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1. INTRODUCTION
Manufacturing is defined as the making of articles in an industry. Manufacturing is the heart and soul of an industry. For an industry to excel in its field, the company must possess the latest technology in manufacturing. One such technology is “Virtual Manufacturing”.
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 today’s 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.
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 space. In particular it is possible to provide a visual simulation of familiar real-world environments, and to make changes within such an environment.
VIRTUAL REALITY SYSTEM
COMPUTERISED VIRTUAL REALITY
Augmented Reality in Manufacturing Augmented Reality (AR) augments a user’s view of the world with computer data and/or graphics models, which brings information into the user’s real world rather than pulling the user into the computer’s virtual world. It is a more natural means of exhibit a design in its real-world context.
VIRTUAL REALITY EXPERIENCE
What is Virtual Manufacturing?
Perhaps one of the most interesting and important of these recent developments is called “Virtual Manufacturing”. Often termed “The Next Revolution in Global 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.
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.
- 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.
DESKTOP AR
Virtual objects are arranged by moving coded cards
THE MULTI-MEDIA HARD HAT, 1995
Concept for imposing the Augmented model on top of the real surroundings
2. FINITE ELEMENT ANALYSIS
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 (1000’s or 100,000’s) 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. 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.
3. STRUCTURE 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 VMO’s could be constructed based on different principles, i.e., a
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.
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 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.
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.
We assume that the proposed design is available as a 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
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 workpiece. The volume resulting from a machining operation is called a machining feature.
More specifically, their approach involves the following steps :-
- 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.
- 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. We consider an FBM unpromising if it is not expected to result in any operation
plans better than the ones which have already been examined. 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.
- 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.
Analysis of Socket Design:
Manufacturing 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. IMACS's output includes an optimal operation plan for the design. As shown below, this plan includes three setups:- (Blue colour indicates-that face of the workpiece is being machined first)
Setup 1:
Setup 2:
Setup 3:
5. VIRTUAL MANUFACTURING OPTIMIZES
ROLL FORMING PROCESS
PROBLEM
improvements in the strength of the door itself is quite effective for passenger safety, particularly in collisions from the oblique direction, or with fixed objects. 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, were analyzed.
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.
7. PLANNING 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.
With 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
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.
It 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 simulated—inside and out, from initial floor plans to functioning assembly lines—before 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.
8. RELIABILITY 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. Finally, the ability to estimate product quality is minimal since there manufacturability studies do not generally use sophisticated process models.
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. On the other hand, modeling the production process will yield queue times, as
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. We are confident that you will also share in this success.
10. CONCLUSION
Virtual 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. Tools that assess manufacturability by generating and evaluating manufacturing plans require more computing time than approaches that try to analyze the design directly, but they also offer more accurate results. 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:
