Assembly Tolerances Research Articles

Simulation and Analysis of Water Pump Bearing Assembly Based on ANSYS

Finite element analysis has been done to analyze pump bearing assembly in interference assembly condition by ANSYS software. The press-in assembly environment has been simulated, and the maximum stress and maximum deformation of inner race have been analyzed. Studies show that with the increase of bearing size, the change law of maximum stress and maximum deformation does not single unidirectionally increase or decrease simply. At the same time, the interference value also influences the change law. So, in the bearing assembly tolerance selection the influence of the interference must be considered fully. The finite element analysis can guide the selection of fit tolerance.

Assembly Operation Optimization Based on Social Radiation Algorithm for Autobody

Assembly dimensional quality affects wind noise and driving steady and whole external appearance. The quality can be improved by reducing part tolerance and fixture tolerance and optimizing key control characteristics (KCCs). However, reducing tolerance should largely increase manufacturing costs, and then the paper assembly tolerance is decreased by selecting optimal KCCs. In this work, a fitness function is presented to evaluate assembly operations based on the linear assembly variation analysis model. Afterwards, a new social radiation algorithm (SRA) is proposed to optimize KCCs, and some test functions are used to evaluate optimum performance between the genetic algorithm (GA) and SRA, and the results show that the performance of SRA is better than that of GA. Finally two cases are used to illustrate process of assembly operation optimization by SRA, and the results show that the SRA has higher precision and efficiency than that of GA.

Dynamic Alignment Control Using Depth Imagery for Automated Wheel Assembly

This paper presents a novel method for dynamic alignment control using infrared light depth imagery to enable automated wheel loading operation for the trim and final automotive assembly line. A key requirement for automated wheel loading is to track the motion of the wheel hub and simultaneously identify the spatial positions and angular orientations of its alignment features in real-time on a moving vehicle body. This requirement is met in this work, where low-cost infrared depth-imaging devices like Microsoft Kinect™ and Asus Xtion™, vastly popular in the gaming industry, are used to track a moving wheel hub and recognise alignment features on both the wheel hub and the wheel in real time in a laboratory environment. Accurate control instructions are then computed to instruct the automation system to rotate the wheel to achieve precise alignment with the wheel hub and load the wheel at the right time. Experimental results demonstrate that the reproducibility error in alignment control satisfies the assembly tolerance of 2mm for the wheel loading operation, and thus the proposed method can be applied to automate wheel assembly on the trim and final automotive assembly line. The novelty of this work lies in its use of depth imaging for dynamic alignment control, which provides real-time spatial data in all 3 axes simultaneously as against the popularly reported RGB imaging techniques that are computationally more demanding, sensitive to ambient lighting and require the use of additional force sensors to obtain depth axis control data. This paper demonstrates the concept of a light-controlled factory where depth imaging using infrared light and depth image analysis is used to enable intelligent control in automation.

Optimizing Multi Characteristics in Drilling of GFRP Composite Using Utility Concept with Taguchi's Approach

In the drilling process of chopped glass fibre reinforced polyester composites; the delamination is a major problem. The delamination reduces the structural integrity of the material, results in poor assembly tolerance and has the potential for long term performance deterioration. Surface roughness is also an important aspect of drilling fibre reinforced polyester which can cause high stress on rivets and bolts, leading to failure. In the modern competitive manufacturing scenario, it is very important to optimize the process parameters to arrive at its full utility. In this present study the utility concept has been applied for multi characteristics optimization and identification of the optimal setting condition of process parameters at various relative weightage values of characteristics. Delamination factor and average surface roughness were taken as the measure of performances for this material and feed rate (f), drill diameter (D), spindle speed (N) and material thickness (t) were chosen as drilling parameters. Experiments were conducted based on Taguchi L9 (34) orthogonal array design. Analysis was performed based on utility method varying the importance of quality characteristics or responses in drilling process. The optimal setting of parameters is expected to be useful for process engineers.

