A tree approach for tolerance charting

A tolerance chart is a very useful tool for process engineers to determine tolerances and mean values of working dimensions of a process plan. This paper presents a tree-theoretic representation for a tolerance chart. Three trees can be generated from blueprint dimensions, stock removals and working dimensions of a tolerance chart. The algorithms for generating the trees are provided, and these trees can be used to identify dimensional chains and solid stock removals in a tolerance chart. Finally, a mathematical model of linear equations for calculating mean working dimensions is formulated from the dimensional chains.     

Increased Surface Integrity in Porous Tungsten from Cryogenic Machining with Cermet Cutting Tool

In order to eliminate the process of backfilling porous tungsten with a plastic infiltrant during machining to prevent unwanted smearing of surface pores, cryogenic machining is investigated as a viable alternative. Porous tungsten is mainly used in the manufacture of dispenser cathodes where demands for surface quality and dimensional tolerances are extremely high. For these reasons, the ability of cryogenic machining to provide increased surface integrity and tool life compared to conventional dry machining is explored. Moreover, some preliminary results of machining with various cutting edge radii and effects on surface stress state are presented. Overall, cryogenic machining does provide significant surface quality and tool wear improvements over conventional dry machining practices.     

Improving automotive dimensional quality by using principal component analysis

Dimensional quality is a measure of conformance of the actual geometry of products with the designed geometry. In the automotive body assembly process, maintaining good dimensional quality is very difficult and critical to the product. In this paper, a dimensional quality analysis and diagnostic tool is developed based on principal component analysis (PCA). In quality analysis, the quality loss due to dimensional variation can be partitioned into a mean deviation and piece-to-piece variation. By using PCA, the piece-to-piece variation can be further decomposed into a set of independent geometrical variation modes. The features of these major variation modes help in identifying the underlying causes of dimensional variation in order to reduce the variation. The variation mode chart developed in this paper provides the explicit and exact geometrical interpretation of variation modes, making PCA easily understood. A case study using an automotive body assembly dimensional quality analysis will illustrate the value and power of this methodology in solving actual engineering problems in a practical manner.     

Boundary element method for <Emphasis Type="Italic">J</Emphasis>-integral and stress intensity factor computations in three-dimensional interface cracks

A general numerical tool for the analysis of three–dimensional bimaterial interface cracks is presented in this paper. The proposed tool is based on a multidomain formulation of the Boundary Element Method (BEM), with the crack located at the interface of the domain. Mixed mode stress intensity factors are computed along the three-dimensional crack fronts using the Energy Domain Integral (EDI) methodology and decoupled via the Interaction Integral. The capability of the procedure is demonstrated by solving a number of examples. The last of these examples consists in a thick centre cracked panel for which the behaviour of the J-integral and the mixed-mode stress intensity factors along the crack front is studied as a function of the material mismatch.     

Performance of surface-textured end-mill insert on AISI 1045 steel

Recently, the surface texturing of tool/work pieces to improve performance has been investigated in the manufacturing industry. Grinding is employed to produce quality products with improved dimensional accuracy. The combination of grinding and end milling is a suitable method for surface texturing. The present study explains the effect of a textured-pattern end-milling tool on AISI 1045 steel. The effects of the pitch and depth of the pattern are investigated in detail, as are the effects of the input parameters on the cutting force and tool wear. The experimental results show that tool wear is reduced by 53% with surface texturing. Moreover, the surface-textured pattern helps to reduce the cutting force. The tool material wastage which can pose economy threats, can be drastically reduced by increasing the tool life using surface texturing.     

Ultrasonic on-machine measurement for internal topographies

The integration of metrology into the manufacturing process is becoming increasingly important for production technology. The measurement directly on machine tools is especially improving manufacturing strategies. So far, optical or tactile measuring systems are the state-of-the-art for dimensional measurements in process metrology. However, the wall thickness of structures with inner cavities cannot be measured with these systems. Owing to these deficits, an ultrasonic system was integrated into the peripheral equipment of a machine tool. Both the extensive signal processing of the acoustic echoes and the developed software tool ' w -sonic' are discussed. The aim is to show the potential of the ultrasonic in-line measurement. A practical application for the individual machining of gas cylinders and initial results are also presented.     

