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عدد المساهمات : 18962 التقييم : 35392 تاريخ التسجيل : 01/07/2009 الدولة : مصر العمل : مدير منتدى هندسة الإنتاج والتصميم الميكانيكى
| موضوع: محاضرة بعنوان Introduction of Machining, Geometry of Tool and Nomenclatu السبت 03 سبتمبر 2022, 2:08 am | |
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أخواني في الله أحضرت لكم محاضرة بعنوان Introduction of Machining, Geometry of Tool and Nomenclature Subject: Manufacturing Science & Technology-II Department of Mechanical Engineering (RME-503) Faculty: Mr. Brijesh Kumar Unit-1 /Lecture No: 1 Manufacturing
و المحتوى كما يلي :
Manufacturing is the application of physical and chemical processes to change the geometry, properties and appearance of a given raw material to make parts or products based on customer's specifications and expectations. Manufacturing commonly employs a man-machine setup with division of labor in a large scale production. Classification of Manufacturing Processes Classification of “material removal” processesMachining • Machining is the process of removing excess material from a work surface in the form of chips. The removal of the material occurs by the shearing action of the cutting tool. The shear stress is developed due to relative motion between tool and work piece. This shear stress causes the plastic deformation of the material in the form of chips. • Objective of Machining: Parts are manufactured either by casting, forming or powder metallurgy process. These parts require further operations before the product is ready for use. So machining of materials is basically adopted to get – 1: Excellent dimensional accuracy 2: Excellent geometrical accuracy 3: Excellent surface finish 4: Complex geometrical features like Sharp corners, grooves, fillets etc. Machining System • A machining system consists of following components: 1: Machine tool 2: Cutting tool 3: Workpiece 4. Work holding devices• Machine Tool: A machine tool is one which is used for machining purpose and operated by external energy. Machine tool holds the cutting tool as well as workpiece and provides necessary relative motion between the cutting tool and work piece. Ex: Lathe machine, drilling machine, milling machine etc. • Cutting Tool: The body which removes the excess material through a direct mechanical contact is called cutting tool. Ex: Single point cutting tool, drill bit, milling cutter etc. • Workpiece: It is the metallic or non-metallic parts needs to be machine. • Work holding devices: Work holding devices are used to hold the workpiece and guide it against the cutting tool. Manufacturing Process Selection Two stage decision process 1. Feasibility Criteria: Can the shape be produced by the process? Can the material be shaped by the process? 2. Process performance criteria: Cycle time Material utilization, Process flexibility, Operating costs Surface finishMachining Conditions 1. Cutting parameters Cutting velocity Depth of cut Feed rate 2. Cutting environment Cutting Fluid Cutting temperature Presence of air (oxygen ) 3. Work and tool holding devices Jigs Fixtures Cutting tool • Both material and geometry of the cutting tools play very important roles on their performances in achieving effectiveness, efficiency and overall economy of machining. • The word tool geometry is basically referred to some specific angles or slope of the salient faces and edges of the tools at their cutting point. • Rake angle and clearance angle are the most significant for all the cutting tools.Rake Angle: It is the angle between rake face of the tool and a plane perpendicular to the machining direction. Rake angle is provided for ease of chip flow and overall machining. Higher the rake angle, less are the cutting forces Increasing the rake angle reduces the strength of the tool tip. There is maximum limit to the rake angle and this is generally 20º for HSS tools cutting mild steel. • It is possible to have rake angles “positive, zero or negative”. Relative advantages of such rake angles are: Positive rake – helps to reduce cutting force and thus cutting power requirement. Negative rake – helps to increase edge-strength and life of the tool. Zero rake – to simplify design and manufacture of the form tools. • Zero or negative rake angles are generally used in the case of highly brittle tool materials such as carbides or diamonds for giving extra strength to the tool tip. Example: HSS: +5° < rake angle< +20° Carbides: -5° < rake angle < +10° Ceramics: -5° < rake angle < -15°Clearance Angle: • It is the angle between the machined surface and the flank face of the tool. The clearance angle is provided such that tool will not rub the machined surface thus spoiling the surface and increasing the cutting force. • A very large clearance angle reduces the strength of the tool tip, and hence normally an angle of the order of 5 - 6º is used. It is always positive. Geometry of single point turning tool• The single point cutting tool have 6 different angles. These are: 1. Back rake angle: The back rake angle is the angle between the face of the tool and a line parallel with base of the tool measured in a perpendicular plane through the side cutting edge. Back rake angle helps in removing the chips away from the workpiece. 2. Side rake angle: Side rake angle is the angle by which the face of tool is inclined side ways. It is the angle between the surface of the flank immediately below the point and the line down from the point to the base. It is provided on tool to provide clearance between workpiece and tool so as to prevent the rubbing of workpiece with end flank of the tool. 3. End relief angle: It is defined as the angle between the portion of the end flank immediately below the cutting edge and a line perpendicular to the base of the tool measured at right angles to the flank. End relief angle allows the tool to cut without rubbing on the workpiece. 4. Side relief angle: It is the angle between the portion of the side flank immediately below the side edge and a line perpendicular to the base of the tool measured at right angles to the side. It provides relief between flank face and the work surface. 5. End cutting edge angle: It is the angle between the end cutting edge and a line perpendicular to the shank of the tool. It provides clearance between tool cutting edge and workpiece. 6. Side cutting edge angle: It is the angle between straight cutting edge on the side of tool and the side of the shank. It is responsible for turning the chip away from the machined surface.Thank You Department of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-1 /Lecture No: 2 (Orthogonal vs. Oblique cutting)Mode of Machining • Based on the orientation of cutting edge with respect to the direction of cutting velocity, there are two methods of metal cutting. 