Uniformity Of Thickness Distribution Research Articles

Investigation of novel laser shock hydroforming method on micro tube bulging

Tubular components are indispensable in manufacturing industry, but when its size decreases to micro level, the formability of micro tube will become undesirable. To improve the formability of micro tube, this study suggested a novel laser shock hydroforming method. This method used laser-induced shock wave as energy source and liquid as medium to transmit pressure wave. It was the pressure wave that forced the material of micro tube to flow into the die cavity and replicated the shape of that. The dynamic forming process of micro tube was first studied by numerical means, and the numerical results agreed with experimental ones. Then, the middle section thickness of formed micro tube was researched experimentally. The results shown that the uniformity of thickness distribution was improved compared to that in quasi-static condition, and the improvement of that was analyzed by numerical means. In addition, the reason for the increase of formability was investigated in the aspect of contact stress, and numerical results confirmed that the impact of the material of micro tube on the die caused the increase in compressive stress, a phenomenon beneficial to the formability enhancement. Finally, the paper compared the deformation behaviors—deformation velocity and strain rate—with and without a die, proving that the die was one factor that contributed to the formability improvement.

Process window diagram of conical cups in hydrodynamic deep drawing assisted by radial pressure

Major defects in forming of conical cups are wrinkles and rupture. Hydrodynamic deep drawing assisted by radial pressure (HDDRP) is a sheet hydroforming process for production of shell cups in one step. In this work, process window diagrams (PWDs) for Al1050-O, pure copper and DIN 1623 St14 steel are obtained for HDDRP process. The PWD is determined to provide a quick assessment of part producibility for sheet hydroforming process. Finite element method is used for this purpose considering the process parameters including pressure path, and the blank material and its thickness. Numerical results are validated by experiments. It is shown that the sheets with less initial thickness and higher strength show better formability and uniformity of thickness distribution on final product. The results demonstrate that the obtained PWD can predict appropriate forming area and probability of rupture or wrinkling occurrence under different pressure loading paths.

Investigation of Process Parameters in Superplastic Forming of Mechanical Pre-Formed Sheet by FEM

Conventional superplastic forming has been applied in automotive and aerospace industries for a few decades. Recently, superplastic forming combined with mechanical pre-forming process has been reported to be capable of forming non-superplastic AA5083 at 400 °C to a surface expansion of 200 % [1]. In this paper, finite element modeling (FEM) was used to develop the combined forming process by using the non-superplastic material AA5083-O. The simulation follows the experimental sequence and was divided into two phases (mechanical pre-forming and superplastic forming). A conventional creep equation based on tensile test data was adopted as a material model for the simulation. The pressure cycle and forming time was simulated according to the actual process route. The thickness distributions obtained from simulation validated the capability of the model to be used for this case. The influence of different parameters, such as holder force, friction, and punch depth was investigated by comparing the final sheet thickness and level of material draw-in. It was found that the punch depth played a significant effect on the uniformity of thickness distribution, from which a more uniform formed part can be obtained by using the punch with higher depth during mechanical pre-forming phase.

A comparison of the thermoformability of a PPE/PP blend with thermoformable ABS. Part I: Small deformation methods

Different factors important in ascertaining the thermoformability of polymeric materials are identified and defined. These include resistance to sag, ease of flow, mold replication, deep draw capability, sensitivity to thermoforming temperature and speed, uniformity of thickness distribution, and post-forming shrinkage and dimensional stability. Methods to study these properties can be classified into small deformation and large deformation methods. The small deformation methods, which are the subject of this paper, include dynamic temperature sweep tests, dynamic frequency sweep tests, stress relaxation time, and creep recovery tests. These tests were used to compare the thermoformabilities of a blend of polyphenylene ether (PPE) and polypropylene (PP) and thermoformable acrylonitrile butadiene styrene (ABS) resin. The dynamic temperature and frequency tests showed that the PPE/PP blend generally has a better viscoelastic balance than ABS implying a better balance between resistance to sag and ease of flow. Creep recovery tests suggested that the PPE/PP blend may offer better mold replication during thermoforming. Studies based on the stress relaxation time showed a lower residual stress build-up in thermoformed PPE/PP blend than ABS implying better dimensional stability and a higher in-service temperature window for the thermoformed PPE/PP blend than ABS. POLYM. ENG. SCI., 45:1369–1376, 2005. © 2005 Society of Plastics Engineers

Digital-Reflectometry Characterization of the Surface Structure and Protective Property of Thin Films

A method is presented for the fast nondestructive inspection of oxide-thickness distribution over a small site of interest on a metal or semiconductor specimen. The method rests on specular reflectometry and is incorporated in a computer-based video microscope. From digital images of small sites, statistical characteristics of the thickness distribution are derived and local topographical images of the film surface are generated using three-dimensional computer graphics. A relationship is established between these data and the protective property of the oxide against corrosion. The practical value of the approach is confirmed by experiment. The experimental data indicate that the instrument and technique employed can accurately quantify the uniformity of thickness distribution.