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How to build a 50k ton forging press

construction-physics.com

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Re: How to build a 50k ton forging press

#11

Post by WJW »

bee_rider wrote: post #4

They talk about machining, casting, and pressing. Mostly with casting and pressing in a good light, machining not so good. As somebody who knows absolutely nothing about this stuff, I wonder—casting, I thought, was generally a lower quality option (like cast iron doesn’t have fantastic high-performance material qualities, and I had some crappy cast pewter toys as a kid). Are there different, higher quality casting pr…

Machining is fine, but in the context of the article the problem is that it usually starts off from plates or otherwise block-shaped materials. That means that if you have a weirdly shaped part full of holes and/or with many protrusions in weird angles (as vehicle parts tend to have), then you either have to combine many smaller parts into a final part or have to machine away a huge amount of material from a solid block to come to the final shape. It would be much better to cast or forge the part into roughly the right shape straight away, so you'd need only minimal finishing work. That is what these presses enabled.

Re: How to build a 50k ton forging press

#12

Post by hwillis »

bee_rider wrote: post #4

They talk about machining, casting, and pressing. Mostly with casting and pressing in a good light, machining not so good. As somebody who knows absolutely nothing about this stuff, I wonder—casting, I thought, was generally a lower quality option (like cast iron doesn’t have fantastic high-performance material qualities, and I had some crappy cast pewter toys as a kid). Are there different, higher quality casting pr…

> like cast iron doesn’t have fantastic high-performance material qualities

Cast iron is a material, not a process. It's an unfortunate legacy term for very high carbon steel (>2% by weight, or The >1% carbon precipitates out into graphite within the steel, causing it to behave totally differently. Less rusting, but weaker and much more brittle when solid. Less viscous when liquid, so you can cast long and thin parts.

> Are there different, higher quality casting processes, and I’ve only seen the bargain bin results?

There are, but it mostly is independent of the material. Some turbine blades are cast as single crystals for heat stability; you can't really cut a single crystal without introducing cracks and issues. There's also vacuum casting and spin casting (using a centrifuge to force liquid into the mold), which lets you cast metals that react with air or cool too quickly for normal methods.

Most of the variation in process is about the final form you cast into, though. Engine blocks are sometimes cast into a one-off ceramic shell that is sprayed onto a sand form. It's an expensive process but it lets you do the whole thing in one step.

> is it all very complicated and material specific?

It is very material specific. Fundamentally its all about shaping the grains. In many steels you can physically alter grains. In others, like precipitation grains (aluminum alloys, some steels) the structure is determined by the cooling and you can't physically shape them. In that case you may often get a better structure by casting since you can choose how to cool parts down, while a billet will have a homogenous structure that is usually worse towards the center.

Re: How to build a 50k ton forging press

#13

Post by mrob »

bee_rider wrote: post #4

They talk about machining, casting, and pressing. Mostly with casting and pressing in a good light, machining not so good. As somebody who knows absolutely nothing about this stuff, I wonder—casting, I thought, was generally a lower quality option (like cast iron doesn’t have fantastic high-performance material qualities, and I had some crappy cast pewter toys as a kid). Are there different, higher quality casting pr…

They also talk about forging. Forging can produce higher quality parts because metal has a grain structure. Just like wood, it's easier to break between grains than across the grain. Forging is deforming the metal without melting it. If the temperature isn't too high, it will deform the grain structure along with it. The grain can be aligned to make the metal stronger along the axis where it needs to resist the most force.

Wikipedia has a image of an connecting rod that has been etched to show the grain:

https://upload.wikimedia.org/wikipedia/commons/5/5c/ForgedCo...

You can see the grain has been stretched along the length of the narrow parts. Wrenches are another example of something that's commonly forged for this reason.

Re: How to build a 50k ton forging press

#15

Post by hedgehog »

hwillis wrote: post #12
bee_rider wrote: post #4

They talk about machining, casting, and pressing. Mostly with casting and pressing in a good light, machining not so good. As somebody who knows absolutely nothing about this stuff, I wonder—casting, I thought, was generally a lower quality option (like cast iron doesn’t have fantastic high-performance material qualities, and I had some crappy cast pewter toys as a kid). Are there different, higher quality casting pr…

> like cast iron doesn’t have fantastic high-performance material qualities Cast iron is a material, not a process. It's an unfortunate legacy term for very high carbon steel (>2% by weight, or The >1% carbon precipitates out into graphite within the steel, causing it to behave totally differently. Less rusting, but weaker and much more brittle when solid. Less viscous when liquid, so you can cast long and thin parts…

Monocrystalline turbine blades are one of those things that make me appreciate how deep the state of the art is for a lot of "simple" things when you look closely.

