Optimization is the search for one or more better solutions to a certain problem. Within this sector, an optimizer is a software able to identify, suggest and eventually verify the ideal set of input variables that provides the best design solutions among all those possible. In most cases, the underlying relationships between the control parameters (called inputs) and the measured performances (called outputs) are unknown or difficult to solve. Sometimes, moreover, in order to obtain the answer of the system it is necessary to use complex numerical models that require a lot of time in order to be able to produce the desired output: a typical example is that of the use of simulators of foundry process, in which the result of the simulation, in function of the chosen parameters, is the fruit of a long and complex calculation of 3D thermofluid dynamics. Figure 1 - Optimization process scheme The IMPROVEit optimization software is able to interface with multiple applications, including the FLOW-3D® CAST (Flow Science inc.) process simulator, and connect them together to completely define a workflow that can be run repeatedly and automatically in order to get the best solution in the shortest possible time, understanding the nature and complexity of the problem. Case study: Optimization of the injection phase In this case study, courtesy of FORM S.r.l., during the design of the moulding for battery covers by HPDC, many areas were found in the structure where the amount of porosity from gas was high. It was therefore decided to use the optimization with the aim of reducing defects by acting on the design of the casting channels and optimizing the speed of the piston. For our purposes, the workflow inputs chosen were the values of the piston speed curve in the first phase and a wide range of geometric parameters of the channels managed by interaction between optimizer and parametric CAD software, while the objectives were the best calibration of the arrival of the metal at the casting connections and the reduction of the amount of air trapped in the alloy during this first phase of filling. The flow is structured as follows: the optimizer interacts directly with a parametric CAD software to automatically change the shape of the casting channels and then exports the geometries in STL format; the latter are then used by the process software to simulate the filling, after which the desired outputs are extracted and processed. Figure 2 - Parameters for the optimization of the injection phase, courtesy of Form S.r.l. When there are two objectives to evaluate at the same time, it is possible to find a series of different optimal results of compromise between the two outputs sought, which is called front of Pareto. Since a workflow cycle takes an average of about 20 minutes, it was decided to perform the optimization on a total of 20 calls. On the basis of these calls, the chosen configuration is positioned in the center of the Pareto front and therefore presents a good compromise to have a low and most uniform possible arrival time at the casting attacks, 10% better than the initial setup, and at the same time obtain a minimum quantity of trapped air, 13% lower than the initial data. Figure 3 - Comparison between initial and optimized solution, courtesy of Form S.r.l. This case study therefore shows how the automation and numerical optimization of product design, simulation, interpretation of results and changes, help to save a lot of time and how it is possible to achieve important improvements even in the face of a limited number of calls. … [Read more...]
Vertical Spike Wave
This simulation was inspired by The Slow Mo Guys’ video “90 ft. Vertical Spike Wave in Slow Mo” which shows the results of an experiment made by the FloWave Ocean Energy Research Facility. We use part of their video to compare results with our own simulation. https://www.youtube.com/watch?v=iWKFPTgkpXo&t=105s The Vertical Spike Wave The Vertical Spike Wave is the result of a concentric wave travelling towards its center. Depending on its velocity, the wave can collide in the middle and form a spike of water. This wave can be generated in a circular pool equipped of moving panels on the entire length of the perimeter that push in one coordinated motion the water towards the center. The pushers have to be activated simultaneously with the same motion in order to have the water travel in one single motion and collide at the same speed with the same energy. If the speed is high enough, the water will rise in the center of the pool in a high spike [Figure 1] and fall back splashing. Figure 1 - Vertical Spike Wave Model setup on FLOW-3D® FLOW-3D was used to setup the simulation of the Vertical Spike Wave, then the result was post-processed on FlowSight. In order to model the circular wave, the mesh was defined on cylindrical coordinates. That allowed to simulate only a part of the pool [Figure 2] then to duplicate it later on Flow Sight to make it look like the entire pool was modeled. Figure 2 - FLOW-3D setup Most of the measurements were given in The Slow Mo Guys’ video, so it was possible to give the simulation the real dimensions. The pool is about 50m wide and is equipped of 168 panels. We estimated that the pushers took 4s to motion back and forth once with an angle of 17.2°. To setup the simulation, a pool was created simply on FLOW-3D using the basic geometry provided by the software, then the panel was imported as an STL file. The pusher was setup as a moving object [Figure 3] to which a motion defined in advance was applied. The water is completely still at first, and a single push is sufficient to create the vertical spike wave. Figure 3 - Panels pushing the water Results The overall motion and energy correspond to the reality with a very good precision. Some differences can be seen only in the disrupted front of the spike: its effects are negligible for our comparison but could be taken into account with a complete 3D and 2-fluid simulation. Figure 4 - Experiment and Simulation side by side … [Read more...]
