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Dimensional and geometric tolerances affect both the cost and the functionality of a given product. Finding the acceptable trade-off between the two is among the common engineering tasks. Thus, many tolerance analysis methods are developed to help engineers and assist in the decision-making process. In this article, the authors have assessed four tolerance analysis methods by applying them to the open- loop assembly. The results obtained by the tolerance chart (worst-case) method, Monte- Carlo simulation, vector-loop analysis, and the Unified Jacobian-torsor model were analysed and compared. Additionally, the overview and application guidelines are included for each of the methods, aiming to help both researchers and practitioners. The results have confirmed that there are significant variations in the outputs across the observed methods, implying the need for informed method selection.

Sheet metal parts are widely used in automotive, aerospace, ship and consumer goods industries. The final dimensions of a sheet metal assembly result from the parts deformation, which in turn is affected by many variations in material, thickness and single parts dimensions. The tolerance analysis on sheet metal assemblies improve the knowledge about the process. Advanced simulations enable the optimization of product features, GD&T scheme and assembly process. Moreover, Variational Models of both the product and the assembly system enable to assess the sources of 3D error propagation from the different contributors. However, the simulation results are very affected by the modelling approach of critical components, such as the Fixture Systems. The present paper firstly introduces a strategy to model the Fixture System and the assembly process for compliant parts. Then, a robust analysis of the variations in the model with respect to the modelling factors is performed by a Design of Experiments. A case study on an automotive fender is discussed. The results demonstrate that the modelling strategy of the clamping operation have the main effects, while the modelling of locators scheme, spot joints and FEM meshing are less important.

When talking about a large batch production of a certain mechanical product it generally comes along with specific requirements in terms of dimensional management to guarantee a consistently high product quality ensuring that customer requirements are met. Therefore, this contribution is about the effect that the elasticity of the observed assembly has on the formation of the limiting positions of the considered key product characteristics arising from tolerance analysis. On the example of an automotive door assembly a developed approach based on existing methodologies is explained in detail containing CAT and FEM simulations.

This work presents a method to support product design, since it shows how to use together tolerance assignment and analysis for choosing among different set of tolerances assigned to the same product. It starts from tolerance assignment that produces different sets of tolerances for the product components which are all acceptable from a functional point of view. It translates each assigned set of tolerances into one or more groups of tolerances that are recognized by the software used for tolerance analysis. Therefore, the software for tolerance analysis is applied to each group of tolerances by means of a Monte Carlo simulation approach. Finally, the obtained results are intersected or compounded to obtain the trend of product functional requirements that allows to identify the best set of tolerances assigned to the product components. The developed method was applied to a skillet, a platform of an industrial plant that is made of five parts connected by screws. The obtained results show how the developed new method is a valid tool to support design for industrial application.

A simulation of tolerance analysis in assemblies using Sigmund Computer Aided Tolerancing (CAT) software is validated through the example of an automobile locking device. Simulation with CAT, applying criteria on both the statistical distribution and the rivet pin position in the hole used in the example, will allow us to predict the functional dimension tolerances in these assemblies with greater accuracy in the preliminary design phase. These tolerances will subsequently define the manufacturing specifications. The statistical distribution, in the example, that best fits the overall set of tolerances, is the triangular distribution followed by the normal distribution; the position of the rivet pin axis in its hole is off-centre by 53 % with regard to its maximum value.

In automotive and aeronautic fields, within the common context of manufacturing and assembly of flexible products, such as sheet metal parts, controlling the final shape of the assembly is a key issue. Even assuming as known the shape errors in single manufactured parts, the assembly process can cause wide variability due to the flexibility of parts and to the choice of fixture and clamping frames as well as to the fastening technique adopted. Variations at part level propagate through the assembly due to both assembly sequence and process variability; therefore it is strategic to analyse different assembly configurations at the beginning of the design phase and chose the one that assures less variability on the key characteristics to be achieved. The paper presents a computer tool, based on finite element analysis, which is able to statistically analyse variations occurring in assembly processes of flexible parts. The tool offers a graphical environment to import finite element shell meshes and pre-process them by assigning fixtures, clamping points as well as fastening joints and related statistical variability. Contacts between parts can be also assigned. The output is given in terms of statistical variability of the key characteristics both graphically and numerically. The linear model behind the tool allows to quickly spam a variety of design solutions predicting failures and controlling final variations. Therefore, the tool could be used to anticipate the analysis of flexible assemblies providing useful and necessary information related to joint configurations and positions of fixtures as well as to assembly sequences.