Overview of the Lecture Manufacturing systems approaches. Basic manufacturing processes. (Casting, Forming process, Fabrication process, Material removal process) Advanced Machining processes (ECM, EDM, EBM, LBM, AJM, USM processes) Micro-manufacturing processes (Etching, Deposition, Lithography, Replication and molding, Dip-pen lithography, Compression molding, Nano-imprint lithography)
Manufacturing Systems Approach Definition of Manufacturing Technology: Manufacturing technology provides the tools that enable production of all manufactured goods. These master tools of industry magnify the effort of individual workers and give an industrial nation the power to turn raw materials into the affordable, quality goods essential to today’s society. Thus manufacturing process really represents adding value to a raw material and creation of wealth. Manufacturing Facility Add Value InputOutput Replenish Wealth Manufacturing System comprising of manufacturing processes Sales fluctuations Raw materials cost and availability Business environment Social Pressure Resources and plans Production rate, quality and delivery Profit Reputation Manufacturing Process is the key to wealth generation
Casting Processes These are the only processes where liquid metal in used. Casting is the oldest known manufacturing process. It requires preparation of a cavity usually in a refractory material to resemble closely to the object to be realized. Molten metal is poured into this refractory mould cavity and is allowed to solidify. The object after solidification is removed from the mould.
Equilibrium Phase Diagrams A convenient way of describing the phase transformations is a diagram where the phases at different combinations of temperatures and compositions are indicated. Such a diagram is called an equilibrium phase diagram. The word equilibrium is indicative of the fact that at every temperature sufficient time is provided at every temperature to complete all diffusion processes. The diagram in the left shows a phase diagram of Ni-Cu alloy which forms a solid solution without any restriction on % composition. The diagram has been obtained by study of the cooling curves for various composition of the alloys.
Forming Processes These are solid state manufacturing processes involving minimum amount of material wastage and faster production. Metal is heated to a temperature which is slightly below the solidus temperature and then a large force is applied such that the material flows and take the desired shape. The desired shape is controlled by means of certain tools called dies which may be completely or partially closed during manufacture. These processes are normally used for large scale production rates. Rolling Process Drop forging Extrusion Wire Drawing
Fabrication processes These are secondary manufacturing processes where the starting raw materials are processed by any of the previous methods. It essentially involves joining pieces either temporarily or permanently so that they would perform the necessary function. The joining can be achieved by both heat and pressure and / or a joining material. Gas Welding Arc Welding Resistance Welding
Material Removal Processes These are also secondary manufacturing processes where the additional unwanted material is removed in the form of chips from the blank material by a harder tool so that a final desired shape can be obtained. Material removal is the most expensive manufacturing process because more energy is consumed, and also a lot of waste material is generated in the process. Turning Milling Shaping Drilling Grinding Sawing
History of Machining Mankind used bones, sticks and stones as hand tools since the earliest times The most ancient Paleolithic stone tool industry the Oldowan was developed by the earliest members of the genus Homo such as Homo habilis around 2.6 million years ago. and contained tools such as choppers, burins and awls. During the Upper Paleolithic further technological advances were made such as the invention of Nets, bolas, the spear thrower the bow and arrow.
History of Machining Ceremonial giant dirk of the Plougrescant-Ommerschans type, Plougrescant, France, 1500-1300BC. Bronze Age weaponry and ornaments Hand held tools from Bronze Age developed around 1 million years back. Upto almost the seventeenth century all tools were either hand operated or done so by other very elementary methods. Introduction of water, steam and later electricity as useful sources of energy led to the concept of power driven machine tools. John Wilkinson in 1774 first constructed a precision machine for boring engine cylinders, powered by steam.
