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Technical Paper

Inverse Method for Measuring Weld Temperatures during Resistance Spot Welding

2001-03-05
2001-01-0437
A new monitoring system predicts the progression of welding temperature fields during resistance spot welding. The system captures welding voltages and currents to predict contact diameters and simulate temperature fields. The system accurately predicts fusion lines and heat-affected zones. Accuracy holds even for electrode tips used for a few thousand welds of zinc coated steels.
Technical Paper

Space Life Support from the Cellular Perspective

2001-07-09
2001-01-2229
Determining the fundamental role of gravity in vital biological systems in space is one of six science and research areas that provides the philosophical underpinning for why NASA exists. The study of cells, tissues, and microorganisms in a spaceflight environment holds the promise of answering multiple intriguing questions about how gravity affects living systems. To enable these studies, specimens must be maintained in an environment similar to that used in a laboratory. Cell culture studies under normal laboratory conditions involve maintaining a highly specialized environment with the necessary temperature, humidity control, nutrient, and gas exchange conditions. These same cell life support conditions must be provided by the International Space Station (ISS) Cell Culture Unit (CCU) in the unique environment of space. The CCU is a perfusion-based system that must function in microgravity, at unit gravity (1g) on earth, and from 0.1g up to 2g aboard the ISS centrifuge rotor.
Technical Paper

Economic and Environmental Tradeoffs in New Automotive Painting Technologies

1998-02-23
981164
Painting is the most expensive unit operation in automobile manufacturing and the source of over 90 percent of the air, water and solid waste emissions at the assembly plant. While innovative paint technologies such as waterborne or powder paints can potentially improve plant environmental performance, implementing these technologies often requires major capital investment. A process-based technical cost model was developed for examining the environmental and economic implications of automotive painting at the unit operation level. The tradeoffs between potential environmental benefits and their relative costs are evaluated for current and new technologies.
Technical Paper

Chain Representations of Dimensional Control: A Producibility Input for Concurrent Concept Design

1998-06-02
981846
Two critical milestones that must be achieved during concept design are 1) definition of a product architecture that meets performance, producibility, and strategic objectives, and 2) estimation of the integration risk in each candidate concept. This paper addresses these issues by describing the role played by the producibility members of an Integrated Product Team (IPT) during concept design. Our focus is on the execution of the what we call the “chain method”, which illustrates the structure of function delivery in a concept in a simple pictorial way and helps the IPT to understand the advantages or disadvantages of using a modular or an integral product architecture. The producibility members play a central role in capturing and evaluating the chains for different candidate concepts and decompositions.
Technical Paper

A Look at the Automotive-Turbine Regenerator System and Proposals to Improve Performance and Reduce Cost

1997-02-24
970237
The adoption of turbine engines for automotive power plants has been hampered by the high cost, high leakage and high wear rate of present designs of ceramic-matrix regenerators. Proposals are made and analyzed here for design directions to achieve substantial improvements in all three areas. These include lower-cost extruded and pressed matrices; and clamping seals coupled with incremental movement of the rotary-regenerator matrix.
Technical Paper

Cost Awareness in Design: The Role of Data Commonality

1996-02-01
960008
Enhanced information management techniques made available through emerging Information Technology platforms hold a promise of providing significant improvements in both the effectiveness and efficiency of developing complex products. Determining actual management implementations that deliver on this promise has often proven elusive. Work in conjunction with the Lean Aircraft Initiative at MIT has revealed a straight forward use of Information Technology that portends significant cost reductions. By integrating previously separate types of data involved in the process of product development, engineers and designers can make decisions that will significantly reduce ultimate costs. Since the results presented are not specific to particular technologies or manufacturing processes, the conclusions are broadly applicable.
Technical Paper

Predicting Product Manufacturing Costs from Design Attributes: A Complexity Theory Approach

1996-02-01
960003
This paper contains both theorems and correlations based on the idea that there is a uniform metric for measuring the complexity of mechanical parts. The metric proposed is the logarithm of dimension divided by tolerance. The theorems prove that, on the average, for a given manufacturing process, the time to fabricate is simply proportional to this metric. We show corrleations for manual turning (machine lathe process), manual milling (machine milling process), and the lay-up of composite stringers. In each case the accuracy of the time estimate is as good as that of traditional cost estimation methods, but the effort is much less. The coefficient for composite lay-up compares well to that obtained from basic physiological data (Fitts Law).
Technical Paper

3D Vortex Simulation of Intake Flow in a Port-Cylinder with a Valve Seat and a Moving Piston

1996-05-01
961195
A Lagrangian random vortex-boundary element method has been developed for the simulation of unsteady incompressible flow inside three-dimensional domains with time-dependent boundaries, similar to IC engines. The solution method is entirely grid-free in the fluid domain and eliminates the difficult task of volumetric meshing of the complex engine geometry. Furthermore, due to the Lagrangian evaluation of the convective processes, numerical viscosity is virtually removed; thus permitting the direct simulation of flow at high Reynolds numbers. In this paper, a brief description of the numerical methodology is given, followed by an example of induction flow in an off-centered port-cylinder assembly with a harmonically driven piston and a valve seat situated directly below the port. The predicted flow is shown to resemble the flow visualization results of a laboratory experiment, despite the crude approximation used to represent the geometry.
Technical Paper

