Effects of Variable Punch Speed and Blank Holder Force in Warm Superplastic Deep Drawing Process

A cylindrical deep drawing test was conducted for the purpose of improving the drawability, product accuracy, and quality in warm deep drawing using a superplastic material with large strain rate dependence. Then, the effects of blank holding force (BHF) and punch speed (SPD) on the flange wrinkle behavior and wall thickness distribution were investigated by experiments and theoretical analysis. A Zn-22Al-0.5Cu-0.01Mg alloy superplastic material SPZ2 with a sheet thickness of 1 mm was employed as the experimental material, and a cylindrical deep drawing experiment with the drawing ratio (DR) of 3.1 and 5 was performed at 250 °C. A good agreement was qualitatively obtained between the elementary theory on the flange wrinkle limit, the fracture limit, and the experimental results. In addition, the authors examined each variable BHF and SPD method obtained from the theory and experimentally demonstrated that the variable BHF method has a great effect on uniform wall thickness distribution and that variable SPD has a great effect on shortening the processing time for superplastic materials. Furthermore, the authors demonstrated the effectiveness of the variable BHF/SPD deep drawing method that varies both BHF and SPD simultaneously.

Superplasticity Effect Demonstrated by Gas Forming Hot Bent AA5XXX Sheets into V-Shaped Trough Containing Uneven Concavities

Using low gas pressure as a tool to form metal sheets is certainly feasible. However, the intrinsic flow properties of metal sheet are often a key factor in determining degree of formability, which has not been emphasized or explained well. Most metals, for examples aluminum alloys, can be either superplastic or non-superplastic depending on their original processing history or route (consequently, yielding suitable microstructure) and forming conditions, i.e. mostly temperature and strain rate. This superplasticity effect is clearly demonstrated by gas forming superplastic AA5083 and non-superplastic AA5052 into a V-shaped deep trough containing uneven concavities. The results show the superiority of superplastic material when harsh product standard is required.

Determination of Superplastic Material Properties for Parent Material and Friction Stir Welded Joint of Al-Alloy AA6061-T6

Superplastic forming (SPF) takes the advantage of the metallurgical phenomenon of superplasticity (SP) to form complex and highly intricate bulk and sheet metal parts. SP refers to the extraordinary formability of certain metals and alloys, ceramics, composites (both metallic- and ceramic-based), dispersion strengthened materials, nanostructured materials and bulk metallic glasses, which allows them to suffer elongations of several hundred percent under the action of tensile forces. The superplastic forming characteristics of materials like aluminium, titanium and magnesium alloys have been clearly identified in order to produce complicated near-net shapes. These materials are used in the aeronautical manufacturing industry and automotive manufacturing industries due to the significant weight (by ∼ 30%) and cost (by ∼ 50%) saving that is possible. Some research work has proved superplastic forming of friction stir welded (FSW) joints also. The FSW joint efficiencies have been characterized by mechanical and metallurgical examination. Studies are also available on the behavior of FSW joints of similar and dissimilar metals. Information on the performance of friction stir welded joints during superplastic forming is rather limited, but it is important to achieve excellent properties in the friction stir welded joints also during superplastic forming. FSP (friction stir processing) – SPF (superplastic forming) is presently being promoted as a very viable near-net shape technology for making very large and complicated sheet metal products. To achieve this superplastic material parameters are much required in industry to develop new shapes. One has to understand the flow rule relationship and mechanics involved during sheet metal forming at high temperature to select the material and forming tool with selected process parameters. This paper deals with the determination of superplastic material properties of non-superplastic aluminum alloy AA6061-T6. The superplastic material properties like strain rate sensitivity index, flow stress and strain rate were determined for both the selected material and friction stir welded sheets at various tool rotation speeds. The superplastic free blow forming experiments were performed for various constant temperatures and pressure for the parent material. Similarly the superplastic free blow forming experiments were performed for the friction stir welded joint for various tool rotation speed at constant temperature. The methods were used to determine the material properties are straight line fit method and polynomial regression method. The superplastic forming height is significantly high in case of the FSW specimens at 2000 rpm, the initial forming rate is faster and the strain rate sensitivity index obtained is also higher when compared to the parent material properties. The strain rate sensitivity index obtained for friction stir welded specimen during superplastic forming was foundto have improved when compared to the parent material.

Mathematical Modelling to Evaluate the Superplastic Material Constants by Bulge Test

The mechanical behaviour of a superplastic material is often modelled by the power law relationship between the equivalent flow stress, the equivalent strain and the equivalent strain-rate at least over a limited range of strain rates. This paper introduces an original mathematical modelling to determine the superplastic material constants m, n and K by means of experimental tests carried out using a standard forming die geometry.

Numerical-Experimental Comparison to Validate a Mathematical Model for the Determination of the Superplastic Material Constants

This paper shows a numerical-experimental comparison to validate a mathematical model which is able to determine the superplastic material constants by means of experimental tests carried out using a standard forming die geometry. In particular, the constants m, n and K for the lead-tin alloy PbSn60, for the alloy AZ31 at different forming temperatures and for the alloy AA5083 are evaluated.

Surface Roughness and Initial Pressure Effect on Superplastically Carburized Duplex Stainless Steel

Superplastic carburizing (SPC) is a carburizing process that combines carburizing with superplastic deformation. Since SPC involves direct interaction between the superplastically deformed surface and the solid carbon medium, the effect of surface roughness on the process cannot be disregarded. This paper presents the study of surface roughness and initial pressure effects on superplastic carburizing of duplex stainless steel (DSS). SPC was conducted under four different surface roughness (Ra) conditions of 0.9, 0.3, 0.1 and 0.03 μm. The microstructure, surface hardness, and carburized layer thickness were studied. Comparisons were also done on non-superplastic material which has a coarse microstructure. The results showed that the surface roughness strongly affected the properties of the superplastically carburized duplex stainless steel while its effects on the non-superplastic material were not that obvious.

Material Superplastic Parameters Evaluation by a Jump Pressure Blow Forming Test

In this work a method, based on bulge tests performed on a blow forming equipment, for evaluating the superplastic material characteristics is proposed. The pressure imposed on the sheet and the height of the dome of the specimen during the test are used as characterizing parameters. Different pressure levels are applied subsequently in the same test and the strain rate sensitivity index is calculated starting with analytical considerations and then with an inverse approach based on a simple finite element numerical model of the test. The change of the slope in the specimen dome height curve, due to the change of the pressure, is correlated to the strain rate in the sheet. The method has been verified applying other load profiles on the sheet and good agreement has been found between experiments and numerical results obtained by the inverse analysis.

Compression Method for Superplastic Boronizing of DSS

Superplastic boronizing (SPB) is a new surface hardening technique utilizing the ultra high plasticity phenomenon in metals in carrying out boronizing process. In boronizing, boron atoms are diffused into the metal substrate to form a hard boride layer. In this research, a new compression method for the SPB process was introduced. A clamp with an initial compressive load of about 1960 N was used. Thermo-mechanical treated duplex stainless steel (DSS) with fine grain microstructure which can show superplastic behavior at high temperatures was used as the superplastic material. SPB experiments were conducted at temperatures between 1123 and 1223 K for durations of 1 - 6 hours. The boronized specimens demonstrated thin, smooth and compact morphology of boride layer. The boride layer thickness was within ±10 0m - ±46.2 0m. On the boride layer, only the favorable single phase of Fe2B was detected. High value of surface hardness was observed in the range of ±847 HV - ±2914 HV. The overall results from the study show that the SPB process can significantly improve the surface properties of DSS.