Hi, Rich.
Rich N.: Hello, Mike.
Mike P.: This afternoon, I’m with Rich Nielsen. He’s the Director of Engineering at IMS Buhrke-Olson. They are a metal stamper. Rich has been involved with stamping and fabrication his entire life. He worked for his father, in his stamping shop, and he’s been with Buhrke-Olson for a long time, as well. Thanks for joining me, Rich.
Rich N.: Certainly.
Mike P.: My first question is, what processes do you have at Buhrke-Olson?
Rich N.: We have stamping presses from 30 tons up to 600 tons. Almost all of them, with straighteners and feeders, so that we can run continuous from coil. Most, we’ll use a progressive die stamping method to produce a complete part, with every stroke of the press. These are all mechanical presses. They run off of a crankshaft, with a flywheel and clutch and brake.
In addition to metal stamping, where we can produce parts that are complete, we also have several joining methods available. We will do riveting, welding, toxing, staking, as well as resistance welding of studs or nuts to the stampings that we make. In that way, we can make not only stampings, but assemble them together. Often, we’ll make five to ten metal stampings, and we’ll rivet, weld, spot-weld, whatever, MIG weld, or join them together.
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Mike P.: You work mainly for OEMs?
Rich N.: 90% of our work is automotive, and we work for the tier one suppliers that will deliver their assemblies direct to the assembly plants.
Mike P.: What materials are you typically working with?
Rich N.: Steels, red metals. Mostly cold-rolled steel. It can be anywhere from .1 millimeters thick up to maybe four or five millimeters, depending on the material thickness. They could be ductile steels that are made for forming. For example, draw steels, they sometimes are harder steels to form.
We do some work with red metals. It’s not a majority of our work, but we also do stainless steels and aluminum. We do a fair amount of work in aluminum, as well – cold-rolled.
Mike P.: Are there any materials that are more or less difficult to work with than others?
Rich N.: Sure, depending on what needs to be done to them, what shapes we need to create. In general, the materials that have a higher percentage of elongation are more forgiving, friendlier to the forming process.
Mike P.: What materials are those? This would be like deep draw steel?
Rich N.: Yeah, the deep draw steels. You just have to look at the percent of elongation, and the yield strength versus the tensile strength, and see what forces are required, and how much springback you can expect to see.
(2:46) Mike P.: Is there sometimes any negotiation between you and the designer, over strength versus elongation?
Rich N.: Yeah. If we see a problem in forming a part out of a certain material with a low elongation, we will ask for and recommend using a steel with a higher elongation. But of course, that sacrifices some strength, and sometimes they’ve already looked at that and decided that they could not use softer material and more forgiving material, because it would have to be thicker, in order to produce the strength that they need.
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Mike P.: What ends up happening, then?
Rich N.: We have to either change the design to be formable, to be feasible, or in some cases, it’s adding to the design. In some cases, it may be introducing additional offline hits, in order to complete the part, because we would not be able to complete it in the progressive die.
(3:55) Mike P.: This gets to the having to do extra steps that might add to the cost of the part, because the part is not easily manufactured out of the material that’s been selected.
Rich N.: What we’ve run into in the past year or so have been more and more parts to be made out of high strength and extra high strength materials. These are new products, that we’re not familiar with, so we’re in a learning curve. And often, I can tell that the designers designed it just as though it’s cold-rolled steel or highly formable stuff, and it’s not. Then, we’re all going through a learning curve.
We rely on forming simulation software, as much as possible, but that’s difficult to do, because in order to get a really true simulation, we need to design the tooling. That requires a commitment, and some time and investment right off the bat, before you can even really try it out and see what you can get. We have some forming simulation software that – I call it just a one-shot. It’s not for a multi-stage progressive die type simulation. That tells us some things, right off the bat.
