VIRTUAL MANUFACTURING 2014

VIRTUAL MANUFACTURING 2014

CHAPTER 1INTRODUCTIONManufacturing is an indispensable part of the economy and is the central activity that encompasses product, process, resources and plant. Nowadays products are more and more complex, processes are highly-sophisticated and use micro technology and mechatronic, the market demand (lot sizes) evolves rapidly so that we need a flexible and agile production. For an industry to excel in its field, the company must possess the latest technology in manufacturing. One such technology is Virtual Manufacturing. Moreover manufacturing enterprises may be widely distributed geographically and linked conceptually in terms of dependencies and material, information and knowledge flows. To achieve their goals, the use of a virtual manufacturing environment will provide a computer-based environment to simulate individual manufacturing processes and the total manufacturing enterprise. Virtual Manufacturing systems enable early optimization of cost, quality and time drivers, achieve integrated product, process and resource design and finally achieve early consideration of producibility and affordability. The natural instinct of an engineer who wants to make a new device is to go to a workshop, find some scrap aluminum or mild steel, and to machine up what is required. The engineer will do this visually by eye where dimensions are not critical and by measurement where they are. He or she will make mistakes of course, holes may be drilled in the wrong place initially or, more seriously, material may be cut which is subsequently needed to support some other part of the component. But eventually a rough hack at a prototype will emerge. The idea of Virtual Manufacturing system is to allow designers to follow that instinct, but with the added luxury of cost free second thoughts. The system is a virtual world representing machine shop in which engineering components can be made and almost as importantly, unmade. Many people have produced simulation systems that will replay a predetermined sequence of machining operations inside a computer, but we are not aware of any fully interactive system that is intended to be a source of such operations and which is intended to be used by the designers as a design system.

1.1 Drawbacks of the conventional manufacturing systems In conventional manufacturing, there is lots of time and money wasted on building the physical prototypes of the manufacturing processes to be used before the actual production starts. This takes a lot of time which can be used to optimize the product design and market the product in a better way. There is also lots of money and material wastage if more physical prototypes are required. With increasing competition in todays world, the conventional way of setting up production processes causes the company a fortune. It was time for an innovation and this is how Virtual Manufacturing was born. The first step toward successfully launching the VM initiative was taken at a Users Workshop on VM, held in Dayton on 12-13 July 1994. The workshop was held to ensure that the needs and directions of those involved in and responsible for defense manufacturing are accommodated in the VM initiative. Before defining virtual manufacturing lets define Virtual Reality. 1.2 What is Virtual Reality? Virtual Reality (VR) is an exciting new technology for which the most important benefits are the ability to do human-in-the-loop, real time, "what if" scenarios, reducing development time and reducing time to deliver products to the market. Virtual reality promises a ready ability to interact in three dimensional spaces. In particular it is possible to provide a visual simulation of familiar real-world environments, and to make changes within such an environment.

Fig 1.1 Computerized Virtual RealityVIRTUAL REALITY SYSTEM

Fig 1.2 Virtual Reality Systems1.3 Augmented Reality in Manufacturing Augmented Reality (AR) augments a users view of the world with computer data and/or graphics models, which brings information into the users real world rather than pulling the user into the computers virtual world.

Fig 1.3 Virtual Reality Experience1.4 What is Virtual Manufacturing? Perhaps one of the most interesting and important of these recent developments is called Virtual Manufacturing. Virtual manufacturing involves the simulation of a product and the processes involved in fabrication. Virtual Manufacturing (VM) is defined to be an integrated, synthetic manufacturing environment exercised to enhance all levels of decision and control. In simple words, the vision of Virtual Manufacturing is to provide a capability to Manufacture in the Computer. Virtual Manufacturing (VM) is defined to be an integrated, synthetic manufacturing environment exercised to enhance all levels of decision and control. In essence, VM will ultimately provide a modeling and simulation environment so powerful that the fabrication/assembly of any product, including the associated manufacturing processes, can be simulated in the computer. This powerful capability would take into account all of the variables in the production environment from shop floor processes to enterprise transactions. In other words, VM will accommodate the visualization of interacting production processes, process planning, scheduling, assembly planning, logistics from the line to the enterprise, and related impacting processes such as accounting, purchasing and management.

