05 June, 2011

Harder materials shaping softer

It seems to me a recurring theme occurring in engineering is how progressively harder and harder materials are used to shape the previous material.

For example, you want to build a plastic part using injection moulding. To make the mould, you need a material that is harder than the plastic at processing conditions. Maybe you use steel. To shape that mould, again you need a harder material, maybe a ceramic like tungsten carbide. It's the same with forging metals.

One thing in this chain is that as materials get harder and harder, they become more difficult to shape. The steel mould above can be made by drilling out unwanted material. However, the material for the drill itself can only be made into simple shapes, like rods, sheets, or most often powders.

Sometimes, we "cheat" and use heat or energy to shape the hardest materials. Some very hard materials can only be worked at high temperatures. Or we might use electricity, plasma or lasers to shape them, the energy being "infinitely" hard.

Does this mean we can't use the hardest materials without a harder material to shape them?

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