FACTORS INFLUENCING HYDROEROSION SURFACE TOPOGRAPHY

Ján KMEC, Technical University of Košice, Faculty of Mechanical Engineering, Mäsiarska 74, 040 01 Košice, Slovakia, jan.kmec@tuke.sk
Ľuba BIČEJOVÁ, Technical University of Košice, Faculty of Manufacturing Technologies, Štúrova 31, 080 01 Prešov, Slovakia, luba.bicejova@tuke.sk

ABSTRACT: Waterjet cutting technology represents modern approach to the shape cutting and variety of materials separation providing cold cut without heat influence of material on cutting edge. The presented paper is aimed at analysis of complex factors defining cutting erosion surface.
KEYWORDS: Waterjet cutting technology, cold cut, hydroerosive technological factors

1. INTRODUCTION
A water jet technology is a rather complicated high pressure hydrodynamic process which can be described as a field of jet technologies. The process itself requires as effective and economical use of the water jet energy as possible. It is directly related to optimal determination of water jet production and technology parameters considering basic physical properties of liquid as a cutting medium and hydrodynamic laws.

The factors influencing the erosion surface both directly and indirectly can be expressed in three categories and consecutively identified:
1. Factors of liquid basic physical properties and their hydrodynamic regularities.
2. Technical factors influencing hydroerosive production process.
3. Technological factors influencing hydroerosive surface of the cutting.

2. FACTORS INFLUENCING PHYSICAL PROPERTIES OF FLUID AND SOME RELATED HYDRODYNAMIC REGULARITIES
The identification of fluid basic physical properties is based on fundamental properties and equations related to hydrodynamic processes.

From angle of essence of the high pressured water jet technological process, other jet technological methods applying the field mainly of very high pressure on the base of physical properties and hydrodynamic regularities, are being developed. The basic physical properties and hydrodynamic regularities of the liquids used at hydrodynamic processes and which are significant for jet technology hydrodynamic processes are presented in Table 1:

For common consumer and industrial practice the following names for dispersion systems were created by various combinations of phases and are shown in Table 2.

For the water jet technology, especially fluid (water), solid phase (abrasive) and suspension (water flow-jet covered with abrasive) are the most significant.

Then, the compressibility coefficient is defined as a ratio of relative volume decrease to pressure increment which caused this decrease. Selected fluids characterized by density p [kg.m-3] and by compressibility coefficient Bp are listed in Table 3.

3. TECHNICAL FACTORS INFLUENCING HYDROEROSIVE PRODUCTION PROCESS

In this section is listed a summary of technical factors depending on a model of a high-pressure pump, for example a pump 50 Hp Streamline SL-V which belongs to the most popular pumps. These parameters and their design and settings influence resulting smoothness outcome of technological process and its impact on machined surface.

3.1 Basic power factors
 Pump model – model; engine power, maximal working pressure, maximal flow rate
 Noise level – model, noise level [dB (A)].

3.2 Environmental factors
 Surrounding environment
 Surrounding temperature.

3.3 Factors of water specification
 Factors of cutting water input – lowpressure water system
 Factors of cooling water input – recirculation system
 Factors of water quality – substances values requirements.

3.4 Factors of hydraulic system and of high pressure water system
 Hydraulic system
 Pneumatic control valve
 High pressure water system Maximum flow rate.

3.5 Factors of water and abrasive nozzles selection
 Recommended water nozzle inner diameter
 Recommended combinations of both water and abrasive – focusing nozzle sizes
 Selection of water nozzle depending on engine performance and pump pressure
 Factors of water nozzles number depending on pump working performance.

4. TECHNOLOGICAL FACTORS INFLUENCING HYDROEROSIVE CUT SURFACE

The analysis of technological factors related to their impact onto erosion surface represents determination of optimal values which have basic and qualitative influence on erosion surface. It is useful to separate individual groups of factors in following structure according to (for example, a high pressure pump SL-V 50 Hp is assumed):

4.1 Performance and operational factors
 High pressure pump power
 High pressure pump oil cooler power
 Input water: cutting water; cooling water
 Air pressure in bar.

