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FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA. Fundamental Of Machining. FUNDAMENTAL OF MACHINING 2 nd PHASE. FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA. Fundamental Of Machining. Chapter Outline. Mechanics of Cutting Cutting Forces and Power

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FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA

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  1. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA Fundamental Of Machining FUNDAMENTAL OF MACHINING 2nd PHASE

  2. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA Fundamental Of Machining Chapter Outline • Mechanics of Cutting • Cutting Forces and Power • Temperatures in Cutting • Tool Life: Wear and Failure • Surface Finish and Integrity Machinability

  3. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TEMPERATURES IN CUTTING • Temperature riseis a very important factor in machining because of its major adverse effects such as: • Excessive temperature lowers the strength, hardness, stiffness, and wear resistance of the cutting tool; tools also may soften and undergo plastic deformation; thus tool shape is altered. • Increased heat causes uneven dimensional changes in the part being machined, making it difficult to control its dimensional accuracy and tolerances. • Excessive temperature rise can induce thermal damage and metallurgical changes in the machined surface, adversely affecting its properties.

  4. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TEMPERATURES IN CUTTING Temperature Distribution? Because the sources of heat generation in machining are concentrated in the primary shear zone and at the tool–chip interface, it is to be expected that there will be severe temperature gradients in the cutting zone. Next Fig. shows the typical temperature distribution in the cutting zone. Note the severe temperature gradients within the tool and the chip, and that the workpiece is relatively cool.

  5. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TEMPERATURES IN CUTTING

  6. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TEMPERATURES IN CUTTING Temperature Distribution (con’t) Fig below shows the temperatures developed in turning 52100 steel: (a) flank temperature distribution and (b) tool–chip interface temperature distribution.

  7. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TEMPERATURES IN CUTTING Devices for Measuring Temperature 1. Temperatures and their distribution in the cutting zone may be determined from thermocouples embedded in the tool and/or the workpiece. 2. This technique has been used successfully, although it involves considerable effort.

  8. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TOOL LIFE: WEAR & FAILURE • We have seen that cutting tools are subjected to: • high localized stresses at the tip of the tool, • high temperatures, especially along the rake face, • sliding of the chip along the rake face, and • sliding of the tool along the newly cut workpiece surface. • Wear is a gradual process, much like the wear of the tip of an ordinary pencil. • The rate of tool wear depends on tool and workpiece materials, tool geometry process parameters, cutting fluids, and the characteristics of the machine tool.

  9. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TOOL LIFE: WEAR & FAILURE Tool wear and the changes in tool geometry during cutting manifest themselves in different ways, generally classified as: -flank wear, -crater wear, -nose wear, -notching, -plastic deformation of the tool tip, -chipping, and gross fracture.

  10. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TOOL LIFE: WEAR & FAILURE • Flank wear and crater wear in a cutting tool; the tool moves to the left. • View of the rake face of a turning tool, showing various wear patterns. • View of the flank face of a turning tool, showing various wear patterns. • Types of wear on a turning tool: thermal cracking on rake face;

  11. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TOOL LIFE: WEAR & FAILURE Flank Wear - Flank wear occurs on the relief (flank) face of the tool. - It generally is attributed to (a) rubbing of the tool along the machined surface, causing adhesive and/or abrasive wear and (b) high temperatures, which adversely affect tool-material properties. - The following approximate relationship was established: where V is the cutting speed, T is the time (in minutes) that it takes to develop a certain flank wear land, n is an exponent (that depends on tool and workpiece materials and cutting conditions), and C is a constant.

  12. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TOOL LIFE: WEAR & FAILURE Flank Wear (con’t) - Table below shows the ranges of n values for the various tool materials:

  13. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TOOL LIFE: WEAR & FAILURE Flank Wear (con’t) - Optimum cutting speed We have noted that as cutting speed increases, tool life is reduced rapidly. - On the other hand, if the cutting speed is low, tool life is long, but the rate at which material is removed is also low. - Thus, there is an optimum cutting speed !!!!!!.

  14. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TOOL LIFE: WEAR & FAILURE • Crater Wear • Crater wear occurs on the rake face of the tool. • Crater wear generally is attributed to a diffusion mechanism, that is, the movement of atoms across the tool–chip interface.