Design and optimisation of assembly technique for auto-body components

The dimensional quality of auto-body relates to the whole external appearance, wind noise, the effect of closing the door and even driving smoothness of vehicles. The assembly dimensional quality can be improved by optimising assembly operations between parts and reasonable allocating tolerances of components. A multi-attribute directed liaison graph is proposed to describe precedence relationships and key control characteristics (KCCs) to eliminate unfeasible assembly sequences. A hybrid particle swarm optimisation and genetic algorithm is presented to optimise assembly operations for selecting the best assembly sequence. Based on the above, tolerances of the optimal KCCs are designed by using NSGA-II algorithm according to assembly tolerances and manufacturing costs. To improve optimisation effectiveness, the initial population uses the orthogonal experimental design and sensitivity coefficients of KCCs to generate chromosomes. Finally, the work applied the method by illustrating the process of assembly sequence optimisation and tolerance allocation, and the results show that this case verified the proposed method.

Constructing a meta-model for assembly tolerance types with a description logic based approach

There is a critical requirement for semantic interoperability among heterogeneous computer-aided tolerancing (CAT) systems with the sustainable growing demand of collaborative product design. But current data exchange standard for exchanging tolerance information among these systems can only exchange syntaxes and cannot exchange semantics. Semantic interoperability among heterogeneous CAT systems is difficult to be implemented only with this standard. To address this problem, some meta-models of tolerance information supporting semantic interoperability and an interoperability platform based on these meta-models should be constructed and developed, respectively. This paper mainly focuses on the construction of a meta-model for assembly tolerance types with a description logic ALC(D) based approach. Description logics, a family of knowledge representation languages for authoring ontologies, are well-known for having rigorous logic-based semantics which supports semantic interoperability. ALC(D) can provide a formal method to describe the research objects and the relations among them. In this formal method, constraint relations among parts, assembly feature surfaces and geometrical features are defined with some ALC(D) assertional axioms, and the meta-model of assembly tolerance types is constructed through describing the spatial relations between geometrical features with some ALC(D) terminological axioms. Besides, ALC(D) can also provide a highly efficient reasoning algorithm to automatically detect the inconsistency of the knowledge base, a finite set of assertional and terminological axioms. With this reasoning algorithm, assembly tolerance types for each pair of geometrical features are generated automatically through detecting the inconsistencies of the knowledge base. An application example is provided to illustrate the process of generating assembly tolerance types.

Closed-form solutions for multi-objective tolerance optimization

Component tolerances have important influence on the cost and performance of products. In order to obtain suitable component tolerances, multi-objective tolerance optimization model is studied, in which the combined polynomial and exponential functions are used to model manufacturing cost. In this paper, analytical methods are proposed to solve the multi-objective optimization model. In this model, the objective function is not a monotone function, and it is possible that the assembly tolerance constraint, including worst-case method and root sum square method, is inactive. Therefore, two closed-form solutions are proposed for each component tolerance in terms of the Lambert W function. When the assembly tolerance constraint is not considered, the component tolerances are obtained and named as the initial closed-form solutions. If the initial solutions satisfy assembly tolerance constraint, it is the final value of optimal tolerances. Otherwise, constrained optimization model is established and Lagrange multiplier method is applied to obtain the new closed-form solution of component tolerances as the final value of optimal tolerances. Several simulation examples are used to demonstrate the proposed method.

Probe alignment and design issues of microelectromechanical system based optical coherence tomography endoscopic imaging

Endoscopic optical coherence tomography (OCT) imaging has been demonstrated using microelectromechanical system (MEMS) technology by several research groups. The focus of this work is to study how the OCT imaging performance is affected by the radius of curvature of MEMS mirrors as well as the optical alignment accuracy inside small imaging probes. The goal of this study is to provide guidance for assembly tolerance and design optimization of OCT endoscopic probes. Gaussian beam propagation is used for theoretical analysis which is confirmed by optical simulation and verified experimentally with a time-domain OCT system as well. It has been found that the OCT imaging is very sensitive to the distance from the fiber end to the gradient-index (GRIN) lens, which needs to be controlled within 0.1 mm to achieve working distance (WD) longer than 3.5 mm and lateral resolution around 25 μm. The impact on image quality of the MEMS mirror is negligible if the radius of curvature of the mirror surface is greater than 200 mm. In addition, we studied the astigmatism introduced by cylindrical plastic tubing; the maximum astigmatism ratio is 1.1 when the WD is around 2.5 mm.

