Warm Hydromechanical Deep Drawing Research Articles

An investigation of the effect of temperature variability of the tools on FEA of the warm hydromechanical deep drawing process

Warm hydromechanical deep drawing process is an innovative manufacturing technology that offers considerable increase in the formability of the materials. However, the weakness of the process lies in its complexity. For a successful process, the optimum temperature distribution of the material must be achieved. In addition, optimum loading profiles (pressure of fluid and force of blank holder) should be applied according to the punch position. These conditions can most easily be determined with the proven finite element analysis (FEA). In this study, the effect of the temperature variability of the tools on the results of the FEA was investigated. Namely, the study aims at investigating whether the temperature variability of the tools needs to be modeled or not in FE analysis. For a simple and fast analysis, it is generally accepted that the tools have a homogeneous temperature distribution and the temperature is constant throughout the process. However, in the experiments in this study, the temperatures of the tools changed considerably. The temperature variability of the tools was first measured in the experiments and then modeled in the FEA. In the analysis performed for the AA 5754 aluminum alloy, the thickness distribution of the deep drawn part was compared with the results of an FEA performed at a constant and same temperature condition. Results in both conditions were very close to each other and indicated that there is no need to obtain and model the temperature distribution or temperature variability of the tools throughout the process. It was possible to perform the FEA with acceptable accuracy by assuming a constant and homogeneous temperature distribution in the tools throughout the process.

Numerical optimization of warm hydromechanical deep drawing process parameters and its experimental verification

Abstract Warm Hydromechanical Deep Drawing (WHDD) is considered as an effective sheet metal forming process to overcome low formability problems of lightweight materials, such as aluminum and magnesium alloys, at room temperature. WHDD process combines the advantages of Hydromechanical Deep Drawing (HDD) and Warm Deep Drawing (WDD) processes. In this study, interactive and combined effects of Pressure (P) and Blank Holder Force (BHF) variation on the formability of the AA 5754 aluminum alloy sheets in the WHDD process were investigated experimentally and numerically. Different from available studies, the optimal fluid pressure (P) and blank holder force (BHF) profiles, which were determined numerically using adaptive FEA integrated with fuzzy logic control algorithm (aFEA-FLCA), were validated experimentally for the first time in literature. Consequently, limiting drawing ratios (LDR) of AA5754 material were recorded as 2.5, 2.625, and 3.125 for HDD, WDD, and WHDD processes, respectively. Thus, it was demonstrated that the formability of lightweight materials, such as AA5754, could be increased significantly using the WHDD process through the proposed optimization method. This method was also implemented into the WHDD of an industrial part with complex geometry, successfully forming sharp features with minimal thinning at reduced levels of force, pressure, and time. Consequently, it is reasonably to state that the method developed in this study can be adopted for the manufacturing of any other part using the WHDD process.

Mechanics analysis of aluminum alloy cylindrical cup during warm sheet hydromechanical deep drawing

To obtain the stress states of the sheet metal and understand the potential forming mechanism under the influences of fluid pressure and temperature during the warm hydroforming of 5A06-O aluminum alloy sheets, mechanics analysis was conducted for the warm hydromechanical deep drawing of a cylindrical cup, taking into account through-thickness normal stress induced by fluid pressure. By considering the additional stress during bending using a variable-stiffness pure bending model as equal to that determined using a bending moment model, the additional stress at the die corner during bending was solved. The force equilibrium equations for the cup near the die corner, which were classified by whether the blank contacted the die, were also established and the results were in good agreement with those obtained via the finite element method. Furthermore, mechanics analysis was also performed for the straight-wall region, and the results revealed that the error was slightly greater when the liquid pressure was used to approximately equal to through-thickness normal stress because the ratio of thickness to radius was not sufficiently large.

Investigation on the Effect of Type of Cooling on the Properties of Aluminum Alloy during Warm/Hot Hydromechanical Deep Drawing

The warm sheet cylindrical deep drawing experiment of aluminum alloy was carried out and macro-mechanical properties and microstructure evolution of hydro-formed cups with different cooling medium were analyzed, which aimed to investigate the effects of different types of cooling on mechanical properties and microstructure of cylindrical cups hydro-formed by warm Hydro-mechanical Deep Drawing (HDD). Results show that, under the condition of warm hydroforming, the mechanical properties such as yield stress and ultimate strength were influenced very little by air or water cooling. Grain coarsening of these hydro-formed cups can be inhibited to a certain extent with subsequent rapid water cooling. Moreover, it shows that the processing with warm sheet hydroforming and subsequent rapid cooling of 7075-O aluminum alloy has a positive significance in maintaining the stability of macro mechanical properties and inhibiting the degradation of the microstructure of materials.

Warm Hydromechanical Deep Drawing of AA 5754-O and Optimization of Process Parameters

Abstract Warm hydromechanical deep drawing (WHDD) has increasingly been implemented by automotive industry due to its various benefits including mass reduction opportunities in auto body-in-white components and improved formability for lightweight alloys. In the first part of the current study, WHDD of AA 5754-O was studied. In order to obtain the highest formability, an optimization study was performed for AA 5754-O WHDD process parameters (tool temperature, hydraulic pressure (HP), and blank holder force (BHF) loading profiles) through finite element analysis (FEA) + experimentation approach. Results showed that the optimal temperature for punch is 25 °C and 300 °C for die and blank holder. In addition, HP was found to be more effective on formability when compared to BHF. Both fast increasing HP and blank holder loading profiles contributes to higher formability.

