FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA FORMAT

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA FORMAT REPORT 1. Title and Front Cover 2. Objective 3. Brief of project (1 page) 4. Working method and procedure existing project. For CNC include programming. 5. Working method and procedure for proposed project (new project proposed by student. (For CNC include programming) 6. Discussion -Problem encountered -Countermeasure -Suggestion 7. Safety precaution 8. Conclusion 9. Appendix (if any) Report not more 30 pages comb binding; 1. 5 line spacing; font size 12. Submit date: Last working day of Report Week. Penalty will be imposed for late submission.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA Fundamental Of Machining FUNDAMENTAL OF MACHINING 2

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA Fundamental Of Machining Chapter Outline 1. 2. 3. 4. 5. 3 Mechanics of Cutting Forces and Power Temperatures in Cutting Tool Life: Wear and Failure Surface Finish and Integrity Machinability

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA INTRODUCTION l 1. 2. 4 Cutting processes remove material from the surface of a workpiece by producing chips. Some of the more common cutting processes are as follow: Turning, in which the workpiece is rotated and a cutting tool removes a layer of material as it moves to the left. Cutting-off operation, where the cutting tool moves radially inward and separates the right piece from the bulk of the blank.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA INTRODUCTION l 3. 4. 5 Cutting processes remove material from the surface of a workpiece by producing chips. Some of the more common cutting processes are as follow: Slab-milling operation, in which a rotating cutting tool removes a layer of material from the surface of the workpiece. End-milling operation, in which a rotating cutter travels along a certain depth in the workpiece and produces a cavity.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA INTRODUCTION l 6 Fig BELOW shows some examples of common machining operations.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA INTRODUCTION l 7 Fig BELOW shows the schematic illustration of the turning operation showing various features.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA INTRODUCTION l l l 8 Next Fig shows the schematic illustration of a two-dimensional cutting process, also called orthogonal cutting: (a) Orthogonal cutting with a well-defined shear plane, also known as the Merchant model. Note that the tool shape, depth of cut, and the cutting speed, V, are all independent variables (b) Orthogonal cutting without a well-defined shear plane.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA INTRODUCTION 9

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING l l 10 The factors that influence the cutting process are outlined in Next Table. In order to appreciate the contents of this table, let’s now identify the major independent variables in the cutting process as follows: (a) tool material and coatings; (b) tool shape, surface finish, and sharpness; (c) workpiece material and condition; (d) cutting speed, feed, and depth of cut; (e) cutting fluids; (f) characteristics of the machine tool; and (g) workholding and fixturing.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING 11

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING l l l 12 Dependent variables in cutting are those that are influenced by changes in the independent variables listed above, and include: (a) type of chip produced, (b) force and energy dissipated during cutting, (c) temperature rise in the workpiece, the tool, and the chip, (d) tool wear and failure, and (e) surface finish and surface integrity of the workpiece.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING l 13 Fig below (a) shows the schematic illustration of the basic mechanism of chip formation by shearing. (b) Velocity diagram showing angular relationships among the three speeds in the cutting zone.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Cutting Ratio l It can be seen that the chip thickness, tc, can be determined by knowing the depth of cut, to and α and Φ. l The ratio of to / tc is known as the cutting ratio (or chip-thickness ratio), r, and is related to the two angles by the following relationships: 14

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Cutting Ratio l The reciprocal of r is known as the chipcompression ratio or factor and is thus a measure of how thick the chip has become compared to the depth of cut; hence, the chip-compression ratio always is greater than unity. l The depth of cut also is referred to as the undeformed chip thickness. 15

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Cutting Ratio l The reciprocal of r is known as the chipcompression ratio or factor and is thus a measure of how thick the chip has become compared to the depth of cut; hence, the chip-compression ratio always is greater than unity. l The depth of cut also is referred to as the undeformed chip thickness. 16

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Shear Strain l The shear strain, , that the material undergoes can be expressed as l 17 Note that large shear strains are associated with low shear angles or with low or negative rake angles.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Shear Strain l The shear angle has great significance in the mechanics of cutting operations. l It influences force and power requirements, chip thickness, and temperature. l This analysis yielded the expression l 18 where β is the friction angle and μ is related to the coefficient of friction, at the tool–chip interface by the expression μ = tan β.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Shear Strain l Among the many shear–angle relationships developed, another useful formula that generally is applicable is l 19 The coefficient of friction in metal cutting generally ranges from about 0. 5 to 2, indicating that the chip encounters considerable frictional resistance while moving up the tool’s rake face.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Velocities in the cutting zone l Since mass continuity has to be maintained, l 20 A velocity diagram also can be constructed, where from trigonometric relationships, we obtain the equation

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Velocities in the cutting zone where Vs is the velocity at which shearing take place in the shear plane. l Note also that l 21 These velocity relationships will be utilized further when describing power requirements in cutting operations.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting l The four main types are: 1. Continuous Built-up edge Serrated or segmented Discontinuous 2. 3. 4. 22