Fig 1.4 Virtual ManufacturingIn addition, VM also reduces the cost of tooling, eliminates the need for multiple physical prototypes, and reduces material waste. This allows everyone to get it right the first time.VM utilizes nonlinear finite element analysis technologies to provide detailed information about a product, which is then used for optimization of factors such as manufacturability, final shape and residual stress and life-cycle estimations. At the core of VM lies nonlinear FEA technology.

Fig 1.5 A virtual part in a machining center.One can use such concept to effectively debug and verify a process planning.

1.5 Three Paradigms of Virtual ManufacturingThree major paradigms have been proposed for VM are Design-Centered VM, Production-Centered VM and Control-Centered VM. Figure 1 depicts the relationships among these three types of VM with respect to the virtual product life-cycle. In this figure, the three blocks represent the three types of VM; the relevant interactions (or information flow) are represented by directed arcs. For example, the information (such as product models) provided by Design-centered VM to Production-centered VM, is represented by a directed arc from the Design-centered VM block to the Production-centered VM block. These three different types of VM have the following characteristics: Design-centered VM provides an environment for designers to design products and to evaluate the manufacturability and affordability of products. The results of design-centered VM include the product model, cost estimate, and so forth. Thus, potential problems with the design can be identified and its merit (in form of cost and other metrics) can be estimated. The Design-Centered VM is the use of manufacturing-based simulations to optimize the design of product and processes for a specific manufacturing goal such as: design for assembly; quality; lean operations; and/or flexibility. Production centered VM provides an environment for generating process plans and production plans for planning resource requirements (new equipment purchase, etc) and for evaluating these plans. Production centered VM adds simulation capability to manufacturing process models with the purpose of allowing inexpensive, fast evaluation of many processing alternatives. In order to maintain the manufacturing proficiency without actually building products, production-centered VM provides an environment for generating process plans and production plans, for planning resource requirements (new equipment purchase, etc.), and for evaluating these plans. This can provide more accurate cost information and schedules for product delivery. By providing the capability to simulate actual production, control-centered VM offers the environment for engineers to evaluate new or revised product designs with respect to shop floor related activities. Control-centered VM provides information for optimizing manufacturing processes and improving manufacturing systems. Control-Centered VM is the addition of simulation to control models and actual processes, allowing for seamless simulation for optimization during the actual production cycle. In summary, Design-centered VM provides Manufacturing information to the designer during the design phase. Production-centered VM uses simulation during production planning to optimize lines/shop floors, including the evaluation of processing alternatives. Control-centered VM uses machine control models in simulations, the goal of which is process optimization during actual production.

Virtual objects are arranged by moving coded cardsFig 1.6 Desktop AR

Fig 1.7 THE MULTI-MEDIA HARD HAT, 1995Concept for imposing the augmented model on top of the real surroundings

CHAPTER 2FINITE ELEMENT ANALYSIS At the core of virtual manufacturing lies a technology called Nonlinear Finite Element Analysis (NFEA) that uses a powerful computer and modeling and analysis software to simulate a product's performance and the processes involved in its fabrication Finite Element Analysis is a very powerful engineering design tool that enables engineers and designers to simulate structural behavior, make design changes, and see the effects of these changes. The finite element method works by breaking the geometry of a real object down into a large number (1000s or 100,000s) of elements (e.g. cubes). These elements form the mesh and the connecting points are the nodes. The behavior of each little element, which is regular in shape, is readily predicted by set mathematical equations. The summation of the individual element behavior produces the expected behavior of the actual object. The mesh contains the material and structural properties that define how the part reacts to certain load conditions. In essence, FEA is a numerical method used to solve a variety of engineering problems that involve stress analysis, heat transfer, electromagnetism, and fluid flow. FEA is in effect a computer simulation of the whole process in which a physical prototype is built and tested, and then rebuilt and retested until an acceptable design is created. In essence, FEA is a numerical method used to solve a variety of engineering problems that involve stress analysis, heat transfer, electromagnetism, and fluid flow. Nonlinear FEA uses an incremental solution procedure to step through the analysis. In contrast to linear FEA, where a solution is achieved in one step, nonlinear FEA may require hundreds, even thousands of steps. There are three major types of nonlinearities:- Material plasticity, creep, viscoelasticity. Geometric large deformations, large strains, snap-through buckling. Boundary contact, friction, gaps, follower force. A nonlinear analysis can include any combination of these. In the case studies to follow, you will encounter examples including all of these solution types.