Mathematical Model for Assembly Tolerance Consistence Evaluation

An assembly is described by a geometric model of its parts and their relative placement. Assembly tolerances are the result of parts of varying shape and size being put together to make the finished product. This paper considers the case where parts have tolerance geometry. Its main contribution is to use a tensor space to describe assembly features. The mathematical models are developed. The proposed approach is based on assembly feasibility analysis of shaft and hole features.

Enhanced Groove Geometry for Herringbone Grooved Journal Bearings

Although gas-lubricated herringbone grooved journal bearings (HGJB) are known for high rotordynamic stability thresholds, small clearance to diameter ratios are required for stable rotor operation. Tight clearances not only increase bearing losses but also yield challenging manufacturing and assembly tolerances, which ultimately translate into cost. Traditionally, the grooves of HGJB are of helical nature with constant cross section and pitch. The current paper aims at increasing the clearance to diameter ratio and the stability threshold of grooved bearings by introducing enhanced groove geometries. The axial evolution of groove width, depth, and local pitch are described by individual third order polynomials with four interpolation points. The expression for the smooth pressure distribution resulting from the narrow groove theory is modified to enable the calculation of bearing properties with modified groove patterns. The reduced order bearing model is coupled to a linear rigid body rotordynamic model for predicting the whirl speed map and the corresponding stability. By introducing a critical mass parameter as a measure for stability, a criterion for the instability onset is proposed. The optimum groove geometry is found by coupling the gas bearing supported rotor model with a multiobjective optimizer. By maximizing both the clearance to diameter ratio and the rotordynamic stability it is shown that with optimal groove geometry, which deviates from helicoids with constant pitch and cross section, the critical mass parameter can be improved by more than one order of magnitude compared to traditional HGJB geometries. The clearance to diameter ratio can be increased by up to 80% while keeping the same stability margin, thus reducing both losses and manufacturing constraints. The optimum groove pattern distributions (width ratio, angle, and depth) are summarized for a variety of L/D ratios and for different compressibility numbers in a first attempt to set up general design guidelines for enhanced gas-lubricated HGJB.

An assembly tolerance representation model based on spatial relations for generating assembly tolerance types

The main advantage of polychromatic sets-based assembly tolerance representation model is that the number of feature types to be processed is larger. However, the number of recommended assembly tolerance types generated by the model is somewhat large for the same feature surfaces. Furthermore, the model cannot be directly applied to further assembly tolerance analysis and synthesis due to the fact that the information of degrees of freedom cannot be processed in polychromatic sets. To further reduce the number of recommended assembly tolerance types and to lay foundation for further assembly tolerance analysis and synthesis, a spatial relation layer is introduced into the polychromatic sets-based model and an assembly tolerance representation model based on spatial relations for generating assembly tolerance types is proposed. The proposed model is hierarchically organized and consists of part layer, assembly feature surface layer, spatial relation layer and assembly tolerance type layer. Each layer is defined with an adjacency matrix, respectively. By the mapping from spatial relations to assembly tolerance types, the number of recommended assembly tolerance types generated by the mapping from feature surfaces to assembly tolerance types is able to be further reduced. In addition, the information of degrees of freedom can be attached in the elements of adjacency matrices when recommended assembly tolerance types are generated by spatial relations so that the proposed model can be directly applied to further assembly tolerance analysis and synthesis. The effectiveness of the proposed model is demonstrated by an approach for generating assembly tolerance types and a practical example.

Application of the Jacobian–torsor theory into error propagation analysis for machining processes

The Jacobian–torsor theory is used to provide mathematical models of tolerance analysis, establishing a mathematical relationship between the open loop and closed loop of tolerances. The model allows additional chain of torsors joining them. So it is easy to model new ones. Therefore, the ability to calculate the end tolerance of assembly is useful in error propagation analysis. This paper formulates the error propagation model based on the Jacobian–torsor theory. With this theory, workpiece, fixtures, machine tool, and tool are regarded as an assembly. As a result, error sources can be grouped in a sequential manner and described by the parameters of the small displacement torsor. Moreover, the corresponding error propagation model can consider nonpunctual contacts of the fixture assembly, overcoming the limitation of the 3-2-1 layout. An experiment was conducted to demonstrate the model application and verify the effectiveness of the proposed methodology.