But the problem we have is that in order to really determine if we can successfully make the part, we either have to build a tool and try it, or we have to design a tool, and run those stations and the tools through a simulation that’s capable of doing that high level multi-step processing of the simulation. We don’t have that software. It’s very expensive
But I can outsource it. In some cases, some our tool shops, our tool vendors may have it, and they will do some of that for us. But that’s presenting a problem, because in the case of dual-phase steel, this stuff is designed to harden as it’s formed, so that it absorbs energy in a crash. Well, that’s what we’re doing when we’re forming it. We’re crashing it. We’re crushing it into a different shape.
So, it’s resisting being formed, and it’s absorbing a lot of energy and giving us a lot of springback, so it becomes very challenging to make parts using that material.
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(6:14) Mike P.: So, someone has to make a commitment to you, for you to be able to get the tooling to do the experiment, so it’s not risk-free for them either then, is it?
Rich N.: Correct. What we’ve done in some cases, when it’s possible, we have made some temporary tryout tools, to just trying forming it, either just in a small press, or even a screw press or something like that, or a hydraulic press, so that we can actually measure the springback in certain conditions. We’ve had to introduce a lot of tricks to fight the springback, and to accommodate that.
We’ve found that for these really super high strength steels, that 90 degree bends are hard enough. But when it’s a complex drawn, highly complex geometry, it’s nearly impossible to predict. We’ve had to add, for example, ribs on a formed flange of a part, in order to form it without having it turn into a potato chip.
This part here is very recent. This is dual-phase 980 steel, very tough stuff. High springback, real high springback. You can kind of see what’s happening along this drawn edge. You see the wrinkling that’s happening there, and the stress and the high pressure marks. What this did was – yeah, we can form it. It doesn’t really come out to a full straight 90. There’s too much springback.
But the result of trying to form that creates an unflat condition, not flat condition, on this surface, which they need that flat. So, we ended up actually having to put ribs all along here, to gather up some material. It wants to wrinkle anyway, so what we did was we just gave it a place to wrinkle to, and control that, but that took so much extra time and effort and money that was just not at all something, that was planned for.
8:17 Mike P.: If the design engineers had come to you earlier in the project, could some of the problems been avoided?
Rich N.: Yes. We’ve had other customers that have come to us and said “We know this is going to be a tough job, so what do you think? What can we do? What can you hold? What kind of tolerances? Where do you need to open up tolerances, and where can we keep them tighter, and how can we achieve this? Would you recommend any changes?”
This was one that was kind of dropped in on us. They were already months late, so there was no time to do anything, much less have a reasonable discussion. I think one of the biggest things that you need, one of the most important things that’s needed for this kind of part with this kind of material, is an expectation that we may have to change the part, and time to do that. That’s what’s sorely lacking, many times.
(9:10) Mike P.: What’s the typical process for a customer working with a company like yours?
Rich N.: We’re tier two automotive. Our customers are tier one. They’re the ones that have designed the seatbelts or the airbags, or the seat construction , or whatever it is – radiators or whatever the component is. They’re the ones that design that whole component, to be ready at the assembly line, for the car manufacturers. That’s tier one.
Then, they will design all their parts. Then, they have to go to their supply base, which is us, for stamped metal parts, or another supplier for plastics, electronics, whatever it is. They have to contract us to design and build tools to make those parts, and to make those components for them. So, we work directly with those tier one guys.
In some cases, they have good experience in metal forming, and they know where the pitfalls might be. In other cases, they have no clue.
In the best case scenario, they have designed the assembly and the components they want us to make, and they come to us early enough to have us have face-to-face or online evaluations with their designers and their engineering team, to identify and address potential issues with forming the part, like I talked about. If that’s done early enough in the whole process, then there’s time to address those things, and they’re willing to listen, either because they’ve had prior experience and they know they’ll do better if they listen, or because they know their knowledge of it is not as deep as ours.
(10:57) Mike P.: What about the case when someone doesn’t ask for your help or input?