Design optimization for mass production
Introduction The development of a product involves various phases of calculation and design that provide a series of predefined steps to follow in order to reach mass production. With this aim in mind and considering the high number of parts to be produced, any material saving is advantageous and relevant from an economic perspective. The parties involved in the production need to reduce the waste material (relevant for the foundry) and to reduce the weight of the components (relevant for the end customer). Optimizing the shape of the product helps both parties (foundry and customer) to reach the right compromise to make the adequate savings while obtaining the highest quality parts. In this article we will show the design optimization process of a foundry product destined for mass production using an optimization software and a process simulator. The aim is to analyze the solidification of the metal present in the system of interest and to evaluate how the optimization helps both parties to benefit from it. Component to produce The component to optimize in this study is produced by sand molded casting technique, one of the oldest, simplest and most economical techniques. The preliminary design phase has provided a prototype in stereolithography format (STL), which is already potentially good for production (courtesy of Flow Science Deutschland). In the image [Figure 1] you can see the feeding system (in yellow) and the geometry of the part to be produced (in red). The weight of the part itself in this starting configuration is 2,197kg, and the whole system weight is 3,126kg. The main objective is, by acting on some details of the geometries themselves, to obtain a total weight of the system as small as possible without having significant porosity in the part. In order to obtain the best possible result, the parameters chosen to be modified are the size of the feeder [Figure 2], the thickness of the vertical wall closest to the feeder and the thickness of the transition zone between the two walls [Figure 3]. Figure 2 - First optimization parameter Figure 3 - Second and third optimization parameters The considered variables are thus potentially multiple and exploring manually all the possible combinations can be a very long and complex work. That is why we have chosen to use a numerical optimizer able to explore the solutions independently. Therefore, IMPROVEit was chosen, which thanks to its simple interface allows to perform both the setup phase and the processing of results easily. FLOW-3D® CAST was chosen as the process simulator for its precision, reliability and simple use in foundry simulations. As for modifying the geometrical shape, the optimization software allows both to interact directly with parametric CAD if the file is in original format, and to modify an STL file directly inside IMPROVEit if, as it is the case in this test, only the latter is available. Once the parameters to be corrected have been selected, the software is able to internally modify the shape of the geometries, launch the solidification simulations interacting with the FLOW-3D® CAST process software using the modified geometries, extract the results of the analyses and process them with suitable mathematical nodes to obtain the right optimized quantity. [Figure 4] shows the workflow of our case study. Figure 4 - Optimization workflow In order to detect the shrinkage porosity dimension present at the end of the solidification simulation, four control volumes divide the geometry in four distinct zones: the top part is in dark blue, the central part in yellow, the left part in cyan and the right part in magenta. According to the customers’ exigences, among those four parts only three are relevant for optimization: the porosity in the top part (dark blue) is not considered. In the initial configuration, the total shrinkage porosity volume in the three control volumes is 581mm3. Figure 5 - Control volumes Execution For the purpose of the optimization process, two objectives and one constraint were chosen: minimizing the feeding system and the part’s weight while having the amount of porosity in the three control volumes below a threshold low enough to be able to consider the part free from visible defects. Setting up an optimization with two objectives and a constraint makes the understanding of the problem complex; nevertheless, the IMPROVEit engine being developed specifically for this type of problem, it allows to obtain an excellent result with just a few calls of the process simulator. Since each optimization cycle lasts only a few minutes, it was decided to allow the execution of fifty cycles. Considerations After fifty cycles, IMPROVEit was able to propose a wide range of solutions that reduce the weight of the system with tolerable thresholds of porosity, which was our objective. Moreover, by analyzing the panorama of the solutions found, it is possible to … [Read more...]
Increasing Discharge Capacity with the Piano Key Weir
Piano Key Weir Characteristics The Piano Key Weir is a particular model of the labyrinth discharge spillway. It is composed of an alternation of reclined surfaces, one is the direction of the flow, the other in the opposite direction. Each of these slopes is separated by a vertical wall that follows the geometry of the shape. Seen from above, it is a series of rectangles cut in equally sized sections widthwise. For each of these sections one of the side perpendicular to the stream is pushed down, creating a slope on which the water can either flow or accumulate, depending on which side the section is lowered. This structure tops a smaller wall. The Piano Key Weir is generally used at the outbound of a dam, the idea being to dispose of a construction that is solid enough to resist the pressure created by a high quantity of water contained in a dam or a river during flood season, that can evacuate the overflow of water, and that is simple enough not to be too expensive. Usage of the Piano Key Weir The Piano Key Weir is a free flow discharge spillway. Its geometry allows for a significantly higher evacuation capacity. The studies conducted on this type of spillway have two aims: build solid and cheap discharge spillways, as well as reinforce the older structures. This enables engineers to avoid accidents of dams that break or that don’t have the capacity to discharge water correctly and in a controlled manner when there is a flood. Usually the weir is placed after the dam and before the cities so as to allow a controlled discharge of water. This type of discharge spillway presents several crucial advantages. First it is easy to install on structures that are already there, as opposed to classic labyrinth discharge spillways. Moreover, its shape that alternates between ascending and descending slopes allows the formation of two different flows depending on whether the water arrives on one or the other slope. When the water flows over the descending slope it forms a jet that goes towards the bottom of the dam, and when it is first contained by an ascending slope it forms a kind of film which then flows towards the jet below. This division of flow slows the stream down consequently in a much more efficient way than classic dams do. Simulation results In order to observe the effects of the Piano Key Weir we used FLOW-3D® to make a simulation displaying the weir in a stream. The model setup is the most basic one, given that it has been proved that it enabled the results to be as close to reality as possible. The simulation shows the characteristic flow of the water over the “keys” of the piano as well as the decrease of the flow rate after the weir. We can see that the error percentage between experimental results and the simulation using FLOW-3D is only between 2% and 4% on average. The only determining factor is the mesh resolution when it comes to the accuracy of the simulation, but it only changes the error of 3% or 4% maximum, which means that overall the simulation doesn’t go above an error of 6%. … [Read more...]
