Mg Concepts for the Vehicle Structure

DLR and Meridian technologies (link) developed a lower middle range car Front End Carrier (FEC) with topology optimization. Methodology-wise, it is interesting that they utilised predefined forces applied to spring elements in order to obtain a realistic force distribution, instead of using rigid constraints. This way, the lack of the rest of the car body did not cause errors in the simulation. The optimized structure was translated to an injection cast magnesium structure, which integrates many functions and replaces 12 steel molded sheets. Thus the cost of the structure remains the same as steel one, while offering around %50 weight savings. It is reported that the structure is lighter than aluminium structures too, however only marginally lighter than steel-polymer hybrids which we covered before (1) , (2).

Also techniques for corrosion protection of Mg structures are briefly discussed.

 

Also check our previous article featuring Meridian.

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Gear shifter Housing and Contact Benchmarks

In the thesis study by Naresh Kalidindi and Mohamad Fardmoshiri (link) of Jönköping Institute of Technology, a magnesium gear shifter housing of a VW group car was optimized. Due to the die draw direction imposed most of the structure remained untouched, and presumably no big gains were obtained. However the much more interesting part of the thesis is the contact benchmarks. It is really interesting to see structures with and without contact boundary conditions being optimized.

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Detection of Planar Regions in Volume Data for Topology Optimization

In this great work by Ulrich Bauer and Konrad Polthier (link) from Freie Universität Berlin, a method for determining planar regions in topology optimization results is developed. The results look very promising. Such a tool is very important for the sake of topology optimization usage, as topology optimization software are very good at what they do, but user interpretation of the results forms a weak point in the process. This misinterpretation can be caused by the user not trusting the software enough, being unable to comprehend the 3D structure, being unable to find a manufacturing method etc.

Such  a tool would reveal an almost readily producible structure to the user, for sheet metal structures at least, which is a very big segment of mechanical structures. It can also speed the design cycle, which is already improved by topology optimization, even more.

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POLYMER METAL HYBRID STRUCTURE

Clemson University and BMW studied (link) automotive
body-in-white (BIW) structural components made of polymer metal hybrid (PMH) similar to a previous one we discussed. The structure was optimized by means of topology, size and shape. Stiffness, strength and buckling resistance were optimized (separately). Buckling resistance was optimized with both linear and non-linear simulations. The manufacturability of the polymer injection molded insert was simulated and the cost related issues are discussed. It is a very comprehensive article.

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Non-Line-of-Sight Cannon (NLOS-C) Turret Saddle

Non-Line-of-Sight Cannon (NLOS-C) Turret Saddle was topology optimized by BAE (link). Maybe I am being a bit too negative nowadays but it is hard to see decently optimized structures. This one is not different too. Lets continue with pictures from the article.

The picture above depicts the original saddle, the design space and the resulting optimized topology.

This structure above is the revised version of the turret saddle based on the optimization. It is hard to see the connection between the optimization and this.

And finally this one is the final structure obtained after size and Topometry optimization. As you can see there is almost no connection between the steps. In the first step they topology optimized the structure, but the resulting structure was not manufacturable by welding of profiles and sheet metal, so it seems they decided to ignore it and design another structure loosely based on it. Instead they coud have changed the parameters of the optimization process and tried again. Or they could have used manufacturing constraints. It is almost always possible to obtain a truss structure from topology optimization by using the right parameters, which can be welded from profiles. The later stages are out of scope of our blog, but I cannot see the connection between inputs and outputs. As a result the weight gain was 7.8%, which is low by topology optimization standards.

Maybe we shall start some courses on practical applications/interpretations of topology optimization.

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Heidenreich & Harbeck

Heidenreich & Harbeck applies topology optimization (link) to a slide for a high-speed milling machine to be cross-accelerated with 2 g. The structures topology was manually altered (we cannot call a manual trial and error study as optimization, as far as my understanding of optimization dictates) and deformation was reduced by %50 and weight by %15. Then automatic topology optimization was carried and %65 reduction in deformation was obtained. Also time required to design the structure was reduced to %22 engineering time and %32 computing time.

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SA-SIMP

N. P. Garcia-Lopez et al. developed “An improved hybrid topology optimization approach coupling Simulated Annealing and SIMP (SA-SIMP)” (link). The topologies found by SA-SIMP method are reported to have round %6 higher rigidity than SIMP topologies and there are no gray elements, which have intermediate densities. However these results seem a bit artificial, the lack of gray points may be directly the cause of high rigidity. To be clearer, the topologies shown are almost exactly same except the gray elements. The point is if they were translated to real physical components, they would have to be smoothed and the resulting structures would be exactly the same. The stiffness of the topology optimization result is of no importance if it cannot be reflected to the real component. Practically SA-SIMP results are identical to SIMP results.

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Pininfarina bonnet

I came across this article (link) by Pininfaria about the optimization of a car bonnet. The car is Argento Vivo concept, which seems to be very beautiful, made for Honda but unfortunately was not produced. However the optimization is not quite beautiful. It is a rare article where the properties of the structure is degraded. This seems to be mainly due to the early date of the article (1998) when topology optimization was not widely used, even some of the popular algorithms were not even discovered. I believe a great company like Pininfaria would not make the same mistakes today. The problem is quite trivial, they did not expand the design space to the full usable volume, but used the intuitively designed bonnet as the design space, so there was not much left for the topology optimization software to do, as it was required to remove volume from an already designed volume.

Beautiful

Not beautiful

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Beam Structure Optimization for Additive Manufacturing based on Principal Stress Lines

Yongqiang Li, Yong Chen of Epstein Department of Industrial and Systems Engineering, University of Southern California, have developed a novel way of topology optimization for truss structures (link). The method relies on determining principle stress lines and forming a truss structure following the main lines. It seems to be a very fast way of optimization, if truss optimization is required. The method and the article does not seem to be related to Additive Manufacturing anymore than any other topology optimization method. Actually solid based topology optimization is more closely related, as most of the topologies can only be produced with  Additive Manufacturing methods.

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ELEMENT EXCHANGE METHOD

ELEMENT EXCHANGE METHOD studied by Mohammad Rouhi is a non-gradient based method (link). It relies on exchanging lowest and highest strain energy elements, thus step by step reaching convergence. In the thesis it is shown that the method finds similar solutions to SIMP, despite not as efficient, as it requires more iterations. It is however faster than other non-gradient based methods. There are no intermediate densities, which is an advantage in many cases. The method deals with checkerboard problem in a novel way. Also the initial distribution is random.

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