Rich N.: We give them our input, whether they ask for it or not. What happens is when we get a proposal and we have to quote on it, and it looks like it’s getting serious, then we will mark up drawings or prepare a PowerPoint presentation, with views of the part, and maybe some data from a simple forming analysis, a forming simulation, and let them know, or try to give them the data behind why we think there would be a problem in a certain area, why we need to change something, or why we need more tolerance for one item or another.
We’ll do that, regardless of whether we’re asked, just because it gives us a leg up on it. It doesn’t always change their minds. It depends on who you’re talking to. Sometimes we’ll just hear “This is what we need. We have to have it.”
(11:55) Mike P.: In that case, what happens?
Rich N.: If it’s a serious enough problem, we may back away and say “We’re just not capable of making the part the way you want it.” Most often, what will happen is we agree that we will get as close as we can, and we’ll discuss it again after we get the tool made, and we’ve fine-tuned, we’ve debugged the tool to the extent possible. Then, we’ll see them.
“We can’t hold the tolerance you did want, but we can hold this. How about this?” Then, we’ll negotiate a new tolerance, on the basis of that. If everyone is working in good faith, that works okay.
( 12:40) Mike P.: It’s interesting that you mentioned the thing about having to back away from a project, because the ease of fabrication is just not going to be there. When you’re quoting things, and you’re assessing the materials that have been selected and the design, does ease of fabrication influence what you’re going to end up charging per part?
Rich N.: Yes, it does, insofar as we will have an extra charge, or will include extra money, if we know there is going to be a high degree of development, a lot of time to develop the tool, a lot of trial and error, or a lot of outside expense for either making prototypes, trial and error that way, or outside expense for the high level of forming simulation that we might have to outsource.
Another thing that we may do is we try to quote parts as often as possible, on what we call “prog complete.” That is out of a progressive die with many, many stations, that’s progressively pierced and formed and crushed into shape, and finally the part is complete, at the end of the tool. That’s the most cost effective way to make these parts. That way, you’re really making best use of the economy of metal stamping by progressive die method.
If we think there’s a chance that we might not be able to get that tolerance or that bend, or whatever it is, we may include a secondary offline re-strike of the part, which of course, is physically handling it in and out of the tool much slower than getting it complete, off of the progressive die. In that case, we would have the cost of the progressive die, the cost of running it and all the materials, but we would also have the cost of an additional step or multiple steps, that may be needed to complete the part.
If there’s no budging on it, we would have to either – like I said – back away, or include extra steps, to try to make it. We have to be careful what we promise.
(14:36) Mike P.: Does this apply to all materials?
Rich N.: Some materials are more friendly to forming than others, so we really have to watch closely what materials are selected by the customers, and another suggestion might be a different material.
(14:54) Mike P.: Different materials have different ease of fabrication. There’s a tradeoff between strength and ductility or elongation, and also there’s work hardening, too, because different materials work harden at different amounts. Some materials are very easy to work with, because they don’t work harden a lot. They have high ductility. Other materials are more difficult. It could be because of their strength, or it could be because of their composition.
Rich N.: Yeah. And these materials, they’re designed and created for certain purposes, so they suit a certain function. But that doesn’t mean they’re easy to work with.
15:32 Mike P.: Yeah, it’s important for designers to think about not just the mechanical properties for a component’s application, but also think about ease of fabrication, regardless of the fabrication processs. From a project management perspective, it’s important to have discussions with a stamper early in the design process. That can have a big impact on preventing problems and mitigating risk.
Rich N.: Unfortunately, I don’t have an engineering degree. I didn’t go to mechanical engineering school, but I’ve been told that in those courses, in that course of study, they may spend a month or something covering metal stamping. Of course, they’re going to be exposed to some basics, some very basic knowledge. But if you try to design stamped metal parts with only that kind of exposure, you’ll be very limited and you could quickly get yourself into trouble. As opposed to – I’m an old guy. We used to have high schools where you’d make some stamped metal parts. You’d do some casting, you’d mold some plastic and weld some parts.
So, there was a little more hands-on understanding of what was involved in some of those processes. So, I think a little clearer understanding of the limitations, as well as the capabilities, often that’s where we have to fill in the gap.
