Mechanics of boring processes - part II - multi-insert boring heads

Abstract

Holes with large diameters are usually bored with boring heads having multiple inserts. This article presents a mathematical model for the cutting force system as a function of tool goemetry, chip load, cutting edge contact length and process parameters (such as feedrate, cutting speed, radial depth of cut) based on the physics, kinematics and mechanics of the boring process. The model also includes the possible process faults such as axial and radial runouts on each insert and deviation between the longitudinal hole and boring head axes. The cutting forces for each insert are modeled as presented in Part I of the article (Atabey, Lazoğlu and Altıntaş, Int J Mach Tools and Manuf (submitted 2001)). The cutting forces contributed by all inserts having radial and axial runouts are modeled, and compared favorably with experimental measurements. When the runouts are absent in the system, the normal cutting forces are zero due to force cancellations. However, when there are runouts on the inserts, while feed force is constant, the cutting forces normal to the hole axis become periodic at the tooth passing frequency. The model developed here can be used in the process planning of boring operations with inserted boring heads so that the surface finish and dimensional quality of the holes are maintained by avoiding excessive forced vibrations.