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Aerospace blade is the most important part for pneumatic performance with expensive material and cost. Precise NC machining after near-net forming is a trend for aerospace blade machining. If the billet cannot cover the machining surface, the localization is necessary before machining. Because of little machining allowance and various tolerance requirements, free-form surface localization of aerospace blade becomes a puzzle. Traditional free-form surface localization researches focused on finding an appropriate position for design surface to guarantee the enough machining allowance. Different from traditional free-form surface localization research, the form tolerance is considered in the localization optimization. The localization result needs to satisfy the machining allowance and tolerance requirements. To achieve this target, the characteristics of blade modeling and inspection are analyzed. And then, a tolerance constraint is introduced into localization to ensure that the machining surface could satisfy the tolerance requirements. The traditional localization method and the new method considering design tolerance are applied on a compressor blade localization, respectively. From a comparison, the necessity of form tolerance constraint is verified. [ABSTRACT FROM AUTHOR]

Although the influence of nose geometry of a cutting tool insert on the surface roughness of the finished workpiece has been studied in detail, the effect of the tool nose profile tolerance in new cutting inserts on the surface roughness has not been investigated in the past. In this paper, we study the effect of tool nose profile tolerance in new inserts on the surface roughness using simulation and experimental methods. In the simulation study, a high-resolution optical metrology system was used to capture an image of the tool nose. A sub-pixel edge detection approach combining moment invariance operator with modified Sobel 2-D filter operator was used to extract the nose edge profile. The workpiece profile was then generated digitally using the extracted nose profile, and the effect of the nose profile deviation on the surface roughness was assessed. The maximum differences in the surface roughness parameters R, R, and R between the surfaces generated by the actual tool nose and the ideal (circular) tool nose images were found to be 40.3, 26.1, and 24.5 %, respectively. The simulation study showed that the nose profile deviation alone can cause the surface roughness to vary as much as 40.3 % ( R) although the same type of inserts are used. The simulation results for R and R were found to agree well with the experimental data with less than 10 % difference for 79 % of the tool edges. Our study shows that although the nose radius tolerance is within the 10 % allowed in the ISO3685 standard, the nose profile deviation has a significant influence on the surface roughness. [ABSTRACT FROM AUTHOR]

The quality of any product depends upon its component tolerance and assembly variations. Most products are composed of more than one component. These products require some type of assembly during production. Assembly is the process of joining two or more parts together. The functional performance of an assembled product and its manufacturing cost are directly affected by the individual component tolerances. However, tolerance is inevitable because manufacturing exactly equal parts is impossible. When the components are assembled together interchangeably, the assembly tolerance is the sum of the component tolerances. If the required assembly tolerance variation is less than the sum of the components' tolerances, the rejection rate of assemblies will be more. In such cases, the selective assembly is the method to achieve tight assembly tolerance with the components manufactured at wider tolerances. This is accomplished by partitioning produced components into groups prior to random assembly. The mating components in the selective groups are then assembled at random. In this paper, artificial immune system (AIS) algorithm is developed to obtain the best combination of selective group with minimum variation in the assembly tolerance and least loss value within the specification range. The concept of Taguchi's loss function is applied into the selective assembly method to evaluate the deviation from the mean. The selection of number of groups for selective assembly is also analyzed in this paper. [ABSTRACT FROM AUTHOR]

In production engineering, highest surface qualities and low tolerances are produced by grinding processes. Defects of the grinding wheel caused by unbalance, wrong dressing cycles, cavities, or waviness result in vibrations and damage of workpiece or spindle. Therefore, monitoring of the tool is important in practical use. In order to avoid scrap, small faults of the grinding wheel and very small amplitudes of the resulting vibrations are of major interest. This paper presents a new monitoring method, which estimates the defects recursively during the grinding process. Different sensors are analyzed using this method. Among sensors for academic purposes, typical sensors in grinding machines such as the displacement, acceleration, motor current, and acoustic emission are in use for monitoring. Compared to monitoring in the frequency domain and signal feature extraction by filtering, the recursive estimation can reduce noise. In cylindrical plunge grinding, wavy tool defects may result in unequal wear and self-exiting waviness of the wheel over a long period of grinding and start at very low amplitudes. This regenerative chatter is subject of monitoring of highest productivity of grinding processes and is therefore analyzed in this paper as well as the strongly depending selection of dressing cycles initiated by the monitoring algorithm. [ABSTRACT FROM AUTHOR]

In this paper, a new variable sampling plan using the exponentially weighted moving average (EWMA) statistic based on the yield index is developed for lot sentencing. The proposed plan considers the quality of the current lot as well as the preceding lots through the EWMA statistic. The sample size and the critical value of the proposed plan are determined by considering the acceptable quality level at the producer's risk and the lot tolerance percent defective at the consumer's risk. The plan parameters are tabulated according to the smoothing constant of the EWMA statistic and various combinations of two risks. An example is provided for illustrating the proposed plan. [ABSTRACT FROM AUTHOR]

Analysis of assembly tolerance is an important method to evaluate the reasonableness of tolerance allocation in product design. For the purpose of convenient applications, the method to assembly accuracy prediction presented in the paper is to extract the related assembly information from the CAD assembly model directly, which is managed in the way of data structures with inter-relationship and accessed with database technology. From the extracted assembly information, 3-D assembly dimension chains was automatically generated through searching the assembly constraints and their dependence and related dimension positions in the database. Then, the dimension chain is optimized by using ant colony algorithm to create an optimal one. Based on the input tolerance or actual dimension for each dimension/constraint, the assembly accuracy of the product can be predicted by the dimension chain and the accuracy prediction model. Taking a machine tool as an example, the accuracy prediction result shows that the predicted assembly accuracy meets the design specifications. [ABSTRACT FROM AUTHOR]

