Avoidance of thin flash formation for precision forging of aluminum parts

In the burr-free forging of aluminium, material can unintentionally penetrate into the gap areas between the tool elements, thus creating so-called tinsel burr.

Burr makes handling and positioning of the components in subsequent forging or machining operations more difficult and thus leads to position and tolerance errors on the component. In this thesis, two different methods for the first numerical prediction of the formation of flake burr were developed.

For specific areas of finished parts, it was possible to qualitatively predict the formation of flake burr in all areas considered. Furthermore, a method for the reduction of flake burr by geometrical optimization of preforms using evolutionary algorithms was developed. The optimized preforms met or exceeded the established quality requirements compared to conventionally developed preforms with a significantly reduced optimization time of less than ten minutes.

Solid forming, burr-free forging, flash, forecast, optimization

In this paper, the investigation of thin flash generation in precision forging process of an aluminum long flat part is described. The aim was to derive a predictive simulation method for thin flash generation in order to increase both process and part quality in the future. The forging processes were varied by use of different preforms with equal volumes but different mass distributions while using the same final part geometry. The experimentally forged parts were analyzed concerning the amount and part area of the generated thin flash. The conducted FE simulations were analyzed concerning the hydrostatic pressure values p in the part areas near to the tool gap between upper and lower die immediately before form-filling. For a more detailed comparison, single p values were included to hydrostatic pressure functions P. The comparison between the P functions and the experimentally determined thin flash height shows, that high pressure values as well as high gradients of the P functions indicate less thin flash generation. The method therefore allows a qualitative prediction of thin flash generation. It can provide two kind of information. First: The prediction of the specific locations where thin flash is likely to occur in one final part by use of one single preform. Second: The qualitative prediction of the specific final part areas were thin flash is likely to occur depending on different preform geometries. This method will decreases the necessity of time-consuming forging trials and can shorten the preform designing process in the future.

forging flashless precision forging FEA aluminum predictive simulation method

The investigation of thin flash generation in a precision forging process of an aluminum long part using finite elements analysis (FEA) and corresponding forging trials is described in the presentation. Thin flash generation leads to bad handling and positioning in subsequent process steps and therefore tolerance defects. For investigation purpose, the forging processes were varied by use of different preforms with equal volumes but different mass distributions, while the geometrical parameters of the final part were not varied. 

The forging processes were analyzed by FEA with focus on the value of the form-filling simultaneity depending on the preform geometry. Afterwards, corresponding forging trials were carried out for validation.The results of the experiments and the FEA showed good agreement concerning the part areas were thin flash generation was predicted by FEA and actually occurred in experiments.Preforms with higher values of form-filling simultaneity showed less thin flash generation while preforms with lower values of form-filling simultaneity showed significantly increased thin flash generation.

forging, aluminum, FEA, thin flash generation, prediction

The investigation of thin flash generation in a precision forging process of an aluminum long part using finite elements analysis (FEA) and corresponding forging trials is described in the presentation. Thin flash generation leads to bad handling and positioning in subsequent process steps and therefore tolerance defects. For investigation purpose, the forging processes were varied by use of different preforms with equal volumes but different mass distributions, while the geometrical parameters of the final part were not varied. 

The forging processes were analyzed by FEA with focus on the value of the form-filling simultaneity depending on the preform geometry. Afterwards, corresponding forging trials were carried out for validation.The results of the experiments and the FEA showed good agreement concerning the part areas were thin flash generation was predicted by FEA and actually occurred in experiments.Preforms with higher values of form-filling simultaneity showed less thin flash generation while preforms with lower values of form-filling simultaneity showed significantly increased thin flash generation.

forging, flashless forging, aluminum, FEA, thin flash, prediction

In the automotive industry, aluminum forged parts must fulfill lightweight and heavy duty performance requirements. The generation of thin flash between die halves and in the small gaps between the die and punch must be prevented during the flashless forging process in completely enclosed dies. However, thin flash formation is neither predictable nor preventable.

A numerical model is developed based on finite element analysis to investigate and predict the generation of thin flash in aluminum flashless precision forging processes. The significance and effects of the main influencing input parameters, including billet temperature, forming velocity, and width of gap, on different resulting parameters are evaluated. Among all resulting parameters in the established numerical model, hydrostatic pressure and the forming force in the main forming direction have been identified as the most suitable for predicting thin flash generation.

aluminum forging, forging in completely enclosed dies, flashless forging, FEA

A numerical model using FEA is developed to investigate the generation of thin flash in aluminum forging. Significance and effects of the influencing parameters temperature, forming velocity and width of flash gap on the thin flash generation are shown by statistical analysis carried out with the established model. Experimental trials have been made to verify the model.

FEA, aluminum, forging, flashless forging, thin flash

Intensive research work on flashless precision forging of steel materials has been made at the IPH in the past. In aluminum forging processes a thin flash often occurs in the gap areas between the forming elements. This thin flash adversely affects the component quality. For this reason flashless aluminum forging previously could not be realized. In this publication, the approach for the investigation of the thin flash formation is explained. A FEM model of a one-stage upsetting process in a closed die has been created. With this model the influence of the parameters workpiece temperature, forming velocity, the wideness of the flash gap and the pressing forces on the thin flash formation can be examined. Owing to these research activities a possibility for aluminum forging without flash and thin flash shall be provided.

flashless, forging, thin flash, aluminum, FEA