A R C H I V E S O F M E C H A N I C A L T E C H N O L O G Y A N D A U T O M A T I O N Vol. 33 no. 4 2013 KRZYSZTOF GRZE KOWIAK, MARCIN WOJCIECHOWSKI KAMIL SYTEK THE EFFECT OF THE METHOD OF POURING LIQUID METAL INTO MOULD ON MISRUN FORMATION IN THE CASTINGS MADE WITH LOST-WAX CASTING TECHNOLOGY The paper presents analysis of the relationship between the way of pouring AlSi7Mg alloy into moulds and misrun formation in the castings made with lost-wax casting method, with the use of gypsum mass. The casting moulds have been filled with liquid metal with three various methods (using gravity force, centrifugal force, and vacuum). Estimation of the quality of the obtained castings (i.e. the degree of mould filling) allowed to assess the effectiveness of particular methods of filling the moulds used for production of small-module castings. In result, it was found that the highest mould filling degree is achieved with the use of vacuum technology. Key words: mould filling method, misrun, lost-wax casting technology 1. INTRODUCTION Foundry engineering is one of the earliest methods of manufacturing of products. The history of precision foundry began around 5000 years ago, together with the beginning of the demand for shaped metal products, tools, and weapons [2]. In the 19 th century, precision casting was used for the first time for manufacturing utilizable castings, among others implants and dental instruments. In 30- -ties of the 20 th century the first attempts of casting the parts of aircraft engines with this method [3] were made. Final goal of any casting process is production of a casting complying with customer s requirements. Taking into account the lost-wax casting method the customers usually expect the castings free of any faults [8]. One of the most important faults occurring in the castings is a misrun, that may be caused both by pouring temperature being too low and insufficient castability of the liquid metal [1]. Dr in. Institute of Materials Technology, Poznan University of Technology. Mgr in. Mgr in. Institute of Mechanical Technology, Poznan University of Technology.
16 K. Grze kowiak, M. Wojciechowski, K. Sytek In case of manufacturing thin-walled products with lost-wax casting technology, when the liquid metal is introduced into the mould cavity with the use of gravity force, the problem of proper filling of the casting often becomes very important. In order to achieve high quality castings made with the lost-wax casting method the moulds are frequently filled with the use of centrifugal force or vacuum [4, 5]. Therefore, the paper presents the effect of mould filling method on misrun formation in the castings made with lost-wax casting technology. 2. METHOD OF THE RESEARCH The research was devoted to the castings made with the use of wax models of the diameter of 1.2 mm and length of 43 mm, made with lost-wax casting method (Figure 1). The choice of such a model was the result of a minimum wall thickness of the castings in molds made of gypsum mass, which is from 1.0 to 1.5 mm [6]. The casting module was 0.03 cm. a) b) c) Figure 1. Castings and gating systems filled with the use of: a) gravity force, b) centrifugal force, c) vacuum In order to make the casts, the casting models and gating systems of jewellery wax have been prepared. The set of the models have been formed with Gold Star XL gypsum mass. The gypsum mass was made in accordance with the guidelines of gypsum manufacturer. Before filling all the moulds were annealed (i.e. gradually heated up to 730 C). The last stage of the preparation process consisted in mould cooling
