Airborne acoustic emission of an abrasive waterjet cutting system as means for monitoring the jet cutting capability

Abrasive waterjet cutting is a manufacturing technology making use of a high-speed waterjet with abrasive particles in suspension, for cutting materials with different mechanical properties. Product quality requirements are pushing towards an improvement of tracking and stabilization methods of the relevant process variables. Amongst those, the jet kinetic power defines the cutting capability and has a significant impact on the final cut features. This variable is subject to relevant fluctuations versus time. Besides, the current state of the art does not provide means for its in-line monitoring. The aim of this contribution is to monitor the airborne acoustic emission of an abrasive waterjet cutting head and investigate its correlation with the jet kinetic power. The investigation is carried out by means of factorial studies, in which the jet is fired at various water pressures and abrasive feed rates, providing different kinetic powers. The acoustic emission is synchronously monitored by means of a condenser microphone, installed on the cutting head. Data at frequencies above 40 kHz is found to constitute a robust and selective acoustic signature of the airborne jet. The acoustic signature is proven to be an effective in-line indicator of the jet kinetic power and its pressure-induced variations, whilst abrasive-induced variations remain undetected. A calibration procedure is presented, for translating the acoustic data into a jet kinetic power. The method is validated by means of further experiments that envisage its deployment in a real scenario. Overall, the presented method constitutes a robust tool for monitoring pressure-induced variations of the jet cutting capability

CFD aided design and experimental validation of an innovative Air Assisted Pure Water Jet cutting system

Water jet cutting has always been a promising technology because of its extreme simplicity and flexibility, even if it often suffers a lack of control on its process parameters, especially if compared to technologies such as laser cutting or electro-discharge machining. Recent studies have showed how the presence of water inside the orifice causes disturbances and instabilities which systematically affect the jet structure, both during the jet formation and the cutting process. These disturbances can be neglected in industrial applications, but they can play a relevant role in case of high-precision water jet machining. The aim of the research presented in this paper is to develop an innovative system able to modify the orifice flow field by means of a simple modification of the standard cutting head geometry; the system allows the controlled injection of air inside the primary orifice to prevent the jet instabilities and to adapt the level of jet coherence to the specific machining operation. The fluid dynamics aspects of the outflow process are investigated by means of a 3D numerical simulation with the Ansys Fluent CFD solver, while considerable experimental efforts are provided in order to validate the numerical model and finally evaluate the system performances on real case studies

Influence of machining parameters on part geometrical error in abrasive waterjet offset-mode turning

Geometrical error in abrasive waterjet turned parts is an important challenge toward the commercialization of abrasive waterjet turning process. A systematic study has not been done yet to investigate the effects of process parameters on geometrical error in abrasive waterjet offset-mode turning. In this article, a comprehensive study has been performed to investigate the influence of several machining parameters on the geometrical error (part diameter percent error) in turning AA2011-T4 aluminum alloy round bars. Water pressure, cutting head traverse speed, workpiece rotational speed, abrasive mass flow rate and depth of cut were considered as the main machining parameters in a five-level statistical experimental design. Based on central composite rotatable design, a total of 52 experiments were carried out. The main effects of the parameters and interactions among them were analyzed based on the analysis of variance technique, and the response contours for the part geometrical error were obtained using a quadratic regression model (i.e. response surface methodology). The model predictions were found to be in good agreement with experimental data. Furthermore, among the significant parameters, water pressure, depth of cut and traverse speed are the most influential parameters, with percent contribution of almost 25% each. Abrasive mass flow rate is the least influential parameter with a percent contribution of 4%

Improvement of surface flatness in high precision milling

The use of high precision micro components has increased in various industrial fields in recent years. Repeatable techniques are needed to face very tight tolerances and make micro fabrication processes industrially feasible against current micro machining limitation. Improving surface flatness in high precision milling is the main target of the present research. Critical issues such as machining strategy, spindle thermal transient management and tool wear compensation were considered for machining operations on a representative part

Sintering behaviour of 3D-printed 18K 5N gold alloy by binder jetting: a preliminary study

Binder jetting is a versatile additive manufacturing technique suitable to produce alloys that are difficult to obtain by powder bed fusion techniques, such as precious metals, due to their high reflectivity and thermal conductivity. In this study, a 18K 5N gold alloy powder was employed in the printing process. Different heat treatments and densification processes were employed to achieve final-stage sintering and remove residual porosity, whilst controlling the evolution of copper oxides by reduction with hydrogen and graphite. Powder, green and sintered samples were characterised at the microstructural level by X-ray diffraction, microscopy and energy dispersive X-ray spectroscopy to assess phase transitions and secondary-phase formation. Oxide-free components with a final relative density above 90% were achieved by densification at 830 °C combined with carbon- and CO-induced reduction of tenorite and cuprite. The optimal manufacturing route was chosen to produce a bezel, as a case study for the adoption of this technique in the jewellery industry