1. Orthogonal Cutting 2. Oblique Cutting Orthogonal Cutting: When the cutting edge of the tool is perpendicular to the direction of cutting velocity, the process is called orthogonal cutting. The chip generated flows on the rake face of the tool and the chip velocity is perpendicular to the cutting edge. The cutting forces act along X and Z directions only.Oblique Cutting: When the cutting edge of the tool is inclined at an Angle “i” with the normal to the direction of cutting velocity, the process is called oblique cutting. • The chip generated flows on the rake face at an angle approximately equal to “i” with normal to the cutting edge. The cutting forces acts along all the three X, Y and Z directions. • In actual machining, Turning, Milling, Drilling etc/ cutting operations are oblique cutting Difference between orthogonal and oblique cutting Orthogonal cutting • The cutting angle of tool make right angle to the direction of motion. • The chip flow in the direction normal to the cutting edge. • In orthogonal cutting only two components of force considered cutting force and thrust force which can be represent by 2D coordinate system, so it is known as 2D cutting. Oblique cutting • The cutting angle of tool not make right angle to the direction of motion. • The chips make an angle with the normal to the cutting edge. • In oblique cutting three component of force are considered, cutting force, thrust force and radial force which is represented by 3D coordinate system, so it is known as 3D cutting.Difference between orthogonal and oblique cutting Orthogonal cutting • The chips flow over the tool. • The shear force act per unit area is high which increase the heat developed per unit area. • This tool has lesser cutting life compare to oblique cutting. Oblique cutting • The chips flow along the sideways. • The shear force per unit area is low, which decreases heat develop per unit area hence increases tool life. • This tool has higher cutting life. THANK YOUDepartment of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I /Lecture No: 3 (Mechanics of chip formation, types of chips) Mechanics of chip formation • Machining is a process of gradual removal of excess material from the work surface in the form of chips. Knowledge of basic mechanism of chip formation helps to understand the characteristics of chips and to attain favorable chip forms. • Two mechanics of chip formation are: 1. Mechanics of chip formation in ductile materials 2. Mechanics of chip formation in brittle materials1. Mechanics of chip formation in ductile materials • During continuous machining the uncut layer of the work material just ahead of the cutting edge is subjected to compression. Due to such compression, shear stress develops, within that compressed region, and rapidly increases in magnitude. Whenever the value of the shear stress exceeds the shear strength of that work material in the deformation region, yielding takes place resulting shear deformation in that region along the plane of maximum shear stress. Then the deformed metal (called chip) flows along the tool rake face. • The region of maximum shear stress is called primary shear zone. If the friction between the tool rake face and the underside of the chip is considerable, the chip gets further deformed, which is termed as secondary shear zone. In ductile material, the chips are initially compressed ahead of the tool tip, the final deformation is accomplished mostly by shear in machining ductile materials.Primary and secondary deformation zone: The pattern and extent of total deformation of the chips due to the primary and the secondary shear deformations of the chips ahead and along the tool face is shown in fig. Machining of ductile materials generally produces flat, curved or coiled continuous chips. 2. Mechanics of chip formation in brittle materials • During machining, first a small crack develops at the tool tip as shown in fig. due to wedging action of the cutting edge. At the sharp crack-tip stress concentration takes place. In case of ductile materials immediately yielding takes place at the crack-tip and reduces the effect of stress concentration and prevents its propagation as crack. But in case of brittle materials the initiated crack quickly propagates, under stressing action, and total separation takes place from the parent workpiece through the minimum resistance path as indicated in fig. • Machining of brittle material produces discontinuous chips and mostly of irregular size and shape.Mechanics of chip formation in brittle materials…….. • During machining of brittle materials, chip formation occurs due to brittle fracture of the work material. Types of Chip • Depending on the properties of work material and cutting conditions, three basics types of chips are produced by the machining process. These are: 1. Continuous chips 2. Continuous chips with Built-Up Edge 3. Discontinuous chipsContinuous Chip: • Continuous chips are normally produced when machining ductile metals at high cutting speeds. Continuous chip which is like a ribbon flows along the rake face of the tool. Production of continuous chips is possible because of the ductility of the metal. Thus on a continuous chip you do not see any notches. • Some ideal conditions which promote the formation of continuous chips are: 1. Ductile work material 2. Small uncut thickness 3. High cutting speed 4. Large rake angle 5. Sharpe cutting edge 6. Less friction Continuous Chip with BUE: • In the cutting zone, when friction is high while machining ductile materials, some particles of the chip get welded to the tool rake face near the tool tip. • Such sizeable particles piles upon the rake face and forms the built-up edge. • The BUE grows up to a certain size but finally breaks due to the increased forced exerted on it by the adjacent flowing material. After it breaks, the broken fragments adhere to the finished surface and the chip surface, results in a rough finish.• Some ideal conditions which promote the formation of continuous chip with BUE chips are: 1. Ductile work material 2. Large uncut thickness 3. Low cutting speed 4. Small rake angle 5. High friction between chip-tool interface Discontinuous chips • When brittle materials like cast iron are cut, the deformed material gets fractured very easily and thus the chip produced in the form of discontinuous segments. In this type the deformed material instead of flowing continuously gets ruptured periodically. • Conditions which promote the formation of discontinuous chips are: 1. Brittle work material 2. Low cutting speed 3. Small rake angle 4. Large uncut thicknessTHANK YOU Department of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I / Lecture No: 4 (Shear angle relationship)Shear Angle (φ) • It is the angle made by the shear plane with the direction of cutting speed. Higher the shear angle better is the cutting performance. Importance of shear angle: • If all other factors remain the same, a higher shear angle results in a smaller shear plane area. Since the shear strength is applied across this area, the shear force required to form the chip will decrease when the shear plane area is decreased. This tends to make machining easier to perform, and also lower cutting energy and cutting temperature. Determination of Shear angle• Chip thickness ratio (r ) also known as cutting ratio. • Chip thickness ratio is always less than 1. this is because, chip thickens and due to volume constancy shortens. • 1/r is known as chip compression ratio.THANK YOU Department of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I / Lecture No: 5 (Merchant’s force circle diagram)Orthogonal machining Forces in orthogonal metal cutting • Forces in the secondary deformation zone: 1- Friction force along the rake face, Fr 2- Force perpendicular to rake face, Nr • Forces in the Primary deformation zone: 1- Force along the shear plane, Fs (shear force) 2- Force normal to the shear plane, Ns • Forces on the cutting tool: 1- Cutting force, Fc 2- Thrust force, Ft1. Forces on the cutting tool 2-Forces in the secondary deformation zone:3-Forces in the Primary deformation zone: The resulting diagram Merchant,s force circle diagramForce analysis 1- Friction force along the rake face F = F c sin α + Ft cosα 2- Force perpendicular to rake face F c cosα - Ft sinα 3-Force along the shear plane (shear force) F c cosφ - Ft sin φ 4- Force perpendicular to the shear plane F c sin φ + Ft cosφ Shear strain in chip formationShear strain rate Shear strain rate (γ ) is given by: • where Δt is the time required for the metal to travel the distance Δs