Monday, August 07, 2006

More on Die Casting




Several people have asked me how Crowley and Tripp ribbon microphones are made. The answer is that we machine them (or have parts machined at local shops) from solid pieces of steel and stainless steel. Die cast parts,like that seen in this EV V1,2,3 series ribbon case, are not used here.

Machining is a process in which metal is cut until the desired shape is obtained. Typical machining processes involve milling, lathe turning, and drilling and tapping. Machining is often the more expensive process but offers the highest quality and precision. Machined parts may be made to very tight tolerances. We select the machining process for this reason.

Casting and Die Casting are processes by which molten metal is either poured or injected into a mold. The advantage is low cost, good detail (as seen above). Some expensive high quality castings can achieve tight dimensional tolerances. Cheaper die cast parts are often irregular and have poor surface finish and corrosion resistance, and low strength. There are a lot of cheap die cast parts used in some recent mics, and we avoid those types of parts.

Forging is the process in which a piece of heated metal, such as steel or iron, is shaped while in a semi plastic state. Blacksmiths forge materials, like fences and door hardware, by physically hammering the material on an anvil. Drop forging is a process in which a slug of red hot metal, like steel, is put into a strong die, and hammered, usually once, with a very strong press. Typical forged items include wrenches, ratchets and sockets. Drop forging deforms the material and can produce a very strong part which usually must be further finished by grinding, polishing and plating. I have never seen a microphone with a forged part in it.

There are other metal shaping processes used in microphones, such as deep drawing (like for making the bottom cup of a 77DX), spinning, punching, various laser processes, and chemical machining and etching.

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