Papers by Keyword: Powder Compaction

Abstract: In this paper, based on the determination of the stress-strain relationship of sintered W-40wt.%Cu by upsetting tests, the hot extrusion process of the materials covered with a steel cup has been simulated by DEFORM. The effect of the thickness of steel cup, extrusion temperature and extrusion ratio on the extrusion process has been studied, so that a group of optimal parameters could be obtained which is useful to the experiment of powder compact by extrusion with cups.

Abstract: The finite element method was conducted to simulate the pharmaceutical powder compression process by using Drucker–Prager Cap model and elastic-plastic deformation theory. The effects of different friction coefficient on tablet property were systematically studied. The results show that the pressure-density curves shift towards right-hand side with slight decrease at smaller friction coefficient. The fluidity of powder remains the inverse decrease with the friction coefficient, and the density distribution changed more uniform. The maximum Mises stress becomes larger with the friction coefficient increased. The powder displacement decreases near die as the friction coefficient increasing. The research can both predict the tablet property and provide the theory reference for tablet practice production through the finite element analysis of pharmaceutical powder compaction.

Abstract: Utilization of titanium components made by powder metallurgy methods has had limited acceptance largely due to the high cost of titanium (Ti) powder. There has been renewed interest in lower cost economical powders and several Ti reduction methods that produce a particulate product show promise. This talk summarizes work done at Oak Ridge National Laboratory to consolidate these economical powders into mill products. Press and sinter consolidation, hot isostatic pressing (HIP) and direct roll consolidation to make sheet have been explored. The characteristics of the consolidated products will be described as a function of the consolidation parameters.

Abstract: In this paper, a new hybrid production technique is presented. It exploits the advantage of high temperatures and high forces in the ring rolling process. This manufacturing technique is not only suitable to increase the ring’s diameter but also to apply and compact powder metallurgical multi-functional coatings onto solid substrate rings with the same process. In order to design this new process parameterized 2D and 3D FE models are created in ABAQUS/EXPLICIT on the basis of a viscoplastic material model formulation. The control capability of the conventional control mechanisms are based on the assumption of volume consistency. However, this assumption is not well applicable for a ring furnished by multi-functional surfaces with non-isochoric plastic deformation behavior. Therefore, this paper deals with the implementation of a new control mechanism. Finally the paper is concluded with the integration of heat treatment of the rolled ring into the subsequent cooling process.

Abstract: The strength of a green compacts formed through warm powder compaction route is strongly dependent on the forming load and temperature. As the forming load increases, the powder particles move from its initial position by sliding among them and die wall. This movement results in new arrangement and packing order of the particles. However, due to this movement, pores among the particles are generated that affects the mechanical properties of the green compacts. Having pores in green compacts lead to strain intensification at ligaments between pores during sintering at later stage, hence serve as areas for crack initiation. Therefore, as the powder forming relates directly to the load and temperature, strength to porosity relationship has to be analyzed based on those parameters. This paper presents the effect of porosity to the strength of green compacts formed at different load and temperature (70 kN to 130 kN; 30°C to 200°C). The bending strengths of green compacts are measured while Scanning Electron Microscopy is used for porosity evaluation. It has been found from the results that porosity and strength are related to each other at all forming parameters. In addition, high forming load and temperature give better strength due to porosity reduction.

Abstract: Die compaction of powders is a process which involves filling a die with powder, compaction using rigid punches to form a dense compact and ejection from the die. The process can be treated as a large deformation plasticity problem. The challenge is to develop and implement appropriate constitutive models that capture the evolution of the powder from a loose state into a dense compact. In this paper we describe data analysis procedures and calibrate classic incremental plasticity models, such as Cam-Clay, Drucker-Prager cap models. The complexity of the models is increased from models with a hardening law to more complex constitutive models using density as state variable. The compaction behaviour of a range of powder materials is characterized experimentally. Numerical simulation of the compaction of simple parts and complex parts is demonstrated. The merits of various models are evaluated in terms of the balance between complexity and practicality. The discussion is illustrated with case studies exploring the applicability of the models specific to various powder pressing scenarios.

Abstract: Densification of metallic powders by means of extrusion is regarded as a very attractive processing technique that allows obtaining a high level of relative density of the compact. However, the uniformity of the relative density depends on that of strain distribution and on the processing parameters. Several variants of extrusion can be used for compaction of metal particulates, including the conventional extrusion (CE) and equal channel angular pressing (ECAP), often referred to as equal-channel angular extrusion. Each of these processes has certain advantages and drawbacks with respect to compaction. A comparative study of these two extrusion processes influencing the relative density of compacts has been conducted by numerical simulation using commercial finite element software DEFORM2D. The results have been validated by experiments with titanium and magnesium powders and chips.

Abstract: In powder compaction, the great influence of the drive structure upon the electromagnetic force is a key problem to be addressed. A simulation is carried out to analyze the parameters of electromagnetic compaction drive structure by using ANSYS software. And in the two-dimensional model, the study focuses on the effects on electromagnetic pressure, which are produced by the bore and height of the coil, the radius and resistivity of the driver slice, and interval between coil and driver slice. The final results show that electromagnetic pressure of inverse correlates with other parameters of different forms and will grow slowly if the radius is increasing. On the basis of simulation, we draw the general rules of plane coil and driver slice parameter selection.

Abstract: The densification behavior of mixtures of nanocrystalline and conventional microcrystalline zirconia powders undergoing uniaxial pressing was investigated. The mixtures were obtained with ratios between 10 and 80 wt.% of nanoparticulate powder added to the microparticulate powder. Nitrogen and Mercury porosimetry were used to measure the pore size distributions of the compacts. The powders and the fracture surfaces of the compacts were observed via SEM. The results showed that compacts of the powder mixtures attain higher densities during pressing than the unmixed powders. The powder mixture with 80 wt. % of nanoparticles showed the better particle packing efficiency. A comparison between density values of uniaxial and isostatic pressing also was done and indicated that the best results were obtained by the isostatic method.

Abstract: In this paper, we present a modified density-dependent Drucker-Prager Cap (DPC) model with a nonlinear elasticity law developed to describe the compaction behavior of pharmaceutical powders. The model is implemented in ABAQUS with a user subroutine. Using microcrystalline cellulose (MCC) Avicel PH101 as an example, the modified DPC model is calibrated and used for finite element simulations of uniaxial single-ended compaction in a cylindrical die. To validate the proposed model, finite element simulation results of powder compaction are compared with experimental results. It was found that finite element analyses gave a good prediction of both the loading-unloading curves during powder compaction and the compaction force required for making a tablet with a specified density. Further, the failure mechanisms of chipping, lamination and capping during tabletting are investigated by analysing the stress and density distributions of powders during the three different phases of the tabletting processes, i.e. compression, decompression and ejection. The results indicate that the model has excellent potential to describe the compaction process for generic pharmaceutical powders.