In the process of Layered Object Manufacturing (LOM), achieving high precision in prototype creation is a complex challenge influenced by various factors, such as CAD model conversion, slicing software settings, and material properties. To minimize errors and enhance the quality of prototypes, several control measures can be implemented during the LOM production process. These measures aim to address common sources of inaccuracies and optimize the manufacturing workflow. Below are key strategies to improve the accuracy of layered solid prototyping.

1. Optimize STL Conversion Precision

When converting CAD models to STL files for LOM prototyping, it’s essential to balance conversion accuracy with the complexity of the part. Although a high precision setting in the conversion process might seem beneficial, it can lead to unnecessarily large files and extended processing times. Therefore, it is recommended to avoid overly high precision settings while ensuring the model’s shape remains smooth and intact.

Recommended Approach:

• For complex parts with fine details, a higher precision setting (0.01 to 0.05 mm) is appropriate to capture small features.
• For simpler parts, a lower precision setting (0.02 to 0.08 mm) is sufficient and helps improve the processing speed without compromising part quality.

By adjusting the precision according to the part’s complexity, you can maintain a balance between file size, processing speed, and part quality.

2. Match STL File Precision with Slicing Software Settings

The accuracy of the STL file produced by the CAD software should align with the precision settings in the slicing software. If there is a significant mismatch between these values, it could result in inconsistencies during the slicing process, leading to errors in the final part.

Key Considerations:

• Ensure that the slicing software’s processing precision matches the STL output precision of the CAD model. Generally, setting these values close to each other yields the best results.
• For prototypes with fine details, increase both the CAD model’s STL output precision and the slicing software’s handling precision.
• For simpler parts, lowering the slicing software’s precision can improve processing efficiency and surface smoothness without compromising accuracy.

3. Optimize Model Orientation

The orientation of the model during the prototyping process significantly impacts the dimensional accuracy, surface finish, strength, and overall material costs. In LOM, it is more challenging to control dimensional accuracy in the Z-axis (height), so parts with strict dimensional requirements should be oriented along the XY plane.

Recommended Approach:

• Parts that require high precision, such as those with cylindrical features or circular holes, should be placed in the XY plane to ensure better accuracy in the Y direction.
• Avoid placing critical features in the Z direction, as this is more prone to warping during the printing process.

Proper orientation can not only improve dimensional accuracy but also reduce the time and cost associated with the prototyping process.

4. Adjust Grid Size for Efficiency

The size of the grid used in LOM to separate waste material plays a significant role in both the efficiency and accuracy of the prototyping process. Adjusting the grid size based on the part’s complexity can lead to better material usage and surface quality.

Key Guidelines:

• For simple parts, use larger grid sizes to speed up the prototyping process without affecting the surface quality.
• For parts with complex geometries or internal voids, use a smaller grid size to ensure easy removal of waste material and prevent defects in the final prototype.
• A variable grid size can also be used, where larger grids are employed for the outer layers and smaller grids are used for the inner layers to optimize efficiency while maintaining part integrity.

5. Control Thermal and Moisture-Induced Deformation

One of the biggest challenges in LOM prototyping is controlling deformation caused by thermal and moisture fluctuations. These deformations can occur both during the manufacturing process and after the part is finished. To minimize these issues, several strategies can be implemented:

• Use New Materials and Adhesive Techniques: Advanced materials and improved adhesive methods can help reduce the effects of thermal expansion and moisture absorption, leading to more stable prototypes.
• Post-Processing Adjustments: After the prototype is complete, it may be necessary to apply corrective measures, such as heat treatment or environmental stabilization, to prevent warping.
• Pre-Compensation for Thermal Deformation: CAD models can be adjusted to account for anticipated thermal deformations, ensuring that the final part maintains its desired dimensions even after cooling.

6. Post-Manufacturing Cooling and Handling

After the layered prototype is created, it’s important to manage the cooling and waste removal processes to maintain accuracy and prevent deformation.

Key Procedures:

• Pressurized Cooling: Applying a light pressure to the prototype during the cooling phase can help minimize warping caused by internal stresses. Once the part is sufficiently cooled, the pressure can be removed to prevent residual deformations.
• Avoid Immediate Waste Removal: After the prototype is completed, it’s best to allow the part to cool while still supported by the waste material. This helps prevent bending or warping due to the part’s insufficient rigidity, particularly in more complex shapes.

7. Timely Surface Treatment

To prevent moisture absorption and swelling, it’s important to treat the surface of the prototype as soon as the waste material is removed. Immediate surface treatment helps to enhance the strength and stability of the part.

Recommended Surface Treatment:

• Coatings: Applying surface coatings like epoxy resin, polyurethane, or strong adhesives can improve the part’s strength and moisture resistance, ensuring it remains stable and functional over time.
• Prevention of Moisture Effects: This treatment helps to protect the part from swelling caused by humidity, which could lead to dimensional inaccuracies or structural weaknesses.

Conclusion

Improving the accuracy of layered solid prototyping in LOM involves addressing various factors, from STL conversion precision and slicing software settings to material handling and post-processing techniques. By optimizing each stage of the process, from the initial CAD model to the final surface treatment, manufacturers can significantly enhance the quality and precision of their prototypes. Proper management of thermal and moisture effects, along with careful attention to cooling and handling, can ensure that the final part meets all design specifications and functional requirements.