Hard Turning (Newer) (Machining Process) (Better)
A special case of turning is hard turning, in which hard metals are finish machined using ceramic or polycrystalline tools. This process is sometimes used in place of rough turning, hardening and finish grinding for parts made of tool steels, alloy steels, case hardened steels and various hard irons. Very fine finishes and tolerances can be produced by this process and in some cases part quality is better than can be optained with grinding because intermediate chucking operations and associated setup errors are eliminated. In appropriate applications, hard turning also requires less capital invesment, removes material more rapidly, and raises fewer enviromental concerns than grinding. Hard turning become possible with the advent of hot-pressed ceramic and especially polycrystalline cubic boron nitride (PCBN) tools. Hard turning also requires high machine and toolholder rigidity, and strong insert shapes (negative rakes, large wedge angles and special edge preparations such as chamfers. Modern CNC lathes usually have adequate rigidity for hard turning.(D. Stephenson, J. Agapiou, Metal Cutting Theory and Practice, pg.20)
Hard Turning (25.03.2011 01:23) (older)
The clear attraction to hard turning (Figure 1.8) is the possibility of eliminating grinding operations. However, for many shops, the process of repeatedly turning parts that are harder than 45 HRC to grinding-level accuracies is still unclear. Moreover, the economics of such a process is not well understood as efficiency of the process and cost per unit depend on many parameters, varying from one shop to another. A properly “dialed-in” hard-turning process can deliver surface finish of Ra 0.4 – 0.8 μm, roundness of 2–5 μm, and diameter tolerance of ±3–7 μm. Such performance can be achieved on the same machine that “soft” turns the part prior to hardening, maximizing equipment utilization. However, some shops misstep by initially using the wrong (that is, less expensive) tool insert for the application. Others may not be sure if their machine possesses the rigidity to handle the highly dynamic thrust component of the cutting force that can be twice that of a typical turning operation.
Though a material of hardness 47 HRC is hard turning’s starting point, hard turning is regularly performed on parts of hardness 60 HRC and even higher. Commonly hard-turned materials include tool, bearing, and case-hardened steels. Although Inconel, Hastelloy, Stellite, and other exotic materials are often considered as falling in the category of hard turning [34], it is not correct as their hardness is much less than 47 HRC and thus the mechanism of chip formation and process requirements including tool materials are considerably different.
(Davim J. P.,Machining of Hard Materials, 2011, p. 15)
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Shape Deposition Manufacturing (SDM) (older)
Shape Deposition Manufacturing (SDM) is a layer manufacturing technology in which the layers are shaped by CNC. Thus, it is an additive- cum-subtractive process. A temporary material is used for building support cum-subtractive process. A temporary material is used for building support layers needed for overhanging, undercut, and disjoint features. The technology is capable of creating multi-material objects, functionally graded materials, and objects with embedded sensors, advance tooling, and other electronic devices. (Rapid Prototyping, Venuvinod, p.300)
Shape Deposition Manufacturing (SDM) (Newer) (Better) (Manufacturing Technology)
SDM is a sloid freeform fabrication process which systematically combines material depositiıon with material removal processes. The purpose of the process is to anable the rapid manufacture of high-quality, functional parts and complex designs which couldn't be practically fabricated with conventional manufacturing process, and to take advantage of the vast, existing CNC milling machine infrastructure throughout the world by creating SFF processes which can be implemented by simply adding deposition apparatus to CNC machines.
Most SFF systems are based upon a material additive, layered manufacturing paradigm. CAD Models are first decomposed into thin 2-1/2D cross-sectional layer representations, then physical parts are built up in custom fabrication machines, layer-by-layer, using material additive processes. Layers of sacrifical structures are simultaneously built up to fixture and support the groving shapes. While layered manufacturing facilitates rapid prototyping of arbitrarily complex shapes, the resulting surface finish and accuracy, which are critical factors for being able to fabricate functional parts, can be compromised by the discretization process. High accuracy and quality surface finishes, required for such applications as custom tooling, precision assemblies and structural ceramics are best achieced with material removal processes such as 3 and 5-axis CNC Milling.
