Terry D. Hinnerichs

Milling machine for the 21st century: goals, approach, characterization, and modeling

Ingersolls Octahedral Hexapod--a milling machine for the future--is described. The specific target applications and the performance goals for an enhanced version of the machine are illustrated. The approach to achieving the goals by incorporating of advanced composites and active chatter and vibration control using smart materials is discussed. The machine characterization performed on an existing machine, the FE models developed and the plans to use the characterization and the validated models in designing an enhanced machine are described.

Vibration Control for Precision Manufacturing Using Piezoelectric Actuators

Piezoelectric actuators provide high frequency, force and stiffness capabilities along with reasonable stroke limits, all of which can be used to increase performance levels in precision manufacturing systems. This paper describes two examples of embedding piezoelectric actuators in structural components for vibration control. One example involves suppressing the self-excited chatter phenomenon in the metal cutting process of a milling machine and the other involves damping vibrations induced by rigid body stepping of a photolithography platen. Finite element modeling and analyses are essential for locating and sizing the actuators and permit further simulation studies of the response of the dynamic system. Experimental results are given for embedding piezoelectric actuators in a cantilevered bar configuration, which was used as a surrogate machine tool structure. These results are incorporated into a previously developed milling process simulation and the effect of the control on the cutting process stability diagram is quantified. Experimental results are also given for embedding three piezoelectric actuators in a surrogate photolithography platen to suppress vibrations. These results demonstrate the potential benefit that can be realized by applying advances from the field of adaptive structures to problems in precision manufacturing.

Active chatter control in a milling machine

The use of active feedback compensation to mitigate cutting instabilities in an advanced milling machine is discussed in this paper. A linear structural model delineating dynamics significant to the onset of cutting instabilities was combined with a nonlinear cutting model to form a dynamic depiction of an existing milling machine. The model was validated with experimental data. Modifications made to an existing machine model were used to predict alterations in dynamics due to the integration of active feedback compensation. From simulations, subcomponent requirements were evaluated and cutting enhancements were predicted. Active compensation was shown to enable more than double the metal removal rate over conventional milling machines.

Assessment of Efficiency for a Hybrid Explicit/Implicit Code Simulation of a Multiple Impact Crash Scenario

Sandia National Laboratories has developed a new explicit nonlinear transient dynamic finite element code called Presto and an associated implicit code called Adagio. This paper describes a process used to assess the ability and efficiency for sharing the computational workload of a multiple impact crash simulation between the explicit (Presto) and the implicit (Adagio) codes to minimize computation time. A numeric example of this hybrid simulation process is given that applies to a dynamic beam impact scenario. Results from simulations using each code will be compared with the hybrid simulation and discussed.© 2005 ASME

Mitigation of Chatter Instabilities in Milling by Active Structural Control

This report documents how active structural control was used to significantly enhance the metal removal rate of a milling machine. An active structural control system integrates actuators, sensors, a control law and a processor into a structure for the purpose of improving the dynamic characteristics of the structure. Sensors measure motion, and the control law, implemented in the processor, relates this motion to actuator forces. Closed-loop dynamics can be enhanced by proper control law design. Actuators and sensors were imbedded within a milling machine for the purpose of modifying dynamics in such a way that mechanical energy, produced during cutting, was absorbed. This limited the on-set of instabilities and allowed for greater depths of cut. Up to an order of magnitude improvement in metal removal rate was achieved using this system. Although demonstrations were very successful, the development of an industrial prototype awaits improvements in the technology. In particular, simpler system designs that assure controllability and observability and control algorithms that allow for adaptability need to be developed.

