Lorelei Gherman

Manufacturing Technology: Micro-machining

Micro-machining technologies have been the subject of many studies and developments over recent decades due to their importance in the production of micro-moulds, micro-valves, medical components, micro-electrical-mechanical-systems, sub-miniature actuators, motors and micro-products generally. This chapter defines some key terms (in the context of micro-machining) and then outlines material considerations, challenges in obtaining the desired surface finish, simulation techniques, process and machine aspects of micro-machining, and it finally provides examples of micro-manufacturing sectors and applications.

Rapid Manufacturing of Microwave Circuits on Low-Cost Substrates Using Laser Machining

Microwave and millimeter wave (MMW) planar structures are sensitive to printed circuit manufacturing tolerances. A promising alternative to the conventional photolithographic fabrication technique is laser structuring. This paper presents the study and the experiments conducted to investigate the possibility of employing low-cost commercially available substrates for microwave and MMW circuits using laser ablation process. At least two of such materials (a) glass reinforced ceramic filled teflon (PTFE) and (b) glass reinforced hydrocarbon have been used to design and fabricate microwave and MMW passive structures such as edge-coupled bandpass filter (BPF) using laser machining. The experimental results exhibit the suitability of glass reinforced hydrocarbon materials for microwave circuits employing laser ablation process. However, it is deduced that the laser ablation process alters the complex permittivity characteristics of the ceramic filled PTFE materials. The measured results of laser ablated passive structures on both materials are presented along with the simulation results.

Machining of External Cylindrical Surfaces on a RAM Electrical Discharge Machine

As other nonconventional machining methods, the electrical discharge machining is applied when the workpieces materials are difficult to be machined by classical machining methods or the surfaces could not be obtained in efficient conditions by classical machining methods. Such a situation could appear, for example, when test pieces must be separated from materials whose machining by classical methods is difficult. Taking into consideration the necessity to detach a cylindrical test piece from a workpiece made of a high resistance metallic alloy, the problem of using the electrical discharge machining was formulated. An initial experimental test by using the common work motion of the tool electrode from up to down highlighted high shape errors, due to the accumulation in the work zone of the particles detached from the workpiece and from the tool electrode, as a consequence of electrical discharge machining process. A second set of experiments were developed, placing the test piece over the electrode tool and ensuring a work motion of workpiece from up to down; in this situation, a diminishing of the shape error was noticed. The second set of experiments highlighted a relatively reduced conicalness of the machined surface and a low decrease of the machining speed. as the penetration depth of the tool electrode in the workpiece increases, too.

Some Aspects Regarding Micro-Scale EDM Drilling Process

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Possibilities of using a 1070 nm laser in machining of some metallic materials

Possibility to machine the metallic materials by means of a laser beam depends on the capacity of these materials to absorb the respective laser radiation. In the case of a laser beam heaving a wave length λ=1070 nm, the experimental researches showed that among the common metallic materials, the steel absorbs the laser radiation, allowing the applying of some laser beam machining processes, while the copper, the aluminum and the bronze cannot be machined by means of the laser, for an output power of the laser equipment up to 300 W. Due to their high capacity to reflect the above mentioned laser radiation, such metallic materials (aluminum, copper, brass) cannot be significantly affected by the laser beam action and, therefore, they could not be machined by means of the laser radiation having a wave length of 1070 nm. Some considerations were elaborated by taking into account the phenomena developed at the contact zone between the laser beam and the surface layer of the workpiece. A part of the laser beam energy is absorbed, determining the material melting and vaporizing; another part of the laser beam is reflected by the workpiece surface in the case of copper, aluminum and brass. Some explanations concerning the effect of the laser beam exploited during the laser beam machining were developed, inclusively by means of the thermal properties of the workpiece materials.

Small Diameter External Cylindrical Surfaces Obtained by Ram Electrical Discharge Machining

Electrical discharge machining uses the pulse electrical discharges generated between the closest asperities existing on the workpiece surface and the active surface of the tool electrode in dielectric fluid. Essentially, some distinct electrical discharge machining schemas could be used in order to obtain cylindrical external surfaces; within this research, one preferred a machining schema based on the use of a cooper plate in which there were small diameter holes, by taking into consideration the existence of a ram electrical discharge machine. The results of the machining process analysis were presented. A thin copper was considered to be used as tool electrode, in order to diminish the spurious electrical discharges, able to generate shape errors of the machined surface. Some experimental researches were developed by changing the sizes of the process input parameters. As output factors, the test piece and tool electrode masses decreases were considered. Power type empirical mathematical models were determined, in order to highlight the influence exerted by the pulse on time, off time and machining process duration on the output parameters values.

Machinability Evaluation by Single Electrical Discharge

Electrical discharge machining is widely used in processing complex shaped parts. The method uses a tool electrode having a specific geometry, but the tool wear can affect such geometry in time. An affordable material for obtaining tool electrodes with complicated profiles can be electrolytic copper. Some issues appear when workpiece materials made also out of copper or copper alloys are processed, as the copper tool life span decreases. Machinability is the property of a material that indicates good process outcomes for the manufacturer, such as a high material removal rate and low tool wear. In order to determine some machinability indicators such as tool wear and material removal rate, a set of experiments were designed for single discharge machining using thin sheets of copper as tool electrodes and thin sheets of brass as test pieces, with workpiece thicknesses of 0.1 mm. The craters obtained after discharge were analyzed by means of a digital microscope. Based on these results, a statistical analysis was developed and the influence of input process factors was evaluated.

Diminishing Shape Errors at Electrical Discharge Machining of External Cylindrical Surfaces

Electrical discharge machining is a method that could be applied in order to detach cylindrical parts from a workpiece made of electroconductive material. If cylindrical tube is used as tool electrode, the machined surface could have a conical shape, due to the presence in the work gap of the electroconductive particles, detached from electrodes. Experimental researches were developed in order to obtain information concerning the shape error of machined surface. As a result of the experimental observation, improved technological solutions were identified and investigated. The experimental results proved certain possibilities of shape error decrease.

Electrode Tool Wear at Electrical Discharge Machining

As consequence of the development of electrical discharge machining process, the electrode is affected by wear; knowing the evolution of the electrode wear, a better estimation of its service life is possible. It is expected that the electrode wear depends on the energy of the electrical discharges and the mass of the electrode. It is known also that the nature of the workpiece material exerts influence on the evolution of the electrode wearing process. In the paper, some theoretical considerations are used to highlight the above mentioned aspects. A set of experimental tests was designed and developed in order to highlight the influence exerted by the nature of the workpiece material and by the size of the cross section of the electrode, respectively, on the electrode wear. Empirical mathematical models corresponding to the evolution of the electrode wear were established.