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Continuous chips l l l 23 Continuous chips usually are formed with ductile materials, machined at high cutting speeds and/or high rake angles. The deformation of the material takes place along a narrow shear zone called the primary shear zone. Continuous chips may develop a secondary shear zone because of high friction at the tool–chip interface; this zone becomes thicker as friction increases.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting a) b) c) d) e) 24 Continuous chip in cutting brass Secondary shear zone in cutting copper Built Up edge in cutting sintered tungsten Serrated chip in cutting S. steel Discontinuous chip in cutting brass

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Continuous chips l Deformation in continuous chips also may take place along a wide primary shear zone with curved boundaries. l This problem can be alleviated with chip breakers (to follow) or by changing parameters, such as cutting speed, feed, depth of cut, and by using cutting fluids. 25

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Built-up edge chips l A built-up edge (BUE) consists of layers of material from the workpiece that gradually are deposited on the tool tip—hence the term builtup. l Built-up edge commonly is observed in practice. l It is a major factor that adversely affects surface finish, however, a thin, stable BUE usually is regarded as desirable because it reduces tool wear by protecting its rake face. 26

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Built-up edge chips l The tendency for BUE formation can be reduced by one or more of the following means: 1. Increase the cutting speeds 2. Decrease the depth of cut 3. Increase the rake angle 4. Use a sharp tool 5. Use an effective cutting fluid 27 6. Use a cutting tool that has lower chemical affinity

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Serrated chips l Serrated chips are semicontinuous chips with large zones of low shear strain and small zones of high shear strain, hence the latter zone is called shear localization. l Metals with low thermal conductivity and strength that decreases sharply with temperature (thermal softening) exhibit this behavior, most notably titanium. 28

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Discontinuous chips l l 1. 29 3. Discontinuous chips consist of segments that may be attached firmly or loosely to each other. Discontinuous chips usually form under the following conditions: Brittle workpiece materials, because they do not have the capacity to undergo the high shear strains involved in cutting. Workpiece materials that contain hard inclusions and impurities or have structures such as the graphite flakes in gray cast iron. Very low or very high cutting speeds

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Discontinuous chips 4. Large depths of cut. 5. Low rake angles. 6. Lack of an effective cutting fluid. 7. Low stiffness of the toolholder or the machine tool, thus allowing vibration and chatter to occur. 30

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Discontinuous chips l Because of the discontinuous nature of chip formation, forces continually vary during cutting. l Consequently, the stiffness or rigidity of the cutting-tool holder, the workholding devices, and the machine tool are important in cutting with serrated chips as well as with discontinuous chips. 31

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Chip Curl l In all cutting operations performed on metals, as well as nonmetallic materials such as plastics and wood, chips develop a curvature (chip curl) as they leave the workpiece surface. l Among factors affecting the chip curl are: 1. 2. 32 3. The distribution of stresses in the primary and secondary shear zones. Thermal effects. Work-hardening characteristics of the workpiece material.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Chip Curl 4. 5. l l 33 The geometry of the cutting tool. Cutting fluids. Generally, as the depth of cut decreases, the radius of curvature decreases; that is, the chip becomes curlier. Also, cutting fluids can make chips become more curly (the radius of curvature decreases), thus reducing the tool–chip contact area and concentrating the heat closer to the tip of the tool. As a result, tool wear increases.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting 34 Chip Breakers l Continuous and long chips are undesirable as they tend to become entangled and severely interfere with machining operations and also become a potential safety hazard. l Next Fig(a) shows the schematic illustration of the action of a chip breaker. Note that the chip breaker decreases the radius of curvature of the chip and eventually breaks it. (b) Chip breaker clamped on the rake face of a cutting tool. (c) Grooves in cutting tools acting as chip breakers. Most cutting tools used now are inserts with built-in chip-breaker features.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting 35

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Chip Breakers l l l 36 Chip breakers have traditionally been a piece of metal clamped to the tool’s rake face, which bend and break the chip. However, most modern cutting tools and inserts now have built-in chip-breaker features of various designs. Next Fig shows the chips produced in turning: (a) tightly curled chip; (b) chip hits workpiece and breaks; (c) continuous chip moving radially away from workpiece; and (d) chip hits tool shank and breaks off.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting 37

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting Chip Breakers l In interrupted-cutting operations (such as milling), chip breakers generally are not necessary, since the chips already have finite lengths. 38

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting 39 Controlled contact on tools l Cutting tools can be designed so that the tool–chip contact length is reduced by recessing the rake face of the tool some distance away from its tip. l This reduction in contact length affects chip-formation mechanics. l Primarily, it reduces the cutting forces and, thus, the energy and temperature. l Determination of an optimum length is important as too small a contact length would concentrate the heat at the tool tip, thus increasing wear.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Types of chips produced in metal cutting 40 Cutting nonmetallic materials l A variety of chips are encountered in cutting thermoplastics, depending on the type of polymer and process parameters, such as depth of cut, tool geometry, and cutting speed. l Many of the discussions concerning metals also are applicable generally to polymers. l Because they are brittle, thermosetting plastics and ceramics generally produce discontinuous chips.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Oblique Cutting l l l 41 The majority of machining operations involve tool shapes that are three-dimensional, thus the cutting is oblique. Whereas in orthogonal cutting, the chip slides directly up the face of the tool, in oblique cutting, the chip is helical and at an angle i, called the inclination angle. Next Fig(a) shows the schematic illustration of cutting with an oblique tool. Note the direction of chip movement. (b) Top view, showing the inclination angle, i. (c) Types of chips produced with tools at increasing inclination angles.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Oblique Cutting 42

