Die Surface Structures and Hydrostatic Pressure System for the Material Flow Control in High-Pressure Sheet Metal Forming

Abstract

A promising approach to control the material flow within deep drawing and workingmedia based forming processes is the structuring of the tool surfaces in the contact zones between workpiece and die. In order to obtain a sufficient and an optimised material flow respectively – especially for non-symmetric or non-uniform workpiece geometries – a locally adapted distribution of surface structures is a practicable solution. The macroscopic, and also the microscopic surface structures can be manufactured sufficiently by means of a high-speed cutting process. The shape of the tool surface structure has a significant influence on the tribological conditions between workpiece and die. To adjust the surface structure distribution to the required material flow distribution, detailed knowledge about the correlation of the material flow from the tribological conditions between sheet and the forming tool is required. A further innovative approach, particularly for decreasing the friction coefficient, is the use of an innovative hydrostatic pressure system using fluid ducts. Its functional principle is based on the reduction of the contact shear stress at the sheet surface in the contact zone with the forming tool by means of locally applying a hydrostatic fluid pressure. To obtain information about the correlation of the material flow from the tool surface structures and from the parameters of the hydrostatic pressure system respectively, fundamental investigations have been carried out. In order to optimise the material flow, these toolbased approaches can be used as stand-alone solution, or in addition to other systems. If the surface structures and a hydrostatic pressure system are used in combination with the multi-point blank holder, which has already been qualified for the high-pressure sheet metal forming (HBU), a powerful system for the material flow control is available.

The Influence of Tool Texture on Friction and Lubrication in Strip Reduction Testing

“…These effects can be enhanced by utilizing transverse roughness profiles and oblong pockets oriented transverse to the sliding direction. In this way, lubricant entrapment is promoted, which can lead to low friction and prevent galling by micro-plasto-hydrodynamic lubrication [15,16]. In addition, larger sliding speed reduces the tendencies of mechanical gripping effects of the workpiece into the pockets as the normal pressures increases [17].…”

A mathematical model for thinning rate prediction of sheet double hydro-forming

“…Kitayama, Satoshi et al proposed a sequential approximation optimization model to save blank material in sheet metal forming by optimizing the input blank geometry and using the method of varying the blank holder force by different regions [14]. Rainer Krux, Werner Homberg et al Studied the surface structure of the die and the hydro-forming system combined with the multi-point blank holder method to optimize the flow of workpiece material into the die cavity, applied to parts with symmetrical and asymmetrical geometries [15]. Bharatkumar Modi & D. Ravi Kumar used the Taguchi method and regression model to build the relationship function between the maximum pressure and the variable blank holder force to predict the minimum wall thickness and bottom corner radius when hydro-forming square cups from AA5182.…”

The Influence of Tool Texture on Friction and Lubrication in Strip Reduction Testing

“…These effects can be enhanced by utilizing transverse roughness profiles as well as oblong pockets oriented transverse to the sliding direction. In this way lubricant entrapment is promoted which can lead to low friction and prevent galling by micro-plasto-hydrodynamic lubrication [15][16]. In addition, larger sliding speed reduces the tendencies of mechanical gripping effects of the workpiece into the pockets as the normal pressures increases [17].…”