CHAPTER 3STRUCTURE OF VIRTUAL MANUFACTURING PROCESS Each VM process is an ordered collection of individual steps called virtual manufacturing operations (VMO). Each VMO changes the attributes of the starting virtual work part, and requires a combination of a virtual machine tool and virtual tooling. The VMO is essentially a set of physics-based process models derived from first principles. Different VMOs could be constructed based on different principles, i.e., a virtual machining operation, a virtual assembly operation, a virtual inspection operation, etc. The virtual machining operation is defined as a set of physics-based analytical and numerical models that describe the phenomena of chip formation zone including the mechanics and thermodynamics of the process, tribology, and tool wear. The virtual machining operation, as part of the virtual manufacturing process, communicates with the other objects in the immediate vicinity of the VM system (the virtual machine tool, virtual prototyping system, and virtual inspection system) by exchanging information as shown in Figure 2.

Fig 3.1 The virtual manufacturing operation neighborhood The virtual machining operation interfaces with the VP system. When the VP system interacts with the VMO as in Figure 2, it provides VMO with information about the geometrical and material specifications of the work part. In return, the VMO will send back to the VP system information about the manufacturability of the prototype. Additional information may be exchanged between VP and VMO to enhance design and manufacturing functions, which would in essence emulate the Design Manufacturability related activities. Also, VP will interact with the other objects in the virtual manufacturing, for example the virtual machining tool and virtual inspection system, to provide and receive information on the various aspects involved. Another object of the subsystem illustrated in figure 2 is the virtual machine tool. A virtual machine tool is a computer- based subsystem of the VM system exercised to improve the machine tool characteristics like dimensional accuracy, productivity, and machining performance. The virtual machining operation provides the virtual machine tool with information about the cutting forces and temperatures required to calculate the elastic and temperature deformations. In return, the VMO receives input on the machining parameters, tool geometry and materials, and the spatial positions of the virtual work part and cutting tool. Additional information may be exchanged between virtual machine tool and virtual machining operation to enhance machining functions and machine functionalities. The virtual inspection system is an object that is created based on the real inspection units used in the manufacturing process. For example, the virtual inspection station will have a virtual coordinate measuring machine with virtual probes and a virtual fixture to hold the virtual work part. The virtual inspection unit contains metrology model that simulates the working principle of the measuring device, like the CMM machine, optical comparator, etc., kinematic models to simulate the working of the machine, error generation models, and calibration models which are exercised to measure the virtual work part. Just like the other system elements, the virtual inspection unit communicates with the other objects. It receives information about the real geometry of the virtual work part as calculated by superimposing the ideal geometry provided by the VP system with the error envelope created during the VMO and checks the work part geometry for compliance with the geometrical tolerances. The information generated by the virtual inspection unit is then fed back to the virtual machine tool and the virtual machining operation to compensate for the error or change the machining conditions to ensure that the work part produced is within design specifications. In addition, the virtual inspection system may incorporate a quality module to facilitate the statistical process control. The proposed virtual inspection system uses conventional algorithms adopted by modern coordinate measurement processes as well as the latest free-form surface evaluation techniques to provide a robust framework for virtual forging error assessment.3.1 Illustrative example A simple orthogonal machining process has been developed to illustrate the virtual machining operation concept. It consists of a heat-transfer model, a two-dimensional model of the mechanics of chip formation, and a cutting tool wear model. These three models take the input values for various parameters like tool geometry, tool material properties, cutting conditions, and work material properties from the virtual prototyping system and the virtual machine tool. The model provides feedback to the virtual inspection system and the virtual prototyping system through the dimensional error calculator explained elsewhere. For the purpose of this work, the heat-transfer model and the mechanics of chip formation model have been developed in a non-linear hybrid finite element/analytical formulation. The analytical model of the chip formation produces data for velocities, stresses, and strain rates in selected points in the chip formation zone. This information is then entered into the finite element model (FEM) to calculate the temperature fields in the work, tool, and chip. The FEM has an adaptive re-meshing to account for the change in the geometry. The elemental temperatures generated by FEM are then used to update the material properties in the chip formation model. The finite element method plays an extremely important role in process design as it provides a valid means to quantify errors and thereby govern die shape modification to improve the dimensional accuracy of the component. However, this dependency on process simulation could raise significant problems and present a major drawback if the finite element simulation results were inaccurate. The hybrid model accounts for important features of the process such as frictional conditions at the tool-chip interface, the change in material properties with temperature, strain, and strain-rate. It is fully predictive and requires data only for the mechanical and thermal properties and tool materials as well as cutting conditions and tool geometry from the virtual prototyping system and the virtual machine tool. The volumetric tool wear model is comprised of a set of analytical models of the principle wear mechanisms acting in metal cutting diffusion, adhesion, and abrasion. The outcomes of the wear model are the volumetric tool wear and the width of wear land (VB) defined as the cutting time required for the cutting tool to develop a flank wear land of width VB, the so-called wear criterion.