Automatically generating assembly tolerance types with an ontology-based approach

In most cases, designers have to manually specify both assembly tolerance types and values when they design a mechanical product. Different designers will possibly specify different assembly tolerance types and values for the same nominal geometry. Furthermore, assembly tolerance specification design of a complex product is a highly collaborative process, in which semantic interoperability issues significantly arise. These situations will cause the uncertainty in assembly tolerance specification design and finally affect the quality of the product. In order to reduce the uncertainty and to support the semantic interoperability in assembly tolerance specification design, an ontology-based approach for automatically generating assembly tolerance types is proposed. First of all, an extended assembly tolerance representation model is constructed by introducing a spatial relation layer. The constructed model is hierarchically organized and consists of part layer, assembly feature surface layer, and spatial relation layer. All these layers are defined with Web Ontology Language (OWL) assertions. Next, a meta-ontology for assembly tolerance representations is constructed. With this meta-ontology, the domain-specific assembly tolerance representation knowledge can be derived by reusing or inheriting the classes or properties. Based on this, assembly tolerance representation knowledge is formalized using OWL. As a result, assembly tolerance representation knowledge has well-defined semantics due to the logic-based semantics of OWL, making it possible to automatically detect inconsistencies of assembly tolerance representation knowledge bases. The mapping relations between spatial relations and assembly tolerance types are represented in Semantic Web Rule Language (SWRL). Furthermore, actual generation processes of assembly tolerance types are carried out using Java Expert System Shell (JESS) by mapping OWL-based structure knowledge and SWRL-based constraint knowledge into JESS facts and JESS rules, respectively. Based on this, an approach for automatically generating assembly tolerance types is proposed. Finally, the effectiveness of the proposed approach is demonstrated by a practical example.

Analytical method for optimal component tolerances based on manufacturing cost and quality loss

Optimal component tolerances can reduce product cost and improve enterprise competitiveness. In order to obtain optimal tolerances accurately and efficiently, analytical methods are applied to solve tolerance optimization model. In this article, both manufacturing cost and quality loss are included in the total cost, and two kinds of constraints, including assembly tolerance constraint and process accuracy constraints, are considered in the tolerance optimization model. In order to allocate the optimal tolerances among the related components, the following procedure is presented. First, the two kinds of constraints are ignored, and analytical method is applied to find the initial values of component tolerances. If the initial component tolerances cannot satisfy assembly tolerance constraint, the Lagrange multiplier method is executed and the Lambert W function is applied to solve the corresponding equations to obtain the new values of component tolerances. Then, process accuracy constraints are satisfied through the adjustment of component tolerances. Finally, an example is used to demonstrate the effectiveness of the method proposed in this article.

The WEST project: PFC shaping solutions investigated for the ITER-like W divertor

Among major issues for PFCs design, the impact of leading edges (exposed surface) which would be directly intersected by particles following magnetic field lines at glancing incident angles in the high heat flux areas is much discussed. This paper presents the key outcome of a thermal analysis performed on different shaping solutions for the ITER-like W monoblocks occurred for the components of the WEST (WEnvironment for Steady state Tokamak) divertor which could shadow any direct leading edge and to counteract a potential misalignment due to assembly tolerance. The results, in terms of surface temperature rise and wall heat flux into the cooling channel, are discussed for magnetic field lines incident at glancing angles expected in the higher heat flux regions of divertor (i.e. close to the strike point regions) and for perpendicular incident heat flux up to 20MW/m2.

