Research regarding simulation and optimization trajectory for a NACA profile surface.

Paraschiv, Marius Daniel ; Ispas, Constantin ; Ivan, Ioana Carmen 等

1. INTRODUCTION

This paper containes: simulation, corection of trajectory and generation of NC file for machining using CATIA V5R17.

By using certain commands for trajectory generation, it is possible to virtual machining a surface wich can have different degrees of difficulty.

This file will be imported into NCSIMUL software, used for simulation with respect of the real machining conditions for a milling machine tools.

2. GENERATION, SIMULATION AND ANALYS OF TRAJECTORY IN CATIA V5R17

CATIA V5R17 allows CAM simulation for different sceneries of machining. This can be used to generate and to optimize machining trajectories for different surface.

The "NC Manufacturing" software will generate a correct NC program for machining.

This software presents the following advantage:

* flexible administration of the programs, based on a simple and intuitive interface;

* operate with tools and tools library;

* can operate with machine tools with two up to five CNC axes.

Design of the blade is presented in Fig. 1. The surface of this piece is based on a NACA profile. The workpiece for the blade has following dimensions: 70x30x106 mm.

Due to the complex profile, it is difficult to machine this surface, but with the help of CATIA V5R17, we were able to machine it. We use Isoparametric machining, operation which can be found in module Machining--Advanced Machining.

The surplus material was removed in two cutting process. The first it was used a roughness machining in order to remove a lot of thickness from the half finished block, and the second was a finishing cutting process in order to obtain the necessary surface quality (Vlase, 1993).

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After choosing the necessary operation, we have to specify some settings, for each operation. If the operation and details are different, we have five main categories (Fig. 2.).

In the first category we have to choose the trajectory settings such as: machining type, radial set-up and the inclination of tool axis. The second category is the machining pattern. Here we select the points for machining on the workpiece: part surface and corner used for machininig. In the third category we establish tool used for machining. In the fourth category, we set-up the necessary speed for the machine and tool. Here we choose also the approach and retract speeds, also, the spindle speeds. And in the last category are the finely set-up parameters the approach, retract clearance, linking retract and linking approach (Bernard, 2003).

After choosing the optimal cutting process, it was choose the parameters of machining: Machining, Radial and Tool Axis.

For machining strategy it was used a tolerance of 0,5 mm, because, the first operation is the roughing, and is no need for a very precise tolerance. In the second window, it was possible to choose the scallop height. This value represents errors which appear between real and theoretical surface of the blade. After that, it was set up the depth of cut. Number of steps represented the maximum number of crossing made by the tool in order to obtain the surface (Fig. 3.). It is not necessary to execute all the steps imposed. The program will execute the optimal number of steps (only the necessary steps). Also it was set up the start and the end extension.

In the third window it is the possibility of defining the trajectory of machining. It is very important because CATIA considers the machine table fixed. On the real machine tool used, the tool is able to move only in 3 translation axis on X, Y, and Z, and the machine table can move by rotation on two axis: A (around x direction) and C (around z direction).

After that, it was chosen the surface and the starting and the ending point of machining. We choose to have 2 mm of material, which represents the necessary surplus for the last operation, finishing (Ispas, 2008).

The cutting tools used, were:

--for roughing: a mill with 6 teeth and 028 mm diameter;

--for finishing: a ball mill carbide with 2 teeth and 020 mm diameter.

The value of machining speeds for approach and retract, and the tool speed were set up also.

In the last step it was chose the type of approaches and retract for the process of machining.

After that the trajectory of machining was checked, for roughing and the finishing.

After the cutting tool trajectory was computed, some visualization can be made. The second operation used to machine this blade is the finishing operation.

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This operation is has almost the same set-up parameters as the precedent, but, the differences between them are the roughness obtain after finishing operation. After finishing operation exist the possibility to measure machining piece, in CATIA, by comparising with initial model, to identify form and dimensional deviation. To obtain a very good surface, we have to make different modification at the parameter described above.

3. GENERATION, SIMULATION AND ANALYS OF TRAJECTORY IN CATIA V5R17

After the simulation, an APT file was generated. The type of Catia output file was .apt file, because of high compatibility with other machining simulation software. The .cnc output file from Catia could contain errors because of Catia postprocessors and a limited simulation of the cutting process (according only with tool and pieces without machine tool)

So, to generate the program of machining it was used Generate NC Output in Batch Mode command, and the generated file, it is type .apt.

Another important aspect is the number of lines for the .apt file. For the machining with the tolerance of 0.02mm, the program has 4687 lines. This file was inserted in to another software for simulation in according with the machine tool structure and kinematics. This software has the possibility to create all the elements which take part in the machining process Fig. 5:

It has to be mentioned that it is absolutely necessary, a 3D model of the part in order to check the errors of machining and the resulting tolerance after machining.

In order to complete this simulation, it is necessary to make the following steps:

--uploading the necessary elements for machining (machine tool, tool, the fixed vice, the mobile vice, the workpiece and part).

--positioning of the parts on the machine table.

--uploading the APT file generated by CATIA.

--making necessary adjustments for simulation.

--setting up the collision detection.

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The element used for simulation are : 1-machine tool; 2-cutting tool; 3-fixed vice; 4-mobile vice; 5-workpiece; 6-piece

Is possible to make different set-up starting with conditions of contact between different elements up to the desired tolerances, and collision detection between different element wich compose the simulation.

And finnaly after the simulations is finished, we can analyze the difference between the obtained surface and the imposed surface Fig. 6.

4. CONCLUSION

By simulation it could be obtain the optimum machining parameters in order to assure the surface quality. Also, is recomendate to verify twice a machining operation in order to avoid errors or collision wich can often can appear in real machining process.

We used two simulation software, becose in the fisrt software we are able to generate the file for machininig operation, and in the secondary software we verify the correct solution offer by Catia simulation in order with machine cinematics.

In the conclusion, this paper offer the posibility of development of machining simulation in case of complex surface.

5. REFERENCES

Bernard, A. (2003), Fabrication assistee par ordinateur (Computer Aided Manufacturing), Traite IC2, serie Productique, February 2003

Ispas, C., Paraschiv, M., Laboureau, L. & Anania, D. (2008). Research concerning the numerical errors correction for a naca profile surface on a 5 axis machine tool. Academic Journal of Manufacturing Engineering, Vol., No.6, (May, 2008) pp. 75-80, Timisoara, ISSN 1583-7904

Vlase, A., Sturzu, A., Stancescu, C. & Neagu, C. (1993). Tehnologii de prelucrare pe masini de frezat (Machining technologies for milling operations), Editura Tehnica, ISBN 973-31-0243-1, Bucharest

http://www.windmission.dk/workshop/BasicBladeDesign/ bladedesign.html Accessed: 2008-02-27

http://www.ncsimul.tm.fr Accessed: 2007-11-12