Non-rigid Parts Research Articles

Inverse procedure for mechanical characterization of multi-layered non-rigid composite parts with applications to the assembly process

In assembly process, non-rigid parts in free-state may have different forms compared to the designed model caused by gravity load and residual stresses. For non-rigid parts made by multi-layered fiber-reinforced thermoplastic composites, this process becomes much more complex due to the nonlinear behavior of the material. This paper presented an inverse procedure for characterizing large anisotropic deformation behavior of four-layered, carbon fiber-reinforced polyphenylene sulphide, non-rigid composite parts. Mechanical responses were measured from the standard three points bending test and the surface displacements of composite plates under flexural loading test. An orthotropic hyperelastic material model was implemented as a UMAT user routine in the Abaqus/Standard to analyze the behavior of flexible fiber-reinforced thermoplastic composites. Error functions were defined by subtracting the experimental data from the numerical mechanical responses. Minimizing the error functions helps to identify the material parameters. These optimal parameters were validated for the case of an eight-layered composite material.

A Novel Model for the Tolerancing of Nonrigid Part Assemblies in Computer Aided Design

In the design step, the realistic modeling of the product represents an industrial requirement and a digital muck up (DMU) improvement. Thus, the tolerance integration in the computer aided design (CAD) model with the neglect of important physical factors, such as the components’ deformations during the mounting and assembly operation, causes a deviation between the numerical and the realistic models. In this regard, this paper presents a new model for the tolerance analysis of CAD assemblies based on the consideration of both manufacturing defects and deformations. The dimensional and geometrical tolerances are considered by the determination of assemblies’ configurations with defects based on the worst case tolerancing. The finite elements (FEs) simulation is realized with realistic models. An algorithm for updating the realistic mating constraints, between rigid and nonrigid parts, is developed. The case study of an assembly with planar and cylindrical joints is presented.

A novel approach to the inspection of deformable bodies by adapting the coherent point drift algorithm and using a clustering methodology

The dimensional and geometric inspection of non-rigid mechanical parts still presents a real challenge to the automotive and aerospace industry. Much research has been devoted to automating the inspection of these parts in order to eliminate the cost of specialized fixtures that cause productivity problems for manufacturers. A registration step between the part’31s nominal CAD model and its corresponding scan is required for an automatic inspection. The coherent point drift (CPD) is one of the existing algorithms for registration and is widely used in imaging applications. It has been recently adapted with regard to the mechanical field for the fixtureless dimensional inspection problems of deformable bodies, notably the IDB-ACPD algorithm. In this paper, an improvement of the optimization phase by reformulating the objective function of the algorithm is put forward. A correction matrix associated with the importance of each measurement point, and therefore with the local rigidity of the part during the registration operation, was introduced and incorporated. In addition, the measurement points representing the same rigidity have been clustered based on mechanical metrics using a fuzzy c-mean algorithm. The effectiveness of the proposed approach is demonstrated on different case studies from the transport industry and the results provide an improved registration of non-rigid parts leading to better dimensional and geometric errors detection.

Thermal power stabilization of shapes of non-rigid shafts

This article reviews the design of thermal power units for performing thermal operations of hardening and tempering of non-rigid parts of the “shaft” type. The authors describe the thermal power treatmenttechnology, the residual deformation analysis and the optimal conditionsdefinition. The units operation principles and algorithms are given.

Thermal power treatment of step shafts

This article reviews the design of thermal power units for performing thermal operations of hardening and tempering of non-rigid parts of the “shaft” type. The authors describe the thermal power treatment technology, the residual deformation analysis and the optimal conditions definition. The units operation principles and algorithms are given. The developed technology and the design of the frame for thermal operations make it possible to maintain accuracy throughout the term of the product use.

The processes of formation and reduction in technological residual deformations of non-rigid parts

The processes of formation and reduction in technological residual deformations of non-rigid parts

Suggestions of Define Methods by Rigid/Non-Rigid Parts’ Definitions

Defining and measuring non-rigid or flexible parts has been controversial in industry for many years. There are two primary areas of controversy. The first is agreeing on what exactly a non-rigid part is. The second is agreeing on how to define and measure a non-rigid part. The subject of non-rigid parts is further complicated by the brief coverage it receives in the national and international standards. This leaves each company to improvise or create its own rules for non-rigid parts. There are some who believe that Geometrical Dimensioning and Tolerancing (GD&T) should not be used on non-rigid parts. This is not true. The ASME Y14.5M standard applies to rigid parts as a default condition. However, there is no definition given for a rigid part. The term rigid part has been used in industry for so long that it has gained a definition by its general use. When most people in industry say rigid part, they are referring to a part doesn’t move (deform or flex) when a force (including gravity) is applied. How much force is relative based on the part characteristics. In reality, all parts will deform (or flex) if enough force is applied. Using this logic, all parts would be considered non-rigid. However, we all know that this is not how parts are treated in industry. Although GD&T defaults to rigid parts, it should also be used on non-rigid parts with a few special techniques. Actually 50~60% of all products designed contain parts or features on parts that are non-rigid. Therefore, we try to suggest the definitions of rigid and non-rigid parts and method to measure non-rigid parts.

