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About this book

This book reports on recent advances in the rapidly growing field of high-speed water jet technology, discussing research, developments and applications related to cutting, machining, repair of structures and buildings, cleaning, removal of coatings and layers, mining, and abrasive materials. It also explores special applications of high-pressure techniques, as well as important environmental aspects and solutions for technology transfer. Thanks to the balance of theory and practical findings, the book offers a timely snapshot for researchers and industrial communities alike, and a platform to facilitate communication and collaboration between the two groups.

Table of Contents

Frontmatter

Keynote Lectures

Frontmatter

Effect of Particle Fragmentation on Cutting Performance in Abrasive Waterjets

Abstract
Abrasive waterjets have become a standard tool for machining a wide variety of materials. Today’s applications of abrasive waterjet cutting can be found in many different industries that range from producing very small high precision parts to making rough separation cuts of thick steel plates. Advancements in understanding of the physics of the abrasive waterjet cutting process continues to further advance the state of the art in predictive modeling and motion control software of the abrasive waterjet cutting process. Considerable research has been devoted towards studying how the various abrasive waterjet process parameters affect one another and their influence on the final cutting results. While several approaches have evaluated the effect of hydraulic energy from the water jet itself, in this paper the focus is laid on the effect of the particles that are interacting with the material. In this paper the kinetic behavior and fragmentation of particles has been analyzed in a wide range of different conditions. New insights into fragmentation of the particles especially at higher pressures can explain the behavior of experimental cutting studies where higher pressures did not provide a significant improvement and in many cases a decrease of cutting performance. Studies like this will not only help us understand the very processes that are involved in the cutting operation but also help us to optimize the overall process to increase performance and reliability and also be competitive against other cutting methods while providing ample new applications in the future.
Axel Henning, Michael Lo, Ernst Schubert, Peter Miles

Measurement of the Effective Waterjet Diameter by Means of Force Signals

Abstract
The application of both pure and abrasive waterjets is well established in manufacturing and related processes like surface preparation. Particle free surface processing in order to avoid any particle residuals on the machined workpiece surfaces was addressed as core requirement by quality engineers who had to fight against induced failure of functionalized surfaces after surface preparation by e.g. sand blasting.
Due to the need of multi-path processing for generating surfaces it is necessary to monitor the effective geometry of the impact zone of the waterjet and the related impact forces. By getting these data it becomes possible to calculate the necessary grade of overlapping of the neighbouring traces. This becomes more ambitious by permanently changing waterjet shapes caused by very little and not preventable changes of the micro structure inside the used nozzle. A nozzle change mostly induces a change of the jet shape and related geometry of the impact zone on the hit surface.
In this paper an apparatus and method for waterjet shape measurement are presented. By using this method it is possible to generate necessary information on nozzle wear related jet shape changes or new jet shapes after nozzle change which enables the operator to recalibrate the process parameters. The effect of machining velocity on waterjet characteristics is studied. Also the capability of sorting of not acceptable nozzles becomes possible and can avoid damage of surfaces to be processed.
Mikhail Kliuev, Frank Pude, Josef Stirnimann, Konrad Wegener

Effect of Ventilation to Abrasive Suspension Jet Under Submerged Condition

Abstract
High-speed water jet shows a peculiar processing property in cutting submerged objects, but its processing ability decreases quickly with the standoff distance under submerged conditions. For improving the performance of submerged cutting by abrasive suspension jet (ASJ) a ventilation nozzle system has been developed but the flow structure of ventilated jet is still unclear. Focused on the effect of ventilation, high-speed camera observations of air ventilated submerged water jets are conducted in this work and the structure of air ventilated ASJ is identified by similarity analysis. Experiments show that air-coated suspension jet may be generated by increasing the ventilation flowrate to a certain extent so that ventilation air spreads out of the sheath in the form of large cavity covering the jet. The air-coated jet pulsates periodically and the dominant frequency of air-layer pulsation decreases with increasing of the ventilation flowrate. The Strouhal number of jet pulsation is dependent upon an altered cavitation number. The performance of air-ventilated ASJ is then examined by cutting tests with specimens of aluminum alloy under different ventilation conditions. The result demonstrates that the kerf depth of air-ventilated ASJ in submerged condition reaches to almost the same level of ASJ cutting in air. The cutting ability of ASJ in submerged condition is effectively enhanced by air ventilation.
Guoyi Peng, Yukiteru Tamura, Yasuyuki Oguma, Jiri Klich

