Investigation of a moveable flash gap in hot forging

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 volume, 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%).