1997 TMS Annual Meeting: Tuesday Session

APPLICATIONS OF SENSORS AND MODELING TO MATERIALS PROCESSING: Session IV

Session Chairs: J.C. Malas, Wright-Patterson AFB, OH 45433-6533; V.L. Acoff, Dept. of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487

2:30 pm

ELECTRONIC PROTOTYPING: TOWARDS VIRTUAL MATERIALS RESEARCH: S.R. LeClair, Wright Laboratory, Materials Directorate, Wright-Patterson AFB, OH 45433-7746; S.L. Thaler, PanAptics, Inc., 12906 Autumn View Dr., St. Louis, MO 63146-4331

The most significant first step toward electronic prototyping (EP) in the research community has been the pursuit of intelligent processing (i.e., closed-loop process control), effectively using in situ sensors to monitor both process parameters (energy input), material behavior (changes in bulk structure, temperature, etc.), and characterize materials at the atomic scale, wherein material properties such as strength, residual stresses, composition, phase, compressibility, modulus, etc., are monitored and controlled in real-time. Of interest are the identity of interrelationships between sensed variables which enable fault detection - discover and monitor, in real-time, an evolving taxonomy (a set of linear and other meaningful relationships) which can be classified as "faults"; process stability analysis - establish a measure of stability, in real-time, by assessing process response/noise in the context of energy input, apparatus actuation, and the control algorithm requisite variety; and response time - establish a measure of performance, in real-time, of "sensor-actuator" limits to affect specific processing requirements. Yet these capabilities are merely near-term - the more interesting, longer term capability is the pursuit of process discovery, i.e., how these relationships and measures might provide insight into explaining phenomena of interest and/or enable the development of a material or process model in situ.

2:55 pm

ACCURATE, RELIABLE CONTROL OF PROCESS GASES BY MASS FLOW CONTROLLERS: J. Hardy, T. McKnight, Instruments and Controls Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6003

The thermal mass flow controller, or MFC, has become an instrument of choice for the monitoring and controlling of process gas flow throughout the materials processing industry. MFCs are used on CVD processes, etching tools, and furnaces and in the semiconductor industry are used on 70% of the processing tools. Reliability and accuracy are major concerns for the users of MFCs. Calibration and characterization technologies have been developed and implemented for mass flow devices. A test facility is available to industry and universities to test and develop gas flow sensors and controllers and evaluate their performance related to environmental effects, reliability, reproducibility, and accuracy. Additional work has been conducted in the area of accuracy. A gravimetric calibrator was invented that allows flow sensors to be calibrated in corrosive, reactive gases to an accuracy of 0.3% of reading. This paper will present possible sources of error in MFC process gas flow monitoring and control, and will present an overview of corrective measures which may be implemented with MFC use to significantly reduce these sources of error.

3:20 pm

MONOLITHIC MICRO-SPECTROMETER FOR LOW-COST LIQUID AND GASEOUS CONSTITUENT PROCESS MONITORING: S. Rajic, C.M. Egert, Engineering Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-8039

A monolithic miniature spectrometer suitable for a variety of sensing applications including industrial process monitoring has been developed. The device consists of a solid structure with a volume less than 6 cubic centimeters. All optical components of the spectrometer including two aspheric mirrors, a diffration grating, and entrance and exit surfaces are fabricated onto the surface of the structure. All light paths are internally contained within the structure. The result is a small, rugged spectroscopic sensor ideally suited for use as a process monitor. Due to its monolithic nature, the device requires no post-fabrication alignment; nor can it be knocked out of alignment during use. The prototype device discussed here was produced in PMMA by precision diamond turning; however, lower cost manufacturing approaches involving injection molding (using diamond turned molds) are under development to produce an affordable sensor. Due to its rugged monolithic design, small footprint, and low cost, the monolithic micro-spectrometer is ideally suited for distributed process monitoring applications often required for industrial processes. It is expected that specific sensor designs will be required for specific applications so as to maximize the performance and resolution over the operating range. The performance of this device as well as the design tradeoffs necessary to optimize performance for given applications will be discussed in the report.