(16:50) Mike P.: I think that’s where it requires the designer understanding the limitations, or their limitations in terms of knowledge, and reaching out to you or to whatever stamper they’re working with, to get the input required, in order to make sure that things go more smoothly. We can’t be experts in everything.
Rich N.: No, we certainly can’t. Right. So, we have the best results when we do just like you say. We have a good conversation and understanding of what the challenges will be on a particular part.
(17:26) Mike P.: Alright. I think that’s it, Rich. Thanks a lot for meeting with me. That was a great discussion.
Rich N.: You’re welcome. I enjoyed it, too. It was good talking to you again.
This interview is with Mike Connelly, retired VP of Engineering and Quality at Casey Products, a fastener distributor. We discussed various aspects of fastener engineering and fabrication.
During the interview we discussed:
Mike Connelly (left) and Mike Pfeifer
Mike P.: Today, I’m with Mike Connelly. Mike is retired now. He worked at Casey Products for 27 years. He was the VP of Engineering and Quality. Good afternoon, Mike.
Mike C.: Good afternoon.
Mike P.: Thanks for joining me. Today, Mike is going to talk about fasteners. What types of fasteners did you work with?
Mike C.: A huge variety of it. We worked with machine screws, tapping screws. There’s also hex head bolts, or hex head screws. Generally speaking, the difference between a bolt a screw is a bolt takes a nut. A screw will go into a blind hole, like a casting. There’s also rivets, spring clips, Tinnerman nuts, Spiralock product, pop rivets, aluminum pop rivets, made out of a wide variety of materials.
Mike P.: What are the most common alloys that you worked with?
Mike C.: As a fastener distributor, we touched on a broad base of alloys; low carbon steels, low alloy steels, stainless steels, super alloys. The most common alloys we worked with are low carbon steel; 1008, 1010, 1020. You know, alloy steels, such as 4037, 4140, 8640, 15B41. Those are the big materials.
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Mike P.: How are machine screws fabricated?
Mike C.: What you’re going to have is material that looks like wire. If you’ve ever been on the highway you see these giant coils of steel that look like giant slinkies, that’s usually fastener wire. The first step will be to do a spheroidized anneal on it, to get the material with the proper grain size and a proper carbide distribution, so that they can form the material.
After that’s done, they’ll pull that through a straightening die set, that brings it to its final size. Then it goes through a heading operation. A heading operation is described as it’s a cold forging operation that puts the head of the fastener on, and it also reduces the shank of the bolt to the pitch diameter, so that they can roll the threads.
Now, on a machine screw, all of the strength comes from this cold-working process. They’re not hardened, they’re not heat treated, they’re not a class fastener. That is something that’s going to go into hex bolts. Then, they’ll run them through thread dies. Another way of doing this is to have a bolt maker, where the thread rolling process and the heading operation are all In one machine. It comes out, you have a completed part, ready to be packed up and shipped.
Mike P.: So, the final microstructure is spheroidized steel that’s been cold-worked?
Mike C.: Yes. If you were to do a cross section on that, you would see the deformation from the thread rolling process, as the material flows into that thread shape.
Mike P.: They’re relatively low strength screws.
Mike C.: Yes.
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Mike P.: How are the self-tapping screws made, and what alloys are used for that?
Mike C.: Self-tapping screws will be heat treated, because the screw has to be harder than the material that it’s going into. It pretty much follows the same processes, in that you’re going to be using – let’s say a 1020 steel, a little more carbon. It gets spheroidized annealed, it gets drawn to size. Then you get the heading operation, the trimming operation, and then they roll the threads.
The pitch on the thread, it’s a larger pitch. There’s more spacing between the threads. After the thread form is made, then these will go out to heat treat, and they’ll either be carburized and hardened, or carbonitrided and hardened. The material will become harder, and it will reach a hardness of somewhere around 50-55 Rockwell C. So, we have a hard skin, and underneath we’ll have a tough core.
