Increased precision in variation simulation by considering effects from temperature and heat

Every manufactured product deviates from the intended product. In a production series a number of noise sources will influence the product resulting in geometric variation. This variation leads to functional and aesthetical variation of the product. In geometry assurance, focus is on knowledge, methods, and tools to assure that the aesthetical and functional properties of a product are maintained for the non-nominal product. In this thesis, the effect of temperature and heat are considered in combination with variation. The relative ease of the manufacturing techniques and their flexible physical properties has made plastics an attractive alternative to metals in many industries. However, the thermal expansion of plastics is often much larger than metal, and is often of the size of other effects considered in geometry assurance. During assembly welding is a common joining technique. During welding a large amount of heat is induced into the welded assembly. It has previously been shown that welding deformations depend on positioning errors prior to welding. Therefore, in order to evaluate the robustness of an assembly that is welded; variation- and welding simulation need to be considered in combination. For this, methods and tools need to be developed. In this thesis an interview study is performed that reports current issues and problems when simulating for robustness in plastic design. This led to a framework for descriptive studies for robust plastic design where part-, assembly and functional assembly are considered as different levels of robustness. This study influenced the focus of this thesis toward temperature and heat. A study on the combination of thermal expansion and variation showed that geometric variation is dependent on temperature. In order to evaluate the effect of variation in combination with thermal expansion a method and tool to simulate the distribution of stresses was developed. Including contact modeling in variation simulation considering thermal expansion was shown to lead to long simulation times in some instances. Therefore, a new contact modeling approach for variation simulation has been developed and shown to reduce simulation time significantly. A study focusing on rattle and squeak simulation showed that this is a further area where thermal expansion for the non-nominal geometry needs to be considered. In order to enable variation simulation of welded assemblies, a method called the Steady state, Convex hull, Volumetric shrinkage-method (SCV-method) has been developed in a number of studies, giving reasonable results. Also, the influence of using clamps to reduce the effect of variation on weld induced deformation has been studied

Joining in Nonrigid Variation Simulation

Geometrical variation is closely related to fulfillment of both functional and esthetical requirements on the final product. To investigate the fulfillment of those requirements, Monte Carlo (MC)-based variation simulations can be executed in order to predict the levels of geometrical variation on subassembly and/or product level. If the variation simulations are accurate enough, physical tests and try-outs can be replaced, which reduce cost and lead-time. To ensure high accuracy, the joining process is important to include in the variation simulation. In this chapter, an overview of nonrigid variation simulation is given and aspects such as the type and number of joining points, the joining sequence and joining forces are discussed

Towards Geometry Prediction in Additive Manufacturing by Considering Variation in the Inherent Strain

The inherent strain method is commonly employed to predict part distortion in the additive manufacturing (AM) process simulations. However, mean inherent strain values are considered which could hinder the prediction accuracy. Therefore in this paper, variation in inherent strain values are considered to predict the geometric distortion. In the first step, a five layer mesoscale thermo-mechanical model is employed to estimate the varying inherent strain values in each of the five layers. This serves as an input to the inherent strain method to predict geometric distortion at the part level. A comparison between mean versus varying inherent strain approach is shown to highlight the differences in geometric distortion prediction accuracy

Efficient spot welding sequence simulation in compliant variation simulation

Geometric variation is one of the sources of quality issues in a product. Spot welding is an operation that impacts the final geometric variation of a sheet metal assembly considerably. Evaluating the outcome of the assembly, considering the existing geometrical variation between the components can be achieved using the Method of Influence Coefficients (MIC), based on the Finite Element Method (FEM). The sequence, with which the spot welding operation is performed, influences the final geometric deformations of the assembly. Finding the optimal sequence that results in the minimum geometric deformation is a combinatorial problem that is experimentally and computationally expensive. For an assembly with N number of welds, there are N! possible sequences to perform the spot welding operation. Traditionally, spot welding optimization strategies have been to simulate the geometric variation of the spot-welded assembly after the assembly has been positioned in an inspection fixture, using an appropriate measure of variation. In this approach, the calculation of deformation after springback is one of the most time-consuming steps. In this paper, the cause of variation in the deformations after the springback, between different sequences is identified. The relative displacements of the weld points in the assembly fixture, when welded in a sequence, is the source of such behavior. Capturing these displacements leads to large time savings during sequence optimization. Moreover, this approach is independent of the inspection fixture. The relative weld displacements have been evaluated on two sheet metal assemblies. The sequence optimization problem has been solved for the two assemblies using this approach. The optimal sequence, the corresponding final assembly deformations, and the time-consumption have been compared to the traditional approach. The results show a significant correlation between the weld relative displacements in the assembly fixture, and the assembly deformation in the inspection fixture. Considering the relative weld displacement makes each assembly evaluation less time-consuming, and thereby, sequence optimization time can be reduced up to 30%, compared to the traditional approach

A Virtual Design of Experiments Method to Evaluate the Effect of Design and Welding Parameters on Weld Quality in Aerospace Applications

