Machine Tooling and Environmental Impact and Issues of Sustainability - Report Example

Materials Engineering Report Machine Tooling Name Course Institution Date Machine Tooling Introduction During machining operations, the selection of a material for use in the operation is important for the success of the operation. This is because the operation being performed requires various specifications that have to be achieved. Selection of a material determines the machinability of the product and the final surface finish. Davis (1995) stated that the composition of the product also determines the type of material for selection of the tool. For instance, some materials like tool steels have high carbide contents and high hardness while others like low alloy construction steels and plain carbon steels have low carbide contents. This implies that the tooling material selected for such products will have to be different. This paper shall present a report on the material selection for machine tooling. It will analyze the various factors that should be considered in selecting the materials along with providing information on the different types of materials for machine tools. Types of materials for machine tooling There are various materials that are used in machine tooling operations. The variety in tooling materials has been brought about by the different specific attributes of the cutting tool material. It is these attributes that make the tool usable in metal cutting. In determining the applicability of a tool cutter, the criteria of performance is based on two factors: these are the toughness of the material and its thermal hardness. The toughness refers to its ability to resist fracture or its ductility. Thermal hardness refers to its ability to resist heat. The materials for cutting tools are categorized into five: High speed steel Tungsten carbide Cermets Ceramics and Diamonds Materials, use and appropriate engineering use High speed steel HSS was invented in 1905, and was later superseded by other tool materials. HSS is basically composed of W 18 %, Cr 4%, V 1%, C 0.7 % and the remaining composition is iron (Fe). A tool material with the HSS can be used to machine mild steel jobs at speeds of about 20 to 30 m/min. Selection of the tool with this material composition is based on the following factors: When the geometry of the tool and the chip formation mechanics are complex; like drilling helical twists, cutters for gear shaping, broaches and reamers When handling jobs that involve shock loads When other tools are costlier When the desired speed and feed are low High speed steel tools are also own for their high resistance to wear and their high working hardness. They also have the strength to stop breakage of the tool at the cutting edge. However, their ability to retain heat is poor. Each of the alloying elements that have been used in high speed steel plays a role in boosting its properties. For instance, carbon increases its resistance to wear. Tungsten and molybdenum improve hardness retention and its red hardness while improving its strength at high temperature. Chromium enhances its hardening depth while cobalt improves the red hardness and hardness retention. Through these alloys, the complete set of HSS is formed with the ability to function optimally. Image of High Speed Steel Tungsten carbide This material was first used in making cutting tools in Germany in 1926. Tungsten carbide has been used in metal cutting mainly due to their ability to perform at high speeds and with increased feeds. In addition, they provide longer lies for the tools. According to Upadhyaya (1998), tungsten carbide has been used to make most carbide cutting tools. Tungsten carbide has been used to make 70 % of total machining using carbide. These constitute additives of tantalum carbide while some have titanium carbide. The remaining 30 % is done using coated inserts of cemented titanium carbide and cermets. Generally, tungsten carbide is stiffer than steel and is also denser when compared to titanium or steel. The melting point of tungsten carbide is high, at 2870 ºC. It also has a high boiling point at 6000 ºC when subjected to a pressure equal to 760 mm Hg. This material is extremely hard and its Vickers number is 1700 – 2400. It also has high yield stress (6800 MPa). The structure of the material takes the form of a rock salt structure. This is the beta form of the material. It also has another form, the hexagonal form that takes the shape of hexagonal layers that are closely packed together. The layers can be seen to lying one on top of the other while the carbon atoms are seen to fill the interstices hence making the tungsten and carbon a trigonal prismatic form. When used in making cutting tools, the tools become resistant to abrasion and they can also stand high temperatures. These cutting surfaces are used to machine jobs that are made of stainless steel and carbon steel. They are also used in situations where there is a likelihood of the tool wearing away like in production of high quantity runs. Their surface finish is better than tools made with other materials. Since they can allow high temperatures, they are used for faster machining. It is for this reason that this material is used in making tools that are used in high speed drilling operations. The process of making these tools is done through the sintering process. Structure of tungsten carbide Cermets Use of this material started after the Second World War. Cermets are composite materials that are made from a combination of ceramics and metals. They are therefore designed to have a combination of properties from ceramics and those from metals. Properties from ceramics include high resistance to temperature and high hardness. The metallic properties that can be seen in cermets are the great ability to go through plastic deformation. The metals used in forming cermets are used as binders for carbide, a boride or an oxide. The metal elements that are sued in forming cermets include molybdenum, cobalt and nickel. The volume of meal composition in making a cermet is usually less than 20 %. In the making of some saws and brazed tools, cermets have been used in place of tungsten carbides. This is because they have superior properties in terms of wear and corrosion. To form tools that can last for longer, complex cermet materials known as cermet II have been developed. The choice of a tool made from ceramics is made when considering high speed, high temperatures, and high resistance to abrasion. In addition, when