Volumetric adaptive slicing of manifold mesh for rapid prototyping based on relative volume error

Purpose Compared with cusp height and area deviation ratio, volume error (VE) caused by the layer height could represent the stair-case effect more comprehensively. The proposed relative volume error (RVE)-based adaptive slicing method takes VE rather than cusp height as slicing criteria, which can improve part surface quality for functionalized additive manufacturing. Design/methodology/approach This paper proposes a volumetric adaptive slicing method of manifold mesh for rapid prototyping based on RVE. The pre-height sequences of manifold mesh are first preset to reduce the SE by dividing the whole layer sequence into several parts. A breadth-first search-based algorithm has been developed to generate a solid voxelization to get VE. A new parameter RVE is proposed to evaluate the VE caused by the sequence of the layer positions. The RVE slicing is conducted by iteratively adjusting the layer height sequences under different constraint conditions. Findings Three manifold models are used to verify the proposed method. Compared with uniform slicing with 0.2 mm layer height, cusp height-based method and area deviation-based method, the standard deviations of RVE of all three models are improved under the proposed method. The surface roughness measured by the confocal laser scanning microscope proves that the proposed RVE method can greatly improve part surface quality by minimizing RVE. Originality/value This paper proposes an RVE-based method to balance the surface quality and print time. RVE could be calculated by voxelized parts with required accuracy at a very fast speed by parallel.

A novel adaptive slicing algorithm based on ameliorative area ratio and accurate cusp height for 3D printing

Purpose Adaptive slicing is a key step in three-dimensional (3D) printing as it is closely related to the building time and the surface quality. This study aims to develop a novel adaptive slicing method based on ameliorative area ratio and accurate cusp height for 3D printing using stereolithography (STL) models. Design/methodology/approach The proposed method consists of two stages. In the first stage, the STL model is sliced with constant layer thickness, where an improved algorithm for generating active triangular patches, the list is developed to preprocess the model faster. In the second stage, the model is first divided into several blocks according to the number of contours, then an axis-aligned bounding box-based contour matching algorithm and a polygons intersection algorithm are given to compare the geometric information between several successive layers, which will determine whether these layers can be merged to one. Findings Several benchmarks are applied to verify this new method. Developed method has also been compared with the uniform slicing method and two existing adaptive slicing methods to demonstrate its effectiveness in slicing. Originality/value Compared with other methods, the method leads to fewer layers whilst keeping the geometric error within a given threshold. It demonstrates that the proposed slicing method can reach a trade-off between the building time and the surface quality.

On the evolutionary advantage of multi-cusped teeth

A hallmark of mammalian evolution is a progressive complexity in postcanine tooth morphology. However, the driving force for this complexity remains unclear: whether to expand the versatility in diet source, or to bolster tooth structural integrity. In this study, we take a quantitative approach to this question by examining the roles of number, position and height of multiple cusps in determining sustainable bite forces. Our approach is to use an extended finite-element methodology with due provision for step-by-step growth of an embedded crack to determine how fracture progresses with increasing occlusal load. We argue that multi-cusp postcanine teeth are well configured to withstand high bite forces provided that multiple cusps are contacted simultaneously to share the load. However, contact on a single near-wall cusp diminishes the strength. Location of the load points and cusp height, rather than cusp number or radius, are principal governing factors. Given these findings, we conclude that while complex tooth structures can enhance durability, increases in cusp number are more likely to be driven by the demands of food manipulation. Structural integrity of complex teeth is maintained when individual cusps remain sufficiently distant from the side walls and do not become excessively tall relative to tooth width.

