May 14, 2014 -- Development teams at TE Connectivity (TE) in Japan (formerly known as Tyco Electronics) engineer B-type barrel designs to further enhance the gastight solder-free connection between barrel and stranded wire. The electrical and mechanical connection characteristics are tested and simulated to accurately model the barrel design. TE engineers use Optimus software to coordinate and automate crimp and tensile analyses in search of optimized design variants combining highest crimp connection quality and robustness. Optimus automatically drives the execution of ANSYS Workbench and LS-DYNA when performing design of experiments (DOE) and design optimization studies. The automated simulation process enables TE engineers to identify robust optimum barrel design variants and speed up the development cycle. In a next step, they plan to incorporate thermal and vibration analyses into the Optimus-driven barrel design process.
Setting up automated process for barrel design optimization
Contact resistance versus tensile strength
TE Connectivity in Japan develops a range of crimp connection types used across markets worldwide. The B-crimp type is a common wire crimp shape, offering short cycle time, high flexibility and low overall cost. Upon forming the barrel wings during the crimping process, the individual wire strands move symmetrically within the barrel space. TE engineers performed physical testing and virtual simulations to evaluate the quality of crimp connections through a number of parameters, such as crimp height and width. “Cross sectional analysis reveals crimp area compression and local stress distribution in barrel and wire strands,” explains Kazushige Sakamaki of Tyco Electronics Japan G.K., a TE Connectivity company. “A destructive pull test determines whether the connection meets the required tensile testing force curve. The target is a barrel design that consistently leads to sufficiently crimped connections with limited yet evenly spread stress distribution, offering high tensile strength and low electrical contact resistance.”
Integrated barrel development process
To manage the complex interplay between crimp barrel design parameters, the TE engineering team formalized the development process in Optimus. Kazushige Sakamaki says that the Optimus process integration and design optimization framework enabled TE to coordinate the development tasks, and validate the virtual prototyping models with the available test data. The TE engineers sketched the simulation process flow in the graphic drag-and-drop Optimus process integration editor, and defined the design parameter ranges as well as the design objectives and constraints. Optimus’ underlying direct interfaces support the fully automatic updating of the ANSYS Workbench barrel design and driving the associated LS-DYNA finite element simulation.
Up-front engineering insight
Crimping is a transient dynamic and non-linear process. The obtained crimp connection characteristics largely depend on the force applied by the punch tool, the barrel characteristics (shape, material and thickness) and the boundary conditions such as the tool/barrel contact that changes over time. Not to mention the presence of transversal serration notches in the barrel bottom and the springback of the barrel wings that are taken into account. “To acquire up-front insight into the unexplored barrel design potential, we performed design of experiments (DOE) in Optimus to sample the design space in the most effective way,” Sakamaki states. “Response surface modeling (RSM) condensed the DOE results into a so-called surrogate model. The RSM graphs helped us define the crimp height working range that limits the punch force and allows for balancing high tensile strength with low electrical contact resistance.”
Optimizing barrel performance and robustness
Best-performing barrel design candidates
After setting up the optimization process, the automated Optimus-driven search was started to identify the optimum set of barrel design parameter values. A proven second-order polynomial optimization algorithm efficiently traced those design candidates that best match the performance objectives while respecting all applicable design constraints. The constraints covered punch force range, barrel dimensions and maximum local stress values. Sakamaki says that the TE design engineers picked the most optimal barrel design candidates for further in-depth evaluation. “The barrel design optimization yielded promising results, but also revealed that the designs were sensitive to variations in barrel manufacturing and crimping.” It is often more costly to control the causes of manufacturing variation than making product performance insensitive to these variations. In this regard, Optimus incorporates Taguchi methods, which allowed TE to develop barrel designs exhibiting high crimp connection quality and robustness.
Wire barrel robustness optimization using Taguchi methods
The TE development team applied the L81 Taguchi design table to generate the signal/noise (SN) ratio values for each design variable, and have them displayed in Optimus column effect plots for easy interpretation. “Using these plots, we decided on the combination of design parameters that enable them to most effectively increase barrel design robustness,” Sakamaki explains. “This entails selecting the levels for which the SN ratio is high for each design variable, and tune the crimp connection performance to target through analysis of the design parameter sensitivities. The parameters evaluated in this respect include stress, contact pressure, contact area, contact force, extension, area index and tensile strength.” Optimus supports the automated execution of the Taguchi robust design optimization process, enabling faster turnaround.
Entire barrel optimization process run in Optimus
The engineers at TE ran the entire process in Optimus. The automated barrel design optimization sequence incorporates all required algorithms, including Taguchi methods and interfaces with parametric modeling and simulation packages. Sakamaki concludes that the automated Optimus robust design optimization process is suitable for complex barrel development. “Optimus contains all necessary functions to automatically execute Taguchi methods from start to end, considerably saving development time and cost. In a next step, TE plans to incorporate thermal and vibration analyses into the Optimus-driven crimp design process. TE also anticipates tracing the effects of barrel shape differences, serration characteristics and wire cross section sizes.”
"To acquire up-front insight into the unexplored barrel design potential, we performed design of experiments (DOE) in Optimus to sample the design space in the most effective way.”
Kazushige Sakamaki of Tyco Electronics Japan G.K.
“The automated Optimus robust design optimization process is suitable for complex barrel development. Optimus contains all necessary functions to automatically execute Taguchi methods from start to end, considerably saving development time and cost.”
Kazushige Sakamaki of Tyco Electronics G.K.
All graphics: Copyright Tyco Electronics Japan G.K. , courtesy TE Connectivity
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