How Does Pre-Polishing With High-Precision Sandpaper Assist In The Tpf Of Lpbf Molded Parts? Enhance Surface Fidelity

Pre-polishing acts as a critical corrective step that bridges the gap between the roughness of 3D printing and the precision required for forming. By using high-precision sandpaper on Laser Powder Bed Fusion (LPBF) parts, you mechanically remove inherent manufacturing artifacts—specifically stair-step effects and adhered un-melted powder—to create a defect-free surface.

Core Insight: The fidelity of Thermoplastic Forming (TPF) is strictly limited by the quality of the initial interface. Pre-polishing removes physical barriers, allowing the Zirconium-based Bulk Metallic Glass to mirror the mold’s fine textures with high uniformity and accuracy.

Addressing the Limitations of As-Printed Parts

The raw output of an LPBF process is rarely suitable for high-precision forming immediately after printing.

Eliminating the "Stair-Step" Effect

Additive manufacturing builds parts in layers, resulting in a microscopic staircase topography on curved or angled surfaces.

High-precision sandpaper levels these ridges effectively. This flattens the geometry to match the intended design rather than the limitations of the printer's resolution.

Removing Adhered Un-Melted Powder

During the printing process, loose powder particles frequently adhere to the part's surface without fully melting.

Polishing strips away these loosely bonded particles. If left continuously, these particles creates surface noise that interferes with the contact area during the forming process.

Optimizing for Thermoplastic Forming (TPF)

Once the defects are removed, the physics of the forming process change significantly.

Creating a Smoother Initial Interface

TPF relies on close contact between the mold and the material.

Pre-polishing ensures that the initial contact interface is smooth and uniform. This maximizes the surface area available for bonding or shaping during the thermal cycle.

Enhancing Texture Mirroring

The ultimate goal is to transfer the mold's fine textures onto the Zirconium-based Bulk Metallic Glass (BMG).

Because the surface is free of artifacts, the BMG can flow into the mold's features without obstruction. This results in a final part where the mold's texture is mirrored accurately across the entire surface.

The Risks of Neglecting Surface Preparation

While adding a manual polishing step increases production time, avoiding it creates significant quality issues.

Compromised Replication Accuracy

If the substrate is not polished, the TPF process will essentially "copy" the defects of the print.

The stair-step patterns will prevent the fine mold textures from transferring correctly. The final BMG part will exhibit a hybrid texture of the intended mold design overlaying the original printing errors.

Inconsistent Surface Uniformity

Un-melted powder creates random high points on the surface.

These irregularities prevent uniform pressure distribution during forming. Consequently, the final texture will appear patchy or distorted rather than continuous.

Making the Right Choice for Your Goal

To ensure your LPBF parts are ready for TPF, consider your specific requirements for the final Zirconium-based BMG component.

If your primary focus is surface fidelity: You must pre-polish to remove all stair-stepping, ensuring the BMG mirrors the mold's texture without interference.
If your primary focus is dimensional consistency: Use high-precision sandpaper to remove adhered powder, which prevents random surface irregularities from distorting the final form.

Preparation is not merely cosmetic; it is the functional prerequisite for accurate thermoplastic forming.

Summary Table:

Step Type	Physical Correction	Functional Benefit
Leveling	Removes "Stair-Step" ridges	Aligns geometry with intended design CAD
Stripping	Clears un-melted adhered powder	Prevents surface noise and contact interference
Smoothing	Creates uniform initial interface	Maximizes contact area for thermal bonding
Mirroring	Removes obstruction for BMG flow	Ensures accurate replication of mold textures

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References

Maximilian Frey, Ralf Busch. Thermoplastic forming of additively manufactured Zr-based bulk metallic glass: A processing route for surface finishing of complex structures. DOI: 10.1016/j.matdes.2020.109368

This article is also based on technical information from Kintek Press Knowledge Base .