Design, Fabrication, and Experimental Validation of a Warm Hydroforming Test System

In this study, a hydroforming system was designed, built, and experimentally validated to perform lab-scale warm hydromechanical deep drawing (WHDD) tests and small-scale industrial production with all necessary heating, cooling, control and sealing systems. This manuscript describes the detailed design and fabrication stages of a warm hydroforming test and production system for the first time. In addition, performance of each subsystem is validated through repeated production and/or test runs as well as through part quality measurements. The sealing at high temperatures, the proper insulation and isolation of the press frame from the tooling and synchronized control had to be overcome. Furthermore, in the designed system, the flange area can be heated up to 400 °C using induction heaters in the die and blank holders (BH), whereas the punch can be cooled down to temperatures of around 10 °C. Validation and performance tests were performed to characterize the capacity and limits of the system. As a result of these tests, the fluid pressure, the blank holder force (BHF), the punch position and speed were fine-tuned independent of each other and the desired temperature distribution on the sheet metal was obtained by the heating and cooling systems. Thus, an expanded optimal process window was obtained to enable all or either of increased production/test speed, reduced energy usage and time. Consequently, this study is expected to provide other researchers and manufacturers with a set of design and process guidelines to develop similar systems.

Finite Element Analysis and Experimental Validation of Warm Hydromechanical Deep Drawing Process

This study intended to establish finite element analysis (FEA) model of warm hydro mechanical deep drawing process (WHMD) of cylindrical cups by means of commercial FEA package Ls-Dyna The validity of established FEA model is verified by means of WHMD experiments through several studies. It was noted that the established model successfully simulated the real process leading to significant cost and time spent on trial-error stage in hydromechanical deep-drawing of lightweight alloys.

Effect of through thickness normal stress on forming limit at elevated temperature investigated by using modified M–K model

The formability can be improved in warm/hot sheet hydroforming due to two important factors of temperature and through thickness normal stress. An extension of M–K model is presented in this paper with consideration of the liquid pressure induced through thickness normal stress. The through thickness normal stress is introduced by using the general form of Hill48 yield criterion. The effects of temperature and through thickness normal stress on the formability improvement can be predicted by using the modified M–K model with the combination of a proposed temperature dependent constitutive equation. The Newton–Raphson method is used and the numerical procedure is approved stable and correct. The yield loci show a significant dependence on temperature and through thickness normal stress. Size shrinking caused by the elevated temperature and location shifting due to the increasing thickness normal stress are observed. Comparison of the experimental FLDs of AISI1012 at plane stress and room temperature, STKM-11A for tube hydroforming at room temperature and 5A90 at plane stress and elevated temperature with the theoretical results show good agreements. The key parameters, such as inhomogeneity factor f0, n value, m value and initial thickness T0, grain size d, initial surface roughness R0, show a strong dependence on FLDs and increase of FLD0. The increase of FLD0 is formulized in a full quadratic form, which is a function of temperature and through thickness normal stress. The cylindrical cup warm hydromechanical deep drawing was carried out and the effects of temperature and through thickness normal stress on formability can be observed.

EFFECT OF HYDRAULIC PRESSURE ON WARM HYDRO MECHANICAL DEEP DRAWING OF MAGNESIUM ALLOY SHEET

The uniaxial tensile test and hydraulic bulging test of AZ31 magnesium alloy sheets were applied to study the influence of temperature on the material properties and obtain the forming limit curves at different temperatures. Numerical simulations of warm hydro mechanical deep drawing were carried out to investigate the effect of hydraulic pressure on the formability of a cylindrical cup, and the simplified hydraulic pressure profiles were used to simulate the loading procedure of hydraulic pressure. The optimal hydraulic pressure at different temperatures were given and verified by experimental studies at temperature 100°C and 170V.

A study on the analytical modeling for warm hydro-mechanical deep drawing of lightweight materials

The warm hydroforming process has become an emerging technology in recent years to reduce the weight of automotive body structure and minimize the number of process steps. In this study, analytical models were developed to investigate the effects of process conditions such as temperature, hydraulic pressure, blank holder force and forming speed. The analytical model under hydro-mechanical deep drawing (HMD) condition was developed based on experimental results in the literatures. FE models were also developed to validate the analytic models. Then, the analytic model was validated through comparisons with both existing experimental results and FE results. The analytical model provided rapid and reasonably accurate results for the design of warm hydroforming process. Based on this analytic model, several parametric studies were performed regarding to the temperature, hydraulic pressure, blank holder force, and punch speed conditions. It was demonstrated that the process windows for a successful part forming could be rapidly predicted with a reasonable accuracy by the analytic model compared to lengthy and costly thermo-mechanical FEA or experimental trial and error.