WATERJET CUTTING MACHINES HIGH SPEED WATER JETS DYNAMIC CHARACTERISTICS RESEARCH I.A.

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1 WATERJET CUTTING MACHINES HIGH SPEED WATER JETS DYNAMIC CHARACTERISTICS RESEARCH I.A. Znamenskaya, D.S. Naumov, D.A. Nersesyan, N.N. Sysoev, Y.N. Shirshov Lomonosov Moscow State University, , Moscow, Russia Introduction Abrasive waterjet material treatment technology is used in a huge number of industrial technological processes. Any known hard and amorphous materials like stone, metal, glass, ceramic, rubber, polyethylene and etc. can be processed with abrasive waterjet technics. High speed water and abrasive particles mixture acts as a working body in this technology. There are many advantages of this technology comparing to other cutout technologies for example delicate material processing without thermal shock. A number of experimental and theoretical works in the last years were aimed to study abrasive waterjet processing as well as flows in different parts of the machine: jet forming orifice, which creates high pressure jet, focusing accelerating tube where abrasive particles receive jet impulse. These works give new information about multiphase flows under extreme conditions and device engineering design optimization [1, 2]. At the same time jet initiation process, being important in material erosion process analysis, is not well studied. Shock wave configurations were visualized at the supersonic fuel jet initiation process [3]. In the present paper jet initiation process was recorded with the high speed camera and shadow method was realized in order to study dynamic jet characteristics which outflows from focusing tube of waterjet cutting machine. Experimental setup description Industrial waterjet cutting machine model Flow WaterJet Mach3 was used to generate high speed jet. Machine is able to produce a high speed water flow which comes through the 0.35 diameter orifice under the 100 MPa or 400 MPa pressure and has speed about three times more than the sound speed in air [4, 5]. This flow passes abrasive mixing chamber and 74 length focusing tube with 1.05 channel and spreads into air under normal conditions ( Fig. 1). Jet center zone diameter is about 1 [6]. The jet outflow from focusing tube process under the pressure of 400 MPa and without abrasive is studied. Fig. 1 Waterjet cutting head. High pressed liquid inputs from the pump, it travels through the abrasive mixing chamber, then travels through the focusing tube, and outflow to the air as mixture of water and abrasive particles, which is working body in abrasive waterjet technology of material cutting. 1 jet formation orifice, 2 abrasive input channel, 3 nozzle (focusing tube). I.A. Znamenskaya, D.S. Naumov, D.A. Nersesyan, N.N. Sysoev, Y.N. Shirshov,

2 Fig. 2. Experiment scheme. 1 Flow WaterJet Mach3 machine, 2 water jet; 3 high speed camera Photron FASTCAM SA5, 4 probe lamp, 5 PC 1 for camera control, 6 PC 2 for cutting machine control. High speed optical camera model Photron FASTCAM SA5 which is able to record video up to 2 seconds with 1M fps was used with objective Nikon AF NIKKOR to capture video of jet forming process. Camera and jet synchronization was realized just by operator because 2 seconds of camera video memory is pretty enough and much more then time period needed for jet to get into stationary mode and there is no need in high accuracy synchronization system. Initiation process optical registration There were series of forming jet process first stage high speed video registration experiments. Setup scheme is shown in Fig. 2. Camera objective jet sample length was 44 cm. Pump pressure was 400 MPa. Shadow method realized with the probing lamp of 500 W with long filament oriented vertically. Fig. 3 Top and bottom areas in scale with jet. 2

3 Two video recording areas named as top area and bottom area are determined by distance from focusing tube end since camera video area at required resolutions is less then jet height which was 130 approximately (Fig. 3). Visible length in the top area was 22, at the bottom area was 36. Camera speed and resolution were /50000/30000 fps and / / pixels. Neutral optical filter was used in order to reduce luminous power. Focusing tube feed pipe was opened (see Fig. 1) which allowed air inflow in some experiments. The same time in a number of experiments inner cutting head volumes were blew off with compressed air. Results analysis Jet formation process video films were recorded. Whole jet initiation and formation process time was 1ms. There were 100 sequential images collected during 0.35 ms required jet to pass through the top area. Light scattering (Fig. 4) and probe lamp sounding light absorption (Figs. 5, 6) by jet tow-phase media is the main mechanism of visualization on photo images. Light dissipation zones are registered in central jet zone two phase shell which visualize high speed co-flow structures. Central jet zone speed is supersonic in a stationary mode [5]; but supersonic perturbation generated by co-flow streams was not registered. Fig. 4. Leader outflow and jet formation process visualization (light scattering), fps. Every tenth image of jet leader outflow from focusing tube is shown in Figs. 4 and 5. Jet configuration in top area varied in different experimental conditions. Jet leader vertical position was determined in pixels for each picture, position then was converted into with help of reference picture. Jet leader was visually determined by boundary point of non-transparent area in vertical line flow axis of syetry. Leader position determination accuracy was 1. 3