The effect of the method of pouring liquid metal into mould 17 down to 400 C, i.e. the temperature of filling it. Total annealing process lasted 12 hours. Nine casting moulds have been prepared as mentioned above. This allowed to make three pouring trials with each of the filling methods, i.e. with the use of the gravity force, centrifugal force (Figure 2), and vacuum (Figure 3). Centrifugal mould filling was carried out with the use of the F.lliGiacetti equipment, that enabled to attain constant rotational velocity, equal to 300 r.p.m. For the vacuum casting, the mould was at first filled with liquid metal under gravity force and, afterwards, a device reducing the pressure down to about 5 kpa was used. With each of the filling methods, 36 castings have been made. Figure 2. A mould during centrifugal filling in the F.lliGiacetti device a) b) Figure 3. Vacuum filling: a) view of a filled mould, b) process scheme The material serving as castings was a hypo-eutectic aluminum alloy AlSi7Mg [7]. In the time of mould filling, the liquid metal temperature was equal to 745 C in all the trials. In order to determine the sizes of misruns formed during filling the moulds with various methods the dimensions of wax models and the castings have been measured. A measure of the misrun size was equal to the degree of mould filling expressed by the following formula (1): WO SW 100 [%] (1) W M
18 K. Grze kowiak, M. Wojciechowski, K. Sytek where: SW degree of mould filling [%], W O the casting dimension [mm], W M model dimension [mm]. For each of the filling method, the average SW and standard deviation have been calculated. 3. RESULTS OF THE RESEARCH Figure 4 presents a plot of average SW values in the moulds under various filling methods. 100 100 Average SW value of the moulds [%] 90 80 70 60 50 40 30 20 10 0 8,99 54,98 Filling with gravity force Filling with centrifugal force Filling with vacuum Filling me thods Figure 4. A plot of average SW values for various filling methods According to Figure 4, the poorest mould filling occurred during gravity force casting. It amounted to 8.99 %. Better results were obtained using the centrifugal force filling method, nevertheless, the value of 54.98 % obtained in this case was still unsatisfactory. Vacuum casting provided the average mould filling degree equal to 100 %. 4. CONCLUSIONS In result of the study on the effect of method of pouring liquid metal into moulds on misrun formation in the castings made with lost-wax casting technology, the following conclusions may be stated:
The effect of the method of pouring liquid metal into mould 19 vacuum assisted pouring of liquid metal into moulds gave full filling of the mould (without misruns), pouring liquid metal into moulds under gravity or centrifugal force should not be used in case of filling the moulds of small-modules, as the misruns occurred in these conditions, in order to fill the casting moulds under centrifugal force and vacuum a special equipment is required, which increases the cost of castings. REFERENCES [1] Atlas wad odlewów, Kraków, CIATF Instytut Odlewnictwa 2004. [2] Baker J., Five thousand years of investment castings, BICTA Bulletin, 1997, no. 26, p. 6 8. [3] Ford D.A., Investing in technology from hindsight to foresight, Foundry Trade Journal, 2000, vol. 174, no. 3573. [4] Ken-ichiro Suzuki, The high-quality precision casting of titanium alloys, JOM: the Joumal of the Minerals, Metals & Materials Society, 1998, 50, 9, p. 20 23. [5] Liu Z. et al., Evaluation of the effect of vacuum on mold filling in the magnesium EPC process, Journal of Materials Processing Technology, 2002, vol. 120, no. 1, p. 94 100. [6] Perzyk M. et al., Odlewnictwo, Warszawa, WNT 2000. [7] PN-EN 1706:2011P Aluminium i stopy aluminium Odlewy Sk ad chemiczny i w asno ci mechaniczne. [8] Shimizu H. et al., Mold filling of titanium alloys in two different wedle-shapes molds, Biomaterials, 2002, vol. 23, issue 11, p. 2275 2281. WP YW SPOSOBU ZALEWANIA FORM CIEK YM METALEM NA POWSTAWANIE NIEDOLEWÓW W ODLEWACH WYKONANYCH METOD WYTAPIANYCH MODELI S t r e s z c z e n i e W artykule przedstawiono analiz zwi zku mi dzy sposobem zalewania form stopem AlSi7Mg a powstawaniem niedolewów w odlewach wykonanych metod wytapianych modeli z u yciem mas gipsowych. Formy odlewnicze wype niano ciek ym metalem trzema sposobami: z u yciem si y grawitacji, si y od rodkowej i podci nienia. Na podstawie jako ci otrzymanych odlewów (stopnia wype nienia formy) oceniono skuteczno zastosowanych sposobów zalewania form, w których s wytwarzane odlewy o ma ych modu ach. W wyniku bada stwierdzono, e najwy szy stopie wype nienia form otrzymano, gdy stosowano podci nienie. S owa kluczowe: sposób zalewania, niedolew, metoda wytapianych modeli