CHAPTER 4 CASE STUDY: IMACS(INTERACTIVE MANUFACTURABILITY ANALYSIS AND CRITIQUING SYSTEM) The ability to quickly introduce new quality products is a decisive factor in capturing market share. Because of pressing demands to reduce lead time, analyzing the manufacturability of the proposed design has become an important step in the design stage. As shown below, the IMACS project is extending the design loop to incorporate a manufacturability analysis system that can be used once the geometry and/or tolerances have been specified. This will help in creating designs that not only satisfy the functional requirements but are also easy to manufacture.

Fig 4.1 Interactive Manufacturability Analyses and Critiquing System We assume that the proposed design is available as solid model, along with the tolerance and surface finish information as attributes of various faces of the solid model. We assume we have information about the available machining operations, including the process capabilities, dimensional constraints, etc. As shown on the next page, our approach is to generate alternative interpretations of the part as collections of machining features, map these interpretations into operation plans, and evaluate the manufacturability of each operation plans. The ultimate goal of the IMACS project is to provide tools for manufacturability analysis as part of the CAD systems used by designers. We believe our work will help designers design products that are easier to manufacture. This will reduce the need for redesign, resulting in reduced lead time and product cost. In addition, it will help to speed up the evaluation of new product designs in order to decide how or whether to manufacture them. Such a capability will be especially useful in flexible manufacturing systems, which need to respond quickly to changing demands and opportunities in the marketplace.Fig 4.2 Interactive Manufacturability Analyses and Critiquing System4.1 Manufacturability Analysis Given a computerized representation of the design (i.e. a solid model) and a set of manufacturing resources, the automated manufacturability analysis problem can be defined as follows:1. Determine whether or not the design attributes (e.g., shape, dimensions, tolerances, surface finishes) can be achieved.2. If the design is found to be manufacturable, determine a manufacturability rating, to reflect the ease (or difficulty) with which the design can be manufactured.3. If the design is not manufacturable, then identify the design attributes that pose manufacturability problems. In general, a design's manufacturability is a measure of the effort required to manufacture the part according to the design specifications. Our approach to measuring manufacturability is to estimate the manufacturing time and cost. Since all manufacturing operations have measurable time and cost, these can be used as an underlying basis to form a suitable manufacturability rating. Moreover, they present a realistic view of the difficulty in manufacturing a proposed design and can be used to aid management in making make-or-buy decisions. In a machining operation, a cutting tool is swept along a trajectory, and material is removed by the motion of the tool relative to the current work piece. The volume resulting from a machining operation is called a machining feature. More specifically, their approach involves the following steps: 1. Build the set of all potential machining features by identifying various features which can be used to create the part from the stock. Each of these features represents a different possible machining operation which can be used to create various surfaces of the part. 2. Repeat following steps until every promising feature-based model (FBM) has been examined: A. Generate a promising FBM from the feature set. An FBM is a set of machining features that contains no redundant features and is sufficient to create the part. B. Do the following steps repeatedly, until every promising operation plan resulting from the particular FBM has been examined: I) generate a promising operation plan for the FBM. This operation plan represents a partially ordered set of machining operations. We consider an operation plan to be unpromising if it violates any common machining practices. II) Estimate the achievable machining accuracy of the