1,876 research outputs found
The effect of pressure fluctuations on the cutting ability of pure water jet
No full textThe Waterjet and Abrasive Waterjet technology is the object of a concentrated research. This research area is oriented
to understand the material removal mechanisms and to optimise the process parameters (fluid dynamical and
technological) of various applications. The optimisation of the process parameters is especially difficult because of their
instability during the process.
Many authors have inquired into the physical-mechanical aspects of the interaction between the jet and the mechanical
properties of the material and they developed models and different interpretations. However, the existing models,
mostly, try to describe the cutting mechanism only for AWJ technology.
The interpretation of the mechanism of striation formation in AWJ cutting does not explain the striation formation in
the pure WJ process. In fact, whereas in the cutting surface realised by pure WJ cutting along the whole surfaces there
are irregularities (striations), the surface generated by AWJ cutting is characterized by a streaked morphology in the
bottom zone of the cutting surface.
Previous studies have demonstrated that the cutting surface realised by WJ has not influenced either the pressure
fluctuations or the pressure signal form but depends strongly on the exogenous and endogenous vibrations. In fact, a
considerable reduction of these vibrations allows obtaining remarkable improvements on the surface quality, especially
as regards the striation morphology.
Although the pressure fluctuation does not have a substantial effects on the WJ surface quality, it should have influence
on the depth of cut.
In this work, the effect of the pressure fluctuation on the depth of cut, in no-passing WJ cuts, has been analysed. In
order to do this, the thrust trend of the water jet on a plane surface has been analyzed. The aim of this experimentation
has been to analyze the penetration ability trend of the jet at the exit of a passing cut; afterwards, the correlation
between the thrust signal and the bottom profile generated by a no-passing cut on polycarbonate slabs has been analyzed
The effect of pressure on the surfaces generated by waterjet: preliminary analysis
No full textThe pressure fluctuation in the waterjet (WJ) process is due to the mechanism of high pressure generation, characterized by a cyclical working, and to physical causes (water compressibility at the exercise pressures). This phenomenon cannot, at present, be removed; however, it can be dampened, depending on the selected constructive system, by installing a pulsation attenuator below the intensifier or by conveniently phasing the pumping cycles of more intensifiers in parallel. In this paper, the effects of the pressure on the WJ process have been investigated. The pressure signals generated by a double-acting reciprocating intensifier pump system have been analysed; the effects of the pressure fluctuation and of the pressure signal form on the cutting quality have been studied through the acquisition of the roughness profiles of the surface of various materials (rubber, polycarbonate, plasticine) generated by waterjet
The effect of cutting head vibrations on the surfaces generated by waterjet cutting
No full textAfter a first period in which the research has been focused on the optimisation of the process parameters, the attention is now focused on aspects that were usually neglected. However, they are very important in order to understand the physics of the waterjet/abrasive waterjet cutting process and to improve the cutting quality. Particularly, it has been demonstrated that, in the pure waterjet cutting (and in the abrasive waterjet cutting too), there are irregularities, called striations, along the generated surface. The striation formation depends mainly on the jet instability caused by vibrations during the cutting process. Vibration signals have been measured whilst varying the cutting conditions. A model has been studied which estimates the mean spacing and the frequency of the striations, as a function of the period and the amplitude of the jet vibration. This model has been completely validated through measurements of plasticine surfaces generated by waterjet cutting. © 2005 Elsevier Ltd. All rights reserved
The effect of pressure fluctuation on the cutting ability of pure waterjet
No full textThe Waterjet and Abrasive Waterjet technology is the object of a concentrated research. This research area is oriented to understand the material removal mechanisms and to optimise the process parameters (fluid dynamical and technological) of various applications. The optimisation of the process parameters is especially difficult because of their instability during the process.
Many authors have inquired into the physical-mechanical aspects of the interaction between the jet and the mechanical properties of the material and they developed models and different interpretations. However, the existing models, mostly, try to describe the cutting mechanism only for AWJ technology.