4.2 Technological and input factors
a) Hydraulic factors:
 Liquid pressure in MPa
 Water nozzle diameter in mm
 Abrasive nozzle inner diameter in mm.
b) Abrasive factors:
 Type of abrasive
 Abrasive granularity in MESH
 Weight flow of abrasive in g/min.
c) Material factors:
 Kind of material
 Thickness of material in mm
 Surface processing of material.

4.3 Technological and manufacturing factors
a) Directly regulatory:
 Cutting speed control
 Liquid pressure control

 Regulation of ratio of water nozzle diameter to abrasive nozzle
 Regulation of flow weight flow
 Jet dynamic stability
 Stroke of nozzle above material in mm
 Jet falling angle in degrees.
 Jet transition number – used very rarely.
b) Indirectly regulatory:
 Width of cutting opening
 Cutting depth
 Time of material penetration
 Kind of abrasive
 Cutting direction.
4.4 Production, qualitative and output factors
 Measuring of product dimensional precision quality
 Measuring of cutting edge quality – roughness of cutting quality
 Angularity of cutting edge

 Wear – sharpness of upper erosive edge at place of jet penetration into material
 Difference between jet input and output
 Fan-shaping of bottom part of cutting edge
 Waste water quality.

These basic factors represent qualitative extend of evaluation of cutting topography result created by hydroerosion.

5. RESULTS
On the base of the given complex specification, a graphic model of factors complex was designed. It was designed and realized in the firm WATING Prešov and at The Department of Technologies and Materials of Faculty of Engineering TU in Košice as a mode KMF1 which is
schematically presented in Table 4.

Verification of the formulated factors was finally performed with material AISI 304 samples; thickness 8 mm. Figure 1 shows cut 9 pieces of verified samples.

The cutting parameters of given verified samples were evaluated and processed in the graph, which is shown in Figure 2.

6. CONCLUSION
The complexity and the factors defining cutting erosion surface is listed in the presented paper. For contemporary practice and from economy aspect of hydroerosion jet cutting, for example, flow rate fluctuation survey represents a relatively wide clarification of water jet technology
parameters themselves, with the ambition to find a way how to define cutting parameters
warranting output qualitative technology aspect and in the same time economy aspect
of water jet cutting process, at optimal hydroerosion factors.

This work was supported by the Ministry of Education of the Slovak Republic under grant VEGA No. 1/0396/11.

REFERENCES
[1] SPIŠÁK, E.: Matematické modelovanie a simulácia technologických procesov – ťahanie (Mathematical modeling and simulation of technological processes – drawing). Typo Press, Košice, 2000, ISBN 80- 7099-530-0 (in Slovak);
[2] KMEC, J., BIČEJOVÁ, Ľ.: Rozdelenie vodného lúča do dvoch rezacích hlavíc (Distribution of water jet into two cutting heads). In: Operation and diagnostics of machines and production systems operational states: Scientific Papers. Brno: Tribun EU, 2008. pp. 100-107, ISBN 978-80-7399-634-5;
[3] KMEC, J.: Technológia vodný lúč – Modelovanie ekonomických nákladov rezania (Waterjet Technology – Modelling the economic cost of cutting). In: CD-Proceedings of Technology Systems Operation. Prešov: FVT TU, 2007, pp. 1-3, ISBN 978-80-8073- 912-6 (in Slovak);
[4] KMEC, J., SOBOTOVÁ, L.: Lúčové technológie vody, 25 rokov na Slovensku (Jet technology of water, 25 years in Slovakia). 1st electronic optical disc (CD-ROM). In: Nekonvenčné technológie (Non-conventional Technologies) 2010: 9th Int. Scientific Conference: Strečno, 22nd June 2010 – Ţilina: ŢU, 2010, pp. 1-8, ISBN 978-80-554-0222-2 (in Slovak).