Basic Manufacturing Process - Ch.7.3

Q.6    With the help of schematic sketch, describe the basic working principle of milling machine. Differentiate between up milling and down milling.                                                  (AKTU - 2008-09)
Related Questions -
Q.    Differentiate between down milling and up milling.                                        (AKTU - 2011 - 12)
Ans.    Milling Machine: -       
                                                                                (AKTU - 2010 - 11)
    The milling machine is most versatile of all machine tools. A large number of operations can be performed on a milling machines like cutting key way, slitting, sawing, slab and face milling, gear cutting and shaping irregular pieces. Alongwith good surface finish, milling machine provides rate of production and higher accuracy and, therefore, in many cases it has largely replaced shapers and slotters. But it is not very much suitable for large jobs.
    In milling machine metal is removed from workpiece with a rotating cutter. This rotating cutter is known as milling cutter. Milling cutter is a multipoint cutting tool (unlike lathe and shaper tools which are single point cutting tools). For cutting workpiece is fed into the rotating milling cutter and metal is removed in form of chips.
Classification of Milling Operations: -
(i)     Down milling
(ii)     Up milling
(i) Down Milling: -
    When the cutting and feed motion are in same direction, it is called down milling. In down milling there is tendency of workpiece being dragged into the cutter. However, down milling results in better surface finish and longer tool life. The process is good for thin and frail workpieces. When the cutting edges are helical the cutting operation is smoother and better surface finish is obtained; this is because of gradual engagement of cutting edge.
(ii) Up Milling: -
    In up milling the cutting tool rotates in the opposite direction to the motion of feed. This tends to lift the workpiece from table. There is possibility that the cutting tool will rub the workpiece before starting the material removal. However, the process is safer and is commonly done.
Advantages of Milling: -
(a)     Very good for one-off objects.
(b)     Virtually any material can be milled with a proper cutter.
(c)     Complex parts with high detail.
(d)     Tolerances of 0.001² to 0.003² are possible.
Disadvantages: -
(a)     A more reduced set of features possible. Certain features are not possible.
(b)     More materials waste than casting type processes.
(c)     Quite slow.

Q.7    Explain in brief :
(i) Plain (slab) milling.    (ii) End milling.        (iii) Face milling.
(iv) Form milling.    (v) Gang milling.
Ans.    (i) Plain (slab) milling:
This process is used to produce. Flat surfaces, parallel to the axis of the cutting tool with the help of a plain or slab milling cutter.
(ii) End Milling: In this process, the cutter generally rotates on axis vertical to the work piece. The cutter can be tilted to machine tapered surfaces. Cutting teeth are located on both end face of the cutter and periphery of the cutter.
 (iii) Face Milling: In this process, the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece. The milled surface is obtained from the action of cutting edges located on periphery and face of the cutting tool.
(iv) Form Milling : Form milling is used to machine those surfaces which are of irregular shape and size. Cutter used for form milling is called form milling cutter.
(v) Gang Milling : In milling process more than two cutters are used on a common arbor to machine a number of flat horizontal and vertical surfaces of a workpiece simultaneously.

                                                                                                                          Next Page