Design for Additive Manufacturing (DFAM) Features Detection for CAD Model
Product: Siemens NX, NXOpen
Introduction
Figure 1: Integrated GUI within NX for detecting small openings, thin regions, sharp corners, thin to thick transitions, thin walls and recoater arm collisions.
Powder Bed Fusion Additive Manufacturing (PBFAM) or Direct Metal Laser Sintering (DMLS) process is an industrial additive manufacturing (AM) techniques that can build fully functional metal components using metal powder. DMLS technology uses a high-power laser to melt metal powders locally and fuse it into solid parts. Parts are constructed additively, one layer at a time. The critical nature of this layer-by-layer method of fabricating parts as well as the inherent process constraints associated with DMLS processes make it necessary for the designer to consider design for manufacturing guidelines (DFAM) during the design phase. This helps in preventing multiple iterations during the design process and avoiding excessive costs and material consumption while building the part.
Design for Additive Manufacturing (DFAM) guidelines need to be considered before proceeding to building a part to avoid the problems or failures during the build. Detection of critical geometric features helps the designer to identify alternate build orientations or make appropriate modifications to the part design in the design phase to avoid any build problems downstream during the final build. The Center for Global Design and Manufacturing at the University of Cincinnati have developed a computational geometry-based preprocessing and simulation tools for assessing and iterating product designs and attributes of the additive manufacturing process in order to create a ‘digital twin.’ Those tools are seamlessly implemented in Siemens PLM NX environment using C++, NX API and Ufunc routines. Stand-alone modules with GUI’s were developed within the NX environment that allowed the students to conduct the analysis on sample geometry as shown in Figure 1.
Students were able to simulate the layer-by-layer process analysis using a virtual toolset that allows detection of several important DFAM features including small openings, thin features, sharp corners, thin to thick transitions, thin walls, and recoater arm collisions for a given part build orientation. This analysis helps the students identify problems in the existing design from a manufacturability viewpoint and make appropriate design changes before building the part in a specific orientation. This enables the user to identify manufacturability problems and correct them at the design stage thus preventing multiple iterations of manufacture.
Small openings detection
Small openings are considered as gaps within each layer whose dimensions are below the minimum manufacturable size of an opening for a given AM machine. This is due to the minimum laser spot size for a given machine. The small openings could be a hole or a narrow slot. These features may fuse during the laser sintering process depending on the laser diameter and may pose problems when building the part. So, it is important for the designer to consider the deigns that could minimize the small opening features to improve manufacturability.
University of Cincinnati have developed their own slice-based algorithm for identifying problematic small openings in the part model. Using the custom GUI, Students can rotate a part with adjustable threshold values and slice thickness, then the tool will detect all the small holes and gaps in the geometry. Critical small opening areas are highlighted in the CAD model, and total small opening areas is calculated and displayed as output shown in Figure 2.
Figure 2: Custom GUI and result output for small opening detection in Siemens NX Modeling
Thin regions detection
Thin features are regions within each layer where the size of the feature is below the threshold value of a given AM machine. Part with thin features are challenging to manufacture with AM since the accuracy of the features is compromised due to resolution limit of an AM machine. The thin features can also cause warping or bending due to the thermal residual stress within the thin regions during AM process.
The purpose of this tool is to detect the thin features in each layer of the geometry as shown in Figure 3. Students can input the rotation angle around the x and y axes, and the threshold value of thin feature. The tool will highlight the critical thin sections in the CAD model with green color and display the total area of the thin region as result.
Figure 3: Custom GUI and result output for thin feature detection in Siemens NX Modeling
Sharp corner detection
Sharp corners are identified as tips within each layer where the angle of the tip is less than threshold value of the AM machine. If the angle is too small, these sharp corners in the geometry may be difficult to manufacture during the laser sintering process due to the size of the laser diameter. This tool can rotate a part and highlights critical sharp corners in the geometry and calculate the number of the sharp corners in each layer as shown in Figure 4.
Figure 4: Custom GUI and result output for sharp corner detection in Siemens NX Modeling
Thin to thick detection
Thin to thick transitions are transition areas from a low area layer to a high area layer along the build direction. It’s a very important factor especially in DMLS process. Because the laser melts the metal powders and fuses them together. The heat energy in the current layer is transferred to the substrate through the layers beneath it. If the transition area between any consecutive layers is too small, it may cause thermal distortion due to impediments to heat transfer during DMLS process. This tool is designed to detect those transition areas that may pose problems. The tool can scan each layer and predict the transition layers that are too thin for heat transfer, such layers will be highlighted and shown in the CAD model, and the location of the layers will be displayed in the text. Then the designer could adjust the CAD design directly from the result. Figure 5 shows result output for thin to thick transition.
Figure 5: Custom GUI and result output for thin to thick transition in Siemens NX Modeling
Thin walls detection
Thin wall is vertical wall structure where the thickness of the wall is too small. Thin walls are very challenge to manufacture duo to the laser spot diameter or FDM nozzle size. So, it is necessary to detect thin walls as they may cause build failures due to increased thermal stresses and distortion.
This tool can detect all the wall features in the geometry. The user can input the threshold thickness of the thin wall feature. The tool will display all the thin walls whose thickness is less than the threshold value on the CAD model with contrasting colors as shown in Figure 6. In addition, the location and the height of each thin wall is also shown as results.
Figure 6: Custom GUI and result output for thin wall detection in Siemens NX Modeling
Recoater Arm collision
The re-coater arm, which is responsible for depositing each layer of powder, may collide with the part geometry if the part has a long edge parallel to the re-coater arm. This tool can rotate a part and specify the recoater direction and identify areas of the part that may be prone to recoater damage. As shown in Figure 7, it can highlight the potential geometry/deformation areas of the parts that may be damaged due to recoater arm collision, then designer can utilize this knowledge and can come up with a better part layout plan, build orientation and part design that prevents these collisions from happening, thus preventing rebuilds and material wastage.
Figure 7: Custom GUI and result output for recoater arm collision detection in Siemens NX Modeling