ENS3105-Milling Machine Bearing Design – Engineering Assignment Help

Assignment Task

Task 

Milling Machine Bearing Design
A small milling machine (depicted in Figure 1) uses two rolling element bearings to support the spindle in the quill. The work piece is clamped to the worktable, while the chuck and cutter that are attached to the spindle rotate. The spindle is supported by two rolling element bearings, where the bearing closest to the chuck is a SKF bearing 6014 and the bearing furthest from the chuck is a SKF bearing 16014. Dimensions of the bearing locations are illustrated in Figure 2, where the average milling cutter diameter and length (from bearing 6014) are 25mm and 150mm respectively.

This milling machine will be used to manufacture small components that largely require three machining operations, namely drilling, plunging and milling. (Note: Plunging is where the very edge of the cutter is used to notch the workpiece). The average time fraction that the machine spends at each of these operations are 35%, 25% and 40% respectively. Due to various cutting conditions and intermittent machining operations, the application factors for drilling, plunging and milling are 1.1, 1.4 and 1.2 respectively.

For improved machine cutting, different cutting speeds are required for the three machining operations, namely 1250 RPM for drilling, 2500 RPM for plunging and 4000 RPM for milling. A torque read-out on the machine indicates that, on average, plunging operations require 20Nm of torque and milling operations require 12.5Nm of torque to overcome the machining forces. In addition, the operation feed-forces (in the feed-directions shown in Figure 2) are 50% and 25% of the machining forces (that attribute to cutter torque) for plunging and milling operations respectively. Furthermore,
it is observed that the quill imparts 550N on the cutter during drilling operations.

With a confidence of 99%, calculate the number of hours that this spindle can operate prior to requiring a bearing replacement and which bearing is likely to require replacement?
Please read the notes at the end of the assignment question sheet. The facts and numbers used in this problem are purely fictional and do not relate to the milling machine illustrated in Figure 1.

Note:
I. Please include full calculation working-out in the space provided below (add pages as necessary)
II. Assume there is no weight of the components and spindle
III. Assume that cutter diameter is simply an average diameter as shown in the diagram
IV. Assume that the milling force is at an average length as shown in the diagram
V. Assume that the plunging force acts at cutter outer edge as shown in the diagram
VI. The Plunging operation feed-direction is parallel the spindle axis
VII. The milling feed-direction is perpendicular to the spindle axis
VIII. The drilling feed-direction is coaxial to the spindle

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