operation plan. If the operation plan cannot produce the required design tolerances and surface finishes, then discard it and go to Step 1. III) Estimate the production time and cost associated with operation plan. 3. If no promising operation plans were found then exit with failure, otherwise exit with success, returning the operation plan that represents the best tradeoff among quality, cost, and time.4.2 Analysis of Socket Design:Fig 4.3 Socket Design Fig 4.4 Feature Based ModelManufacturing Processes-Machinable by drilling and end-milling operations. The best plan requires 13 operations in 3 different setups. Total time required to machine the socket: 31.13 minutes. As shown below, this plan includes three setups: (Blue color indicates-that face of the work piece is being machined first)

Fig 4.5 Setup 1 Fig 4.6 Setup 2

Fig 4.7 Setup 3CHAPTER 5VIRTUAL MANUFACTURING OPTIMIZES ROLL FORMING PROCESS5.1 PROBLEM Cold formed roll profiles are important structural elements in almost any area of engineering. This includes automotive, and construction, where a large variety of open or closed section bar shaped profiles are used. In the continuous roll forming process, flat sheet metal is formed by driving pairs of contoured rolls into a finished profile through several stages without any intended reduction in sheet thickness. The final profile shape can be influenced by longitudinal strains causing sheet edge waviness and bowing. Also, residual stresses in the profile produce spring-back, and can deform the final profile shape. In order to speed up tool design, virtual manufacturing based techniques are required to aid in planning of the pass sequence development, calculation of the spring-back angle, and estimation of the strip edge elongation.5.2 SOLUTION The planning for a new part begins with a definition of the finished section, the design of the pass sequences, and the sizing of the different rolls in the CAD system. In this analysis, the CAD data was fed into the MSC. Marc FEA solver and the simulation were run. The results were analyzed to determine the deviations in shape and dimensions of the finished section. The longitudinal strains of the sheet edge revealed the quality of the roll forming process. Some of the characteristics that were checked included, dimensional tolerances, angular tolerances, longitudinal bow, twist sheet edge waviness, and profile end deformation. After optimizing the manufacturing process in this virtual environment, the manufacturer was able to manufacture the tools and run a test in the mill. This analysis avoids high costs derived from improperly designed tools needing adjustment and rework in the mill to fit a new profile.

CHAPTER 6SIDE IMPACT ANALYSIS OF A CAR DOOR 6.1 PROBLEM Based on the most harmful event, side impact accounts for 25 percent of fatalities for passenger car and light truck crashes in the USA. For passenger cars, side impact accounts for approximately 30 percent of the fatalities in passenger car crashes. Likewise, side impact accounts for roughly 15 percent of light truck fatalities. In comparison with frontal collisions, the space between the occupants and the intruding element in side crashes is extremely small. In addition, the side impact crash occurs much more rapidly. Consequently, occupant protection in side crashes presents a challenge to engineers designing a vehicle for safety. In car accidents, side impacts result in numerous injuries because the side structure of the car, including the occupant compartment, is crushed. During design, the strength of the door should be stressed for passenger safety. It is a common belief that improvements in the strength of the door itself are quite effective for passenger safety, particularly in collisions from the oblique direction, or with fixed objects. In the crashes, accelerometers were installed in the door and door frames of the struck vehicle. Using the accelerometers on the vehicle structure and in the side impact dummy, the crash event was investigated. In this research, MSC Marc was used for static compression analysis and dynamic impact analysis to understand the crash worthiness of the door. Experiments were also performed for comparison purposes. In addition, the effectiveness of the door-beams, which were installed within the doors, was analyzed.

