Self Excited Vibratory Drilling
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 summer project pal Active In SP Posts: 308 Joined: Jan 2011 15-01-2011, 06:44 PM SELF-EXCITED VIBRATORY DRILLING : A DIMENSIONLESS PARAMETER APPROACH FOR GUIDING EXPERIMENTS Sameer Salim Roll No: 44 S7 Mechanical   SELF-EXCITED VIBRATORY DRILLING.ppt (Size: 1.84 MB / Downloads: 136) Introduction This technology is very compact and can be used on every conventional machine tool In order to guide the experiments a dimensionless approach has been used to choose the cutting conditions and vibratory tool holder properties. This approach permits the number of tests to be reduced, since the machining process can be entirely described with only three dimensionless parameters instead of nine physical parameters Objectives To show the benefits of self excited vibratory drilling technology To show how the dimensionless parameters approach makes the setting up of the process easier. Self excited vibratory drilling Chips are naturally fragmented to small pieces implying that there is no need to perform the stripping operations classically used to split up chips. The friction of chip on the manufactured hole surface is limited which leads to improved hole quality. Self-Excited vibratory drilling device Dynamic drilling models Basis of the theory of self-excited vibratory drilling In conventional drilling, the uncut chip thickness measured in the spindle axis direction is equal to the feed rate (h0) divided by number of lips (Z) i.e. h0/Z In vibratory drilling this thickness is modified by the deflection of the drill holder h = h0/2 + ώ(t) – ώ(t – 1/fz­) ………….3 mώ(t) + cώ(t) + kώ(t) = Z.kc.R [h0/2 + ώ(t) – ώ(t – 1/fz­)]q …………………………………4 ώ0 = kc/k. Z1-q R h0q ………………….5 Limits of the theory to predict optimal vibratory conditions The use of linear solving method does not make it possible to describe strongly the non-linear vibratory motion that exists in the unstable field. The ploughing phenomenon, which occurs near the centre of drill, is not taken into account, which acts like damper of vibration, when the vibration frequency becomes increasingly important in front of rotational frequency. Dimensionless approach The field of investigation has been reduced by grouping all the physical parameters into three dimensionless parameters Dimensionless stiffness K=kc/k Dimensionless frequency F=f0/fz Damping ratio Z=2c/√km Advantages of Dimensionless Approach It allows starting from an identified satisfactory set, the new characteristics of the vibratory drill holder for a new diameter, a new spindle speed, or a new material to be determined quickly. Moreover, this approach is only slightly affected by imperfections or gaps in the model. Experimental setup Experimental results highlights Interest in self-excited vibratory drilling compared with conventional drilling. The influence of parameter k and F on vibration. The modification of tool holder properties keeping k constant for drilling at different spindle speed. The modification of tool holder properties keeping k and f constant for drilling in a new material with different diameter. Experimental comparison of vibratory drilling and conventional drilling Conclusion The contribution of this paper is two fold It presents the first experimental results of a new drilling technology assisted with low frequency vibration. It shows an interesting use of a dimensionless approach to guide the experimentation and to determine the best vibratory conditions.