Chensong Dong

Prediction and Compensation of Dynamic Errors for Coordinate Measuring Machines

Coordinate measuring machines (CMMs) are already widely utilized as measuring tools in the modern manufacturing industry. Rapidly approaching now is the trend for next-generation CMMs. However, the increases in measuring velocity of CMM applications are limited by dynamic errors that occur in CMMs. In this paper, a systematic approach for modeling the dynamic errors of a touch-trigger probe CMM is developed through theoretical analysis and experimental study. An overall analysis of the dynamic errors of CMMs is conducted, with weak components of the CMM identified with a laser interferometer. The probing process, as conducted with a touch-trigger probe, is analyzed. The dynamic errors are measured, modeled, and predicted using neural networks. The results indicate that, using this mode, it is possible to compensate for the dynamic errors of CMMs.

Reducing the Dynamic Errors of Coordinate Measuring Machines

Coordinate measuring machines (CMMs) are already widely utilized as measuring tools in the modern manufacturing industry. Fast and accurate probing is the current trend for the next generation of CMMs. However, measuring velocity of CMM applications are limited by dynamic errors that occur in CMMs. In this paper, the dynamic errors of coordinate measuring machines are analyzed theoretically and experimentally. The limited stiffness of air bearings were found to cause dynamic errors due to the existence of Abbes offsets. The characteristics of the air bearings used on CMMs were modeled by the finite element analysis (FEA). The load capacity and stiffness of the air bearings were computed. Using this model, the dynamic errors of the CMM were reduced through revising the air bearing design. To verify the effectiveness of this approach, the performance of the air bearings was tested both statically and dynamically. The results show that the dynamic errors can be significantly reduced.

Assembly dimensional variation modelling and optimization for the resin transfer moulding process

The increasing demand for composite products to be affordable, net-shaped and efficiently assembled makes tight dimensional tolerance critical. Due to lack of accurate process models, resin transfer moulding (RTM) dimensional analysis and control are often performed using trial-and-error approaches based on engineers experiences or previous production data. Such approaches are limited to specific geometries and materials and often fail to achieve the required dimensional accuracy in the final products. This paper presents an innovative study on the dimensional variation prediction and control for fibre reinforced polymeric matrix composites. A dimensional variation model was developed for process simulation based on thermal stress analysis and finite element analysis (FEA). This model was validated against experimental data, analytical solutions and data from the literature. Using the FEA-based dimensional variation model, the deformations of typical composite structures were studied, and a regression-based dimensional variation model was developed. By introducing the material modification coefficient, this comprehensive model can account for various fibre/resin types and stacking sequences. The regression-based dimensional variation model can significantly reduce computation time by eliminating the complicated, time-consuming finite element meshing and material parameter defining process and providing a quick design guide for composite products with reduced dimensional variations. The structural tree method (STM) is proposed to compute the assembly deformation from the deformations of individual components as well as the deformation of general shape composite components. The STM enables rapid dimensional variation analysis/synthesis for complex composite assemblies when used along with the regression-based dimensional variation model. The work presented here provides a foundation to develop practical dimensional control techniques for composite products.

Formation of Resin-Rich Zones in Composites Processing

Resin-rich zones are a common phenomenon in liquid composite molding processes. These resin-rich zones cause unwanted residual stress and deformation, and part-to-part variation, and thus they need to be studied in the design of composite structures. An experimental study on the formation of resin-rich zones in angled composite parts is presented in this paper. Two open-channel mold sets were designed and fabricated. Fiber preforms were loaded into these molds and the gaps formed were visually inspected by a microscope. The influences of corner radius, fiber volume fraction, enclosed angle, and stacking sequence were investigated, and significant factors affecting gap thickness were identified by Design of Experiments (DOE). It can be concluded from the experimental results that: 1) Fiber volume fraction is the most significant factor affecting gap thickness. Gap thickness is inversely proportional to fiber volume fraction; 2) Gap thickness is inversely proportional to radius; 3) The gap thickness of unidirectional preforms is larger than that of the cross-ply preforms.