along the shear plane. • Δy is the distance between two successive shear planes. • A reasonable value of spacing between successive planes (Δy) would be around 25×10-4 mm.Velocity analysis in orthogonal machining THANK YOUDepartment of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I / Lecture No: 7 (Cutting forces, power required in metal cutting) Force analysis From Merchant,s force circle diagramCoefficient of friction between chip-tool interface • The coefficient of friction between two sliding surfaces is defined as • Here, it is implied that the forces F and N are uniformly distributed over the entire chip-tool contact area. Shear angle relationship based on Merchant’s theoryWhat the Merchant’s relation tells us? To increase shear plane angle Increase the rake angle Reduce the friction angle (or coefficient of friction)Cutting energy or power requirement • The cutting energy required for machining depends on the cutting force and cutting velocity. It can be express as: Cutting energy = Cutting force × Cutting velocity Parameters which affects the cutting force & power requirement The variables that have significant effect on tool life are: 1- Cutting conditions > Speed > Feed > Depth of cut 2- Tool geometry > Rake angle > Clearance angle > Nose radius 3- Work material 4- Cutting fluid 5- Built-Up-EdgeTHANK YOU Department of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I / Lecture No: 7 (Thermal aspects of machining)Thermal Aspect of Machining Process The machining operation is basically a deformation process of the work material through the application of force by the cutting tool. In all the machining processes where plastic deformation is involved, the mechanical energy dissipated in cutting is converted into heat which in turn, raises the temperature in the cutting zone. During machining almost 99% of the energy is converted in to heat. Sources of Heat Generation in Machining: The heat generation occurs in three distinct regions: 1- Primary shear zone 2- Secondary shear zone (at chip-tool interface) 3- Tool-work interface • Primary shear zone: In primary shear zone heat is generated due to plastic deformation of the work material. About 80 – 85% heat is generated in this zone. • Secondary shear zone: In this zone, heat is generated due to frictional rubbing between the rake face of the tool and chip. Some plastic deformation also occurs in this zone. About 15 – 20% heat is generated in this zone. • Tool – Work Interface: At the tool-work interface, heat is generated due to frictional rubbing between flank face of the tool and machined work piece surface. • In this region only 1 – 3% heat is generated.Heat Flow in Metal Cutting The heat generated is shared by the chip, cutting tool and the workpiece. The percentage of sharing that heat depends upon the configuration, size and thermal conductivity of the tool – work material and the cutting condition. About 80 – 85 % of the total heat generated during machining is carried away by the chip. About 15 – 20% of the total heat is flows in to the tool. Less than 5% heat is conducted in to the work piece.Temperature distribution in metal cutting process • Figure shows temperature distribution during orthogonal cutting. The workpiece material is free cutting mild steel where the cutting speed is 0.38 m/s, the depth of cut is 6.35 mm.Temperature distribution in metal cutting process • From figure it is clear that the maximum temperature in the cutting process occurs not at the tool tip but at some distance away from the cutting edge. • Point X. The material at point x gets heated as it passes through the shear zone and finally leaves as chip. • Point Y. Material at point y first heated in shear zone but heating is continued until they cross the frictional heat zone. This point losses some shear zone heat while moving up but gains more frictional heat. • Point Z. Point such as z remains in the workpiece and are heated due to conduction of heat into the workpiece as they pass below the cutting edge. • The above factors cause maximum tool temperature to occur at some distance away from the cutting edge. Effect of the High Cutting Temperature on Tool and Job The high temperature in machining zone is harmful for both the tool and the job. The major portion of the heat is taken away by the chips. But it does not matter because chips are thrown out. So attempts should be made such that the chips take away more and more amount of heat leaving small amount of heat to harm the tool and the job. Effect of cutting temperature on the tool: 1- Rapid tool wear, which reduces tool life. 2- Plastic deformation of the cutting edges if the tool material is not enough hot-hard . 3- Chipping of the cutting edges due to thermal stresses. 4- Built-up edge formation.Effect of cutting temperature on the machined job: 1. Dimensional inaccuracy of the job due to thermal distortion and expansion-contraction during and after machining. 2. Surface damage by oxidation, rapid corrosion, burning etc. 3. Excessive temperature rise can induce metallurgical changes in the machined surface, adversely affecting its properties 4. Induction of tensile residual stresses and micro-cracks at the surface / subsurface. Factors Affecting the heat generation in Cutting Zone The following factors influence the cutting temperature: 1- Machining parameters > Speed > Feed rate > Depth of cut 2- Properties of workpiece material > Hardness > Strength 3- Tool geometry > Rake angle > Clearance angle > Nose radius 4- Cutting fluids 5- Built-up-edgeTHANK YOU Department of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I / Lecture No: 8 (Cutting fluid)Cutting Fluids • Need: During machining process, friction between work-tool and chip-tool interfaces causes high heat generation which results high temperature in machining zone. The effect of this generated heat decreases tool life, increases surface roughness and decreases the dimensional accuracy of work material. This case is more important when machining of difficult-to-cut materials, when more heat would be observed. Due to this reason, most machining operation is carried out in the presence of a cutting fluid. Functions of a cutting fluid 1- Lubrication: Lubrication at the chip–tool and tool-work interface to reduce friction force and thus the amount of heat generation. Lubrication of cutting zone is very important at low cutting speeds. 2- Cooling: Cooling of the job and the tool to reduce the detrimental effects of cutting temperature on the job and the tool. The cooling of the workpiece is very important at high cutting speeds. 3- Cleaning: Cleaning the machining zone by washing away the chip – particles and debris which, if present, spoils the finished surface and accelerates damage of the cutting edges. 