Make digital models your prime reference when designing multi-material assemblies for lightweight body & chassis

The value of high-accuracy virtual tests throughout various product development and manufacturing steps

by Mark Vrolijk
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With regards to the electrification challenge, multi-material assemblies are critical to producing vehicle bodies with the best cost-lightweight ratio and increasing energy efficiency during production. However, higher investments for powertrains translate into more conservative investments for the body and chassis. This increases the pressure to achieve better cost efficiency in the engineering and manufacturing of those vehicles. Automakers like Ford and Nissan are shifting towards a fully streamlined and virtual prototyping approach to assess feasibility, predict assembly processes, and validate performance at very early development stages to solve this conundrum.

Being able to introduce manufacturing information early in the virtual prototyping chain is beneficial for all stages in the product development cycle. So then, how does this ability concretely support engineers in their day-to-day challenge of getting multi-material assemblies right the first time?

  • Engineers in product design start with early manufacturing feasibility analysis to assess and optimize the feasibility of new designs made of novel high-strength aluminum steel – even without comprehensive manufacturing knowledge.
  • Performance engineering connect welding simulation with virtual performance analyses to include accurate manufacturing and joining history. This helps engineers validate body performances as manufactured and brings early confidence in vehicle performance predictions for crash, stiffness, and NVH. In addition, by using welding simulation to validate chassis durability, engineers predict chassis assemblies’ fatigue life with higher accuracy by accounting for residual stresses introduced during the manufacturing & welding process.
  • Manufacturing engineers simulate the manufacturing processes and get innovative materials parts right by ensuring the highest dimensional part quality and required mechanical properties for common manufacturing processes (casting, composites, sheet metal forming). In addition, they virtually validate perceived quality for external Class-A surfaces to ensure the highest dimensional and perceived part quality and eliminate visible defects upfront.
  • Assembly engineers applying distortion simulation software achieve expected tolerances for body-in-white assemblies by building the right joining and assembly process as well as optimizing the proposed tooling and work-cell layout from a shop-floor perspective by:
    • using realistic component properties and dimensions
    • following actual clamping and joining conditions and sequences
    • including the thermal effects introduced during the assembly process

The possibilities of joining multi-material assemblies are endless. So next, we will focus on one specific example: doors and closures. Engineers at this stage can simulate the entire process chain to predict dimensional and perceived quality for door & closure assemblies. By defining, optimizing, and validating the assembly processes they reach expected tolerances and cosmetic quality through a virtual process chain – from single part stamped geometries to joining process impact assessment & optimization and the hemming process.

Spotlight on multi-material doors & closures

As doors and closures are a unique selling proposition of any auto brand, the key for automakers getting them right is the ability to assess the full picture of the final component throughout the entire value chain from individual part stamping to sub-assembly of the inner components. Holding & joining need to be considered as most of the distortions are coming from the fact that engineers use non-nominal geometry. During the weld with spot welding or laser welding, distortions are introduced simply due to small data gaps. Additionally, heat effects of the welding process can further distort the shape, something which is usually more applicable to seam welding as these welds are bigger. The hemming process, which comes next, can also introduce additional distortions. This is due to the bending of the outer panel over the inner panel, which can result in waviness, splits, bend line curvature, etc. Finally, this door assembly is put in a fixture to check the final distortions versus the nominal CAD shape. This is where engineers typically get deviations.  

And let’s not forget about cosmetic defects, which are extremely important for outer panels - since they are visible to the naked eye, they must be perfect. This is the reason why automakers have started to shift away from 'single part focus' towards 'holistic assembly focus', concentrating less on the final shape of the individual panels until the final assembly meets the requirements.

It is all about being able to predict any potential cosmetic defect with regards to both the location and the severity of the defect at the early design stages before the tools and components have been physically manufactured.

So, the question becomes how and where to correct it? Simulation allows you to use the scanned data as a basis for process modifications to see if the countermeasures are improving the situation or not. Then, a robust process can be established for doors and closures assembly, such that it will obey all the cosmetic and dimensional specifications. That is exactly what our solution for doors and closures is targeting: ensuring a correct assembly before any tools have been physically manufactured, at a stage where cost and risk of changes are still acceptable. Simulation can help you identify how to correct issues and exactly where to correct them for single parts, hemming, and assembly by using the scanned data as a basis for process modifications to see if your countermeasures led to a better outcome or not. This is why we believe in numerical simulation to create sustainable, safe and performant product and processes.

Dive Deeper With Our Experts

True-to-size body and chassis assemblies require a lot of prototyping and physical testing. The renowned German Springer Media House and its lead automotive magazine "ATZ" will host a webinar with ESI experts to show you concretely how to predict the impact of manufacturing processes on assembly quality with simulations, thereby reduce development time and physical prototypes and develop and manufacture more sustainably with end-to-end virtual prototyping.

Click here to register.

Category: Automotive
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