Boundary element analysis of the thermal behaviour in thin-coated cutting tools

Temperature measurement and prediction have been a major focus of machining for several decades, but now these problems become more complex due to the wider use of advanced cutting tool coatings. In all literature items cited the boundary element method (BEM) were used to find the distribution of temperature inside the uncoated tool body or along the tool–chip interface in the machining processes. The BEM-based approach proposed in this paper overcomes this limit and the temperature distribution in thin coated layers is well studied. In this study, a general strategy based on a nonlinear transformation technique is introduced and applied to evaluate the nearly singular integrals occurring in two dimensional (2D) thin-coated structures. For the test problems studied, very promising results are obtained when the thickness to length ratio is in the orders of 1.0E?6 to 1.0E?10, which is sufficient for modeling most thin-coated structures in the micro- or nano-sclaes.     

The spectral element method for elastic wave equations—application to 2‐D and 3‐D seismic problems

A spectral element method for the approximate solution of linear elastodynamic equations, set in a weak form, is shown to provide an efficient tool for simulating elastic wave propagation in realistic geological structures in two‐ and three‐dimensional geometries. The computational domain is discretized into quadrangles, or hexahedra, defined with respect to a reference unit domain by an invertible local mapping. Inside each reference element, the numerical integration is based on the tensor‐product of a Gauss–Lobatto–Legendre 1‐D quadrature and the solution is expanded onto a discrete polynomial basis using Lagrange interpolants. As a result, the mass matrix is always diagonal, which drastically reduces the computational cost and allows an efficient parallel implementation. Absorbing boundary conditions are introduced in variational form to simulate unbounded physical domains. The time discretization is based on an energy‐momentum conserving scheme that can be put into a classical explicit‐implicit predictor/multicorrector format. Long term energy conservation and stability properties are illustrated as well as the efficiency of the absorbing conditions. The accuracy of the method is shown by comparing the spectral element results to numerical solutions of some classical two‐dimensional problems obtained by other methods. The potentiality of the method is then illustrated by studying a simple three‐dimensional model. Very accurate modelling of Rayleigh wave propagation and surface diffraction is obtained at a low computational cost. The method is shown to provide an efficient tool to study the diffraction of elastic waves and the large amplification of ground motion caused by three‐dimensional surface topographies. Copyright © 1999 John Wiley & Sons, Ltd.     

Thermophysical properties of elastomers

The following account describes investigations of dimensional and stiffness characteristics of representative polyacrylic and silicone rubbers over the approximate temperature range 20 °C–175 °C. The results have led to a quantitative understanding of distinctive features in the behaviour of these elastomers, encountered during the course of their repeated use as tool materials in composite component manufacture, conforming with an explanation in terms of thermally induced cross-linking. It is concluded that silicone rubber offers more promise than polyacrylic rubber in applications where behavioural stability and a reasonable degree of control are required.     

Evaluation Metrics for the Rating and Optimization of Snap-fits

Current snap-fit design guides recommend sizing snap-fit features on the basis of insertion force and allowable strain during assembly. Retention force information in such guides is often inaccurate, although this is considered to be the primary attribute of the snap-fit after assembly. The authors contend that these (insertion force, allowable strain, retention force) are not the only critical performance criteria for snap-fit features. Designers have to contend with several other constraints and design requirements. Additional performance metrics for snap-fit features are proposed by drawing upon considerable experience with plastic part design issues. Locking ratio, dimensional and volumetric retention force, consideration of the characteristic dimension of the joint and snap-fit, feature stiffness, required over-insertion and consideration of snap-fit strength relative to part strength are proposed to supplement currently used metrics for evaluating and rating snap-fit designs. The applicability of these metrics is illustrated with real-life examples, and their merits and demerits discussed. A chart of achievable locking ratios for different snap-fit topologies is presented for use as a design tool for the initial selection of snap-fit topologies. Its use as a rational basis for selection and optimization of snap-fits is suggested. Adoption of proposed metrics will allow designers to better quantify, and thereby optimize the performance of, snap-fit features. These ideas will be built upon in the future, and used as a basis for a comprehensive snap-fit selection and detailed design tool.     

