Sponsored by: MDMD Solidification and SCAMP Committees
Program Organizers: E.F. Matthys, Mechanical Engineering Department, University of California, Santa Barbara, CA 93106; W.G. Truckner, Technical Director--Product Development, Alcoa Technical Center, Alcoa Center, PA 15069
Monday, PM Room: B3
February 5, 1996 Location: Anaheim Convention Center
Session Chairperson: D. Thoma, Los Alamos National Laboratory, MST-6, Mail Stop G770, Los Alamos, NM 87545; W. Truckner, Alcoa Technical Center, Alcoa, PA 15069
2:00 pm Invited
PROGRESS IN STEEL CONTINUOUS CASTING: Alan W. Cramb, Department of Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213
In the last ten years steel casting has gone through a revolution that has allowed new steel mills to be constructed for flat products for the first time since the early sixties. These new mills will contribute 18 million tons of extra capacity by 1997 and mark the largest expansion of the US Steel industry since the second world war. The casting of thin slabs has caused this expansion and yet strip casting may not be far from a commercial reality. This paper will focus on reviewing thin slab and strip casting in North America and around the world to critically assess the technologies and discuss potential future trends.
2:40 pm
THERMAL ISSUES IN SHAPE DEPOSITION MANUFACTURING: Cristina H. Amon, Kevin S. Schmaltz, Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
Shape Deposition Manufacturing (SDM) is a layered manufacturing process that combines the benefits of Solid Freeform Fabrication (SFF), thermal spray and other manufacturing processing operations for fabricating multi-material objects of arbitrary three-dimensional geometric complexity with controlled microstructures and for embedding electronic components and sensors in conformal shape structures. SDM involves molten metal droplet deposition, remelting and solidification as well as the use of sacrificial support materials. Therefore, a thorough understanding of the thermal aspects of the process is required for selecting SDM process parameters and for enabling the integration with SDM CAD-based design systems. Important thermal issues in the production of high-quality SDM objects are the creation of inter-layer metallurgical bonding through substrate remelting, the control of cooling rates of both the substrate and the deposition material, and the minimization of residual thermal stress build-up which may induce warping and deboding between deposited layers. This paper presents brief descriptions of the thermal modeling approach, numerical predictions of the cooling rates and substrate remelting depths of steel deposited on steel and on copper, and experimental verifications by temperature measurements and optical metallography.
3:05 pm
FACTORS LEADING TO THE MICROSTRUCTURAL REFINEMENT AND ELIMINATION OF MICROPOROSITY IN DROPLET-BASED FREEFORM FABRICATION OF STRUCTURAL MATERIALS: M. Orme, J. Courter, C. Huang, K. Willis, Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA 92717-3975
The development of a droplet-based solid freeform fabrication technique for the fast manufacture of structural components directly from CAD information is presented. The technique relies on the use of precisely controlled molten nano-liter droplets as the deposition element. Encouraging experimental results indicate that typical material porosities as low as 0.03% and microstructures with grain sizes on the order of a micron can be achieved with molten droplet throughout rates as high as .18 ml/s with a single droplet stream. Extremely high control of the droplet trajectories (measured angular dispersions of the order of 1 micro-radian), and droplet speeds (measured speed dispersions of the order of 3 x 10-7 times the average stream speed) provides the ability for precise control over the solidification characteristics and hence microstructure. Experimental results in combination with numerical analyses on the solidification characteristics of the droplets determine a control scheme for achieving a component with minimum porosity and microstructure.
3:30 pm BREAK
3:50 pm
ON THE HEAT TRANSFER AT THE INTERFACE BETWEEN A SOLIDIFYING METAL AND A SOLID SUBSTRATE: G.-X. Wang, E.F. Matthys, Department of Mechanical Engineering, University of California, Santa Barbara, CA 93106
The interfacial thermal conductance between a solidifying molten metal layer and a cold substrate is a critical parameter for many applications in material processing and manufacturing such as continuous slab casting, strip casting, melt-spinning, spray deposition and others. Relatively few quantitative data on the interfacial thermal conductance for such applications are available, however, and -accordingly- we have initiated an experimental study to investigate further this issue. In these experiments, a thin molten metal layer was put into contact with a thicker solid metal substrate. The interfacial heat transfer coefficient between the melt and substrate can then be estimated by matching calculations from a phase change model to the measured temperature of the top surface of the layer. Estimates of the variation of this coefficient with time can then be generated. The results indicate that the interfacial heat transfer coefficient varies significantly as the liquid/solid interface becomes a solid/solid interface. The results also showed a strong effect of the layer/substrate material combination, of the melt superheat, and of the substrate surface roughness on the interfacial conductance. Some of the results from these parametric studies will be presented and discussed. The effect of the surface roughness on the thermal conductance will also be discussed in terms of the contact surface characteristics.