Applicability of abrasive waterjet cutting to irradiated graphite decommissioning

Characterization, dismantling and pre-disposal management of irradiated graphite (i-graphite) have an important role in safe decommissioning of several nuclear facilities which used this material as moderator and reflector. In addition to common radiation protection issues, easily volatizing long-lived radionuclides and stored Wigner energy could be released during imprudent retrieval and processing of i-graphite. With this regard, among all cutting technologies, abrasive waterjet (AWJ) can successfully achieve all of the thermo-mechanical and radiation protection objectives. In this work, factorial experiments were designed and systematically conducted to characterize the AWJ processing parameters and the machining capability. Moreover, the limitation of dust production and secondary waste generation has been addressed since they are important aspects for radiation protection and radioactive waste management. The promising results obtained on non-irradiated nuclear graphite blocks demonstrate the applicability of AWJ as a valid technology for optimizing the retrieval, storage, and disposal of such radioactive waste. These activities would benefit from the points of view of safety, management, and costs

Geometrical quality improvement of high aspect ratio micromilled pins

Mechanical micromachining is a reference process for producing 3D complex microparts and specifically tools for other processes as molds for micro injection molding and males for microextrus ion. High aspect ratio features as bars , ribs , pins , etc. are very common in these cases and their quality strongly affects the final plastic part quality. This paper focuses on high aspect ratio steel pins, since they are one of the most challenging features to be manufactured on microextrusion males. The pin geometrical quality has been defined according to the standards and a suitable measurement procedure has been set up with the aim to study the micromilling process parameters effects on the most representative pin quality characteristics . The statistical analysis results point out some criteria for selecting the best process parameters

Preserved decision making ability in early multiple sclerosis

Background : The purpose of this study was to assess decision making in patients with multiple sclerosis (MS) at the earliest clinically detectable time point of the disease. Methods : Patients with definite MS (n = 109) or with clinically isolated syndrome (CIS, n = 56), a disease duration of 3 months to 5 years, and no or only minor neurological impairment (Expanded Disability Status Scale [EDSS] score 0-2.5) were compared to 50 healthy controls using the Iowa Gambling Task (IGT). Results : The performance of definite MS, CIS patients, and controls was comparable for the two main outcomes of the IGT (learning index: p = 0.7; total score: p = 0.6). The IGT learning index was influenced by the educational level and the co-occurrence of minor depression. CIS and MS patients developing a relapse during an observation period of 15 months dated from IGT testing demonstrated a lower learning index in the IGT than patients who had no exacerbation (p = 0.02). When controlling for age, gender and education, the difference between relapsing and non-relapsing patients was at the limit of significance (p = 0.06). Conclusion : Decision making in a task mimicking real life decisions is generally preserved in early MS patients as compared to controls. A possible consequence of MS relapsing activity in the impairment of decision making ability is also suspected in the early phase of M

Applicability of an orthogonal cutting slip-line field model for the microscale

Mechanical micromachining is a very flexible and widely exploited process, but its knowledge should still be improved since several incompletely explained phenomena affect the microscale chip removal. Several models have been developed to describe the machining process, but only some of them consider a rounded edge tool, which is a typical condition in micromachining. Among these models, the Waldorf’s slip-line field model for the macroscale allows to separately evaluate shearing and ploughing force components in orthogonal cutting conditions; therefore, it is suitable to predict cutting forces when a large ploughing action occurs, as in micromachining. This study aims at demonstrating how this model is suitable also for micromachining conditions. To achieve this goal, a clear and repeatable procedure has been developed for objectively validating its force prediction performance at low uncut chip thickness (less than 50 mm) and relatively higher cutting edge radius. The proposed procedure makes the model generally applicable after a suitable and nonextensive calibration campaign. This article shows how calibration experiments can be selected among the available cutting trial database based on the model force prediction capability. Final validation experiments have been used to show how the model is robust to a cutting speed variation even if the cutting speed is not among the model quantities. A suitable set-up, especially designed for microturning conditions, has been used to measure forces and chip thickness. Tests have been performed on 6082-T6 Aluminum alloy with different cutting speeds and different ratios between uncut chip thickness and cutting edge radius