Purpose: The purpose of this paper is to carry out an assembly tolerance analysis by means of a combined Jacobian model and skin model shape. The former is based on small displacements modeling of points using 6 × 6 transformation matrices of open kinematic chains in robotics. The latter easily models toleranced features with all kinds of geometric deviations. Design/methodology/approach: This paper presents the procedure of performing tolerance analysis by means of the Jacobian model and skin model shape for assemblies. The point cloud-based discrete representative is able to model the actual toleranced surfaces instead of the ideal or associated ones in an assembly, which brings the simulation tools closer to reality. Findings: The proposed method has the advantage of skin model shape which is suitable for geometric tolerances management along the product life cycle and contact analysis of kinematic small variations, as well as, with the Jacobian, enabling transformation of locally expressed parts deviations to globally expressed functional requirements. The result of the case study shows the accuracy of the method. Research limitations/implications: The proposed approach has not been developed fully; other functional features such as the pyramid are still ongoing challenges. Practical implications: It is an effective method for supporting design, manufacturing and inspection by providing a quantitative analysis of the effects of multi-tolerances on the final functional key characteristics and for predicting the quality level. Originality/value: The paper is original in taking advantages of both Jacobian model and skin model shape to consider all geometric tolerances in assembly.

Herein, a novel laser cladding process of hydraulic column based on Fe-based alloy is presented. The microstructure and properties of 27SiMn steel was used as the base material for the pillar of mining support after laser cladding overlapping and to improve its surface properties. The macroscopic appearance and microstructure of the samples were characterized by optical microscope, scanning electron microscope and EDS dispersive spectrometer. The hardness of the coating cross-section was measured with micro-hardness tester which concluded that the microstructure of single pass cladding layer is composed of columnar crystal and equiaxed crystal. Moreover, the microstructure of single-pass cladding layer is composed of columnar and equiaxed grains. After lapping, columnar grains become coarser and show various dendritic growth patterns and the boundary between the inner and outer layers of the cladding layer in the overlap zone was obvious which is related to the preheating and secondary thermal effect of the substrate. Moreover, the difference of microstructure between the inner and outer layers is obvious and the size of equiaxed grains in the inner layer of the cladding layer boundary is related to the thickness of the cladding layer attached to the surface. The inter-dendritic segregation exists in the overlap cladding layer and the average hardness of the cladding layer reaches to 668.1 HV, which is three times higher than that of the substrate.

Purpose: Long life and high hydrogen sensitivity are the crucial performance parameters for an optical fiber hydrogen sensing membrane, and these are the fundamental areas of study for an optical fiber hydrogen sensor. Considering that a traditional optical fiber hydrogen sensor based on pure palladium cannot meet the expectations for long life and rapid sensitivity simultaneously, the experiment in this paper designed a kind of reflective optical fiber bundle hydrogen gas sensor based on a Pd_0.75–Ag_0.25 alloy to achieve a hydrogen sensing system. This paper aims to discuss the issues with this system. Design/methodology/approach: A reflective optical fiber bundle hydrogen sensor was made up of an optical fiber bundle and a Pd_0.75–Ag_0.25 alloy hydrogen membrane. A combination of optical fiber light intensity measurements and the reference calculation method were used to extract the hydrogen concentration information from within the optical fiber, and the relationship between the hydrogen concentration changes and the reflective light intensity in the optical fiber was established. Findings: The reflective optical fiber bundle hydrogen gas sensor based on a Pd–Ag alloy membrane was shown to provide an effective way to detect hydrogen concentrations. The experimental results showed that a 20-30-nm-thick Pd_0.75–Ag_0.25 alloy membrane could reach high hydrogen absorption and sensitivity. Key preparation parameters which included sputtering time and substrate temperature were used to prepare the hydrogen membrane during the DC sputtering process, and the reflectivity of the Pd–Ag alloy membrane was enough to meet the requirements of long life and high hydrogen sensitivity for the optical fiber hydrogen sensor. Originality/value: This paper seeks to establish a foundation for optimizing and testing the performance of the Pd–Ag alloy hydrogen sensing membrane for an optical fiber bundle hydrogen sensor. To this end, the optimal thickness and key preparation parameters for the Pd–Ag alloy hydrogen sensing membrane were discussed. The results of this research have proved that the reflective optical fiber hydrogen sensor based on a Pd_0.75–Ag_0.25 alloy is an effective approach and precisely enough for hydrogen gas monitoring in practical engineering measurements.