Production Of Net Shape Parts Research Articles

Prediction of fracture in cold forging with modified Cockcroft-Latham criterion

Cold forging technology provides production of net shape parts that required very little or no further machining. Meanwhile one of the technological problems of the cold forging is fracture of the workpiece during production. This is especially important when using less ductile high strength materials or technological schemes that require significant deformation. The use of reliable fracture criteria implemented in metal forming software can help predict possible cracks and find ways to avoid them. There are many criteria that can be used for this task, for example, Gurson and its modifications, Johnson-Cook, Wierzbicki and Cockcroft-Latham. The latter one is the most widely used due to its simplicity since only the first principal component of stress is required for calculation. On the other hand, in this simple form, it does not take into consideration the influence of the stress state and the path of plastic deformation. In the presented work, a comparative analysis of different criteria has been done to find out the relations among them and a modified Cockcroft-Latham criterion of fracture has been proposed. It considers both the influence of the normalized first principal stress and the influence of the stress state scheme. A new approximation of the surface of critical plasticity has also been proposed that considers the limit values of the normalized average stress. The modified Cockcroft-Latham criterion was programmed as a subroutine in QForm metal forming simulation software and it has shown good accuracy in tests for different practical cold forming processes.

Numerical analysis of the process chain for the production of PM components with integrated information storage

The powder metallurgical production offers a number of advantages compared to other manufacturing technologies. A few examples are the high level of material utilization, the production of net-shape parts and an extensive amount of alloying options. This paper describes the production process to integrate component relevant information in the component to increase its functional range. The analysis of the production process is done by means of numerical simulation. Therefore, the process chain, consisting of die pressing and sintering, is modeled based on a finite-element-analysis.

Effective Stochastic Simulation for the Optimization of Time, Costs and Quality in Cold Forging

In cold forging tool life is limited in most cases by fatigue and characterized by distinct scatter depending on the scatter of the process parameters. This fact is also obstructing the production of net shape parts. Due to the scatter, a single simulation run with average values is known to be not appropriate to predict the desired output quantities. This paper describes an innovative method using a mathematical model of the forging process with a deterministic and a statistical component. According to the strength versus load concept (SVL-concept), a combination of the parametric and the statistical model leads to an integrated statistical process model which enables tool life prediction by taking statistical effects into account. In order to improve tool life an approach of avoiding tensile stresses and strains in the die has been successfully used for steel and cemented carbide tools.

Influence of container on numerical simulation of hot isostatic pressing: final shape profile comparison

Hot isostatic pressing (hipping) is a manufacturing process capable of producing mechanical parts in only one operation by the hot forming of metal powders. The aim of this process is the production of net shape parts notably for aeronautics or nuclear applications. In the past, the trial and error method was used in order to find the right container and insert geometries giving the net shape parts. Several prototypes must therefore be manufactured before a successful conclusion is reached. This forming procedure results in expensive developing costs due to the quasi unitary production, pressure and temperature environment and the high temperature tooling involved.Numerical simulation raises hopes on the optimisation of this manufacturing process through the use of viscoplastic constitutive equations implemented in the finite elements software PRECAD/M.The rheological functions of this viscoplastic model are usually determined by assuming that the mean pressure in the sample is homogeneous and equal to the external applied pressure. The numerical simulations of hipping experiments show that this assumption is often false: pressure is partially transmitted to the powder because of the container rigidity. New rheological functions have been determined with the stress values obtained by numerical simulation of these tests. The new numerical simulations are then in better agreement with the experimental values and the prediction of an industrial complex part final shape is also improved.

Dissolution and soldering behavior of nitrided hot working steel with multilayer LAFAD PVD coatings

Soldering and corrosive dissolution are the primary causes of die non-performance in permanent mold and die casting production of net shape parts for the transportation industry. At worst, these corrosive reactions result in core pin or sprue dissolution, and at the least, some soldered cast metal remains behind when the casting is ejected. The objective of this work was to explore the possibility of surface engineering of the die steel surface to reduce the dissolution and soldering tendencies of the surface. This paper presents a duplex surface treatment approach for dissolution resistance that consists of nitrided hot working die steel substrate coated by multi-layer titanium-based coatings applied by the large area filtered arc deposition technique. The dissolution behavior of the coating candidates is evaluated by measuring weight loss after dipping them in molten aluminum for a predetermined time. Results are compared with those of single layer coatings and surface treatments. The chemisorption and adhesion behavior is evaluated by measuring ejection force of the soldered material. The duplex coating is found to significantly reduce both the dissolution and adhesion tendencies of the coated steel surface.