Mike P.: How are larger fasteners (bolts) fabricated?
Mike C.: Once you get past like one inch, 1-1/8th inch in diameter, you know, 30 millimeters – when you get above that, you start going into the realm of where they’re hot heading the bolt. On a high production run for bolts, the way they’re made is that once again, we get wire. Even though the diameter of the wire could be 30 millimeters, 36 millimeters, it’s stilled called wire. It goes through a spheroidizing process, to get that cementite in a nice round spheroidal shape, so it takes less energy to displace it. I can use a smaller press or a smaller header. Then it goes through the drawing process. Then, it will go into a bolt maker. The bolt maker does the heading operation and the trimming operation – you know, trim the length.
And the head part is multiple steps, in that you start out with a round button. They heat up the head in a forge furnace or an induction coil, and then they upset the head, to give the head configuration. Then, what they’ll do is machine the washer face on the head and the shank. Then they’ll machine the threaded end, down to the pitch diameter. Then, depending upon what the requirements are, they may either roll the threads or cut the threads. You want rolled threads.
There’s a set of dies in there, and they’re called flat dies. The flat die rollers will put the threads on. Once again, it’s rolled threads. Now, when they go through heat treating, all the beneficial cold-work stresses that you’ve got, they go away. Once it comes out of that furnace, it goes into the quench.
That as-quenched hardness is going to come out right around 50 Rockwell, 55, somewhere in there. Then, we run it through a tempering furnace.
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Mike P.: Why are rolled threads better than cut threads?
Mike C.: The thread profile, when you roll the thread, is going to be a radius. So, when you get down into the root of the thread, you’re going to see a radius. There are actually thread forms called UNJ or MJ, where that root radius is controlled very tightly, to improve the fatigue life. When you cut the threads, you wind up with a sharp V down at the bottom of that root. and you get some tearing in there, and you wind up throwing material away, because you’re making chips now.
Mike P.: So, cut threads have lower fatigue resistance than rolled threads?
Mike C.: Yeah, they do.
Mike P.: Why would someone get them cut, instead of rolled?
Mike C.: Convenience. If the quantity required is small, if the size of the bolt is large, it becomes easy to just cut the threads in, as opposed to rolling the threads.
Mike P.: It seems that for a fastener that will be used in a fatigue application, even if only a small quantity will be purchased, it’s still worthwhile to have the threads rolled, rather than cut.
Mike P.: What’s the difference between rolling the threads and then heat treating the bolts versus heat treating first and then rolling the threads.
Mike C.: If you make those threads before heat treatment, any of the beneficial cold-work that you’ve got, it goes away once you stick it in the heat treat furnace. If parts are heat treated, and then they’re rolled. Then, you’re looking at bolts where the stress level is going to be 180,000 PSI, or like 1,070 megapascals.
Mike P.: They’re cold-working it after heat treating, to get the additional strength associated with cold-working.
Mike C.: Right, and better fatigue life.
Mike P.: Are there things a designer can do to make sure that they get what they really need for their application?
Mike C.: What I would do is get proficient in standards. Invest some time in looking at the consensus standards, and see how it aligns with what you’re trying to do. Try not to reinvent the wheel.
A good place to go for that is the Industrial Fastener Institute. The IFI has several volumes. One is for metric and one is for inch. It’s the Inch Fastener Standards, and it will have those standards in there. Another good book is An Introduction to the Design and Behavior of Bolted Joints, by Bickford. The other standards I would get close to me are the ASTM standards, SAE, the ISO standards. ISO is becoming the predominant fastener standard for metric fasteners.
Take a course. There are folks out there that train people in understanding fastener standards.
Mike P.: What are the common standards?
Mike C.: The common fastener standards will be SAE J429. That’s the grade 5, the grade 8, the grade 2. You also have ASTM standards. Within those ASTM standards, usually they’ll have the stress located in the title for the fastener, so that you can get a grasp of what’s going on.
