MODERN MANUFACTURING METHODS

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Modern Manufacturing MethodsLECTURE NOTESONMODERN MANUFACTURINGMETHODS2018 – 2019IV B. Tech I Semester (JNTUA-R15)Mr. K.SURESH, Assistant ProfessorCHADALAWADA RAMANAMMA ENGINEERING COLLEGE(AUTONOMOUS)Chadalawada Nagar, Renigunta Road, Tirupati – 517 506Department of Mechanical Engineering

Modern Manufacturing Methods

Modern Manufacturing MethodsUNIT-IMANUFACTURINGManufacturing processes can be broadly divided into two groups:a) primary manufacturing processes: Provide basic shape and sizeb) secondary manufacturing processes : Provide final shape and size withtighter control on dimension, surface characteristicsMaterial removal processes once again can be divided into two groups1. Conventional Machining Processes2. Non-Traditional Manufacturing Processes or non-conventional ManufacturingprocessesTRADITIONAL MACHININGTraditional, also termed conventional machining Processes removematerial in the form of chips by applying forces on the work material with awedge shaped cutting tool that is harder than the work material undermachining condition.The major characteristics of conventional machining are: Generally macroscopic chip formation by shear deformation Material removal takes place due to application of cutting forces Cutting tool is harder than work piece at room temperature as well as undermachining conditionsDemerits of conventional machining processes: In conventional machining, metal is removed by chip formation which isan expensive and difficult process Chips produced during this process are unwanted by-products Removal of these chips and their disposal and recycling is a very tediousprocedure, involving energy and money. Very large cutting forces are involved in this process. so proper holdingof the workpiece is most important Due to the large cutting forces and large amount of heat generatedbetween the tool and the workpiece interface, undesirable deformationand residual stresses are developed in the workpiece.

Modern Manufacturing Methods It is not possible to produce chips by conventional machining process fordelicate components like semi conductor.NON-TRADITIONAL MACHINING nalmachiningprocesses. Unconventional machining processes is defined as a group ofprocesses that remove excess material by various techniques involvingmechanical, thermal, electrical or chemical energy or combinations of theseenergies but do not use a sharp cutting tools as it needs to be used fortraditional manufacturing processes. Extremely hard and brittle materials aredifficult to machine by traditional machining processes such as turning, drilling,shaping and milling. Non traditional machining processes, also called advancedmanufacturing processes, are employed where traditional machining processesare not feasible, satisfactory or economical due to special reasons as outlinedbelow. Very hard fragile materials difficult to clamp for traditional machining When the work piece is too flexible or slender When the shape of the part is too sseshavebeendeveloped to meet extra required machining conditions. When these processesare employed properly, they offer many advantages over traditional machiningprocesses.Merits of unconventional machining process: It increases productivity It reduces number of rejected components close tolerance is possible The tool material need not be harder than workpiece material as inconventional machining Harder and difficult to machine materials can be machined by thisprocess The machined surface do not have any residual stresses

Modern Manufacturing MethodsMATERIAL REMOVAL PROCESSESFig. Material removal processes.NEED FOR NON-TRADITIONAL MACHINING (NTM) Extremely hard and brittle materials or Difficult to machine materials aredifficult to machine by traditional machining processes. When the workpiece is too flexible or slender to support the cutting orgrinding forces. When the shape of the part is too complex.Intricate shaped blind hole – e.g. square hole of 15 mmx15 mm with adepth of 30 mm Deep hole with small hole diameter – e.g. φ 1.5 mm hole with l/d 20 Machining of composites.

Modern Manufacturing MethodsCLASSIFICATION OF NON-TRADITIONAL MACHINING (NTM)PROCESSESClassification of NTM processes is carried out depending on the nature ofenergy used for material removal.1. Mechanical Processes Abrasive Jet Machining (AJM) Ultrasonic Machining (USM) Water Jet Machining (WJM) Abrasive Water Jet Machining (AWJM)2. Electrochemical Processes Electrochemical Machining (ECM) Electro Chemical Grinding (ECG) Electro Chemical Honing (ECH) Electro Chemical Deburring (ECD)3. Electro-Thermal Processes Electro-discharge machining (EDM) Laser Jet Machining (LJM) Electron Beam Machining (EBM)4. Chemical Processes Chemical Milling (CHM) Photochemical Milling (PCM)PROCESS SELECTION:SELECTION OF PROCESSESS FOR DIFFERENT MATERIALS:All methods are not suitable for all materials. Depending on the materialto be machined, following methods can be used as shown in the tables.no.1MaterialNon-metals like ceramics,Method of MachiningUSM, AJM, EBM, LBMplastics and glass2RefractoriesUSM, AJM, EDM, EBM3TitaniumEDM4Super alloysAJM, ECM, EDM, PAM

