in order to gain a better control of dimensional stability of sand castings. The information will also provide valuable information for casting process modelers. The university is currently working with the American Foundry Society and NISA to organize a multi-university industry research con- sortium to improve the dimensional repeatability of sand castings. Additional information on consortium efforts can be obtained from Steve Robison at AFS, stever@afsinc.org or (800) 537-4237 x227.


Casting Research Summaries from MS&T–Missouri University of Science and Technology


Aging of Graphitic Cast Irons and Machinability Cast Metals Coalition Funding


Previous studies showed that aging of gray iron at room tem- perature and at slightly elevated temperature for acceleration affected both iron mechanical properties and casting machin- ability. Recent efforts are focused on in-depth understanding of aging phenomena in irons. The effect of alloying elements on the magnitude of age strengthening and process kinetics is a particular interest during this phase of the research. This effect has not been studied previously but could be useful for foundry practice. Different levels of nitrogen with varia- tions in third elements (sulfur and manganese) have been explored. A series of heats were performed and aging ki- netics was studied by evaluation of iron strengthening and electrical resistivity changes. For theoretical understanding, an approach using Monte-Carlo statistical distribution of Mn clusters in Fe-BCC and first principal “ab-initio” methods was applied to examine the effect of alloying elements on iron aging. The results of the kinetics evaluations can be used in industry for minimizing cast iron aging time while improving casting machinability.


Aging and Machinability Interactions in Ductile Iron AFS Funding


Ductile iron processing influences casting structure and has a possible aging effect because magnesium treatment decreases nitrogen content, which is the main continuance responsible for iron aging. The effects of room temperature natural aging in industrially produced sand mold and con- tinuously cast ductile irons were experimentally investi- gated. These two processes provided significantly different cast surface topology, near-surface microstructure (“cast- ing skin”) and graphite nodule count in the casting body. Machinability measurements were conducted during face cutting and casting body cutting of ferritic/pearlitic ductile irons. Cutting forces and tool wear were measured for dif- ferent machining parameters. Quantitative microstructure analysis was used to correlate graphite structure in ductile iron to chip formation. Additionally, some beneficial ef-


76


fects of age strengthening were observed on machinability. These tests will provide data that can be used for machin- ing process planning.


Casting Process Development U.S. Army Benet Laboratory and SWC Funding


Current research has been tasked to develop a process for production of high strength steel castings of complex ge- ometry for small lot sizes. Rapid prototype foam and SLA pattern/ceramic shell processes have been the focus of re- cent investigations. The main directions of this research are in three areas—shell cracking prevention, engineered shell permeability, and mold-metal interactions between steel and investment shells.


a) Stress in Shell and Crack Prevention This includes experimental and FEM modeling of stress in the shell during pattern removal for the prevention of crack formation in large shells with deep pockets. Mechanical and physico-chemical properties and kinetics of thermal decomposi- tion of different foam pattern materials were ex- perimentally evaluated using the set of apparatus customized for the load and temperature ranges of interest. Data was incorporated in an ABACUS FEM model and predicted results were compared to an experimentally fired shell. The computational and experimental methods developed can be used for prediction of stress and designing processes to avoid cracking in industrial mold shells. This is be- ing applied to both high density foam patterns (Fo- Pat) and SLA (QuickCast) pattern materials.


b) Engineering of Shell Permeability A shell process design methodology to optimize the combined requirements of shell loading capac- ity and shell air permeability has been developed. The phenomenon of formation of open, connected channels was modeled using Monte-Carlo stochas- tic simulation of spherical pore bridges formation, and CFD modeling was used to examine air flow in these pores. Theoretical predictions were veri- fied by experimentally built and tested shells. Con- trolled porosity in these shells was engineered by carbon particle additions. The results indicated that engineered shell structure can obtain a different combination of shell mechanical loading capacity and overall ceramic mold permeability. An optimal combination of these parameters can be applied for production of large castings, which put high loads on the shell but require a short fill time.


c) Shell Mold/Liquid Steel Interactions Interactions of liquid steel with preheated ceramic shell molds can adversely affect the surface quality of investment castings and increase casting clean- ing and finishing expenses. This phenomenon was experimentally studied using a special cube-shaped


International Journal of Metalcasting/Winter 11


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87