Fig 6.1 Side Impact Analysis of a car door6.2 SOLUTION The doors used for this experiment were the front doors of four door sedans. The door panels, hinges, locks, and other necessary mechanisms were used, while the windows and door trims were removed. Hinges and latches were constrained. For static compression and dynamic impact, the loading device was applied laterally on the center of the door. Experimental results of a door in the body show different characteristics from the results of a door alone, mainly because the door contacts with the center pillar and side sill; therefore, the force on the door is distributed rather than concentrated on the latch. However, the latch part still receives most of the force. In fact, experimental results of the door within the car body showed cracks in the latch part, just like the results with the door alone. The importance of the strength of the latch part should be stressed for the strength of the door itself. From the static compression analysis and dynamic impact analysis of a door, as well as the experiments, it was found that the strength of the door hinge and door latch strongly affected the crush resistance of a door itself. In the experiments, it was found that once crack propagation occurred in the latch, the force drastically decreased. It was also necessary to consider reinforcing the latch even when a door has a door-beam. It was also found that by attaching a door-beam, absorption of the deformation energy increased and deformation of the door decreased upon impact.CHAPTER 7PLANNING A PLANT USING VIRTUAL MANUFACTURING Only a decade ago, it took many years for a spacecraft to move from the drawing board to the launch pad. It now takes only about two years to design and build a satellite, thanks to recent advances in computer-aided design and other technological techniques. It used to take five to seven years before a new model car was ready for market. Today, that cycle has been shortened to two or three years. And time to market continues to drop, even as the size and the complexity of satellites and automobiles grow. Still, market pressures are pushing manufacturers for even more reductions in time to market. VM allows manufacturers to simulate factory layout digitally, in order to see how the plant would function under the proposed arrangement and to predict out potential problems on the line.

Fig 7.1 Planning using Virtual ManufacturingWith VM, engineers are able to design individual assembly-line workstations via computer for smooth functioning and to guard workers against repetitive-motion injuries. Contrary to what it may sound like, digitizing the factory, as it's sometimes called, doesn't mean replacing all the workers in a plant with high-tech robots. Instead, the software can help ensure that a product is manufactured in the most streamlined method possible. CAD tools help engineers take care to come up with optimal product design. But VM makes sure the product can be manufactured in the right quality with reliable processes, within the shortest time frame, and with the best factory layout. Digital factory software is used for more than just laying out a plant floor on computer. It serves a number of functions around the manufacturing plant, including designing individual workstations in order to guard employees against repetitive motion injuries. VM lets manufacturing engineers visualize the production process via computerwhich allows an overview of factory operations for a particular manufacturing job. There are three areas to consider before actually laying out a real factory. First, engineers have to determine the assemblies, fabrication, and machining needed for the specific manufacturing process. Second, they need to figure out what tooling, fixtures, and equipmentdown to the nuts and boltswill be needed. Then, they must lay out a factory floor plan. VM is useful for each of these steps. Virtual factory software allowed engineers to test how operators, tools, and material-handling systems would work together even before construction began. If engineers decide to change the design of a part while the part is still only a CAD model, they can use VM to demonstrate the effect of the new design at every stage of the manufacturing process. The redesigned part, for example, might need more clearance on the automotive line.

