Analysis of the Mechanical and Preforming Behaviors of Carbon-Kevlar Hybrid Woven Reinforcement

Carbon-Kevlar hybrid reinforcement is increasingly used in the domains that have both strength and anti-impact requirements. However, the research on the preforming behaviors of hybrid reinforcement is very limited. This paper aims to investigate the mechanical and preforming behaviors of carbon-Kevlar hybrid reinforcement. The results show that carbon-Kevlar hybrid woven reinforcement presents a unique “double-peak” tensile behavior, which is significantly different from that of single fiber type reinforcement, and the in-plane shear deformation demonstrates its large in-plane shear deformability. Both the tensile and in-plane shear behaviors present insensitivity to loading rate. In the preforming process, yarn slippage and out-of-plane yarn buckling are the two primary types of defects. Locations of these defects are closely related to the punch shape and the initial yarn direction. These defects cannot be alleviated or removed by just increasing the blank holder pressure. In the multi-layer preforming, the compaction between the plies and the friction between yarns simultaneously affect the quality of final preforms. The defect location of multi-layer preforms is the same as that of single-layer, while its defect range is much wider. The results found in this paper could provide useful guidance for the engineering application and preforming modeling of hybrid woven reinforcement.

Numerical simulation and optimization of fine-blanking process for copper alloy sheet

When the fine-blanking process is used, secondary grinding or processing can be omitted because the shear surface of fine-blanking parts can achieve almost zero fracture zone requirements. The primary objective of the fine-blanking process is to reduce the fracture zone depth and die roll zone width. This study used a 2.5-mm-thick central processing unit (CPU) thermal heat spreader as an example. Finite element analysis software was employed to simulate and optimize the main eight process parameters that affect the fracture zone depth and die roll zone width after fine-blanking: the V-ring shape angle, V-ring height of the blank holder, V-ring height of the cavity, V-ring position, blank holder force, counter punch force, die clearance, and blanking velocity. Simulation analysis was conducted using the L18 (21 × 37) Taguchi orthogonal array experimental combination. The simulation results of the fracture zone depth and die roll zone width were optimized and analyzed as quality objectives using Taguchi’s smaller-the-better design. The analysis results revealed that with fracture zone depth as the quality objective, 0.164 mm was the optimal value, and counter punch force made the largest contribution of 25.89%. In addition, with die roll zone width as the quality objective, the optimal value was 1.274 mm, and V-ring height of the cavity made the largest contribution of 29.45%. Subsequently, this study selected fracture zone depth and die roll zone width as multicriteria quality objectives and used the robust multicriteria optimal approach and Pareto-optimal solutions to perform multicriteria optimization analysis. The results met the industry’s fraction zone depth standard (below 12% of blank thickness) and achieved a smaller die roll zone width.

Numerical Investigation of Tool Parameters Influence on the Interlock Forming During Flat Clinching Process

Tool parameters play a vital role in the mechanical interlock formation during the flat clinching process, to understand the influence of tool parameters on the interlock formation, the finite element software DEFORM-2D was used to build the numerical model of the flat clinching process, and the numerical model was verified by the experiment. The influences of the punch radius, punch fillet radius, and blank holder radius on the interlock formation of the clinched joint were investigated using the numerical model. Then, the relationship between the punch radius and blank holder radius was studied. The results showed that the interlock gradually increases with the increase of the blank holder radius, after that, the interlock begins to decrease. To maximize the interlock, the punch radius and the blank holder radius should be increased simultaneously. It can be concluded that the blank holder radius and the punch radius should keep in a linear relationship when designing the geometric dimensions of the flat clinch tools, which can promote the application of flat clinching process in car body manufacturing.