When calculating the tolerance of an assembly dimension chain with compensation loop, the value calculated by the basic formula for dimension chains must be a negative or imaginary number; this value is referred to as virtual tolerance in this paper. Virtual tolerance is not covered by tolerance theory. However, after reviewing such relevant concepts such as negative and positive numbers, the essence of virtual tolerance can be defined as follows: the absolute value of virtual tolerance (or the imaginary part) is the error compensation amount and the size between the upper and lower deviations is the compensation range. Therefore, the amount and range of error compensation are both added to the scope of tolerance so that they can be described in a digital way; in the meantime, the range of tolerance is extended to any number. Based on the concept of virtual tolerance, the tolerance and the error compensation amount can be calculated synchronously, leading to a simplified analysis and calculation process; computer-aided design is also facilitated. According to probability theory and the relevant concepts of dimension chains, the only correct result is that the error compensation amount is the imaginary part of virtual tolerance. But since the error compensation amount calculated by the probabilistic method does not ensure assembly accuracy, a theoretical basis is provided to calculate the assembly dimension chain with compensation loop by the probabilistic method. [ABSTRACT FROM AUTHOR]

This paper presents a 3D formalization of manufacturing tolerancing which associates the concept of small displacements, the functional constraints, and manufacturing process capability. This approach would make it possible to establish relations which limit the surface variations of the production mechanism by the functional specifications. These relations have a number of requirements imposed by designer and are sufficient to evaluate the manufacturing process. The variations of the manufacturing process are defined in relation to variations measured by 3D measuring. [ABSTRACT FROM AUTHOR]

Tolerances within an assembly are defined during the setting of engineering specifications in the design phase. However, during assembly process execution, certain assembly variations arise from the individual components, manufacturing imperfections, material compliance, the means by which they are fastened and the assembly sequence used. The implementation work reported in this article utilises in-process assembly measurement information for predicting dimensional variation of the aero structure assembly process. A framework is exploited in the case study for predicting the dimensional influence of (1) designed tolerances, (2) designed assembly processes and (3) component and sub-assembly level measurement data for revising the assembly sequence if any concessions were issued on manufactured components. Considerable learnings are achieved while managing dimensional variation of in-process aerospace assembly structure. Dimensional variation simulation is found to be overestimating variation spread even after considering compliance of non-rigid components. Thus, in-process measurement data (component and sub-assembly level) has to be integrated in the variation analysis in order to reduce variation spectrum. Case-based scenarios are discussed where design and measurement data can be utilised for estimating dimensional variation of the in-process assembly. [ABSTRACT FROM AUTHOR]

Circular saw blades are fundamental cutting tools applied to cut off materials. Inspection of finished products of circular saw blades is important in order to ensure their manufacturing quality and sawing performance. Traditionally, a contact inspection method is adopted to measure the runout amounts of circular saw blades. In order to improve the quality of the runout inspection, a non-contact inspection method based on machine vision is required. In this paper, an automated optical inspection (AOI) system was developed exclusively for inspecting the runout tolerance of circular saw blades. Based on the integration of motion control and image processing techniques, calibration and automated inspection processes for the developed AOI system were then established. Experiments to inspect circular saw blade samples were also conducted in order to test the feasibility and reliability of the developed AOI system. From the experimental results, the developed AOI system, in combination with the automated inspection process, could achieve sufficient repeatability and was verified to be able to inspect the runout tolerance of certain circular saw blades. [ABSTRACT FROM AUTHOR]

Two-component (2k) injection moulding is an important process technique at the present state of technology, and it is growing rapidly in the field of precision micro moulding. Besides combining different material properties in the same product, two-component moulding can eliminate many assembly steps in the manufacturing process chain. One of the biggest technical challenges associated with 2k moulding is the unavailability of suitable material combinations which can meet the diverse requirement from both product and process point of views. When it comes to the point of micro application, the precise dimensional requirement and tolerance make the 2k moulding a technically challenging process. This paper presents an industrial case study of 2k micro moulding covering all the important issues like product design, material selection, moulding and functionality testing of the micro moulded 2k parts. An intensive search for suitable 2k materials is made and few combinations of plastic materials are presented in the paper which can be used for highly demanding application areas like hearing aids. By using these material combinations, a demonstrator 2k micro part has been fabricated. The moulding machine was a state-of-the-art 2k micro machine from DESMA. The fabricated micro part was a socket house integrated with a sealing ring for the receiver-in-canal hearing instrument. The test performed on the demonstrator showed the potential of the 2k moulding technology to be able to solve some of the existing problems associated with hearing instruments. [ABSTRACT FROM AUTHOR]

This paper proposes a game theoretic approach for concurrent tolerance design considering the practical manufacturing process and assembly process, to achieve lower manufacturing cost and good product assemblability. The optimization objectives and constraints for concurrent tolerance design for manufacture and assembly are discussed, and the key technologies for concurrent tolerance design with game theory are investigated, including the strategy set division, payoff calculation, and Nash equilibrium evolution. An optimization algorithm is proposed to achieve concurrent tolerance design with a game theoretic approach, and the genetic algorithm is used to conclude the Nash equilibrium of the game for manufacture and assembly. Finally, a case study is given to verify the proposed approach. [ABSTRACT FROM AUTHOR]

Simultaneous optimization of multiple-quality characteristics and determining the process settings is a critical and difficult task for practitioners. Such types of problems are generally referred to as 'multiple-response optimization' problems. To handle high-dimensional multiple-response problems, a popular strategy, using desirability functions, is recommended by various researchers. Various types of desirability index functions are recommended to convert multiple scale-free desirability measures to a single composite desirability (or single objective) value. Thus, the objective is then to maximize the single composite desirability for a specific problem. In this paper, a new adaptive penalty function-based 'maximin' desirability index is proposed, which provide superior solution as compared to existing maximin approach, for close (or tight) engineering tolerances of response characteristics. The superiority was proved based on statistical comparison using varied case situations and different swarm intelligent search strategies. [ABSTRACT FROM AUTHOR]

