Tham khảo tài liệu 'drilling and associated technologies part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Drilling and Associated Technologies 127 also be reduced by utilising a different boring bar material as this will improve its coefficient of elasticity45. In boring-out roughing operations any vibrations present are only a problem if they lead to insert damage. For finish-boring operations vibrational conditions that may occur could be the difference between success and failure for the finished machined part. So the boring bar s ability to dampen any vibrational source becomes imperative once a fine-boring operation is necessary. Vibrations can occur in any number of ways that could affect the boring operation from the constructional elements of the machine tool through to slideways or their recirculating ball bearings etc. Hence the joints in a machine tool can be regarded as a complicated dynamic system with any slideway motion of vibrating contact faces necessitating lubricating oil to not only reduce any stiction and frictional effects but to help dampen these structural elements. Machine tool builders are acutely aware that certain machine tool materials damp more readily than others. Cast iron and in particular Granitan . a product of crushed granite and epoxy resin can predominantly act as built-in dampening media for any vibrational sources present. The main source for any vibrations in boring results from the long overhangs necessary to machine the hole depth of the component s feature. Therefore the magnitude of vibrations in the overall system result from the dampening capabilities of the actual boring bar. Tuned Boring Bars A boring bar that has been tuned has the ability to dampen any generated vibrations between the workpiece and the cutting edge while machining. The dampening effect is achieved through a vibration absorbing device see Figs. 61a and 62b this has the consequence of increasing the bar s dynamic stiffness giving it the ability to withstand oscillating forces. The 45 Coefficient of elasticity for a steel boring bar composition E .
