Lecture-14 Apparent mean shear strength of work material

Many analyses of the metal cutting processes have been developed. In general, assumptions have to be made which are often valid only for a restricted range of conditions. A particular difficulty in formulating an analysis off the metal cutting process is the lack of constraint in the process that reduces the range of boundary condition that can be applied. A unique solution does not exist for a particular set of cutting conditions and further that parameters such as the cutting forces, cutting ratio and so on that occurs in a particular case, depends on the conditions that exist when the tool first Contacts the workpiece. A further complication is that different forms of the chip formation mechanism occur at various cutting conditions. 

• Ernst & Merchant suggested that: - 

 Apparent shear strength  

As = Shear plane area 

Experiment work of ”P.W. Wallance and G. Boothroyd” in 1964 show that the apparent shear strength calculated in the way remains constant for a given work material over a wide variety of cutting condition. It has been observed, however, that all small feeds, apparent shear strength increases with a decrease in the feed. This exception of the constancy of apparent shear strength can be explained by the existence of a constant plowing force. If plowing force is subtracted from the resultant cutting force (Fr), then F’r (the force required to remove the chip and acting on the Tool face). 

Now, above given apparent shear strength remains constant with respect to changing in the feed.