10 ms·
> 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 un
by hwillis 2y ago
> 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!
- thaumasiotes 2y ago> Blacksmiths had a legitimately intellectual job back in the day! ACOUP noted that blacksmiths might be assisted by unskilled laborers, strikers, who had the actual job of lifting the hammer and hitting the object with it.
- NegativeLatency 2y agoUnskilled feels unfair, it requires a fair bit of skill, and you're also learning how to forge while doing it.
- droopyEyelids 2y agoThis has been such a frustrating culture war definitional argument.
- knodi123 2y agoNot necessarily a culture war thing. People who aren't familiar with the subject might take "unskilled" in the plain-english sense, as a pejorative. And who can blame them? We're english speakers before we're technical speakers. Make gracious assumptions.
- deleted 2y ago[deleted]
- jessebro 2y agoAnyone who has worked in a job classified 'unskilled' generally doesn't need a pejorative to feel unloved. It's the nature of the game. Digging ditches generally sucks, same as I imagine being a striker, but most anyone can do it (until their body gives out, anyway, which in some cases is 'immediately').
- bell-cot 2y agoThe reality is that, depending on circumstances, a highly skilled craftsman of yesteryear could have any number of obviously less-skilled assistants. Some would be "career track", some semi-skilled seasonal help, some minimally-skilled (whether due to youth, infrequent day labor, poor talent, or social status), and some in supporting type of skilled work - animal handling, cooking, bookkeeping, etc.
- Terr_ 2y agoI tried to maintain a certain kind of optimistic humility, that almost anything which employs a person full-time is a problem-area that has fractal layers of complexity one don't have to know from the outside. The only question is whether someone will pay you for doing the fancy skill/science tricks or not.
- 2y ago
- ethbr1 2y agoOne of the most interesting things I learned about blacksmithing (aside from all the metallurgy because I'm not a ME), was how much more valuable "the right hit" was than "the heavy hit." Sure, it takes a ton of muscle, but you can quickly screw up a piece by repeatedly beating the hell out of it.
- HPsquared 2y agoThis effect also applies to polymers! Perhaps even more so. Take a polyethylene bag (LDPE) and stretch the material in one direction. You might notice the material becomes thinner but also stronger. This is due to the polymer chains becoming aligned. Eventually you get "drawn fibers" where the molecular strands are aligned with the fibers for optimum tensile strength.
- 01HNNWZ0MV43FF 2y agoThat makes sense, if I don't rip open a bag on the first try it'll just stretch and never open
- kragen 2y agoit varies a lot with polymers, and it's a different effect. steel is entirely crystalline; ldpe is mostly amorphous. a big part of what's happening in the strain hardening of ldpe, aside from making it uniaxially oriented, is that it's crystallizing; the crystalline domains become larger, greatly reducing the amorphous volume fraction. (there are also other ways of achieving this effect, such as annealing, which you will notice softens steel rather than hardening it.) ldpe's strength isn't determined by crystal dislocation density in the same way as steel's, and of course steel doesn't have polymer chains to align
- wizardforhire 2y agoThis is exactly what dyneema is only with hdpe.
- pfdietz 2y agoI wonder if it's possible to do additive manufacturing with pre-elongated snippets of wire.
- hwillis 2y agoannealing, which resets the grain structure, happens at a lower temperature than melting or sintering.
- kragen 2y agotrue, conventional welding or sintering would be a bad idea. but you can connect them together with brazing, laser-welding, explosive welding, ultrasonic welding, self-propagating high-temperature synthesis of an intermetallic like nickel aluminide, electrodeposition, lashing, or globs of glue
- pfdietz 2y agoDoesn't annealing take hours, particularly at the lower range of temperatures? Perhaps the additive process can keep the metal hot for a much shorter time. Granted, this also means stresses from the manufacturing process will not be removed.
- metal_am 2y agoMost forms of metal AM require melting, which gives solidification microstructures. There are solid state (no melting) forms of metal AM though. Look up AFSD. MELD just got (part of) a billon dollar contract from the air force for it.
- kragen 2y ago> just squishing steel does NOT make it stronger just squishing steel does actually make it stronger, because it increases the number of dislocations in its crystal structure. smaller grains mean higher strength even without the variable grain direction. also, peening, which is not exactly the same as forging but is also just squishing steel, can give you higher strength for a third reason: areas with residual compressive stress can't initiate cracks until you overcome that stress, which increases strength. even more, though, it increases fatigue resistance
- samstave 2y agoI have had this question in my mind for decades: >"Can you forge metals in a highly controlled and directed magnetic field where you can orient the grain/alignment of atoms/fields in whatever direction you want. Further, if true, what happens when you make damascus from varying plated that have particular alignments/grains - and what are the features of this material?