4:15 pm
FLUID AND HEAT FLOW IN PLANAR-FLOW MELT-SPINNING: EXPERIMENTS AND MODELING IN THE LINEAR GROWTH REGIME: Paul H. Steen, Cornell University, Department of Chemical Engineering, Ithaca, NY 14853; Tetsuhara Ibaraki, Nippon Steel Corporation, Kimitsu, Japan
The success of steady planar-flow casting requires that the rates of delivery of mass and removal of latent heat from the solidification front be compatible. This requirement couples the fluid mechanics and heat transfer. On the other hand, in the regime of linear (on average) front growth, the fluid flow is only weakly coupled to the heat flow. We study this regime by casting 5 cm wide aluminum ribbons on a copper-beryllium wheel in air. High speed cinematography of the menisci (yielding the puddle length) and temperature probes within the substrate wheel (yielding the mold temperature) give the key measurements. These data are input into 1D fluid and heat flow models. The heat flow model delivers the heat-transfer coefficient (puddle/wheel) to within 5%. Both models (independently) deliver a growth rate. In addition to these results, we shall present evidence that the 'sink-of-masss' effect of the solidification front exerts a considerable influence on the fluid flow.
4:40 pm
CONTINUOUS CASTING AND RAPID SOLIDIFICATION OF WIRES PRODUCED BY SHAPE FLOW CASTING - SFC-TECHNIQUE -- PROCESS DEVELOPMENT, PARAMETER SIMULATION, MICROSTRUCTURES: G. Frommeyer, W. Frech, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany
A new production technique for wires by continuous shape flow casting has been developed in order to reduce the steps required to fabricate wires up to 3 mm in diameter by conventional processing routes. An instrumented and computerized melt spin facility allows quantitative parameter studies with subsequent process modelling. The achieved microstructures are correlated with the governing process parameters, such as superheat of the melt, velocity of the melt jet, nozzle geometry and adjustment, etc. The paper describes the principles and the technology of the SFC-process which enables a flexible production of wires out of aluminum, nickel base alloys, and stainless steels.
5:05 pm
SIMULATION OF MOLTEN STEEL FLOWFIELD IN INTERMEDIATE THICKNESS SLAB CASTER OF THE TSP(TM) PROCESS: Sung-Woo Lee, Changwon Research Institute, Samsung Heavy Industries, Changwon Co., Korea
The TSP is a new method of thin slab casting and cost-effective getting to
high quality hot strip production designed to satisfy the mini-mill company.
Here the casting width can be from 1000 to 2500 mm or up to 3000 mm wide, and
the facility consists of: casting thickness of 100 to 150 mm, a straight mould
of conventional design, width and taper with adjustable during casting, a
casting radius of approximately 5.5 m, casting speeds of 1.0 to 3.5 m/min
depending upon grade and slab dimensions, a roller apron using split by closely
spaced rollers arranged in segments, computer controlled air-mist cooling for
different grades and casting speeds to improve internal soundness and low
maintenance deign of components, etc. Basically the TSP caster combines the
benefits of thin slab as well as the traditional thick slab casters by using
conventional mould design. The main features of this research paper are a
flowfield control of molten steel of intermediate thickness slab in the TSP.
The simulation method is suggested using a computer modelling in order to
describe the turbulent properties of molten steel. The formulation of molten
steel behaviour is based on 3-dimensional turbulent Navier-Stokes equation in
which allowance is made for spatially distributed turbulent properties.
Namely, the basic governing equations are those of 3-dimensional, steady state,
incompressible transport of mass, momentum and enthalpy. The simulation model
using two-equation k-e turbulent model, in which it is assumed that the
influence of turbulence on the transport of momentum can be modelled by the
addition of a 'turbulent viscosity' to the existing laminar viscosity, has been
applied. In addition to cold modelling, a considerable help in the research for
the flow visualization comes from the use of 0.5 scale models of tundish and
mould in which water is used as operation fluid. The measurement data were
obtained by using 3-dimensional Laser Dopper Velocimeter.
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