A Viscoplastic Constitutive Model for Polyurethane Foams

A series of experiments was recently performed to characterize the mechanical response of several different rigid polyurethane foams to large deformation. In these experiments, the effects of load path, loading rate, and temperature were investigated. Results from these experiments indicated that rigid polyurethane foams exhibit significant volumetric and deviatoric plasticity when they are compressed. Based on these experiments, a foam plasticity model that captures volumetric and deviatoric plasticity was developed. This model has a yield surface that is an ellipsoid about the hydrostat. These polymeric foams were also found to be very strain-rate and temperature dependent. Thus, a new viscoplastic foam model was developed to describe the mechanical response of these foams to large deformation at a variety of temperatures and strain rates. This paper includes a description of recent experiments and experimental findings. Next, development of a foam plasticity model and a viscoplastic foam model is described. Finite element simulations with the new models are compared with experimental results to show behavior that can and cannot be captured with these models.Copyright

Characterization of Mechanical Behavior of Polyurethane Foams Using Digital Image Correlation

Polyurethane foams have good energy absorption properties and are effective in protecting sensitive components from damages due to impact. The foam absorbs impact energy by crushing cells and undergoing large deformation. The complex deformation of the foam needs to be modeled accurately to simulate the impact events. In this paper, the Digital Image Correlation (DIC) technique was implemented to obtain the deformation field of foam specimens under compression tests. Images of foam specimen were continuously acquired using high-speed cameras. The full field displacement and strain at each incremental step of loading were calculated from these images. The closed-cell polyurethane foam used in this investigation was nominal 0.32 kg/m^3 (20 pcf). In the first experiment, cubic specimens were compressed uniaxially up to 60%. The full-field displacements and strains obtained using the DIC technique provide detailed information about the inhomogeneous deformation over the area of interest during loading. In the second experiment, compression tests were conducted for a simple foam structure - cubic foam specimens with a steel cylinder inclusion. The strain concentration at the interface between steel cylinder and foam was studied to simulate the deformation of foam in a typical application. In the third experiment, the foam was loaded from the steel cylinder during the compression. The strain concentration at the interface and the displacement distribution over the surface were compared for cases with and without a confinement fixture to study the effects of confinement. These experimental results demonstrate that the DIC technique can be applied to polyurethane foams to study the heterogeneous deformation. The experimental data is briefly compared with the results from modeling and simulation using a viscoplastic model for the foam.Copyright

A New Aluminum Honeycomb Constitutive Model for Impact Analyses

A new constitutive model for large deformation of aluminum honeycomb has been developed. This model has six yield surfaces that are coupled to account for the orthotropic behavior of the cellular honeycomb being crushed on-axis and off-axis. Model parameters have been identified to fit uniaxial and biaxial crush test data for high density (38 lb/ft3 ) aluminum honeycomb. The honeycomb model was implemented in the transient dynamic Presto finite element code for dynamic impact simulations. In order to extract useful constitutive-parameter information from crush tests, each test configuration and process is simulated with a Presto finite element model to analyze the non-uniform strain/crush behavior within the test samples. Results from the suite of honeycomb crush tests that were used to calibrate the new honeycomb model are shown. Also, the honeycomb model’s predictions are compared with test data and with the older Orthotropic Crush Model predictions.Copyright

On the use of active structural control to enhance the cutting performance of a milling machine

An active structural control system was developed and implemented on a hexapod milling machine to increase metal removal rate of the machine. The control system hardware consisted of dynamic actuators, sensors, processors and a telemetry system. The control law was implemented in software in the control processor. The objective of the control system was to reduce the dynamic response of the milling tool thereby improving its stability and its maximum depth-of-cut. System design including sensor and actuator development was guided using finite element modeling techniques. The components were constructed, and a successful experimental demonstration resulted.

Shear Deformation of High Density Aluminum Honeycombs

The orthotropic crush model has commonly been used to describe the constitutive behavior of honeycomb [1]. To completely define the model parameters of a honeycomb, experimental data of axial crushes in T, L, and W principal directions as well as shear stress-strain curves in TL, TW, and LW planes are required. The axial crushes of high-density aluminum honeycombs, e.g., 38 pcf (pound per cubic foot), under various loading speeds and temperatures have been investigated and reported [2]. This paper describes experiments and model simulations of the shear deformation of the same high-density aluminum honeycomb. Results of plate shear test, beam flexure test, and off-axis compression are presented and discussed.Copyright