- hwillis 2y ago> Can you forge metals in a highly controlled and directed magnetic field where you can orient the grain/alignment of atoms/fields in whatever direction you want. This is how you make magnets. "Soft" ferromagnets have small, round grains that rotate to reinforce outside fields. "Hard" ferromagnets have permanent fields of their own and long grains that can't reorient. Forging with a field has a very low impact on the material properties because of how weak a magnetic field is compared to the forces moving atoms- same reason steel loses its magnetic properties when it gets hot. > what happens when you make damascus from varying plated that have particular alignments/grains "Damascene" is the layered look most often made from acid etching sandwiched and forge-welded layers of different steels. Damascus is a single alloy for which the pattern is named. Since in both cases the material is melted together, it's far too hot for any magnetic properties to have any impact.
- samstave 2y agoThanks for that. Though I was thinking of super intense magnetic fields (like in CERN), however, Ill leave it to my Comic Book Science collection, then :-)
- metal_am 2y agoElectromagnetic stirring is used in continuous casting for grain refinement. It’s also used sometimes in welding.
- samstave 2y agoI wonder what would happen to a material properties if you combined this with friction stir welding.
- abe_m 2y agoI'd really like to see some backing of these claims. I've seen "grain flow" claiming big gains for years in various enthusiast magazines (bike, motorcycles, cars, etc) as to why components are forged. Then I started working in engineering, and I can't find any support for these claims. For sure when a steel bar is worked down to become wire for a steel rope, it cannot be pulled to an elongation of 100x increasing strength. A36 steel which is a basic structural steel has an elongation at break of 23% in a 2" gauge length [1]. In every rolling mill I've been in, there is a limited amount of reduction per pass through the mill, after which the metal needs to go for thermal treatment to be annealed to remove all the cold work. Every time you anneal the material, you completely resets the elongation (internal plastic strain) and strengthening due to work hardening. If they do too much reduction in one pass or at too low of a temperature, it cracks the material and makes it weaker. For sheet metal, there is lore about the material being stronger in the rolling direction as that is the direction of grain flow. I have yet to find a source that can point to any large difference. In papers like this [2] there are claims of certain orientations of samples relative to rolling direction have different tensile properties, but when you look at the tensile charts, there is minimal difference. The yield strength in these charts isn't reported, but all three orientations look to yield at the same point. In this test the across the grain (90 degree to rolling direction) orientation had the highest tensile strength which is the opposite of the expectation of the forging "grain flow" promoters. But the magnitude of the difference isn't large, and is small relative to normal factors of safety in a reasonable design. When designing automotive components, I've only ever seen forging methods selected for efficiency of production. If a part mostly fills the envelope of a bar or plate, it is cut from bar or plate in all cases. If there is a lot of void volume in the part, the calculation will be made to determine if the cost of developing forging tooling and development will get paid back in reduced material and machining cost. I have yet to see the dimensions of the part change with manufacturing method, which would be needed if the non-forged part was significantly weaker. And finally, a lot of forged parts are subsequently heat treated. When heat treating steel all of the grains in the steel have to be destroyed and recrystallized. That is the mechanism by which heat treatment works. Depending on the exact process and part geometry, this process removes or reduces the grain flow in the finished parts. Having said that, the claim of superiority of forging persists, and I'd love to see a technical reference that shows the magnitude of the change from someone who has plausibly actually tested the effect. [1] https://matweb.com/search/DataSheet.aspx?MatGUID=d1844977c5c8440cb9a3a967f8909c3a https://matweb.com/search/DataSheet.aspx?MatGUID=d1844977c5c... [2] https://www.researchgate.net/publication/283447700_The_effect_of_rolling_direction_to_the_tensile_properties_of_AA5083_specimen https://www.researchgate.net/publication/283447700_The_effec...
- mywacaday 2y agoI studied construction for a year, always remember being totally baffled why this makes a beam stronger in certain cases, https://www.grunbauer.nl/eng/waarom.htm https://www.grunbauer.nl/eng/waarom.htm https://www.sciencedirect.com/science/article/pii/S0045794915001418 https://www.sciencedirect.com/science/article/pii/S004579491...