CHAPTER 3: Metal Machining COURSE: Manufacturing Processes of Engineering COURSE CODE: 404020 This slide is based on the chapter 1 of this course’s textbook: “Groover, Mikell P., [2019], Fundamentals of modern manufacturing: materials processes, and systems, 7th edition, John Wiley & Sons.” 2/24/2022 404020 - Manufacturing Processes of Engineering 1 3.1. Overview of Machining Technology 3.1.1 Introduction Chip Phoi 2/24/2022 404020 - Manufacturing Processes of Engineering 2 Material removal processes: 1. Turning 2. Drilling 3. Milling Machining is a manufacturing process in which a sharp cutting tool is used to cut away material to leave the desired part shape. Machining is important commercially and technologically for several reasons: 1. Variety of work materials. 2. Variety of part shapes and geometric features. 3. Dimensional accuracy. +/- 0.025 mm, 0.001 mm 4. Good surface finishes. Roughness values less than 0.4 microns 1 micron = 0.001 mm 2/24/2022 3 2/24/2022 4 Cutting speed v Feed f Depth of cut d Typical units used for cutting speed are m/s (ft/min) Feed in turning is expressed in mm/rev (in/rev), and depth of cut is expressed in mm (in). 2/24/2022 5 Machining operations usually divide into two categories, distinguished by purpose and cutting conditions: roughing cuts and finishing cuts. Roughing operations are performed at high feeds and depths—feeds of 0.4–1.25 mm/rev (0.015–0.050 in/rev) and depths of 2.5–20 mm (0.100–0.750 in) are typical. Finishing operations are carried out at low feeds and depths—feeds of 0.125– 0.4 mm (0.005–0.015 in/rev) and depths of 0.75–2.0 mm (0.030–0.075 in) are typical. Cutting speeds are lower in roughing than in finishing 2/24/2022 6 3.1. Overview of Machining Technology 3.1.1 Introduction 2/24/2022 404020 - Manufacturing Processes of Engineering 7 3.1. Overview of Machining Technology 3.1.1 Introduction 2/24/2022 404020 - Manufacturing Processes of Engineering 8 3.1. Overview of Machining Technology 3.1.2 Theory of Chip Formation in Metal Machining 2/24/2022 404020 - Manufacturing Processes of Engineering 9 3.1. Overview of Machining Technology 3.1.2 Theory of Chip Formation in Metal Machining 2/24/2022 404020 - Manufacturing Processes of Engineering 10 3.1. Overview of Machining Technology 3.1.2 Theory of Chip Formation in Metal Machining Stress and strain Shear strain 2/24/2022 404020 - Manufacturing Processes of Engineering 11 3.1. Overview of Machining Technology 3.1.3 Theory of Chip Formation in Metal Machining = 2/24/2022 404020 - Manufacturing Processes of Engineering 12 3.1. Overview of Machining Technology 3.1.3 Theory of Chip Formation in Metal Machining Example 1: r=0.5/1.125=0.444 =2.38 2/24/2022 404020 - Manufacturing Processes of Engineering 13 3.1. Overview of Machining Technology 3.1.3 Force Relationships and the Merchant Equation 2/24/2022 404020 - Manufacturing Processes of Engineering 14 3.1. Overview of Machining Technology 3.1.3 Force Relationships and the Merchant Equation 2/24/2022 404020 - Manufacturing Processes of Engineering 15 3.1. Overview of Machining Technology 3.1.3 Force Relationships and the Merchant Equation Using the shear force, the shear stress that acts along the shear plane between the work and the chip can be defined: 2/24/2022 404020 - Manufacturing Processes of Engineering 16 3.1. Overview of Machining Technology 3.1.3 Force Relationships and the Merchant Equation If cutting force and thrust force are known, these four equations can be used to calculate estimates of shear force, friction force, and normal force to friction. 2/24/2022 404020 - Manufacturing Processes of Engineering 17 3.1. Overview of Machining Technology 3.1.3 Force Relationships and the Merchant Equation Merchant started with the defi nition of shear stress expressed in the form of the following relationship: The relationship named after Merchant is obtained: Because this assumption is violated in practical machining operations, Equation above must be considered an approximate relationship rather than an accurate mathematical equation 2/24/2022 404020 - Manufacturing Processes of Engineering 18 Example 2: Suppose in Example 1, cutting force 559 N, thrust force 1271 N. width of cutting w= 3 mm. determine shear strength of work material. Shear stress = shear strength 2/24/2022 19 Example: 2/24/2022 20 3.1. Overview of Machining Technology 3.1.3 Force Relationships and the Merchant Equation 2/24/2022 404020 - Manufacturing Processes of Engineering 21 3.1. Overview of Machining Technology 3.1.3 Force Relationships and the Merchant Equation 2/24/2022 404020 - Manufacturing Processes of Engineering 22 3.1. Overview of Machining Technology 3.1.4 Power and Energy Relationships in Machining The product of cutting force and speed gives the power (energy per unit time) required to perform a machining operation: 2/24/2022 404020 - Manufacturing Processes of Engineering 23 3.1. Overview of Machining Technology 3.1.4 Power and Energy Relationships in Machining The gross power required to operate the machine tool is greater than the power delivered to the cutting process because of mechanical losses in the motor and drive train in the machine. These losses can be accounted for by the mechanical efficiency of the machine tool: 2/24/2022 404020 - Manufacturing Processes of Engineering 24 3.1. Overview of Machining Technology 3.1.4 Power and Energy Relationships in Machining 2/24/2022 404020 - Manufacturing Processes of Engineering 25 3.1. Overview of Machining Technology 3.1.4 Power and Energy Relationships in Machining 2/24/2022 404020 - Manufacturing Processes of Engineering 26 3.1. Overview of Machining Technology 3.1.4 Power and Energy Relationships in Machining 2/24/2022 404020 - Manufacturing Processes of Engineering 27 =1557.100/60=2595 W f=w=3 mm 2/24/2022 28 3.1. Overview of Machining Technology 3.1.5 Cutting temperature The increase in temperature at the tool–chip interface during machining 2/24/2022 404020 - Manufacturing Processes of Engineering 29 3.1. Overview of Machining Technology 3.1.1 Power and Energy Relationships in Machining Rake angle: 12 degree Chip thickness before cut: 0.6 mm chip thickness after the cut 1.15 mm Cutting force: 1620 N, Thrust force: 1280 N Cutting speed: 120 m/min Determine Shear plane angle, shear strain shear strength of the work material Specific energy 2/24/2022 404020 - Manufacturing Processes of Engineering 30 ASSIGNMENT Review: [1]: 3.1 Do homework. 2/24/2022 404020 - Manufacturing Processes of Engineering 31
