Search Results

During sheet metal forming processes, the friction conditions have a decisive influence on forming limits, the robustness of the production process and the quality of the parts produced, with significant forces required to overcome friction between the sheet and the tools. If lot-to-lot reproducibility is to be guaranteed, an appropriate method of characterizing the sheet surface topography is needed to monitor the sheet metal fabrication process. Newly developed optical measurement techniques and computer workstation technology are presented which enable the topography of sheet surfaces to be described in three dimensions.

In order to reduce fuel consumption light weight vehicles are in development. For this HSLA- steel, bakehardening- steels, stainless-steels and aluminum will be used for the body in white of personal cars. To form inner automotive parts of high dimensional accuracy out of steel with high strength or out of aluminum and to form automotive parts of high surface quality as well as of high dimensional accuracy a reproducible forming process is needed. For low volume cars tools and dies have to be as cheep as possible. The press has to be able to take over die functions and over the stroke steerable blankholder forces. Tools and dies for high volume parts can use expensive tools and dies like dies with nitrogen cylinders. In the future these cylinders will have the possibility to steer the pressure and so in turn the blankholder force over the stroke. See paper „Force- Stroke- Curve of Gas Springs” (State-of-the-Art Stamping) held on the same conference.

The application of coated steel sheets is gaining importance in the automotive industry. To determine the friction and the forming behavior, tests were carried out to investigate the influence of different lubricants and tool materials. A segmented draw die was developed for measuring friction and punch forces during the deep drawing process using segments made out of different tool materials. The forming behavior was investigated using a draw part of the size of an typical automotive body part. The change of surface topography parameters due to the forming process was determined with a laser topography device.

According to the present state of knowledge, the use of “Tailored Blanks” with different sheet thicknesses and/or grades represents an interesting manufacturing alternative in the design and development of sheet metal parts in the automotive industry. In order to assess the forming behavior, fundamental research was conducted on laser and mash seam welded blanks. Based on this experimental findings, a segmented draw die was designed and built to determine the limits of the metal forming process by deep drawing of car body parts. The results with this draw die showed that a uniform blankholder pressure must be guaranteed during the forming process in the flange region of the part. This necessitated definite slots in the region of the weld line for the mash seam welded blanks. Furthermore, a die concept was presented to enable an equalization of both sheet thickness steps and sheet thickness fluctuations, without requiring replacement of the respective draw die components.

The drawing forces during wire and tube drawing can be reduced by ultrasonically oscillating dies. A major problem of conventional wire and tube drawing is to introduce high forces into the forming area. Compared to conventional wire and tube drawing, the forming process limits can be extended by superimposing ultrasonic waves due to decreasing drawing forces. Different techniques can be used to exite the die. One possibility is the variation of the vibration mode. In tube and wire drawing, the dies are usually exited longitudinally. If the vibration direction is parallel to the drawing direction, the main influence will be on the friction between workpiece and die. The Institute for Metal Forming Technology of the University of Stuttgart, Germany started a project to investigate the effect of ultrasonic waves on the tribology and on the the formability of the workpiece. The objective of this investigation is to separate the ultrasonic effect on the surface from the volume effects.

This paper shows the benefits of a new draw die design. To achieve an optimized contact pressure between blankholder and blank a segment-elastic blankholder in combination with a prismatic designed draw ring can be used. In this case the blankholder pressure is very equal distributed and can be influenced locally by varying the cushion pin forces. For this a multipoint cushion system is required. Within a new press concept as shown in this paper, this multipoint cushion system can be realized by short stroke hydraulic cylinders.

In sheet metal forming, metal flow into the die is determined by the restraint imposed by both the blankholder force and the drawbead penetration. This paper describes an experimental investigation in which both advanced binder force and drawbead technologies are used to study their effect on draw depth in the drawing of an AA6111-T4 generic non-symmetric panel. Multipoint binder loading using individual pin force adjustment applied to especially designed binder structures as well as the use of variable blankholder force were investigated in one laboratory in Germany. In another laboratory in the USA, active drawbeads were applied to the drawing of the generic panel. The results of both approaches, which are shown to be successful, are presented and discussed.