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Shrinkage, Water Absorption, and Expansion Characteristics of 3D-Printed Products

Introduction

In addition to appearance and strength, understanding the dimensional stability of 3D-printed products is crucial when developing precision prototypes. Product shrinkage, material water absorption, and expansion after water absorption are three key physical properties that influence dimensional accuracy. Although the website article you provided focuses primarily on the application characteristics of each process and does not provide specific physical data, we can understand the relevant characteristics by looking at the principles of these processes.

Detailed Explanation of Dimensional Stability of Products by Various Processes

Stereolithography (SLA)
The core of SLA technology is the chemical curing reaction of liquid photosensitive resin. During this process of transitioning from liquid to solid, the molecular chains rearrange and draw closer together, resulting in volumetric shrinkage. Professional industrial-grade SLA equipment and slicing software precisely compensate for shrinkage before printing to minimize this effect, which is one of the reasons SLA can achieve such high precision. However, after printing, SLA resin products can still absorb trace amounts of water if exposed to moisture for extended periods, which can cause very subtle dimensional changes.

Fused Deposition Modeling (FDM)

FDM uses thermoplastics, which are melted by heating and then cooled and stacked. During this thermal expansion and contraction process, shrinkage is the most significant characteristic. Especially for materials like ABS, uneven shrinkage is often the main cause of part warping and lifting from the build platform. Furthermore, many FDM materials (such as ABS, Nylon, and PETG) are hygroscopic, absorbing moisture from the air. Damp filament not only affects print quality, but also causes slight dimensional expansion of the printed part in a humid environment due to moisture absorption.

Selective Laser Sintering (SLS)

SLS primarily uses nylon (PA) powder. Similar to FDM, SLS is a high-temperature molding process. When the sintered part is removed from the hot powder vat and cools to room temperature, it also experiences volumetric contraction. Professional SLS equipment takes this shrinkage into account to ensure the accuracy of the final product. Nylon itself is a highly hygroscopic engineering plastic. SLS finished products gradually absorb moisture upon contact with air until they reach equilibrium with the environment. This moisture absorption process causes a slight dimensional expansion, while also increasing the material’s toughness and slightly decreasing its hardness.

Key Concepts

Shrinkage: refers to the percentage decrease in volume or linear dimensions of a material during the cooling process after molding. This is a physical phenomenon common to all thermal processes.

Water Absorption: refers to the ability of a material to absorb water at a specific temperature and humidity.

Expansion: primarily refers to the dimensional increase in a material due to water absorption or temperature changes.

Conclusion

In summary, all 3D printing processes involve a certain degree of shrinkage during the molding process, which professional manufacturers compensate for through software and process control. Furthermore, many engineering-grade printing materials (particularly nylon) absorb moisture, causing the finished product to slightly expand in a humid environment. When validating designs that require extremely precise fits, it is important to take the physical properties of these materials into account and ensure that samples have been adequately conditioned in a stable environment before testing.