Toward Support-Free 3D Printing: A Skeletal Approach for Partitioning Models

Abstract

Minimizing support structures is crucial in reducing 3D printing material and time. Partition-based methods are efficient means in realizing this objective. Although some algorithms exist for support-free fabrication of solid models, no algorithm ever considers the problem of support-free fabrication for shell models (i.e., hollowed meshes). In this paper, we present a skeleton-based algorithm for partitioning a 3D surface model into the least number of parts for 3D printing without using any support structure. To achieve support-free fabrication while minimizing the effect of the seams and cracks that are inevitably induced by the partition, which affect the aesthetics and strength of the final assembled surface, we put forward an optimization system with the minimization of the number of partitions and the total length of the cuts, under the constraints of support-free printing angle. Our approach is particularly tailored for shell models, and it can be applicable to solid models as well. We first rigorously show that the optimization problem is NP-hard and then propose a stochastic method to find an optimal solution to the objectives. We propose a polynomial-time algorithm for a special case when the skeleton graph satisfies the requirement that the number of partitioned parts and the degree of each node are bounded by a small constant. We evaluate our partition method on a number of 3D models and validate our method by 3D printing experiments.

Object Partitioning for Support‐Free 3D‐Printing

“…More specifically, we learned the probabilities to select each procedure, P base , P tip , P T , as well as a fourth option of randomly sampling a cutting‐plane P rand , and performing additional calls within a recursion level, P call and q . This fourth option is added for the purpose of comparing our geometry‐derived planes with the random planes current methods use [YYT*17, WQZ*18]. We make this sampling more cost‐effective by limiting the distribution of the planes offset to the objects extents (while their orientation is uniformly sampled from the unit sphere).…”

“…The method in [WQZ*18] guarantees the printability of the decomposed skeleton, however this method also focuses on printing shell models. The latter leads to an increase in the geometric complexity of the models, and hence this method produces a higher object count.…”

“…In comparison to both these works, our method performs considerably less plane‐cuts, which is the most time‐consuming step. Wei et al [WQZ*18] explore 8k skeletal partitions, and to evaluate each one, do many plane‐cuts. Yu et al [YYT*17] carry out 2.5k fitness evaluations, each consisting of a few object‐plane cuts.…”

“…Wei et al [WQZ*18] focus on locally‐cylindrical shell‐models which they model as a graph based on the object skeleton that they compute. Partitioning is then found through a stochastic search in which a random vertex in the graph is selected and a planar cut perpendicular to its edges is considered.…”

“…The restriction to pyramidal hulls leads to a higher number of subparts than needed as existing printers are capable of printing protrusions with a slope up to 150°. Wei et al [WQZ*18] concentrate on shell models and derive a randomized skeleton‐based algorithm that is applicable to locally‐cylindrical objects. Yu et al [YYT*17] operate on general meshes by also searching the partitioning via a randomized search.…”