The hard grains of the coating are built up by CrAlN. They are embedded into an amorphous matrix of silicon nitride (SiNx). This generate the Nanocomposite structure with a much higher hardness than the hardness of standard PVD coatings. Due to the amorphous silicon nitride the coating possesses a high toughness and low internal residual stress, which makes a thin coating on sharp cutting edges possible. On the top of the hard coating we deposit a soft carbon based coating as a DLC (diamond like coating). This lubrication layer decreases the friction coefficient (down to µ<0.1) and therefore avoids the so called build up edges, the sticking of the green material on the cutting edges of the tool. Beside green machining is successfully tested under industrial conditions for cutting high alloyed materials, like INOX, Hasteloy etc. Due to the high heat hardness and the low friction coefficient the coating fundamentally supports the dry environmental friendly production. The coating is trademarked as nACVIc® (nACRo® +CBC).The coating is commercial available for industrial use.
The part quality with respect to breakouts, surface roughness has been investigated for turning of softmagnetic materials. For turning the SMC materials coated carbides and super hard PCBN tools can be recommended. For rough machining the coated carbides should be used. For finishing operations sharp PCBN inserts are suitable because of the better surface and breakout qualities. In particular, it is planned to publish results of the project in one or more of the following journals: - International Journal of Advanced Manufacturing Technology, - Journal of Material Processing and Manufacturing, - Journal of manufacturing Science and Engineering Transaction of the ASME.
Classical analysis of powder sintering is not relevant to describe the sintering of dense metal powder compacts. In particular it cannot explain the deformation of such compacts, which is very small (typically less than 1%), strongly anisotropic and significantly affected by pressing and dewaxing conditions. From the information collected by various methods (dilatometry, impulse excitation technique, mechanical testing, X-ray microtomography) a description of the dewaxing and sintering process of steel powder compacts has been worked out. It points out the prominent role of so-called contact pores, which are created during compact ejection, on the deformation and strengthening of the material during heating. These pores are more numerous in denser compacts and preferentially oriented perpendicularly to the pressing direction. They tend to open during dewaxing, which results in swelling and weakening of the compact, and to close early during sintering, which leads to a larger shrinkage in the pressing direction with respect to the transverse direction.
A PM material combining a standard stainless steel and a stainless tool steel have been developed and tested with respect to drill resistance, corrosion resistance and toughness. All being important material characteristics that have not been possible to combine in single details within the lock industry. A material with these criteria s will be very hard to machine in the sintered state, therefore green machining is a preferred route for this type of material. The work with analyzing the component manufacturing is merely in its beginning. Before the material can be commercially used there needs to be manpower directed at relating the influence of the major process variables (alloy composition, sintering atmosphere, holding temperatures and times, cooling rates etc) seen from the limits defined from industrial partners within the powder metallurgy industry. Drilling in the green state have been performed and is seen as a possibility for this material given the right lubricant and curing. Whether turning and milling is possible in the green state have not been evaluated. During the time span of the project other materials fulfilling the same criteria’s have been developed and refined by other companies which have decreased the need for industrializing of this material.
To guarantee the Minimal Quantity Lubrication (MQL)-Function, the shank ends of the tools were optimised regarding responding behaviour and distribution of the oil mist.
Green strength is an important physical property of a metal powder compacted part. The importance of sufficient green strength becomes increasingly apparent if a green machining operation is intended to be performed. In general, stainless steel powder materials not only achieve low green densities by compaction but also low green strength values compared to regular low-alloy powder. A way to increase both green strength and green density is to use the warm compaction technique. The warm compaction technique comprises both heated pressing tools and powders (approx 130ºC). During the PM MACH project an alternative way to increase green strength for a stainless steel powder, without using the warm compaction technique, was tested. By using an certain lubrication, mixed together with the stainless steel powder, and combined with a heat treatment (approx. 225ºC, 1 hour) after compaction, a remarkable enlargement in green strength can be obtained. This enlargement is almost four times higher compared with the green strength obtained with warm compaction.
In turning PM-materials in the green state dust and particles pollute the machining system and increase cleaning maintenance effort is required. Especially for turning a sinter hardenable PM material a dust removal system has to be used. Therefore different principles are possible. The fan principle is easy to install but the rotating components in the dust and particle stream are high cumbered. Another possibility is the use of an injector. Regarding the fact that a pressured air system is installed at the machining system the injector principle is also easy to install, it makes less noise and is easy to maintain. The dust removal system based on the injector principle has been implemented in the turning lathe and was found to be effective for the Distaloy AE (D+, D-) and Astaloy CrM (A+, A-) chips. A significant reduction of dust-like chips is observed in the working place when the system is operating. The support of potential manufacturers is planned by different ways like publishing articles, hosting workshops and conferences especially for SMEs as well as taking part in fairs etc. In particular, it is planned to publish results of the project in one or more of the following journals: - International Journal of Advanced Manufacturing Technology, - Journal of Material Processing and Manufacturing, - Journal of manufacturing Science and Engineering Transaction of the ASME.
