Material Removal & Machining Processes PDF

SMP14203 Introduction to Engineering Technology Material Removal & Machining Processes FAKULTI PERNIAGAAN & KOMUNIKASI (FPK) Universiti Malaysia Perlis (UniMAP) Material Removal & Machining Processes LECTURE OUTLINE: MATERIAL REMOVAL & MACHINING PROCESS...

SMP14203 Introduction to Engineering Technology Material Removal & Machining Processes FAKULTI PERNIAGAAN & KOMUNIKASI (FPK) Universiti Malaysia Perlis (UniMAP) Material Removal & Machining Processes LECTURE OUTLINE: MATERIAL REMOVAL & MACHINING PROCESSES TURNING PROCESS MILLING PROCESS DRILLING PROCESS TYPE OF CUTTING FLUIDS Material Removal & Machining Processes OBJECTIVES: DEFINE THE FUNDAMENTAL OF CUTTING. MACHINING PROCESS TO PRODUCE DIFFERENT KIND OF SHAPES DESCRIBE THE CUTTING TOOL MATERIAL, CUTTING FLUID  Machining  A material removal process in which a sharp cutting tool is used to mechanically cut away material so that the desired part geometry remains. ▪ Most common application: to shape metal parts. ▪ Most versatile of all manufacturing processes in its capability to produce a diversity of part geometries and geometric features with high precision and accuracy.  Casting can also produce a variety of shapes, but it lacks the precision and accuracy of machining.  TURNING ▪ Turning is a machining process in which a single point tool removes material from the surface of a rotating cylindrical workpiece ; the tool is fed linearly in a direction parallel to the axis of rotation. ▪ Turning is traditionally carried out on a machine tool called a lathe, which provides power to turn the part at a given rotational speed and to feed the tool at a specified rate and depth of cut. Lathe machine Turning process Turning process Turning Process Turning is performed at various: i. rotational speeds, (N) of the workpiece clamped in a spindle ii. depths of cut, (d) iii. feeds, (f) depending on the workpiece materials, cutting tool materials, surface finish, dimensional accuracy Types of Turning Operation  Facing  Contour turning  Straight turning  Taper turning  Form turning  Chamfering  Cut off /parting  Grooving  Knurling  Types of Turning Operation Instead of feeding tool parallel to axis of rotation, tool follows a contour that is other than straight, thus creating a contoured shape Tool is fed radially inward Figure: facing Figure : contour turning Types of Turning Operation Figure: (a) straight turning, (b) taper turning Forming to Create Shape form turning Types of Turning Operation Figure: chamfering Figure: cut off The tool is fed radially into the rotating Cutting edge cuts an angle work at some location along its length to on the corner of the cylinder, cut off the end of the part. forming a "chamfer" This operation is sometimes referred to as parting. Types of Turning Operation  Tool is fed radially into rotating work at some location to produce a groove on work piece. Figure: grooving Types of Turning Operation Knurling Produce rough textured surface For Decorative and/or Functional Purpose Lathe machine / Turning Operation Milling Machines  Milling machines can be classified as horizontal or vertical. a) A horizontal milling machine has a horizontal spindle, and this design is well-suited for performing peripheral milling on work parts that are roughly cube-shaped. b) A vertical milling machine has a vertical spindle, and this orientation is appropriate for face milling, end milling and surface contouring on relatively flat work parts. horizontal milling machine vertical milling machine  MILLING OPERATION Milling is a machining operation in which a work part is fed past a rotating cylindrical tool with multiple cutting edges. The axis of rotation of the cutting tool is perpendicular to the direction of feed. This orientation between the tool axis and the feed direction is one of the features that distinguishes milling from drilling. The cutting tool in milling is called a milling cutter and the cutting edges are called teeth. The machine tool that traditionally performs this operation is a milling machine.  MILLING OPERATION The geometric form created by milling is a plane surface. Milling is an interrupted cutting operation; the teeth of the milling cutter enter and exit the work during each revolution. This interrupted cutting action subjects the teeth to a cycle of impact force and thermal shock on every rotation. Therefore, the tool material and cutter geometry must be designed to withstand these conditions. Two Forms of Milling Figure: Two forms of milling: (a) peripheral milling, and (b) face milling. Peripheral Milling (a) Slab milling. (b) Slotting. (c) Side milling. (d) Straddle milling. In peripheral milling, the rotation direction of the cutter distinguishes 2 forms of milling i.e. up milling and down milling. In down milling, the cutter is engaged in the work for less time per volume of material cut – higher tool life. Two forms of milling with a 20-tooth cutter : (a) up milling, and (b) down milling.  Types of Face Milling ~Cutter ~Cutter diameter overhangs is less than work work on both width, so a slot is sides cut into part Figure: (a) conventional face Figure: end milling milling Types of Face Milling ~Form of end milling in which the outside periphery of a flat ~Another form of end part is cut milling used to mill shallow pockets into flat parts Figure: profile milling Figure: pocket milling Types of Face Milling  Ball-nose cutter fed back and forth across work along a curvilinear path at close intervals to create a three- dimensional surface form Figure: surface contouring Milling Operations Drilling  Drilling is a machining operation used to create a round hole in a workpart.  