A polygons Boolean operations-based adaptive slicing with sliced data for additive manufacturing

In order to increase the efficiency of additive manufacturing, this paper proposes a novel adaptive slicing approach of sliced data with minimum thickness based on Boolean operations of polygons. It can greatly handle the balance between the build time and the surface precision of additive manufacturing. The proposed adaptive slicing is available for the single solid model, the support of additive manufacturing, and simultaneously manufactured multiple models. At first, the Boolean operations of polygons are used to gain the relationship of the adjacent layers to serve as the topological information. Second, two parameters are proposed to evaluate the precision of sliced surface: the ameliorative area ratio and variation of the cusp height. Ameliorative area ratio overcomes the drawbacks of original area deviation ration criteria and can work on the large and complex models. Variation of the cusp height makes the calculation of cusp height suitable for sliced data of model, and it is independent of the normal vector of surfaces. Third, the adaptive slicing is realized by removing unnecessary layers based on two parameters and the maximum allowable thickness. The thicknesses are times of the minimum thickness. Moreover, the adaptive slicing for support of additive manufacturing is developed through dividing the support into two parts according to its height and location. Slicing of multiple models is also proposed by choosing the maximum ameliorative area ratio and variation of the cusp height among all models in the same z level as the two parameters. Finally, the adaptive slicing for the three types is tested with some special models, and corresponding models are printed with FDM technology based on slicing results of the proposed approach. Results show that the proposed adaptive slicing approach is effective.

Volumetric Error Control in Layered Manufacturing

This paper presents a novel method for adaptive slicing based on volumetric error considerations for Layered Manufacturing (LM). In the general LM process uses constant layer thickness throughout the part height which leads to poor surface finish at inclined surfaces. Therefore, adaptive slicing was proposed to control the surface roughness by adaptively selecting the layer thickness based on surface finish at a particular angle or slope of the surface. Most of the researchers used the cusp height concept for adaptive slicing. However, limitation of cusp height based adaptive slicing procedure is that, it does not have any direct control on volumetric error and it is quite possible that with a very little variation in cusp height a large variation in volumetric error may occur on steep slopes of surface. In the proposed work an algorithm is developed and implemented for adaptive slicing to control/select layer thickness based on user specified volumetric error/loss. A model is developed to calculate volumetric loss for the particular layer considering the geometry of the model.

Method to Decide Paths and Postures of Flat End Mill for 5-Axis Control Machining Based on Minimum Cusp Height

Generally, ball end mills are used for free-form surface machining. When machining curved surfaces with large curvature change using ball end mills, it is necessary to use tools with larger curvature of the cutting edges than the maximum curvature of the surface and minute pick feeds or to change tools for fitting the curvature of one part of the surface. However this causes poor machining efficiency. The curvature of the cutting edge of a flat end mill can be fitted to the curvature of a point on machined surfaces by adjusting the tool posture. Therefore, flat end mills can efficiently cut almost all curvature curved surfaces without tool change. This paper proposes two methods for deciding tool posture and tool path for 5-axis control machining based on minimum cusp height. To decide the tool path, one method defines tool paths along isoparametric curved lines, while the other defines tool paths along curved lines along the minimum curvature direction. The basic system was constructed based on the proposed method, and the effectiveness of the proposed method was verified.

Profile Tolerance Allocation for Rapid Prototyping of Sculptured Surfaces in a Direct Slicing Process

Layer-based manufactured parts and surfaces are inherently subject to stair case effect which can be quantified by cusp height. Cusp height of a layer is the maximum distance measured along a surface normal between the ideal surface and the produced layer. Although calculation of local cusp high is a simple task but estimating the overall deviation zone of the produced surface is a highly nonlinear and complicated problem. This paper presents a practical approach to predict the actual profile tolerances of the surfaces. This prediction is used to allocate profile tolerances for the rapid prototyping process. Also the methodology can be used to select the optimum uniform layer thicknesses that compromise between the number of layers and the desired accuracy of the final surfaces. The unified developed methodologies are capable to analyse complex surfaces and geometries. Variety of experiments is carried out to study the effectiveness and practicality of the presented methodology. The developed methodology can be employed efficiently during design of rapid prototyping parts.