During the first two years of the project, the overall shrinkage of warm-pressed Astaloy CrM and Distaloy AE test-bars after dewaxing and sintering has been investigated. Additionally, various in situ high temperature techniques (dilatometry, bending, DSC, high temperature impulse excitated resonant frequency analysis and microtomography) together with computer aided thermodynamic calculations have been used in order to obtain additional data for the modelling and a better understanding of the physical and chemical phenomena occurring during sintering. The results of the characterisarion of shrinkage obtained showed for both laboratory and industrial conditions, a very limited but clearly anisotropic shrinkage for Distaloy AE with higher values in the axial direction (0.2%) than in both transversal directions (less than 0.1%). The results obtained for Astaloy CrM showed slight shrinkage or swelling lower than 0.1%. During dewaxing, a significant swelling was observed in the denser A+ and D+ specimens in good agreement with the overall shrinkage data measured. Viscosity (characterised through in-situ bending tests) has shown to increase linearly with the sintering time during isothermal sintering. HT-IET and DSC results were correlated with equilibrium thermodynamics by means of multicomponent phase diagrams calculated by the Thermo-Calc software and the SSOL database. The temperatures for aèg transformation, magnetic transition, M23C6 precipitation in Astaloy CrM and copper melting in Distaloy AE were identified and correlated by both experimental techniques. In spite of the rather poor correlation with calculated equilibrium temperatures (especially during the heating segment of the thermal cycle), good agreement between DSC and HT-IET was achieved. The correlation during heating was notably improved when the Fe-C binary phase diagram was considered. The non-destructive in-situ microstructural characterisation by synchrotron tomography has showed evidence of predominant disappearing of contact interfaces in the direction perpendicular to the pressing direction. This phenomenon should be correlated with the macroscopic anisotropic deformations measured.
This result is a series of technical papers that have publicly disseminated in scientific journals. The common theme of the papers is new approaches to accurately determining the green properties of powder compacts. This development has been recognised as being essential if advanced manufacturing techniques, such as green machining, are to be exploited successfully. The papers discuss how the green strength of powders designed for such applications, was measured using several different test methods. Fracture statistics were correlated with compact density and test method employed, and the Weibull modulus calculated for each case. It was found that Weibull analysis accurately predicted the green strength dependence on the test configuration utilised and therefore can be used as a predictive technique. A new method for the production of samples for measuring the fracture toughness of green compacts has also been developed.PublicationsC.C. Degnan, A.R. Kennedy and P.H. Shipway, Powder Metall., 46, 4, 2003, 365 - 370C.C. Degnan, A.R. Kennedy and P.H. Shipway, Mater. Sci. Tech., 20, 2004, 731 -738C. Degnan, A.R. Kennedy and P.H. Shipway, J. Mater. Sci, 39, 2004, 2605-2607C.C. Degnan, A.R. Kennedy and P.H. Shipway, J. Mater. Sci., 40, 15, pp. 4117-4119, 2005.
To make the process secure for the operator and the machine tool it self a dust removal system was made adjusted to the used tools and development this for industrial use.
The restrictions for clamping green parts with lower densities were examined. For this various FEM-simulations were performed and analysed. The necessary clamping force and clamping surface for several machining operations were determined. Different clamping systems were valued by requirements as clamping force, clamping accuracy, contact pressure, easy adaptable, easy to exchange and costs. In the technical view clamping systems as power operated chucks with glass fibre reinforced plastic jaws, power operated mandrels and collets are suitable for clamping green parts. The reachable clamping accuracies and clamping forces of these systems are sufficient for the task. The occurring maximum contact pressures relative to the size of the contact areas of the different clamping systems are nearly equal. But the use of glass fibre reinforced plastic jaws have some advantages regarding to the costs, the easy possibilities of adaptation and the easy and fast exchange of the clamping system. The support of potential manufacturers is planned by different ways like publishing articles, hosting workshops and conferences especially for SMEs as well as taking part in fairs etc. In particular, it is planned to publish results of the project in one or more of the following journals: - International Journal of Advanced Manufacturing Technology - Journal of Material Processing and Manufacturing - Journal of manufacturing Science and Engineering Transaction of the ASME.