4- Corrosion Protection. A thin layer of the cutting fluid sticks to the machined surface and thus prevents it from harmful atmospheric gases like SO2, O2, NxOy present in the atmosphere.Principles of cutting fluid action The chip-tool contact zone is usually comprised of two parts; plastic or bulk contact zone and elastic contact zone as indicated in Fig. Principles of cutting fluid action..................... • The cutting fluid cannot penetrate or reach the plastic contact zone but enters in the elastic contact zone by capillary effect. With the increase in cutting velocity, the fraction of plastic contact zone gradually increases and covers almost the entire chip-tool contact zone. Therefore, at high speed machining, the cutting fluid becomes unable to lubricate and cools the tool and the job only by bulk external cooling. • The chemicals like chloride, phosphate or sulphide present in the cutting fluid chemically reacts with the work material at the chip under surface under high pressure and temperature and forms a thin layer of the reaction product. The low shear strength of that reaction layer helps in reducing friction.Essential properties of cutting fluids: • It should have high thermal conductivity and specific heat. • Have low viscosity and molecular size (to help rapid penetration into the chiptool interface). • Should have good spreading and wetting ability. • Friction reduction at extreme pressure and temperature. • Chemical stability, non-corrosive to the tool and work materials. • Odourless and also colourless. • Non toxic in both liquid and gaseous stage. • Easily available and low cost. Types of Cutting Fluid: Generally, cutting fluids are employed in liquid form but occasionally also employed in gaseous form. Only for lubricating purpose, often solid lubricants are also employed in machining and grinding. The cutting fluids, which are commonly used, are: 1. Compressed air 2. Water 3. Straight oils (or neat oils) 4. Water Soluble oils ( or soluble oils) 5. Synthetic oils (chemical fluid) 6. Solid or semi-solid lubricant• Compressed Air: Machining of some materials like grey cast iron become inconvenient or difficult if any cutting fluid is employed in liquid form. In such case only compressed air is recommended for cooling and cleaning purpose. • Water: For its good wetting and spreading properties and very high specific heat, water is considered as the best coolant and hence employed where cooling is most urgent. • Straight Oils: These fluid composed of a base petroleum oil or vegetable oils with extreme pressure additives of chlorine, sulphur and phosphorus. Straight oils provide the best lubrication and the poorest cooling characteristics among all the cutting fluids. These fluids are used where cutting speed is very low, feed and depth of cut is high. • Water Soluble Oils: (water + mineral oil + emulsifier agent + rust inhibitor agent and EPA). These oils are used in diluted form and provide good lubrication as well as cooling performance. Soluble oils are widely used in industry. Water....................Provides cooling Mineral oils...........Provides lubricity Emulsifier..............Breaks oil into small globules Rust inhibitor....... Since water can cause rusting • Synthetic Oils: Synthetic Fluids contain no petroleum or mineral oils. These oils are formulated from alkaline inorganic and organic compounds along with EPA additives for corrosion inhibition. Synthetic fluids provide the best cooling performance among all cutting fluids but limited lubricity. • Solid or semi-solid lubricant: Paste, waxes, soaps, graphite, Moly-disulphide (MoS2) may also often be used as cutting fluids.Cutting Fluid Application Methods The effectiveness and expense of cutting fluid application significantly depend also on how it is applied in respect of flow rate and direction of application. In machining, depending upon the requirement and facilities available, cutting fluids are generally employed in the following ways. • Flood Application: In this method tool and workpiece are supplied with high volume of the cutting fluids which are generally in liquid condition. • Jet Application: In this method the cutting fluids which may be either gas or liquid are applied with high pressure on the tool and workpiece. • Mist (atomised) Application: In this method cutting fluid is atomised by a jet of air and the mist is directed at the cutting zone. This method gives maximum cooling effect.THANK YOU Department of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I / Lecture No: 9 (Cutting tool materials)Cutting Tool Materials • Since machining is accomplished by the deformation of work material and so cutting tool is subjected to : High temperatures High contact stresses Rubbing along the chip-tool and tool-work interface. • Under these condition, the stability of geometric form (or shape) of the tool is key factor. Thus, the cutting tool must provide the maximum resistance to any tendency of alteration of its geometric form. To achieve this, the cutting tool material must be properly selected. Desirable properties of cutting tool material The cutting tool materials must possess a number of important properties to avoid excessive wear, fracture failure and high temperatures in cutting. The following characteristics are essential for cutting materials to withstand the heavy conditions of the cutting process and to produce high quality and economical parts: 1- High Hardness 2- Hot hardness (or Red hardness ) 3- Toughness 4- Wear resistance 5- Low friction 6- High thermal conductivity and specific heat 7- Chemical stabilityHigh Hardness: A cutting tool material must have higher hardness than that of the workpiece material being machined, so that it can penetrate into the work material. Hot hardness: It is defined as ability to retain hardness at elevated (high) temperatures in view of the high temperatures existing in the cutting zone. Thus, the tool retains its shape and sharpness. This requirement becomes more and more important when machining under high cutting speeds to increase the production rate. Diamond is having the highest hot hardness. Ceramics also maintain their hardness at high temperatures. While carbon tool steels rapidly begin to lose their hardness at moderate temperatures (cannot be used at high speeds Æ high temperatures). Toughness: Toughness is a resistance to shock or impact forces. Higher the toughness, more shock load material can withstand. It is desired so that impact forces on the tool encountered repeatedly in interrupted cutting operations (such milling) do not chip or fracture the tool. Wear resistance: It is the ability of material to resist wear. Wear resistance depends on hardness as well as undissolved carbides. It is desired so that an acceptable tool life is obtained before the tool has to be replaced. Low friction: The coefficient of friction between the tool and work should be low. This will lead to improve the surface finish, reduction in frictional heat generation and absorbs less cutting energy. High thermal conductivity and specific heat: These properties ensure rapid dissipation of heat generated during cutting process, thus avoid softening of the cutting tool material and improves its life.Chemical stability: A cutting tool material should be chemically stable with respect to the work material and cutting fluid, so that any adverse reaction contributing tool wear are avoided. Types of Cutting Tool Material • The demand for higher productivity has led to the development of a variety of cutting tool materials with vastly improved properties. Each stage of development has facilitated the use of higher cutting speeds. No one cutting material is best for all purposes. No tool material has been able to fully replace the older one since each one of them has a unique combination of properties. The following cutting tools materials are still in use are: 1- High carbon steel 2- High speed steel 3- Cemented Carbides 4- Ceramics 5- Cubic boron nitride (CBN) 6- DiamondHigh Carbon Steel • This is the oldest material used for making cutting tools is much less used today. It contains 0.8 – 1.2% carbon and some very small alloy additions such as manganese, tungsten, molybdenum, chromium and vanadium. • These steel have very good hardenability and wear resistance at low temperature. The major disadvantage of these cutting tool materials is their inability to withstand high temperature. • Beyond 200ºC they lose their hardness and become soft. Therefore, they are useful only for very low cutting speeds (about 0.15 m/s). Due to this, high carbon steel mainly used with low temperature