Development of a Combined Bulging-Piercing Technique to Reduce Forming Load for a Long Semi-Hollow Stepped Part

This paper aims to develop a new forming technique to manufacture a long semi-hollow stepped part. Traditionally, hot backward extrusion is used. This technique is not suitable, because it requires a very high forming load acting on the die and punch especially at the contact between punch and workpiece. As a result, the service life of the punch is very low. Therefore, a new technique to overcome this problem is needed. A combined bulging-piercing technique was proposed and developed in this research. The main concept of this technique is to bulge the part by upsetting the workpiece between the punch and the counter-punch to generate high frictional contact pressure which will help to restrain the material sliding down to the die cavity during the piercing step. In other words, this technique utilizes frictional force at the die-workpiece interface to reduce the forming load of the punch. Finite element modeling was employed to investigate and determine the suitable level of the bulging which can reduce the forming load without generating any significantly high force to the counter-punch. Only experiments with the minimum forming load were selected and implemented to validate this concept, because other conditions with high load will risk to damage the punch and the machine press of the product line. The results show that this technique can reduce the forming load by almost 40%, and also control a good concentricity of the part and reduce the wall thickness variation.

Energy Similitude Correction Method for Free Vibration of Cylinders

Similitude theory has been applied to design scale models in many fields of engineering. As for free vibration of cylinders, the wall thickness is too thin to manufacture scale model, which leads to similitude distortion. The aim of this study is to correct the similitude distortion and establish the distorted similitude relationship for free vibration of cylinders. First, the complete and partial similitude relationships are deduced while the similitude distortion of wall thickness is discussed. Then, with analysis of similitude for energy, an equation with prediction of modal frequencies for prototype is established and the energy similitude correction method is proposed. Finally, through numerical examples, this method is verified and the influence of wall thickness variation on the accuracy of the proposed method is analyzed.

A Design Approach of Porthole Die for Flow Balance in Extrusion of Complex Solid Aluminum Heatsink Profile with Large Variable Wall Thickness

In this study, porthole die used for extrusion of a solid heatsink profile with wall thickness variation ratio up to 15.3 was designed using finite element (FE) simulations. To improve the flow balance in the die, a design approach was introduced to find the appropriate die structure, which includes the porthole and pocket geometry correction, the bearing length adjustment, and the port bridge structure modification. Using the proposed die, the predicted velocity relative difference (VRD) and the maximum velocity difference (ΔV) of extrudate were significantly lower than those of an initial die, which was preliminarily designed based on general design experiences. The required extrusion force and the residual stress in the product were also reduced significantly. Then, the effects of the port bridge structure and welding chamber height on the behavior of the metal flow in the die were investigated. To verify the proposed die design, experimental extrusions were conducted on a 930-ton extruder. The experiment results showed that the extruded product fulfilled the requirements for dimensional tolerances. The design approach presented in this paper can be useful for practical implementation of die design when extruding similar solid heatsink profiles with large wall thickness variation.

Fließpressen hohler Wellen mit Wanddickenvariation/Cold forging of hollow shafts with wall thickness variation – Numerical investigation of a hollow forward extrusion process with adjustable deformation zone

Die Fertigung von Hohlwellen mit komplexer Innengeometrie bedingte bisher meist aufwendige Prozessrouten. Ein am Institut für Umformtechnik der Universität Stuttgart entwickeltes Kaltfließpressverfahren soll nun die wirtschaftliche und flexible Fertigung von Hohlwellen mit Wanddickenvariation ermöglichen. In diesem Beitrag werden das Verfahren beschrieben und die Ergebnisse der numerischen Untersuchung des Einflusses der Werkzeugkinematik auf die erzielbare Pressteilgeometrie dargelegt.   Usually, the production of hollow shafts with complex internal geometry by cold forging requires extensive process routes. A novel cold forging process developed at the Institute for Metal Forming Technology at the University of Stuttgart allows for an economical and flexible production of hollow shafts. This article describes the manufacturing process and presents the results of a numerical investigation for determining the influence of tool kinematics on the achievable part geometry.

The Investigation of Pipe Ends Formation under Reduction Mill Rolling

The paper presents the results of the experimental study of the longitudinal and transverse wall thickness variation at the ends of a oil-well tubing during reduction procedure. It is established that the greatest "contribution" to wall thickness data spread is made by the pipe facets, which is caused by the influence of the reduction regimes and the rolls calibration due to the metal flow into the tapers of groove. In the course of work, recommendations were also made that, in order to reduce the wall thickness variation of pipes, it is necessary to develop the calibration ensuring the decreasing of the intensity of metal flow into the tapers of groove, as well as decrease the reduction at the mill stands, and increase the coefficient of kinematic tension between the stands of the stretch-reducing mill.

ANALYSIS OF THE WALL THICKNESS VARIATION OF PIPES UNDER INTERNAL PRESSURE

A computer simulation of the internal pressure expanding was performed for pipes with uneven wall thickness made of steel, aluminum and titanium alloys. For this simulation software tool ESI Virtual-Performance 2016.0 was used that implements the finite element method. The convergence and accuracy of the solution was estimated by comparison with known solutions. A full factorial computational experiment was performed by varying factors: the initial wall thickness variation of pipes, D/S and parameter of alloys hardening. The regression equations were obtained by the internal pressure at the time of destruction and final wall thickness variation from these factors. It was found that the variation in wall thickness in the distribution pipe rupture occurs in the thin wall. A wall with minimum thickness continues thinning with an almost constant maximum wall thickness, which leads to an increase in the transverse variation in wall thickness. It was concluded that the increase of the initial variation in wall thickness pipe speeds up the process of rupture in the area of thin wall. It is recommended in conduits conducting high-pressure fluid to apply pipes with minimal variation in wall thickness.