Minimizing air entrainment in shot sleeve
M. Barkhudarov, Flow Science Inc., Santa Fe, New Mexico; S. Mascetti, XC Engineering, Italy; R. Pirovano, XC Engineering, Italy Abstract High pressure die casting is one of the most complex processes in the foundry world due to the wide range of physical phenomena and process parameters that control the outcome. A particular challenge is achieving optimal conditions in the shot sleeve from which metal is injected into the die cavity. The speed of the plunger in a horizontal shot sleeve must be carefully controlled to avoid unnecessary entrainment of air in the metal and, at the same time, minimize heat losses in the sleeve. The paper presents a general solution for the flow of metal in a shot sleeve, based on the shallow water approximation of the interaction of the moving plunger and liquid metal. The derived analytical solution allows engineers to precisely control the behavior of metal in the shot sleeve during the slow-shot stage of the high pressure die casting process, minimizing the risk of air entrainment. Results are validated with three-dimensional numerical modeling of the process. Coupled with parametric optimization, the numerical model can improve the process conditions predicted by the analytical model. Introduction The speed of the plunger in a horizontal shot sleeve must be carefully controlled to avoid unnecessary entrainment of air in the metal and at the same time minimize heat losses in the sleeve. If the plunger moves too fast, large waves are created on the surface of the liquid metal that may overturn and entrain air into the metal, which will then be carried into the die cavity. A plunger moving too slow results in waves reflecting from the opposite end of the shot sleeve. The reflected waves prevent proper expulsion of air into the die cavity. In either case, the outcome is excessive porosity in the final casting. Moreover, a slow plunger increases also oxidation of the free surface of liquid metal, and the heat losses because of the long contact time with the mold walls. In this article two approaches are used to limit these effects: a general solution for the plunger speed as a function of time and a full-physics, three-dimensional CFD optimization. Mathematical model The dynamics of waves in a horizontal shot sleeve can be analyzed by drawing an analogy with flow in an open channel. A detailed analysis is possible by modeling the flow of metal in a rectangular shot sleeve of length L and height H (justified for initial fill fractions in the range of 40-60% [1]) using the shallow water approximation [3]. In this approximation the flow in the vertical direction is neglected in comparison with the horizontal velocity component. The flow is modeled in two dimensions, with the x axis directed along the direction of motion of the plunger, and the z axis pointing upwards. If viscous forces are omitted, then the flow has only one velocity component, u, along the length of the channel. The plunger speed in the positive x direction is given by dX/dt=X’(t), where X(t) defines the position of the plunger at time t>0. At the moving surface of the plunger, the velocity is defined as . As the plunger moves along the length of the channel it sends waves traveling forward along the metal surface. Each wave is associated with a small segment of the metal free surface and the column of metal directly below it (Fig. 1). The location, metal speed and depth in a wave that separates from the surface of the plunger at time t=tp are given by [3]: (1) Where According to Eq. (1), the metal speed, u, and depth, h, in each wave are constant and depend only on the time of the wave separation from the plunger, tp. They both increase with the speed of the plunger X’. Therefore, the first conclusion is that to maintain a monotonic slope of the metal surface in the direction away from the plunger, the latter must not decelerate. If this condition is not satisfied, then there will be waves sloped in both directions. When they reflect off the end of the sleeve and travel back towards the plunger, it creates unfavorable conditions for the evacuation of air from the sleeve and into the die cavity. Figure 1: Schematic representation of the flow in a shot sleeve and the coordinate system. Controlling the Waves Once a wave detaches from the plunger it travels at a constant speed given by (2) If the plunger accelerates, then each successive wave will move faster than the waves generated earlier. This will lead to a steepening of the surface slope as the waves travel further down the channel, and can potentialy result in overturning. If the speed of the plunger can be controlled as to limit the wave steepening during the slow shot stage, then the overturning can be avoided. Figure 2: The illustration for calculation of the slope of the metal’s free surface. Let us analyze the evolution … [Read more...]