Regular Papers

Frontmatter

Systematic Change of Abrasive Size Distribution

Abstract
The continuous suspension (ConSus) technology is a new coming approach that promises performance advantages over industrially used abrasive waterjet (AWJ) systems in production scenarios. However, it currently lacks practical experience and process parametrization is typically still empirical of either using a 2-phase abrasive suspension jet (ASJ) or a 3-phase injection AWJ tool. A practical comparison of respective AWJ tool characteristics of prior work piece contact is needed for fundamental parametrization.
An experimental approach was used to compare the respective AWJ systems. The abrasive material was compared before and after going through either an injection AWJ head or a ConSus ASJ system. Typical abrasive materials and mesh sizes for AWJ machining were systematically investigated. This paper shows that current AWJ cutting systems yield different results when using equal abrasive material. ConSus shows almost no significant effect on abrasive size distribution while commonly used injector systems shifts a tremendous portion of the original abrasive to smaller grain sizes. Therefore, the results enhance process understanding and revision of existing process models for future applications.
Thomas Bergs, Manuel Schüler, Tim Herrig, Jan Fernolendt, Marco Linde

Effect of Abrasive Water Jet Machining on the Geometry of Shapes in Selected Tool Steels

Abstract
The presented article is focused on the abrasive water jet machining of tool steel material. Selected tool steels Uddeholm Dievar and Böhler K110 were machined and final pockets were evaluated based on the side angle of the pocket. Sequentially were created pockets with increasing depth from 1 to 5 mm for both materials. Evaluation of pocket angle is crucial factor for determination of machining allowance for finishing cuts. Also metallography analysis for both materials was created for observation of removal process and for detection of cracks produced during abrasive water jet machining. In terms of corrosion of presented tool steels can be stated that due to higher number of alloying elements is corrosion on machined surface acceptable for further processing of created shapes. Obtained results can extend application possibilities of AWJ milling for rough machining of tool steels, especially for thin-walled components with reduction of induced residual stresses and deformations of shapes.
František Botko, Petr Hlaváček, Dominika Lehocká, Vladimír Foldyna, Michal Hatala, Vladimir Simkulet

Erosion of Titanium and Aluminium Alloys Using Pulsating Water Jet: Effect of Standoff Distance

Abstract
The disintegration of the material by PWJ technology depends upon many technological parameters of the equipment and particular material properties. This paper deals with the erosive effects of PWJ on the polished surfaces of metallic materials such as titanium (Ti6Al4V) and aluminium (ENAW1050AH24) alloy. The evaluation and comparison of the extent of disintegration are done on the basis of the erosion depth achieved. The nozzle movement over the material followed an ascending equidistant trajectory from z = 15 to 41 mm with a vertical step height of 2 mm. PWJ transitions over the material were performed with a sonotrode frequency f = 20.19 kHz, liquid pressure p = 40 MPa and a feed rate v = 0.25 mm.s−1. The depth value of the grooves formed was then measured using a MicroProf FRT contactless measuring device and evaluated in the SPIP 6.7.8 software. For aluminium sample, the deepest average depth value is h = 1583.2 µm (z = 29 mm), while the titanium material has eroded to a much smaller depth, h = 283.2 µm (z = 31 mm). By comparing the achieved hydrodynamic effects of PWJ on titanium and aluminium, significant differences in the depth of erosion and its course can be observed due to the different mechanical properties of the materials.
Dominik Čuha, Akash Nag, Alice Chlupová, Sergej Hloch

