UNIT 1 NEAR NETSHAPE MANUFACTURING

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1 UNIT 1 NEAR NETSHAPE MANUFACTURING --- Structure 1.1 Introduction Objectives 1.2 Different Processes of Netshape Manufacturing 1.3 Methods of Near Netshape Manufacturing 1.4 Basics of Near Netshape Manufacturing 1.5 Projected Growth for Ceramic Near Netshape Manufacturing Near Netshape Machining Desinging the Chip Groove 1 S.3 Strengthening Exercise 1 S.4 Semi-solid Processing : New Advances in Netshape Forming 1 S.5 Netshape Components 1.6 Summary 1.7 Key Words 1.8 Answers to SAQs 1.1 INTRODUCTION There is tremendous growth in the Advanced Manufacturing Technology. Near Netshape Manufacturing is a new concept in Advanced Manufacturing Technology. In this unit, you will be introduced to the concept of Near Netshape Manufacturing. Near netshape is an innovative concept in industrial manufacturing. The main focus of this technology is to produce parts, as near as possible close to their final shape and contour, implementing non-chipping techniques. In this way the manufacturing gives the possibility of a finished product with minimal cutting. Near netshape technology also generates the opportunity to reduce the productive steps for a given process chain. Both the above mentioned characteristics have the same goal : achieving cost reduction. This will lead to quality improvement of the finished product. Near netshape manufacture is a new concept in manufacturing technology, which implies that parts of a product should be produced by high technology enabled manufacturing processes which can impart sufficient accuracy and produce dimensions, having tolerances close enough to the final tolerances specified on the finished component drawings. The work 'net shape' means the final shape and size of the component, as required by the designer. 'Near-net shape' implies that the size and shape produced by the primary or secondary manufacturing process, shall be close enough to the net shape,and generation of the net shape subsequently would need marginal finishing operations,ncurring minimum cost of production. Near-net shape manufacture is not any particular ~echnique or process of manufacture, but it is more philosophy, or an objective, a concept or an approach to improve the production system so as to make production more t:conomical, imparting greater accuracy and reliability in the product, with improved work culture and better quality of work life. Objectives fi fter studying this unit, you should be able to understand the basic concepts of Near Netshape Manufacturing, explain the different processes of Near Netshape Manufacturing, describe some reported works of Near ~etsh'a~e Manufacturing, know the projected growth for Ceramic Near Netshape Manufacturing, and appreciate the application of Near Netshape Manufacturing.

2 Advanced Manufacturing 1.2 DIFFERENT PROCESSES OF NETSHAPE MANUFACTURING Near netshape manufacturing is the subject of considerable attention. Let us discuss the different processes of near netshape manufacturing. Primary processes may include rolling, metal casting, metal forging or extrusio~i processes. Usually, these methods produce rough shapes with coarse tolerances, and heavy machining allowance have to be provided in order to obtain final sizes by machining operations. This increases the cost of production considerably as the machining operations are more expensive than casting or forging operations; besides other losses are incurred due to : extra metal provided for removal by machining, extra cost of power and labour required for machining, and extra overheads due to need for expensive machining equipment and skilled labour. Thus, efforts are made to use improved technology and modem methods of casting and forging which can enable production of components to closer tolerances in the as-cast or as-forged condition itself. The sizes obtained by these newer and improved methods are much closer to final sizes, even before machining and so subsequent machining operations are eliminated considerably. The advantages accrued are obvious, for example, material consumption is reduced, power requirements are reduced, skilled labour and need for heavy equipment required for machining are reduced, cycle time of production gets reduced and quality of the product also improved METHODS OF NEAR NETSHAPE MANUFACTURING In order to obtain near-net shapes during casting process, some methods are adopted : Investment casting Shell moulding, hot box and cold box processes Ceramic moulding and graphite mould casting process (d) High pressure moulding (e) Mercast process using mercury patterns (f) Die casting, low pressure die casting and squeeze casting processes. Similarly, during forging, near-net shapes are obtained by methods, such as closed die-forging and isothermal forging. As seen from the above discussion, machining allowance provided on different surfaces plays a vital role in affecting material conservation, quality improvement and overall cost reduction, the three main objectives of near-net shape philosophy. Factors affecting machining allowance are : work material and its composition. Nominal size, and shape. Method of manufacture adopted at the primary or secondary stage. (d) Method used for setting up for machining. (e) Distortion produced during heat treatment and carburisation after forging operation.

