Dimensional accuracy in quick plastic forming of aluminum alloy using demolding mechanism

This study focuses on quick plastic forming (QPF), product dimensional tolerances, and removal methods. The traditional curled metal shell mold in QFP, has limitations such as long process time and unstable quality. Therefore, this investigation designed a demolding mechanism, in order to improve the process efficiency and dimensional accuracy of QPF, in the manufacture of metal casings. The research results show that the proposed mechanism can significantly decrease the process time, because it replaces most of the operations of specimens movement after forming completely. The shorter process time reduce the die temperature loss during operation, thus also improving the efficiency by eliminating the need to wait for the die to return to its operation temperature. In terms of dimensional tolerance, the tolerance grade of QPF process was determined using the standard deviation, and found to be between IT10 and IT14. This range covers the scope of CNC cutting and stamping processing, indicating that the process has commercial value in the production of metal casings, because the current mainstream manufacturing process of metal casings comprises casting, stamping and CNC machining.

Hot Tensile Behavior of Superplastic and Commercial AA5083 Sheets at High Temperature and Strain Rate

Since the last two decades, the automotive industry has dedicated an increasing attention to the manufacturing of sheet components made of high-resistant aluminium alloys; the superplastic AA5083 grade is currently utilized in both the conventional superplastic forming and the recently patented quick plastic forming, which assures higher productivity compared to that of superplastic forming, while the commercial AA5083 grade is rarely employed. The objective of the paper is to compare the hot tensile behaviour of commercial and fine-grained AA5083 sheets when processed at high temperature and strain rate, which are typical of hot stamping processes. The results are presented and commented in terms of flow stress, anisotropy, strain at failure, microstructural and hardness features as a function of temperature and strain rate. On the basis of the obtained results, the set of optimal forming conditions for the two grades is identified.

Effect of Lubrications on Quick Plastic Forming Behavior of AZ31 Magnesium Alloy Sheet

Lubrication plays important role in Quick Plastic Forming (QPF). Friction coefficient between AZ31B magnesium alloy and the die steel was examined by ring upsetting tests at 400°C with no lubrication, boron nitride (BN), graphite and molybdenum disulfide respectively. The effect of the four lubrication conditions on bulging height and wall thickness distribution of conical, rectangular and cylinder components in QPF within 300s was investigated. Macroscopic and microscopic morphology of the formed part surface in the four conditions was observed.

Sheet Orientation Effects on the Hot Formability Limits of Lightweight Alloys

The formability curves of AZ31B magnesium and 5083 aluminum alloy sheets were constructed using the pneumatic stretching test at two different sets of forming conditions. The test best resembles the conditions encountered in actual hydro/pneumatic forming operations, such as the superplastic forming (SPF) and quick plastic forming (QPF) techniques. Sheet samples were deformed at (400 °C and 1 × 10−3 s−1) and (450 °C and 5 × 10−3 s−1), by free pneumatic bulging into a set of progressive elliptical die inserts. The material in each of the formed domes was forced to undergo biaxial stretching at a specific strain ratio, which is simply controlled by the geometry (aspect ratio) of the selected die insert. Material deformation was quantified using circle grid analysis (CGA), and the recorded planar strains were used to construct the forming limit curves of the two alloys. The aforementioned was carried out with the sheet oriented either along or across the direction of major strains in order to establish the relationship between the material’s rolling direction and the corresponding limiting strains. Great disparities in limiting strains were found in the two orientations for both alloys; hence, a “composite FLD” is introduced as an improved means for characterizing material formability limits.

Quick Plastic Forming Behavior of AZ91 Magnesium Alloy Sheet

The quick plastic forming (QPF) behavior for fine-grained AZ91D magnesium alloy sheet with the thickness of 1.0 mm and the grain size of 6.0 µm was investigated. Free gas bulging tests were conducted under different gas pressure for 300 s in the range of 250-400°C to investigate how the temperature and pressure impact on the formability of QPF. Free gas bulging test results show that the bulge height of semisphere part exist the peak value of 33 mm under the gas pressure of 0.5 MPa at 400°C. QPF tests of cup part were performed based on the free gas bulging test results. A cup part with the height of 20 mm which both of surface quality and fillet radius were satisfactory was formed using a two-stage loading path at 400°C during 300 s. Furthermore the microstructural revolution law during the QPF was discussed. The larger the thinning rate of parts is, the smaller the grain size will be.

High-Temperature Forming of a Vehicle Closure Component in Fine-Grained Aluminum Alloy AA5083: Finite Element Simulations and Experiments

Fine-grained AA5083 aluminum-magnesium alloy sheet can be formed into complex closure components with the Quick Plastic Forming process at high temperature (450oC). Material models that account for both the deformation mechanisms active during forming and the effect of stress state on material response are required to accurately predict final sheet thickness profiles, the locations of potential forming defects and forming cycle time. This study compares Finite Element (FE) predictions for forming of an automobile decklid inner panel in fine-grained AA5083 using two different material models. These are: the no-threshold, two-mechanism (NTTM) model and the Zhao. The effect of sheet/die friction is evaluated with five different sheet/die friction coefficients. Comparisons of predicted sheet thickness profiles with those obtained from a formed AA5083 panel shows that the NTTM model provides the most accurate predictions.

Reverse Bulging in Hydro/Pneumatic Sheet Metal Forming Operations: Is it Worth It?

The merits of warm and elevated temperature hydro/pneumatic sheet metal forming operations, most prominently superplastic and quick plastic forming, have been ever counteracted by two major drawbacks: slow forming rates and non-uniform thickness distribution with potentially severe thinning. Trying to resolve one of the two issues has generally led to escalating the other, so a compromise based on the nature of the part being formed is often targeted. To tackle the latter of the two issues, imposing a pre-thinning reverse bulging step has been shown to ease the problem with specific part geometries that involve large plastic strains and intricate details. The aerospace industry, however, is the prime sector that is able to afford the “seemingly” prolonged forming times associated with this approach. Yet with the lack of adequate details on the implications of utilising reverse bulging, this effort explores some of the hidden merits of the approach. A recently-developed simple monitoring technique for providing a direct feedback on the sheet’s advancement during pneumatic forming operations, coupled with an interrupted testing methodology, are utilised to have a closer look at the process. The results reveal significant time-savings that can be achieved with the proper use of reverse bulging, for both simple and complex part geometries.