Water Jet as a Promising Tool to Disperse Carbon Nanotubes in Water Solution

Abstract
This paper is focused on obtaining a homogenous dispersion of carbon nanotubes in water solution treated by the pulsating and continuous water jet technology. Our experimental setup consists of Kärcher HD 6/18 plus pump, ABB robot IRB 6640, pulsating jet generator and Hammelmann nozzle with a diameter d = 0.3 mm. Carbon nanotubes were in the concentration of 0.375 wt%. Three types of samples were prepared. Carbon nanotubes were mixed with no surfactant, half concentration of surfactant and with a standard concentration of surfactant, which was optimized in previous experiments (1.5 wt%). Based on our previous experimental results, we used a naphthalene based superplasticizer. A spectrum of pressures of 1 MPa, 5 MPa, 10 MPa and 15 MPa was used to induce both cavitation and non-cavitation phenomena. Samples were kept in idle state to investigate if they were subject to re-agglomeration. Consequently, all Carbon nanotubes solutions were measured on the Malvern nanosizer.
Vladimir Foldyna, Josef Foldyna, Michal Zelenak

Influence of Concrete Age on Resistance to Fast-Flowing Liquids

Abstract
It is generally known that the properties of concrete, particularly the strength, vary depending on the concrete age due to the chemical-mechanical processes occurring in the structure of concrete during ageing (maturing). The issue often is the time needed for concrete to reach its desired safety before a concrete structure made of fresh concrete can be partially or completely loaded. In structures coming into contact with flowing liquids, the resistance of surface layers to erosion caused by abrasion or cavitation is also important, in addition to the strength. Therefore the analysis of effects of the concrete age from 7 days to 1 year on the concrete resistance to fast-flowing liquids is the subject of this paper. A method of accelerated hydraulic-mechanical simulation of the surface layer loading by means of a pure high-speed water jet and a water jet with abrasive particles was used in order to investigate the concrete erosion resistance. The influence of the concrete age on the resistance to fast-flowing liquids has been proven. After a year, the concrete resistance increased by about 36% in the case of the pure water jet, and 28% in the case of the abrasive water jet.
Petr Hlaváček, Libor Sitek, Lenka Bodnárová, Rudolf Hela, Kamil Souček, Vendula Zajícová, Vladimír Foldyna

Optimal Abrasive Mass Flow Rate for Rock Erosion in AWJ Machining

Abstract
Erosion process of the Abrasive Water Jet (AWJ) machining on a rock material depends on various parameters. A brittle rock material is removed predominantly by the deformation wear. Abrasive grains can enhance the machining since their hardness and therefore material removal is better than work of pure water. However, to this day, determination of an optimal dosage of the abrasive matter entering into the mixing chamber was rather neglected. Based on the laws of conservations of momentum and energy combined with some empirical facts, it is possible to derive an equation for erosion of the material and subsequently another relation that provides estimation of the optimal mass flow rate of an abrasive matter. The main equation for erosion consists of six experimental coefficients, for an intensive AWJ only four, describing the effectivity of the water jet kw and abrasive jet ka impacting the material. It seems that the energy that is used for erosion is very small and the ideal dosage of the abrasive material is approximately a ≈ w·(1 − 2kw/ka), where a and w are the abrasive and water mass flow rates. Such an equation could be used for setting of AWJ machines. The economical optimum (eo) for cutting is proposed via the relation eo = E/Emax − R/Rmax, with the erosion E and its maximum value and the resistivity R and its maximum value.
Petr Jandačka, Jiří Ščučka, Petr Martinec, Miloslav Lupták, Ivan Janeček, S. M. Mahdi Niktabar, Michal Zeleňák, Petr Hlaváček

