Metal Casting Simulation on the Cloud

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1 ABSTRACT Technical article for publication in MMR Magazine Metal Casting Simulation on the Cloud Dr. B. Ravi Cloud-based metal casting simulation empowers small and medium foundries to improve their quality and yield, without any major investments. Hundreds of students and working professionals are accessing IIT Bombay s E-Foundry through the Internet to learn and apply casting simulation technology. INTRODUCTION A typical manufacturing firm uses many different software packages ranging from basic accounting to high end process simulation. The increasing cost of procuring and maintaining engineering software is however, leading to considerable dissatisfaction among small and medium firms who are Tier-I and Tier-II suppliers to original equipment manufacturers. The OEM customers want their suppliers to embrace software technology for better quality assurance, but are reluctant to pay for an increase in manufacturing costs. Cloud computing promises a way out by providing pay-per-use access to the latest software programs along with reliable storage of user files. Normally, users keep the software programs (for example, Microsoft Word) and related documents (.Doc files) in the same personal computer. There are two limitations of this approach. First: the programs need to be purchased, installed, and maintained (updated with the latest version), and the cost is the same irrespective of the extent of usage. Secondly, if the computer gets damaged or stolen, the software programs as well as the files and data are lost. With increasing number of software applications and criticality of the data, such disruptions can cause irreparable damage. Cloud computing overcomes these problems by maintaining both programs and user files in remote servers, which are accessed by users through the Internet, using a standard web browser (like Microsoft Internet Explorer, Mozilla Firefox, and Google Chrome). The major requirement is a fast, reliable and affordable access to Internet, through any suitable computing device (desktop, laptop or tablet PC), which has become a reality in most of the industrialized world. This article focuses on casting simulation, which involves visualizing molten metal flow and solidification in a sand or metal mould to predict internal defects. This is useful for evaluating and optimizing the methods design (feeding and gating systems) of castings. The relevant software programs cost from US$ 20,000 to US$ 80,000 for a perpetual license, plus 15-20% for annual maintenance (technical support plus upgrades). A large foundry can potentially recover the cost through a single project, if the order size is significant (say 200,000 pieces of a 10-kg

2 part), by 10-15% reduction in energy cost alone (which is nearly one kwh per kg of casting) through yield improvement. For this purpose, several alternate methoding layouts are modeled and simulated, and the optimal layout that gives the desired quality, but has the smallest volume of the feeders and gates, is selected (see Fig.1). Each iteration (modeling, simulation and interpretation of results) takes only a few hours, and the project can be completed within days, including a shop-floor trial to verify the optimal layout. If there are a limited variety of castings to be optimized (true for production foundries), the software utilization can however, be as low as 10%. Often, persons trained on the software move somewhere else, and any delay in hiring and training a new person further reduces the software usage. The utilization is usually higher for jobbing foundries, who have to develop and send sample castings for several new orders every month. This is becoming an increasing trend with OEM customers insisting on quality assurance plans, including simulation results, along with sample castings. Unfortunately the jobbing foundries, usually small or medium enterprises, are unable to adapt and benefit from simulation technology owing to the high initial cost of software. Fig.1 Casting design optimization by simulation The phenomenal success of cloud-based pay-per-use software such as Salesforce.com, a customer relation management system, prompted the following question. Can cloud-based casting simulation provide a viable alternative to the traditional stand-alone simulation technology, and empower SME foundries to improve the quality and yield of their castings without any major initial investment?