To help address this issue, Shape Deposition Manufacturing (SDM) is a SFF Process which systematically combines the advantages layered manufacturing with the advantages of material removal processes. The basic SDM fabrication methodology is to deposit individual segments of part and support material structure, as near net-shapes, then machined each to net-shape before depositing and shaping additional material. This method takes advantageof the basic SDM Decomposition strategy which is to decompose shapes into segments, or 'compacts', such that undercut features need not be machined, but formed by depositing onto previously deposited and shaped segments. Each compact in each layer is deposited as a near-net-shape using one of several available deposition processes. The thickness of each compact depends not only on the local part geometry, but also on deposition process constraints. After the entire part is built up, the sacrifical support material's removed to reveal the final part. (S. Regalla, Computer Aided Analysis and Design, pg.124)
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Shape Deposition Manufacturing (SDM) (older)
Shape Deposition Manufacturing (SDM) is a layer manufacturing technology in which the layers are shaped by CNC. Thus, it is an additive- cum-subtractive process. A temporary material is used for building support cum-subtractive process. A temporary material is used for building support layers needed for overhanging, undercut, and disjoint features. The technology is capable of creating multi-material objects, functionally graded materials, and objects with embedded sensors, advance tooling, and other electronic devices. (Rapid Prototyping, Venuvinod, p.300)
Shape Deposition Manufacturing (SDM) (Newer) (Better) (Manufacturing Technology)
SDM is a sloid freeform fabrication process which systematically combines material depositiıon with material removal processes. The purpose of the process is to anable the rapid manufacture of high-quality, functional parts and complex designs which couldn't be practically fabricated with conventional manufacturing process, and to take advantage of the vast, existing CNC milling machine infrastructure throughout the world by creating SFF processes which can be implemented by simply adding deposition apparatus to CNC machines.
Most SFF systems are based upon a material additive, layered manufacturing paradigm. CAD Models are first decomposed into thin 2-1/2D cross-sectional layer representations, then physical parts are built up in custom fabrication machines, layer-by-layer, using material additive processes. Layers of sacrifical structures are simultaneously built up to fixture and support the groving shapes. While layered manufacturing facilitates rapid prototyping of arbitrarily complex shapes, the resulting surface finish and accuracy, which are critical factors for being able to fabricate functional parts, can be compromised by the discretization process. High accuracy and quality surface finishes, required for such applications as custom tooling, precision assemblies and structural ceramics are best achieced with material removal processes such as 3 and 5-axis CNC Milling.
To help address this issue, Shape Deposition Manufacturing (SDM) is a SFF Process which systematically combines the advantages layered manufacturing with the advantages of material removal processes. The basic SDM fabrication methodology is to deposit individual segments of part and support material structure, as near net-shapes, then machined each to net-shape before depositing and shaping additional material. This method takes advantageof the basic SDM Decomposition strategy which is to decompose shapes into segments, or 'compacts', such that undercut features need not be machined, but formed by depositing onto previously deposited and shaped segments. Each compact in each layer is deposited as a near-net-shape using one of several available deposition processes. The thickness of each compact depends not only on the local part geometry, but also on deposition process constraints. After the entire part is built up, the sacrifical support material's removed to reveal the final part. (S. Regalla, Computer Aided Analysis and Design, pg.124)
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Sintered Carbide (Hardmetal) (25.03.2011 01:23) (Older) (Machine Tool Material)(Better)
Sintered carbide tools, also known as hardmetal tools or cemented carbide tools are made by a mixture of tungsten carbide micrograins with cobalt at high temperature and pressure. Tantalum, titanium or vanadium carbides can be also mixed in small proportions.
Therefore two main description factors define a hardmetal grade:
- The ratio of tungsten carbide and cobalt. The latter usually ranges from 6 to 12 % and it acts as binder. Cobalt has a high melting point (1493 °C) and forms a soluble phase with tungsten carbide grains at 1275 °C which helps to reduce porosity.
- The grain size, thus micrograin grades include particles smaller than 1 ìm, and submicrograin are smaller than a half of a micron; the smaller the grain, the harder the hardmetal. Hardness increases with the reduction in binder content and tungsten carbide grain size, and vice versa, with values from 600 to 2100 HV.
Hardmetal tools are manufactured in two forms:
- Integral tools: they are manufactured by grinding a raw hardmetal rod, obtaining an endmill, a ball-endmill (Figure 2.3) or a drilling tool. The main advantage is the perfect balance of these rotary tools, but the main disadvantage is their high price, taking into account that only a little and very specific zone of the tool is worn by the cutting process. Several resharping of each tool are possible.