Assembly is a type of production process in which a number of components are combined to yield a final product. Although the concept of interchangeable parts has long been known as the fundamental principle of assembly processes, randomly picking some bulked components with dimensions varying in predefined tolerances may not be a valid approach to obtain special final products with considerably tighter tolerances. Therefore, each of the components needs to be measured and classified into dimensional groups in advance so that quality products can be obtained by matching components from suitable groups. This assembly scheme is called as 'selective assembly.' In this work, we consider an assembly case with a pair of components in which one is manufactured on a given number of parallel processes whose settings can be changed to affect the dimensional distribution of the yield while the other component with a slightly bigger tolerance is manufactured on a single process with constant settings. In order to minimize the number of components which could not have been matched with their counterparts, we develop a nonlinear mathematical model to determine the optimal machine settings corresponding to the nominal mean of the component dimension which follows a normal distribution when it is machined. The solution of the mathematical model not only provides the individual settings for the parallel processes producing the same type of component but also the optimal batch sizes at each trial. We have finally used a simulation model of the whole production system, in order to prove that the solution of the mathematical model is able to provide the machine settings which minimize the number of unmatched parts at each trial. [ABSTRACT FROM AUTHOR]

Process planning is an essential component for linking design and manufacturing process. Setup planning and operation sequencing are two most important functions in the implementation of CAD/CAPP/CAM integration. Many researches solved these two problems separately. Considering the fact that the two functions are complementary, it is necessary to integrate them more tightly so that performance of a manufacturing system can be improved economically and competitively. This paper presents a generative system and genetic algorithm (GA) approach to process plan the given part. The proposed approach and optimization methodology analysis constraints such as TAD (tool approach direction), tolerance relation between features and feature precedence relations to generate all possible setups and operations using workshop resource database. Tolerance relation analysis has a significant impact in setup planning for obtaining the part accuracy. Based on technological constraints, the GA algorithm approach, which adopts the feature-based representation, simultaneously optimizes the setup plan and sequence of operations using cost indices. Case studies show that the developed system can generate satisfactory results in optimizing the integrated setup planning and operation sequencing in feasible condition. [ABSTRACT FROM AUTHOR]

Runout is a composite tolerance that is usually specified to ensure proper alignment and rotational accuracy for axially symmetric features. The procedure for evaluation of runout defined in American Society of Mechanical Engineers (ASME) Y14.5M-1994 [] and International Organization for Standardization (ISO)/TR 5460-1985(E) [] depicts the rotation of a part around its datum axis while a dial gauge measures the variations in the feature's surface. These standards do not address the evaluation of runout using modern measurement technologies using discrete point clouds that dominate the metrology industry. This research presents a comprehensive methodology for evaluating runout tolerance using discrete data that closely replicates the requirements specified by the ASME and ISO standards. This work builds upon previous work by the authors, reported in Turek et al. [] and presents a comprehensive methodology for evaluating circular and total runout for flat, tapered, and cylindrical features using discrete data. The methodology was tested using simulated datasets and the analysis reaffirmed the results reported in Turek et al. [] regarding the choice of minimum circumscribing cylinder as the preferred datum axis evaluation technique. Subsequently, the approach presented in this paper was applied to discrete data acquired from two manufactured parts. The results obtained were compared with traditional runout measurements acquired with a dial gauge. This comparison required the filtering of the discrete data to compensate for the finite radius of the dial gauge tip, and led to the development of a novel filtering technique to appropriately compare results. The results using the filtered data closely match the results obtained from the dial gauge, confirming the accuracy of the presented runout assessment algorithms. This work presents a first step in assessing runout using discrete data and justifies the use of modern metrology techniques in runout evaluation. [ABSTRACT FROM AUTHOR]

The profile tolerance of diamond cutting tool's edge is one of the key factors in affecting machining accuracy. With the development of ultra-precision machining technology for optical free-form surfaces and optical microstructures, the demand for high-precision round nose diamond cutting tools is increasing. In this study, an on-machine image processing approach is applied to cutting edge geometry truing process, and profile data of cutting edge in sub-pixel precision is acquired using a series of image processing methods. According to the profile captured, the deviation from an ideal cutting edge is calculated and feedbacked to the controller. The lapping system is employed to lap the cutting edge pertinently using the deviation and the corresponding position captured, and the round edge of high accuracy is obtained efficiently. This method can avoid the error caused by the process of refixturing for offline measurement in the traditional lapping method of diamond cutting tool and reduce the influence of human factors. A truing experiment for cutting edge of the monocrystal diamond cutting tool is carried out at the developed lapping system based on on-machine image measurement, and round cutting edge of profile tolerance less than or equal to ±0.5 μm is achieved. [ABSTRACT FROM AUTHOR]

Quality of an assembly of any manufactured product is mainly based on the quality of mating components. Due to random variations in sources such as materials, machines, operators, and measurements, mating components manufactured by even the same process may vary in their dimensions. When mating components are assembled linearly, the resulting assembly tolerance will be the sum of the mating components tolerances. All precision assemblies demand for a closer assembly tolerance. A significant amount of research has already been done to minimize assembly variation using selective assembly, when the dimensions of components follow normal distribution. However, in reality, the dimensions of components produced especially in smaller to medium size batches, invariably have some skewness (non-normality), which makes the methods developed and reported in the literature, often not suitable for practice. In this work, batch selective assembly methodology is proposed for components having non-normal distributions to minimize the assembly tolerance variations. The proposed method which employs a genetic algorithm for obtaining the best combination of mating components is able to achieve minimum variations in assembly tolerances and also maximum number of acceptable assemblies. The proposed algorithm is tested with a set of experimental problem datasets and is found outperforming the other existing methods found in the literature, in producing solutions with minimum assembly variation. [ABSTRACT FROM AUTHOR]