3 These processes produce parts in a manner which does allow use of rules to relate design attributes to manufacturing ones. Hence rule based systems found much success here. However recent trend is to use the process physics knowledge and simulation to find out the manufacturability. These processes also have process-specific manufacturing defects associated with it. In many cases the rules associate the design attributes to the probability of occurrence of different types of defects. The production process is also usually two step, one has to account for the manufacturability of the tooling, and the manufacturability of the actual part to realistically determine manufacturability. Near Netsbape Manufacturing 1.4 BASICS OF NEAR NETSHAPE MANUFACTURING Near Netshape Manufacturing is a two-step materials processing technique, in which nano-particles are formed via mechanical attrition, from which nano-composites are formed by consolidation and densification using Hot Isostatic Pressing (HIP). The technique is general to all materials classes: metals, ceramics, polymer and even biological materials. The significant new accomplishments in this area are related to the extension of Near Net-Shape Manufacturing techniques into new classes of hybrid materials, particularly those involving polymers. Polymer-polymer, and polymer-ceramic nano-composites are two examples, in which improved blends and improved membrane performance, respectively, have been linked to the interfacial characteristics of the component nano-particles. In Nafiontceramic nano-composite proton-exchange membranes, concurrent increases in operating temperature, reduction in water uptake, and increased proton conductivity have been linked to the interfacial formation between polymer and ceramic components at the nano-scale. Similarly, polymer-polymer blends from immiscible polymers have been formed using Near Net-Shape Manufacturing. The resulting impact to the field of nano-composite formation is that while the energy imparted during mechanical attrition can manifest itself in different ways in different materials; e.g., molecular weight reduction in polymers vs. amorphization of metals, the production of highly interfacial regions in the nano-composite is common to all materials classes. It is these interfacial regions that lead to bulk property control, and ultimately, to property. -. enhancement in nano-composites. Besides these, micro direct metal deposition (p - DMD) technology is under development for precision components with micron scale feature, through additive process. This involves direct deposition of metal powders and fusion through focused laser beam. Metal Injection Moulding (MIM) offers'netshape manufacturing of small metal or alloy components. Find metal powder intimately mixed with plastic binders is injected into the die. Subsequently, the thermal debinding and sintering gives the dense metallic product in net form. SAQ 1 What are the Different Processes of Near Net Shape Manufacturing? Briefly describe the methods of Near Net Shape Manufacturing. Describe some reported works of Near Net Shape Manufacturing. 1.5 PROJECTED GROWTH FOR CERAMIC NEAR NETSHAPE MANUFACTURING Ceramic near net shape processing involves fabricating a ceramic material into a shape that requires minimal post sintering machining to achieve the desired dimensions. Such processing can reduce significantly the manufacturing costs of ceramic components, since traditionally, advanced ceramics have been machined from a fired or prefired

4 t~dvanced Manufacturing 8 (green) blank to the final desired shape. Machining costs, sometimes as much as 75% of the total manufacturing cost (typically, expensive diamond wheels are used), become prohibitively expensive with more complex shapes. Near net shape processes in use today include uniaxial or dry pressing, isostatic pressing, slip casting, injection moulding and extrusion. All have advantages and limitations and often, some are combined with green machining, where the part is machined in its unfired state. Over the next five years, newer processes are expected to be limited to niche applications and will not take any major market share away from the more conventional processes. Achieving the insertion of advanced ceramics into technological applications is, of course, critical to increasing the use of near net shape manufacturing. Historically, design engineers have expressed some hesitance in using advanced ceramics as engineering materials. This is because they often cannot be counted on for performance reliability like metals and plastics. This reluctance stems from the fact that ceramic properties vary widely with processing parameters, making standardisation difficult and reliability poor. Efforts are being made to improve both of these areas and some progress has been noted. The rapid introduction of a newly discovered, easily produced advanced ceramic would cause a large jump in these figures. However, based on past history, it is unlikely that this will occur. For instance, although high-temperature superconductors were discovered in 1986, it is only now that they are beginning to find wide commercial use. Now we shall introduce a thermally scanned material deposition control method for near netshape manufacturing of metal parts by welding. To eliminate thermal distortion and the required intermediate-layer milling steps, and to control the material structure, plasma arc scan welding under infrared pyrometry sensing regulates the temperature field by providing in-process heat treatment of the part. In laboratory tests, the material is simultaneously deposited by a gas metal arc welding torch, with monitoring of the weld profile by two laser stripe profilometers. These sensors provide measurements of the bead width for its feedback control by modulation of the wire feed. To compensate for measurement delays, real-time prediction by a deposition model is employed, with its parameters identified during the process. Preview of the geometric surface irregularities in front of the deposition is used as feedforward to ensure the desired layer deposition patterns in adjacent beads. The performance of this bead-size control scheme is assessed experimentally on a robotic laboratory station, and applications of the thermally scanned material deposition technique are explored in rapid manufacturing of customized metal products. In such welding-based rapid manufacturing, however, the molten material deposition is accompanied by heat transfer, giving rise to a dynamic, distributed temperature field in the part. This results in material structure transformations affecting the mechanical properties of the product. It also yields residual stresses and distortions due to local differential thermal expansion and contraction of the deposition. Material transformations and residual stresses usually debilitate the part yield strength, fracture toughness, and performance in a chemically active environment, for example, by stress-corrosion cracking. In addition, thermal distortions, that is, deviations from layer planarity, create difficulties with further processing and compromise the dimensional accuracy and the maximum size of the part that can be fabricated. To overcome this latter difficulty as well as the layer surface roughness (due to wetting effects of the deposited molten droplets in adjacent beads), intermediate flat machining (such as by peripheral milling) of each surface is typically employed between successive layer depositions. However, such machining and chip removal steps add to the complexity, cost, and time of processing waste-deposited material and drastically reduce the productivity of this technology. Moreover, the material quality of the product is adversely affected by occasional burrs and undercuts left on the layers. These, upon incomplete fusion conditions in subsequent depositions, yield internal pores and cracks, acting as fracture initiation sites. To overcome these welding-related limitations in rapid manufacturing, current research implores active in-process control of the mass and heat transfer conditions during material deposition. In particular, it is clear that structural transformations and the resulting material properties, as well as residual stresses and thermal distortions, are all

