Wyniki 1-3 spośród 3 dla zapytania: authorDesc:"Miroslav TOMÁŠ"

Formability prediction of complicated pressing's shape by numerical simulation of the reverse drawing DOI:10.15199/24.2018.8.5


  Introduction. New materials, methods and processes are applied in the forming processes today [1, 2], even conventional ones, such as reverse drawing also take a place. Reverse drawing is defined as drawing of blank against the initial drawing direction and it is considered as the second drawing operation. Thus, the direction of material flow changes and outside pressings surface after the first drawing operation is redrawn inside the pressing, while inner pressings surface is passed outwards [3]. When large asymmetric pressings are deep-drawn, especially with straight parts and various corner radii, stresses and strains vary along its circumference and they are nonuniform. Usually, restriction beads along the straight parts are used to uniform plastic flow during deep-drawing. Otherwise, partial compound reverse drawing method is used for these types of pressings [4]. The method consists of two drawing operations: the first one is stretching and the second one is reverse drawing. The principle lies in prestraining the blank in the first drawing operation, followed by the second redrawing operation by final punch shape. The method of partial compound reverse drawing is shown in Fig. 1: blankholder 3 keeps holding the blank 2 against the drawing die 4, bottom punch 5 pre-strains the blank and moves back, punch 1 shapes the blank, bottom punch 5 ejects the pressing. Partial compound reverse drawing method allows: - Intensify the plastic strain at the pressings bottom, improving its stiffness a[...]

Wpływ spawania laserowego na właściwości stali nierdzewnej i przewidywanie jego plastyczności za pomocą symulacji numerycznej DOI:10.15199/24.2018.10.2


  Introduction. Stainless steels are used not only in house- holds, but also in various industries - chemical, petrochemi- cal, food and automotive as well. In today’s car, about 20 kg of stainless steel is used for exhaust systems and fuel tanks to increase corrosion resistance, but also to improve safety features - energy absorption at crash, increase in strength, stiffness, fatigue resistance the car body components. Other reasons are weight and emission reduction, more attractive appearance, less care demands, good formability and weld- ability [1]. Interesting are automotive applications of stainless steel designed by KVA STAINLESS™ for Removable Chassis Components (bumper beams, frame crossmembers, suspen- sion control arms, subframes, etc.), Safety/Intrusion Man- agement Components (side impact beams, roof bows, roof rails, B-pillars, etc.), Entire Chassis Frame Rails, Fuel/Hy- draulic Lines, Fuel Injection Rails, Exhaust System Com- ponents and Tubing, Vehicle Seat Frames and Supports and other Vehicle accessories (tow hooks, racks, running boards, etc.) [2]. Typical applications are austenitic stainless steel 309 (25% chromium, 20% nickel), austenitic stainless steel 304 (18% chromium, 9% nickel) or 409 ferritic steel (12% chromium) [2, 3]. Due to the very good formability of stainless steels, parts of exhaust systems and fuel tanks are manufactured by hydro- or hydromechanical forming of standard or la- ser welded blanks (Fig. 1) [3]. Other progressive forming methods can also be applied [4]. Applications of stainless steels result in savings of 15% to 25% of the material when compared to the original conventional or microalloyed steel [1-3]. TWBs are prepared by linear or nonlinear l[...]

Models of determination the friction coefficient for simulation of steel sheet stamping DOI:10.15199/24.2019.8.4


  Introduction. Formability of steel sheets depends on material properties (mechanical, micro geometry of contact surfaces), geometry and micro geometry of contact surfaces of die, blankholder pressure, applied lubricant, etc. [1-5]. Accurate determination of the influence of individual parameters on technological characteristics is ambiguous because single parameters are changed from one case to another and their impact on formability is changed as well. It is possible to predict the influence of material properties, geometry of die, stamping conditions on sheet formability using simulation methods which enable us to optimize the utilization of material properties under specific conditions. With the increasing importance of the FEM analysis in pre-production, the need for exact values of input data for FEM simulation, is becoming more and more important. These input data are important for accurate description of material behavior and contact conditions. In order to predict sheet formability, it is important to define the friction coefficient on the die contact surfaces. Friction conditions were the subject of the study [6-9]. Demands for accurate information on the friction coefficient increased at the moment when manufacturers of stamping parts started to use simulation methods for prediction of sheet formability, also to apply new high-strength materials, materials with special surface treatments. Tribological properties of new steel sheets are often different from classical ones applied for stamping. This means that the lubricant which is suitable for classical steel sheet may not be suitable for sheets with a special surface treatment [2-7]. Stamping processes (deep drawing, stretching and bending) can be characterized by the types of contacts between the steel sheet and the die shown in Fig. 1. Type of contact (Fig. 1a) occurs during bending or deep drawing of squared stamped parts in their straight parts. Blank is no[...]

 Strona 1