Analytical Investigation of Roller Skew and Tilt in a Spherical Roller Bearing

The objective of this investigation was to analytically investigate the performance of a spherical roller bearing operating under various loading and speed combinations. In order to achieve the objective, a full six degree of freedom spherical roller bearing dynamic model was developed. The model was corroborated with results in open literature. An adaptive slicing method was developed to optimize the accuracy and computational effort of the roller force, skew, and tilt calculations. A comprehensive roller-race contact analysis in terms of slip velocity and contact area was then carried out to identify how bearing load and inner race speed variations change slip velocity and skew at the roller-race contact. The results from this investigation demonstrate that roller skew increases with inner race speed, while the roller tilt remains relatively constant. The inner race speed and roller slip velocity correlate well, which causes the traction force to increase and therefore produce greater skew. Skew and tilt angles also increase with applied axial load. However, at a certain load the skew angle begins to decrease.

Slicing strategy and process of laser direct metal deposition (DMD) of the inclined thin-walled part under open-loop control

Purpose The purpose of this paper is to improve the dimensional accuracy of inclined thin-walled parts fabricated by laser direct metal deposition (DMD) under an open-loop control system. Design/methodology/approach In this study, a novel method of the adaptive slicing method and DMD process with feedback adjustment of deposition height has been developed to successively fabricate complex inclined thin-walled square tube elbow parts. The defocus amount was used as a variable to the matching between the deposition thickness and the adaptive slicing height. Findings The low relative error of dimensional accuracy between experimental and designed parts shows that the matching of the single-layer deposition thickness and the adaptive slicing height can be realized by optimizing the defocusing amount. The negative feedback of the thin-wall part height can be achieved when the defocus amount and the z-axis increment are less than deposition thickness. The improvement of dimensional accuracy of inclined thin-walled parts is also attributed to the optimized scanning strategy. Practical implications The slicing method and deposition process can provide technical guidance for other additive manufacturing (AM) systems to fabricate metal thin-walled parts with high dimensional accuracy because the feedback control of deposition height can be realized only by the optimized process. Originality/value This study provides a novel adaptive slice method and corresponding the deposition process, and expands the slicing method of AM metal parts.

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.

Smart-cut-like laser slicing of GaN substrate using its own nitrogen

We have investigated the possibility of applying lasers to slice GaN substrates. Using a sub-nanosecond laser with a wavelength of 532 nm, we succeeded in slicing GaN substrates. In the laser slicing method used in this study, there was almost no kerf loss, and the thickness of the layer damaged by laser slicing was about 40 µm. We demonstrated that a standard high quality homoepitaxial layer can be grown on the sliced surface after removing the damaged layer by polishing.

Parametric point-cloud slicing for facade retrofitting

This work presents a method for retrieving 3D building contours usable in facade retrofitting projects, which uses a parametric modeling workflow that utilizes a point-cloud slicing method to retrieve such 3D contours. Since current commitments by European governments seek to reduce energy consumption as a means to reduce carbon emissions from building stock by 2050, facade retrofitting appears as an alternative for addressing operational and embedded building emissions. Within such a context, the main contribution of this work consists of a workflow and a 3D reconstruction solution that uses a parametric environment for capturing building topology and bypassing ground-level occlusions. A real case study and a strategy for converting 3D building contours into Industry Foundation Classes entities, directly from the parametric modeling environment, served as a scenario for testing the capabilities of a Grasshopper solution and open new perspectives for this approach.

Tracking linear deformable objects using slicing method

In this paper, an efficient novel method for tracking the linear deformable objects (LDOs) in real time is proposed. The method is developed based on recursively slicing a pointcloud into smaller pointclouds with sufficiently small variance. The performance of this method is investigated through a series of experiments with various camera resolutions in simulation when a robot end effector tracking an LDO using an RGBD camera, and in real word when the camera tracks a rope during a swing. The performance of the proposed method is compared with another state-of-the-art technique and the outcome is reported here.