In the last two decades, many researchers have addressed the superior system performance resulted from the integration of process planning and scheduling functions. However, most of the published solution methods in this field fall short in three accounts. First, while integrating with scheduling, they ignore the checking of process planning feasibility with respect to tolerances allocation. Thus, operational tolerances may stackup beyond the blue print tolerances making the process plans infeasible. Second, they ignore the machines capabilities during the integration modeling which make these solution models practically inapplicable. Third, they focus on time consideration, such as makespan or lateness, and do not consider manufacturing cost related to operations-machines assignment. This paper presents an innovative model for the integration of process planning and scheduling in a job-shop environment. The model simultaneously serves three purposes: allocating operational tolerances while minimizing its manufacturing cost, minimizing the work in process inventory, and figuring the operation-machine assignments. The preemptive-goal programming method is used to solve the proposed multiobjective non-linear mixed integer model, and an implementation example is presented to demonstrate the effectiveness of the proposed modeling approach. [ABSTRACT FROM AUTHOR]

The riveting process of aeronautical thin-walled structures (ATWS) with 'Frame-type' automated riveter systems is always multi-state. The changing of fixtures and datum in riveting process would lead to the difficulty of positioning error analysis, and the positioning error will influence the tolerance characteristics of final product and the fatigue durability. This paper presents an efficient method for positioning error analysis in ATWS multi-state riveting. Firstly, the whole riveting process is divided into two stages according to the changing of riveting fixtures, and the model of positioning error in each stage is developed on base of the mismatch error analysis. Secondly, by defining key characteristic points (KCPs) according to anchor points and joining points, the positioning error of ATWS is represented as the error of KCPs, and the scheme of anchor points and joining points is developed according to the 'N-2-1' positioning principle. Thirdly, on base of positioning error propagation analysis in each stage, components of positioning error are discussed in detail, and the mathematical model of each component is developed, according to the manufacturing error, position accuracy as well as the mismatch error. Lastly, a wing panel which is made up of a skin and four stringers is studied as a case to calculate the positioning error. The comparison between computing result and measurement proves that the purposed positioning error analysis method can solve the positioning error analysis problem for ATWS multi-state riveting efficiently. [ABSTRACT FROM AUTHOR]

Tolerances play an important role in product fabrication and have a significant impact on manufacturing costs. The factors affecting manufacturing cost (geometry, material, etc.) of a part are fuzzy or subjective in nature since they have no appropriate numerical measure. This paper proposes a framework that overcomes the drawbacks of traditional tolerance control methods and reduces subjectivity via fuzzy comprehensive evaluation and conjoint analysis. In the fuzzy comprehensive evaluation process, the relationship between the machining costs and part tolerance is expressed through a mathematical formula, with the objective of minimizing the total machining cost. The conjoint analysis method is introduced to provide a systematic method of deciding weights for each of the factors in the tolerance allocation procedure. The application of the framework is demonstrated with practical engineering problems of allocating tolerances of an accumulator's O-ring seal and a clutch assembly. [ABSTRACT FROM AUTHOR]

The aim of this paper was to present a tolerance modeling method of complex features. Geometric deviation of a characteristic/feature is divided into intrinsic deviation and situation deviation based on the new generation geometrical product specification in the paper. On the basis of vector parametric representation of theoretical surface, intrinsic deviation between substitute surface and ideal surface is described by vector function. Based on 3D rigid body kinematics, homogeneous transformation matrix-based method is used to describe the situation deviation of the substitute surface relative to the reference feature in Euclidean space. An example was given using the proposed modeling method. [ABSTRACT FROM AUTHOR]

In mechanical assemblies, individual components are placed together to deliver a certain function. The performance, quality, and cost of the mechanical assembly are significantly affected by its tolerances. Toleranced dimensions inherently generate an uncertain environment in a mechanical assembly. This paper presents a proper method for tolerance analysis of mechanical assemblies with asymmetric tolerances based on an uncertainty model. This mathematical approach is based on fuzzy logic and tolerance accumulation models such as worst-case and root-sum-square methods. A fuzzy-based tolerance representation is developed to model uncertainty of tolerance components in the mechanical assemblies. According to this scheme, toleranced components are described as fuzzy numbers with their membership functions constructed using the statistical distributions of manufactured variables. In this way, the uncertainty of assembly requirements and accumulation of tolerances are represented in the form of fuzzy number. In this paper, a new factor, the fuzzy factor, is introduced that helps converting the membership functions into fuzzy intervals that can be used for modal interval analysis. Equations for estimation of percent contributions of individual tolerances are introduced in terms of uncertainty parameter. These equations yield percent contributions of upper and lower bounds of independent variables (manufactured dimensions) on the upper and lower bounds of dependent variables (assembly dimensions). The proposed method is applied to an example, and its results are discussed. [ABSTRACT FROM AUTHOR]

first sight, the establishment of cost-tolerance relations for manufacturing processes may seem to be a fully developed topic. Nevertheless, many real cases in industry have made it clear that a solution that satisfies the practical requirements in this field has not yet been reached. The applicability of the developments of this topic depends greatly on the validity of the cost-tolerance relation values of each specification in a mechanical part, which is subject to tolerances. Nevertheless, none of the studies carried out thus far that consider suppositions of former developments to be valid have made a careful study of this relation. The current study puts forth a new method for establishing the cost-tolerance relation of a manufacturing process based on the variability of the equipment involved in the process. In other words, the proposed method is based on the ability of a specific process to achieve performance within the assigned tolerances at the materialised magnitude. It makes it possible to obtain practical results directly linked to the production process at every time. Furthermore, this method is a key for future developments related to tolerance synthesis or analysis. [ABSTRACT FROM AUTHOR]

