ME364_machining_milling

ME364_machining_milling - Valery Marinov Manufacturing...

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Milling 103 Valery Marinov, Manufacturing Technology 6.2 MILLING Introduction Milling is a process of producing flat and complex shapes with the use of multi-tooth cutting tool, which is called a milling cutter and the cutting edges are called teeth . The axis of rotation of the cutting tool is perpendicular to the direction of feed, either parallel or perpendicular to the machined surface. The machine tool that traditionally performs this operation is a milling machine . Milling is an interrupted cutting operation: the teeth of the milling cutter enter and exit the work during each revolution. This interrupted cutting action subjects the teeth to a cycle of impact force and thermal shock on every rotation. The tool material and cutter geometry must be designed to withstand these conditions. Cutting fluids are essential for most milling operations. Milling operation. The cutter is lifted to show the chips, and the work, transient, and machined surfaces. Cutting conditions in milling In milling, each tooth on a tool removes part of the stock in the form of a chip. The basic interface between tool and workpart is pictured below. This shows a only a few teeth of a peripheral milling cutter: Basics of a peripheral (slab) milling operation.
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Milling 104 Valery Marinov, Manufacturing Technology Cutting velocity V is the peripheral speed of the cutter is defined by V = π DN where D is the cutter outer diameter, and N is the rotational speed of the cutter. As in the case of turning, cutting speed V is first calculated or selected from appropriate reference sources (see Section 5.10 Selection of Cutting Conditions) , and then the rotational speed of the cutter N, which is used to adjust milling machine controls is calculated. Cutting speeds are usually in the range of 0.1~4 m/s, lower for difficult-to-cut materials and for rough cuts, and higher for non-ferrous easy-to-cut materials like aluminum and for finishing cuts. Three types of feed in milling can be identified: feed per tooth f z : the basic parameter in milling equivalent to the feed in turning. Feed per tooth is selected with regard to the surface finish and dimensional accuracy required (see Section 5.10 Selection of Cutting Conditions). Feeds per tooth are in the range of 0.05~0.5 mm/tooth, lower feeds are for finishing cuts; feed per revolution f r : it determines the amount of material cut per one full revolution of the milling cutter. Feed per revolution is calculated as f r = f z z z being the number of the cutter’s teeth; feed per minute f m : Feed per minute is calculated taking into account the rotational speed N and number of the cutter’s teeth z, f m = f z zN = f r N Feed per minute is used to adjust the feed change gears. Types of milling There are two basic types of milling, as shown in the figure: down ( climb ) milling, when the cutter rotation is in the same direction as the motion of the workpiece being fed, and up ( conventional ) milling, in which the workpiece is moving towards the cutter, oppos- ing the cutter direction of rotation: Two types of peripheral milling. Note the change in the cutting force direction.
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