During multidisciplinary design of welded aircraft components, designs are principallyoptimized upon component performance, employing well-established modelling and simulationtechniques. On the contrary, because of the complexity of modelling welding process phenomena,much of the welding experimentation relies on physical testing, which means\ua0 welding producibility aspects are considered after the design has already been established. In\ua0 addition, welding optimization research mainly focuses on welding process parameters, overlooking the potential impact of product design. As a consequence, redesign loops and welding rework increases product cost. To solve these problems, in this article, a novel method that combines the benefits of design of experiments (DOE) techniques with welding simulation is presented. The aim of the virtual design of experiments method is to model and optimize the effect of design and welding parameters interactions early in the design process. The method is explained through a case study, in which weld bead penetration and distortionare quality responses to optimize. First, a small number of physical welds are conducted to develop and tune the welding simulation. From this activity, a new combined heat source model is presented.Thereafter, the DOE technique optimal design is employed to design an experimental matrix that enables the conjointly incorporation of design and welding parameters. Welding simulations are then run and a response function is obtained. With virtual experiments, a large number of design and welding parameter combinations can be tested in a short time. In conclusion, the creation of a meta-model allows for performing welding producibility optimization and robustness analyses during early design phases of aircraft component

Strong peak immunogenicity but rapid antibody waning following third vaccine dose in older residents of care homes

Third-dose coronavirus disease 2019 vaccines are being deployed widely but their efficacy has not been assessed adequately in vulnerable older people who exhibit suboptimal responses after primary vaccination series. This observational study, which was carried out by the VIVALDI study based in England, looked at spike-specific immune responses in 341 staff and residents in long-term care facilities who received an mRNA vaccine following dual primary series vaccination with BNT162b2 or ChAdOx1. Third-dose vaccination strongly increased antibody responses with preferential relative enhancement in older people and was required to elicit neutralization of Omicron. Cellular immune responses were also enhanced with strong cross-reactive recognition of Omicron. However, antibody titers fell 21–78% within 100 d after vaccine and 27% of participants developed a breakthrough Omicron infection. These findings reveal strong immunogenicity of a third vaccine in one of the most vulnerable population groups and endorse an approach for widespread delivery across this population. Ongoing assessment will be required to determine the stability of immune protection

Speech Communication

Contains table of contents for Part IV, table of contents for Section 1, an introduction, reports on seven research projects and a list of publications.C.J. Lebel FellowshipDennis Klatt Memorial FundNational Institutes of Health Grant T32-DC00005National Institutes of Health Grant R01-DC00075National Institutes of Health Grant F32-DC00015National Institutes of Health Grant R01-DC00266National Institutes of Health Grant P01-DC00361National Institutes of Health Grant R01-DC00776National Science Foundation Grant IRI 89-10561National Science Foundation Grant IRI 88-05680National Science Foundation Grant INT 90-2471

Speech Communication

Contains table of contents for Part IV, table of contents for Section 1 and reports on five research projects.Apple Computer, Inc.C.J. Lebel FellowshipNational Institutes of Health (Grant T32-NS07040)National Institutes of Health (Grant R01-NS04332)National Institutes of Health (Grant R01-NS21183)National Institutes of Health (Grant P01-NS23734)U.S. Navy / Naval Electronic Systems Command (Contract N00039-85-C-0254)U.S. Navy - Office of Naval Research (Contract N00014-82-K-0727

Speech Communication

Contains table of contents for Part V, table of contents for Section 1, reports on six research projects and a list of publications.C.J. Lebel FellowshipDennis Klatt Memorial FundNational Institutes of Health Grant R01-DC00075National Institutes of Health Grant R01-DC01291National Institutes of Health Grant R01-DC01925National Institutes of Health Grant R01-DC02125National Institutes of Health Grant R01-DC02978National Institutes of Health Grant R01-DC03007National Institutes of Health Grant R29-DC02525National Institutes of Health Grant F32-DC00194National Institutes of Health Grant F32-DC00205National Institutes of Health Grant T32-DC00038National Science Foundation Grant IRI 89-05249National Science Foundation Grant IRI 93-14967National Science Foundation Grant INT 94-2114

Geometric Variation Simulation for the Development of Products with Plastic Components

Every manufactured product deviates from the intended product. Furthermore, in a series of products geometrical variation is always present. This variation will lead to functional and aesthetical variation of the product. Geometrical variation stems from variation in the manufacturing of parts and fixtures and variation in assembly operations. Also, functional variation is dependent on environmental variation during the user phase.The source of variation accumulates during production. Often, it is difficult or expensive to reduce the source of variation. Therefore, instead of diminishing the source of variation it is preferable to reduce the effect of this variation. This is the case in a robust design. In connection to geometrical variation a robust design is often related to the way parts are located to other parts in a product.It is in the early phase of product development that most design solutions are determined. Design changes that are introduced later in the product development process often generate a high cost. Hence, to gain confidence during the design phase, that critical measures and key characteristics are within their requirements for the manufactured product it is important to be able to predict product behavior. This is done using virtual product development tools and/or prototypes. Virtual tools have a lot of advantages in comparison to physical prototypes. It is, however, important that simulations are accurate and that all relevant phenomena are considered.In this work the focus is on variation simulation for plastics. The increasing environmental concern has led a number of industries to investigate the possibilities to reduce the weight of their products. The relative ease of the manufacturing techniques and their flexible physical properties have made plastics an attractive alternative. However, this leads to new challenges in virtual product development.In this thesis an interview study is performed that reports current issues and problems when simulating for robustness in plastic design. This led to a framework for robust plastic design where part-, assembly and functional assembly are considered as different levels of robustness.A procedure is proposed where commercial injection molding techniques are used in combination with statistical methods to predict part variation resulting from manufacturing variation. This is implemented to study the effect of manufacturing variation on assembly variation.Furthermore, a tool is developed to simulate thermal expansion in combination with assembly variation. A case study reveals that there are combined effects.Finally, a method to stabilize the numerical calculation of the thermal elasto-plastic problems is developed