Tool development concerning substrate, geometry, coating, cutting conditions and machining strategies
Development and production of drills for machining Distalloy, Astalloy, SMC Components and stainless steels. Drilling tests were carried out with different kinds of drills regarding breakouts at the work pieces, torque and feed forces, temperature, surface quality, diameter precision and wear resistance.
Development of an anisotropic constitutive equation and a related data base for modelling the sintering of metal powder compacts
Finite element simulation has been proved to be a useful tool for predicting shape changes of powder compacts during sintering. Most constitutive equations proposed so far for describing powder behaviour are isotropic whereas metal powder compacts obtained by die pressing exhibit a strong anisotropy that should be taken into account for a relevant prediction of dimensional changes during sintering. Within PM MACH project, the development of an anisotropic constitutive equation for sintering powder compacts has been based on the results of an extensive experimental study of the behaviour of warm pressed 316L steel compacts during sintering. This study used dilatometry measurement and provided data on free sintering deformation and viscosity as function of relative density and temperature in pressing and transverse directions. The proposed constitutive equation is of the transversely-isotropic type with regard to the direction of compaction. It contains several material parameters that should be fitted from experimental data. It can be easily implemented in any finite element code devoted to PM process simulation.
The strategy is a special technology for milling PM materials in green state with minimum break outs and optimum smooth surface. The technology is using right and left hand milling cutters, end mills with cylindrical shanks. The fundamental idea is to start always with a cut in using the down hill milling method. The milling with the starting tool will be interrupted before a cut out, before completing the milling path. To finish the milling path a new tool will be changed in. This tool starts with a cut in again but on the opposite side of the work piece. This second tool should have the opposite oriented helix (e. g. left hand oriented if the first tool was right handed). The path will be completed where the path of the first tool was interrupted. The technology is applicable for roughing and for finishing, especially for mould and die milling with simple (groove) and complicated 3D contours. The technology makes the green machining possible without break outs and smooth surfaces. The process uses minimum lubrication to avoid high pressure coolant and to protect the environment.
Certain green powder metallurgy materials can present considerable machining difficulties; notably very rapid rates of tool wear and excessive surface and edge "breakouts". Considering the composition and microstructure of green PM materials, the levels of tool wear experienced are unexpected and have been identified as somewhat unique among the more usual tool wear mechanisms (associated with the machining of conventional cast or wrought work materials).With regards to the issue of component quality, a series of cutting tool edge geometries were designed and manufactured and following turning tests at the Technical University of Berlin, were found to result in a considerable improvement in surface quality due to reduced surface-breakouts. For drilling applications, several methods were assessed for the production of PCBN-tipped drills. One method, comprising a tapered PCBN segment brazed to a cemented carbide drill blank was used by Guehring for the production of twist drills and in a series of drilling tests on green PM materials, was found to result in excellent (mirror-like) surface quality and minimal edge breakouts.With regards to the issue of cutting tool wear, only one particular soft magnetic composite (SMC) PM material was found to result in significant rates of tool wear. Following extensive testing and investigation of the tool wear mechanisms, a series of novel cutting tool materials were produced using newly developed proprietary technology which despite not providing the anticipated improvements in wear resistance will help advance cutting tool materials technology for PM materials and beyond. Arising from the wear mechanism studies, Element Six also promoted the use of machinability-enhancing additives to the SMC material the results are somewhat positive through not in all machining applications.
Knowledge about machining strategies and technology parameters for turning sinter hardenable PM parts in the green state
The economic production of PM parts requires a specific machining technology for the green compacts including clamping systems as well as specific cutting parameters and tool materials. Technologies for conventional iron based materials like steel are not useful to machine green compacts. Therefore, IWF is going to provide guidelines for machining green compacts. The support of potential manufacturers is planned by different ways like publishing articles, hosting workshops and conferences especially for SMEs as well as taking part in fairs etc. In particular, it is planned to publish results of the project in one or more of the following journals: - International Journal of Advanced Manufacturing Technology, - Journal of Material Processing and Manufacturing, - Journal of manufacturing Science and Engineering Transaction of the ASME, - CIRP Annals Manufacturing Technology, - Industrial Diamond Review, - WGP Annals Production Engineering. Furthermore, the results are going to be transferred to the technology centre ultrahard cutting materials at IWF. Here the results are going to be disseminated by marketing measures such as press information or participation in fairs.