A little OT - Powder Metallurgy

What got me interested in this was the recent stories in the press about Sky Marshals and watching "Air Force One", where an awful lot of high speed lead flew about inside a Boeing 747 at 30,000 feet, inflicting no apparent damage on the pressure hull!

Bullets can now be made frangible-meaning that they will fragment into small particles on impact with hard surfaces, resulting in minimal ricochet rates. Powder Metallurgy is a much used engineering practice these days. In an earlier age, the process was called sintering where powdered metal is brought together under great pressure in controlled circumstances in order to produce materials that have a controlled amount of void space within them. An example we'll all recognise is Oilite bushes, typically only about

80% solid.

The process has moved right along from the early days and now new materials of metal or ceramics are manufactured to the highest tolerances, producing shapes and characteristics unobtainable in other ways.

Most turning and milling inserts are made this way, also High Speed Steel /Cobalt conventional milling cutters. This enables the part to be made with high accuracy, so cutting down the finishing time when grinding is required, often in the throat of a cutter to eliminate swarf friction . Vapour deposited Titanium nitride and other exotic coatings also improve this property. Small gears - such as those used in small electric starters etc - are often made this way.

The lobes of Ford OHC vee eight cams are precision formed under pressure by a sintering process, saving the machining time needed on a cam grinder. These are then assembled on a common hollow shaft, holding them in precisely aligned positions which can be readily varied in order to change the characteristics of the engine for which they are required.

I thought this thread might bring news of both this and other interesting modern engineering methods.

Regards,

Kim Siddorn,

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J K Siddorn
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