Barry K. Fussell

Modeling of cutting geometry and forces for 5-axis sculptured surface machining

5-Axis sculptured surface machining is simulated using discrete geometric models of the tool and workpiece to determine the tool contact area, and a discrete mechanistic model to estimate the cutting forces. An extended Z-buffer model represents the workpiece, while a discrete axial slice model represents the cutting tool. Determination of the contact area for a given tool move requires a swept envelope (SWE) of the tool path. The SWE is used to find the intersections of the tool envelope with Z-buffer elements (ZDVs) representing the workpiece. A 3-axis approximation of the 5-axis tool movement is used to simplify the calculations while maintaining a desired level of accuracy. The intersection of the SWE with each ZDV yields segments which are used to find the contact area between the cutter and the workpiece for a given tool path. The contact area is subsequently used with the discrete force model to calculate the vector cutting force acting on the tool.

Robust Feedrate Selection for 3-Axis NC Machining Using Discrete Models

This research effort is focused on improving the efficiency of CNC machining by automatic computer selection of feedrate for 3-axis sculptured surface machining. A feedrate process planner for complex sculptured end milling cuts is developed from mechanistic and geometric end milling models. The selection program uses tool deflection, surface finish, tool failure and machine power to set constraints on the cutting force and the feed-per-tooth for rough, semi-finish, and finish passes. A NC part program is processed one tool move at a time by the planner. For each tool move a geometric model calculates the cut geometry, and an inverse mechanistic model uses this information along with the constraint force to calculate a desired feedrate. The feedrate is written into the part program resulting in a file that contains a feedrate for each tool move. Experimental results for a sculptured surface show the accuracy of the algorithms in maintaining a desired force.

A Low Cost Wireless Tool Tip Vibration Sensor for Milling

A low cost, wireless vibration sensor system has been developed for noninvasive integration into commercial end milling tool holders. Electret based accelerometers are used as the sensors and a Bluetooth compatible digital transmitter is used as the sensor interface. The use of mass market consumer electronic components is low cost and plug and play with modern PC hardware. Two prototypes were built and, in both cases, were able to collect good quality data at high sampling rates. The objective of the research is to enable accurate observation of NC metal cutting system dynamics. Initial results indicate the system can be used to estimate tool runout and detect the onset of regenerative chatter, prior to workpiece damage.Copyright

Energy Based Cutting Force Model Calibration for Milling

AbstractAccurate estimation of cutting forces requires that the predictive model be properly calibrated. Calibration typically requires a time consuming process and an expensive force measurement device. In this paper, an energy based process is described for calibrating a force estimation model using motor spindle power. Experimental results for flat and ball end mills are given. The method has been shown to be accurate for estimating forces for a wide variety of cutting conditions. Furthermore, we show how the calibration process can be done either off-line with a quick and simple process, or on-line while cutting in a production process. An additional benefit of the method is that the continuous calibration process can be used to help diagnose tool wear.

Process simulation and feedrate selection for three-axis sculptured surface machining

This research is focused on improving the efficiency of Computer Numerical Control (CNC) machining by enabling automatic feedrate selection. Model accuracy and utility are improved by a calibration process that uses spindle motor power and a wide variety of test cut geometries. A low-cost noninvasive spindle motor power sensor is combined with geometric and mechanistic models of the cutting process. Different constraints are set for rough, semi-finish and finish passes. A Numerical Control (NC) part program is processed one tool move at a time by the feedrate selection planner. For each tool move, a geometric model calculates the cut geometry. The selection algorithm then chooses the fastest possible feedrate, subject to constraints on part quality, tool health and machine tool capabilities. Experimental results for a sculptured surface bottle mould show the value of the method as an aid to process planning.

A NOVEL INTEGRATED ELECTRIC MOTOR/PUMP FOR UNDERWATER APPLICATIONS

This article presents a novel electric motor/pump system that combines an axial field, permanent magnet motor with a centrifugal pump. This system, unique because the motor permanent magnet rotor and pump impeller vanes are a single unit, provides a compact, reliable, low‐noise, and high‐power density electrically driven centrifugal pump suitable for underwater applications in which minimizing noise, vibration, and volume are major design objectives. Performance tradeoffs for the electromagnetic analysis were made by three‐dimensional finite element analysis models in conjunction with a lumped parameter magnetic circuit model.

