Showing papers in "Journal of Engineering for Industry in 1995"

A Mechanistic Approach to Predicting the Cutting Forces in Drilling: With Application to Fiber-Reinforced Composite Materials

Abstract: In this paper models are developed to predict the thrust and torque forces at the different regions of cutting on a drill. The mechanistic approach adopted to develop these models exploits the geometry of the process, which is independent of the workpiece material. The models are calibrated to a particular material using the well-established relationships between chip load and cutting forces, modified to take advantage of the characteristics of the drill point geometry. The models are validated independently for the cutting lips and the chisel edge for drilling both metals and fiber-reinforced composite materials for a wide range of machining conditions and drill geometry. While the cutting-lips model predictions agree well with the experimental data for both materials, only the chisel-edge model proposed for metals agrees well with the experimental data.

Energy Partition to the Workpiece for Grinding with Aluminum Oxide and CBN Abrasive Wheels

Abstract: An experimental investigation is reported of the energy partition to the workpiece for grinding of steels with aluminum oxide and cubic boron nitride (CBN) abrasive wheels. The energy input to the workpiece was obtained by measuring the temperature distribution in the workpiece using an embedded thermocouple technique and match­ ing the results with analytically computed values. It was found that 60-75 percent of the grinding energy is transported to the workpiece as heat with an aluminum oxide abrasive wheel, as compared to only about 20 percent with CBN wheels. An analysis of the results indicates that the much lower energy partition to the workpiece with CBNcan be attributed to its very high thermal conductivity whereby a significant portion of the grinding heat is transported to the abrasive instead of to the workpiece. The much lower energy partition to the workpiece with CBN wheels results in much lower grinding temperatures and a greatly reduced tendency for thermal damage to the workpiece.

Finite Element Simulation of Orthogonal Metal Cutting

Abstract: The development and implementation of a plane-strain finite element method for the simulation of orthogonal metal cutting with continuous chip formation are presented. Detailed work-material modeling, including the effects of elasticity, viscoplasticity, temperature, large strain, and high strain-rate, is used to simulate the material deformation during the cutting process. The unbalanced force reduction method and sticking-sliding friction behavior are implemented to analyze the cutting process. The deformation of the finite element mesh and comparisons of residual stress distributions with X-ray diffraction measurements are presented. Simulation results along the primary and secondary deformation zones and under the cut surface, e.g., the normal and shear stresses, temperature, strain-rate, etc., are presented revealing insight into the metal cutting process

Automated Monitoring of Manufacturing Processes, Part 1: Monitoring Methods

Abstract: This paper presents a systematic study of various monitoring methods suitable,for automated monitoring of manufacturing processes. In general, monitoring is composed of two phases: learning and classification. In the learning phase, the key issue is to establish the relationship between monitoring indices (selected signature, features) and the process conditions. Based on this relationship and the current sensor signals, the process condition is then estimated in the classification phase. The monitoring methods discussed in this paper include pattern recognition, fuzzy systems, decision trees, expert systems and neural networks. A brief review of signal processing techniques commonly used in monitoring, such as statistical analysis, spectral analysis, system modeling, bi-spectral analysis and lime-,frequency distribution, is also included

Sensing and Control of Weld Pool Geometry for Automated GTA Welding

Abstract: Weld pool geometry is a crucial factor in determining welding quality, especially in the case of sheet welding. Its feedback control should be a fundamental requirement for automated welding. However, the real-time precise measurement of pool geometry is a difficult procedure. It has been shown that vision sensing is a promising approach for monitoring the weld pool geometry. Quality images that can be processed in real-time to detect the pool geometry are acquired by using a high shutter speed camera assisted with nitrogen laser as an illumination source. However, during practical welding, impurities or oxides existing on the pool surface complicate image processing. The image features are analyzed and utilized for effectively processing the image. It is shown that the proposed algorithm can always detect the pool boundary with sufficient accuracy in less than 100 ms. Based on this measuring technique, a robust adaptive system has been developed to control the pool area. Experiments show that the proposed control system can overcome the influence caused by various disturbances.

