Papers by Author: Yi Qin

Abstract: Forming of micro-components from powder with fields-activated sintering technology (FAST) renders different forming and sintering mechanisms, comparing to that occurring during the forming of macro-sized components with a similar technology. Establishing a good understanding of these mechanisms would help process design and control aiming at achieving desired quality of the components to be formed. This paper presents a study and the results on the sintering kinetics of the powder during Micro-FAST for the fabrication of micro-gears (the module is 0.2 and the pitch diameter 1.6 mm) from copper powder. The results showed that the densification of copper powder is related largely to the bulk plastic-deformations of the particles and the melting of the particles at contact interfaces. Particularly, it is revealed that plastic deformations of the copper particles mainly occurred at approximately 340 °C and melting of the particle-interfaces at approximately 640 °C. Differently, in a densification process with a traditional powder sintering method, grain growth and neck growth would, normally, be two dominant mechanisms that achieve the densification of powder.

Abstract: The importance of the effect of particle deformation under Micro-forming Fields Activated Sintering Technology (Micro-FAST) has been summarized in this paper. Micro-FAST is involved in the coupling of stress field, temperature field and electric field wherein these fields work simultaneously rather than independently. By using Gleeble-1500D thermal simulation instrument, the micro-cylinders with size of Φ1.0mm×1.0mm were formed from 316L stainless steel powders. It has been found that the maximum relative density of sintered samples reaches up to 99.2% close to the full density. Moreover, the microstructure of specimens has also been investigated. Especially, the metal powders have been simulated as globular plasticine particles in the structure to elucidate the deformation of particle under Micro-FAST.

Abstract: Spur gears are the most common type of gears for industry, due to its simple structures and low costs of manufacture. Under the complex loading conditions, failures can easily occur in the form of de-bonding, pitting, spalling or crushing of coating structures. Failure may originate from initiation of cracks, and its growth and propagation, however, basic failure mechanism is still not clear. In order to investigate the failure mechanism of coating structure failure for the spur gears, this paper presents some understandings about the coating damage at the teeth flank of a spur gear, based on a novel Finite Element simulation-procedures. This modeling procedure was developed based on several modeling approaches including: parameterized FE modeling, Cohesive-Zone Model and sub-modeling technique. The numerical model of spur gear was based on 42CrMo4 steel with PVD coating deposited as TiN/CrN multilayer structures. It was found that greater load bearing capacity exist for spur gears with the coating of nitride states deposited on 42CrMo4 steel.

Abstract: This work provides a novel idea of fabricating MnZn bulk ferrite materials. MnZn ferrite powders with a composition of Zn0.8Mn0.2Fe2O4 (wt%) are sintered to form cylindrical bulk ferrite with diameters of 1.0mm, and heights of 1.0mm under multi-physical field coupling with Gleeble-1500D thermal simulation instrument. The results show that sintered ferrite has a spinel structure, and that some magnetic properties like maximum energy product and remanence of the Multi-physical Field Coupling sintered sample are better than that obtained by conventional sintering. Densification process and solid phase reaction are promoted by alternating magnetic field and high frequency wave generated by AC current.

Abstract: Dynamic characteristics of a micro-forming machine system are of significant importance to be considered if high-precision micro-parts are to be produced. This is because forming tolerances may be within a range of sub-microns up to 5-15% of the thickness of a thin sheet-metal (e.g. <100µm) being used in micro-sheet-forming. Achievability of the quality parts often vary with the machine-system performance and process parameters being set, and it largely depends on the understanding of the machine and tool system’s dynamic characteristics and effectiveness of the control of the machine and the process. Nevertheless, there has been lack of the effort in this field of research. Significant number of the efforts in this field were focused mainly on discrete and/slow processes where the dynamic characteristics of the forming systems were often neglected. This paper presents the dynamic characteristics of an autonomous micro-sheet-forming machine system and its effect towards the produced parts’ quality. These have been studied by combining finite element analysis and forming experiment, with a particular focus on the combined effects from the machine, tooling system and the sheet-metal feeding system (the strip feeder). The results showed that, besides importance of the dynamic performance of the machine and the tool-system, dynamic characteristics of the material-feeding plays an important part in determining the parts’ quality produced.

Abstract: A web-based collaborative design advisory system for designing micro products is being developed, which is based on use of both knowledge and rules. The system is aimed at helping designers to assess/optimise the design of micro products to be manufactured with micro-forming. The Microsoft C# programming language, ASP.Net technique and Microsoft Access database system have been used to develop this system. The system is composed of various assessment modules such as product geometry features, forming processes, materials, machines, tools and cost assessment modules. Clients can use/browse the user interface of the integrated system through the internet to import a CAD design model and define design parameters. The system is not only able to assess the client’s design but also to generate preliminary process plans for the selected micro-forming processes. A micro-pin design is used as an example to test the capability of the 1st prototype system. With such a system, some advantages such as increasing the design efficiency in the web-based collaborative design environment have been identified.