3 One must appreciate the fact that metal casting is a very complex process, with simultaneous flow and solidification of molten metal in geometrically intricate mould cavities and the properties of both molten metal and mould material continuously changing with temperature. The process physics and boundary conditions related to industrial practices are difficult to understand, mathematically model, and incorporate into user-friendly software programs. It is not surprising that most of the commercial casting simulation programs available in the market today originated in research institutes over 20 years back, and consumed hundreds of humanyears to evolve into their current versions. All casting simulation programs rely on space and time decomposition, and application of fundamental equations of heat transfer and fluid flow to obtain the temperature and flow history of each element. A complex shaped casting may be divided into several million elements to obtain the desired accuracy of the results. Based on the shape of the elements, and method of calculations, the software can be classified as based on finite element (FEM), finite difference (FDM), or finite volume (FVM) method, each with specific advantages and limitations. All of them are however, quite computation-intensive, and take several hours to obtain the results for typical castings on even powerful computers. Another stumbling block is that the programs require many inputs from the users, starting from the element size, material properties and boundary conditions, to program settings for the main computation, and later for post-processing, viewing and interpreting the results. The above two factors: computation intensity and 3D graphics user inputs, make the programs unsuited for cloud computing, which uses thin-client fat-server architecture. This means light-weight computation including interactive inputs on the user side, and automated heavy computations on powerful remote machines being accessed. E-FOUNDRY AND 3D HOTSPOT The award winning Gradient Vector Method (GVM) a fast and accurate method for casting simulation is found to be the most suitable for cloud computing, since it requires very few inputs from the user, and the computation is quite fast for even complex shaped parts. The method has been successfully benchmarked with the Modulus Vector Method developed at the Indian Institute of Science, Bangalore in early 1990s, as well as numerical approaches (FDM, FEM, and FVM) implemented in commercial software. It has been validated by matching the predicted location of hot spots with the observed location of shrinkage porosity defects in experimental castings of all major alloys. A cloud-based casting simulation facility using GVM has been created at E-Foundry ( with support from the National Knowledge Network of the Ministry of Communications and Information Technology, New Delhi. It is primarily meant for engineering and polytechnic students as well as teachers, consultants and working professionals. The online casting simulation lab allows users to upload a 3D model of casting, and view basic simulation results, without purchasing or installing any other software. The simulation program resides in a powerful server maintained in the E-Foundry lab at IIT Bombay. Users can access the program through the Internet, using a web browser (Fig.2).

4 Fig.2 Online simulation facility at E-Foundry Fig.3 Results of casting simulation at E-Foundry

5 The main input is a 3D model of the casting, in standard.stl format. This can be created using any commercial CAD program (ex. Autodesk Inventor, CATIA, SolidWorks, UG-NX) and saved into the user s computer. The user has to only upload the.stl file from his computer to the online simulation facility in E-Foundry. The upload time depends on the file size and connection speed. It is typically a few seconds for a small file (less than 100 kb) to several minutes for a large file (say 1-5 MB) on a standard connection (256 mbps). The online simulation program then generates the numerical mesh, applies default boundary conditions, and computes the temperature at all points inside the casting at the moment when the hottest spot reaches solidus temperature. The temperature results are shown as a colourcoded image, with white-yellow denoting hot spots (probable location of shrinkage defects) and blue denoting early freezing regions (usually hard spots). User can save the image to his own computer for future reference. Once file upload is complete, the simulation results typically take less than ten minutes to appear on the user s computer (Fig.3). For lab exercises, students can first upload and simulate a cast part to find the location of hot spots. Then they can design and attach feeder models to the part using a regular CAD program, save the file, and upload the casting file for online simulation. If needed, they can repeat the steps until an optimal feeder design is obtained; the goal is to eliminate shrinkage defects in the casting while obtaining an acceptable yield. Industrial users require multiple views of the simulation results, as well as better security of their data, including an option to delete the results. For this purpose, an industrial version of the cloud-based simulation facility has been created by 3D Foundry Tech Pvt. Ltd., a company incubated in IIT Bombay ( Till date, over 500 castings have been simulated at the E-Foundry and 3D Foundry Tech systems by about 300 users including foundry engineers, product designers, consultants, teachers and researchers. Both systems are currently free, and are suitable for solidification simulation of simple to medium complex castings. For full-fledged 3D methoding and simulation, including design and solid modeling of cores, mold cavity layout, feeders, feedaids and gating, as well as coupled simulation of mold filling and casting solidification, engineers can use stand-alone software such as AutoCAST-X ( CONCLUSION Cloud-based casting simulation systems have been developed for both academic and industrial application, using a novel, fast and accurate computation method developed at IIT Bombay. This is supported by online learning resources, casting simulation project management and consultation systems. These innovations provide a low-cost, risk-free and painless introduction of simulation technology and rapid learning curve for the foundries The author is an Institute Chair Professor in Mechanical Engineering Department at IIT Bombay, Mumbai. He can be contacted at prof.b.ravi@gmail.com.