generating operations or machining of the soft materials such as wood, magnesium, brass and aluminium etc. High Speed Steel • These steel are called high speed steel because they can cut metal at three to five times higher speeds than that can be done by the high carbon steel. They can retain their hardness up to about 650ºC. • These are carbon steel with major alloying elements such as tungsten, molybdenum, chromium, vanadium and cobalt. • Toughness of HSS is highest among all the cutting tool materials. Thus they are extensively used in interrupted cutting such as milling. HSS also used for making drill, reamer, milling cutter, single point cutting tool etc.Cemented Carbides • Three group of cutting tool materials just described (high carbon steel, HSS and cast-cobalt alloys) possess the necessary toughness, impact strength and thermal shock resistance. But, still these materials are limited in their hot hardness, wear resistance and strength. Consequently, they cannot be used very effectively where high cutting speeds (and therefore high temperature) are required. To meet the challenge of higher speeds for higher production rates, cemented carbides were developed around 1930 in Germany. • Cemented carbide tool consists of carbide particles (carbides of tungsten and titanium) bound together in a cobalt matrix by powder metallurgy process. • The two groups used for machining are : 1- Tungsten carbide 2- Titanium carbide Ceramics • Ceramics are inorganic compounds, and usually made either of oxides, carbides, or nitrides. The following ceramic materials used as cutting tool material: 1- Aluminium Oxides (Al2O3) or alumina 2- Silicon Carbides (SiC) 3- Silicon Nitrides (Si3N4) 4- Titanium Carbide 5-Titanium Oxides Properties: • Ceramic cutting tools are harder and more heat-resistant than carbides tools, but more brittle. • They can withstand very high temperatures, due to which the cutting edge retains its hardness almost up to 1200ºC. • They have higher wear resistance than other cutting tool materials. • They are chemically more stable than carbides.• Cubic boron nitride (CBN): Cubic boron nitride is the second hardest material available for machining purpose. It is not a natural material, it is produced in laboratory. • CBN mainly used as coating material. But cubic boron nitride tools are also made in small sizes without a carbide insert. • Diamond: Diamond is the hardest known material that can be used as cutting tool material. Diamond tools are available as insert. Diamonds are suitable for cutting very hard materials like glass, ceramics and other abrasive materials. Use is limited because it gets converted into graphite at high temperature (700 °C). Graphite diffuses into iron and makes it unsuitable for machining steels. • The curve shows that: > High speed steel is much better than carbon tool steel (high carbon steel). > Cemented carbides and ceramics are significantly harder at elevated temperatures.THANK YOU Department of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I / Lecture No: 10 (Tool life)Tool Life • During machining, the cutting edge of the tool gradually wears out and it does not perform satisfactorily. When the wear reaches a certain stage, it is said that the tool has lost its utility and its life is over. It must be reground or replace by a new tool if machining is to be continued. > The time interval during which a cutting tool performs given function satisfactorily is called tool life. > Flank wear generally considered as the decisive factor to measure the tool life. > However, at higher cutting speed, crater wear also used as tool failure criterion. • Measuring tool life: There are various ways in which tool life can be specified. > Actual cutting time to failure. > Length of work cut to failure. > Volume of metal removed to failure. > Number of components produced to failure. Taylor's equation of tool life • Wear and hence tool life of any tool for any work material is governed mainly by the level of the machining parameters i.e., cutting velocity, feed, and depth of cut . Cutting velocity affects maximum and depth of cut minimum. • Taylor gave the relation between cutting speed and tool life. That is: Where V= cutting speed(m/min) T=tool life(in minutes) C=machining constant n= Tool life exponent(it depends on tool material)Parameters Affecting Tool Life 1-Cutting conditions > Speed > Feed > Depth of cut 2- Tool geometry > Rake angle > Clearance angle > Nose radius 3- Tool material Hardness Wear resistance Thermal conductivity 4- Work material 5- Cutting fluid 6- Built-Up-Edge Effect of cutting conditions on tool life 1- Speed: The tool life decreases with the increase in cutting speed. This is because; temperature in the cutting zone increases with increase in cutting speed, which makes the tool soft. Higher cutting temperature also increases the rate of abrasive, adhesive, and diffusion wear. 2- Feed: Tool life decreases with increase in feed rate. This is because cutting force increases with the increase in feed rate. Due to increase in cutting force, temperature in cutting zone increases and finally tool life decreases. 3- Depth of Cut: Tool life decreases with increases in depth of cut. This is because, as the depth of cut increases, the chip-tool contact area and cutting force increases which rises the temperature due to increasing frictional heat.Tool Life Criteria The following are some of the possible tool life criteria that could be used for limiting tool life. Direct Criteria (based on tool wear). • Wear land size • Crater depth and width. • Total destruction of the tool Indirect Criteria (based on effects of a worn tool). • Limiting value of surface finish. • Limiting value of change in component dimensions. • Limiting value of increase in cutting force. Wear land size: Wear land size on the flank face of the tool is widely used criteria to assess tool life. When the wear land reaches a critical value, cutting becomes difficult and tool leaves rough marks on the machined surface. Under this condition it is said that life of the tool is over. The length of wear land is not of uniform. It is larger near the two ends of the active portion of the side cutting edge. The maximum width of the wear land is at the rear end of the flank face. The tool life values as suggested by ISO are: VB = 0.3 mm, if the flank is regularly worn in zone B VB max = 0.6mm, if the flank is irregularly worn in zone BCrater depth and width: At high speeds and feeds crater wear is more, therefore, it is also used as tool life criteria. Since, larger the depth of crater, weaker is the tool. According to ISO recommendation, the maximum allowable crater depth can be given as: KT = 0.06 + 0.3f (f = feed in mm/rev) Total destruction of the tool: Tool destruction occurs when the tool is unable to support the cutting force over the tool-chip contact area and results in fracture of small part of cutting edge. It is Common in interrupted cuts and in non rigid setups. Limiting value of surface finish: According to this criterion, the surface is continuously monitored and RMS values of surface roughness are compared with the limiting value. Whenever, the measured value of the surface roughness exceeds the limiting value, the tool is said to have failed and must be reground. Limiting value of change in component dimensions: In this method, the dimensions of the each component are measured. When the dimensional accuracy falls below a limiting value, the tool is said to have failed. Limiting value of increase in cutting force: The change in cutting force is measured with the help of a tool dynamometer or power meter. If the cutting force increases beyond a limiting value, the tool is said to have failed.THANK YOU Department of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I / Lecture No: 11 (Tool wear)Failure of Cutting Tools • The success of machining process depends on the sharpness of the tool. The use of a blunt tool results in a large power consumption and poor surface finish. • When a cutting tool unable to cut, consuming large power, and cannot produce an acceptable surface finish, it is considered to have failed. The failure of a cutting tool may be due to one or a combination of the following modes: 1- Plastic deformation of the tool. > Plastic deformation of the tool occurs due to high temperature and stresses. 