Dimensional Variation Analysis and Synthesis for Composite Components and Assemblies

This paper presents a study on dimensional variations and tolerance analysis and synthesis for polymer matrix fiber-reinforced composite components and assemblies. A composite component dimensional variation model was developed with process simulation based on thermal stress analysis and finite element analysis (FEA). Using the FEA-based dimensional variation model, the deformations of typical composite structures were studied and the regression-based dimensional variation models were developed. The regression-based dimensional variation models can significantly reduce computation time and provide a quick design guide for composite products with reduced dimensional variations. By introducing a material modification coefficient, the comprehensive regression models can handle various fiber and resin types and stacking sequences, which eliminates the complicated, time-consuming finite element meshing and material parameter defining process. A structural tree method (STM) was developed for rapid computation of composite assembly dimensional variations resulting from deformations on individual components, as well as the deformation of composite components with complex shapes. With the STM and the regression-based dimensional variation models, rapid design optimization was conducted to reduce the dimensional variations of composite assemblies. Cost-tolerance functions were developed using a fuzzy multiattribute utility theory based cost-estimation method. Based on the developed dimensional variation and cost-tolerance models, composite assembly tolerance analysis and synthesis were performed in this study. The exploring research work presented in this paper provides a foundation for developing practical and proactive dimensional control techniques for composite products.

Assembly deformation and stresses of compliant structures

Compliant components such as large sheet metal components are commonly used in various products including automotive, aircraft and home appliances. Because of part-to-part variations, deformation and stresses are induced in the assembly process. An approach to the assembly tolerance analysis of compliant structures is presented in this paper. Given component deformation, assembly deformation and stresses are derived by finite element analysis (FEA). The influence of component deformation on assembly deformation and stresses is studied by response surface methodology (RSM), and a regression model is developed. Using the developed regression model, Monte Carlo simulation was conducted to study assembly tolerance and stresses. This approach is illustrated by an example.

Experimental Study on Strengthening of Steel Structures with Fiber Reinforced Plastic

An experimental study on the strengthening of steel structures with FRP (Fiber Reinforced Plastic) is presented in this paper. Test coupons were prepared by applying FRP patches on both sides of steel coupons. Standard tensile tests were conducted to the test coupons. Two types of CFRP (Carbon Fiber Reinforced Plastic) and one type of GFRP (Glass Fiber Reinforced Plastic) were studied. The load and strain data were recorded, and the stiffness and strength were derived. The results show that CFRP provides better strengthening than GFRP, but there is no significant difference between PAN graphite/epoxy and pitch graphite/epoxy laminates.

A Generic Model for Predicting the Permeability of Fiber Mats

A new empirical model for predicting the permeability of fiber mats is presented in this paper. Permeability data were collected from the NIST reinforcement permeability database and categorized according to the material architecture. It is seen from the data that for each category, permeability is proportional to fiber volume fraction. In order to describe the behavior of permeability vs. fiber volume fraction, the location, scale and shape parameters were introduced for each material category. The model was validated against the experimental data and good agreement was found.

Mold Development for Resin Transfer Molding with Dimension Variation and Deformation Compensation

A method for achieving better dimensional control for composites based on deformation compensation in mold design is presented in this paper. The process-induced deformation of a general angled part, i.e. spring-in, was studied statistically to account for the processing-related uncertainties. The part geometry was modified based on the results from the statistical analysis for offsetting the deformation. The modified part geometry was used to design the mold for resin transfer molding and the mold was made by the CNC wire electrical discharge machining (WEDM) process. Five sample parts were fabricated using the mold and the spring-in angles were measured. The results show that the process-induced deformation is significantly reduced through deformation compensation. This method presented in this paper provides an approach to minimizing the overall process-induced deformation of resin transfer molded parts.

Dimensional Variations of General Curved Composite Parts

With the increasing demands of energy efficiency and environment protection, composite materials have become an important alternative for traditional materials. Composite materials offer many advantages over traditional materials including: low density, high strength, high stiffness to weight ratio, excellent durability, and design flexibility. Despite all these advantages, composite materials have not been as widely used as expected because of the complexity and cost of the manufacturing process. One of the main causes is associated with poor dimensional control. General curved composite parts are often used as the structural components in the composite industry. Due to the anisotropic material nature, process-induced dimensional variations make it difficult for tighttolerance control and limit the use of composites. This research aims to develop a practical approach for the design of general curved composite parts and assembly. First, the closed-form solution for the process-induced dimensional variations, which is commonly called spring-in, was derived. For a general curved composite part, a Structural Tree Method (STM) was developed to divide the curve into a number of pieces and calculate the dimensional variations sequentially. This method can be also applied to an assembly of composite parts. The approach was validated through a case study. The method presented in this paper provides a convenient and practical tool for the dimensional and tolerance analysis in the early design stage of general curved composite parts and assembly, which is extremely useful for the realization of affordable tight tolerance composites. It also provides the foundation of Integrated Product/Process Development (IPPD) and Design for Manufacturing/Assembly (DFM/DFA) for composites.