Optimal strategies for corrective assembly approach applied to a high-quality relay production system

In the assembly of high-quality products in a corrective assembly approach, measurement and reprocessing errors occur in the measuring and reprocessing stages, and these unexpected errors can lead to the erroneous selection of the reprocessing machine, and produce unsatisfactory products. In this paper, we consider the part flow in a high-quality relay production system applying the corrective assembly approach by incorporating machining, measurement and reprocessing errors simultaneously, and formulate the production rate of high-quality products satisfying the predetermined assembly tolerance. Optimization is used to yield the maximum production rate by using reprocessing machine selection and design strategies. The results indicate the following: (1) the proposed optimization methodology effectively yields the maximum production rate and presents the optimal selection range and the optimal adjustment size of the reprocessing machine, and (2) the reprocessing accuracy affects the maximum production rate but has little effect on the optimal selection range and the optimal adjustment size.

Optimum tolerance design using component-amount and mixture-amount experiments

The tolerance design problem involves optimizing component and assembly tolerances to minimize the total cost (sum of manufacturing cost and quality loss). Previous literature recommended using traditional response surface methodology (RSM) designs, models, and optimization techniques to solve the tolerance design problem for the worst-case scenario in which the assembly characteristic is the sum of the component characteristics. In this article, component-amount (CA) and mixture-amount (MA) experiment approaches are proposed as more appropriate for solving this class of tolerance design problems. The CA and MA approaches are typically used for product formulation problems, but can also be applied to this type of tolerance design problem. The advantages of the CA and MA approaches over the RSM approach and over the standard, worst-case tolerance-design method are explained. Reasons for choosing between the CA and MA approaches are also discussed. The CA and MA approaches (experimental design, response modeling, and optimization) are illustrated using real examples.

Influence of Assembly Tolerance on Dynamic Characteristics of Motor Rotation Assembly

The motor rotation assembly of machine tools is mainly composed of spindle, rotor and bearings, it is to some extent the most important component, and its dynamic characteristics directly affect the machining accuracy and efficiency. Although the finite element method is effective to solve such dynamic problem, the conventional method generally ignores the influence of assembly tolerance between the spindle and the rotor .This probably would lead to a larger error result. A new method is described to evaluate the results obtained from finite element analysis .Firstly, a finite element mathematical model of motor rotation assembly is established, and then the model is tested by means of modal experiment, finally, the mathematical model results calculated by MATLAB software is compared with that of modal experiment, the results show that this modeling method is accurate and efficient. Furthermore, rotors of different inner diameters are mounted onto the spindle of same size, and then modal experiment and a finite element analysis are applied to obtain the dynamic characteristics of the motor rotation assembly under different assembly tolerances. This research can provide some reference values for the tolerance design of the motor rotation assembly.

Three Dimensional Assembly Tolerance Analysis of Gear Drivetrain

Assembly accuracy has a crucial impact on the movement, load and fatigue of gear drivetrain. In this paper, a methodology on the accuracy prediction and control of complex drivetrain is presented. The proposed approach tries to simplify the assembly tolerance computation but grasping main assembly error factors in the assembly process of gear drivetrain. Jacobian -Torsor method is used in the analysis process, and results show a proper performance which indicates a potential opportunity for further deep and wide research on the 3D assembly analysis and simplification method.

Tolerance Analysis and Re-distribution of A Machine Tool Spindle by Negative Tolerancing

Machine tool spindle is among the most precise components which require both high accuracy and high repeatability. It has been an issue how to distribute components’ tolerances in order to reduce production cost while keep the tolerance target under control. This paper investigates the method for tolerance re-distribution of a spindle in order to keep its high assembly tolerance. The dimensional chain of the spindle is first constructed to analyze the assembly tolerance. While the assembly tolerance is out of the target, the reverse process that re-distributes the target tolerance to each component is investigated such that the target can be satisfied and controlled. Tightening tolerances of spindle parts is the most straightforward approach to reduce the assembly tolerance that, however, increases manufacturing cost. An approach to re-distribute the components’ tolerance based on the IT precision grade is then assigned and analyzed. This approach, however, still fails to achieve the required tolerance target. The “negative tolerancing” approach is then employed. The retaining ring of the spindle severs as the adjusting component which carries “negative tolerance” to compensate the assembly tolerance. The result shows that the tolerance target can be achieved using this approach without paying high manufacturing cost.