Tài liệu 07 machining processes

ADVANCED MANUFACTURING ENGINEERING 7: Machining Processes December 2016 Material removal mechanisms • Cutting: machining allowance is removed in the form of visible chips. Cutting 2 Material removal mechanisms • Abrasion: machining allowance is removed in the form of minute and invisible chips by hard, tiny, randomly oriented abrasive grit (bonded or loose) of indefinite number and shape. Abrasion 3 Material removal mechanisms • Erosion: machining allowance is removed in the form of successive surface layers as a result of dissolution, melting and vaporization of the material being machined. Schematic of laser cutting test setup, Shyha et al 2013 4 Classification of cutting processes Machining by Cutting Single point Turning Boring Shaping Planing Classification of cutting processes based on number of cutting points/edges Multi point Drilling Reaming Milling Broaching Sawing Filing 5 Machining by cutting • The tool is penetrated into the w.p by a depth of cut. • Cutting tools have definite number of cutting edges of a known geometry. • The machining allowance is removed in the form of visible chips. • The shape of the workpiece produced depends on the tool and workpiece relative motions. Chip Cutting speed Depth of cut Tool Cut surface Workpiece 6 General aspects of machining technology 7 Machining productivity • Machining productivity can be raised using the following: • High machining speeds • High feed rates • Multiple cutting tools • Stacking multiple parts • Minimization of the secondary (noncutting) time • Automatic feeding and tool changing mechanisms • High power densities 8 Drilling of composites Fishbone diagram detailing factors affecting the drilling of CFRP (Shyha, 2010) 9 Lathe operations • Turning means that the part is rotating while it is being machined. (mm/rev) (mm) Centre lathe Terminology used in a turning operation on a lathe, where f is the feed (in mm/rev) and d is the depth of cut. 10 Lathe operations • Lathes are employed for: • turning external cylindrical, • tapered, and contour surfaces, • boring cylindrical and tapered holes, • cutting external and internal threads, • knurling, • centring, drilling, counter-boring, countersinking, • spot facing, • reaming of holes, • cutting off, and other operations. 11 Lathe operations and tools Cylindrical turning Taper turning Facing of a WP with a facing tool while the WP is:clamped by a half centre mounted in a chuck 12 Lathe operations and tools Finish turning with a 4a. board-nose finishing tool 4b. straight finishing tool with nose radius Necking or recessing with a: 5a. recessing tool 5b. wide recessing tool 13 Lathe operations and tools Parting off with a parting-off tool Boring of cylindrical hole 8a. External threading 8b. Internal threading 14 Lathe operations and tools Drilling with a twist drill 9a. Drilling 9b. Enlarging 10. Face grooving 11. Profiling 12. Turning and external grooving 15 Lathe operations and tools 13. Cutting with a form tool 14. Boring and internal grooving 15. Knurling 16 Turning tools N df do d f 17 Methods of taper turning • Tapers can be manufactured on the engine lathes by: a) rotating the compound rest to a required angle α. The tool is fed manually by rotating handle (1). This method is used for turning short internal and external tapers with large taper angles, while the work is held in a chuck and a straight turning tool is used. 18 Methods of taper turning b) c) using a straight-edge broad-nose tool. The tool of width that exceeds the taper being turned is crossfed. The work is held in a chuck or clamped on a faceplate. using a taper-turning attachment. This is best suited for long tapered work. The cross slide (1) is disengaged from the cross feed screw and is linked through the tie (2) to the slide (3). (c) 19 Holding workpieces on lathe WP fixation on an engine lathe depends mainly upon the geometrical features of the WP and the precision required. The WP can be held between centres, on a mandrel, in a chuck, or on a faceplate. 1. Holding the WP between centres. It is an accurate Plate Driving dog method for clamping a long WP which is rotating at high speed.  Workpiece Holding the work between centres 20