the effect of the method of pouring liquid metal into mould

the effect of the method of pouring liquid metal into mould

ARCHIVES OF MECHANICAL TECHNOLOGY AND AUTOMATION
Vol. 33 no. 4
2013
KRZYSZTOF GRZEĝKOWIAK, 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 19th century, precision casting was used for the first time for manufacturing utilizable castings, among others implants and dental instruments. In 30-ties of the 20th 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 inĪ.
Mgr inĪ.
Institute of Materials Technology, Poznan University of Technology.
Mgr inĪ. – Institute of Mechanical Technology, Poznan University of Technology.
16
K. GrzeĞkowiak, 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
730qC). 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 400qC, 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 Figure 2. A mould during centrifugal filling
in the F.lliGiacetti device
used. With each of the filling methods,
36 castings have been made.
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 745qC 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):
SW
WO
100 [%]
WM
(1)
18
K. GrzeĞkowiak, M. Wojciechowski, K. Sytek
where: SW – degree of mould filling [%],
WO – the casting dimension [mm],
WM – 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
Average SW value of the moulds [%]
100
90
80
Filling with gravity
force
70
54,98
60
Filling with
centrifugal force
50
40
Filling with vacuum
30
20
8,99
10
0
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 – Skáad chemiczny i wáasnoĞci
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.
WPàYW SPOSOBU ZALEWANIA FORM CIEKàYM METALEM
NA POWSTAWANIE NIEDOLEWÓW W ODLEWACH
WYKONANYCH METODĄ WYTAPIANYCH MODELI
Streszczenie
W artykule przedstawiono analizĊ związku miĊdzy sposobem zalewania form stopem AlSi7Mg
a powstawaniem niedolewów w odlewach wykonanych metodą wytapianych modeli z uĪyciem
mas gipsowych. Formy odlewnicze wypeániano ciekáym metalem trzema sposobami: z uĪyciem
siáy grawitacji, siáy odĞrodkowej i podciĞnienia. Na podstawie jakoĞci otrzymanych odlewów
(stopnia wypeánienia formy) oceniono skutecznoĞü zastosowanych sposobów zalewania form,
w których są wytwarzane odlewy o maáych moduáach. W wyniku badaĔ stwierdzono, Īe najwyĪszy stopieĔ wypeánienia form otrzymano, gdy stosowano podciĞnienie.
Sáowa kluczowe: sposób zalewania, niedolew, metoda wytapianych modeli