On-Machine Estimation of Workpiece Deformation for Thin-Walled Parts Considering Fixture Clamping Sequence

Due to the higher structure efficiency and lightweight characteristic, thin-walled parts are widely used in the modern manufacturing industry. However, from another point of view, these parts are complex in structure, weak stiffness and high precision demand. During the machining process, because of the material properties and structural characteristics, the action of elastic deformation in machining is heavily affected by the accuracy of thin-walled parts. Recently, novel near-net-shape machining methods which can be applicable to small-lot production such as thin-walled casting, additive manufacturing, and so on becomes common technology. Finish machining of these thin-walled and complex shape workpiece is an important target of machining. In the small lot production, most of fixturing process is executed as manual operations, which generate large process variations. These variations lead to deteriorate machining accuracy. Especially, the wrong operation for the fixture clamping sequence generates different workpiece deformation. The objective of this research is to estimate actual workpiece deformation by utilizing locally measured strains and fixturing simulation in order to detect unallowable workpiece deformation caused by the wrong clamping sequence. In this research, workpiece deformations for different clamping sequences are evaluated based on the engineering experiments. Verifications of estimated workpiece deformations are carried out. Through this research, we can effectively estimate the workholding situation of the thin-walled parts during the machining process.

Numerical and experimental investigation of bulk stress distribution in edge under different clamping sequence

Purpose The edge is a typical aero-structural compliant part, whose length-width ratio is about 60:1 and height-thickness ratio is about 30:1. Distortion of the edge is mainly caused by the bulk stresses which come from the manufacturing process of the plates. This paper aims to investigate the effect of clamping sequence on the bulk stress distribution in the edge. Design/methodology/approach The paper conducts the numerical and experimental investigations to predict the bulk stress distribution in the edge under different clamping sequences. A finite element model of the plate with residual stress after quenching and stretching is constructed. The edge is milled from the plate numerically and is ready for clamping. The contact model between the clamper and the edge is constructed to simulate the clamping process. Then the edge is virtually clamped in different clamping sequences, and different deformations and bulk stresses are obtained. An experimental edge milled from the plate and a designed clamping platform are used to precisely control clamping force to verify the effect of clamping sequence on the bulk stress distribution in the edge. The experimental edge’s distortions, relative displacements between the edge and the clamper and clamping forces validate the proposed numerical model. Findings The primary cause of bulk stress redistribution is the friction between the rigid clamper and the compliant edge. The edge exhibits different deformation under different clamping sequences because of its compliant characteristics. Originality/value The proposed numerical model of the edge could predict the bulk stress distribution in the edge under different clamping sequence. The developed clamping platform could be used to conduct clamping experiments, including experiments with different clamping forces, sequences and different clamping positions. It will help to systematically improve the compliant assembling efficiency in civil aircraft industry.

Study on the Effect of Clamping Sequence on Bulk Stress Redistribution of Long Edge

For a given assembly process, fixture-related operations contribute to the dimensional variations of compliant part. When the manufactured components are within the specified tolerances, the bulk stresses distribution of the assembly are respected. In addition to fixture geometric errors and clamping forces, the clamping sequence can also affect part bulk stress redistribution. This paper presents a numerical simulation of bulk stress redistribution in a long edge assembling with different clamping sequences. A finite element model of the plate with residual stresses after quenching and stretching is constructed. The edge is milled from the numerical plate, and the edge with the initial deformation and residual stresses is ready for clamping. The contact model between the clamper and edge is constructed to simulate the practical clamping process, especially considering the friction contact between the clamper and edge. Then the edge is virtually clamped in different clamping sequences, and its deformation and bulk stresses are obtained. The simulation results show that there are differences in the stains of edge under different clamping sequences, and the edge’s bulk stresses under different clamping sequences are different with each other also. The proposed numerical model could predict the edge’s bulk stresses under different clamping sequences. It will help obtaining optimal stresses of the edge by certain clamping sequence, and help systematically improving the compliant assembling efficiency in civil aircraft industry.

An Approach to Determine Clamping Forces and Clamping Sequence of Thin-Walled Workpiece during Milling Process

The clamping force and clamping sequence in the process of thin-walled parts is an important factor affecting the quality of the workpiece. This article focused on solving the parts clamping force of the locating point and clamping sequence, according to the process of clamping force on the workpiece, by the means of screw theory and the minimum modulus principle, taking the contact friction into account, the article established a mathematical model. Furthermore, a new approach to optimize clamping and clamping sequence has been put forward combining Matlab optimization toolbox, which provided guidance basic theory for the preload design of the clamping process and flexible clamping. Finally a detailed discussion was conducted to the calculation of clamping force and clamping sequence by using some practical examples.

Needleless Connectors: Improving Practice, Reducing Risks

Purpose: To assess the knowledge gap of healthcare workers about practice with needleless connectors. Background: Catheter-related bloodstream infection (CR-BSI) and lumen occlusion can be directly related to practices of cleaning needleless connectors, IV administration set management, and flushing and clamping methods. Review of Relevant Literature: Five publications report outbreaks of CR-BSI from hospitals in the US and Australia. A significant increase in CR-BSI rates after an organizational change of products was observed. No randomized controlled trials are available from the USA comparing types or designs of needleless connectors. Device instructions state some devices can be locked with normal saline. Two randomized clinical trials assessed outcomes with catheter lock solution. Both reported higher rates of occlusion with the use of normal saline only and one documented a higher rate of CR-BSI. Methods: An invitation to participate in a survey with 22 questions was sent electronically to approximately 4000 healthcare workers with a response from 554 in clinical practice. Results: The specific type of needleless connector being used was unknown by 25% and correct clamping sequence was chosen by 52.8% of respondents. The majority, 94.3% reported that they always clean these devices before each use, however there are differences in technique. Conclusions: There is a significant gap of knowledge about the specific needleless connectors being used, the most appropriate cleaning, flushing, and clamping sequence for the specific device. Implications for Practice: Staff education should focus on the connections between needleless connectors, CR-BSI and lumen occlusion. Frequent product training on needleless connectors, the specific type in use and correct techniques are necessary.

Optimal Clamping Scheme of Thin-Walled Cavity Workpiece

The thin-walled cavity workpiece with insufficient rigid property is liable to deform during the machining process and the request of accuracy is very strict. The paper takes typical aeronautic aluminum-alloy for example, fixture is an important consideration in the operation. To reveal the influences of locating points, clamping sequence and loading ways on the distortion of thin-walled cavity part, finite element models were established to simulate the clamping operation. The result shows the preferable scheme is that the distance of the clamping locations are far each other, clamping forces are firstly applied on the surface with high rigid and all clamping forces are applied in many steps. The scheme can effectively control the deformation of clamp ,and furthermore improve the machining accuracy.

Optimization of the Clamping Scheme of the Aero Monolithic Component Based on Even-Bedded Residual Stress Distribution

Uneven distribution of the residual stress is the main factor causing the distortion of a workpiece. Different clamping scheme may cause different clamping stress. Clamping stress coupling with the residual stress inside the part induces different stress distribution, which affects components’ machining distortion and service life. To reflect the relationship between clamps and residual stress , finite element model with different clamping schemes were bulit and the clamping process was simulated. And the chip removal effect was taken into account using a material removal approach based on element death technique. Stress distribution in the workpiece is analyzed and compared under different clamping conditions. It is verified that clamping position has a significant effect on the residual stress. Otherwise the clamping sequence has a little effect on the stress redistribution.