Mechanisms to regulate a variable flash land and their impact on die filling in respect to deviations in die wear and billets' volume within closed die forging process

Theme
Industry 4.0
Tool- and Mold-Making
Project title Mechanisms to regulate a variable flash land and their impact on die filling in respect to deviations in die wear and billets' volume within closed die forging process (Gesteuerte Gratbahn)
Project duration 01.08.2011 – 31.07.2013
Video
Download
Press release
The most common method of bulk forming processes is closed die forging with flash. In this process a surplus of material is used to ensure a complete filling of the cavity of the forging die. The surplus material is driven out of the die through the flash land, thus the design of the flash land has a major influence on the filling of the die. All dimensions of the flash land are typically fixed during the manufacturing process of the die and cannot be changed within the forging process. By use of a moveable flash gap that can be actively changed during the forging process the material flow can be altered. Thereby the filling of the cavity can be improved.

Publications about the project

The most common method of bulk forming processes is closed die forging with flash. In these processes a surplus of material is used to avoid forging defects such as a missing filling of the cavities. The surplus material is driven through the flash gap and forms the flash. Therefore, the flash gap design has a distinct influence on the material flow within the die and thereby on the cavity filling, the material usage and other process parameters. In indus-try the flash gap is fixed once the dies are manufactured and cannot be changed without additional manufacturing.

A moveable flash gap, which can be changed vertically during the forging operation, was developed within this thesis. It can be used to influence the material flow within the forming process. Thus, the filling of the cavity can be improved. By the use of a variable flash gap in the forging process of a trial part, a maximum increase in the cavity filling of 4.6 mm (17.2 %) was achieved. Furthermore, the influences of different process properties, such as the billet temperature, the trigger force or the height of the moveable flash gap, were evaluated.

To allow the application of a variable flash gap to different forging parts, a guideline was designed. For that purpose, forging parts were classified into characteristic zones. Within the zones the influence of differently designed flash gaps were evaluated using FEA. The result of this evaluation is a recommendation on possible designs of a variable flash gap for differ-ent forging parts, to allow an improvement of the cavity filling.

bulk forming, finite element analysis (FEA), flash gap, material flow, die design

The most common method of bulk forming processes is closed die forging with flash. In these processes a surplus of material is used to ensure a complete filling of the cavity of the forging die. The surplus material is driven out of the die through the flash land, thus the design of the flash land has a major influence on the filling of the die. All dimensions of the flash land are typically fixed during the manufacturing process of the die and can not be changed within the forging process. By use of a moveable flash gap that can be actively changed during the forging process the material flow can be altered. This permits to improve the filling of the cavity. In this paper a moveable flash gap for a hot forging process is described and the influence of such a system on the filling of the die cavity is determined. This is done by a comparison to a conventional forging process with a fixed flash land. Furthermore, the results of experimental trials are compared to results of corresponding FEA simulations. Additionally, the influence of the initial billet temperature is investigated. Experimental trials showed that the moveable flash gap has a distinct influence on the material flow. The higher the flash ratio, the bigger is the influence of the moveable flash gap. The moveable flash gap is designed as a flash brake of a height of 2 mm. Its usage lead to differences in height of the parts up to 4.5 mm, which correspond to 16.6% of the parts height, compared to parts forged with a fixed flash land. If the forging temperature is decreased from 1200 °C to 1000 °C, the influence of the moveable flash gap is reduced. The average differences in height are about 0.5 mm (about 3%).

forging, die design, material flow, FEA, flash land, flash gap

The most common bulk forming process is closed die forging with flash. One goal of the industry is to reduce flash. For geometrically difficult parts like crankshafts flash reduction can be achieved by flashless preforming and flash-reduced final forging. The corresponding process design is challenging and defects like an insufficient cavity filling often occur in final forging. A controlled, moveable flash gap enables the alteration of the material flow, increasing the filling of the cavity again. In this paper, the flashless preforming for crankshafts and the influence of a controlled flash gap on cavity filling are described.

Forging, die design, material flow, FEA, flash land

Different billet dimensions or progressive die wear increase the geometric fluctuations of forged parts. This can lead to waste. Mostly this geometric fluctuations are compensated by increased billet masses which leads to lower efficiency in the manufacturing process. In a research project a controlled, moveable flash gap was examined, that enables the alteration of the material flow to increase the part quality.

forging, die design, material flow, FEA, flash land

Forged parts have geometrical fluctuations for example caused by die wear. The investigation of a controlled, movable flash gap by FEA for compensation purpose showed how far the material flow can be varied during the forming operation. A potential to improve forging results is derived.

forging, die design, material flow, FEA, flash land

Sponsor

The project no. NI 1187/12-1 received funding from the German Research Foundation (DFG).

Your contact person

Dr.-Ing.

Jan Langner

Manager process technology