Title page for ETD etd-121608-125755

Document Type dissertation

Author Name Dewhirst, Brian A

Email Address b.dewhirst at gmail.com

URN etd-121608-125755

Title Castability Control in Metal Casting via Fluidity Measures: Application of Error Analysis to Variations in Fluidity Testing

Degree PhD

Department Materials Science & Engineering

Advisors
Diran Apelian, Advisor
Richard Sisson, Department Head
Makhlouf, M. Makhlouf, Committee Member
Jianyu Liang, Committee Member
Fred Major, Committee Member

Keywords
castability
metal casting
error analysis
casting fluidity
a356
solidification processing
fluidity

Date of Presentation/Defense 2008-12-05

Availability unrestricted

Abstract
Tautologically, castability is a critical requirement in any casting process. The two most important factors impacting castability are the susceptibility of a metal to hot tearing and the degree of casting fluidity a material possesses. This work concerns itself with fluidity of molten metal. Since experimental investigations into casting fluidity began, researchers have sought to maximize fluidity through superheat, mold temperature, alloy chemistry, melt cleanliness, and mold design. Researchers who have examined the published results in the field have remarked on the difficulty of making quantitative comparisons and drawing conclusions from the data. Ragone developed a horizontal vacuum fluidity apparatus and an analytical expression for fluid length to help resolve these issues. This was expanded on by Flemings et al. Still, the comparison of results is complicated by experimental uncertainties and a plurality of experimental procedures. This work seeks to resolve these issues through an analysis of experimental uncertainties present in existing fluidity tests and the development of an improved test and procedure which is very precise, accurate, and reliable. Certain existing tests and software packages have been shown to be unsuitable for quantitative fluidity measurement. Expressions for experimental uncertainty in fluidity testing have been derived. The capability to predict variations in fluidity as a function of alloy chemistry and other variables whose range of values are intrinsic to the economics of the process will help to more accurately determine the superheat needed for successful castings and will in turn lead to a decrease in scrap rates. This will enable metal casters to more reliably cast thin sections, and to reduce cycle time or scrap rate to achieve productivity goals. Superheat was shown to remain the dominant factor in fluidity, but the test allowed investigation of alloy modifications within an alloy specification in this alloy system. Factors known to have negative effects on structural properties were found often to have neutral or positive impacts on fluidity. A deep understanding of variations in fluidity measurements is the next necessary step in a century-long quest to understand how best to make metal castings through the use of fluidity experiments.

Files
BRIAN_DEWHIRST_PHD.pdf

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Document Type	dissertation
Author Name	Dewhirst, Brian A
Email Address	b.dewhirst at gmail.com
URN	etd-121608-125755
Title	Castability Control in Metal Casting via Fluidity Measures: Application of Error Analysis to Variations in Fluidity Testing
Degree	PhD
Department	Materials Science & Engineering
Advisors	Diran Apelian, Advisor Richard Sisson, Department Head Makhlouf, M. Makhlouf, Committee Member Jianyu Liang, Committee Member Fred Major, Committee Member
Keywords	castability metal casting error analysis casting fluidity a356 solidification processing fluidity
Date of Presentation/Defense	2008-12-05
Availability	unrestricted
Abstract Tautologically, castability is a critical requirement in any casting process. The two most important factors impacting castability are the susceptibility of a metal to hot tearing and the degree of casting fluidity a material possesses. This work concerns itself with fluidity of molten metal. Since experimental investigations into casting fluidity began, researchers have sought to maximize fluidity through superheat, mold temperature, alloy chemistry, melt cleanliness, and mold design. Researchers who have examined the published results in the field have remarked on the difficulty of making quantitative comparisons and drawing conclusions from the data. Ragone developed a horizontal vacuum fluidity apparatus and an analytical expression for fluid length to help resolve these issues. This was expanded on by Flemings et al. Still, the comparison of results is complicated by experimental uncertainties and a plurality of experimental procedures. This work seeks to resolve these issues through an analysis of experimental uncertainties present in existing fluidity tests and the development of an improved test and procedure which is very precise, accurate, and reliable. Certain existing tests and software packages have been shown to be unsuitable for quantitative fluidity measurement. Expressions for experimental uncertainty in fluidity testing have been derived. The capability to predict variations in fluidity as a function of alloy chemistry and other variables whose range of values are intrinsic to the economics of the process will help to more accurately determine the superheat needed for successful castings and will in turn lead to a decrease in scrap rates. This will enable metal casters to more reliably cast thin sections, and to reduce cycle time or scrap rate to achieve productivity goals. Superheat was shown to remain the dominant factor in fluidity, but the test allowed investigation of alloy modifications within an alloy specification in this alloy system. Factors known to have negative effects on structural properties were found often to have neutral or positive impacts on fluidity. A deep understanding of variations in fluidity measurements is the next necessary step in a century-long quest to understand how best to make metal castings through the use of fluidity experiments.
Files	BRIAN_DEWHIRST_PHD.pdf