In hot forging process, the common failure modes of forging die are wear, fatigue fracture and plastic deformation. Normally die wear is occurred the most frequently and it influents directly to shape, dimension and surface quality of product. For this research, the hot forging process of idle gear was studied to focus on die wear. This product is forged in three steps. There are preform step, rougher step and finisher step. Height of preform shape in preform step was a parameter to study effect on die wear. Archard’s wear model in finite element modeling was used to predict die wear. The finite element modeling was verified by real hot forging process for reliable model and then it was used to determine the optimum preform height to reduce die wear. Finally the result showed that the maximum wear depth on the forging die was reduced 41.2% from original industry process.

Material property that can describe its behavior under repetitive impact is an important data for the design and failure analysis of any engineering part. Study of this behavior by measuring the size of apparent damaged area at the surface (crater depth) and tracking the damage intensity is extremely difficult for small area. An attempt to develop the understanding of different response behavior during repetitive impact of stainless steel was made in this work. This paper presented the relation of the response signal to the contact surface condition in the repetitive impact test by mean of spectrum analysis. Acceleration response of a specimen under impact load could be affected by contact condition since contact area and local thickness of the specimen could be changed. The testing machine was developed to provide the repetitive impact force to the specimen. Surface morphology and depth of the crater were captured by optical microscope and 2D-stylus profilometer. The appearance in the peak spectrum amplitude of a response signal was found to be a noticeable response behavior that can differentiate the damaged specimen from the healthy specimen. Results of the response spectrum gave a clear relation to the damage intensity of the specimen. The increase in the peak amplitude during the number of impact cycles was found in the damaged specimen while the non-damaged specimen conditions the peak amplitude of the response is constant throughout the test.

Finite Element Modeling (FEM) has been employed widely to analyze material flow behavior and identify potential defects in a hot forging process before try-out. Normally, the isothermal assumption should be used to simulate this process because the forming time was extremely shot around 0. 5 s – 1 s due to a high velocity of a press machine. However, in some cases when the contact pressure and contact area are extremely high, the heat could significantly dissipate to the forming dies. In case of Yoke flange simulation the isothermal condition could not be used to identify the defect as occurring in the real process. The forging defect (i.e. insufficient gap) was found at the apex of a workpiece in the rough or preform step. In this study, the non-isothermal assumption was used for investigating the defects. The forming process was divided in 3 steps; namely the transportation step when the billet was transferred from an induction furnace to the forging dies by conveyer, the rough forging and the finish forging steps. Temperatures, loads and gaps between workpiece and die at each step of the forming processes were measured and compared with the simulation results. For developing the reliable simulation model, the suitable heat transfer coefficients for each step would be determined. The heat transfer during the forming steps had an effect on the material flow and, the non-isothermal simulation model and could identify the insufficient gap in the rough step.