A Mechanistic Approach to the Prediction of Material Removal Rates in Rotary Ultrasonic Machining

Abstract: An approach to modeling the material removal rate (MRR) during rotary ultrasonic machining (RUM) of ceramics is proposed and applied to predicting the MRR for the case of magnesia stabilized zirconia. The model, a first attempt at predicting the MRR in RUM, is based on the assumption that brittle fracture is the primary mechanism of material removal. To justify this assumption, a model parameter (which models the ratio of the fractured volume to the indented volume of a single diamond particle) is shown to be invariant for most machining conditions. The model is mechanistic in the sense that this parameter can be observed experimentally from a few experiments for a particular material and then used in prediction of MRR over a wide range of process parameters. This is demonstrated for magnesia stabilized zirconia, where very good predictions are obtained using an estimate of this single parameter. On the basis of this model, relations between the material removal rate and the controllable machining parameters are deduced. These relationships agree well with the trends observed by experimental observations made by other investigators

A Dual-Mechanism Approach to the Prediction of Machining Forces, Part 1: Model Development

Abstract: A cutting-process model addressing the chip removal and edge ploughing mechanisms separately yet simultaneously is presented. The model is developed such that it is readily applicable in an industrial setting, its coefficients have physical meaning, and it can be calibrated with a concise quantity of orthogonal cutting data. The total cutting and thrust forces are each the summation of its individual components acting on the rake face and clearance face. These components are calculated using the rake and effective clearance angles from the normal and friction forces acting on each of these tool surfaces. These normal and friction forces are calculated by the chip removal and edge ploughing portions of the model, respectively, using four empirical coefficients. To calculate the clearance face forces, the interference volume is required, the calculation of which is based on a geometrical representation of the clearance face interference region. This representation is characterized in part by the depth of tool penetration, which is influenced by thermal energy generation and is therefore determined using a fifth empirical model.

Analysis of Energy Partition in Grinding

Abstract: An analysis is presented for the fraction of the energy transported as heat to the workpiece during grinding. The abrasive grains and grinding fluid in the wheel pores are considered as a thermal composite which moves relative to the grinding zone at the wheel speed. The energy partition fraction to the workpiece is modeled by setting the temperature of the workpiece surface equal to that of the composite surface at every point along the grinding zone, which allows variation of the energy partition along the grinding zone. Analytical results indicate that the energy partition fraction to the workpiece is approximately constant along the grinding zone for regular down grinding, but varies greatly along the grinding zone for regular up grinding and both up and down creep-feed grinding. The resulting temperature distributions have important implications for selecting up versus down grinding especially for creep-feed operations

A Realistic Friction Model for Computer Simulation of Sheet Metal Forming Processes

Abstract: A realistic model for friction in lubricated sheet-metal forming which takes account of the different lubrication regimes which may occur at the sheet/tooling interface is developed. Friction is expressed in terms of internal interface variables (mean lubricant film thickness, sheet roughness and tooling roughness) in addition to the more traditional external variables (interface pressure, sliding speed and strain rate). The new model has been coupled to an existing finite element membrane analysis of axisymmetric stretch forming. Numerical results using the coupled codes showed excellent agreement with measured strain distributions over a range of operating conditions. Computational times with the refined friction model were typically increased by about 10 percent compared to those with a simple Amontons-Coulomb constant friction coefficient model

A Customized Neural Network for Sensor Fusion in On-Line Monitoring of Cutting Tool Wear

Abstract: A customized neural network for sensor fusion of acoustic emission and force in on-line detection of tool wear is developed. Based on two critical concerns regarding practical and reliable tool-wear monitoring systems, the minimal utilization of «unsupervised» sensor data and the avoidance of off-line feature analysis, the neural network is trained by unsupervised Kohonen's Feature Map procedure followed by an Input Feature Scaling algorithm. After levels of tool wear are topologically ordered by Kohonen's Feature Map, input features of AE and force sensor signals are transformed via Input Feature Scaling so that the resulting decision boundaries of the neural network approximate those of error-minimizing Bayes classifier. In a machining experiment, the customized neural network achieved high accuracy rates in the classification of levels of tool wear. Also, the neural network shows several practical and reliable properties for the implementation of the monitoring system in manufacturing industries

Surface Roughness Measurement by Ultrasonic Sensing for In-Process Monitoring

Abstract: This paper presents a new surface roughness measurement technique suitable for in-process monitoring in production machining processes. The technique is based on the utilization of focused ultrasonic beams with non-zero incidence angle and measurement of reflected intensities. Fundamental principles and the measurement system developed are described along with experimental results. The tests were conducted to test the sensitivity and robustness of the proposed technique with various milled surfaces and materials. The results show excellent correlations with those obtained by a profilometer. In addition, it is shown that the periodicities of the surface profile corresponding to feed marks can be extracted from the measured ultrasonic signals, thus providing the possibility of profiling. Finally, in-process monitoring of surface roughness during machining is demonstrated with the proposed technique.