CAD/tolerancing integration: a new approach for tolerance analysis of non-rigid parts assemblies

The tolerancing integration in CAD model is among the major interests of most mechanical manufacturers. Several researches have been established approaches considering the geometrical and dimensional tolerances on the CAD modelers. However, the hypothesis of rigid parts is adopted in the digital mock-up. Thus, several physical factors are neglected; especially the deformations. In this regard, this paper presents a model for considering both tolerances and deformations in CAD model. The dimensional and geometrical tolerances are taken into account by the determination of assemblies configurations with defects basing on the worst case tolerancing. The finite elements (FE) computations are realized with realistic models. A method for modeling the realistic mating constraints, between rigid and non-rigid parts, is developed. Planar and cylindrical joints are considered. The proposed tolerance analysis method is highlighted throughout two cases study: the first comprises planar joints and the second comprises cylindrical parts in motion.

Characterization of multilayered carbon-fiber–reinforced thermoplastic composites for assembly process

The aim of this research work is to characterize the mechanical behavior of multilayered carbon-fiber–reinforced polyphenylene sulfide composites with the application to assembly process of nonrigid parts. Two anisotropic hyperelastic material models were investigated and implemented in Abaqus as a user-defined material. An inverse characterization method was applied to identify the parameters of these material models. Finite element simulations at finite strains of a flexible composite sheet were carried out. Numerical results of sheet deformation were compared with the experimental results in order to evaluate the appropriateness of the material models developed for this application.

“What-if” scenarios towards virtual assembly-state mounting for non-rigid parts inspection using permissible loads

Recent developments in the fixtureless inspection of non-rigid parts based on computer-aided inspection (CAI) methods significantly contribute to diminishing the time and cost of geometrical dimensioning and inspection. Generally, CAI methods aim to compare scan meshes, which are acquired using scanners as point clouds from non-rigid manufactured parts in a free-state, with associated nominal computer-aided design (CAD) models. However, non-rigid parts are deformed in a free-state due to their compliance behavior. Industrial inspection approaches apply costly and complex physical inspection fixtures to retrieve the functional shape of non-rigid parts in assembly-state. Therefore, fixtureless inspection methods are developed to eliminate the need for these complex fixtures and to replace them with simple inspection supports. Fixtureless inspection methods intend to virtually (numerically) compensate for flexible deformation of non-rigid parts in a free-state. Inspired by industrial inspection techniques wherein weights (e.g., sandbags) are applied as restraining loads on non-rigid parts, we present a new fixtureless inspection method in this article. Our proposed virtual mounting assembly-state inspection (VMASI) method aims at predicting the functional shape (in assembly-state) of a deviated non-rigid part (including defects such as plastic deformation). This method is capable of virtually mounting the scan mesh of a deviated non-rigid part (acquired in a free-state) into the designed assembly-state. This is fulfilled by applying permissible restraining forces (loads) that are introduced as pressures on surfaces of a deviated part. The functional shape is then predicted via a linear FE-based transformation where the value and position of required restraining pressures are assessed by our developed restraining pressures optimization (RPO) approach. In fact, RPO minimizes the orientation difference and distance between assembly mounting holes on the predicted shape of a non-rigid part with respect to nominal ones on the CAD model. Eventually, the inspection is accomplished by examining the mounting holes offset on the predicted shape of the scan model concerning the nominal CAD model. This ensures that the mounting holes on the predicted shape of a scan model in assembly-state remain in the dedicated tolerance range. This method is evaluated on two non-rigid parts to predict the required restraining pressures limited to the permissible forces during the inspection process and to predict the eventual functional shape of the scan model. We applied numerical validations for each part, for which different types of synthetic (numerically simulated) defects are included into scan meshes, to determine whether the functional shape of a geometrically deviated part can be virtually retrieved under assembly constrains.

Non-rigid surface recovery with a robust local-rigidity prior

It is generally much harder to reconstruct the 3D structures of a non-rigid object than that of a rigid object, because of the increased degrees of freedom. To overcome the ill-posed nature of this problem, there have been many researches that incorporate prior assumptions on the object. An attractive approach is to assume the local parts to be rigid, because there might be a possibility to reduce some degrees of freedom that have to be estimated. Unfortunately, this assumption is not strictly true for general objects, and rigid and non-rigid parts are usually mixed in an object. This issue may be circumvented if we can utilize a robust local-rigidity prior to enforce rigidity on local parts selectively. In this paper, we provide a simple cost function that imposes a rigidity prior on each local triangular patch, and the proposed algorithm minimizes this cost to reconstruct a non-rigid surface. Non-rigid local parts are handled as outliers in the proposed algorithm, which makes the algorithm capable of reconstructing a near-locally-rigid surface that might contain a few non-negligible deformations. Experimental results show that the proposed method provides the state-of-the-art performance for well-known dense surface data sets.

