| Author | Narongsak Thammachot |
| Call Number | AIT Diss. no.ISE-12-18 |
| Subject(s) | Metal castings
|
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Design and Manufacturing Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. ISE-12-18 |
| Abstract | Incomplete filling is one of the most important problems in the casting of sterling silver jewelry products using the investment casting process. In the casting process of a typical sterling silver jewelry company, the highest percentage of casting defects is incomplete filling (cold shut and misrun).The causes of incomplete filling are related to poor gating systems, incorrect pouring and molding temperature. A suitable shape and dimension of the gating system will increase the melt flow while it is feeding into the mold cavity by eliminating excessive pouring and molding temperatures. The objective of this study is to develop a new design of gating system for eliminating incomplete filling. The new shape and dimensions of pouring cup, main sprue and sprue base are proposed and investigated. The computational flow model is solved with the aid of computer simulation. The targets of an optimum solution are increasing the efficiency of metal flow and reducing turbulence. The experiments are conducted to validate the simulation data. The results of this research will aid in the elimination of casting defects and increase the productivity.In the first section of this dissertation, the statistical and experimental classification of casting defects was done from the industrial case study. The data oncasting defects of year 2006 is collected and the grand total and the highest percentage of defects are reported. The QCC activity was applied in year 2007 for improving the productivity by decreasing the percentage of casting defects. The type of casting defects that were selected for QCC activity include incomplete filling, porosity, metal insolute, pin cracked, body cracked (ring), fins, wrong cutting position and body distortion. The percentage of casting defects was reduced from 1.28% (January-July, 2007) to 0.74% (August-November, 2007) after QCC activity. The highest percentage reduction is body crack (ring), wrong cutting and metal insolute respectively. The lowest percentage reduction is incomplete filling. This can be improved by increasing the pouring temperature and mold temperature. However, increasing the pouring temperature will be the cause of cracking inside the plaster mold, which is followed by the generation of fins defects. In the second section of this dissertation, the new gating system is developed to increase the performance of metal filling into the mold cavity to prevent incomplete filling defects. The components of the new design are the pouring cup, main sprue and sprue base. The new modified pouring cup has a narrower inlet and is greater in height, and has a smooth edge at the connection between the pouring cup and the main sprue. This design improves the flow velocity of molten metal. The shape of the new modified main sprue is that of a reverse tapered sprue. This design increases the feeding time off all ingate steps. The difference in flow velocity of molten metal between the upper ingates step to the lower ingates step of the new design is the smallest. The new modified sprue base shape has an apple-like shape. This design contains the upward stream energy inside the sprue base, so the fluctuation of velocity is smoother in the steady state. The experimental results show that the efficiency of the new gating system is higher because it can fill more completely than a conventional tapered sprue. In the last section of this dissertation, it is recommended that further work be concerned with the following conditions: 1) to analyze and simulate the thermal properties of the casting and to further improve the design; 2) to study the different angles between the main sprue and ingate for metal filling into the mold cavity; 3) to modify the shape and size of ingate for metal filling into the mold cavity; and 4) to study the effect of this new design on other alloys used in jewelry such as gold, brass and platinum. |
| Year | 2012 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. ISE-12-18 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Industrial Systems Engineering (DISE) |
| Academic Program/FoS | Industrial Systems Engineering (ISE) |
| Chairperson(s) | Bohez, Erik L. J.; |
| Examination Committee(s) | Pongsak Dulyapraphant;Afzulpurkar, Nitin V.;Seng, Gabriel;Chua, Chee Kai; |
| Scholarship Donor(s) | Rajamangala University of Technology Isan, Thailand; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2012 |