Modern Manufacturing Methods5SteelECM, CHM, EDM, PAMSELECTION OF PROCESSESS FOR APPLICATION CONSIDERATIONS:Typical applications of nontraditional processes include special geometricfeatures and work materials that cannot be readily processed by conventionaltechniques. In this section, we examine these issues. We also summarize thegeneral performance characteristics of nontraditional processes.Workpart Geometry and Work Materials: Some of the specialworkpart shapes for which nontraditional processes are well suited are listed inTable below along with the nontraditional processes that are likely to beappropriate.Table::Workpart geometric features and appropriate nontraditionalprocessess.noGeometric FeatureLikely Process1Very small holes. Diameters less than 0.125mm (0.005 in), in some cases down to 0.025mm (0.001 in), generally smaller than thediameter range of conventional drill bits.EBM, LBM2Holes with large depth-to-diameter ratios,e.g., d/D 20. Except for gun drilling, theseholes cannot be machined in conventionaldrilling operationsHoles that are not round. Non-round holescannot be drilled with a rotating drill bit.Narrow slots in slabs and plates of variousmaterials. The slots are not necessarilystraight. In some cases, the slots haveextremely intricate shapesMicromachining. In addition to cutting smallholes and narrow slits, there are othermaterial removal applications in which theworkpart and/or areas to be cut are verysmall.Shallow pockets and surface details in flatparts. There is a significant range in the sizesof the parts in this category, frommicroscopic integrated circuit chips to largeaircraft panels.ECM, EDM3456EDM, ECMEBM, LBM, WJC,wire EDM,AWJCPCM, LBM, EBMCHM

Modern Manufacturing Methods7Special contoured shapes for mold and dieapplications.Theseapplicationsaresometimes referred to as die-sinkingEDM, ECMLimitations of Unconventional machining process: Unconventional Machining processes are more expensive Metal removal rate is low AJM, CHM, PAM, and EBM are not commercially economical processesRapid prototypingPrototyping or model making is one of the important steps to finalize a productdesign. It helps in conceptualization of a design. Before the start of fullproduction a prototype is usually fabricated and tested. Manual prototyping bya skilled craftsman has been an age- old practice for many centuries. Secondphase of prototyping started around mid-1970s, when a soft prototypemodeled by 3D curves and surfaces could be stressed in virtual environment,simulated and tested with exact material and other properties. Third and thelatest trend of prototyping, i.e., Rapid Prototyping (RP) by layer-by-layermaterial deposition, started during early 1980s with the enormous growth inComputer AidedDesign and Manufacturing (CAD/CAM) technologies whenalmost unambiguous solid models with knitted information of edges andsurfaces could define a product and also manufacture it by CNC machining.Year of inception Technology 1770Mechanization 1946First computer 1952First Numerical Control (NC) machine tool 1960First commercial laser 1961First commercial Robot 1963First interactive graphics system (early version of Computer Aided Design)1988 First commercial Rapid Prototyping system

Modern Manufacturing MethodsBASIC PRINCIPLE OF RAPID PROTOTYPING PROCESSESRP process belong to the generative (or additive) production processes unlikesubtractive or forming processes such as lathing, milling, grinding or coiningetc. in which form is shaped by material removal or plastic deformation. In allcommercial RP processes, the part is fabricated by deposition of layerscontoured in a (x-y) plane two dimensionally. The third dimension (z) resultsfrom single layers being stacked up on top of each other, but not as acontinuous z-coordinate. Therefore, the prototypes are very exact on the x-yplane but have stair-stepping effect in z-direction. If model is deposited withvery fine layers, i.e., smaller z-stepping, model looks like original. RP can nerationofmathematical layer information and 2 generation of physical layer modelRAPID PROTOTYPING PROCESSESThe professional literature in RP contains different ways of classifying standardofproduction processes classifie RP processes according to state of aggregationof their original material and is given in figure.,