Investigation of the dimensional stability of carbon epoxy cylinders manufactured by resin transfer moulding

The prediction of process-induced dimensional variability and residual stresses occurring during the manufacturing of composite structures is critical to produce parts where tight tolerances are required. Therefore, the development of material constitutive models and processing properties, and the validation of these models, are two essential steps in order to accurately simulate the behaviour of the materials involved. In this paper, the material constitutive models of a one-part epoxy resin were implemented in a three-dimensional finite element software based on the ABAQUS/COMPRO platform to investigate the dimensional stability of a composite structure manufactured by resin transfer moulding (RTM). A simplified geometry was used as a representative structural component with different layup configurations. Both heat transfer analysis and stress analysis were conducted. Contact interactions were implemented in the stress analysis to simulate the tool–part interaction. The presented analysis predicted the angle variation and the composite debonding caused by the coefficient of thermal expansion mismatch between the mould and the composite part and the resin volumetric chemical shrinkage.     

Prediction of machining quality due to the initial residual stress redistribution of aerospace structural parts made of low-density aluminium alloy rolled plates

During the machining of thick, large and complex aluminium parts, the redistribution of initial residual stresses is the main reason for machining errors such as dimensional variations and the post-machining distortions. These errors can lead to the rejection of the parts or to additional conforming operations increasing production costs. It is therefore a requirement to predict potential geometrical and dimensional errors resulting from a given machining process plan and in taking into consideration the redistribution of the residual stresses. A specific finite element tool which allows to predict the behaviour of the workpiece during machining due to its changing geometry and to fixture-workpiece contacts has been developed. This numerical tool uses a material removal approach which enables to simulate the machining of parts with complex geometries. In order to deal with industrial problems this numerical tool has been developed for parallel computing, allowing the study of parts with large dimensions. In this paper, the approach developed to predict the machining quality is presented. First, the layer removal method used to determine the initial residual stress profiles of an AIRWARE^? 2050-T84 alloy rolled plate is introduced. Experimental results obtained are analysed and the same layer removal method is simulated to validate the residual stress profiles and to test the accuracy of the developed numerical tool. The machining of a part taken from this rolled plate is then performed (experimentally and numerically). The machining quality obtained is compared, showing a good agreement, thus validating the numerical tool and the developed approach. This study also demonstrates the importance of taking into account the mechanical behaviour of the workpiece due to the redistribution of the initial residual stresses during machining when defining a machining process plan.     

Limitations in gap width measurements by X-ray radiography

The use of radiography as a quantitative tool for determining the width and depth of cracks is discussed. It is shown that in most cases the extraction of dimensional information from radiographs may lead to erroneous results. The effects of oblique geometry and a blurring line spread function are modelled. The calculated results are compared with experimental findings.     

Dual-Comb Ranging

Absolute distance measurement is a fundamental technique in mobile and large-scale dimensional metrology. Dual-comb ranging is emerging as a powerful tool that exploits phase resolution and frequency accuracy for high-precision and fast-rate distance measurement. Using two coherent frequency combs, dual-comb ranging allows time and phase response to be measured rapidly. It breaks through the limitations related to the responsive bandwidth, ambiguity range, and dynamic measurement characteristics of conventional ranging tools. This review introduces dual-comb ranging and summarizes the key techniques for realizing this ranging tool. As optical frequency comb technology progresses, dual-comb ranging shows promise for various professional applications.     

Triaxial behavior of granular material under complex loading path by a new numerical true triaxial engine

A new numerical true triaxial engine based on discrete element method accounting for rolling resistance contact is developed. By this engine, we have simulated mechanical behavior of granular materials under complex stress loading path in this study. Stress-strain responses of a kind of typical granular sand under several stress loading path in meridian and deviatoric stress space are provided. The results show that the three dimensional effects like the intermediate principal stress play an important role in the modeling processes. Theoretical analysis in strength characteristic implies the strength criteria with three parameters such as unified strength criterion and van Eekelen strength criterion are capable of describing cohesionless granular material behaviors in three dimensional stress states. Moreover, the case study for Chende sand further demonstrates the numerical true triaxial engine, is a potential tool. As compared to conventional triaxial compression test, this new developed apparatus could be widely used to “measure” elastic-plastic behavior in three dimensional stress space for finite element analysis in geotechnical problems.     

