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ME 350 – Lecture 6 – Chapter 23

ME 350 – Lecture 6 – Chapter 23. CUTTING TOOL TECHNOLOGY Tool Life Tool Geometry Cutting Fluids. 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:

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ME 350 – Lecture 6 – Chapter 23

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  1. ME 350 – Lecture 6 – Chapter 23 CUTTING TOOL TECHNOLOGY • Tool Life • Tool Geometry • Cutting Fluids

  2. 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:

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

  4. 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.

  5. 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.

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

  7. 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

  8. 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?

  9. 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

  10. 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

  11. 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

  12. 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.

  13. Coated Carbide Tool Photomicrograph of cross section of multiple coatings on cemented carbide tool (photo courtesy of Kennametal Inc.)

  14. 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

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

  16. 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.

  17. 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.

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

  19. 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:

  20. Cutting Fluids (Lubricants and Coolants) Function is to improve cutting performance: • Improvechip • Reduce • Improve surface Types of cutting fluids: • Generally water based: – more effective at cutting speeds that are: • Generally oil based: – more effective at cutting speeds that are:

  21. Quotes: • To be able to look back upon one's past life with satisfaction is to live twice. -Marcus Valerius Martial • He who will not reason is a bigot; he who cannot is a fool; and he who dares not, is a slave - Sir William Drummond • It is better to be a lion for a day than a sheep all your life. – Elizabeth Kenny • Dance like no one is watching, Love like you'll never be hurt,Sing like no one is listening, Live like it's heaven on earth. – William Purkey

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