Papers by Author: Taylan Altan

Abstract: Progressive and transfer dies are used for forming of sheet metal parts in large quantities. For a given part, the design of progressive die sequence involves the selection of the number of forming stages as well as the determination of the punch and die dimensions at each stage. This design activity is largely experience-based and requires prototyping involving several trial and error operations. In some cases, empirical data and the experience based design procedure can be combined with Finite Element Method (FEM) based analysis to reduce time and cost. Often, when using FEM in progressive die design, friction and its effect upon temperatures is not adequately considered. However, at each forming station the plastic deformation and the tribological conditions influence the material flow as well as the temperatures and pressures at the tool/workpiece interface. The performance of the lubricant and coolant, used in progressive die forming, is affected significantly by interface pressure and temperatures. Therefore, a progressive process and die design methodology should include the consideration of metal flow as well as temperatures and pressures. Heat transfer coefficient, friction, plastic deformation, forming speed at each forming stage, time for part transfer from one stage to the next, and the ability of the used lubricant to cool the dies, have considerable effect upon a successful stamping. This paper describes a method for designing a progressive die sequence for forming axisymmetric sheet metal parts. The methodology for process sequence design combines experience based empirical data obtained through previous designs, design rules and numerical simulations including plastic deformation and friction. The initial experience-based design was refined using FEM and the thinning of the material in each successive drawing stage was calculated. The thermo-mechanical model was obtained using a constant friction coefficient along the tool/workpiece contact zone. Finally, the tool/workpiece interface temperature and the normal pressures were estimated in order that the lubricant can be selected based on these process conditions. The design predictions, made by using empirical data and FEM, were compared with experimental data.

Abstract: Production of light weight and crash resistant vehicles require extensive use of AHSS (DP,TRIP,TWIP) and Al alloys to form complex shapes. This paper discusses practical determination of material properties and selection of lubricants for forming AHSS using a die set, designed for deep drawing. Tests were conducted in a 300 ton servo press. Thinning at the critical area of the formed part were measured and compared with FE simulation. Prediction of temperatures in deep drawing of selected DP steels and Al alloys in servo press is also discussed.

Abstract: Experimental investigation on the formability limits of aluminum and magnesium alloys are conducted through hydraulic bulging and deep drawing. New tube hydroforming tooling was designed and the submerged tool concept is introduced. Tube hydroforming experiments were conducted with and without axial feed by using AA6061 tubes. The formability of Mg AZ31-O sheets are determined by hydraulic bulging using similar submerged tool. Finally the effect of temperature and initial blank size on the attainable highest punch velocity is investigated and round cups from Mg AZ31-O were successfully formed in a heated tool with punch speeds up to 300 mm/s.

Abstract: Tube Hydroforming is a well accepted production technology in automotive industry while sheet hydroforming is used in selected cases for prototyping and low volume production. Research in advanced methods (warm sheet and tube hydroforming, double blank sheet hydroforming, combination of hydroforming and mechanical sizing, use of multi-point and elastic blank holders) is expanding the capabilities of hydroforming technologies to produce parts from Al and Mg alloys, as well as Ultra High Strength Steels. In the development of advanced hydroforming methods, experience based knowledge is not readily available. Thus, robust process simulation is required, along with adequate material modeling and identification of friction coefficients as input to process simulation. This paper gives an overview of advanced hydroforming methods, including examples of novel machine and tooling designs. The use of reliable process simulation is illustrated with examples that demonstrate the significance of material and friction date for making accurate predictions. Advanced simulation methods for warm forming and for programming multiple-point blank holder are also discussed. This review illustrates that hydroforming continues to make advances and has the potential to make many contributions to production technology in the near future.