Crosslinking Strategies for 3D Bioprinting of Polymeric Hydrogels

Three‐dimensional (3D) bioprinting has recently advanced as an important tool to produce viable constructs that can be used for regenerative purposes or as tissue models. To develop biomimetic and sustainable 3D constructs, several important processing aspects need to be considered, among which crosslinking is most important for achieving desirable biomechanical stability of printed structures, which is reflected in subsequent behavior and use of these constructs. In this work, crosslinking methods used in 3D bioprinting studies are reviewed, parameters that affect bioink chemistry are discussed, and the potential toward improving crosslinking outcomes and construct performance is highlighted. Furthermore, current challenges and future prospects are discussed. Due to the direct connection between crosslinking methods and properties of 3D bioprinted structures, this Review can provide a basis for developing necessary modifications to the design and manufacturing process of advanced tissue‐like constructs in future.     

Structural integrity of pipelines: T-stress by line-spring

The elastic T‐stress is an important constraint parameter for characterizing elastic–plastic crack‐tip fields and in fracture assessment procedures. However, many of the methods reported in the literature for estimating T‐stress are not easily suited for surface‐cracked pipes because these are three‐dimensional in nature. Here, the line‐spring method is demonstrated to be an efficient and accurate tool for the constraint estimation in surface‐cracked pipes. Detailed three‐dimensional analyses are performed to verify the line‐spring results. Using the line‐spring method, the effects of different crack geometries and diameter‐to‐thickness ratio on stress‐intensity factor (SIF) and T‐stress in circumferentially surface‐cracked pipes are examined. Further, a compendium of normalised SIF and T‐stress values for surface‐cracked pipes in remote tension and bending, calculated from a total of 1000 analyses, is tabulated. Finally, the application of an ‘elastic–plastic’ T‐stress under large‐scale plasticity is explored.     

A semi-analytical simulation strategy and its application to warpage of autoclave-processed CFRP parts

The manufacturing of composite structures is accompanied by fabrication induced deformations. Those deformations are undesirable and lead to transgression of geometric tolerances in the finished parts. In order to get the part within aspired dimensional tolerances, geometrical compensation of the tool is necessary. This often iterative conducted tooling-rework is commonly time consuming and costly. This paper presents an shell element based. semi-analytical simulation approach focusing on warpage deformations due to tool part interaction, in order to account for manufacturing induced deformations within the tool design process. Deviation measurements on test specimen level serve as inputs for the calculation of equivalent coefficients of thermal expansion according to the proposed analytical model. Thus, ‘warpage properties’ of different prepreg – tool–material combinations are determined. The use and the practicability of the developed approach is demonstrated by means of the calculation of a warpage compensated tool surface.     

A STOCHASTIC CHARACTERIZATION OF THE MACHINE TOOL WORKPIECE SYSTEM IN BTA OEEP HOLE MACHINING Part I: Mathematical Modelling and Analysis

A three dimensional model of the BTA deep-hole machining system is presented by modelling each of the components separately and later combining to represent the total system. A model for the interaction between the workpiece and the cutting tool is also included. Such a model can determine the response of any component of the machine tool as well as the individual influence on the system performance. Based on this, physical models representing the three working methods in the BTA process can be studied, from which stochastic differential equations are derived to represent the resultant force system on the machine tool

A physical model for the stationary workpiece and rotating cutting tool working method is developed. The assumed modes method along with the Lagrange' equation is used to obtain the stochastic differential equation to represent the influence of axial force and torque, in order to obtain the response of the system under the action of the axial force and torque to predict the stability behaviour.     

Electrode wear phenomenon and its compensation in micro electrical discharge milling: A review

Micro electrical discharge machining (µEDM) is playing a significant role in the world of miniaturization, especially in micro electro mechanical systems, biomedical devices, micro die/molds, etc. Micro electrical discharge milling (µED-milling) is a variant of µEDM used for producing complex 3D features with a simple shaped tool. The material removal mechanism of µEDM depends on electro-thermal energy between the tool electrode and workpiece. µEDM inherently being a non-contact machining process, leads to produce miniaturized features in hard to machine materials. Besides erosion of the workpiece material, intrinsic feature of the process leads to tool wear (TW) and introduces dimensional inaccuracy in the micro features. Thus, it is essential to know the factors influencing the TW, and thereby compensate the TW to achieve dimensional stability of the machined features. The critical factors affecting the wear phenomenon of a tool and various techniques applied to compensate TW in µED-milling along with future trends of their application are presented. The key issues of µED-milling and challenges faced in implementing a TW compensation technique are highlighted. The concept of intentional wear of tool electrode and associated advantages in EDM is also demonstrated.