Rough machining

Fig. I — (Left) 81-mm. shell forging as made by old method required rough machining before being nosed. (RIghf) New upset method completely noses shell os forged.

Metal shavings are generated when a tool used to finish rough-machined work is presented at a tangent to the piece and travels over it removing a thin layer or metal. 

High cBN content materials are used in rough machining apphcations, whereas lower cBN content tools tend to perform better in finishing applications where shallow depths of cut are being taken and a good surface finish is required. 

Figure 2 shows three different types of carbide cutters. The third mie has chip-breaking grooves and is used for rough machining operations. The first and the second tools can be used for fine machining. 

Machining of CSI materials using both Si3N4-based ceramic and CBN tools is optimal in terms of energy consumption, especially for medium and rough machining operations. 

Figure 16.28 MERLIN Mark 2. (From Cundill, The MERLIN Road Roughness Machine User Guide, TRL Report 229. Crowthorne, UK Transport Research Laboratory, 1996.)...

After rough machining (and the working out of faults in the glass, if required), the blanks are converted from the glassy condition into the semi-crystalline condition through a thermal treatment. Due to that treatment the material also receives the property of zero thermal expansion. 

Any permanent stresses present should be so small that the casting is capable of withstanding rough machining. 

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