Re: engineering questions

[Jaap Bouma <j.h.bouma@domain.elided>]

At 09:54 AM 5/10/99 -0400, Andrew Watry wrote:
>Two engineering/manufacturing questions not directly related to Alfas:
>
>1.  What is "friction welding" and how does it work?  I've heard Porsche or
>BMW uses this method in making wheels.
>2.  Some modern connecting rods are made as one piece, then fractured in
>half to allow for the split to assemble around the crank journal.  How do
>they keep the fracture precise?
>
>Thanks
>Andrew Watry
> 

Friction welding is a method where the heat requireed to melt the material
in the weld is generated through friction, rather than an electric arc or a
flame. I remember seeing halfshaft-like parts being made using this method.
The shafts were made in two halves, and certain parts of the joints at the
ends had to be fitted from the back of the joint, i.e. slid along the shaft
towards the end. This was why the shafts were made in two halves. 
Next, the ends of the shaft halves to be welded were pressed together and
rotated/spun in opposite directions. The friction caused the metal to glow
red hot, at which point the rotation was stopped and the shaft halves
pushed together slightly. This welded the two halves together. 
Another way of generating the relative motion is through ultrasonic
vibration of one of the two parts relative to the other.

Re splitting the conrods: a V-groove is machined in the side of the conrod
facing away from the bearing, at the point where the fracture is wanted.
The conrod is clamped in a flat position to a big piece of netal, with the
part to be broken off projecting into the path of another very large piece
of metal coming down. This lump of metal hits the conrod, which
understandably breaks. The stress concentration in the tip of the V-groove
causes the break to start there, growing from this crack initiation point
towards the next weakest point: the hole for the crank journal. 
Of course, the actual approach is a little more refined than the
two-lumps-of-metal method described here, but you get the idea.



Best, Jaap Bouma (Netherlands)
'87 GTV6 2.5 Grand Prix

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