Aggregate Vehicle Emission Estimates for Evaluating Control Strategies

1994-03-01
940303
Currently, states that are out of compliance with the National Ambient Air Quality Standards must, according to the Clean Air Act Amendments of 1990 (CAAA), develop and implement control strategies that demonstrate specific degrees of reduction in emissions-with the degree of reduction depending upon the severity of the problem. One tool that has been developed to aid regulators in both deciding an appropriate course of action and to demonstrate the desired reductions in mobile emissions is EPA's Mobile 5a emission estimation model. In our study, Mobile 5a has been used to examine the effects of regulatory strategies, as applied to the Northeast United States, on vehicle emissions under worst-case ozone-forming conditions.
Technical Paper

Effect of Composition, Particle Size, and Heat Treatment on the Mechanical Properties of Al-4.5 wt.% Cu Based Alumina Particulate Reinforced Composites

1998-02-23
980700
The quest for higher efficiency and performance of automotive vehicles requires application of materials with high strength, stiffness and lower weight in their construction. Particulate-reinforced aluminum-matrix composites are cost-competitive materials, which can meet these requirements. MMCC, Inc. has been optimizing particulate-reinforced alloy systems and developing the Advanced Pressure Infiltration Casting (APIC™) process for the manufacture of components from these materials. This paper discusses the results of a recent study in which composites reinforced with 55 vol.% alumina were cast using two sizes of alumina particulate and eight different matrix alloys based on Al-4.5 wt.% Cu with varying amounts of silicon and magnesium. Optimum heat treatments for each alloy were determined utilizing microhardness studies. The tensile strength and fracture toughness were evaluated as a function of alloy chemistry, particulate size, and heat treatment.
Technical Paper

Decoupled Design of Cylinder Liner for IC Engines

1991-11-01
911231
Concept of a new decoupled cylinder liner design for internal combustion (IC) engines is presented from the framework of axiomatic design to improve friction and wear characteristics. In the current design, the piston rings fail to satisfy their functional requirements at the two dead centers of the piston stroke where lubrication is poor. It is proposed that by using undulated cylindrical surfaces selectively along the cylinder liner, much of the existing friction and wear problems of IC engines may be solved. The main idea behind undulated surface is to trap wear particles at the piston-cylinder interface in order to minimize plowing, and thus maintain low friction even in areas where lubrication fails to be hydrodynamic. In dry sliding tests using a modified engine motored at low speeds, undulated cylinders operated for significantly longer time than smooth cylinders without catastrophic increase in friction.
Technical Paper

Parametric Analysis of Resistance Spot Welding Lobe Curve

1988-02-01
880278
A linearized lumped parameter heat balance model was developed and is discussed for the general case of resistance welding to see the effects of each parameter on the lobe shape. The parameters include material properties, geometry of electrodes and work piece, weld time and current, and electrical and thermal contact characteristics. These are then related to heat dissipation in the electrodes and the work piece. The results indicate that the ratio of thermal conductivity and heat capacity to electrical resistivity is a characteristic number which is representative of the ease of spot weldability of a given material. The increases in thermal conductivity and heat capacity of the sheet metal increase the lobe width while increases in electrical resistivity decrease the lobe width. Inconsistencies in the weldability of thin sheets and the wider lobe width at long welding times can both be explained by the heat dissipation characteristics.
Technical Paper

Draw Bead Penetration as a Control Element of Material Flow

1993-03-01
930517
Draw beads are widely utilized as a mechanism for providing proper restraining force to a sheet in a forming operation. In this paper, numerical simulations using the nonlinear finite element method are conducted to model the process of drawing a sheet through various draw bead configurations to study the mechanics of draw bead restraint. By examing the sensitivity of the draw bead restraining force due to the change of the draw bead penetration, the work shows that the penetration has the potential to be a very good element for varying and controlling restraining force during the process. A closed-loop feedback control of draw bead penetration using a proportional-integral controller is achieved by the combination of the original finite element simulation and a special element which links penetration to a pre-defined restraining force trajectory.
Technical Paper

A CAD-Driven Flexible Forming System for Three-Dimensional Sheet Metal Parts

1993-03-01
930282
A novel system for the forming of three dimensional sheet metal parts is described that can form a variety of part shapes without the need for fixed tooling, and given only geometry (CAD) information about the desired part. The central elements of this system are a tooling concept based on a programmable discrete die surface and closed-loop shape control. The former give the process the degrees of freedom to change shape rapidly, and the latter is used to insure that the correct shape is formed with a minimum of forming trials. A 540 kN (60 ton) lab press has been constructed with a 0.3 m (12 in) square pair of discrete tools that can be rapidly re-shaped between forming trials. The shape control system uses measured part shapes to determine a shape error and to correct the tooling shape. This correction is based on a unique “Deformation Transfer Function” approach using a spatial frequency decomposition of the surface.
Technical Paper

