Altia Fontanafredda S.r.l.

Abstract

The object of this study was simulating and optimizing the cold forging process for a silent block bush steel sleeve. A block bush consists of two concentric steel sleeves with rubber securely bonded between them to fill up the void and absorb torsional, axial and radial loads. Silent block bushes are typically used in suspension systems in the automotive industry to absorb load and minimize suspensions. A silent block bush is traditionally used in the linkage system of a car suspension, in railway carriages and in agricultural machinery.

There were multiple objectives attached to this study. Specifically:

optimize the material flow inside the dies and predict defects such as folds, cracks and underfills
calibrate the press kinematics
verify compliance with the original design blueprint
estimate the maximum forging load at each forging stage
and all of these while minimizing the costs and lead time

Setting up the Forging Simulation Parameters

Setting up the simulation environment could not have been easier. Transvalor ColdForm comes with a large reference database containing the properties of more than 200 steel, aluminum, brass and titanium materials. In fact, the material used in this study, CB4FF steel – UNI 7356, 1974 – at 20?C was already included and we, therefore, did not need to input any material properties.
Furthermore, the elasticity and plastic strain of the material were both accounted for by ColdForm; this enabled accurate residual stress and geometrical dimensions to be obtained after forming.
The simulation also took into account the heat transfer between the work piece and the dies, as well as the elastic spring back at each forging stage.

The Cold Forging Simulation Results

The objectives above were all met by the simulation, and the results are best expressed in the words of Gianfranco Marcandella, R&D technical lead at Altia Fontanafredda S.r.l.

"Thanks to ColdForm™ we achieved multiple objectives: irregular behavior (folds) in the material was identified; the structural integrity of the component after the whole manufacturing process was verified; and the die geometries were optimized for compliance with the design blueprint for the part. We also calculated the total forging load at each of the forging stages which allowed us to choose the most suitable press for the job. Finally die wear was predicted and optimized, allowing us considerable cost savings due to improved durability. Thanks to the guidance and training from the EnginSoft engineers, we were able to learn more about the simulation results allowing us to minimize physical prototypes and reduce waste, while reducing the lead time and overall production costs"

Real and simulated workpiece at the end of each forging stage, before the elastic spring back (left); close-up after the first (top-right) and fifth forging stages (bottom-right)

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Cold Forging of a Silent Block Bush Steel Sleeve

Minimize physical prototypes and reduce waste, while reducing the lead time and overall production costs