  15. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TOOL LIFE: WEAR & FAILURE Crater Wear (con’t) Fig below shows the relationship between crater-wear rate and average tool–chip interface temperature: (1) High-speed steel, (2) C1 carbide, and (3) C5 carbide. Note how rapidly crater-wear rate increases with an incremental increase in temperature.

  16. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TOOL LIFE: WEAR & FAILURE Crater Wear (con’t) - Fig below shows the interface of a cutting tool (right) and chip (left) in machining plain-carbon steel. The discoloration of the tool indicates the presence of high temperatures.

  17. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA TOOL LIFE: WEAR & FAILURE • Nose Wear • rounding of a sharp tool, due to mechanical and thermal effects • Plastic Deformation - Due to temperature rises in the cutting zone, which can easily reach 1000°C in machining steels and can be higher for stronger materials.

  18. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA SURFACE FINISH & INTEGRITY - Surface finish influences not only the dimensional accuracy of machined parts but also their properties and their performance in service. - The term surface finish describes the geometric features of a surface and surface integrity pertains to material properties, such as fatigue life and corrosion resistance, which are strongly influenced by the nature of the surface produced.

  19. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA SURFACE FINISH & INTEGRITY • Factors influencing surface finish & integrity are: • Temperatures generated during processing and possible metallurgical transformations. • Surface residual stresses. • Severe plastic deformation and strain hardening of the machined surfaces, tearing, and cracking.

  20. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA MACHINABILITY • - The machinability of a material is usually defined in terms of four factors: • Surface finish and surface integrity of the machined part. • Tool life. • Force and power required. • The level of difficulty in chip control. • - In machining practice, tool life and surface roughness generally are considered to be the most important factors in machinability

  21. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA MACHINABILITY of ferrous metal Steels - Because steels are among the most important engineering materials their machinability has been studied extensively. - An important group of steels is free-machining steels, containing sulfur and phosphorus. - Sulfur forms manganese-sulfide inclusions (second-phase particles), which act as stress raisers in the primary shear zone. - As a result, the chips produced break up easily and are small, thus improving machinability.

  22. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA MACHINABILITY of ferrous metal • Steels • Phosphorusin steels has two major effects: • (a) it strengthens the ferrite, causing increased hardness and resulting in better chip formation and surface finish, and • (b) it increases hardness and thus causes the formation of short chips instead of continuous stringy ones, thereby improving machinability.

  23. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA MACHINABILITY of ferrous metal Effects of various elements in steels - The presence of aluminum and siliconin steels is always harmful, because these elements combine with oxygen to form aluminum oxide and silicates, which are hard and abrasive. - As a result, tool wear increases and machinability is reduced. - Other alloying elements (such as nickel, chromium, molybdenum, and vanadium), which improve the properties of steels, generally reduce machinability.

  24. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA MACHINABILITY of ferrous metal Stainless steels - Austenitic (300 series) steels generally are difficult to machine. - Chatter can be a problem, necessitating the need for machine tools with high stiffness. - Precipitation-hardening stainless steels are strong and abrasive, thus requiring hard and abrasion-resistant tool materials.

  25. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA MACHINABILITY of ferrous metal Stainless steels - Gray ironsgenerally are machinable, but they can be abrasive depending on composition, especially pearlite. - Free carbides in castings reduce their machinability and cause tool chipping or fracture. - Nodular and malleable irons are machinable using hard tool materials.

  26. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA MACHINABILITY of nonferrous metal Aluminum is generally very easy to machine, although the softer grades tend to form a built-up edge, resulting in poor surface finish. Beryllium generally is machinable, but because the fine particles produced during machining are toxic, it requires machining in a controlled environment. Cobalt-based alloys are abrasive and highly work-hardening. They require sharp, abrasion-resistant tool materials and low feeds and speeds. Copper in the wrought condition can be difficult to machine because of built-up edge formation, although cast copper alloys are easy to machine.

  27. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA MACHINABILITY of nonferrous metal Magnesium is very easy to machine, with good surface finish and prolonged tool life. However, care should be exercised because of its high rate of oxidation (pyrophoric) and the danger of fire. Molybdenum is ductile and work-hardening. It can produce poor surface finish, thus sharp tools are essential. Nickel-based alloys and superalloys are work-hardening, abrasive, and strong at high temperatures. Their machinability depends on their condition and improves with annealing. Etc…..

  28. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA THE END THANK YOU ANY QUESTIONS?? Feel Free to Ask

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