4 Fig. 5. Leader outflow and jet formation process visualization (light absorption), fps. Fig. 6. Jet development in a bottom area with fps video recording. 4

5 Jet leader coordinate depending on time graphs were achieved. Then jet leader speed depending on its coordinate also was obtained as well. Average velocity value and its evolution are determined for all experiments. Jet formation process in bottom area is shown in Fig. 6. Fig. 7 Jet leader coordinate to time dependence in the top area. Jet leader coordinate (x) depending on time for the top area is shown in Fig. 7. It was shown that speed changes from 50 m/s to 80 m/s during jet initiation process in the top area. Jet leader position depending on time for the bottom area is shown in Fig. 8. Velocity value depending on jet leader position in bottom area is shown in Fig.. We could see that jet leader was accelerating in interval from 60 to 77 and its speed gains 270 m/s close to bottom area lower border where cutting sample is located. Velocity value error is ±20 m/s. Fig. 8. Jet leader coordinate to time dependence in the bottom area. Zero time point corresponds to bottom area upper border with coordinate 48 (see Fig. 3). 5

6 Jet leader dynamics analysis and speed extrapolation are allow us to evaluate probable time required for jet leader to develop supersonic speed as ms after its start or at distance from the focusing tube end. Fig. 9. Jet leader speed versus coordinate dependence in the bottom area. Zero x coordinate corresponds to nozzle end coordinate 0 (see Fig. 3). Conclusions High speed imaging of supersonic water jet issuing from the nozzle and non-stationary process analysis was conducted. The aim of the research was to get new knowledge about the two-phase flow under extreme conditions, and to analyze possibility of jet device design optimization. The process of high-speed water jet outflow from the focusing tube of the hydroabrasive cutting machine, its development process and the stationary flow state overall time period about 1 second was considered. Shadow method was used to visualize an initial stage of water jet outflow from the focusing tube and jet head point movement dynamic for milliseconds period at pressure value 400 MPa. In order to study jet formation process high-speed camera with framing rate frames per second, resolution pixels and exposure time 1 s was used. Videodata and images were processed, high-speed water jet outflow spatial-temporal characteristics were measured as well as the stationary mode establishing process. Jet head part initiation, formation process, and its travel with acceleration dynamic characteristics were quantitative valued. It was found out that jet leader speed changes from 30 to 270 m/s. REFERENCES 1. Maniadaki K., Kestis T., Bilalis N., Antoniadis A. A finite element-based model for pure waterjet process Simulation // Int. J. Adv. Manuf. Technol Vol. 31. P Guha А., Barrona R.M., Balachandar R. An experimental and numerical study of water jet cleaning process// Journal of Materials Processing Technology Vol P Matthujak A., Pianthong K., Takayama K., Milton B.E. Experimental Study of Ignition over Impact-Driven Supersonic Liquid Fuel Jet // Advances in Mechanical Engineering. 02/2013; DOI: /2013/ Latypov R.R., Teregulov N.G., Harlov A.I. Some information about waterjet cutting materials. Ufa: Ufa State Aviation Technical University, Tikhomirov R.A., Babanin V.F., Petukhov E.N. et al. Waterjet cutting shipbuilding materials. Leningrad: Shipbuilding, p. 6. Shirshov Y., Nersessian D., Sysoev N., Ivanov I. Studies the process of forming a jet of water flowing from the nozzle installation waterjet cutting // Materials of the X International Conference on Nonequilibrium Processes in Nozzles and Jets (NPNJ 2014), May, 2014, Alushta. Vol. 1. Moscow: MAI Publ., P