DESCRIPTION OF THE SOFTWARE INTERFACE

ITACAe in agreement with 3D-NT within the Piemonte project “STAMP” has set the requirements for the realization of a software able to manage the user-machine interface, which allows the setting of the parameters and the communication with a non-relational database (DB) in order to define the settings of the "job", that is, of the script containing the implementation process procedure. The DB for the application is a source of numerical data deriving from sensors in the working chamber, spectral images in the visible and near-infrared fields. With the communication with the DB and the predisposition to the insertion of "Machine Learning"

functions, it is possible to certify or reject new non-labelled data and make real-time corrections to the "job file" and delayed to the component during manufacturing.

An application developed by ITACAe interfaces with Application Program Interface (API) created by 3D-NT. The application was developed in C# and contains subroutines developed in Fortran. In particular, the reading of the CLI files takes place through a code developed in Fortran while the call to the API and the management of the laser path was developed in the .Netframework environment using the C# language.

The code has also the function to write FE files, in the Nastran, Abaqus and Ls-Dyna formats to allow viewing of the laser path with any pre-processor and setting process simulations. Some steps lead from the triangulation of the input geometry (file in STL format) to the voxelization (Figure 1), for the process simulation.

Figure 1: Steps from geometrical model to voxelization

Starting from the STL model, the CLI (Common Layer Interface) file is obtained by means of the API created by 3D-NT. The CLI file constitutes the input of the software interface created by ITACAe.

3.1 Common Layer Interface

The CLI format is a universal format for the input of geometry data to model fabrication systems based on layer manufacturing technologies (LMT). The CLI is based on a 2.5D representation. The geometric information of the intersection of a 3D model with a plane is called a slice. The volume between two parallel sections is called a layer.

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3.2 Input file

The application requires the following input information.

1. CLI geometry file (FILENAME.cli)

2. Optional parameter file (FILENAME_par.txt). The parameters that can be supplied are the following:

• Beam diameter;

• Layer thickness;

• Distance between the hatches;

• Base length;

• Width of the base;

• Base height;

• Laser source power;

• Recoating time;

• Releasing time;

• Beam speed.

If the file containing the parameters is not supplied as input, the code deduces the data necessary for calculating the performance of the machine.

Figure 2: Representation of each treats of the laser path through coloured segments

3.3 Output results file

The code outputs three text files: FILENAME.txt, FILENAME_res.txt and FILENAME_lay.txt.

The FILENAME.txt file contains the following information:

1. ID of the points and respective coordinates x, y, z: Point id, x, y, z coordinates

2. ID of the line, ID of the property and identification of the points of departure and arrival of the individual sections of the laser path.

The quantities shown in the output file are:

1. ID_LAY, Layer identifier. The layers are numbered in progressive order starting from the first layer;

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2. ZLAY, dimension in Z of the layer in mm;

3. PATH, path length expressed in mm;

4. TIME, time expressed in s necessary to walk the path;

5. SPEED, beam speed in mm/s;

6. ENERGY, energy spent to make the layer, expressed in mJ.

Considering the layer 2 positioned at Z = 1 mm, the length of the complete path is about 56 m, the time taken to complete it is equal to about 130 seconds, at an average speed of 430 mm/s and with an amount of energy absorbed equal to 5.9 J. The output file FILENAME_lay.txt supplies the process information layer by layer.

The FILENAME_vec.txt file provides more detailed process information. In this case, in the FILENAME_vec.txt file, in addition to the data already present in the FILENAME_lay.txt file, it is possible to read the following additional data:

1. M / J, which identifies the action Move (M) or Jump (J) of the laser. In the case of jumps, as shown on line 1 of, the dissipated power is zero. On the contrary, in the case of Move, the dissipated power is different from zero and is expressed in mW;

2. (Xi, Yi), pair of coordinates in the X and Y plane of the starting point (1) and arrival (2) of the vector, expressed in mm;

3. DIAMETER, beam diameter;

4. Cumulative quantities, sum of the contribution of the generic quantity from the first vector to the current vector.

3.4 Optimization of orientation and generation of supports

The software allows to set the following geometric parameters for the generation of supports:

- Overhang Angle, the angle above which it is no longer necessary to insert supports, - Baseplate Offset, the minimum distance of the component from the plate,

- Contact Edge Size, the length of the contact side between the supports and the part surface,

- Max Unsupported Size, a value that depends on the material and is the maximum length such that the sintered powder is self-sustaining,

- Thickness of the supports,

- Filling factor of the support grid (relationship between these two lengths).

Different types of supports can be chosen: solid, hollow and cross. The orientation of the part is based on different criteria of minimization: supports volume, supports height, process cost or part distortion. A combination of all of them with weighing factors is also implemented.

The tool allows a full customization of both support configuration generation and orientation optimization objective function.

The algorithm was applied to an automotive gear bracket in the frame of the “STAMP”

project (Figure 3). The part was previously topologically optimised by ITACAe for maximum mechanical strength, starting from technical specifications provided by FCA. Two configurations are analysed: not optimised orientation and orientation for minimum distortion.

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Figure 3: Model of an automotive gear bracket obtained from a previous phase of topological optimisation for maximum mechanical strength

Figure 4: Part oriented for minimum distortion

Table 1: Results of the optimization of build orientation

Crit. # Target Part/support data Density Volum

e Mass

AlSi10Mg Dx Dy Dz Area mm³ g mm mm mm mm²

Part Part 99% 251783 673

0 No optimisation Support 70% 467061 883 190 150 102 28500 2 Min variance Support 70% 625955 1183 102 162 184 16524

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4 NUMERICAL SIMULATION