The interpretation of the mechanism of striation formation in AWJ cutting does not explain the striation formation in the pure WJ process. In fact, whereas in the cutting surface realised by pure WJ cutting along the whole surfaces there are irregularities (striations), the surface generated by AWJ cutting is characterized by a streaked morphology in the bottom zone of the cutting surface.
Previous studies have demonstrated that the cutting surface realised by WJ has not influenced either the pressure fluctuations or the pressure signal form but depends strongly on the exogenous and endogenous vibrations. In fact, a considerable reduction of these vibrations allows obtaining remarkable improvements on the surface quality, especially as regards the striation morphology.
Although the pressure fluctuation does not have a substantial effects on the WJ surface quality, it should have influence on the depth of cut.
In this work, the effect of the pressure fluctuation on the depth of cut, in no-passing WJ cuts, has been analysed. In order to do this, the thrust trend of the water jet on a plane surface has been analyzed. The aim of this experimentation has been to analyze the penetration ability trend of the jet at the exit of a passing cut; afterwards, the correlation between the thrust signal and the bottom profile generated by a no-passing cut on polycarbonate slabs has been analyzed
The effects of electrode size and discharged power on micro-electro-discharge machining drilling of stainless steel
No full textThis article is about the measurement of actual micro-electro-discharge machining parameters and the statistical analysis of their influence on the process performances. In particular, the discharged power was taken into account as a comprehensive variable able to represent the effect of peak current and voltage on the final result. Thanks to the dedicated signal acquisition system, a correlation among the discharged power and the indexes representing the process parameters was shown. Finally, linear and non-linear regression approaches were implemented in order to obtain predictive equations for the most important aspects of micro-electro-discharge machining, such as the machining time and the electrode wear
Study of the Law Motion of the Micro-EDM Drilling Process
No full textMicro-EDM is an unconventional technology used to machine every type of electrically
conductive material regardless of its mechanical properties. Material removal occurs through electrical
discharges between the workpiece and the electrode immersed in a dielectric fluid. In drilling
operations, the technology is able to realise microholes with excellent quality in terms of precision,
quality surface, roundness, and taper to the detriment of the machining time, which is less than
other technologies. Several efforts are being made to improve different features related to the process
performance that are severely affected by both the operative conditions, such as the electrode material
or the type of dielectric, and process parameters. The typical indexes used to characterise the
performance are the machining time, the material removal rate, and the geometric indexes. These
indexes are very effective and are easily measurable, but they do not give information about the
evolution of the drilling process, which could be irregular due to the different phenomena occurring
during machining. The aim of this paper is the development of a method able to elaborate the motion
law of the electrode during the micro-EDM drilling operation. In order to do this, a single hole was
manufactured in several steps, recording both the machining time and electrode wear for each step.
In this way, the actual position of the electrode during the drilling can be measured without the use
of a predictive model for electrode wear. It was tested to confirm that the multistep procedure did
not introduce new phenomena, in contrast to the traditional drilling operation. This method was
used to study the effects of the electrode diameter, the type of electrode, the length of the electrode
out of the spindle, and the entity of the run-out on the process performance. The tests were executed
on titanium alloy sheets using a tungsten carbide electrode and hydrocarbon oil as the dielectric. It
was found that the descent of the electrode into the workpiece was not regular, but it depended on
the level of debris concentration in the machining zone. The debris concentration was influenced
by the type and diameter of the electrode, its length out of the spindle, and, to a lesser extent, the
run-out. This method was found to be a useful method for an in-depth analysis of the micro-EDM
drilling process, contributing to a better understanding of the physical aspects of the process
The effect of cutting head vibrations on the surfaces generated by waterjet cutting
No full textAfter a first period in which the research has been focused on the optimisation of the process parameters, the attention is now focused on aspects that were usually neglected. However, they are very important in order to understand the physics of the waterjet/abrasive waterjet cutting process and to improve the cutting quality.
