Innovative system with abrasive water jet.

Ciupan, Cornel ; Morar, Liviu ; Ciupan, Emilia 等

1. INTRODUCTION

Milling and lathing processes have been developed using the erosion effect of the abrasive particles in the AWJ cutting process. AWJ milling is in fact a complex erosion process of the manufactured material. This operation allows the manufacturing of parts with complex surfaces such as moulds, gears, etc. Research on international level in this domain aims at two aspects: perfecting the cutting equipment and optimizing the cutting parameters with the help of adequate control strategies; the development of processing procedures by water jet milling and turning.

Which is the problem? The authors propose to achieve an experimental system for ultra precise processing with energetic beam on a mechatronic support. This system uses an abrasive high speed water jet as the energetic beam.

How is it solved? We can notice a lack of machine tools that attain milling operations of complex surfaces, necessary for making molds, world wide. Even the lathes in water jet cutting machines have a drawback regarding the operations of angled cutting, tapped holes and the quality and the surface accuracy.

What is my plan? The innovation and the originality of the project are assured by the concentration of a single system of the following operations: cutting, drilling, milling. The mathematical model for determining the eroded section, the traverse rate f and the productivity is very important for the control of the system.

What is new? The novelty of the project consists of making a mecathronic product, flexible from the point of view of using the energy from the abrasive water jet for the entire range of possible operations (milling, drilling, cutting). Until now there have been, world wide, researches for separate operations, especially cutting, drilling and milling. For assuring the flexibility in the proposed range of operations, the system will use a numerical command processing machine, with 3 axes of movement (x,y,z) and two axes of orientation of the cutting head (A,B). The mathematical model for establishing the eroded material volume and the shape of the processed surface will be an element of high originality and will fill a gap in this domain.

What is next on the to do list? The authors wish to develop the analytical model so that this would allow control over the eroded surface during the milling process.

2. THE SYSTEM

The proposed system enables carrying out the following operations: cutting, drilling, milling (fig. 1). AWJ cutting allows obtaining parts with a surface which is perpendicular on the positioning surface or positioned under a certain angle. A correction of the kerf is also possible by tilting the cutting head.

[FIGURE 1 OMITTED]

Cylindrical, conical or profiled holes may be obtained similarly with the control over interior or exterior surfaces.

Milling operations will be used for obtaining 3D channels or complex surfaces.

The scheme of a waterjet milling machine is composed of parallel robot and a cutting head with a AWJ jet (Ciupan et al., 2007). The main parts of a parallel robot are a fixed platform , a mobile platform linked through six kinematics axis. The mobile platform along with the cutting head is able to perform 3 translation movements and 3 angular movements which allow obtaining the trajectory and the orientation of the AWJ jet.

A mathematical model for the control of the volume of eroded material and of the shape of the surface resulted will predict the processing depth. It will make it possible to process some 3D surfaces of high dimensions, with applications in the automotive field in conditions of precision and efficiency.

3. THE MATHEMATICAL MODEL

Creating a mathematical model that allows driving the system with the purpose of creating the proposed operation range is a very important objective. If for the cutting operations there are numerous models (Momber et al., 1998, Pop et al., 2004), for the milling operations there aren't any mathematical models that allow the control (prediction) over the resulted surfaces after AWJ erosion.

Fowler has developed a mathematical model that studies the abrasive water-jet controlled depth milling of Ti6Al4V alloy (Fowler et al., 2005, Shipway et al., 2005), but which doesn't allow the prediction of the resulted surface. Vikram and Ramesh have developed a model that enables the study of the topography of the resulted surface (Vikram & Ramesh, 2002).

The mathematical model of the eroded material volume control will form the base of calculating the modelling of the resulted shape of the surface. As a basic model for determining the eroded material volume we have the model (Ciupan & al., 2007).

The following steps were set for the development of the mathematical model for controlling the eroded material volume and the resulted surface:

--the mathematical model for the erosion process with abrasive jet;

--control of the eroded material volume and the resulted surface;

--optimization criteria;

--simulations on the virtual model;

--optimizing the virtual model.

The scheme in figure 2 is used to determine the abrasive particles trajectory. The abrasive particles trajectory is determined in relation to an uw reference system, which has the w axis on the previously manufactured surface and the u axis perpendicular on this.

Considering that the particle speed is slowed by the eroding strength coefficient of the material sM and that the same force will also have a deflection effect on the jet in the direction of the u axis, the following equations may be written:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)

where:

--F, [F.sub.u], [F.sub.w] are the resistant force that act on the particle and its projections on the axes u, w;

--m is the mass of the abrasive particle;

--v, [v.sub.u], [v.sub.w] are the speed of the abrasive particles and its projections on the axes u, w.

The erosion force is determined by equation:

F = [sup.[epsilon][M.sup.[pi][d.sup.2.sub.a] / 4 (2)

where [d.sub.a] represents the diameter of an abrasive particle.

The abrasive particles may be considered spherical and equal to the diameter of the jet in order to simplify their study.

A MathCAD program based on relation (1) and (2) was developed for the study of the particles trajectory, the volume of eroded material and the abrasive mass flow.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

The eroded material surface is determined by the AWJ jet by taking into account the speed of the jet when exiting the focusing nozzle [v.sub.0] and the jet impact angle [[theta].sub.0].

The u, w coordinates are determined based on the (1) and (2) equations. The abrasive particles trajectory is presented in figure 3 for [[theta].sub.0] = [20.sup.0] and v=(600; 800; 1000) m/s.

Figure 4 shows the volume of eroded materials in relation to the jet impact angle 00.

4. CONCLUSION

The proposed system has the following advantages:

--precise processing of parts with plane or profiled surfaces;

--the flexibility of the system with respect to milling, drilling, cutting operations;

--using an energetic beam such as the abrasive water jet allows processing of any material without any limitations.

The proposed model is just one of the first steps in building a working analytical model for the control of the eroded surface.

Optimizing the models, especially those for AWJ milling, simulating and optimizing the virtual model will lead to fulfilling the objectives by studying the technological parameters and command strategies in comparison with the AWJ operation range.

Another advantage of this procedure is the non-thermal influence of the processed area. Unconventional processes by which result similar surfaces with those obtained by milling and turning, can be realized by corrosion with abrasive water jet.

5. REFERENCES

Ciupan C., Pop A., Morar L. (2007). The Mathematical Model of Abrasive Water Jet Milling Process. Advanced Material Research, vol. 23, pp. 187-190.

Fowler, G. et al. (2005) Abrasive water-jet controlled depth milling of Ti6Al4V alloy--an investigation of the role of jet--workpiece traverse speed and abrasive grit size on the characteristics of the milled material. Journal of Materials Processing Technology, vol. 161, pp. 407-414.

Momber, A. W. & Kovacevic, R. (1998). Principles of Abrasive Water Jet Machining, Springer-Verlag, Berlin Heidelberg, 1998.

Pop A. (2004). Study of Computer Control Strategy for Jet Cutting Integrated Systems, Ph.D. Thesis, Technical University of Cluj-Napoca, 2004.

Shipway, P.H.; Fowler, G.& Pashby, I.R. Characteristics of the surface of a titanium alloy following milling with abrasive waterjet. Wear, Vol. 258, Issues 1-4, January 2005, pp. 123-132.

Vikram, G. & Ramesh, N. B. (2002). Modelling and analysis of abrasive water jet cut surface topography. International Journal of Machine Tools & Manufacture, Vol. 42, pp. 1345-1354.