2- Mechanical breakage of the tool. > Mechanical breakage of the tool occurs due to large forces and shocks. The other factors are insufficient strength and toughness of the tool material. 3- Progressive or gradual wear failure. >The progressive wear makes the tool blunt. It occurs due to relative sliding between two surfaces. • The plastic deformation and mechanical failure can be prevented by proper selection of cutting tool material, tool geometry and cutting conditions. • But failure by gradual wear cannot be prevented but can be slowed down only to enhance the service life of the tool.Progressive Tool Wear • The wear is generally defined as loss of material from surfaces. The wearing action takes place on those surfaces along which there is a relative sliding with other surfaces. Thus, the wear takes place on the rake face where the chip flows over the tool. The wear also takes place on the flank face where rubbing between the work and tool occurs. Types of progressive tool wear: The progressive wear of a cutting tool takes place into distinct ways: 1- Crater wear (measured in terms of the “depth of crater”) 2- Flank wear (measured in terms of the “length of the wear land”) Crater Wear: Crater wear occurs on the rake face of the tool due to relative sliding between rake face and chip. In orthogonal cutting this typically occurs where the tool temperature is highest > Diffusion process is mainly responsible in the development of crater wear. • Flank Wear: Flank wear occurs on the flank face of the tool, due to rubbing between flank face and machined surface. It modified the tool geometry and changes the cutting parameters (depth of cut). > The abrasion and adhesion are primarily responsible for the flank wear. > Flank wear directly affects the surface finish produced. Thus there is always a close limit kept on the value of the wear land.Progressive tool wear workpiece tool crater wear flank wear chip Tool Wear Mechanisms: • Under high temperature, high pressure, high sliding velocity and mechanical or thermal shock in cutting area, cutting tool has normally complex wear mechanism. A number of wear mechanisms have been proposed to explain the tool wear phenomenon. These mechanisms are: 1- Abrasion wear 2- Adhesion wear 3- Diffusion wear 4- Oxidation wear 5- Chemical decomposition 6- Chipping (or Thermal fatigue wear)• Abrasion wear: Abrasion wear occurs when hard particle of the chip material abrading (rubbing) the tool surface. The rate of wear depends on the relative hardness of the contacting surfaces, as well as mating geometries. • This is a mechanical wear, and it is the main cause of the tool wear at low cutting speeds. • Adhesion wear: Under high pressure and temperature when two surfaces come in close contact, strong metallic bonds are formed due to welding of the surface asperities. The spot weld results in an irregular flow of chips over the tool face. Sliding of chip causes the fracture of these small weld joints and some tool material carried along with them. Adhesive wear can be reduced by using a suitable cutting fluid which can provide a protective film on the contacting surfaces.• Diffusion wear: Diffusion wear means the material loss due to diffusion of atoms of the tool material into the workpiece moving over it. Requirements for diffusion wear are metallurgical bonding of the two surfaces so that atoms can move freely across the interface and high temperature. • Oxidation wear: Oxidation is the result of a chemical reaction between the tool surface and oxygen at high temperature. It forms a layer of oxides on the surface. When this layer is destroyed during the cutting process by abrasion, another layer begins to form. Tool wear takes as this removal and formation of the corrosive layer is repeated. • Chemical decomposition: This type of wear occurs due to interaction between the tool and work material in the presence of chemicals (cutting fluid). • Chipping: Chipping means breaking away of a small metal piece from the cutting edge of the tool. The chipped piece may be very small or may be relatively large. Unlike gradual wear, chipping results in a sudden loss of tool material and a corresponding change in shape, and has a major detrimental effect on surface finish and dimensional accuracy of the workpiece.• The two main cause of chipping are Mechanical Shock (impact due to interrupted cutting, as in milling) Thermal Fatigue (cyclic variations in temperature of the tool in interrupted cutting). Variables Affecting Tool Wear The important parameters which affect the tool wear are: 1-Cutting conditions > Speed > Feed > Depth of cut 2- Tool geometry > Rake angle > Clearance angle > Nose radius 3- Tool material > Hardness > Wear resistance > Thermal conductivity 4- Work material 5- Cutting fluid 6- Built-Up-EdgeTHANK YOU Department of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I / Lecture No: 12 (Machinineability)Machineability • It is already known that pre-formed components are essentially machined to impart dimensional accuracy and surface finish for desired performance and longer service life of the product. • It is attempted to accomplish machining effectively, efficiently and economically as far as possible by removing the excess material smoothly and speedily with lower power consumption, tool wear and surface deterioration. But this may not be always and equally possible for all the work materials and under all the conditions. • The machining characteristics of the work materials widely vary and also largely depend on the conditions of machining. A term; ‘Machinability’ has been introduced for gradation of work materials w.r.t. machining characteristics. Machineability….. • A term; ‘Machineability’ has been introduced for gradation of work materials w.r.t. machining characteristics or machining properties . • It is defined as “ easy to machine”. • A material is said to have good machineability if; > The tool wear is low > The metal removal rate is high (or high cutting speed) > The surface finish produced is good > Power consumption is low > Good dimensional accuracy > Formation of small chipsCriteria’s for judging Machineability • For judging the machineability, the criteria to be chosen depends on the type of operation and production requirements. The following criteria may be considered for judging the machineability of a metal. 1- Tool life criteria (or tool wear criteria) 2- Surface finish criteria 3- Power consumption criteria 4- Production rate criteria 5- Chip forms • But practically it is not possible to use all those criteria together for expressing machineability. Tool Life Criterion: • When tool life criterion is used, machinability is expressed in terms of ‘cutting speed’for given tool life. • A material with higher cutting speed for a given tool life will have better machinability. • In this method, the effect of surface finish is not accounted. This is most widely used criterion for assessing machinability of a material. Assessing machinability: For assessing machinability, a common material (free steel) is chosen as a standard and the machineability of the other materials is compared and expressed as a machinability index or machinability rating. Let , Vs = Cutting speed of standard material for a given tool life (T). V m = Cutting speed of the test material for same given tool life (T).