In this paper, a general methodology to do tolerance analysis of rigid assemblies is proposed. Firstly, tolerance specification sets, according to GD&T or ISO specifications, are translated into variational features by using 4 × 4 homogenous transformation matrices. In particular, planar and cylindrical features are considered. Then, once all variational features are modeled, assembly constraints among parts are introduced. To solve assembly constraints, an assembly transformation matrix is evaluated. By using point, line, and plane entities and their combinations, kinematic joints are modeled. A numerical procedure is proposed to solve fully and over-constrained assemblies. The best-fit alignment among variational mating features is performed by using optimization algorithms. The proposed method for tolerance analysis of rigid part assemblies allows to simulate different assembly sequences. Finally, in order to show the effectiveness of the proposed methodology, three case studies are described and analyzed. [ABSTRACT FROM AUTHOR]

A tolerance synthesis provides the distribution of tolerances on the functional specifications of parts for a mechanism, with the objective of satisfying a set of functional requirements. This approach involves adjusting the nominal dimensions of parts. The present article offers a six-step solution within an Excel solver environment. The designer is able to control the optimization process using a dashboard. The initial steps detect conflicting requirements and suggest compromises, while the subsequent steps optimize the nominal part dimensions in order to maximize mechanism quality with minimum tolerance. The final steps then seek to maximize tolerances with the aim of minimizing costs. The proposed method can also manage specifications with both maximum and minimum material requirements. [ABSTRACT FROM AUTHOR]

Current localization techniques have been successfully used for aligning sculptured surfaces with CAD models in inspection applications. However, tolerance specifications are not considered as an integral part of the localization process. The tolerance verification and comparison with measured surfaces occur at a later step to accept or reject the manufactured part. This two-step process prolongs the inspection time. For the first time, this paper presents a novel localization algorithm for inspection that integrates the tolerance specifications as an optimality criterion. A closed-form solution algorithm that applies 3D rigid body transformation using quaternion and uses a minimum acceptable deviation zone approach was developed. The formulation is based on the mathematical definitions from ANSI Y14.5.1 standards (American National Standard Institute) for form tolerances. The new iterative minimum acceptable deviation zone localization algorithm is formulated using four types of form tolerances: straightness of a median line, straightness of a surface line, flatness and cylindricity. It is applied and compared to several benchmark examples for validation. The results demonstrated the ability of the new localization approach to achieve comparable results but with less computation effort due to using a constraint satisfaction problem and a closed-form solution algorithm in the formulation. The merit of the new approach stems from its ability to increase the efficiency of tolerance verification during the inspection process. The applicability of the proposed algorithm to various types of tolerance is highlighted. [ABSTRACT FROM AUTHOR]

For mechanical product, tolerance includes Dimensional Tolerance, Form, Profile, Orientation, Location, Runout, and Assembly Mating Tolerance. Generally, the error of part or product is restricted by a kind of tolerance or several kinds of tolerance. In order to analyze error and its stack-up of mechanical product effectively and absolutely, this paper presents an integrated modeling method of unified tolerance representation based on Key Features (KFs) and Graph Theory in order to deal with these types of tolerances simultaneously. The method includes three steps. The first is to build a tolerance-meta model covering KFs, the relationship set of KFs, the type of tolerance, attributes of tolerance, and variational direction of KF. The model of Dimensional Tolerance, Form, Profile, Orientation, Location, and Runout can be built by tolerance-meta model. The second is to build a model of part’s tolerance and Assembly Mating Tolerance based on sum arithmetic of Graph Theory. The third is to build the integrated tolerance model including Dimensional Tolerance, Form, Profile, Orientation, Location, Runout, and Assembly Mating Tolerance. The integrated model is propitious to represent tolerancing experience from engineers. The method is applied successfully to build the integrated tolerance model for a component of aircraft’s fuselage. [ABSTRACT FROM AUTHOR]

Tolerance allocation is a design tool for reducing overall cost of manufacturing while meeting target levels for quality. An important consideration in product design is the assignment of design and manufacturing tolerances to individual component dimensions so that the product can be produced economically and functions properly. The allocation of tolerances among the components of a mechanical assembly can significantly affect the resulting manufacturing costs. In this work, the tolerance allocation problem is formulated as a non-linear integer model by considering both the manufacturing cost of each component by alternate processes and the quality loss of assemblies so as to minimise the manufacturing cost. Metaheuristics techniques such as genetic algorithm and particle swarm optimisation are used to solve the model and obtain the global optimal solution for tolerance design. An example for illustrating the optimisation model and the solution procedure is provided. Results are compared with conventional technique and the performances are analysed. [ABSTRACT FROM AUTHOR]

For aircraft structures, it is clear that the design and the selection of materials play an important role in the performance of the aircraft. The production costs are also important. The concept of tailor-made blanks (TMBs) is based on the use of dedicated blanks, made of different alloys and/or thickness in order to satisfy different demands such as an increase, if necessary, of local strength, stiffness, and damage tolerance. This paper describes the results of a study to assess the potential weight and cost savings of using TMBs in a typical aerospace structure. A bonded structure representing the floor beam of an aircraft has been selected, analyzed, and tested to validate the numerical and analytical predictions made with MATLAB and finite-element method. The results show weight reduction of 12% and 37% for two studied configurations, compared to the reference beam. [ABSTRACT FROM AUTHOR]