- Inserts: small pads with special geometry made with hardmetal, but they are fixed on toolholders made of steel. Turning tools and big milling discs use this configuration, which implies a rapid substitution of worn inserts.
(Davim J. P.,Machining of Hard Materials, 2011, p. 36)
Sintered Carbide (Hard Metal) (Newer)
Sintered carbides or hard metals belong to the most-widely used class of b P/M materials for high-speed machining and other metal removal operations. This class of tool material, also known as cemented carbides were developed as a replacemebnt for tool steels.
Sintered carbides, also konwn as cemented carbides are tool materials unique to P/M, unlike carbon and tool steels which can be made by conventional methods also. Tungsten carbide was first made by Henri Moissan in 1893 during an attempt to produce artifical diamonds. Karl Schroter developed the first sintered carbide in the early 1920's. The first commercial grade (for wire drawing dies) containing tungsten carbide with 6% cobalt binder was produced and marketed in Germany in 1927 by Fredd Krupp. This grade consisted of tungsten carbide particles embedded in a cobalt matrix, exhibiting very high hardness and wear resistance (from carbides) coupled with high toughness and shock resistance (from cobalt binder phase). Most of the subsequent developments in the hard metals have been modifications of the original grade, principally involving replacement of part or all of the tungsten carbide with other carbides, especially titanium carbide and/or tantalum carbide. This led to the development of the present day multi-carbide cutting tool materials permitting the high-speed machining of steel. The hardness of the carbide is greater than that of most other tool materials at room temperature and ıt has the ability to retain it hardness at elevated temperatures, making very high-speed machining possible. They're also called as hard metals, because of their ability to retain properties under red hot conditions.(Angelo & Subramanian, Powder Metalurgy: Science, technology and Applicatiıons, pg.196)
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Hard Broaching (24 Mart 2011 20:28) (Better) (Older)
In the field of metal cutting for mass production of parts with complex profiles, the broaching operation is the most economical method if high production rates combined with great consistency of machined parts are required. The advantages of broaching are based on its technical principle which includes a multi-toothed tool with cutting edges one after the other and graduated in depth of chip thickness. The profile of a part can be broached in single stroke. Internal broaching is started from a pre-machined hole, while external broaching is to machine a surface profile. Broaching is possible in both directions horizontal and vertical. Cutting motion can be linear or helical.
Two different methods of hard broaching are feasible with this tool configuration:
• hard broaching without defined stock removal: the parts are finish-broached before hardening and hard broaching means only clearing the heat distortion;
• hard broaching with defined stock removal (0.1–0.2 mm diametrical), which requires a corresponding finish of the pre-broaching tool considering the expected heat distortion.
(Machining of Hard Materials, J. Paulo Davim; Page:19)
Hard Broaching (Newer) (Machining)
Typical application of Hard Broaching include finishing of a variety of internal profiles such as prismatic internal profiles, internal gear flanks, multiple key ways, polygons and spline profiles. It has also been reported that a PCBN grade with a high PCBN content can be succesfully used in dry broaching operations, but from the performance point of view (cutting distance is the limitting factor ) cutting speeds are substantially lower than in hard turning (60 to a maximum of 90-100 m/min, versus 300 m/min for hard turning) (J. Paulo Davim, Machining: fundamentals and recent advantages, pg.122)
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Sintered carbides, also konwn as cemented carbides are tool materials unique to P/M, unlike carbon and tool steels which can be made by conventional methods also. Tungsten carbide was first made by Henri Moissan in 1893 during an attempt to produce artifical diamonds. Karl Schroter developed the first sintered carbide in the early 1920's. The first commercial grade (for wire drawing dies) containing tungsten carbide with 6% cobalt binder was produced and marketed in Germany in 1927 by Fredd Krupp. This grade consisted of tungsten carbide particles embedded in a cobalt matrix, exhibiting very high hardness and wear resistance (from carbides) coupled with high toughness and shock resistance (from cobalt binder phase). Most of the subsequent developments in the hard metals have been modifications of the original grade, principally involving replacement of part or all of the tungsten carbide with other carbides, especially titanium carbide and/or tantalum carbide. This led to the development of the present day multi-carbide cutting tool materials permitting the high-speed machining of steel. The hardness of the carbide is greater than that of most other tool materials at room temperature and ıt has the ability to retain it hardness at elevated temperatures, making very high-speed machining possible. They're also called as hard metals, because of their ability to retain properties under red hot conditions.(Angelo & Subramanian, Powder Metalurgy: Science, technology and Applicatiıons, pg.196)
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Hard Broaching (24 Mart 2011 20:28) (Better) (Older)
In the field of metal cutting for mass production of parts with complex profiles, the broaching operation is the most economical method if high production rates combined with great consistency of machined parts are required. The advantages of broaching are based on its technical principle which includes a multi-toothed tool with cutting edges one after the other and graduated in depth of chip thickness. The profile of a part can be broached in single stroke. Internal broaching is started from a pre-machined hole, while external broaching is to machine a surface profile. Broaching is possible in both directions horizontal and vertical. Cutting motion can be linear or helical.
