Besides continuing effort in developing MEMS-based manufacturing techniques, latest effort in micro-manufacturing is also in non-MEMS-based manufacturing. Research and technological development in this field is encouraged by the increased demand on micro-components as well as promised development in the scaling down of the traditional macro-manufacturing processes for micro-length-scale manufacturing. This paper highlights some EU funded research activities in micro/nano-manufacturing, and gives examples of the latest development in micro-manufacturing methods/techniques, process chains, hybrid processes, manufacturing equipment and supporting technologies/device, etc., which is followed by a summary of the achievements of the EU MASMICRO project. Finally, concluding remarks are given, which raise several issues concerning further development in micro-manufacturing.

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Micro-manufacturing: research, technology outcomes and development issues

Technology management methodologies and applications A literature review from 1995 to 2003

Microforming is a relatively new realm of manufacturing technology that addresses the issues involved in the fabrication of metallic microparts, i.e., metallic parts that have at least two characteristic dimensions in the sub-millimeter range. The recent trend towards miniaturization of products and technology has produced a strong demand for such metallic microparts with extremely small geometric features and high tolerances. Conventional forming technologies, such as extrusion, have encountered new challenges at the microscale due to the influence of "size effects" that tend to be predominant at this length scale. One of the factors that of interest is friction. The two companion papers investigate the frictional behavior and size effects observed during microextrusion in Part I and in a stored-energy Kolsky bar test in Part II. In this first paper, a novel experimental setup consisting of forming assembly and a loading stage has been developed to obtain the force-displacement response for the extrusion of pins made of brass (Cu/Zn: 70/30). This experimental setup is used to extrude pins with a circular cross section that have a final extruded diameter ranging from 1.33 mm down to 570 μm. The experimental results are then compared to finite-element simulations and analytical models to quantify the frictional behavior. It was found that the friction condition was nonuniform and showed a dependence on the dimensions (or size) of the micropin under the assumption of a homogeneous material deformation. Such assumption will be eliminated in Part II where the friction coefficient is more directly measured. Part I also investigates the validity of using high-strength/low-friction die coatings to improve the tribological characteristics observed in micro-extrusion. Three different extrusion dies coated with diamondlike carbon with silicon (DLC-Si), chromium nitride (CrN), and titanium nitride (TiN) were used in the microextrusion experiments. All the coatings worked satisfactorily in reducing the friction and, correspondingly, the extrusion force with the DLC-Si coating producing the best results.

Study of the Size Effect on Friction Conditions in Microextrusion—Part I: Microextrusion Experiments and Analysis

Microforming using a small machine (or so-called desktop machine) is an alternative new approach to those using full-size heavy equipment for manufacturing microparts. Microparts are commonly defined as parts or structures with at least two dimensions in the submillimeter range, which are used extensively in electronics and micromechanical products. However when scaling down a conventional forming process to microscale, the influence of the so-called size effect needs to be considered. The individual microstructure (size, shape, and orientation of grains) and the interfacial conditions show a significant effect on the process characteristics. In this paper, the process of extrusion is investigated to establish it as a viable process for microforming. A forming assembly is fabricated and used in conjunction with a loading substage to extrude micropins with a final diameter of I mm. The effect of grain size is investigated by using workpieces heat treated to produce grain sizes varying from 32 μm up to 211 μm. Two extrusion dies with different roughness are used to study the effect of surface finish. While experiments lead to interesting questions and new discoveries, theoretical or numerical solutions are necessary tools for process optimization. Here, knowing the limits of the current widely used numerical simulation tools [i.e., the Finite Element Method (FEM)], a new method, the Reproducing Kernel Element Method (RKEM), has recently been developed to address the limitations of the FEM (for example, remeshing issue), while maintaining FEM's advantages, e.g., the polynomial reproducing property and function interpolation property. The new RKEM method is used to simulate the microextrusion problem. Its results are compared with that obtained from the FEM and the experiment result. Satisfactory results were obtained. Future directions on the experimental and simulation work are addressed.

Microforming: Experimental Investigation of the Extrusion Process for Micropins and its Numerical Simulation Using RKEM

Numerical and physical modelling of plastic deformation in 2-turn equal channel angular extrusion

The elastic behaviour of the forming die has a direct influence on the quality of the formed component. Simulation of material flow and of die deflection during forward extrusion was conducted using elastic and plastic considerations to establish the influence of die-elasticity on the form of the component under different processing conditions. The simulations show that the dimensions of the work-material are affected by die-elasticity during both, loading and unloading of the die. The change of the die-geometry does not produce obvious differences in the dimensions of the extrudate; however, it influences the geometric errors of the workpiece which is retained in the die. Larger values of friction in the injection chamber result in the corresponding increase of punch pressure which results in larger radial deflection of the die during extrusion (loading), the consequence being a greater variation in extrudate geometry. High levels of friction reduce the elastic contraction of the die during punch retraction (unloading), and hence, larger form-errors are sustained after unloading. The contraction of the die during unloading phase of the process causes plastic deformation of the work-material remaining in the injection-chamber; this plastic deformation is significant to the overall form-error of the component.

FE simulation of the influence of die-elasticity on component dimensions in forward extrusion

Identification and classification of flow-dependent defects for injection forging of solid billets

A study on the forming limits of the hydromechanical deep drawing of components with stepped geometries

Several types of flaws develop during the injection forging of components; among these a prominent form results from the instability of the free length of the billet. The material in the die cavity buckles or slides laterally along the anvil; consequently, die filling is effected by asymmetrical deformation of the billet. This FE simulation considers the influence of several parameters which influence the developments of flaws during injection forging. By considering friction conditions at the anvil, the aspect ratio of the primary deformation zone, the exit geometry and the inhomogeneity of the material, the types of flaws which are initiated and the subsequent die filling are simulated using ABAQUS code. Marginal changes in the friction conditions influence the stability of the billet; billets which were unstable when μ = 0.01 were, generally, sufficiently stable when μ = 0.03 to effect flawless die filling. Simulation confirms the experimentally proven, limiting aspect ratio of the primary deformation zone to be between T = 1.6 and 1.8. The deformation of the billet graduates from non-symmetrical deformation at aspect ratios greater than 1.7 to bending at ratios greater than 2.0. larger exit radii improve the flow characteristics and had been shown to reduce the energy requirements; however, the simulation shows that instability would occur at a lower aspect ratio when a large exit radius was incorporated in the injection chamber. Lack of inhomogeneity in the material will also result in instability and asymmetrical die filling at low aspect ratios.

Rajendram Balendra

Papers

FE simulation of the influence of die-elasticity on component dimensions in forward extrusion

Identification and classification of flow-dependent defects for injection forging of solid billets

A study on the forming limits of the hydromechanical deep drawing of components with stepped geometries

FE simulation of the development of flaws during injection forging

Secondary yielding of forged components due to unloading