3:45 pm

AN ULTRASONIC SENSOR FOR HIGH TEMPERATURE MATERIALS PROCESSING: Rollie E. Dutton, Materials Directorate, Wright Lab., WL/MLLM, Bldg 655 Ste 1, Wright-Patterson AFB, OH 45433-7817; David A. Stubbs, University of Dayton Research Institute Structural Integrity Division, 300 College Park, Dayton, OH 45469-0120

A sensor has been developed and tested that is capable of emitting and receiving ultrasonic energy at temperatures exceeding 900°C (1652 f) and pressures above 150 MPa (22,500 psi). The sensor works with standard ultrasonic pulser-receivers and has a demonstrated capability of measuring workpiece deformation during hot isostatic pressing (HIP). Details of the sensor design, performance, and the coupling of ultrasonic to the workpiece are described. Ultrasonic data acquired by the sensor, in situ, during HIP runs are presented.

4:10 pm BREAK

4:20 pm

TWO METHODS FOR EMBEDDING OPTICAL FIBERS IN METAL COMPONENTS: L.J. Talarico*, S.W. Allison1, C.A. Blue**, H.M. Meyer III***, L. Riester**; *Engineering Technology Division, Oak Ridge National Laboratory; **Metals and Ceramics Division, Oak Ridge National Laboratory; ***Development Operations, Y-12 Plant; Oak Ridge, TN 37831

Manufacturing or embedding optical fiber sensors in composite materials such as graphite-epoxy, cementitious, plastic or ceramic components is of growing importance to a variety of smart materials and structures applications. A variety of fiber optic sensors can measure strain, pressure, and temperature by observing changes in an output signal fluorescence spectrum or a shift in output signal peak wavelength. The ability to measure these parameters on the surface of, as well as within, a part could provide experimental data for evaluating models, perhaps identifying some inferior parts on-line, and monitoring operating behavior. Some examples are monitoring cure and assessing thermal damage in polymer matrix composites by measuring changes in the epoxy fluorescence spectrum and monitoring densification during powder pressing. Other potential applications include engine diagnostics, condition based maintenance of aircraft and vehicle components, and monitoring and control in the metal forming and materials processing industries.

4:45 pm

EXAMINATION ON THE USE OF ACOUSTIC EMISSION FOR MONITORING METAL FORGING PROCESS: A STUDY USING SIMULATION TECHNIQUE: W.M. Mullins, TMC, Inc., WL/MLIM, WPAFB, OH 45433-7746; R.D. Irwin, Dept of Electrical Engineering and Computer Science, Ohio University, Athens, OH; J.C. Malas III, S. Venugopal, Materials Process Design, Materials Directorate, Wright Laboratory, WPAFB, OH 45433-7746

Physical models for acoustic emission (AE) are introduced and expressions are derived to predict AE activity from such parameters as applied stress, strain, and strain rate. These models are then incorporated into a visco-plastic finite-element simulation program, and the acoustic emission event rate generated during metal-forming operations are predicted. Simulation results are presented for upsetting operations on a typical C-Mn type steel for various friction and die geometry conditions. The AE model predictions compare well with the available experimental results reported in the literature and demonstrate that AE signatures can be reliably simulated. The signatures predicted for metal forging are fairly insensitive to changes in certain processing parameters. This suggests that AE event rate monitoring may not be well suited for monitoring changes in microstructure and friction during forging operations. Some very preliminary studies of event spectral analysis have been performed which show that AE spectral features may be sufficiently dependent on structure and loading to warrant further examination for application to monitoring metal-forging processes.

5:10 pm

SHEAR MODE EMAT AS A SENSOR FOR COMPOSITE LAMINATE FABRICATION: David K. Hsu, Center for Nondestructive Evaluation, Iowa State University, Ames, IA 50011

The polarization direction of shear mode ultrasound interacts strongly with the fiber direction in a composite laminate. Using conventional piezoelectric ultrasonic transducers, we have shown that cross-polarized shear waves were effective for sensing ply orientation errors and ply sequence anomalies. In this paper, we extend the technique to use electromagnetic acoustic transducers (EMAT), particularly for green (uncured) graphite epoxy composite laminates. Preliminary results will be shown and potential applications for quality control will be discussed.