Fig 7.2 Planning using Virtual ManufacturingThe same software that engineers use to simulate plant functioning via computer can also be used to program and site robots on the assembly. VM also allows engineers to simulate robotic functioning. We can see whether the robots can reach all the points it needs to reach. With the help of VM we can decide for each robot where it should stand. In addition to robots, employees themselves can be represented in a digitized version. In this way, engineers can figure out where employees should stand on the line and design workstations for them to both optimize their movements and to ensure they're not under any kind of ergonomic stress. Using VM, engineers can tell if an employee could reach a particular tool on the line and if the employee would be strong enough to lift it. They can see whether an employee could repeatedly perform a task without risking a repetitive-motion injury.

Fig 7.3 Factory SimulationIt used to take five to seven years from design to manufacture to create a new car model. Factory simulation software has helped cut that time in half. One of the major providers of software for virtual manufacturing applications is the Delmia Corp. of Troy, Michigan. Other software and hardware providers in this realm are Tecnomatix Technologies of Herzeliya, Israel; Rockwell Automation of Milwaukee, and EDS of Plano, Texas. DaimlerChrysler of Stuttgart, Germany, is currently digitizing the way its manufacturing plants are designed. Factories will be entirely simulatedinside and out, from initial floor plans to functioning assembly linesbefore they're built. The key is that the investment is expected to reduce new-vehicle production cycles by up to 30 percent, an automaker's Holy Grail. VM is becoming a leading tool in industries today.CHAPTER 8RELIABILITY OF COST, SCHEDULE AND QUALITY ESTIMATES MADE USING VM Reliability of an estimated value of a criterion (such as cost, schedule, or quality) is defined as the closeness of that estimate to the average value of the criterion resulting from actual manufacturing. The manual (or semi-manual) estimation techniques described above require a detailed description of the design, and knowledge of the processes to be used in production. Since they are based on empirical knowledge, which has been derived from years of experience, they typically provide reliable estimates for both the cost and the processing time. Manufacturability-related studies have automated the design critiquing process to a certain extend. The product and process information used in such studies may vary greatly in detail. Some methods assess the manufacturability based on information that is known at the initial design stages. Other methods require a fully developed design. As discussed above, however, most studies use indirect metrics for design critiquing, which quantify the relative and not the absolute difficulty of manufacture. Thus, it is difficult to assess the reliability of the manufacturability estimates. Even these methods that do estimate processing times, do not account for the dynamics of the production system, and therefore they cannot estimate the product's lead (or cycle) time which contains queuing time. (Note that the latter may range from 50 to 95% of the cycle time). Similarly, although it may be possible to estimate material and labor costs, it is not feasible to estimate inventory costs without considering the dynamics of the production system. Virtual manufacturing is able to provide accurate estimates for processing times, cycle times and costs (including inventory), as well as product quality. This is because VM can model both the processes employed for the product's manufacture and the production system dynamics. By employing comprehensive models of manufacturing processes, VM will be able to accurately predict set-up times and run times, and, consequently, labor costs. Furthermore, if these process models are able to predict the variance of key product attributes, then process yields or the values of quality ratios may be obtained by comparing the process capability with the corresponding design tolerances.CHAPTER 9 ADVANTAGES OF VIRTUAL MANUFACTURING FEWER PROTOTYPES The more trials you can simulate in a virtual environment, the less physical prototypes you need to perfect your design. This means you spend more time up front in engineering and design, and less resources running physical trials. Virtual prototyping is cheaper than building physical models and optimizing your design by trial-and-error. It is not complete replacement for physical testing, but it can minimize the effort and enable the resulting physical tests to be more successful. LESS MATERIAL WASTE If you build fewer physical models, you waste less material in the form of prototypes as well as the tooling used to create them. REDUCED COST OF TOOLING Again it follows that if you build fewer prototypes, then you develop fewer tools, which are typically very