Physics of Metal Cutting Machinability of Metals MACHINABILITY

Physics of Metal Cutting & Machinability of Metals

MACHINABILITY AND CHIP FORMATION Introduction ® Machinability is the relative difficulty of a machining operation with regard to tool life, surface finish, and power consumption. ® Softer materials are generally easier to machine than harder ones.

OBJECTIVES After completing this unit, you should be able to … ® Determine how metal cutting affects the surface structures of metals. ® Analyze chip formation. ® Explain machinability and machining behavior of metals.

Principles of Metal Cutting ® In machining, the tool material rotates or moves in a linear motion or the work-piece rotates or moves. ® ® The moving or rotating tool must be made to move into the work material to cut a chip, a procedure called feed. The feed controls the thickness of the chip, and the depth of cut is often called in-feed.

Machining Principles and Operations

Machining Principles and Operations tab 2

Machining Principles and Operations tab 3

Machining Principles and Operations tab 4

Machining Principles and Operations tab 5

Principles of Metal Cutting ®A common misconception is that the material splits ahead of the tool, which it does not. ® The metal is sheared off and does not split ahead of the chip. tab

Principles of Metal Cutting ® The metal is forced/deformed in the direction of the cut, the grains are elongated & distorted ahead of the tool and rupture along a shear plane.

Principles of Metal Cutting Chip-Tool Interface

Principles of Metal Cutting Deformed Zone

Principles of Metal Cutting Plastic Flow

Principles of Metal Cutting Rupture

Chip Formation ® Discontinuous ® Brittle Chip work material ® Small rake angle ® Feed rate ® Low cutting speed (rpm’s) ® Machine chatter

Chip Formation ® Continuous Chip Ductile work ® Feed rate ® Cutting tool edge ® Large rake angle ® High cutting speeds ® Temperature ® Minimized chip flow resistance ®

Chip Formation

Chip Formation ® Continuous ® Affects chip w/ built-up edge tool life ® Surface finish

Temperature & Friction ® Plastic Deformation ® Chip-tool interface ® Tool Life ® Surface Finish ® Accuracy

REVIEW 1. 2. 3. 4. 5. 6. 7. Define Machinability Name 2 methods by which heat is created during machining. How does temperature affect machining operations? What is a built-up edge and what does it affect? Name two different types of chip formations. What conditions can create discontinuous chip? Describe the process of plastic flow during the cutting process.

REVIEW 8. 9. During the cutting process, what is meant by the deformation zone? What is the chip tool interface?

ANY QUESTIONS?