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User Story GE : iSIGHT GE is a major producer of gas turbines for both electrical power generation and aircraft engine applications. It is a leading manufacturer of military and commercial aircraft jet engines. GE also has the largest installed base of steam turbine generators in the industry -- more than 8,000 generators have delivered over one billion hours of operation. Rotating disks in gas turbine engines are generally forged. Using numerical optimization tools, GE engineers have demonstrated the capability to achieve significant material savings on top of manually optimized forging designs for jet engine disks. Forging is still the best way to produce a strong part that can sustain the high stresses in an aircraft engine or power turbine. As a result, it is one of the most critical procedures in the turbine disk manufacturing process. During the forging step, a block of metal, which may be of cylindrical or other shapes, is transformed to a shape close to that of a disk in one or several operations. The part then undergoes heat treatment and is machined to the final disk shape. Each step has special process requirements involving different physical phenomena. All the conditions must be satisfied simultaneously for each step. Therefore, the disk manufacturing process is highly complicated and multidisciplinary. The design specifications for forging are complex and include the following considerations: The forging press must have the capacity to forge the part. The forged part must possess the right material properties. Close correlation has been observed between material properties and forging and heat treat processing conditions. Based on their previous experience, die designers have developed several geometry-related forging rules. Die stress cannot exceed a critical threshold value. Otherwise, a die can be damaged due to excessive stress, which leads to costly repair and even complete replacement of the die. Forging cycle time must be reduced to remain competitive. The time spent on forging a part must be reasonable, i.e., as quick as possible, which is an important productivity consideration. Significant amounts of extra material are included in a forged part, which is subsequently machined to get the final disk shape. This is the preferred way to ensure good material properties and avoid having to scrap the part due to process variability. However, decreasing the material consumption by even a modest percentage can drastically reduce the manufacturing cost of turbine disks. Previous attempts to manually achieve a balance between these two conflicting objectives have not been completely successful due to the complexity of the problem. With the advance of optimization, numerical simulation, and geometry modeling, it is now possible to attack this difficult problem. Dr. Shesh Srivatsa and colleague Dr. Beichang He led a team of GE engineers to address reducing the cost of forging. They formulated a shape optimization model for the design of the turbine disk forging process. The objective is to minimize the forging weight by changing the die geometry parameters. The forging constraints include producibility, material properties, geometry, and forging time conditions presented in the previous paragraph. The team implemented a computer-based design automation and optimization system, known as iSIGHT Forging Optimization System (IFOS), using a forging simulation package, DEFORM, a commercial CAD tool, and iSIGHT as the integration framework and optimization tool. iSIGHT from Engineous Software, Inc. (Morrisville, NC) replaces the manual iterative portion of the traditional design process with an automated, computer-controlled procedure. The software helps link all of the relevant simulation software, then automatically changes the design parameters, runs the analysis codes, assesses the output against the target objectives, and changes the design variables based on instructions from an optimization algorithm chosen for the specific problem. Through a series of iterations among the different packages, an ideal scenario is established. "The whole process iterates without human intervention until an optimal solution is achieved. The GE engineers have applied IFOS to a few selected disk design problems and achieved significant weight reductions. They are able to reduce the total forging weight 5%-10%, over manual design optimization. If the saving in weight is expressed in terms of the excess material added over the smallest geometrically feasible shape to ensure forgeability and satisfaction of other constraints, the weight saving is 50%-80%. Clearly, they have achieved significant material savings of the manually optimized forging designs for jet engine disks. Die designers are now able to explore, with the help of a fully automated software system, a bigger design space, and find a feasible design of the least forging weight. The GE team successfully demonstrates, with real-life forging applications, the power of iSIGHT as a framework to integrate engineering CAD and CAE tools and also as an optimization system to improve product design. By utilizing this technology, the quality of turbine disks is improved, the design process variation is minimized, and the manufacturing cost is reduced. The GE engineers are in the process of further enhancing the iSIGHT Forging Optimization System and put it into production use. For more information, visit www.engineous.com. Author: Laura Carrabine

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