Simulating robotic manipulation of cabling and interaction with surroundings

The manipulation of non-rigid parts, particularly cabling structures, such as the cable harness, raises various issues that require dealing with complex modeling. The first important issue is the prediction of the shape of flexible parts itself. Also, addressing collision detection problems is of high importance. However, both are computationally intensive problems, as well as coupled. More specifically, regarding modeling, the structure of a harness can affect the mechanics (regardless of whether it is modeled like a cable). In this paper, such phenomena have been taken into account. What is more, collision detection between cables and rigid bodies is performed, regarding a quasi-static approach. Furthermore, cable-cable interaction cases are also addressed with the herein presented algorithm. A methodology, based on the geometrical characteristics of a cable, is given, and illustration from implementation in a commercial software is discussed. The simulation of an industrial case of assembling cabling harness in automotive sector is used to prove the usability of the algorithm and the modeling.

A CAD Model for Tolerance Analysis of non-rigid Planar parts assemblies

Currently, the tolerancing integration in CAD model is among the major interests of most mechanical manufacturers. Several studies and researches have been established to consider the geometrical and dimensional tolerances on the CAD modelers. However, the hypothesis of rigid parts is adopted in the digital mock-up. Thus, several physical factors are neglected; especially the deformations. In this regard, this paper presents a model for considering both tolerances and deformations in CAD model. The dimensional and geometrical tolerances are taken into account by the determination of assemblies configurations with defects basing on the worst case tolerancing. The Finite Elements (FE) computations are realized with realistic models. A method for modeling the realistic mating constraints, between rigid and non-rigid parts, is developed. The case study of an assembly with planar joint is presented.

Revealing the technological modes range for ultrasonic surface hardening of cast iron

Prospects of using the ultrasonic surface hardening of different materials as a way of achieving a simultaneous strengthening and finishing effects are presented. It is shown that this method is applicable for non-rigid and brittle parts. Thus, it allows processing gray cast iron. Therefore, the paper is devoted to establishing technologically significant parameters of ultrasonic surface hardening of particular gray cast iron. Research was conducted using mathematical modeling of the process. According to the calculations, the application of the modes revealed makes it possible to achieve the depth of the hardened layer up to 2 mm. Moreover, the parameters of the hardened layer, such as the diameter of a single imprint and the maximum intensity of deformation for specified processing conditions are calculated.

Assessment of the Robustness of a Fixtureless Inspection Method for Nonrigid Parts Based on a Verification and Validation Approach

The increasing practical use of computer-aided inspection (CAI) methods requires assessment of their robustness in different contexts. This can be done by quantitatively comparing estimated CAI results with actual measurements. The objective is comparing the magnitude and dimensions of defects as estimated by CAI with those of the nominal defects. This assessment is referred to as setting up a validation metric. In this work, a new validation metric is proposed in the case of a fixtureless inspection method for nonrigid parts. It is based on using a nonparametric statistical hypothesis test, namely the Kolmogorov–Smirnov (K–S) test. This metric is applied to an automatic fixtureless CAI method for nonrigid parts developed by our team. This fixtureless CAI method is based on calculating and filtering sample points that are used in a finite element nonrigid registration (FENR). Robustness of our CAI method is validated for the assessment of maximum amplitude, area, and distance distribution of defects. Typical parts from the aerospace industry are used for this validation and various levels of synthetic measurement noise are added to the scanned point cloud of these parts to assess the effect of noise on inspection results.

New technologies of manufacturing non-rigid parts made of titanium alloys and stainless steels

The article considers a new approach to solving a topical scientific problem of providing dimensional stabilization of non-rigid aircraft parts made of titanium alloys and stainless steels. It is known that a significant loss of accuracy and a change in the spatial orientation of surfaces of non-rigid parts are associated with the formation of undesirable technological residual stresses in the surface layers. The authors of the work propose a method of reducing the magnitude of residual stresses in the surface layer of cylindrical parts by ultrasonic treatment with an indenter having strip contact with the workpiece. We present the results of experimental research aimed at eliminating the lengthy operation of thermal relaxation of residual stresses in the process of manufacturing non-rigid parts made of titanium alloys and stainless steels through the rational use of technological heredity phenomena and ultrasonic field energy. The developed method is highly efficient and can be used to stabilize dimensional accuracy of non-rigid and thin-walled parts made of hard-to-machine materials.