History of Machining 23 years later, Henry Maudslay made a further advancement in machining when he devised screw cutting engine lathes. James Nasmyth invented the second basic machining tool for shaping and planing. First Universal Milling machine was built by J.R. Brown in 1862. In the late nineteenth century, the grinding machine was introduced. An advanced form of this process is the lapping process used to produce a high quality surface finish and a very tight tolerance
History of Machining In the later part of 19 th and 20 th Centuries the machine tools became increasingly electrically powered. The basic machine tools had further refinements; for instance multiple point cutters for milling machines were introduced. The whole machining paradigm was however still related to an operators judgment who by looking at a part and using his skills would set up an operation sequence and use this for machining the work piece. Accuracy of such a product would depend solely on the operator. The introduction of NC (numerical control) in 1953 lead to computer numeric control and direct numeric control. Present capabilities of these tooling systems have enormously increased due to development in electronic controls and computers and present capabilities enable complex shapes to be produced with finishing accuracy close to a + 1 Micron.
History of Machining In modern machining practices, harder, stronger, and tougher materials that are more difficult to cut are used. So, processes should be independent of material properties of the work piece. Non conventional machining practices came very handy as an alternative to the conventional domain which could handle shape complexity, surface integrity and miniaturization requirements. Hybrid machining made use of the combined enhanced advantages of two or more participating processes. Micromachining had emerged because of this change of capabilities. Recent applications of micromachining include silicon/ glass micromachining, excimer lasers and photolithography.
History of Machining Machines such as precision grinders may be capable of producing an accuracy level of + 1 microns that can be measured using laser instruments and optical fibers. Future trends in micromachining include laser and electron beam lithography and super high precision grinding, lapping and polishing machines. For measurements high precision laser beam based scanners are used for measuring surface finish etc. Nano-machining is a very recent trend in these processes wherein atoms and molecules can be removed instead of chips in conventional machines. Nano-machining was introduced by Tanigushi to cover the miniaturization of components and tolerances in the range from submicron level to that of an individual atom or molecule between 100nm and 0.1 nm.
Abrasive Machining Categories The Metal abrasion action is adopted during grinding, honing and super finishing processes that employ either a solid grinding wheel or sticks in the form of bonded abrasive. Furthermore in lapping, polishing, and buffing, loose abrasives are used as tools in a liquid medium.
Classification of all Material Removal Processes Area of interest
Non Traditional Machining Traditional machining is mostly based on removal of materials using tools that are harder than the materials themselves. New and novel materials because of their greatly improved chemical, mechanical and thermal properties are sometimes impossible to machine using traditional machining processes. Traditional machining methods are often ineffective in machining hard materials like ceramics and composites or machining under very tight tolerances as in micromachined components. New processes and methods play a considerable role in machining for aircraft manufacture, automobile industry, tool and die industry mold making etc. They are classified under the domain of non traditional processes.
Classification of Non Traditional Machining Single action non traditional Machining processes: For these processes only one machining action is used for material removal. These can be classified according to the source of energy used to generate such a machining action: mechanical, thermal, chemical and electrochemical.
Mechanical Machining Ultrasonic Machining (USM) and Waterjet Machining (WJM) are typical examples of single action, mechanical non traditional machining processes. The machining medium is solid grains suspended in an abrasive slurry in the former, while a fluid is employed in the WJM process. The introduction of abrasives to the fluid jet enhances the machining efficiency and is known as abrasive water jet machining. Similar case happens when ice particles are introduced as in Ice Jet Machining.
Thermal Machining Thermal machining removes the machining allowance by melting or vaporizing the work piece material. Many secondary phenomena occur during machining such as microcracking, formation of heat affected zones, striations etc. The source of heat could be plasma as during EDM and PBM or photons as during LBM, electrons in EBM, ions in IBM etc.
Chemical and Electrochemical Machining Chemical milling and photochemical machining or photochemical blanking all use a chemical dissolution action to remove the machining allowance through ions in an etchant. Electrochemical machining uses the electrochemical dissolution phase to remove the machining allowance using ion transfer in an electrolytic cell.
Introduction to Abrasive Jet Machining (AJM) In AJM, the material removal takes place due to impingement of the fine abrasive particles. The abrasive particles are typically of 0.025mm diameter and the air discharges at a pressure of several atmosphere.