Optimal Forming of Aluminum 2008-T4 Conical Cups Using Force Trajectory Control

1993-03-01
930286
In this paper we investigate the optimal forming of conical cups of AL 2008-T4 through the use of real-time process control. We consider a flat, frictional binder the force of which can be determined precisely through closed-loop control. Initially the force is held constant throughout the forming of the cup, and various levels of force are tested experimentally and with numerical simulation. Excellent agreement between experiment and simulation is observed. The effects of binder force on cup shape, thickness distribution, failure mode and cup failure height are investigated, and an “optimal” constant binder force is determined. For this optimal case, the corresponding punch force is recorded as a function of punch displacement and is used in subsequent closed-loop control experiments. In addition to the constant force test, a trial variable binder force test was performed to extend the failure height beyond that obtained using the “optimal” constant force level.
Technical Paper

A Graphical Workstation Based Part-Task Flight Simulator for Preliminary Rapid Evaluation of Advanced Displays

1992-10-01
921953
Advances in avionics and display technology are significantly changing the cockpit environment in current transport aircraft. The MIT Aeronautical Systems Lab (ASL) has developed a part-task flight simulator specifically to study the effects of these new technologies on flight crew situational awareness and performance. The simulator is based on a commercially-available graphics workstation, and can be rapidly reconfigured to meet the varying demands of experimental studies. The simulator has been successfully used to evaluate graphical microburst alerting displays, electronic instrument approach plates, terrain awareness and alerting displays, and ATC routing amendment delivery through digital datalinks.
Technical Paper

Real World Performance of an Onboard Gasoline/Ethanol Separation System to Enable Knock Suppression Using an Octane-On-Demand Fuel System

2018-04-03
2018-01-0879
Higher compression ratio and turbocharging, with engine downsizing can enable significant gains in fuel economy but require engine operating conditions that cause engine knock under high load. Engine knock can be avoided by supplying higher-octane fuel under such high load conditions. This study builds on previous MIT papers investigating Octane-On-Demand (OOD) to enable a higher efficiency, higher-boost higher compression-ratio engine. The high-octane fuel for OOD can be obtained through On-Board-Separation (OBS) of alcohol blended gasoline. Fuel from the primary fuel tank filled with commercially available gasoline that contains 10% by volume ethanol (E10) is separated by an organic membrane pervaporation process that produces a 30 to 90% ethanol fuel blend for use when high octane is needed. In addition to previous work, this paper combines modeling of the OBS system with passenger car and medium-duty truck fuel consumption and octane requirements for various driving cycles.
Technical Paper

Urban Vehicle Design Competition - History, Progress, Development

1972-02-01
720497
The Urban Vehicle Design Competition was inspired by the success of the Clean Air Car Race and the Great Electric Car Race. The academic community recognized the tremendous educational value of these events, and encouraged development of UVDC from its inception. The project was designed by engineering students to benefit students throughout North America. The rules of the competition include technical paper requirements that make the competition extremely attractive to professors who wish to build a course around this theme. The response of more than 2000 engineering students at 80 universities throughout the United States and Canada has indicated the success of the structure of the competition. The first major objective of the UVDC project has been met. Ninety-three teams throughout the country entered the UVDC design portion of the contest. The second portion of the project is the prototype contest of August 1972.
Technical Paper

Metallurgical and Process Variables Affecting the Resistance Spot Weldability of Galvanized Sheet Steels

1984-02-01
840113
Zinc coating integrity, composition, thickness, roughness, and the presence of Fe-Zn intermetallics are being investigated with regard to the mechanisms of weld nugget formation. This information is being used in conjunction with the optimization of the weld process parameters; such as upsloping, down-sloping, preheating, postheating, and double pulsing, to provide the widest range of acceptable welding conditions. Dynamic inspection monitoring of the welding current, voltage, force, and nugget displacement is being used to follow the progression of nugget formation and to assist in the evaluation of optimum process and material characteristics. It has been found that hot-dipped galvanized materials with coatings which have a very thin Fe-Zn alloy layer, have a wider range of acceptable welding conditions than the commercial galvannealed products, which have a fully alloyed Fe-Zn coating.
Technical Paper

Aircraft In Situ Validation of Hydrometeors and Icing Conditions Inferred by Ground-based NEXRAD Polarimetric Radar

2015-06-15
2015-01-2152
MIT Lincoln Laboratory is tasked by the U.S. Federal Aviation Administration to investigate the use of the NEXRAD polarimetric radars* for the remote sensing of icing conditions hazardous to aircraft. A critical aspect of the investigation concerns validation that has relied upon commercial airline icing pilot reports and a dedicated campaign of in situ flights in winter storms. During the month of February in 2012 and 2013, the Convair-580 aircraft operated by the National Research Council of Canada was used for in situ validation of snowstorm characteristics under simultaneous observation by NEXRAD radars in Cleveland, Ohio and Buffalo, New York. The most anisotropic and easily distinguished winter targets to dual pol radar are ice crystals.
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