Particle swarm optimizers are routinely utilized in engineering design problems, but much work remains to take advantage of their full potential in the combined areas of sensitivity analysis and tolerance synthesis. In this paper, a novel Pareto-based multiobjective formulation is proposed to enhance the operations of a particle swarm optimizer and systematically distribute tolerances among various components of a mechanical assembly. The enhanced algorithm relies on nonlinear sensitivity analysis and the statistical root sum squares model to simultaneously optimize product performance criteria, the manufacturing cost, and the stack-up tolerance. It is shown that the proposed algorithm can accomplish its optimization task by successfully shifting nominal values of design parameters instead of the expensive tightening of component tolerances. Several numerical experiments for optimal design of a stepped bar assembly were conducted, which highlight the advantages of the proposed methodology. [ABSTRACT FROM AUTHOR]

Any part cannot be manufactured to the required nominal dimensions due to inherent variations in workmanship, material, and machine. The specification of tolerance on part dimensions plays a major role on performance, quality, and cost of the product. Distribution of tolerance among the components of an assembly is known as tolerance allocation. The selection of alternative processes for tolerance allocation also plays a vital role in reducing manufacturing cost. Near-optimal allocated tolerances are obtained using nontraditional optimization techniques in which the solutions are achieved randomly. Also, there is a chance for omitting the better process for allocation. The results of successive run of the program based on these techniques will not yield consistent results. An attempt has been made in this work to solve the above problem using Lagrange multiplier method for complex assemblies with univariate search method. The methodology has been demonstrated on wheel mounting assembly. The example product after implementing the proposed method would yield 1.4% savings in manufacturing cost as compared with the cost obtained by Singh. [ABSTRACT FROM AUTHOR]

Although image-based inspection has been applied to a wide range of industrial applications, inspection accuracy remains a challenging issue due to the complexity involved in industrial inspection. The common method adopted in industry is to use a qualified image as a template image to inspect each live image on a pixel-by-pixel basis. In this paper, a tolerance method is presented to replace the template image method. The said tolerance is formed by two indices computed from a sample image, instead of using the whole image for inspection. To ensure an accurate tolerance zone, a neural networks method is used to take the noise and uncertainties in the images under inspection into consideration. To improve neural networks training speed, the Taguchi method is adopted to select a minimum number of the sample images needed for training. Once a tolerance zone is obtained, live images are inspected against it. If the indices of a live image fall inside the tolerance zone, the part is regarded as good, otherwise defective. Three examples are given: one for auto part inspection, one for label inspection, and one for machining part inspection. The inspection accuracy achieved is above 94%. [ABSTRACT FROM AUTHOR]

Mechanical products are usually made by assembling many parts. The dimensional and geometrical variations of each part have to be limited by tolerances able to ensure both a standardized production and a certain level of quality, which is defined by satisfying functional requirements. The appropriate allocation of tolerances among the different parts of an assembly is the fundamental tool to ensure assemblies that work rightly at lower costs. Therefore, there is a strong need to develop a tolerance analysis to satisfy the requirements of the assembly by the tolerances imposed on the single parts. This tool has to be based on a mathematical model able to evaluate the cumulative effect of the single tolerances. Actually, there are some different models used or proposed by the literature to make the tolerance analysis of an assembly, but none of them is completely and univocally accepted. Some authors focus their attention on the solution of single problems found in these models or in their practical application in computer-aided tolerancing systems. But none of them has done an objective and complete comparison among them, analyzing the advantages and the weakness and furnishing a criterion for their choice and application. This paper briefly introduces two of the main models for tolerance analysis, the vector loop and the matrix. In this paper, these models are briefly described and then compared showing their analogies and differences. [ABSTRACT FROM AUTHOR]

The first step of a geometrical and dimensional tolerance analysis is to determine kinematic loops that affect the functional requirements and the tolerances that influence the relative positioning between two topological elements of a part. This process is called the interpretation of geometric and dimensional tolerances. The second step is a solution procedure to verify if the functional requirements will be met with the current tolerances. This paper presents the implementation of a C++ library for the interpretation of geometric and dimensional tolerances in order to accomplish the first step of the tolerance analysis process. First, the data structures that allow storing the tolerances, the toleranced part data model, and the assembly graph model are introduced. This is followed by the description of the algorithms for retrieving the relevant kinematic loops from the assembly graph and the tolerances that affect the relative positioning between any two topological elements. Finally, an example demonstrates how to use the interpretation data obtained from the library to calculate and verify the functional requirements. [ABSTRACT FROM AUTHOR]

Specifying proper tolerances for manufactured goods results in greater savings and improved performance, which may ultimately determine whether a product succeeds or fails in the marketplace. In the past, tolerance specification has been more an art than a science, and is largely dependent upon experiences. A more scientific and reliable approach is presented in this paper. A hybrid of Nelder-Mead simplex method and particle swarm optimization (NM-PSO) is introduced for the design of tolerance of the machine elements of an overrunning clutch assembly. The objective is to obtain tolerances of the individual components so that the cost of manufacturing and quality loss is minimized. Experimental results demonstrate that hybrid NM-PSO is extremely effective and efficient in locating best-practice optimal solutions compared to geometric programming (GP), genetic algorithm (GA), and particle swarm optimization (PSO) methods. [ABSTRACT FROM AUTHOR]

Fixture planning is an important aspect of process planning. The steps involved in automatic fixture planning are manufacturing feature recognition, setup planning and fixture configuration planning. In the present work, an integrated setup and fixture planning system is developed for minimum tolerances at critical regions using a data exchanged part model as an input. A platform-independent STEP-based automatic feature recognition system that can recognize both design and manufacturing features, including intersecting features is implemented. An automatic setup planning module is developed for generating setup plans for complete machining of a given component. A fixture planning module is developed applying the criteria of uniqueness, stability, accessibility and tolerance minimization. A case study is presented to demonstrate the capabilities and integration between the various modules of the system. [ABSTRACT FROM AUTHOR]

