Projects / Programmes
Improvement of flowability and density of feedstock used in nanoPowder Injection Moulding (nanoPIM)
| Code |
Science |
Field |
Subfield |
| 2.05.00 |
Engineering sciences and technologies |
Mechanics |
|
| Code |
Science |
Field |
| T000 |
Technological sciences |
|
| Code |
Science |
Field |
| 2.03 |
Engineering and Technology |
Mechanical engineering |
Manufacturing improvements, Powder Injection Moulding, Polymer metal composites, Viscosity, Creep compliance, Flowability, Granular materials, Temperature-Pressure effects
Researchers (14)
Organisations (3)
Abstract
This proposal addresses the key problem of the new nano-powder injection molding technology (nPIM), which is an evolutionary however substantial improvement of the existing PIM technology, and may be considered as one of the ultimate future emerging technologies (FET) for manufacturing metallic and/or ceramic structural elements with complex geometry. The key advantages of parts made with nPIM in comparison with those made with PIM technology are their superior mechanical properties (in particular fatigue resistance), and their surface quality that reaches the grade of “polished surface”. The key problem of nPIM is extremely high processing pressures (several MPa) resulting from poor flowability of polymer-metal and polymer-ceramics mixtures at elevated pressure. Solution of this problem is the ultimate goal of this project.
Nano-powder injection molding (nPIM) is a versatile technology for manufacturing small parts with complex geometry made out of metal or ceramic. nPIM relies on the preparation of a composite material consisting of a polymer matrix and metal or ceramic powders, commonly called feedstock. Automotive, electronics and medical industries could greatly benefit from utilizing nPIM. However there are several factors that affect the widespread of nPIM technology. One of them is the long time required to remove the polymeric matrix material used during molding. This issue has been partially solved by using polymers that undergo fast degradation (e.g. polyoxymethylene - POM) under the appropriate conditions, but new limitations have risen since such polymers have very high viscosity, which requires extremely high pressures during the molding step.
The goal of this project is to find ultimate “composition” of the feedstock based on POM. In line with this goal this project aims to reduce the viscosity of the feedstock material used in PIM and nPIM while maintaining good mechanical properties in solid state. This will be achieved by (i) manipulating the molecular mass distribution of the polymeric matrix material, and by (ii) selecting the appropriate particle size distribution of the filler powders, which will include nano and micro particles. Special attention will be given to (iii) the effect of temperature and pressure on the improved feedstock material, needed for the optimization of the processing parameters. Finally, (iv) the performance of the improved feedstock will be demonstrated by carrying out the complete PIM process and manufacture test parts with complex geometry.
Significance for science
The aim of the project was to improve the formulation of a feedstock material that would exhibit lower viscosity and at the same time good mechanical properties. From the point of view of the development of science, we wish to emphasize two things that emerged as direct result of the project and contribute to the development of science: 1. Appratus and methodology for determining friction in granular materials - Granular Friction Analyzer (GFA) The flow of granulated materials is a complex process and depends on the properties of the material and the conditions to which the material is exposed. It is important to know and control the moment when granular material starts to flow, because it greatly affects the quality of the finished product and its price. Existing methods for determining the flow of granular materials have been well developed and in use for a long time. However, there are no avaliable methods with which one can easily measure the properties of granular systems at different pressure loading. As part of our research, we developed a new apparatus and methodology (GFA). Apparatus is easy to use and with it we can determine friction between granular materials exposed to pressure. The device also provides an analysis of the conditions under which the granulated material begins to move (under the influence of the pressure load), i.e. zero flow rate. In the case of the first prototype device, it turned out that the current method of measuring the properties of the granular materials is not completely optimal, therefore, an upgrade of the GFA device with the optical imaging technique (digital image correlation) is planned. This upgrade will allow for a more accurate monitoring of the behavior of granular materials, where we would like to check the influence of the different types of materials, size and particle size distribution on the flowability of granular materials. 2. Modeling the flow behavior of polymers with a high share of fillers Over the past years, several researchers have tried to predict the behavior of polymers with a high share of fillers using different mathematical models, with the goal of accelerating the development of new composite materials for various applications, as well as to gain a better insight into the interaction of individual components. There are several models available in the literature for predicting the flow behavior of raw materials. Within the project, 3 exponential and 9 power law models were used, but we found that their accuracy was limited. On the one hand, some models do not take into account the viscosity dependence of the shear rate or treat these materials as homogeneous materials, although they are clearly multiphase materials. On the other hand, there are not enough systematically conducted experimental tests to verify these models. This leads to incorrect predictions of flow behavior of materials or their limited usefulness (only in a narrow range) or to the use of these models only for specific combinations of polymers and particles. We can colcuede that currently we do not have sufficiently good tools to describe the flow behavior of polymers with a high share of fillers. A model that will better represent the behavior of such materials should be based on the fact that the polymeric binder is more severely stressed when particles are present in the raw material. Since the filler can be considered as a rigid body, all the deformation in the shear field is carried by the matrix, which means that in fact the matrix is more severely loaded and consequently the effective viscosity of such feedstock material is higher. In addition, the model must also take into account the shear rate, temperature, and the pressure dependence of the feedstock material. Numerical modeling of PIM technological processes is currently not possible! Although the improvement of the models was not one of the goals of this project, it represents motivation for further research.
Significance for the country
The experience and knowledge acquired within the project represent significant intellectual potential, which can lead to technological breakthroughs in various fields of engineering, where polymer composites and composites with high concentration of solid particles are in use. Due to their versatility, such materials can be found in many engineering fields such as the automotive industry, additives manufacturing, manufacturing, biomedicine, ceramics, batteries, magnets, solid fuels, sand glues, etc. Within the project, we looked for an improved formulation of the composition of the feedstock material (polymeric binder and metal particles/fillers) in order to achieve improved conditions for processing the feedstock materials, thus opening up the possibility for the production of an entirely new range of PIM products. Within the project we found that the rheological (processing) properties of the feedstock materials can be improved by the propper choice of the molecular weight of the binder or by the use of additives. We also found that there is a critical limit to which feedstock material can be treated as a Newtonian liquid, and above this limit we must take into account the reduction in viscosity by increasing the shear rate. We have also shown that by correct selection of particle size and particle size distribution we can significantly influence the flowability of the feedstock material. Based on these findings, it can be said that the PIM technology and the findings of the project represent a potential breakthrough in the use of this technology and open up opportunities for entry into various new niches. In this field, Slovenia could play an important role in the production of metal products with complex geometry, using PIM technology. Wider impact on industry Currently, the wide use of PIM technology is not possible. By improving the formulation of the PIM feedstock material on the basis of the project's results, such technology could be used as a primary technique in the production of metal or ceramic parts that are currently produced with worse performance. In this way, PIM technology would allow companies to reduce production costs and reduce the level of negative impact on the environment. Parts that could be manufactured using PIM technology include automotive, electronic components, and medical and pharmaceutical products. These are industries that are heavily present in Slovenia and could, based on these results, increase their competitiveness, as PIM technology improvements make it possible to produce new products at a significantly lower price. Development of higher education The results of the research and the acquired experience within the project were transferred to the study programs carried out by our group: Mechanics of Non-Metallic Materials (Project Application Program, Level I), Polymers Science (Development Research Program, Level I), Mechanics of Polymers and Composites (Level II) and Viscoelasticity Theory (Doctoral Studies). We also included the acquired knowledge and experiences i in practical works, seminars and diplomas. The transfer of the latest findings into study programs provides students better competitiveness.
Most important scientific results
Annual report
2014,
2015,
final report
Most important socioeconomically and culturally relevant results
Annual report
2014,
2015,
final report