Submerged Abrasive Water Jet Piercing/Drilling: Preliminary Tests

Abstract
In the technological process of cutting by means of an abrasive water jet, the so-called piercing is often used when starting the operation of cutting. As the piercing is a time-important part of the process, it is advantageous to reduce the time by using different piercing strategies. This article discusses a nozzle circling method that reduces the time required for piercing. The tested circling diameters varied from 0 to 1.55 mm. It was found that the time required for piercing decreased to one sixth with the biggest circling diameter. Another issue discussed in this article is the piercing in submerged water. This method is mainly used to ensure comfort and safety of operators using the water jet. The advantage is the reduction of dust, noise and jet reflection. However, the jet efficiency decreases. An experiment was carried out at five standoff distance settings. The experiment has shown that the resulting times differed only minimally from the piercing in air. Using a digital microscope and subsequent image analysis, the jet behavior as it passed through the material was examined and recommendations for using the nozzle circling method were designed.
Jiri Klich, Dagmar Klichova, Guoyi Peng

Evaluation of Surface Topography Created by Abrasive Suspension Jet Under Submerged Condition

Abstract
The paper deals with the technology of abrasive suspension jet (ASJ) with a ventilation nozzle system for cutting a metal material (aluminum alloy A5052) submerged under water. SN 214001 standard is used for the quality evaluation of a cut. The standard describes several shape parameters according to which cuts can be compared under different technological conditions. One of the monitored parameters is the air ventilation, i.e. the jet is coated in an air coating. This changes the efficiency and shape of the water jet, and thereafter the shape of the resulting cut. The shapes were scanned using a digital microscope and further analyzed. Furthermore, the article deals with the measurement of the surface roughness according to the ISO 4287 standard in relation to the amount of ventilation air. Roughness values were obtained using an optical profilometer.
Dagmar Klichová, Jiří Klich, Guoyi Peng

Creating a Database for Turned Surfaces

Abstract
This article deals with the evaluation of surface topography created by Abrasive Water Jet (AWJ) technology. The effects of machining parameters on the turned surface was analyzed by roughness parameters. Further attention is paid to the influence of technological factors on the surface quality created by abrasive water jet turning processes. Based on an input and output system, a database design was created providing the evaluation of the surface quality. Various materials were used for the database which should serve to optimize the abrasive water jet turning processes in order to increase the technological efficiency and contribute to its automation.
Dagmar Klichová, Jiří Klich, Dominika Lehocká, Petr Hlaváček, Libor Sitek, Vladimír Foldyna

The Use of High-Pressure Water Assistance in the Rock Mining Process Using Cutting Tools

Abstract
The article presents the possibilities of using high-pressure water assistance in the rock mining process using cutting tools. Currently applied methods are based on the external spraying, in the form of water or air-water curtains, sprinkling whole mining head or internal, the so-called sectoral spraying, sprinkling of individual cutting tools, being in contact with the rock. The advantages and disadvantages of the described methods were presented. An innovative solution for the holder of tangential-rotary picks was proposed, in which high-pressure lubrication with water or emulsion was used. The results obtained during laboratory, field and industrial tests were described.
Krzysztof Kotwica

Effect of the Ultrasonically Enhanced Water Jet on Copper Surface Topography at a Low Traverse Speed

Abstract
The article describes the maximum erosion efficiency of an acoustically enhanced pulsating water jet on CW004A copper surface. The copper surface was disintegrated at a traverse speed v = 0.1 mm.s−1, water pressure of 39 MPa and circular nozzle diameter of 1.321 mm. The effect of the PWJ on the copper surface was evaluated based on a surface topography evaluation using an optical profilometry and a scanning electron microscopy analysis. In the experimental investigation, it was found that a low traverse speed rate has destructive effects on the material with significant weight and volume loss of the material. Surface topography was characterized by a formation of protrusions, depressions and craters. Subsurface material failure of up to 200 µm was detected.
Dominika Lehocká, Jiří Klich, Vladimír Simkulet, František Botko, Karol Kovaľ, Ján Kepič, Zuzana Mitaľová, Michal Hatala

