Abstract
AISI D6 hardened steel is a difficult to cut material that it is employed in mould and die manufacturing where long ball-end mills are frequently required to machine deep cavities. This condition can lead to excessive vibration between tool and workpiece resulting in a poor surface finishing and reduced tool life. This work analyses the dynamic stability of ball-end milling of AISI D6 hardened steel for different tool path orientations at inclined workpiece angles of 15o and 75o. The evaluation of stability is based on the surface texture and spectrum analysis of the vibration signals. The results showed that for workpiece inclination angle of 15o chatter occurred in vertical upward down-milling and vertical downward up-milling. Best surface texture with tool marks consistent with pick feed and feed directions were generated by applying horizontal downward tool paths that produced the least vibration. Only forced vibrations occurred for the workpiece inclination angle of 75o. The highest peaks of the spectra corresponded to the harmonics of the tooth passing frequency closer to the natural frequency of the system. High magnitudes in the spectrum were found for vertical upward down-milling that generated a less uniform surface texture.
Highlights
AISI D6 is a cold work tool steel with excellent resistance to wear and abrasion
Finishing ball-end milling were performed with eight different tool path orientations at inclined surfaces of 15o and 75 o
The direction of the tool marks is consistent with the step and feed direction
Summary
AISI D6 is a cold work tool steel with excellent resistance to wear and abrasion. Its high structural and mechanical features make this material important in mould and die manufacturing. Machine form tools with this material is a difficult task.[1,2] Long ball-end mills with high length to diameter ratios are frequently required to machine deep cavities of moulds and dies. Self-excited vibrations, called chatter, result from a self-excitation mechanism in the generation of chip thickness during machining operations. They may be caused by mode coupling or regeneration of the chip thickness. The regenerative chatter results from phase differences between the vibration waves left on both sides of the chip and occurs earlier than the mode coupling in most machining cases.[3] This type of vibration leads the system to instability
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