• Than the machinability Index (MI) can be calculated as: • Thus, a material with higher cutting speed for a given tool life will have greater machinability. • Surface Finish Criterion: This criterion is used in a situation where poor surface finish is the cause of rejection on machined parts. A material that produces better surface finish under a given set of conditions may be considered to have better machinability. Some materials may permit use of higher cutting speed or lower cutting forces but give poor surface finish. In such situations, the surface finish criterion is important. • Power Consumption Criterion: The power consumption during machining is related to the cutting force. Higher the cutting force, the greater is the power consumption. The material requiring higher cutting forces will have lower machinability. • Production Rate Criterion: The metal removal rate is directly related to the cutting speed, and hence, production rate. For given surface finish and tool life, if a material permits high cutting speeds or higher metal removal rate will have higher machinability.Parameters Affecting Machineability The important parameters which affect the machineability are: 1-Cutting conditions > Speed > Feed > Depth of cut 2- Tool geometry > Rake angle > Clearance angle > Nose radius 3- Tool material Hardness 4- Work material (Hardness, Toughness) 5- Cutting fluid THANK YOUDepartment of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-I / Lecture No: 13 (Machine tool vibration and surface finish) Machining tool vibration • Introduction: Machine tool structures are multi-degree-of-freedom systems and always subjected to vibration during machining. Vibrations during a cutting operation affect the accuracy of the machining, which in turn affects the surface finish and dimensional accuracy. Severe noise is also an important factor which is induced by tool holder vibrations. • The cutting process with variable feed is one of the principles cause of arising of vibrations. That results in the variable dynamic cutting force. • These vibrations affects the machine tool, quality of work-piece, cutting tool and the cutting conditions (feed rate, depth of cut, and cutting velocity.Effect of Vibration The vibration of machine tools during cutting, affects • Life of machine tool , particularly transmission elements • Life of the cutting tool • Quality of the workpiece • Cutting conditions Effect of vibrations on life of machine tool: The machine tool is made of various parts and when vibrations are produced, they also start vibrating at same frequency. If this frequency approaches the natural frequency of vibration of that part then amplitude of vibrations will be very excessive and the part may break even. • Effect of vibrations on life of the cutting tool: As the tool-life is a function of the cutting variables only, the tool-life is greatly affected by presence of vibrations in machine tools. It is found out that the tool life is decreased by about 70—80% of the normal value if vibrations are present. • Effects of vibrations on work-piece: Due to presence of vibrations the surface finish obtained will be very poor and thus this aspect is very important for fine finishing operations of grinding and boring etc. • Due to vibrations, the dimensional accuracy and geometrical accuracy of the job is also affected.• Effect of vibrations on cutting conditions: > Due to presence of vibrations in machine tools, the chip thickness as removed by the cutting tool does not remain constant and so the cutting forces also vary. > Also due to vibrations, vibratory displacement of tool takes place in the direction of motion of the job which results in the chatter of tool. > The penetration rate also varies and therefore penetration force does not remain constant. Further due to vibration of the tool, cutting velocity does not remain constant and it varies about the correct value. Sources of Vibrations Machine tools operate in different configurations (positions of heavy parts, weights, dimensions, and positions of work pieces) and at different regimes (spindle rpm, number of cutting edges, cutting angles, etc.). Due to this machine tool and cutting tool are always subjected to vibration. These vibrations are due to one or more of the following causes: 1. In-homogeneities in the workpiece material. 2. Variation of chip cross section area 3. Disturbances in the workpiece or tool drives. 4. Dynamic loads generated by acceleration/deceleration of moving components. 5. Intermittent cutting. 6. Self-excited vibration .• Vibration Due to in homogeneities in the Work piece: Hard spots or a crust in the material being machined impart small shocks to the tool and work piece, as a result of which free vibrations are set up. When machining is done under conditions resulting in discontinuous chip removals, the segmentation of chip elements results in a fluctuation of the cutting thrust. If the frequency of these fluctuations coincides with one of the natural frequencies of the structure, forced vibration of appreciable amplitude may be excited. • Vibration Variation of chip cross section area: Variation in the crosssectional area of the removed material may be due to the shape of the machined surface or to the configuration of the tool. In both cases, pulses of appreciable magnitude may be imparted to the tool and to the work piece, which may lead to undesirable vibration. Disturbances in the workpiece or tool drives: Unbalance and disturbances in the drives caused due to rotating unbalanced masses, faulty arrangement of drive and fault in the supporting bearings. Dynamic loads generated by acceleration/deceleration of moving components: In dynamically stable system, the amplitude of vibration keeps on decaying with time whereas in dynamically unstable system, it exponentially increases with time Intermittent cutting: Intermittent cutting as in milling. Due to it, forced vibrations may be generated due to elastic nature of system. Self-excited vibration: Self-excited vibration or chatter due to the interaction of cutting process and machine tool dynamicsVibration Control in Machine Tools • The tolerable level of vibration between tool and workpiece, i.e., the maximum amplitude and to some extent the frequency, is determined by the required surface finish and machining accuracy as well as by detrimental effects of the vibration on tool life and by the noise which is frequently generated. The vibration behavior of a machine tool can be improved by: > Rigidify the workpiece, the tool and the machine as much as possible > Choose the tool that will excite vibrations as little as possible (modifying angles, dimensions, surface treatment, etc.) > Choose exciting frequencies that best limit the vibrations of the machining system (spindle speed, number of teeth and relative positions, etc.) > Choose tools that incorporate vibration-damping technology. Surface finish & its importance • Functioning of machine parts, load carrying capacity, tool life, fatigue life, bearing corrosion, and wear qualities of any component of a machine have direct relation with its surface texture. Therefore, these effects made the control of surface texture very important. • The root of any surface irregularity acts as sharp corner and such part fails easily. • Thus in order to increase the life of any part which is subjected to fatigue loading, the