the life of a tool is to be long, the choice of the material is cermet. Additionally, the combination of the metal and ceramic components provides the tools with good toughness and resistance to wear. The general use of such tools is in machining of bearing races and in the general milling and cutting of steel (Seth & Juneja, 2003). Diagram of cermets Ceramics Ceramics have been used in making inserts since 1950. The production of ceramic tools is done through the sintering process. In this process, the main constituent used is alumina (aluminum oxide). Additions of up to 10 % of oxide of elements such as titanium, chromium and magnesium are made. This is done so as to obtain properties that are superior to the parent material. These oxide powders are finely divided and they are compressed to the form that is required on the tips of carbide or steel dies and then the sintering process is done at high pressure and high temperature in an atmosphere that is filled by argon or hydrogen. This is done so as to create an inert environment. Finishing of the blanks is done using wheels that have been impregnated by diamond and bonded with resinoid. Up to a temperature of 1400 ºC, the ceramic tool will retain its hardness. In addition, the resistance of these tools to formation of crater and abrasion wear is better. When used they show a low friction coefficient with many materials of work. It is for these reasons that the tools can be used at speeds that are substantially high and they can therefore be used to achieve high rates of production. However, they have a demerit in their rupture strength. Their traverse rupture strength is low when compared to that of carbides. The tips of ceramics are very brittle. Attaching them to shanks requires the use of epoxy resins. The machine tool should also be highly rigid since the ceramic material cannot take in shock loads. The machine should also be devoid of vibrations. Appropriate use of these materials can be achieved if the tool is given great strength. This can be done by use of a negative rake angle. Working using ceramic machine tools requires work materials that are hard to machine. Such materials include heat treated steels, high temperature alloys and abrasive cast irons. These tools can also be used in boring of long tubes, boring of cylinder liners and in turning of rolls. Additionally, alumina can be used in grinding wheels to act as an abrasive. Tools made from ceramics can be used for high speed operations. However, they are mostly used to machine grey cast iron. This is because the material does not have adequate toughness and this means that it could provide unreliable performance. Cutting at high speeds can be considered when the operation is done on works with continuous chips. Such an operation will require use of a chip breaker to avoid any hazard to the operator (Rao, 2009). Diagram of ceramic pieces Diamonds Diamond tools were used since 1972. Use of diamond as a material for cutting tools can be done in two forms. These are the polycrystalline compact and the single crystal. The single crystal can be used in a natural form or a synthetic form. This form has both the hard and the soft axes. When used in the soft axis direction, or parallel to the cleavage of the plane, the tool wears off rapidly. To produce polycrystalline, the sintering process is used. This is sintered using fine diamond powder at high pressure and temperature. This is then used as inserts of the indexable types of clamps. At times, compacts of polycrystalline diamond are brazed at each corner of the carbide insert. The orientation of particles of diamond in a compact of diamond is random. This implies that any direction can be used during machining since there are no soft or hard axes. One distinguishing feature of the tools made from diamond is their hardness. This hardness is greater than any other material. The material is also inert chemically and its thermal conductivity is high. Even so, oxidation of diamond still begins at 450 ºC and after it begins, the diamond tool could crack. This is the reason as to why the diamond tool has to be kept cool using a constant flow of a coolant during its operation. It also requires that the feed made on the tool is light. Diamond tools are very brittle. The machine tool, holder of the tool and the clamping of the diamond tool on the shank has to be rigid. The vibrations during the cutting operations have to be kept at minimal. Crystal diamond is used in machining operations on non-ferrous metals such as brass, aluminium, bronze and copper. These are operations where high content of silicon is involved. Other non-metallic materials like epoxy resins, plastics, glass, hard rubber and precious metals such as silver, platinum and gold can also be machined. Inappropriate use of diamonds includes machining of ferrous materials. Appropriate use includes high cutting speeds but the rate of feeding should be low. The depth of cut should also be kept below 0.5mm (Seth and Juneja, 2003). Image of a diamond blade Environmental impact and issues of sustainability The environmental impact of machining tool sis felt based on their performance and the cost that the company incurs in obtaining the appropriate tools. While adopting a sustainable approach to selection of materials, consideration has to be made on improving the environmental, social and economic performance of the machine. For this reason, selection has to be mad based on what the material is best suited for. Where the material can overlap its services without causing an extra expense, it is selected for use for instance, high speed steel can be used in place of tungsten carbide where the surface finish is not the main consideration and the temperatures are relatively low. Where there is high chip formation, the appropriate material should be selected, in this case, ceramics, and a chip breaker should be used to prevent the chips from causing any harm to the operator (Kopac, 2009). Bibliography Davis, J. 1995, Tool Materials, New York, ASM International. Kopac, J. 2009, Achievements of Sustainable Manufacturing by Machining, Journal of Achievements in Materials and Manufacturing Engineering, Vol. 34 (2): 180-187. Rao, 2009, Manufacturing Technology Vol- 2E. Tata, McGraw-Hill Education. pp. 30. Seth, N. and Juneja, B. 2003, Fundamentals Of Metal Cutting And Machine Tools, Ed. 2, New Delhi, New Age International. Upadhyaya, G. 1998, Cemented Tungsten Carbides: Production, Properties and Testing, USA, Noyes Publications. Read More