Mechanics of AJM Abrasive particle impinges on the work surface at a high velocity and this impact causes a tiny brittle fracture and the following air or gas carries away the dislodged small work piece particle.
Basics of the USM process The basic USM process involves a tool ( made of a ductile and tough material) vibrating with a very high frequency and a continuous flow of an abrasive slurry in the small gap between the tool and the work piece. The tool is gradually fed with a uniform force. The impact of the hard abrasive grains fractures the hard and brittle work surface, resulting in the removal of the work material in the form of small wear particles. The tool material being tough and ductile wears out at a much slower rate.
Electrochemical Machining (ECM) Electrochemical machining is one of the most unconventional machining processes. The process is actually the reverse of electroplating with some modifications. It is based on the principle of electrolysis. In a metal, electricity is conducted by free electrons but in a solution the conduction of electricity is achieved through the movement of ions. Thus the flow of current through an electrolyte is always accompanied by the movement of matter. In the ECM process the work-piece is connected to a positive electrode and the tool to the negative terminal for metal removal. The figure below shows a suitable work-piece and a suitably shaped tool, the gap between the tool and the work being full of a suitable electrolyte.
Electrochemical Machining With ECM the rate of metal removal is independent of the work-piece hardness. ECM becomes advantageous when either the work material possesses a very low machinability or the shape to be machined is complex. Unlike most other conventional and unconventional processes, here there is practically no tool wear. Though it appears that, since machining is done electrochemically, the tool experiences no force, the fact is that the tool and work is subjected to large forces exerted by the high pressure fluid in the gap.
Electric Discharge Machining EDM is the process of material removal by a controlled erosion through a series of electric sparks. It was developed in USSR around 1943. The basic process is illustrated below. When a discharge takes place between two points of the anode and cathode the intense heat generated near the zone melts and evaporates the materials in the sparking zone. For improving the effectiveness the work-piece and the tool are submerged in a dielectric fluid. (Mineral oils or hydrocarbons) Experiments indicate that in case both electrodes are of the same material there is a prominently more erosion of the electrode connected to the positive terminal.
Schematic view of the e-beam machine The figure below shows the basic schematic view of the electron beam machine. The electrons are emitted from the cathode (a hot tungsten filament), the beam is shaped by the grid cup, and the electrons are accelerated due to a large potential difference between the cathode and the anode. The beam is focussed with the help of the electromagnetic lenses. The deflecting coils are used to control the beam movement in any required manner. In case of drilling holes the hole diameter depends on the beam diameter and the energy density. When the diameter of the required hole is larger than the beam diameter, the beam is deflected in a circular path with proper radius. Most holes drilled with e-beam are characterized by a small crater on the beam incident side of the work.
Introduction to MEMS fabrication NEMS/ MEMS silicon fabrication Formation of structures that could be used to form sensors and actuators. Processing of electrical or non electrical signals. Conventional and new semiconductor manufacturing techniques are used. Etching, Deposition, Photolithography, Oxidation, Epitaxy etc. Deep RIE, Thick plating etc. Bulk and surface micromachining.
Topics Covered Non-traditional Machining processes. (detailed analysis based AJM, USM, ECM, EDM, LBM, PAM, MRAFF, EDD, ECD, MEMS processes, RP processes, rapid tooling techniques) [10-Lectures] Traditional Machining processes.(detailed analysis on turning, milling, drilling, shaping ad planning processes, orthogonal and oblique cutting).[06- Lectures] Introduction to Metrology.(Limits, fits, tolerances, Automated inspection and CMM), [01-Lecture]
Course Requirements (1) 35% of total grade on Mid Semester (2) 35% of total grade on Final Examination (3) 30% of total grade on Experiments. (The rationale of the distribution of 30% is the following: 5% will be on report making, 5% will be based on feedback of supervisorial support, 20% will be done on the basis of a lab quiz that will be taken towards the end of the semester at a mutually convenient date.)