Re: How to build a 50k ton forging press

#16

Post by colechristensen »

bee_rider wrote: post #4

They talk about machining, casting, and pressing. Mostly with casting and pressing in a good light, machining not so good. As somebody who knows absolutely nothing about this stuff, I wonder—casting, I thought, was generally a lower quality option (like cast iron doesn’t have fantastic high-performance material qualities, and I had some crappy cast pewter toys as a kid). Are there different, higher quality casting pr…

Cast iron is a material, it's good for what it's good for but its material properties don't really come from the casting process, just the ratio of iron to carbon.

Casting has problems with thermal expansion, plenty of materials shrink significantly as they cool and complex parts cool unevenly which can cause them to break or deform.

Casting has problems with microstructure, plenty of materials, especially steels develop complex crystal structures with multiple phases of materials as they cool from liquids and even extensively in hot solid phases. It's hard to control this in a cast part.

Casting has problems with precision. The molds just can't be all that precise when in machining, a thousandth of an inch can be a relatively large distance.

However casting gets a bad reputation because most of the time you see it it's because it's actually very cheap, cheap materials, cheap process, minimal post processing. Higher cost things don't necessarily realize the savings from casting as much so they don't use it. And also a lot of higher quality materials have higher melting points which require more advanced tools to melt and handle.

Plenty of things though are cast and then machined, you notice this if you look.

Re: How to build a 50k ton forging press

#17

Post by spenczar5 »

bee_rider wrote: post #4

They talk about machining, casting, and pressing. Mostly with casting and pressing in a good light, machining not so good. As somebody who knows absolutely nothing about this stuff, I wonder—casting, I thought, was generally a lower quality option (like cast iron doesn’t have fantastic high-performance material qualities, and I had some crappy cast pewter toys as a kid). Are there different, higher quality casting pr…

Castings can achieve shapes that are impractical to machine. A classic example is a spoked wheel. The spokes are really hard to make precisely with machining, but fairly straightforward when casting. Bandsaw wheels are virtually always cast, for example.

Also, the processes are not really independent. It can be much cheaper to do a rough casting, and then machine just the critical faces of it, instead of using an “off the shelf” hunk of metal and machining it all into shape. So it’s not really “casting is superior to machining” or vice versa. More that machining is high precision but expensive. Casting has some up-front cost but once the patterns are made, each item will use material quite efficiently.

Re: How to build a 50k ton forging press

#18

Post by PaulHoule »

Nobody in North America has a press that can make a vessel for a nuclear reactor without making it in pieces and welding them together (probably adding a year to the schedule if you don’t use a new welding technique just developed in the UK not to mention people being anxious over the welds)

There is a Canadian company that is gearing up to make small reactor vessels like the BWRX-300 but so far I haven’t seen a sign they aren’t Nuscale 2.0

Re: How to build a 50k ton forging press

#19

Post by bagels »

bee_rider wrote: post #4

They talk about machining, casting, and pressing. Mostly with casting and pressing in a good light, machining not so good. As somebody who knows absolutely nothing about this stuff, I wonder—casting, I thought, was generally a lower quality option (like cast iron doesn’t have fantastic high-performance material qualities, and I had some crappy cast pewter toys as a kid). Are there different, higher quality casting pr…

Other materials can be cast, such as various aluminum alloy. Casting can have a higher cycle time, be cheaper, and require a less expensive equipment.

Re: How to build a 50k ton forging press

#20

Post by hwillis »

> Forgings have the added advantage of variable grain direction which generally can be tailored to the stress patterns of a specific design.

This is a super underappreciated fact! It's often repeated that forging is just stronger, but just squishing steel does NOT make it stronger. Forging a part is so much more than just smashing it into a shape.

Steel cable is made of pretty ordinary steel which is stretched 100s of times its original length. That process alone makes it 2-4x stronger in that direction. You stretch steel and it gets stronger in that direction.

Do you see how complicated that optimization process becomes? The process steps are not just trying to take it to the final shape. Your piston rod needs to be strong lengthwise, so you actually want to start with a short fat ingot and stretch it out instead of one that is near-final size.

Think of making an I-beam. You could hammer out the middle, making it thinner. That would give you a bit of strength there but very little on the edges. If you instead pull the edges out, you create a long continuous stretch that will be very strong against bending. Where, how, and in what order you stretch makes all the difference. You may want to leave extra material and cut it off later, so that your grains are all oriented together instead of tapering to a point.

For any moderately complex part, this process is as complicated as modern engineering problems. With poor steel you genuinely need to understand how to foster and bring out those continuous lines or your corkscrew will unwind like playdough. Blacksmiths had a legitimately intellectual job back in the day!

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