Particle Velocity in Abrasive Waterjets

Abstract
Abrasive particle velocity plays a key role in material removal in abrasive waterjet (AWJ) machining. Understanding how certain operating conditions effect the speed of abrasive particles is important for the improvement of the AWJ process. Without a method of measuring abrasive speed, it is difficult to evaluate the cutting performance of an AWJ using theoretical particle velocity modeling. To measure the velocity of single abrasive particles at a variety of different conditions, a magnetic particle sensor system was designed. In order to increase the accuracy and versatility of the sensors, it was constructed with the ability to capture a large amount of velocity data which allows for outlying data to be filtered and the velocity distribution to be analyzed. The results were used to examine how the velocity data can be used to improve the theoretical particle speed models, the influences of varied operating conditions on velocity spread, and the correlation between kinetic cutting power and material erosion.
Michael Lo, Axel Henning, Kevin Hay, Peter Miles

Multi-criteria Optimization of the Abrasive Waterjet Cutting Process for the High-Strength and Wear-Resistant Steel Hardox®500

Abstract
This paper presents the results of the Abrasive Water Jet (AWJ) cutting process optimization for Hardox® steel. This type of steel makes it possible to reduce the weight of a work piece and increases the service life of steel elements in comparison with common steel applications. The special combination of features, such as hardness, strength, and toughness, allows using elements with smaller cross-sections. The effect of different pressure levels, traverse speeds and abrasive flow rates, on cutting depth, kerf width and roughness on the cut surface of the Hardox® 500 steel was experimentally tested. In order to determine the most beneficial control parameters of the cutting process, multi-criteria optimization by means of the Gray Relation Analysis (GRA) combined with the Taguchi approach was carried out.
Andrzej Perec, Wojciech Musial, Jaroslaw Prazmo, Ryszard Sobczak, Aleksandra Radomska-Zalas, Anna Fajdek-Bieda, Slawomir Nagnajewicz, Frank Pude

Some Investigations into 1,000 MPa Pure Waterjet Cutting

Abstract
This paper documents the application of the maximum available pressure for cutting operations using a special pump. This increase of the water pressure, and its conversion to an ultra-high-speed waterjet results in deeper and/or faster cutting. Theoretical aspects of using these ultra-high-speed waterjets are presented. The behavior of this waterjet when it hits the target material is shown. The thermal properties of the waterjet were analyzed. Research into the influence of selected pressure levels on the quality of the cutting edge of processed carbon fiber composite, and into the wear on the water nozzle subjected to ultra-high pressure (UHP) is presented.
Andrzej Perec, Franz Trieb, Frank Pude

Effect of Standoff Distance on the Erosion of Various Materials

Abstract
The paper describes the interaction between pulsating water jet and surface of three different metals: 316L stainless steel, 6068 Al alloy and Ti6Al4V Ti alloy. The pulsating water jet is formed by using the ultrasonic sonotrode to the pressurized acoustic water chamber. It appears that the shape of the resulting water jet differs at various distances from the nozzle and the state of the surface of tested materials treated by the jet at various standoff distances differs very substantially. Moreover, the three materials are exposed to pulsating water jet at different standoff distances and results are discussed in terms of the capacity to absorb plastic deformation. As expected, at optimal standoff distance, the deepest eroded path appears in the Al alloy and the most resistant material is the Ti alloy.
Jakub Poloprudský, Alice Chlupová, Tomáš Kruml, Sergej Hloch, Petr Hlaváček, Josef Foldyna

Development of an Assistance and Control System for Waterjet Cutting of Free-Form Workpieces