Robust design can significantly improve a producer’s competitive ability to deliver high-quality products with low development cycle time, quality loss, failure cost, and tolerance cost. However, during usage by a consumer, the functional performance of a product or some of its components may change as use time passes, leading to unexpected product failure that is usually costly in both time and money. The cost of these failures may influence the determination of optimal use time and optimal initial settings as compensation for the possible process mean changes during consumer usage. In addition to finding use time and initial settings for proper quality performance, the determination of process mean and tolerance also needs to be considered. As is known, changes in process means acquired quality loss and variability, while process tolerance has an effect on tolerance-related costs and quality loss. Because there exists a dependency among use time, initial setting of process mean, process mean, and process tolerance, these values must be determined simultaneously. Thus, in this paper, an optimization model with an acceptable reliability value is developed to minimize total cost, including quality loss, failure cost, and tolerance cost, by determining optimal use time, initial settings, process mean, and process tolerance, simultaneously. Applications of single and multiple components are presented to explain the proposed models. Finally, sensitivity analysis and model discussions on some decision variables are performed. [ABSTRACT FROM AUTHOR]

The tolerance evaluation of complex forms including prisms has not been studied at any length in literature. This paper investigates the possibility of applying a model that uses Fourier series analysis to verify the form in prisms. In doing so, two unique features are highlighted: the study of prisms for form evaluation, and the application of Fourier methods for form metrology. Experimentation on square, rectangular, and hexagonal prisms was conducted to determine the efficiency of the model. The model was analyzed applying 10,000 harmonics that were used to compare the values of the measured prism against the proposed model. Results from this experiment show that the model is consistent when measuring prisms at different sample sizes. [ABSTRACT FROM AUTHOR]

Several methods have been investigated to determine the deviation of manufactured spherical parts from ideal geometry. One of the most popular is the least squares technique, which is still widely employed in coordinate measuring machines used by industries. The least squares algorithm is optimal under the assumption that the data set is very large and has the inherent disadvantage of overestimating the minimum tolerance zone, resulting sometimes in the rejection of good parts. In addition, it requires that the data be distributed normally. The support vector regression approach alleviates the necessity for these assumptions. While most fitting algorithms in practice today require that the sampled data accurately represent the surface being inspected, support vector regression provides a generalization over the surface. We describe how the concepts of support vector regression can be applied to the determination of tolerance zones of nonlinear surfaces; to demonstrate the unique potential of support vector machine algorithms in the area of coordinate metrology. In specific, we address part quality inspection of spherical geometries. [ABSTRACT FROM AUTHOR]

In conventional design, tolerancing is divided into two separated sequential stages, i.e., product tolerancing and process tolerancing. In product tolerancing stage, the assembly functional tolerances are allocated to BP component tolerances. In the process tolerancing stage, the obtained BP tolerances are further allocated to the process tolerances in terms of the given process planning. As a result, tolerance design often results in conflict and redesign. An optimal design methodology for both dimensional and geometrical tolerances (DGTs) is presented and validated in a concurrent design environment. We directly allocate the required functional assembly DGTs to the pertinent process DGTs by using the given process planning of the related components. Geometrical tolerances are treated as the equivalent bilateral dimensional tolerances or the additional tolerance constraints according to their functional roles and engineering semantics in manufacturing. When the process sequences of the related components have been determined in the assembly structure design stage, we formulate the concurrent tolerance chains to express the relations between the assembly DGTs and the related component process DGTs by using the integrated tolerance charts. Concurrent tolerancing which simultaneously optimizes the process tolerance based on the constraints of concurrent DGTs and the process accuracy is implemented by a linear programming approach. In the optimization model the objective is to maximize the total weight process DGTs while weight factor is used to evaluate the different manufacturing costs between different means of manufacturing operations corresponding to the same tolerance value. Economical tolerance bounds of related operations are given as constraints. Finally, an example is included to demonstrate the proposed methodology. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for the automatic establishment and processing of machine shop and application-specific cost-tolerance functions for the cost-optimum allocation of tolerances in dimensional chains. It can be readily integrated into a CAD environment and overcomes inefficiencies of existing systems. The concept of tolerance element (TE) is introduced that is a generic and machining process related geometric entity with attributes clearly identifiable in conformance with the existing industrial understanding. The system database module, based on a database feedback form filled by the machine shop, once created needs updating only when changes occur in machines, facilities and/or the machine shop expertise. An application example demonstrates the concept. [ABSTRACT FROM AUTHOR]

Tolerance transfer techniques are used extensively for allocation of tolerances for each machining operation in the process sequence, and hence are used to coordinate the process planning and the design activities in the evolution of a new product. This paper deals with an extended approach to allocate process tolerances based on a tree topology called technologically and topologically related surfaces (TTRS) and its subsequent extension to cost optimization. The benefit of this approach is that equations are generated explicitly with regard to tolerance transfer. These have been exploited by implementing the cost function in the generated explicit equations and subsequent optimization. The TTRS approach has been extended which scores over the limitations of some of the already existing techniques in that, it is optimal with respect to two factors namely, cost of producing the required tolerances, as also the process capability of the machines involved in producing the part. This technique has been proved practically feasible as it has been implemented in an industry. To enable a better view of the advantages of the approach, a comparative study with the existing techniques has been carried out in addition to a simulation using the Monte Carlo method. [ABSTRACT FROM AUTHOR]