Drilling is usually performed with a rotating cylindrical tool which has 2 cutting edges on its working end. The tool is called a drill or drill bit.  The rotating drill feeds into the stationary workpart to form a hole whose diameter is equal to the drill diameter.  Drilling is customarily performed on a drill press, although other machine tools can also perform this operation. Through Holes vs. Blind Holes  Through-holes - drill exits opposite side of work  Blind-holes – does not exit work opposite side Figure:Two hole types: (a) through-hole, and (b) blind hole. Operations Related to Drilling (a) Reaming – it is used to slightly (b) Tapping – this operation is enlarge a hole, to provide a better performed by a tap and is used tolerance on its diameter, and to to provide internal screw threads improve its surface finish. The tool on an existing hole. is called a reamer, and usually has straight flutes. Operations Related to Drilling Counterboring – provides a stepped Countersinking – similar to hole, in which a larger diameter counterboring, except that the follows a smaller diameter partially step in the hole is cone-shaped into the hole. A counterbored hole is for flat head screws and bolts. used to seat bolt heads into a hole so the heads do not protrude above the surface.  Operations Related to Drilling Centering – also called centerdrilling. Spotfacing – similar to milling. It is This operation drills a starting hole to used to provide a flat machined accurately establish its location for surface on the workpart in a subsequent drilling. The tool is called localized area. a centerdrill. Types of Drill Press Machine  Upright drill press stands on the floor  Bench drill similar but smaller and mounted on a table or bench Figure: Upright drill press Drilling machine Drilling machine  CUTTING TOOLS AND CUTTING FLUIDS Cutting Tools There are 3 modes of tool failure that can be used to identify some important properties required in a tool material : 1) Toughness Avoid fracture failure, the tool material must possess high toughness. Toughness is the capacity of a material to absorb energy without failing. It is usually characterized by a combination of strength and ductility in the material. 2) Hot hardness Is the ability of a material to retain its hardness at high temperatures. This is required because of the high temperature environment in which the tool operates. 3) Wear resistance Is the single most important property needed to resist abrasive wear. All cutting tool materials must be hard. However, wear resistance in metal cutting depends on more than just tool hardness, because of the other tool wear mechanism. Other characteristics affecting wear resistance include surface finish on the tool (a smoother surface means a lower coefficient of friction), chemistry of tool and work materials, and whether a cutting fluid is used.  Types and Materials of Tool a. High-speed steel (HSS) b. Cast Cobalt Alloys c. Cemented Carbides  Types and Materials of Tool Horizontal Milling Tools  Cutting Fluids Cutting fluids are any liquids or gases that are applied directly to the machining operation to improve cutting performance. Cutting fluids address 2 main problems : (a) heat generation at the shear zone and friction zone (b) friction at the tool-chip and tool-work interfaces. In addition to removing heat and reducing friction, cutting fluids wash away chips (especially in grinding and milling), reduce the temperature of the workpart for easier handling, reduce cutting forces and power requirements, improve dimensional stability of the workpart, and improve surface finish. Cutting Fluids  Types of cutting fluids : (i) Coolants are cutting fluids designed to reduce the effects of heat in the machining operation. They have a limited effect on the amount of heat energy generated in cutting ; instead, they carry away the heat that is generated, thereby reducing the temperature of tool and workpiece. This helps to prolong the life of the cutting tool. Water has high specific heat and thermal conductivity relative to other liquids, which is why water is used as the base in coolant-type cutting fluids. These properties allow the coolant to draw heat away from the operation, thereby reducing the temperature of the cutting tool.  Coolant type cutting fluids seem to be most effective at relatively high cutting speeds where heat generation and high temperatures are problems. They are most effective on tool materials that are most susceptible to temperature failures, such as HSS, and are used frequently in turning and milling operations where large amounts of heat are generated. Coolants are usually water-based solutions or water emulsions, since water has thermal properties that are ideally suited for these cutting fluids. (ii) Lubricants are usually oil-based fluids (since oil possess good lubricating qualities) formulated to reduce friction at the tool-chip and tool-work interfaces. Lubricant cutting fluids operate by extreme pressure lubrication, a special form of lubrication that involves formation of thin solid salt layers on the hot, clean metal surfaces through chemical reaction with the lubricant. Lubricant-type cutting fluids are most effective at lower cutting speeds. They tend to lose their effectiveness at high speeds – above about 120m/min – because the motion of the chip at these speeds prevents the cutting fluid from reaching the tool-chip interface.  Conclusion There are 3 types of removal & machining processes. - Lathe / Turning process - Milling / Vertical & Horizontal Milling process - Drilling process All the machining processes required tools/bits for cutting or removing unwanted material from the surface of an object. During the process Coolant and Lubricant needed for better cutting quality and cutting tools protection. THANK YOU