Abstract
The process accuracy when cutting free-form parts using waterjet technology depends on several factors, including various preparatory tasks, such as defining the workpiece coordinate system. Some manual procedures for determining it are already used. Those methods are based on the usage of laser pointers or dial gauges, which are fixed on the machine head. As a computer-aided alternative, measuring probes can be used to define the zero point offset of a workpiece, or to compare its dimensions to the ones predefined in the CAD data. When processing flat parts, optical systems can be used for layout alignment on the blank material. In order to redefine how the workpiece coordinate system is measured on a waterjet cutting machine, a new assistance and control system is being developed. It features an optical system that scans marked clamping and positioning devices whose relative positions to the machined part are precisely defined. By returning data about their location to the control unit, the workpiece coordinate system can be calculated. This paper describes the steps necessary for developing such a system, as well as the design and work principle of a fixturing system that supports the clamping and positioning of such free-form workpieces.
Nermin Redžić, Felix Pfeiffer, Marco Witt, Philipp Klimant

Pulsating Abrasive Water Jet Cutting Using a Standard Abrasive Injection Cutting Head – Preliminary Tests

Abstract
The paper focuses on research into disintegration effects of a pulsating abrasive water jet using a standard abrasive injection cutting head. Forced pulses of a frequency of 20 kHz were generated by a piezoelectric pulse generator using a sonotrode placed in a high pressure system in front of a water jet nozzle. Several variants of the water jet generation in the cutting head were investigated - a continuous and pulsating water jets without the presence of the focusing tube to verify the pulse formation in the mixing chamber. Consequently, an abrasive water jet and a pulsating abrasive water jet with an installed focusing tube were studied. At a selected water pressure of 70 MPa, an increase in cutting effects of the pulsating abrasive water jet on average by 15–20% compared to the continuous abrasive water jet of the same parameters was observed. The authors consider that the increase in efficiency is mainly caused by better distribution of abrasives over the focusing tube cross-section, largely due to separated slugs of water forming the pulsating water jet. In this regard, the authors see the potential of further increase in the efficiency of abrasive water jets. Modeling and simulation of the water flow using an appropriate computational system can contribute to achieving an optimal configuration of the pulsating abrasive water jet.
Libor Sitek, Petr Hlaváček, Josef Foldyna, Michael Jarchau, Vladimír Foldyna

Mechanical Strengthening of Anti-Corrosive Surface Layers by Water Jet

Abstract
A brief definition of progressive technologies is difficult to implement due to the widely different processes that fall into this category. There is a consensus in the literature that this group includes processes that use conventional forms of energy in a new way. One of such technologies includes strengthening of surface layers with a pulsating water jet, of which we do not yet have enough verified information. Mechanical strengthening of materials is widely used in the automotive and aerospace industries, as well as in the manufacturing of production machines and equipment. The beneficial effects of mechanical strengthening of surface layers, especially for dynamically stressed components, have been known for decades. Evidence of the beneficial effects of mechanical strengthening of surface layers in terms of increasing the service life of components processed in this way is already available. The aim of the present experimental tests is to use a pulsating water jet to solidify the surface layer of materials, specifically chromium-nickel steel, to determine suitable parameters so that the solidified surface has the required properties and is not damaged by the water jet. Evaluation of the experimental verifications was done by measuring microhardness and residual stresses in the surface layer.
Dana Stancekova, Sergej Hloch, Dominik Cuha, Michal Sajgalik

Remarks to Abrasive Waterjet (AWJ) Forces Measurements

Abstract
Measurement of forces during cutting process has a potential to be a method applicable for online monitoring of the AWJ cutting process. Force signal can help with understanding the interaction between jet and material, namely with determination of the cutting to wear mode ratio. The force measurements also detect some undesired effects, such as not fully penetrated material and/or other product distortions. Therefore, such measurements could be efficient tool in the online process monitoring and/or control, when appropriate device for industrial applicability is constructed. Some weak points are discussed in the contribution as well.
Adam Štefek, Libor M. Hlaváč, Martin Tyč, Pavel Barták, Jiří Kozelský