Estimation of Cutting Force Model Coefficients to Track Wear in Milling Using Bayesian Analysis

Our previous research has demonstrated the feasibility of monitoring tool wear during milling by continuously updating the coefficients of a cutting force model. The method requires a robust method for on-line model coefficient estimation. Estimation using Least Square Regression (LSR) is easily implemented but requires that the data points come from different cutting conditions which is not always possible. In this paper, a method for coefficient estimation and wear tracking based on Bayesian updating is described. The Bayesian method has the advantage that it can be used when the cutting conditions are constant.Copyright

Automatic Five-Axis CNC Feedrate Selection via Discrete Mechanistic, Geometric, and Machine Model Integration

The purpose of this research is to determine feasibility and develop software tools for automatically generating adaptive feedrates for use in five-axis CNC end milling. The complicated part geometries often involved with five-axis milling, combined with the rotational degrees of freedom of the machines, make it difficult to manually estimate acceptable feedrates without being overly conservative. Our approach for automatic feedrate generation is to use a computer simulation of the milling process. This software estimates the feeds required to maintain a desired peak cutting force on a per-tool-move basis, and consists of three distinct portions: a discrete mechanistic model, a discrete geometric model, and a model of the specific CNC machine on which the part is to be cut. The mechanistic model estimates cutting forces as a function of cut geometry, cutter-to-stock relative velocity, and material constants. Used in an inverse manner, the mechanistic model may be used to estimate the feedrates necessary to maintain a constant peak cutting force. This force value may be selected to prevent cutter breakage, maintain a desired part tolerance, or to meet some other criteria (e.g. machine constraints). The results of this research have shown that it is possible to automatically generate adaptive feeds that maintain a desired force level using these combined models.

Algorithms and Data Structures for Fast Surface Quality Estimation in Milling

New approaches for fast surface quality estimation in Milling are presented. Dimensional Error, Surface Roughness, and the 3D topological plots of the surfaces are generated. Calculation speed is improved by methods of structural organization and numerical optimizations. Structural organization enables program division into initialization and program-run segments for faster runs. Numerical optimizations are used to help further reduce the run time by reducing variable volume and avoiding unnecessary estimations. Experimental evaluation of the methods for Dimensional Error, Surface roughness and profiles are performed using three different cutting tool types (flat-end, ball-end and insert mills) in order to reveal strengths and weaknesses of the proposed approaches. Comparison of experimental and estimated surface profiles show good correlation. Typical surface profile estimation for one tool rotation takes between 0.04–4.1 seconds depending on the cut and whether or not the tool deflection is included in the algorithm. Surface quality estimation is done quickly enough to be promising for use in feedrate scheduling. Further improvement in the tool deflection model is expected to increase accuracy and further reduce the computational time.Copyright

Residual Strength of Liquefied Sand Measured in a Ring Shear Device

Earthquake-induced liquefaction flow slides have resulted in loss of life and major damage at many sites around the world. In order to better understand the mechanics of such slides, it is necessary to quantify the residual shearing strength of the liquefied soil. Small-scale stress-controlled experiments suggest that this residual strength is not a constant, but that liquefied sand can be modeled as a highly viscous stress-thinning fluid, whose resistance varies with the velocity of flow. We present results obtained with a ring shear device designed specifically to measure the large-displacement post-liquefaction residual strength of sands under strain-controlled conditions. Residual strength of a fine uniform sand was measured for a range of relative densities (Dr) from 19 % to 36 % at four different shear-strain rates, varying from 11 to 44 s−1 representative of flow slide velocities. Measurements show that the strain-rate-dependent Herschel–Bulkley model for stress-thinning fluids applies to the liquefied sand, with resistance increasing as strain rate increases, but suggest that at relative densities higher than perhaps 50 %, relative density dominates, and residual strength can be approximated as a constant.