expensive. Furthermore, by modeling the tools, you can reduce tool wear, thus increasing tool life. CONFIDENCE IN MANUFACTURING PROCESS Even if the tools are properly designed, the control of the tools may affect the quality of the part produced. VM allows you to simulate the part, the tools, and their control. This simulation can let you optimize your tool control before building prototypes, again letting you get it right the first time. IMPROVED QUALITY It improves their part quality by utilizing VM techniques. There are numerous examples throughout this paper, and almost all of them result in a part with quality produced at lower cost than previously attained through traditional prototyping techniques. REDUCED TIME TO MARKET Time to market is becoming increasingly critical in an age where information can be transmitted and shared readily. Although VM may translate into spending more resources in the design and engineering phases, the resulting product will need much less rework downstream. This saves enormously in unforeseen redesign and re-engineering efforts. LOWER OVERALL MANUFACTURING COST The bottom line is that our customers have had success incorporating VM techniques into their processes, and none have gone back to the traditional product design cycle. CHAPTER 10CONCLUSIONVirtual manufacturing, when mature, is expected to greatly support assessing the manufacturability of a candidate design and to provide accurate estimates for processing times, cycle times and costs (including inventory), as well as product quality. This is because VM will be able to model both the processes employed for the product's manufacture and the production process. By employing comprehensive models of manufacturing processes, VM will be able to accurately predict set-up times and run times, and, consequently, labor costs. Furthermore, if these process models are able to predict the variance of key product attributes, then process yields or the values of quality ratios may be obtained by comparing the process capability with the corresponding design tolerances. On the other hand, modeling the production process will yield queue times, as well as Work-In-Process and finished goods inventory. Consequently, accurate estimates of overall cycle times and overall costs may be obtained. As the cost of computing power continues to decrease, we anticipate that such approaches will become increasingly widespread.The potential of VM to support manufacturability assessments and provide accurate cost, lead time and quality estimates is a major motivation for further research and development in this area. There are several advancements, however, that are needed to effectively support manufacturability assessments using virtual manufacturing. These include: Support for computer-aided conceptual design. Integration beyond single applications and single manufacturing domains. Critical role in supporting generative and hybrid approaches to process planning. Necessity to develop methods for integrating product design and process planning with production planning and scheduling. Need to develop product information models that are able to shape information and data that are directly relevant to manufacturing, such as tolerances (dimensional and geometric), and form features. Need to integrate process models into concurrent engineering and VM systems. New information models are necessary to capture the capabilities and performance of production systems.REFERENCES BOOK AND PAPER REFERENCES1. Vijay Ramachandran, 1995, "Information Models for Agile Manufacturing," Master's Thesis, University of Maryland at College Park.2. David W. Rosen, John R. Dixon, Corrado Poli, and Xin Dong. Features and algorithms for tooling cost evaluation in injection molding and die casting. In Proceedings of the ASME International Computers in Engineering Conference, pages 1-8. ASME, 1992.3. Achieving agile manufacturing in the automotive industry: Part I. Automotive Engineering, 102(11):19, November 1994. 4. Achieving agile manufacturing in the automotive industry: Part II. Automotive Engineering, 102(12):13, December 1994. 5. Douglas L. Waco and Yong Se Kim. Geometric reasoning for machining features using convex decomposition. Computer Aided Design, 26(6):477--489, June 1994.6. Erik Lindskog et al: Visualization support for virtual redesign of manufacturing systems, Proc of IEEE, 2013.7. Marcello Colledani et al: Integrated Virtual Platform for Manufacturing Systems Design, Proc of IEEE, 2013.8. Damian Grajewski et al: Application of Virtual Reality Techniques in Design of Ergonomic Manufacturing Workplaces, Proc of IEEE, 2013.

WEB REFERENCES1. www.howstuffworks.com2. www.virtualmanufacturing.com3. www.mscsoftware.com4. www.wiley.comDEPARTMENT OF MECHANICAL ENGINEERING, SJBITPage 24

Shape, Colour, Patterns, Textures, Lighting, Viewpoints, Behaviours

Output devices:Graphics, Sound, Tactile

Input devices:

Head/eye/hand tracking

Person

Computer

Virtual Environment

Network