5 generated by the temperature distribution history during welding. Thus recently, the scan welding technique has been introduced to regulate these temperature field cycles in the part. Scan welding modulates the heat input distribution supplied by a welding source sweeping the part surface on the basis of real-time thermal sensing and feedback. Progress in distributed parameter modeling and control of the welding deposition morphology has been also noted. However, scan welding has never been realized in processes with material deposition, and geometry control has not been applied to thermal scanning methods in rapid manufacturing. The scan welding technique of the material deposition geometry implemented on a thermally scanned GMAW process as a paradigm but also applicable to other welding methods with external metal feed. This is intended to eliminate the need for corrective postprocessing steps in rapid manufacturing technologies, and thus, improve their productivity and product quality Near Netshape Machining One of the benefits of the new generation of grades and grooves is their improved suitability for machining near-net-shape forgings and castings, now used increasingly in a variety of industries. Two prominent examples are cold-formed automotive components, made from high strength, low carbon ductile steels, and stainless steel castings used in aerospace. In addition, tightly controlled powder metal (PM) preforms, which sometimes have only inch of stock to be removed, are now widely used in the electric power tool, lawn equipment, and appliance industries. PM preforms are also making rapid inroads in automotive - where some components may require machining of only one or two dimensions. On a preformed automotive gear, for example, only a face and a bore may need to be machined to ensure that the part runs true. For many near-net-shape parts, typical processing includes cleaning up the part with a single finishing or semi finish cut, heat-treating, and finishing by hard turning or grinding. Challenges Although near-net-shape parts have less stock to be removed and, often from fewer surfaces, turning operations performed on them present a special challenge for effective chip control and good tool life. One challenge is posed by the light depth of cut. It usually produces a thinner chip that is easily bent, but lacks the rigidity for easy breaking. Because much near-net-shape machining is performed at both higher feed rates and higher cutting speeds, control of higher heat generation is a challenge. The chip is produced in an area of the chip groove - on the nose radius, or just past it - where the placement of a hard obstruction to curl the chip for breaking will result in the transfer of excessive heat and pressure to the insert, causing cratering. Finally, cutting forces can be quite high in applications requiring a semi-roughing pass at relatively high feed rates. Typical finishing inserts will not do the job in these cases, because they don't supply enough edge strength to handle either the high feed rates, or the scale or other surface irregularities often left on the part by the casting or forming process Designing the Chip Groove To meet these challenges, chip groove geometries for near-net-shape machining must be designed to break chips at depths of cut that are normal for a finishing tool, but also provide the edge strength needed to handle higher feed rates and withstand part surface irregularities. These performance characteristics are in fact identical to those designed into many reenzineered chip breakers as part of the effort to extend their versatility and create a core chip groove offering. For example, grooves for fine and light- to medium-duty cuts in steel can be designed with varying land widths and angles that provide the required edge strength for effecjive chip breaking over an application range that now includes Near Netshape Manufacturing