Research on High Temperature Stamping Forming Performance and Process Parameters Optimization of 7075 Aluminum Alloy

The stress strain curve of 7075 aluminum alloy in the temperature range of 310 °C to 410 °C was obtained by Gleeble-3800. By Nakazima test, the isothermal thermoforming limit diagrams of 7075 aluminum alloy at different deformation temperatures and stamping speeds were acquired. Moreover, the parameters of automotive S-rail hot stamping process were optimized by GA-BP neural network. The results show that the forming limit curve of 7075 aluminum alloy increases as the deformation temperature and stamping speed increase. The predicted optimal parameters for hot stamping of automotive S-rails by GA-BP neural network are: stamping speed is 50 mm/s, friction coefficient between die and blank is 0.1, and blank holder force is 5 kN. The maximum thinning rate at this process parameter is 9.37%, which provided a reference for 7075 aluminum alloy automotive S-rail hot stamping.

How to Avoid the Detachment of Threads of Varnish during Production, through Cutting and Drawing, in the Manufacture of Lids with a ‘Twist-Off’ Mechanism Used for the Closure of Glass Containers

The lids of glass containers which have a ‘twist-off’ mechanism are manufactured from tinplate through a process of cutting and drawing. Previously, the tinplate was protected with a double layer of a certain epoxy-phenolic varnish. During cutting, the detachment of threads of varnish is produced, and these may reach more than 150 microns in diameter. These threads stick to the equipment, thus hindering the shaping process. After manufacturing thousands of lids, stops must inevitably be made in production in order to clean machinery. Through the application of a fractioned design of experiment (DoE) application, carried out on an industrial scale, the effect of a number of factors on the detachment of threads of varnish was studied. Some to these factors refer to coating, others to the substratum and others to the process of cutting and drawing. It is concluded that the detachment is greater in the disk areas which are parallel to the forward direction of the production line. This problem could be substantially reduced, and even eliminated, if the direction of the rolling of the sheet metal were perpendicular to that of the forward direction of the production line, if the blank-holder is situated at 4 bar, if the time between the curing process and cutting is no more than 3threedays, if the clearance in the cutting is situated at 0.06 mm, and if the grammage of the varnish and the grammage of the layer of tin are increased.

Fully-coupled micro–macro finite element simulations of the Nakajima test using parallel computational homogenization

The Nakajima test is a well-known material test from the steel and metal industry to determine the forming limit of sheet metal. It is demonstrated how FE2TI, our highly parallel scalable implementation of the computational homogenization method FE$$^2$$ 2 , can be used for the simulation of the Nakajima test. In this test, a sample sheet geometry is clamped between a blank holder and a die. Then, a hemispherical punch is driven into the specimen until material failure occurs. For the simulation of the Nakajima test, our software package FE2TI has been enhanced with a frictionless contact formulation on the macroscopic level using the penalty method. The appropriate choice of suitable boundary conditions as well as the influence of symmetry assumptions regarding the symmetric test setup are discussed. In order to be able to solve larger macroscopic problems more efficiently, the balancing domain decomposition by constraints (BDDC) approach has been implemented on the macroscopic level as an alternative to a sparse direct solver. To improve the computational efficiency of FE2TI even further, additionally, an adaptive load step approach has been implemented and different extrapolation strategies are compared. Both strategies yield a significant reduction of the overall computing time. Furthermore, a strategy to dynamically increase the penalty parameter is presented which allows to resolve the contact conditions more accurately without increasing the overall computing time too much. Numerically computed forming limit diagrams based on virtual Nakajima tests are presented.

Surrogate model–based inverse parameter estimation in deep drawing using automatic knowledge acquisition

In this paper, we propose a new approach for the simulation-based support of tryout operations in deep drawing which can be schematically classified as automatic knowledge acquisition. The central idea is to identify information maximising sensor positions for draw-in as well as local blank holder force sensors by solving the column subset selection problem with respect to the sensor sensitivities. Inverse surrogate models are then trained using the selected sensor signals as predictors and the material and process parameters as targets. The final models are able to observe the drawing process by estimating current material and process parameters, which can then be compared to the target values to identify process corrections. The methodology is examined on an Audi A8L side panel frame using a set of 635 simulations, where 20 out of 21 material and process parameters can be estimated with an R2 value greater than 0.9. The result shows that the observational models are not only capable of estimating all but one process parameters with high accuracy, but also allow the determination of material parameters at the same time. Since no assumptions are made about the type of process, sensors, material or process parameters, the methodology proposed can also be applied to other manufacturing processes and use cases.