Particularly, it has been demonstrated that, in the pure waterjet cutting (and in the abrasive waterjet cutting too), there are irregularities, called striations, along the generated surface. The striation formation depends mainly on the jet instability caused by vibrations during the cutting process. Vibration signals have been measured whilst varying the cutting conditions. A model has been studied which estimates the mean spacing and the frequency of the striations, as a function of the period and the amplitude of the jet vibration. This model has been
completely validated through measurements of plasticine surfaces generated by waterjet cutting
Investigation on the effects of exchanged power and electrode properties on micro EDM drilling of stainless steel
No full textAim of this research is to study how the exchanged power and the electrode material and diameter affect the performance of micro EDM drilling of stainless steel. Copper and tungsten carbide electrodes, with two dif-ferent diameters, were taken into account. Different values of the exchanged power were obtained by vary-ing the main electrical parameters, namely peak current, voltage and energy level. A dedicated acquisition system for the measurement of effective electrical parameters during the drilling process was implemented. The considered process parameters and the electrode properties, in terms of both material and diameter, resulted to have influence on the drilling performance. Finally, both a linear and non-linear regression ap-proaches were set up to obtain predictive equations about machining time and electrode wear
A sustainability index for the micro-EDM drilling process
No full textThe increasing attention being paid to environmental protection has resulted in significant changes in all production systems. Moreover, system efficiency and productivity should be improved and manufacturing system design must take ecological constraints into consideration. Accordingly, the definition of an index of sustainability can help in assessing the different and sometimes conflicting aspects of a manufacturing process, such as manufacturing costs, energy consumption, waste management, personnel health, and operational safety. In this study, a sustainability index is defined and applied to a micro-electrical discharge machining (EDM) process in drilling operations. The index is composed of five sub-indices that evaluate a particular aspect: energy consumption, environmental impact, dielectric consumption, wear of electrode, and machining performance in general. Each sub-index is calculated by assigning an economic cost to the undesirable impact through a formulae of coefficients (weights) and variables (such as machining time and electrode wear). High index values mean that the process consumes a significant amount of resources and/or produces environmental pollution that is poorly sustainable. In contrast, lower values indicate that the process consumes fewer resources; therefore, it has a lower impact and is more sustainable. The developed sustainability index is applied to an experimental case: the drilling of micro holes in stainless steel (AISI 316L) and titanium alloy (Ti6Al4V) using two types of electrodes (brass and tungsten carbide). Several types of conventional and innovative dielectrics are used (both liquid and gas): kerosene, demineralised water, vegetable oil, compressed air, and oxygen gas. For each combination of workpiece, electrode material, and dielectric tested, the sustainability index is calculated and the outcomes are analysed. It is found that the dielectric plays a major role in the EDM process, because it significantly influences the machining performance. Moreover, it affects the environment in terms of the quantity of consumed resources and pollution created by the process. The type of electrode also affects the process. Within the limit of the present investigation, water and vegetable oil have the lowest environmental impact. For these dielectrics, brass electrodes halve the impact when stainless steel is processed, while tungsten carbide is better for titanium sheets. The use of kerosene as a dielectric coupled with tungsten carbide as an electrode makes the process less green and should be avoided. The combination of air as a dielectric and tungsten carbide as an electrode proves interesting. Oxygen as a dielectric shows instabilities during the process, thus performing poorly in terms of the index. The proposed model for measuring the sustainability of the micro-EDM drilling process is designed to be useful in industrial applications and is easily computable. The index provides a tool that can assist in the decision-making stage of selecting conditions aimed at minimising environmental impact
An experimental investigation of the effects of Spindle Speed Variation on tool wear in turning
No full textSpindle Speed Variation (SSV) is a well known technique to suppress regenerative chatter vibration both in turning and milling operations but a lack of knowledge regarding the effects of non stationary cutting conditions is still limiting its diffusion in the industrial scenario. In this paper an experimental study regarding the effects of Spindle Speed Variation technique on tool wear in steel turning is presented. The experimental tool wear tests were arranged and performed following a full factorial design: the cutting speed and the cutting speed modulation were the main investigated factors. The flank wear width was the main considered process response and it was monitored continuously during wear tests up to the end of the tool life. The effects of the factors were analyzed through the Analysis of Variance (ANOVA) approach
- …