Evolution of Microstructure of Silicon Steel After Pulsating Water Jet Treatment

Abstract
The present study is focused on the evolution of microstructure of silicon steel (Fe-Si 6 wt%) after treatment by pulsating water jet (PWJ). The various stages of erosion by pulsating water jet have been studied. The initial damage shows formation of depressions and isolates erosion pits. Repeated passing of water initialized further pit formation and coalescence of pits to craters. During this stages small cracks formation was observed. The repeated passing of water induced deepening of the craters and material removal. The PWJ caused plastic deformation and increase of values of hardness of the subsurface region. The cleavage fracture was present on contained eroded surface.
Eva Švábenská, Alice Chlupová, Josef Foldyna, Oldřich Schneeweiss

Evaluation of Cut Quality on AlMg4.5Mn Material Using AWJ Containing Recycled Abrasives

Abstract
Recycling the abrasives used in Abrasive Water Jet cutting is a theme that touches multiple areas. First of all, it is the economic aspect (increasing the price of abrasives on world markets, its availability and ensuring timely supplies, as well as the environmental aspect of abrasives extraction and transport). For used abrasive material recycling the sorting lines are used, which consist of sorting and drying equipment. However, recycled material should achieve sufficient cutting efficiency when reused. To determine whether it achieves recycled abrasive material is sufficiently effective, an experiment was performed. The assessment was evaluated through selected roughness parameters Ra, Rq, Rz and Rt and Abbott-Firestone material fraction curve for AlMg4.5Mn aluminum alloy samples (EN AW 5083). The results of the experiment can contribute to the widespread use of recycled abrasive material.
Miroslava Ťavodová, Nataša Náprstková, Pavel Kraus, Ingrid Görögová

Monitoring of Abrasive Waterjet Cutting and Drilling

Abstract
In order to find a suitable way of on-line monitoring of the drilling and cutting process, the cutting head vibrations during drilling through various metal materials were measured with piezo-electric accelerometers attached around the cutting head. Three different types of experimental designs were carried on: drilling of different metals with the same thickness, operation with different abrasive mass flow rates without any workpiece and drilling of the same material with different types of abrasives. The most promising was the finding that inner dimension of the focusing tube is the most affecting parameter for cutting head vibrations. Continuous measurement of cutting head vibrations may therefore serve as an indicator of worn focusing tube. From the point of view of the on-line monitoring of drilling or cutting efficiency the sensors attached on the cutting head did not bring substantial benefit. No direct connection between dominant frequencies in vibration spectra and machined material was proved. The RMS of the vibration signal grows with the increasing mass flow rate and changes with different types of abrasives, but no significant direct relationship between abrasive characteristics and measured signal was discovered. Therefore, accelerometer placement on the workpiece appears to be much more promising from the point of view of drilling on-line monitoring.
Martin Tyč, Irena M. Hlaváčová, Jiří Kozelský

Effects of the Cutting Angle on the Kerf Formation During Near-Net-Shape Fabrication with the Abrasive Water Jet

Abstract
The abrasive water jet (AWJ) is a suitable tool to cut all kinds of materials, including difficult to machine materials, with constant and low tool wear. Thus, the process is a promising method to reduce the manufacturing costs for these materials. In order to expand the 2.5D cutting abilities of the AWJ to manufacture 3D parts, milling operations have been investigated. In this paper, an AWJ milling approach is investigated, applying only two kerfs along the parts’ boundaries, from different sides of the material. By intersecting the two kerfs, a solid piece of material can be removed from the part and thus, the approach enables a higher material removal rate (MRR) aggregated. The aim of this study is to expand the capabilities of this milling process by the angle of cut, orthogonal to the feed speed, to enable broader manufacturing range. For this purpose, the angle of cut was investigated along with other parameters, using design of experiments to obtain the effects and limitations of the milling operation. In order to understand cutting behavior in depth, further tests with single passes of the AWJ were conducted. The results reveal the capabilities of the milling operation for a broad range of the angle of cut. Furthermore, the application of the operation was demonstrated on a turbine blade’s fir tree connection.
Eckart Uhlmann, Constantin Männel

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