Irina Beşliu

Kerf generation during the plasma cutting process

The plasma beam cutting is a machining method applied in order to detach parts or workpieces from plate type workpiece. Essentially, a plasma jet is sent to workpiece, determining melting, vaporizing and removing of the material from the workpiece. If there is a relative movement between the plasma jet and the workpiece, a kerf gradually appears. Many factors exert influence on the kerf characteristics. A full factorial experiment with three independent variables at two levels was designed, in order to highlight the influence exerted by the cutting speed, workpiece thickness and arc current on the kerf width in the superior and inferior zones and on the kerf taper angle, respectively. Power type empirical mathematical models were determined by mathematical processing of the experimental results.

Results of an Experimental Research Concerning the Evaluation of Machinability by Drilling under Constant Feed Force

The knowledge about machinability indices for distinct machining processes allows finding the most appropriate values of the relevant factors for definite machining operations. Several criteria can be used to characterize machinability, such as the tool wear, the magnitude of the cutting forces, the roughness of the machined surfaces, or the shape of the chips that are formed during the machining process. One of the methods for studying the machinability is based on the analysis of drilling operations that are made under constant feed force. A drill press is probably the most readily available device to implement an experimental setup for drilling machinability tests. In normal operation, however, the chip accumulation at the dead end of the machined hole has a detrimental impact on the results of machinability tests, so that an improved setup was designed. A two-level, full factorial experiment with three independent factors (the drilling tool diameter, the rotational speed of the spindle and the feed force) has proven the suitability of the new experimental setup. Using it, we could find a power-type empirical model that explains the impact of the input factors in the depth of a hole that is machined in a pre-defined time interval.

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.

Surface roughness at vibroburnishing

Vibroburnishing is a finishing method of metallic surfaces based on plastic deformation of workpiece surface layer under the action of a ball which is pressed and rolls on the workpiece surface. As main process results, the surface roughness and the thickness of the layer affected by the burnishing tool pressure are considered. Some theoretical considerations highlighted some groups of process input factors able to affect the size of roughness corresponding to burnished surface. An experimental research was designed and developed in order to highlight the influence exerted by some vibroburnishing process input factors (frequency and amplitude of vibratory motion, radius of spherical surface corresponding to ball burnishing tool and the force exerted by the ball on the test piece surface) on the size of the Ra surface roughness parameter. Empirical mathematical models were established and analyzed.Vibroburnishing is a finishing method of metallic surfaces based on plastic deformation of workpiece surface layer under the action of a ball which is pressed and rolls on the workpiece surface. As main process results, the surface roughness and the thickness of the layer affected by the burnishing tool pressure are considered. Some theoretical considerations highlighted some groups of process input factors able to affect the size of roughness corresponding to burnished surface. An experimental research was designed and developed in order to highlight the influence exerted by some vibroburnishing process input factors (frequency and amplitude of vibratory motion, radius of spherical surface corresponding to ball burnishing tool and the force exerted by the ball on the test piece surface) on the size of the Ra surface roughness parameter. Empirical mathematical models were established and analyzed.

Nanoreliefs Obtained by Various Machining Methods

The nanoreliefs could be defined as surface asperities having height characteristics lower than one micrometer, in order to be expressed in nanometers. There are various applications that need nanoreliefs and this aspect determined the investigation of the possibilities offered by distinct manufacturing processes of obtaining nanoreliefs. A research concerning the manufacturing methods based on the material removal from workpiece was developed. The analysis revealed that there are machining methods by traditional cutting and nonconventional machining methods that use thermal or electrochemical phenomena in order to remove the material from workpiece. Some essential aspects of such machining methods were highlighted. The factors able to affect the asperities heights were showed. Experimental researches facilitated the identification of mathematical empirical models able to offer supplementary information concerning the influence exerted by some of the process input factors on the surface roughness parameter Ra. Surfaces profiles or images were obtained by means of instruments for investigation of the machined surfaces.