A robust and automated FE-based method for fixtureless dimensional metrology of non-rigid parts using an improved numerical inspection fixture

Dimensional inspection is an important element in the quality control of mechanical parts that have deviations from their nominal (CAD) model resulting from the manufacturing process. The focus of this research is on the profile inspection of non-rigid parts, which are broadly used in the aeronautic and automotive industries. In a free-state condition, due to residual stress and gravity loads, a non-rigid part can have a different shape compared with its assembled condition. To overcome this issue, specific inspection fixtures are usually allocated in industry to compensate for the displacement of such parts in order to simulate the use state and accomplish dimensional inspections. These dedicated fixtures, their installation and the inspection process consume a large amount of time and cost. Therefore, our principal objective has been to develop an inspection plan for eliminating the need for specialised fixtures by digitizing the displaced part’s surface using a contactless (optical) measuring device and comparing the acquired point cloud with the CAD model to identify deviations. In our previous work, we developed an approach to numerically inspect the profile of a non-rigid part using a non-rigid registration method and finite element analysis. To do so, a simulated displacement was performed using an improved definition of boundary conditions for simulating unfixed parts. In this paper, we will improve on the method and save time by increasing the accuracy of displacement boundary conditions and using automatic node insertion and finite element analysis. The repeatability and robustness of the approach will be also studied, and its metrological performance will be analysed. We will apply the improved method on two industrial non-rigid parts with free-form surfaces simulated with different types of displacement, defect and measurement noise (for evaluation of robustness).

Combined finish machining of nonrigid parts by the brush electrode

AnnotationThe capacities of extensive use of technology and a combined machining tool by an unshaped brush electrode are discovered. This type of machining occurs during dimensional finish formation of composite parts of small rigidity (including the parts made of difficult-to-machine materials). This process takes place provided that there is required pressure of wire beams in the brush electrode and a combination of electrical modes of the process with tool parameters. The ways of maintaining the process stability, increasing technological parameters, which allows extending the application field of universal high-productive finish machining by an electrode, are presented. This problem has been solved for the first time, and its results make it possible to create items of new generations, which is actual for machine building

Automatic fixtureless inspection of non-rigid parts based on filtering registration points

Computer-aided inspection (CAI) of non-rigid parts significantly contributes to improving performance of products, reducing assembly time and decreasing production costs. CAI methods use scanners to measure point clouds on parts and compare them with the nominal computer-aided design (CAD) model. Due to the compliance of non-rigid parts and for inspection in supplier and client facilities, two sets of sophisticated and expensive dedicated fixtures are usually required to compensate for the deformation of these parts during inspection. CAI methods for fixtureless inspection of non-rigid parts aim at scanning these parts in a free-state for which one of the main challenges is to distinguish between possible geometric deviation (defects) and flexible deformation associated with free-state. In this work, the generalized inspection fixture (GNIF) method is applied to generate a prior set of corresponding sample points between CAD and scanned models. These points are used to deform the CAD model to the scanned model via finite element non-rigid registration. Then, defects are identified by comparing the deformed CAD model with the scanned model. The fact that some sample points can be located close to defects results in an inaccurate estimation of these defects. In this paper, a method is introduced to automatically filter out sample points that are close to defects. This method is based on curvature and von Mises stress. Once filtered, the remaining sample points are used in a new registration, which allows identifying and quantifying defects more accurately. The proposed method is validated on aerospace parts.

Fixtureless profile inspection of non-rigid parts using the numerical inspection fixture with improved definition of displacement boundary conditions

Quality control is an important factor for manufacturing companies looking to prosper in an era of globalization, market pressures, and technological advance. The functionality and product quality cannot be guaranteed without this important aspect. Manufactured parts have deviations from their nominal (CAD) shape caused by the manufacturing process. Thus, geometric inspection is a very important element in the quality control of mechanical parts. We have focused here on the profile inspection of non-rigid parts which are widely used in the aeronautic and automotive industries. Non-rigid parts can have different forms in a free-state condition compared with their nominal models due to residual stress and gravity loads. To solve this problem, dedicated inspection fixtures are generally used in industry to compensate for the displacement of such parts for simulating the use state in order to perform geometric inspections. These fixtures and the inspection process are expensive and time-consuming. Our aim is therefore to develop an inspection method which eliminates the need for specialized fixtures by acquiring a point cloud from the displaced part using a contactless measuring system such as optical scanning and comparing it with the CAD model for the identification of deviations. Using a non-rigid registration method and finite element analysis, we will numerically inspect the profile of a non-rigid part. To do so, a simulated displacement is performed using an improved definition of boundary conditions for simulating unfixed parts. In this paper, we will apply an improved method on two industrial non-rigid parts with free-form surfaces simulated with different types of displacement, defect, and measurement noise.