Min-Max Load Model for Optimizing Machining Fixture Performance

Abstract: Spherical-tipped locators and clamps are often used for the restraint of castings during machining. For structural rigid castings, contact region deformation and micro-slippage are the predominant modes of workpiece displacement. In turn contact region deformation and micro-slippage are heavily influenced by contact region loading. Maximum loading magnitude has been shown to be a good indicator of workpiece displacement. This paper presents an algorithm which uses the min-max loading criteria as a basis for determining the optimal layout of locators and clamps as well as clamp actuation intensifies. The experimentation used for model validation is also discussed along with experimental results

Analysis of Transient Temperatures in Grinding

Abstract: Temperatures generated in the workpiece during straight surface plunge grinding follow a transient behavior as the grinding wheel engages with and disengages from the workpiece, and throughout the entire grinding pass for workpieces which are shorter than needed to reach a quasi-steady state condition. In the present paper, a thermal model is developed for the transient temperature distribution under regular and creep-feed grinding conditions. Numerical results obtained using a finite difference method indicate that the workpiece temperature rises rapidly during initial wheel-workpiece engagement (cut in), subsequently reaches a quasi-steady state value if the workpiece is sufficiently long, and increases still further during final wheel-workpiece disengagement (cut out) as workpiece material is suddenly unavailable to dissipate heat. Cooling by a nozzle directed at the end face of the workpiece should significantly reduce the temperature rise during cut out.

Automated Monitoring of Manufacturing Processes, Part 2: Applications

Abstract: In Part 2 of this paper, three applications of automated monitoring of manufacturing processes are presented to demonstrate the use of monitoring methods discussed in Part 1 of the paper. These applications are: (1) tool condition monitoring in turning, (2) machining condition monitoring in tapping, and (3) metallographic condition monitoring in arc welding. For each application, a background review, monitoring index selection and experimental setup are first presented. Then, monitoring methods discussed in Part 1 of the paper were applied and the test results are investigated. Discussions of the monitoring success rate, sensitivity, robustness, monitoring index selection, and decision under uncertainty are also included.

Algorithm for multiple disassembly and parallel assemblies

Abstract: We consider the geometric problem of generating efficient sequences for disassembling components. First, a classification of assemblies is proposed based on logical, dimensional and geometric complexities, and a simple method is outlined for recognizing parallel and sequential assemblies. Next, an efficient algorithm is outlined for removing multiple components from an assembly. Finally, we consider parallel assemblies and outline two algorithms for their disassembly

Infrared Sensing for On-Line Weld Geometry Monitoring and Control

Abstract: This paper describes a method for on-line weld geometry monitoring and control using a single front-side infrared sensor. Variations in plate thickness, shielding gas composition and minor element content are known to cause weld geometry changes. These changes in the weld geometry can be distinctly detected from an analysis of temperature gradients computed from infrared data. Deviations in temperature gradients were used to control the bead width and depth of penetration during the welding process. The analytical techniques described in this paper have been used to control gas tungsten arc and gas metal arc welding processes.

Design Optimization of a Three Degrees-of-Freedom Variable-Reluctance Spherical Wrist Motor

Abstract: This paper presents the basis for optimizing the design of a three degrees-of-freedom (DOF) variable reluctance (VR) spherical motor which offers some attractive features by combining pitch, roll, and yaw motion in a single joint. The spherical wrist motor offers a major performance advantage in trajectory planning and control as compared to the popular three-consecutive-rotational joint wrist. Since an improved performance estimate is required, a method for optimizing the VR spherical motor’s magnetics was developed. This paper begins with a presentation of the geometrical independent and dependent variables which fully described the design of a VR spherical motor. These variables are derived from examination of the torque prediction model. Next, a complete set of constraint equations governing geometry, thermal limitations, amplifier specifications, iron saturation, and leakage flux are derived. Finally, an example problem is presented where the motor’s geometry is determined by maximizing the output torque at one rotor position. The concept of developing a spherical motor with uniform torque characteristics is discussed with respect to the optimization methodology. It is expected that the resulting analysis will improve the analytical torque prediction model by the inclusion of constraint equations, aid in developing future VR spherical motor designs, improve estimates of performance, and therefore will offer better insight into potential applications.

On the Plastic Deformation of a Tube During Bending

Abstract: The objective of this study is to develop an analytical approach to calculate the relationship between the axial curvature of a bent tube and the resulting deformation of the cross-section. The model accounts for both geometrical and material nonlinearities. An approximate expression in trigonometric form is introduced for the displacement field, which reflects the change of wall thickness and neutral axis shift during bending. The total deformation theory is employed as a constitutive relation. The solution is found using a minimization approach and the energy principle. A better approach for springback prediction might be obtained from the deformation model, which predicts a more accurate moment of inertia change during bending.

