ME 350 – Lecture 4 – Chapter 22

1. ME 350 – Lecture 4 – Chapter 22 Chapter 22 - MACHINING OPERATIONS AND MACHINE TOOLS: • Turning and Related Operations • Drilling and Related Operations • Milling • Machining Centers and Mill-turn Centers • Gear cutting • Broaching

2. Turning Single point cutting tool removes material from a rotating workpiece to generate a cylinder • Performed on a machine tool called a: • Variations of turning performed on a lathe: • Facing • Contour turning • Chamfering • Cutoff • Gear Teach Machining

3. Facing Chamfering Cutoff Cutting edge cuts an angle on the corner of the cylinder, forming a "chamfer" Tool is fed radially into rotating work at some location to cut off end of part Tool is fed radially

4. Threading Contour Turning Form Turning Tool follows a contour that is other than straight Tool has the desired geometry, and is fed directly into workpiece Pointed form tool is fed at a large feed rate, thus creating threads

5. Engine Lathe

6. Holding Workpiece in a Lathe

7. Turret Lathe Tailstock replaced by “turret” that holds up to six tools • Tools rapidly brought into action by indexing the turret • Applications: high production work that requires a sequence of cuts on the part

8. Multiple Spindle Bar Machines • More than one spindle, so multiple parts machined simultaneously by multiple tools. Example: After each machining cycle, spindles (including collets and workbars) are indexed (rotated) to next position

9. Power Requirement the specificenergy: Cutting power per unit volume removal rate Converted to Approximation: U ~Hardness H

10. Specific Energy (U) For Cutting Approximate specific-energy requirements

11. In-class exercise – Cutting force estimation • A 6 inch long, 1.5 inch diameter 304 stainless steel rod • parameters: cutting speed v=1860 in./min, • f=0.03 in/rev., d= 0.02in., • U= 1.47 hp.min/in3, • Find: the cutting force

12. Boring • Difference between boring and turning: • Boring is performed on the diameter of an existing hole • Turning is performed on the outsidediameter of an existing cylinder • Boring machines • Horizontal or vertical - refers to the orientation of the machine spindle’s: axisofrotation

13. Drilling • Creates a round hole in a workpart • Compare to boring which can only enlarge an existing hole • Cutting tool called a drill or drill bit • Machine tool: drill press

14. Reaming Tapping • Enlarges hole, • Provides betterdiametertolerance • Improves surface finish Used to provide internal screw threads on an existing hole. Tool called a tap

15. Operations related to drilling Center Drilling: necessary for creating a relatively large hole Countersinking: Screw holes Spot facing: NOT a milling tool Counterboring: Hiding bolt heads

16. Drill Press & Radial Drill

17. Drilling Rate and Time • D=drill diameter; (length) • N = spindle speed; (rev/min) • f = feed; (length/rev) • d = depth of cut (length)

18. Milling Machining operation in which work is fed past a rotating tool with multiple cutting edges • Axis of tool rotation is perpendicular to feed • Two forms: (a) peripheral milling (b) face or end milling

19. Slab Milling Slotting Basic form of peripheral milling in which the cutter width extends beyond the workpiece on both sides Width of cutter is less than workpiece width, creating a slot in the work

20. Face Milling End Milling Profile Milling Cutter overhangs work on both sides Cutter diameter is less than work width, so a slot is cut into part Form of end milling in which the outside periphery of a flat part is cut

21. Knee-And-Column Milling Machines • (a) Horizontal and (b) vertical knee-and-column milling machines

22. Milling Rate and Time MRR=W×d×v W: width of cut; d: depth of cut v: feed rate (need conversion from # of teeth and spindle speed) v Milling time= (L+2Lc)/v W Lc: extra length for cutter to engage

23. Machining Centers Highly automated machine tool can perform multiple machining operations under CNC control in one setup with minimal human attention • Typical operations are: millinganddrilling • Three, four, or five axes • Other features: • Automatic tool‑changing • Pallet shuttles • Automatic workpart positioning

24. CNC Machining Center

25. Mill-Turn Centers Highly automated machine tool that can perform the operations: turning, milling, anddrilling

26. Machining Gear Teeth • Form milling - use of a form milling cutter • Gear hobbing - also milling but using a special cutter called a hob • Gear shaping - two forms • Single point tool to gradually shape each gear tooth spacing • Cutter has general shape of the gear but with cutting teeth on one side • Gear broaching - for internal and external gears

27. Form Milling of Gear Teeth • The form milling cutter has teeth with the shape of the spaces between teeth on the gear • Gear blank is indexed between each pass to establish correct size of the gear tooth

28. Gear Hobbing • Hob has a slight helix and its rotation must be coordinated with much slower rotation of the gear blank • Performed on special milling machines (called hobbing machines) that accomplish the relative speed and feed motions between cutter and gear blank

29. Gear Shaping • To start the process, cutter is gradually fed into gear blank • Then, cutter and blank are slowly rotated after each stroke to maintain tooth spacing • Performed on special machines called gear shapers

30. Broaching • Moves a multiple tooth cutting tool linearly relative to work in direction of tool axis Broaching Video 1 2 3 4 5 6 Which shape(s) could be made without broaching?

31. Drilling a square hole? • Square hole cutting video • Vikaattachment • Also possible with hexagonal holes