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ME 350 – Lecture 5 – Chapter 22 & 23

ME 350 – Lecture 5 – Chapter 22 & 23. Chapter 22 - MACHINING OPERATIONS AND MACHINE TOOLS: Turning and Related Operations Drilling and Related Operations Milling Machining Centers and Turning Centers Broaching. Turning.

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ME 350 – Lecture 5 – Chapter 22 & 23

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  1. ME 350 – Lecture 5 – Chapter 22 & 23 Chapter 22 - MACHINING OPERATIONS AND MACHINE TOOLS: • Turning and Related Operations • Drilling and Related Operations • Milling • Machining Centers and Turning Centers • 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 • Threading

  3. 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

  4. Threading Contour Turning Facing Tool follows a contour that is other than straight Tool is fed radially Pointed form tool is fed at a large feed rate, thus creating threads

  5. Engine Lathe

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

  7. 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

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

  9. Reaming Tapping • Slightly enlarges a hole • Provides better: • Improves: Used to provide internal screw threads on an existing hole. Tool called a:

  10. Radial Drill Large drill press designed for large parts

  11. 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) (b)

  12. 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

  13. 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

  14. Machining Centers Highly automated machine tool can perform multiple machining operations under CNC control in one setup with minimal human attention • Typical operations are: • Other features: • Automatic tool changing • Pallet shuttles • Automatic workpart positioning

  15. Mill-Turn Centers Highly automated machine tool that can perform the operations:

  16. Broaching • Moves a multiple tooth cutting tool linearly relative to work in direction of tool axis Examples of internal broaching

  17. Chapter 23: CUTTING TOOL TECHNOLOGY • Tool Life • Tool Geometry • Cutting Fluids

  18. Three Modes of Tool Failure • Cutting force is excessive and/or dynamic, leading to brittle fracture: • Cutting temperature is too high for the tool material: • Preferred wearing of the cutting tool:

  19. Preferred Mode: • Longest possible tool life, wear locations: • Crater wear location: • Flank wear location:

  20. Tool Wear vs. Time Tool wear as a function of cutting time. Flank wear (FW) is used here as the measure of tool wear. Crater wear follows a similar growth curve.

  21. Effect of Cutting Speed Effect of cutting speed on tool flank wear (FW) for three cutting speeds, using a tool life criterion of 0.50 mm flank wear.

  22. Tool Life vs. Cutting Speed Log‑log plot of cutting speed vs tool life.

  23. Taylor Tool Life Equation • where v = cutting speed; • T = tool life; and • n and C are parameters that depend on feed, depth of cut, work material, and tooling material, but mostly on material (work and tool). • n is the • C is the _______ on the speed axis at one minute tool life

  24. Example Problem A tool run at 160m/min lasts for 5 min. If the tool is run at 100m/min it lasts for an average of 41 min. What is C and n?

  25. Tool Near End of Life • Changes in sound emitted from operation • Chips become ribbon-like, stringy, and difficult to dispose of • Degradation of surface finish • Increased power required to cut Visual inspection of the cutting edge with magnifying optics can determine if tool should be replaced

  26. Desired Tool Properties • Toughness ‑ to avoid fracture failure • Hot hardness ‑ ability to retain hardness at high temperatures • Wear resistance ‑ hardness is the most important property to resist abrasive wear

  27. Hot Hardness Plain carbon steel shows a rapid loss of hardness as temperature increases. High speed steel is substantially better, while cemented carbides and ceramics are significantly harder at elevated temperatures.

  28. Typical Values of n and C Tool materialnC (m/min)C (ft/min) High speed steel: Non-steel work 0.125 120 350 Steel work 0.125 70 200 Cemented carbide Non-steel work 0.25 900 2700 Steel work 0.25 500 1500 Ceramic Steel work 0.6 3000 10,000

  29. Tool Geometry Two categories: • Single point tools • Used for turning, boring, shaping, and planing • Multiple cutting edge tools • Used for drilling, reaming, tapping, milling, broaching, and sawing

  30. Single-Point Tool Geometry (a) Seven elements of single‑point tool geometry; and (b) the tool signature convention that defines the seven elements.

  31. Holding the Tool Three ways of holding and presenting the cutting edge for a single‑point tool: (a) solid tool (typically HSS); (b) brazed cemented carbide insert, and (c) mechanically clamped insert, used for cemented carbides, ceramics, and other very hard tool materials.

  32. Common Insert Shapes Common insert shapes: (a) round, (b) square, (c) rhombus with two 80 point angles, (d) hexagon with three 80 point angles, (e) triangle (equilateral), (f) rhombus with two 55 point angles, (g) rhombus with two 35 point angles.

  33. Twist Drills • The most common cutting tool for hole‑making • Usually made of high speed steel Standard geometry of a twist drill.

  34. Twist Drill Issues • Along radius of cutting edges cutting speed: • Relative velocity at drill point is _______, (no cutting takes place) a large thrust force must deform the material • Problems: • Flutes must provide sufficient clearance to allow chips to be extracted: • Rubbing between outside diameter of drill bit and hole. Delivery of cutting fluid to drill point is difficult because chips are flowing in opposite direction:

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