Petr Hlaváček

Sandstone Turning by Abrasive Waterjet

The machining of materials with specific mechanical properties causes problems in terms of the required quality, economic efficiency, and overall effectiveness of the process. A number of works have been published which indicate that the subjects of interest are still important (Krolczyk et al. 2013). The machining of the aforementioned materials based on conventional methods does not always meet the requirements of eco-friendly technology nor the efficiency potential of the technological device and tool (Vasilko and Strojný 1967; Krolczyk et al. 2014). The abrasive waterjet (AWJ) represents a suitable technological method that has specific benefits resulting from the nature of the tool. Many scientific reports have been written about using the water jet and the AWJ for cutting (Summers 1972; Ciccu and Grosso 2014), drilling (Teale 1965), turning (Sitek 2009; Sitek 2005, 2011), and for the purposes of underground mining (Summers 1992; Sharma et al. 2011). The AWJ can be used for the creation of rotating symmetric parts from rocks by turning. The production of parts using standard methods is very complicated and even impossible for some rock materials due to their properties (Summers 1972; Agus et al. 1993; Aydin et al. 2013). The use of the AWJ is an option for how to eliminate problems related to the standard method of turning (Sitek et al. 2005). The first results were published by Dr. Hashish (1987) 28 years ago. Ansari and his colleagues (1992) undertook relatively extensive research into turning visualizations using a high-speed camera. Hlavac and Palicka (2006) applied this method for the turning of many materials used in industry. Axinte et al. (2009) applied this method for the turning of grinding wheels. Interesting results were obtained in glass turning (Zhong and Han 2002), alumina ceramic turning (Liu et al. 2014), and the turning of hard-strength materials (Sitek 2009). The application of this turning method enables the machine rotating of semifinished products of varying structures and shapes (Henning 1999).

Surface integrity of Mg-based nanocomposite produced by Abrasive Water Jet Machining (AWJM)

ABSTRACT This paper investigates the influence of jet traverse speed on the surface integrity of 0.66 wt% Al2O3 nanoparticle reinforced metal matrix composite (MMC) generated by Abrasive Water Jet Machining (AWJM). Surface morphology, surface topography, and surface roughness (SR) of the AWJ surface were analyzed. The machined surfaces of the nanocomposites were examined by laser confocal microscope and field emission scanning electron microscope (FESEM). Microhardness and elasticity modulus measurement by nanoindentation testing were also performed across thickness of the samples to see depth of the zone, affected by AWJ cutting. The result reveals that extent of grooving by abrasive particle and irregularity in AWJ machined surface increases as the traverse speed increased. Similarly, the rise in value of surface roughness parameters with traverse speed was also seen. In addition, nanoindentation testing represents the lower hardness and elastic modulus due to softening occurs in AWJ surface.

Influence of Abrasive Water Jet Turning Parameters on Variation of Diameter of Hybrid Metal Matrix Composite

Abrasive water jet turning is one of the recently developed manufacturing technologies. It has gained its importance due to its capability to machine difficult-to-cut material with advantages such as absence of thermal effects, high machining flexibility and little cutting force. In this study, the influence of water jet turning parameters such as abrasive type and abrasive mass flow rate has been analysed on the variation of diameter with the target diameter of metal matrix composite. Composite material A359/Al2O3/B4C fabricated by electromagnetic stir casting process was used in the experiment. To select the level of parameter, one-variable-at-a-time analysis was used. The results revealed that the abrasive type had a greater influence on the deviation of diameter from the target diameter as compared to mass flow rate.

TURNING OF MATERIALS WITH HIGH-SPEED ABRASIVE WATER JET

In addition to already standard cutting of materials by a high-speed abrasive water jet (2D machining), the technology of turning by the high-speed abrasive water jet can be applied for the production of spatial rotation-symmetrical bodies. Turning by the water jet is similar to the conventional singlepoint turning by a mechanical tool on a lathe, since a workpiece rotates and a cutting tool is continually moved parallel to the workpiece axis and incrementally fed toward the axis of the workpiece. Contrary to the classical turning, the water jet can be moved in all directions with much larger lateral increments. Jet forces on the workpiece are negligible. The material removed from the workpiece is converted to very fine debris, as opposed to the chips formed by conventional turning [Hashish 1995]. All advantages of standard cutting by the abrasive water jet can also be applied to the turning with the jet: possibility to machine even difficult-to-machine materials, almost zero thermal effects on the cutting surface of the workpiece, possibility to carry out various operations with the same tool during one clamping of the workpiece, one technological manufacturing method used for various shapes of the workpiece and various materials, etc. (see Fig. 1).

Effect of Water Pressure During Abrasive Waterjet Machining of Mg-Based Nanocomposite

The pressure of the waterjet influences the overall performance of the abrasive waterjet cutting system through operational and phenomenological effects. In this study, the effect of water pressure in surface quality of Mg-based nanocomposite was investigated. The as-machined surfaces were examined by field emission scanning electron microscope to determine the surface morphology. The surface topography of selected nanocomposite was examined and compared. The results show that the surface quality is better at higher pressure. However, at lower water pressure, there is too much interaction among the low-energy abrasive particles and this may cause insufficient material removal. Abrasive waterjet cutting seems to be promising tool for machining metal matrix composites in terms of no thermal damages, no micro-structural changes and negligible sub-surface damages on the machined surface.

Laboratory Experiments on Effects of Water Jet on Heat-Affected Concretes

The paper is dealing with the effects of flat high-speed water jet on concretes affected by high temperature. Research should help to correct use of water jet technology in repair works on concrete structures especially after wildfires in tunnels, underground garages, etc., which are exposed to enormous thermal stress.

Erosion Test with High-speed Water Jet Applied on Surface of Concrete Treated with Solution of Modified Lithium Silicates

The paper focuses on the erosion resistance test based on surface treatment by a high-speed water jet applied on concrete. A reference concrete sample and concrete samples with three types of solution of modified lithium silicates applied on the concrete surface were tested under various erosion conditions. Two different jet impact angles (45° and 90°) were investigated. A significant difference in the erosion rate in the surface layers was observed comparing the untreated concrete and the concrete treated by various solutions of modified lithium silicates, but only in the initial phase of erosion.

Microstructure, Properties and Damage Mechanisms by Water Jet Cutting of TiB2-Ti Cermets Prepared by SPS

Process parameters of abrasive water jet (AWJ) machining of TiB2+Ti ceramic matrix composites with 10%, 15% and 20% of Ti reinforcement were investigated. The article focuses on microstructure damage processes and kerf geometry in AWJ machining of TiB2+Ti composites. Two different abrasive water jet cutting speeds and three sorts of composite materials, together with a reference monolithic one, are considered. Microstructure in machined samples was observed using scanning electron microscope. The characteristics of the cuts such as kerf top width, kerf angle and surface roughness were studied. The influence of cutting speed on abrasive process in composites with various amounts of Ti was investigated. It was found that roughness decreases and kerf taper ratio increases with increase in amount of Ti.