Modern Manufacturing MethodsFig., Classification of RP processesStereolithographyIn this process photosensitive liquid resin which forms a solid polymer whenexposed to ultraviolet light is used as a fundamental concept. Due to theabsorption and scattering of beam, the reaction only takes place near thesurface and voxels of solid polymeric resin are formed. A SL machine consists

Modern Manufacturing Methodsof a build platform (substrate), which is mounted in a vat of resin and a UVHelium-Cadmium or Argon ion laser. The laser scansthe first layer andplatform is then lowered equal to one slice thickness and left for short time(dip-delay) so that liquid polymer settles to a flat and even surface and inhibitbubble formation .In new SL systems, a blade spreads resin on the part as the blade traversesthe vat. This ensures smoother surface and reduced recoating time. It alsoreduces trapped volumes which are sometimes formed due to excessivepolymerization at the ends of the slices and an island of liquid resin havingthickness more than slice thickness is formed (Pham and Demov, 2001). Oncethe complete part is deposited, it is removed from the vat and then excessresin is drained. It may take long time due to high viscosity of liquid resin. Thegreen part is then post-cured in an UV oven after removing support structures.Fig., StereolithographyOverhangs or cantilever walls need support structures as a green layer hasrelatively low stability and strength. These overhangs etc. are supported ifthey exceed a certain size or angle, i.e., build orientation. The main functionsof these structures are to support projecting parts and also to pull other partsdown which due to shrinkage tends to curl up (Gebhardt, 2003). These supportstructures are generated during data processing and due to these data grows

Modern Manufacturing Methodsheavily specially with STL files, as cuboid shaped support element needinformation about at least twelve triangles. A solid support is very difficult toremove later and may damage the model. Therefore a new support structurecalled fine point was developed by 3D Systems (figure 6) and is company strademark.Build strategies have been developed to increase build speed and to decreaseamount of resin by depositing the parts with a higher proportion of hollowvolume. These strategies are devised as these models are used for makingcavities for precision castings. Here walls are designed hollow connected byrod-type bridging elements and skin is introduced that close the model at thetop and the bottom. These models require openings to drain out uncured resin.Selective Laser SinteringIn Selective Laser Sintering (SLS) process, fine polymeric powder likepolystyrene,polycarbonate or polyamide etc. (20 to 100 micrometer diameter)is spread on the substrate using a roller. Before starting CO2 laser scanning forsintering of a slice the temperature of the entire bed is raised just below itsmelting point by infrared heating in order to minimize thermal distortion(curling) and facilitate fusion to the previous layer. The laser is modulated insuch away that only those grains, which are in direct contact with thebeam,are affected (Pham and Demov, 2001). Once laser scanning cures aslice, bed is lowered and powder feed chamber is raised so that a covering ofpowder can be spread evenly over the build area by counter rotating roller. Inthis process support structures are not required as the unsintered powderremains at the places of support structure. It is cleaned away and can berecycled once the model is complete. The schematic diagram of a typical SLSapparatus is given in figure .Fused Deposition ModelingIn Fused Deposition Modeling (FDM) process a movable (x-y movement)nozzle on to a substrate deposits thread of molten polymeric material. Thebuild material is heated slightly above (approximately 0.5 C) its meltingtemperature so that it solidifies within a very short time (approximately 0.1 s)after extrusion and cold-welds to the previous layer as shown in figure 8.

Modern Manufacturing MethodsVarious important factors need to be considered and are steady nozzle andmaterial extrusion rates, addition of support structures for overhangingfeatures and speed of the nozzle head, which affects the slice thickness. Morerecent FDM systems include two nozzles, one for part material and other forsupport material. The support material is relatively of poor quality and can bebroken easily once the complete part is deposited and is removed fromsubstrate. In more recent FDM technology, water-soluble 7 support structurematerial is used. Support structure can be deposited with lesser density ascompared to part density by providing air gaps between two consecutiveroads.APPLICATIONS OF RP TECHNOLOGIESRP technology has potential to reduce time required from conception to marketup to 10-50 percent (Chua and Leong, 2000) as shown in figure 10. It hasabilities of enhancing and improving product development while at the sametime reducing costs due to major breakthrough in manufacturing (Chua andLeong, 2000). Although poor surface finish,limited strength and accuracy arethe limitations of RP models, it can deposit a part of any degree of complexitytheoretically. Therefore, RP technologies are successfully used by

Modern Manufacturing Methodsvarious industries like aerospace, automotive, jewelry, coin making, tableware,saddletrees,biomedical etc. It is used to fabricate concept models, functionalmodels, patterns for investment and vacuum casting, medical models andmodels for engineering analysis (Pham and Demov, 2001). Various typicalapplications of RP are summarized in figure .PART DEPOSITION PLANNINGA defect less STL file is used as an input to RP software like QuickSilce orRPTools for further processing. At this stage, designer has to take an importantdecision about the part deposition orientation. The part deposition orientationis important because part accuracy,surface quality, building time, amount ofsupport structures and hence cost of the part is highly influenced (Pandey etal., 2004b). In this section various factors influencing accuracy of RP parts andpart deposition orientation are discussed.