working and non-working surfaces of that part must be given very good finish.Importance of surface finish • It improves the service life of the components • Better surface finish improves the fatigue strength of the component. • It reduces initial wear of parts due to increased surface to surface contact. • It gives close dimensional tolerance on the parts • It reduce corrosion by minimizing depth of irregularities • It give good surface texture. THANK YOUDepartment of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-II / Lecture No: 14 (Lathe Operations) Introduction to the Lathe • The lathe is a very useful and versatile machine tool and is capable of performing a wide range of machining operations. • The workpiece is held by a chuck in one end and when possible also by a tailstock at the opposite end. The chuck is mounted on a headstock, which incorporates the engine and gear mechanism. The chuck is holding the workpiece with three or four jaws and a spindle engine causes the chuck and workpiece to rotate. • A tool-post is found between the headstock and tailstock, which holds the cutting tool. The tool-post stands on a cross-slide that enables it to move along the workpiece. An ordinary lathe can accommodate only one cutting tool at the time, but a turret lathe is capable of holding several cutting tools on a revolving turret.Types of Lathe 1-Engine Lathe 2- Bench Lathe 3- Automatic Lathe 4- Turret Lathe 5- Computer Controlled Lathe • Engine Lathe : The most common form of lathe, motor driven and comes in large variety of sizes and shapes. • Bench Lathe: A bench top model usually of low power used to make precision machine small work pieces.• Automatic Lathe: A lathe in which the work piece is automatically fed and removed without use of an operator. • Turret Lathe: Lathe which have multiple tools mounted on turret either attached to the tailstock or the cross-slide, which allows for quick changes in tooling and cutting operations. • Computer Controlled Lathe: A highly automated lathe, where both cutting, loading, tool changing, and part unloading are automatically controlled by computer coding.Lathe Operations • Turning: To produce straight, conical, curved, or grooved work pieces . • Facing: To produce a flat surface at the end of the part or for making face grooves. • Drilling: To produce a hole by fixing a drill in the tailstock • Boring: To enlarge a hole or cylindrical cavity made by a previous process or to produce circular internal holes. • Reaming : It is used for finishing internal diameter of holes. • Threading: To produce external or internal threads • Knurling: To produce a regularly shaped roughness on cylindrical surfaces • Parting: To cut a piece in to two or more pieces. • Forming : To generate specific geometry on work surface. • Chamfering: Chamfering is the operation of beveling the extreme end of a workpiece. Chamfering is an essential operation before thread cutting so that the nut may pass freely on the threaded workpiece. Turning OperationFacing Operation Drilling OperationBoring Operation Reaming OperationThreading Operation Knurling OperationParting operation Forming OperationChamfering Operation THANK YOUDepartment of Mechanical Engineering Subject: Manufacturing Science & Technology-II (RME-503) Faculty: Mr. Brijesh Kumar Unit-II / Lecture No: 15 (Shaper, planner, slotter) Shaper Machine • Introduction: Shaper is a machine tool that uses reciprocating straight line motion of the tool and a perpendicular feed of the job or the tool to produce flat work surfaces. The shaper is used primarily for: 1. Producing a flat or plane surface which may be in a horizontal, a vertical or an angular plane. 2. Making slots, grooves and keyways 3. Producing contour of concave/convex or a combination of these. • Features: 1- Single point cutting tool is used for machining. The tool is clamped on the tool post mounted on the ram of the machine. 2- The ram reciprocates to and fro, tool cuts the material in forward stroke only, no cutting during return stroke. 3- It uses linear relative motion between the tool and workpiece. 4- The cross-feed is provided by the machine table on which workpiece is fixed.Working Principle: The job is rigidly fixed on the machine table. The single point cutting tool held properly in the tool post is mounted on a reciprocating ram. The reciprocating motion of the ram is obtained by a quick return motion mechanism. As the ram reciprocates, the tool cuts the material during its forward stroke. During return, there is no cutting action and this stroke is called the idle stroke. The forward and return strokes constituteone operating cycle of the shaper. Construction of shaper The main parts of the shaper are: 1- Base 2- Column 3- Ram 4- Table 5- Cross rail 6- Tool head• Base: The base is a heavy cast iron casting which is fixed to the shop floor. It supports the body frame and the entire load of the machine. The base absorbs and withstands vibrations and other forces which are likely to be induced during the shaping operations. • Column: It is mounted on the base and houses the drive mechanism compressing the main drives, the gear box and the quick return mechanism for the ram movement. • Ram: It is the reciprocating member with tool head mounted on its front face. The ram is connected to with the quick-return mechanism housed inside the hollow of the column. The back and forth movement of ram is called stroke and it can be adjusted according to the length of the workpiece to bemachined. • Table: The worktable of a shaper is fastened to the front of the column. The table moves across the column on crossrails to give the feed motion to the job. • Cross rail: The cross rail is mounted on the front of the body frame and can be moved up and down. The vertical movement of the cross rail permits jobs of different heights to be accommodated below the tool. • Tool Head- It holds the cutting tool and is fastened to the front of the ram. Crank and slotted link mechanism • Slotted link mechanism is very common in mechanical shapers. • It converts the rotary motion of the electric motor into the reciprocating motion of the ram. The return stroke allow the ram to move at a faster rate to reduce the idle time which is known as “quick return mechanism”, reduces the time waste during return stroke. • Bull gear is driven by a pinion which connects to the motor shaft through gear box. • The bull wheel has a slot. The crank pin A secured in to this slot, at the same time it can slide in the slotted crank B.Crank and slotted link mechanism • As the bull gear rotates causes the crank pin A also to turn and side by side slides through the slot in the slotted crank B. • This makes the slotted crank to oscillate about its one end C. • This oscillating motion of slotted crank (through the link D) makes the ram to reciprocate. • The intermediate link D is necessary to accommodate the rise and fall of the crank.Principle of Quick Return Mechanism • When the link is in position AP1, the ram will at extreme backward position of stroke. • When the link position is at AP2, the extreme forward position ram will have been reached. • AP1 and AP2…….Tangent to the crank pin circle. • Forward cutting stroke takes place when the crank rotates through an angle C1KC2. • Return stroke ……the crank rotates through angle C1LC2 • It is seen that C1KC2 > C1LC2 • The angular velocity of crank pin remains constant.Planer Machine • Like shaping machines, planning machines are also basically used for producing flat surfaces in different planes. A planer is generally used for machining large workpieces which cannot be held in a shaper.
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