Conventional process planning of manufacturing operations presets fixed process means and process tolerances for all operations and allows outputs to be distributed around these fixed values, as long as the final outputs meet acceptable specifications. Most of these approaches consider process means and process tolerances to be independent decision variables in process planning with the resultant process means equal or close to the design targets of the blueprint dimensions. Furthermore, these approaches assume that process variability is small in comparison to the quality requirement, and that the phenomena of process shifting or deterioration are not factors of manufacturing operations. For these reasons, conventional approaches to process planning are inappropriate for high value, and precision manufacturing process, particularly of a complex part. Hence, this study introduces a process optimization model which considers process means and process tolerances simultaneously, with sequential operation adjustment to reduce process variability, and with part compensation to offset process shifting. [ABSTRACT FROM AUTHOR]

The tolerance allocation optimization method by fuzzy-set weight-center evaluation is used to derive the manufacturing difficulty coefficient, through quantifying the manufacturing condition factors which all affect the manufacturing cost, including the forming means of the blank, element size, machining surface features, operator’s skills, and material’s machinability. The coefficient is then converted into a weight factor used in the inversed square model representing the relationship between the cost and tolerance, a cost-objective function model based on optimal tolerance allocation according to the manufacturing conditions is thus established for optimizing and allocating the tolerances. Integrating this model into computer-aided-tolerance-allocation makes it more convenient, accurate, and feasible. [ABSTRACT FROM AUTHOR]

Tolerancing has great impact on the cost and quality of a product. Previous research essentially focussed on one-dimensional tolerancing where sized tolerances accumulate only in one direction. When sized and angular tolerances are considered simultaneously, tolerances accumulate, however, in two different directions in the given view plane. We utilize related tolerance zones to illustrate the accumulation processes of sized and angular tolerances. The orientational tolerances are converted into the equivalent sized or angular tolerances in terms of their engineering semantics. We establish the sequential linear optimization models to maximize the 2D sized, angular, and orientational working tolerances of a 3D machined part based on the process capabilities. At any completion stage of operations, we measure the processed sized dimensions and then substitute them into the dimensional chains to dynamically re-calculate the mean working dimensions for remaining operations. We also re-evaluate the working tolerances for remaining operations using sequential optimization models. This approach can release the working tolerances, reduce manufacturing costs, and enhance the acceptance rate of machined parts when we manufacture the complex, low-volume, and high-value-added parts. The approach is finally illustrated with a practical example. [ABSTRACT FROM AUTHOR]

Precision inspection of free-form surface is difficult with current industry practices that rely on accurate fixtures. Alternatively, the measurements can be aligned to the part model using a geometry-based registration method, such as the iterative closest point (ICP) method, to achieve a fast and automatic inspection process. This paper discusses various techniques that accelerate the registration process and improve the efficiency of the ICP method. First, the data structures of approximated nearest nodes and topological neighbor facets are combined to speed up the closest point calculation. The closest point calculation is further improved with the cached facets across iteration steps. The registration efficiency can also be enhanced by incorporating signal-to-noise ratio into the transformation of correspondence sets to reduce or remove the noise of outliers. Last, an acceleration method based on linear or quadratic extrapolation is fine-tuned to provide the fast yet robust iteration process. These techniques have been implemented on a four-axis blade inspection machine where no accurate fixture is required. The tests of measurement simulations and inspection case studies indicated that the presented registration method is accurate and efficient. [ABSTRACT FROM AUTHOR]

Tolerance on parts dimension plays a vital role as the quality of the product depends on sub components tolerance. Thus, precision products that are manufactured reflect at high manufacturing cost. To overcome this situation, sub components of an assembly may be manufactured with wider tolerance, measured (using latest technologies like image processing) and grouped in partition and corresponding group components may be mated randomly. This present work is to obtain an optimum manufacturing tolerance to selective assembly technique using GA and to obtain maximum number of closer assembly specification products from wider tolerance sub components. A two components product (fan shaft assembly) is considered as an example problem, in which the subcomponents are manufactured with wide tolerance and partitioned into three to ten groups. A combination of best groups is obtained for the various assembly specifications with different manufacturing tolerances. The proposed method resulted nearly 965 assemblies produced out of one thousand parts with 15.86% of savings in manufacturing cost. [ABSTRACT FROM AUTHOR]

To obtain imposed dimensional and geometrical specifications for any mechanical piece, production tolerances must be calculated. So a simulation of workpiece behavior when it is machined, has permitted calculations of deviations on machined surfaces. The method of deviation calculation is based on a comparison between imposed functional tolerance and the tolerance calculated in relation to deviations on two machined surfaces or between a machined surface and the operational datum. The one direction modelling of deviations inquires practical inputs such as the planning process, the operational datum, the deviations on rough surfaces, and deviations on surface datum for any stage of machining. The developed method allows determining the deviations on machined surfaces. Then, tolerances on production dimensions were calculated in three directions. These results have permitted to define average production dimensions, which may be used for NC machine programming and to prepare an optimal rough piece configuration. The developed method has been applied for the machining of a fixing screw. [ABSTRACT FROM AUTHOR]

In current research of computer aided tolerancing (CAT), how to build models with tolerance and how to generate 3D dimension chains automatically have been tough problems and still unsolved. This paper builds a simulated toleranced CAD geometrical model (STCAD model) based on the feature-based original idealized CAD geometrical model (OICAD model), which can simulate real parts with manufacturing dimension errors from different aspects. Further more, an automatic generation method of 3D dimension chains based on some newly proposed definitions is put forward. In this method, firstly the conception of part instantiation (PI) is realized, secondly performance feature is defined, thirdly through building STCAD models, drive dimensions can be obtained which are vectorized to build drive dimension skeleton model (DDSM), and finally 3D dimension chains can be obtained by DDSM and the method of space projection. This method can generate 1D, 2D, and 3D dimension chains of parts or assemblies. It is verified in our own-developed automatic generation system of 3D dimension chains . [ABSTRACT FROM AUTHOR]