Simplified Version of Polymer Rotational Molding Manufacturing Method

Rotational molding is a manufacturing method which supposes the rotation of the mold, during the solidification of the liquid phase material, so that finally a part having a hollow could be obtained. The method could be applied in manufacturing of metallic and nonmetallic parts. Usually, the equipment for rotational molding ensures slow speed rotating of the mold around two axes placed perpendicularly each other and this fact led to relatively complex equipment for achieving rotational molding. The capacity of the liquid material to entirely cover the internal walls of the mold depends essentially on the liquid material viscosity, on the rotation speed and on the movements applied to the mold. Simplified equipment including a single rotation movement could be materialized. In order to test such a solution, a preliminary experiment was designed and materialized, by using a device adapted on universal lathe. Thus, the objective of the research presented in the paper was to study if it is possible to achieve plastic parts made by rotational molding using a single rotation movement. A polyurethane resin obtained from two liquid components was used in order to obtain the liquid material that could be introduced in the mold. The research results proved the possibility to use simplified equipment for achieving a rotational molding process, at least in certain cases and with some technological limits.

Use of Taguchi Method and Grey Relational Analysis for Optimizing a Ram Electrical Discharge Machining Process

There are various factors able to exert influence on the results of electrical discharge machining process. If there are many output factors of the machining process, one can formulate a problem of multicriterial optimization. It is necessary to find adequate values for the input factors so that the output factors have optimized values. The paper presents the results of a research aiming to optimize the material removal rate and the tool electrode wear rate, in the case of ram electrical discharge machining process. As input factors, one used the pulse on time, pulse off time and average peak current intensity. The Taguchi method was applied, in association with the Grey relational analysis. In this way, combinations of values corresponding to the input factors were determined, in order to obtain optimal results for the process output factors.

Investigation of Surface Accuracy Obtained by RAM Electro Discharge Machining of Small Cylindrical Surfaces

The paper deals with the investigations of influence parameters of electro discharge machining (EDM) on the shape accuracy of external cylindrical surfaces machined by EDM process. A Sodick AD3L CNC electrode discharge machine was used to perform the EDM tests. In order to obtain the external cylindrical surfaces by RAM EDM copper cylindrical electrodes were used. Different machining setups and dielectric immersion modes were considered. In order to investigate the influence of the machining parameters on the investigated factors a factorial plan of experiments was considered. The preliminary experimental results highlighted the possibilities to obtain small diameter external surfaces of revolution on a ram electrical discharge machine.

Obtaining Holes in Plexiglas Using Low Power CO2 Laser Beam

The laser beam drilling is generally included in the larger group of laser beam machining methods based on the material removal. The problem addressed in this paper referred to the laser beam drilling of test pieces made of Plexiglas. Some theoretical aspects were highlighted by analyzing the physical effects developed in Plexiglas by the laser beam action. Experimental research was developed in order to highlight the influence exerted by the duration of the CO2 laser beam action on the Plexiglas in obtaining blind and through-holes. Empirical mathematical models and graphical representations allowed formulation of some remarks concerning the results of experimental research.

Premises for Experimental Research of the Electrochemical Machining

The electrochemical machining method ensures conditions for machining workpieces made of electroconductive materials, when the classical machining methods could not be applied or when their use is not able to offer a high efficiency of the machining process. The large diversity of the electrochemical machining procedures needs information about the specific work conditions and adequate establishing of the parameters which characterize the machining process and the factors able to exert influence on the parameters of technological interest. In order to design and materialize some electrochemical machining procedures, an analysis of the conditions specific to the work zone and of distinct subsystems specific to electrochemical equipment was developed. Taking into consideration the results of analysis, equipment for electrochemical machining was designed and materialized. One considered also some possibilities to develop subsequently scientific researches concerning aspects specific to the electrochemical machining process. Preliminary tests proved the possibilities of using the equipment and of its improving in the future.