In the metric world, you’re going to look at ISO or DIN or JIS, which is the Japanese standards, but everybody is going with the ISO. The ISO standards are truly global. Even in the United States, when we make metric fasteners, instead of using ASTM standards or SAE standards, they go right to the ISO, because the product can be used worldwide.
Mike P.: What do you recommend as the being the process for designing a fastener and what should be included in the specification for the fastener?
Mike C.: Land on a standard. If you’re going to stay specifically to sourcing here in the states, then go to SAE J429, if you’re using that type of thread. and that will define what the hardness should be, what the material should be. In material selection, there will be more than one type of steel that you can pick from. The testing requirements will be in there.
If you’re doing metric, go with the ISO standards, and become proficient in them, and look at all the fine print in those things, for exclusions.
Understand your alloy systems. If you’re going to make a hex head cap screw out of Inconel 718, understand what that alloy is. It’s expensive to begin with, and it’s not like an SAE Grade 8. Because it’s 718, it’s going to be difficult to roll the threads. The setup time is going to be amortized over those 12 pieces. If it’s an aircraft part, you’re not going to cut the threads.
You have to understand those things during the quoting process, and when you’re putting that on there. I’ve seen where an Engineer will come back and we would send a price in. “Okay, they want 50 pieces,” or something like this, and they’re going to cost $50 apiece. The design review Engineer goes crazy, because “Oh my God! That’s just too expensive!”
Mike P.: What are the problems with not referencing a known standard, in a fastener specification?
Mike C.: That’s a great question, Mike, because if I’m doing an incoming inspection, and I have on this print, let’s say a 1/2-13 thread on a hex head cap screw, and I want it hard 33 to 39 Rockwell C. Well, there’s nothing in there about what the required stress is, or the tensile test. There’s no decarburization limits that are in there. There’s nothing in there about thread laps, what kind of surface imperfections.
There’s nothing about the material composition. It’s just “Okay, make it out of this stuff, and I want it this hard.” Well, that’s what you’re going to get, then. If you take the standard, you’ve got all of those things are going to be covered in that standard.
The other thing that comes into play is if it’s a standard fastener, the cost is going to be lower. The availability is going to be there, because there are distributors all over the place. You should always start with a standard.
Mike P.: Use the standard as a base, and just modify that standard as needed.
Mike C.: Yes.
Mike P.: What happens when a customer has a problem with a fastener? Let’s say it fails during manufacturing or fails during testing, or during use. What would help the root cause analysis process go more smoothly?
Mike C.: Number one, go pull the blueprint. Pull the engineering standards. Get the print, and articulate the problem as best you can. You would have to get a really good definition of the problem, before you can proceed.
I would actually make a list of questions on my callback. “Okay, you broke this while it was being assembled. What was the torque that you used? Are you lubricating the bolts? Did you do a hardness check? How did you check the hardness?” As much as hardness testing is a very popular test, and it’s easy to do, a lot of people do it wrong.
Mike P.: Does it help to have pictures?
Mike C.: Absolutely. The most important photo you can get when you’re looking at a potential failure, is of the head marks. On the head mark, you’re going to see the manufacturer, you’re going to see the class. You’re going to get a grasp of what that bolt is supposed to be. You can’t send too many pictures.
I can actually sit there and count the threads, and see “Do we have the right pitch? Did somebody put a metric bolt in, where it’s supposed to be an English bolt?”, because there’s a couple of sizes that kind of overlap, like 3/8” and ½”, and 10 millimeter and 12 millimeter.
Also, looking at the fracture surfaces, If it’s a ductile fracture, I’m already looking at it’s either not heat treated properly or they’ve overloaded it. The other thing is where did it fail? Did it fail in the head? A fastener should never fail in the head. It should always fail in the threads.
Mike C.: Yeah, and for us, we’d ask for some samples.” We can tensile test, look at the microstructure, check the dimensions. We can do all of that stuff.
Mike P.: Well, I think that’s it. Thanks, Mike, for giving your time and sharing your expertise.
Mike C.: Thank you for having me.
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