An Adaptive Methodology for Machine Tool Error Correction

Abstract: An adaptive methodology for machine tool error correction is presented in this paper. The estimated errors resulting from the proposed methodology could be used to adjust the depth of cut on the finish pass or correct the probing data for on-machine inspection to improve the accuracy of workpiece. A generalized error model is derived, using rigid body kinematics, to describe the error motion between the cutting tool and workpiece. Process-intermittent gauging and state observation techniques are integrated to monitor the thermally induced errors and then to modify the error model's coefficients as the cutting process proceeds. Analysis-of-variance (ANOVA) is used to identify the significant variables for thermal effect modeling. A multiple linear regression model is derived to identify the dynamics of the time-varying thermally induced errors. Multivariable state observers are constructed to track the thermal effect in real time and to fine tune the error model's coefficients. Experimental results show that the time-varying machine tool errors can be estimated with desirable accuracy.

Effect of Abrasive Waterjet Parameters on Volume Removal Trends in Turning

Abstract: An experimental investigation was conducted to investigate the influence of abrasive waterjet parameters on the volume removal rate in abrasive waterjet turning. Abrasive mass flow rate, abrasive particle size, waterjet pressure, and orifice diameter were the principal variables that were investigated. Limited tests were also conducted with abrasive mixtures. The results show that the volume removal trends in abrasive waterjet turning are similar to those in linear cutting with abrasive waterjets. Increasing waterjet pressure, orifice diameter and abrasive flow rate generally resulted in an increase in volume removal rate. However, the volume removal rate levels off either due to volume sweep rate limit or due to the abrasive waterjet limit. The results also suggest a potential for optimizing the abrasive flow rate and abrasive composition. The volume removal rate showed only a weak dependence on the abrasive particle size.

Digital Gap Monitor and Adaptive Integral Control for Auto-Jumping in EDM

Abstract: This paper reports a monitoring and adaptive integral control strategy for EDM to regulate the cycle time of the periodical retraction (jumping of the tool electrode according to the gap condition. A digital EDM gap monitor has been developed to detect the time ratios of gap states with a resolution of 0.2 μs. The theoretical and experimental analysis of the effect of sensing parameter combinations on control aspects and performance of manual setting, integral control and adaptive integral control methods have been carried out. Experimental verification shows that the proposed system results in higher erosion rate, better machining stability, and complete avoidance of are damage

Helical micro-drill point design and grinding

Abstract: A new drill point geometry, termed the helical drill point, specifically intended for micro-drills, is developed in order to alleviate the disadvantages of existing planar micro-drill points. A mathematical model for this new drill point has been established. It is shown that this model is more general than existing drill point models. The commonly used conical, cylindrical and planar drill point models are only special cases of the helical model. For uniquely determining the grinding parameters of the new drill point as well as guiding the grinder design, the characteristics, the controllability and the sensitivity of the grinding parameters have been analyzed. Finally the geometric characteristics of this new drill point are investigated.

Evaluation of Gear Tooth Stresses by Finite Element Method

Abstract: Stresses developed in the root fillet of the spur gear tooth due to static load are evaluated by using the finite element method. The method is automated with a computer program with which the effects of module, contact ratio, fillet radius, pressure angle and teeth numbers of driving and driven gears are evaluated. The results are compared with previous studies. The formula which gives the closest results to this study is presented

Thermal Expansion of the Workpiece in Turning

Abstract: Thermal expansion of the part can be a significant source of dimensional and form errors in precision machining operations. This paper describes a method for calculating the thermal expansion of an axisymmetric workpiece. The analysis is based on a commercially available boundary element code modified to properly represent concentrated moving heat sources such as those produced in machining. The inputs required are the amount of heat entering the part from the cutting zone and the thermal properties of the workpiece material. Calculations are compared with direct measurements of expansion from tests on large diameter 2024 aluminum sleeves. The agreement between calculated and measured values is generally reasonable, although calculated expansions are consistently smaller than measured expansions. This error is probably due to errors in estimating the heat input to the part, and particularly the neglect of flank friction in heat input calculations. Sample calculations for hard turning of a wheel spindle show that expansions can approach tolerances on critical surfaces. Based on sample calculations, thermal expansion is likely to be significant when hard turning parts with tolerances on the order of 0.01 mm. For these applications, critical surfaces should be machined first, before cuts on other sections heat the part, and gaging should be carried out only after the part has cooled.

