Analysis of Nonlinear Variation Accumulation in Auto-Body Assembly Process

In the assembly process of auto-body, variations in the geometrical dimensions of sheet metal parts and fixtures are inevitable. These variations accumulate through the multi-station assembly process to form the dimensional variations of the final products. Compared with the assembly of rigid parts, the assembly process of the elastic parts is more complex because the variation accumulation patterns rely much on the variations of fixture, jointing methods and mechanical deformation. This paper aims at analyzing the variation transformation mechanism and accumulation characteristics for the assembly of sheet metal parts based on the analysis of dimensional coordination relations among parts and fixtures. Finite element method (FEM) and Monte-Carlo Simulation (MCS) were used to analyze the effect of jointing contact on variation transformation, while a state equation was developed to describe the variation accumulation mechanism. The result of the analysis indicates that the main characteristics of elastic assembly jointing are the overlap jointing methods and elastic contacts action. The fact that the variation transform coefficients (VTC) are variable makes the assembly variation distribution Non-Gaussian even if the dimension variation of parts is Gaussian distribution. The analysis conclusions have potential value for more reasonable tolerance synthesis of elastic parts assembly.

Measurement Scheme Synthesis in Multi-Station Machining Systems

The selection of measurements in multi-station machining systems is currently not a systematic process and it involves expert human intervention. In this paper, the recently introduced formal methods for quantitative characterization of measurement schemes in multi-station machining systems are employed in devising systematic measurement scheme synthesis procedures. The newly proposed synthesis procedures were applied in devising measurement schemes in the process used to machine a car engine cylinder head. It was observed that the measurement scheme synthesis procedure based on a genetic algorithm robustly outperformed the synthesis procedures based on the heuristics of successive measurement removal.

Material Handling Throughput Using a Track Based Multihead Robot

A novel closed loop track based multi-head robot has been developed to increase material handing throughput. This robot allows for waves of robot heads to move materials in the working path by eliminating the traditional return path. Programmable clutching of a constant moving drive chain supplies the source of motion around the loop. This paper discusses the design and impact of such a system configuration, and looks at the required distributed control system.

Model for Acoustic Microscopy Inspection of Microelectronics Packages With Thin Layers

A broadband model is proposed to describe the nature of ultrasonic pulses in multilayered systems with a sub-wavelength thickness layer. This model, which is targeted towards acoustic microscopy of microelectronic devices, can incorporate measured ultrasonic properties of electronic materials and predict the complete ultrasonic pulse-train for all the interfaces in an electronic device. The model is robust, and incorporates material and geometric variables commonly encountered in microelectronics applications. Results are presented to illustrate how delaminations and cracks with foreign material or moisture ingress can appear to be well-bonded and why acoustic images of interfaces with thin layers can sometimes give erroneous indications of the bond state.

Modeling of Deformations in a Ring Shaped Workpiece Due to Chucking and Cutting Forces

This paper presents a theoretical model for predicting the elastic deformations of ring-type workpieces due to in-plane chucking and cutting forces applied in turning processes. The model is derived from classical elasticity theory for bending of thin rings. Experimental results are presented to verify the strengths and limitations of this model. The results from a finite element model are also presented for comparison. For the ring diameters and radial chucking loads considered in this work, it is shown that the theoretical model is accurate to within 11% of the measured radial deformations for rings with inner-to-outer diameter ratio (Din/Dout) of 0.881. The finite element model is shown to yield slightly better results. The applicability of the theoretical model is illustrated by using it to predict the surface error produced in turning of a ring.

Some Theory and Algorithms Pertaining to Machinability and Visibility

In previous work, we and others have developed visibility-based tool path generation schemes. Almost all previous research implicitly assumes that all visible parts are machinable. Though usually true practice, this assumption hides several subtleties inherent to the geometry of the machining process. Here, we define machinability in a stricter sense, as a generalization of the robotic path planning problem. Then, we define various “tight” necessary conditions for strict machinability, and show the connections between these conditions. After demonstrating the richness of the information contained in visibility, we show how to compute visibility effectively. Visible directions constitute an approximate feasible configuration space of a cutting tool. We also address questions pertaining to the topological connectivity of the feasible space. The theoretical results of this paper lay down a firmer foundation of machining path planning.

Experiences in Modeling, Simulation, and Optimization of Chemical Industry Supply Chains

We have developed and applied simulation as well as combined simulation – optimization models to represent process industry plant logistics and supply chain operations. The simulation model represents plant production, inventory, and shipping operations as well as inter-plant shipments. When a combined simulation-optimization approach is used, the simulation periodically invokes a classical production planning optimization model to set production and shipping levels. These levels are retrieved by and used in the simulation model. Process industry supply chain operations include stochastic elements such as customer demands whose expected values may vary in time as well as transportation lead times. The complexity of individual plant operations and logistics must be considered. Simulation provides the methods needed to integrate these elements in a single model. Periodically during a simulation run, production planning decisions that require optimization models may be made. Simulation experimental results are used to determine service levels to end customers as well as to set rail fleet sizes, inventory capacities, and capital equipment requirements for logistics as well as to assess alternative shipping schedules.

Effects of Radial Immersion and Cutting Direction on Chatter Instability in End-Milling

Low radial immersion end-milling involves intermittent cutting. If the tool is flexible, its motion in both the x- and y-directions affects the chip load and cutting forces, leading to chatter instability under certain conditions. Interrupted cutting complicates stability analysis by imposing sharp periodic variations in the dynamic model. Stability predictions for the 2-DOF model differ significantly from prior 1-DOF models of interrupted cutting. In this paper stability boundaries of the 2-DOF milling process are determined by three techniques and compared: (1) a frequency-domain technique developed by Altintas and Budak (1995); (2) a method based on time finite element analysis; and (3) the statistical variance of periodic 1/tooth samples in a time-marching simulation. Each method has advantages in different situations. The frequency-domain technique is fastest, and is accurate except at very low radial immersions. The temporal FEA method is significantly more efficient than time-marching simulation, and provides accurate stability predictions at small radial immersions. The variance estimate is a robust and versatile measure of stability for experimental tests as well as simulation. Experimental up-milling and down-milling tests, in a simple model with varying cutting directions, agree well with theory.

An AI-Based Model for Predicting Instananeous Cutting Force in End Milling

An Artificial Neural Network (ANN) model is developed to accurately predict the instantaneous cutting forces in flat end milling. A unique frequency domain approach is presented and is seen to simulate instantaneous cutting forces reasonably well. A set of eight input variables is chosen to represent the machining conditions and frequency domain parameters of the cutting force signal are generated. Three input parameters are varied, namely Feed, Speed and Depth of Cut. Four output parameters are suggested as a sufficient set to adequately reproduce the instantaneous cutting forces. Exhaustive experimentation is conducted to collect data (consisting of Fx, Fy, and Fz) to train and validate the model.

Free Air Ball Forming Process Parameter Analysis for Wire Bonder

In this paper, we are focusing on the FAB forming technology for fine pitch wire bonding. The parameters that affect the FAB formation include: 1) tail length; 2) spark gap; 3) Electric flame-off (EFO) voltage, current, time; 4) relative position between electrode plate and tail; 5) wire material; and 6) type of capillary. Except the last two items, all the other parameters can be quantified for analysis. By using Taguchi method it was found that EFO time and EFO current are the most important parameters that affect the formation free-air ball. The error-back-propagation neural network was then used to predict suitable EFO time and current setting. The main objective in this research is to find a suitable rule for parameters setting in order to control the FAB ball size as required. The result can be used in the future for optimal parameter setting and prediction of FAB formation.