Modern Manufacturing Methods1. Factors influencing accuracyAccuracy of a model is influenced by the errors caused during tessellation andslicing at data preparation stage. Decision of the designer about partdeposition orientation also affects accuracy of the model.2.Errors due to tessellation: In tessellation surfaces of a CAD model areapproximated piecewise by using triangles. It is true that by reducing the sizeof the triangles, the deviation between the actual surfaces and approximatedtriangles can be reduced. In practice, resolution of the STL file is controlled bya parameter namely chordal error or facet deviation as shown in figure 2. Ithas also been suggested that a curve with small radius (r) should betessellated if its radius is below a threshold radius (ro) which can beconsidered as one tenth of the part size, to achieve a maximum chordal errorof (r/ro) .Value of can be set equal to 0 for no improvement and 1 formaximum improvement.Here part size is defined as the diagonal of animaginary box drawn around the part and is angle control value (Williams etal., 1996).3.Errors due to slicing: Real error on slice plane is much more than that isfelt, as shown in figure 12(a). For a spherical model Pham and Demov (2001)proposed that error due to the replacement of a circular arc with stair-stepscan be defined as radius of the arc minus length up to the correspondingcorner of the staircase, i.e., cusp height (figure 12 (b)). Thus maximum error(cusp height) results along z direction and is equal to slice thickness.Therefore,cusp height approaches to maximum for surfaces, which are almost parallelwith the x-y plane. Maximum value of cusp height is equal to slice thicknessand can bereducedby reducing it; howeverthisresults indrasticimprovement in part building time.Therefore, by using slices of variablethicknesses (popularly known as adaptive slicing, as shown in figure 13), cuspheight can be controlled below a certain value.Except this, mismatching ofheight and missing features are two other problems resultingfrom the slicing. Although most of the RP systems have facility of slicing withuniform thickness only, adaptive slicing scheme, which can slice a model withbetter accuracy and surface finish without loosing important features must be

Modern Manufacturing Methodsselected. Review of various slicing schemes for RP has been done by Pandey etal. (2003a).4. Part buildingDuring part deposition generally two types of errors are observed and arenamely curing errors and control errors. Curing errors are due to over or undercuring with respect to curing line and control errors are caused due to variationin layer thickness or scan position.

Modern Manufacturing MethodsFig.,Applications of RP processes

Modern Manufacturing MethodsUNIT - IIUltrasonic machining (USM) is the removal of hard and brittle materialsusing an axially oscillating tool at ultrasonic frequencies [18–20 kilohertz(kHz)]. During that oscillation, the abrasive slurry of B4C or SiC is continuouslyfed into the machining zone between a soft tool (brassor steel) and theworkpiece. The abrasive particles are, therefore, hammeredinto the workpiece surface and cause chipping of fine particles from it. Theoscillating tool, at amplitudes ranging from 10 to 40 μm, imposes a staticpressure on the abrasive grains and feeds down as the material is removed toform the required tool shape (Fig. 2.1). Balamuth first discovered USM in 1945during ultrasonic grinding of abrasivepowders. The industrial ppeared.USMischaracterized by the absence of anydeleterious effect on the metallic structureof the workpiece material.The machining systemThe machining system is composed mainly from the magneto stricter,concentrator, tool, and slurry feeding arrangement. The magnetostrictor isenergized at the ultrasonic frequency and produces small-amplitude vibrations.Such a small vibration is amplified using the constrictor (mechanical amplifier)that holds the tool. The abrasive slurry is pumped between the oscillating tooland the

Modern Manufacturing Methods It is not possible to produce chips by conventional machining process for delicate components like semi conductor. NON-TRADITIONAL MACHINING (NTM) Non-Traditional machining also termed unconventional machining processes. Unconventional machining processes is defined as a group of

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