An Adaptive Error Correction Method Using Feature-Based Analysis Techniques for Machine Performance Improvement, Part 1: Theory Derivation

Abstract: An adaptive error correction method using a feature-based analysis technique for improving the accuracy of CNC machine tools is presented. The method described in this paper emphasizes the integration of the process-intermittent gauging and analysis techniques with information from pre-process characterization and post-process inspection. The proposed method utilizes the information from pre-process characterization, process-intermittent gauging, and post-process inspection to improve machine performance automatically. Algorithms are derived for analyzing the post-process and process-intermittent inspection data to decouple process-related errors from machine errors and for identifying the residual systematic errors. A feature-based analysis technique is developed to relate the dimensional and form errors of manufactured features to the systematic machine tool errors. Inverse kinematics and statistical methods are used to identify and characterize the contribution of each residual error component on imperfect features. Also a recursive tuning algorithm is developed for fine tuning the geometric-thermal model.

Bearing Localized Defect Detection by Bicoherence Analysis of Vibrations

Abstract: For automatic detection and diagnosis of localized defects in rolling element bearings, bicoherence spectra are used to derive features that signify the condition of a bearing. These features quantitatively describe the degree of phase correlation among any three harmonics of bearing characteristic defect frequencies. In this paper, theory of bicoherence is explored to establish its utilization in the detection of bearing localized defects. Experimental results show that the proposed method is effective in bearing defect detection and sensitive to incipient defects.

Towards Automated Design of the Feed System of Injection Molds by Integrating CAE, Iterative Redesign and Features

Abstract: A prototype software system that automatically designs the gating and runner systems, which comprise the feed system, of injection molds is described. The system, called AMDS (Automated Mold Design System), integrates CAE, with iterative redesign and knowledge stored in a features representation of the part. Gating design involves the generation of the best gating configuration represented by number, location, and type of gates, and the determination of the best conditions under which plastic should enter through the gates. Runner design also involves the generation of a runner layout followed by the sizing of the runner segments. The design of both systems is iterative, whereby the design variables are changed, the new design analyzed, evaluated, and redesigned if necessary, until an acceptable design is obtained. The evaluation of the gating design is based on eighteen performance parameters, while the evaluation of the runner system is based on four performance parameters. The system has been tested on three-dimensional parts made up of planar rectangular wall features with holes as add-on features

Characteristics of abrasive waterjet generated surfaces and effects of cutting parameters and structure vibration

Abstract: We use three-dimensional surface topography analysis for evaluating waterjet generated surfaces. The waterjet generated surface is separated into smooth and striation zones, where striation influence is negligible in the smooth zone. It is found that the smooth zone has a random, moderately isotropic texture, with the height distribution nearly Gaussian. The effects of cutting speed, depth of cut, and abrasive size on the surface roughness are studied for the smooth zone and striation zone separately. This provides useful information for controlling process parameters to obtain smooth finished surfaces. Spectral analysis is used to investigate the surface striation and machine structure vibration. It is found that forced vibration of the mechanical structure strongly influences striations generated in the waterjet machining system.

Cutting Force Dynamics as a Tool for Surface Profile Monitoring in AWJ

Abstract: Abrasive waterjet cut surface is characterized using static and dynamic characterization techniques. A novel method of auto regressive moving average model identification called model distance method is utilized here for surface profile and dynamic force characterization. More information about the surface profile generating mechanism is derived through wavelength decomposition of the ARMA models. The dynamic workpiece normal force in abrasive waterjet is influenced by process parameters such as fluctuations in water pressure, change in abrasive flow rate, vibration of the positioning system, traverse speed, nozzle diameter, etc. An attempt has been made in this paper to link the dynamics of the process to the quality of the generated surface. The feasibility of using the dynamic workpiece normal force as a parameter for on-line monitoring of the surface profile generated by abrasive waterjet is also investigated.

Static and dynamic characteristics of spot welded sheet metal beams

Abstract: Although widely employed as structural components in the auto industry, spot welded sheet metal beams manifest static and dynamic behavior that is not well characterized. For the present study, sample beams of three representative cross-sections-hat, box and box with partition-were fabricated of sheet steel. The spacing between the spot welds that hold these sections together was varied from 25.4 mm (1 in.) to 203.2 mm (8 in.) using a 25.4 mm (1 in.) increment. The beams were subjected to static bending and static torsion tests, and bending and torsional stiffnesses were determined as functions of spot weld spacing. The beams were then vibrated, and significant lower natural frequencies were determined as functions of spot weld spacing. Mode shapes were also observed for these frequencies. Pains were taken throughout the testing to ensure that the results obtained were of good statistical quality. Work was also done to distinguish the effect on results of beam length and end conditions from that of spot weld spacing. As part of the study finite element models of the beams were constructed. The results of finite element analysis (FEA) and experiment are compared and insights are offered concerning the appropriate modeling of such structures.