6 Advanced Manufacturing smaller depths of cut and higher feeds. Added edge strength at higher feeds helps control depth-of-cut notching in both near-net-shape and stainless steel applications. At the same time, the groove designs provide better tool life through their application range. One contributing factor is a positive entrance angle, which promotes free cutting and reduces the chip temperature. Chip control geometry is another factor. For example, making use of a strategically placed "bump" on the insert nose, rather than a hard obstruction, may be used on the insert to curl the chip for breaking. The pressed-in bump helps limit chip contact with the insert to only two points - the entrance angle and the bump itself (the exit angle). In consequence, the transfer of heat and cutting forces into the insert is reduced, improving tool life. The two contact points are also widely spaced, so any diffusion craters caused by a chemical reaction of the chips with the carbide will not grow together Strengthening Exercise To enable more versatile chip grooves to handle both the higher feed rates and surface scale and irregularities common to near-net-shape machining, the cutting edge must be made stronger farther out from the nose - where shallow-cut chip breaking takes place. Computer Aided Design (CAD) makes it possible to design varying land widths and angles to create both more positive, and stronger negative, geometries at the points required Semi-Solid Processing : New Advances in Netshape Forming Net shape and near net shape manufacturing using semi-solid metals has been undergoing a remarkable surge in activity. A number of new companies and initiatives have begun in semi-solid metal and component production. All exploit the well-known advantages of semi-solids, e.g. lower temperatures, reduced porosity, and improved mechanical properties than comparable cast metals. The flow behaviour of semi-solids is still incompletely characterized, however, and must be understood to fully exploit these advantages. This presentation summarizes the last decade of research into the flow of semi-solid metals and discusses the implications of this research for net shape manufacturing using semi-solids. This research includes the effect of temperature, liquid/solid fraction, particle morphology, flow history, and methods for producing the semi-solid state. The presentation closes with a discussion of some particularly exciting new semi-solid processes Net-Shape Components Net- or near-net-shape technology has the potential to greatly lower manufacturing costs by reducing or eliminating machining steps, by reducing the number of parts by combining subcomponents, and by producing parts in configurations that could not be easily produced using other processes. The nearest-term, most promising net- or near-netshape processes for metals include precision forgings, net-shape extrusions, and castings. Net-shape polymeric composite processes include resin transfer molding (RTM) and resin film infusion (RFI) of multiaxial fibre preforms. Cast structural parts can be attractive for aircraft applications due to low cost and lowweight benefits in large and complex shapes. Material-intensive operations involving machining and fastening of metal parts are minimized in the fabrication and utilization of precision castings. Efforts to reduce manufacturing costs of airframe construction in recent years have contributed to the development of economically viable processes based on advanced casting technologies, including new alloys, process controls, and simulation methods. Improved casting technology promises to increase the structural integrity of castings and reduce cost by eliminating the need for many small parts requiring individual manufacturing operations. Currently, the lack of confidence in cast products on the part of the structural design community has limited the use of these products in primary structural applications. Current developmental efforts in casting technologies will result in reductions in manufacturing cost, accelerate the design process for castings, provide a statistical database of critical design properties, and improve the overall quality and confidence of casting applications in primary structural components.

7 RTM of composite components is attractive because the process : (d) reduces the need for finish machining, eliminates fastened or bonded joints, produces complex shapes in a one-step process, and fabricates thick parts without concern for monitoring matrix resin out-of-refrigeration time. The application of net-shape composite processes has been hindered by poor process controls on fibre distribution and volume fraction. Development of more-reliable process controls, improvements in preform fabrication, and the availability of t~ughened matrix polymers that are compatible with RFI processes would enable expanded use of netshape. processes in composite primary structure. SAQ 2 Enumerate the projected growth for Ceramic Near Netshape Manufacturing. What are the different applications of Near Netshape Manufacturing in Near Netshape IManufacturing 1.6 SUMMARY Near netshape manufacturing has great potential to enhance the competitivenss of a manufacturing process as it cuts down the steps to achive the final size and shape of the product. Near netshape is an industrial manufacturing technique. The name implies that the initial production of the item is very close to the final (net) shape. An example is metal injection molding where fine metal powders are injection molded with a polymer or other binder. Then a series of steps removes the binder and the metal powder is fused into its final shape by heat and pressure (sintering). Other near net shape techniques use precision manufacturing methods such as isostatic pressing, gelcasting, superplastic forming, rapid prototyping, etc. require very little finishing work. Reducing traditional finishing such as machining or grinding eliminates more than two-thirds of the production costs in some industries. Near netshape can also be used for structural ceramic production. 1.7 K E WORDS ~ Near Netshape : It is an industrial manufacturing technique. The name implies that the initial production of the item is very close to the final (net) shape. 1.8 ANSWER TO SAQs Please refer the preceding text for all the Answers to SAQs.