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Comment by jameshart | Hacker News Reader

I am not an expert so I am confused by terminology here.

These machines are referred to as ‘presses’, but the technique is referred to as ‘die casting’.

my naive understanding is that pressing to form things would be more a form of ‘forging’ than ‘casting’. Doesn’t casting refer to molding things from molten metal?

Is the distinction that die casting done at higher pressure than some other form of casting, to produce results more akin to injection molding, and therefore requires ‘presses’ to hold the tool dies in place?

Or am I misunderstanding words completely?

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The difference between casting and die casting, is that casting is done with a sacrificial mold at lower pressures, die casting is done at high pressure using a tool die that is reused multiple times. Die casting is essentially stamping out a part at high pressure from semi-molten material, vs liquefying material to be poured into a low pressure mold.

Die casting has a lot of advantages, but is generally much more expensive as a manufacturing process, and that expense scales exponentially with part size.

"Forging" is mostly a marketing term at this point, depending on the type of product you're talking about, but it generally refers to a combination of die casting and CNC machining.

Not sure about forging being a marketing term. Forging in my understanding referee to the raw steel bring red hot and then manipulated by pressing, rolling or hammering into a desired shape. This often requires multiple cycles of reheating and manipulation. This is then often followed by CNC machining.

I also recall that grain structure is different in forged materials compared to casting.

A casted part will often be machined but not reshaped by e.g. hammering.

Isn’t sheet metal ‘stamping’ a forging process? I’m not sure it only has a marketing meaning these days. But then the only time I see stuff marketed as ‘forged’ these days is typically ‘drop forged’ tools, and I realized I also have no sense of what process ‘drop forging’ might involve. I guess I vaguely assumed some sort of drop hammer?

Your comparison to inject molding is correct. The press is used to hold the die mold halves together. I enjoyed this video that explained the process https://youtu.be/FUsicN-wKoY?t=234

I’m confused why the machine needs to apply a ‘pressing’ force to hold the dies together. Once the die is closed, can’t you just slide rigid clamps into place to hold it in position?

I don't think the metal is fully molten. That's why you need the huge pressures to bring it to shape

I don't understand this either.

The mould could have simple locking pins that lock it closed for the actual casting operation, and then unlock to remove the part.

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