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Oblique Cutting l l 43 Note that the chip in previous Fig flows up the rake face of the tool at angle (chip flow angle), which is measured in the plane of the tool face. Angle αi is the normal rake angle, and it is a basic geometric property of the tool. This is the angle between line oz normal to the workpiece surface and line oa on the tool face. The effective rake angle, αe is

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Oblique Cutting l l 44 Next Fig shows the schematic illustration of a right-hand cutting tool. The various angles on these tools and their effects on machining. Although these tools traditionally have been produced from solid tool-steel bars, they have been replaced largely with Next Fig inserts made of carbides and other materials of various shapes and sizes.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Oblique Cutting 45

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA MECHANICS OF CUTTING Oblique Cutting Shaving and skiving l Thin layers of material can be removed from straight or curved surfaces by a process similar to the use of a plane to shave wood. l Shaving is useful particularly in improving the surface finish and dimensional accuracy of sheared parts and punched slugs. 46

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER l 47 Knowledge of the cutting forces and power involved in machining operations is important for the following reasons: • Data on cutting forces is essential so that: a. Machine tools can be properly designed to minimize distortion of the machine components, maintain the desired dimensional accuracy of the machined part, and help select appropriate toolholders and workholding devices. b. The workpiece is capable of withstanding these forces without excessive distortion. • Power requirements must be known in order to enable the selection of a machine tool with adequate electric power.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER l 48 Fig Below (a) shows the Forces acting in the cutting zone during two-dimensional cutting. Note that the resultant force, R, must be colinear to balance the forces. (b) Force circle to determine various forces acting in the cutting zone.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER l l l 49 The thrust force, acts in a direction normal to the cutting speed. These two forces produce the resultant force, R, as can be seen from the force circle. Note that the resultant force can be resolved into two components on the tool face: a friction force, F, along the tool-chip interface and a normal force, N, perpendicular to it. It can also be shown that

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER l l 50 Note also that the resultant force is balanced by an equal and opposite force along the shear plane and is resolved into a shear force, and a normal force. It can be shown that these forces can be expressed as follows:

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER l l l 51 Because the area of the shear plane can be calculated by knowing the shear angle and the depth of cut, the shear and normal stresses in the shear plane can be determined. The ratio of F to N is the coefficient of friction, μ, at the tool–chip interface, and the angle β is the friction angle. The magnitude of μ can be determined as

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER Thrust force l A knowledge of the thrust force in cutting is important because the tool holder, the workholding devices, and the machine tool must be sufficiently stiff to support this force with minimal deflections. l We also can show the effect of rake angle and friction angle on the direction of thrust force by noting from previous Fig. that 52

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER Thrust force l A knowledge of the thrust force in cutting is important because the tool holder, the workholding devices, and the machine tool must be sufficiently stiff to support this force with minimal deflections. l We also can show the effect of rake angle and friction angle on the direction of thrust force by noting from previous Fig. that 53

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER Power l Power is the product of force and velocity. Thus, the power input in cutting is l l 54 This power is dissipated mainly in the shear zone (due to the energy required to shear the material) and on the rake face of the tool (due to tool–chip interface friction). The power dissipated in the shear plane is

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER Power l Letting w be the width of cut, the specific energy for shearing, us, is given by l Similarly, the power dissipated in friction is and the specific energy for friction, uf is 55

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER Power l The total specific energy, ut thus is l l 56 Because of the many factors involved, reliable prediction of cutting forces and power still is based largely on experimental data, such as those given in Next Table. The sharpness of the tool tip also influences forces and power. Because it rubs against the machined surface and makes the deformation zone ahead of the tool larger, duller tools require higher forces and power.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER 57

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER Measuring cutting forces and power l Cutting forces can be measured using a force transducer (typically with quartz piezoelectric sensors), a dynamometer or a load cell (with resistance-wire strain gages placed on octagonal rings) mounted on the cutting-tool holder. l It is possible to calculate cutting force from the power consumption during cutting, provided that the mechanical efficiency of the machine 58 tool is known or can be determined.

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER Example : Relative energies in cutting In an orthogonal cutting operation, to = 0. 13 mm, V = 120 m/min, α = 10º and the width of cut=6 mm. It is observed that tc = 0. 23 mm, Fc = 500 N and Ft = 200 N. Calculate the percentage of the total energy that goes into overcoming friction at the tool-chip interface. 59

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA CUTTING FORCES & POWER Solution The percentage of the energy can be expressed as 60

FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNIKAL MALAYSIA MELAKA THE END THANK YOU ANY QUESTIONS? ? Feel Free to Ask 61