Two different methods of hard broaching are feasible with this tool configuration:
• hard broaching without defined stock removal: the parts are finish-broached before hardening and hard broaching means only clearing the heat distortion;
• hard broaching with defined stock removal (0.1–0.2 mm diametrical), which requires a corresponding finish of the pre-broaching tool considering the expected heat distortion.
(Machining of Hard Materials, J. Paulo Davim; Page:19)
Hard Broaching (Newer) (Machining)
Typical application of Hard Broaching include finishing of a variety of internal profiles such as prismatic internal profiles, internal gear flanks, multiple key ways, polygons and spline profiles. It has also been reported that a PCBN grade with a high PCBN content can be succesfully used in dry broaching operations, but from the performance point of view (cutting distance is the limitting factor ) cutting speeds are substantially lower than in hard turning (60 to a maximum of 90-100 m/min, versus 300 m/min for hard turning) (J. Paulo Davim, Machining: fundamentals and recent advantages, pg.122)
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Preload (Force) (Material Refinment Process)
Preloads may be induced in structures or machine assemblies by forcing two or more parts together or apart (intentionally or unintentionally), then clamping them in such a way that the tension in some parts equlibrates the compression in other parts. A consequence of preloading is that "built-in" stresses are produced within the assembled device, with no externally applied loads. Parts that are preloaded against each other behave as integrated systems of springs in series and/or parallel. Proper preloading has many potential advantages, including elimination of unwanted clearance gaps between parts, increased stiffnesss of machine assemblies and improved fatigue resistance of component parts. Examples of components and/or assemblies that may display significant improvements in performance as a result of proper preloading include bearing assemblies, gear trains, bolted joints, flange-and-gasket seals and springs. Preloading may be used to increase the exial or radial stiffness of rolling element bearings, to eliminate backlash from gear meshes, to avoid seperation of bolted joints subjected to the cyclic loading, to prevent seperation of flange-and-gasket seals under fluctuating loads or pressures and to improve the dynamic response chareacteristics of cyclically loaded assemblies. It's essential to remember, however, that when determing the dimensions of critical cross sections, the "built-in" stresses induced by preloading must always be superposed upon the stresses produced by operational loads. (J. Collins, Mechanical Design of Machine Elements and Machines, pg.224)
Older Version Does Not Exist !!
Preloads may be induced in structures or machine assemblies by forcing two or more parts together or apart (intentionally or unintentionally), then clamping them in such a way that the tension in some parts equlibrates the compression in other parts. A consequence of preloading is that "built-in" stresses are produced within the assembled device, with no externally applied loads. Parts that are preloaded against each other behave as integrated systems of springs in series and/or parallel. Proper preloading has many potential advantages, including elimination of unwanted clearance gaps between parts, increased stiffnesss of machine assemblies and improved fatigue resistance of component parts. Examples of components and/or assemblies that may display significant improvements in performance as a result of proper preloading include bearing assemblies, gear trains, bolted joints, flange-and-gasket seals and springs. Preloading may be used to increase the exial or radial stiffness of rolling element bearings, to eliminate backlash from gear meshes, to avoid seperation of bolted joints subjected to the cyclic loading, to prevent seperation of flange-and-gasket seals under fluctuating loads or pressures and to improve the dynamic response chareacteristics of cyclically loaded assemblies. It's essential to remember, however, that when determing the dimensions of critical cross sections, the "built-in" stresses induced by preloading must always be superposed upon the stresses produced by operational loads. (J. Collins, Mechanical Design of Machine Elements and Machines, pg.224)
Older Version Does Not Exist !!
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