FI92162C - Method of casting metal pieces according to lost foam method and under pressure - Google Patents

Abstract

The invention relates to a lost foam pressure casting process for metal pieces. This process consists, after having filled the mould with metal in the liquid state and before the solidified fraction of metal exceeds 40% by weight, in applying an isostatic gaseous pressure over the entire mould/metal, of which the value is between 1.5 and 10 mPa. The invention applies to the production of pieces, particularly made from aluminium alloys, having improved mechanical characteristics and, in particular, better resistance to fatigue. <IMAGE>

Description

921 62

Method for casting metal parts under pressure using the destructive model technique - Method for the preparation of metal parts under pressure and under the trickk metal method 5

The present invention relates to a method for casting metal bodies, in particular aluminum and metal alloys thereof, by a method according to the preamble of claim 1.

It is well known, in particular through the solution disclosed in U.S. Pat. No. 3,157,924, that molds of polystyrene foam which are embedded in a mold made of mold sand but which does not contain any binder can be used for casting. In such a method, the metal to be cast, which has been pre-melted, is brought into contact with the casting pattern through channels passing through the sand and gradually replaces the latter by burning it and converting it to vapor leaving the sand grains.

This technique has proven to be advantageous on a factory scale, as it avoids the prefabrication of rigid molds by compacting and briquetting powdery, refractory materials, which molds are connected to the cores in a somewhat complex manner through the channels, and because than the easy recycling of castings. However, this technique is deficient for two reasons: 30 - cooling is relatively slow, which promotes the formation of gas bubbles - temperature gradients are relatively weak, which may cause a microscopic shrinkage cavity if the profile of the portion makes it difficult to feed.

I · 92162 2

In order to avoid such disadvantages, the applicant has developed a casting method using the technology of the destructive model, which is the subject of a patent application published in France under number 2,606,688.

5 This application discloses that when the mold is filled with molten metal, i.e., when the metal has completely destroyed the mold and the foams produced by the foam have been removed, and most preferably before the metal begins to cool, the mold and metal are formed. isostatic gas pressure. This pressure is applied with increasing values over time in order to avoid the penetration of the metal into the sand, so that the maximum possible value is reached in less than 15 seconds.

15 Castings made under these conditions have a higher tightness, which is reflected in an improvement in mechanical properties, especially in terms of strength.

20 However, in that application, the applicant stated that it was advantageous to apply a pressure of at most between 0.5 and 1.5 MPa and that it was unnecessary to exceed that limit.

In fact, after more detailed studies, the applicant found that if the pressure was increased further, in addition to mechanical properties such as the breaking strength Rm, the elastic limit LE and the elongation A, the fatigue strength F was also improved.

Thus, there is the present invention, which comprises a method for casting metal bodies, especially aluminum and metal alloys thereof, under pressure using a fading model technique in which an organic foam casting pattern from a casting body is not embedded in a mold, -this binder, the mold is filled with molten metal, which replaces the foam and gradually cools, and the increasing isostatic gas pressure is directed simultaneously

II

92162 3 mold and metal as soon as possible at the end of filling. The invention is characterized by what is defined in the characterizing part of claim 1.

Thus, the invention involves the use of pressures in the range of 1.5 to 10 MPa and most preferably in the range of 5 to 10 MPa, which value is reached before the amount of solidified metal exceeds 90% by weight.

As in French patent application 2,606,688, the application of pressure can be effected by means of a sealed box in which the mold is placed, said box being provided with one or more openings suitably placed in its wall and connected to a gas source.

Within the selected pressure scale, the applicant stated that the manifestations that occurred during the application of pressure were completely different from those of the prior art.

20

In fact, the main function of the pressure between 0.5 and 1.5 MPa is to accelerate the flow of molten metal between the dendrites of the metal in the solidified state, and the effect ceases when the solid entity has reached a certain development.

25 In particular, such low pressures enable the core hood to operate efficiently so as to avoid shrinkage due to the shrinkage of the cooling metal.

Instead, under a pressure of more than 1.5 MPa, and especially when 30 exceeds 5 MPa, the flow rate of molten metal, which remains predominant at the beginning of solidification, is gradually replaced by the heat-forming manifestations of the already solidified metal assembly. % ar-35 vot, depending on the type of alloy cast. The use of high pressures thus results in a kind of isostatic forging which is applied to the entire surface of the cast part.

92162 4

The accompanying Figure 1 is a microscopic examination of the mixture A-S7G03 cast according to the invention under a pressure of 7 MPa and subsequently heat-treated. This microscopic examination reveals a permanent deformation caused to the dendritic structure, which causes the porosity to be filled, and illustrates well the forging effect under which the metal is subjected in this method.

Under these conditions, it is found that the mechanical characteristics of the bodies have substantially improved; especially tear strength. Pressures above 10 MPa bring only very minor improvements.

This new pressure scale is most preferably applied before 15 when the amount of solidified metal is 40% by weight, so that the flow of molten metal can be affected.

It is also preferred that the maximum directional pressure is reached before the amount of solidified metal exceeds 20% by 90% in order to be completely cooled by the deformation effect.

As in French Pat. of balance. In fact, the bath causes a relatively large load in the loss of pressure transmission, and as a result, at the level of the metal in contact with the sand, this pressure tends to push the Lomasa of the metal sand grains and cause the casting to deform.

The invention can be illustrated by the following exemplary embodiment: hollow, cylindrical bodies with an outer diameter of 45 mm and a wall thickness of 4 mm, with parallel edges and projections of 20 x 20 x 80 mm;

II

92162 5 was cast according to the previous method and the method according to the invention, i.e. an isostatic gas pressure corresponding to air-5 pressure and values of 1 MPa, 5 MPa and 10 MPa was applied inside the cavity containing the mold just before the onset of solidification.

The pieces were made from two types of alloys with good mechanical properties: 10 - A-S7G03 had a composition in weight percent: Fe 0.20;

Si 6.5-7.5; Cu 0.10; Zn 0.10; Mg 0.25-0.40; Mn 0.10; Ni 0.05; Pb 0.05; Sn 0.05; Ti 0.05-0.20; Jåånnos Al; A-U5GT had the following composition: Fe 0.35; Si 0.20; Cu 4.20-15.00; Zn 0.10; Mg 0.15-0.35; Mn 0.10; Ni 0.05; Pb 0.05; Sn 0.05; Ti 0.05-0.30; Jåånnos Al.

After the heat treatments according to the standard, the mixture A-S7G03 Y23 and the mixture A-U5GT Y24, the mechanical tests performed on said bodies 20 made it possible to measure the following characteristics according to the applied pressures.

- in the mixture A-S7G03 the quality factor Q as MPa value corresponding to the formula Q = R + 150 log A, where R is the strength as MPa value and A elongation as a percentage in both thick and thin zones.

- in the mixture A-U5GT the tensile limits LE in MPa values, the strength R in 30 MPa values and the elongation A in percent, both in both thick and thin zones.

In addition, for each mixture and for each directed pressure, the fatigue strength F as MPa was measured as a starting point for a tensile-35 test piece machined 107 revolutions using the drilling method. F applies to both thick and thin zones, as it does not depend on the rate of freezing but on the porosity and thus the applied pressure.

The results are shown in the following table.

5 T ^ ulukko

A-S7G03 A-U5GT

thick thin F thick area dhut area F

10 area area

QQ LE R A LE R A

Freezing in the air 15 at P 240 325 40 235 340 8 260 355 7 90 Braking in the value of 1 MPa 335 420 65 240 365 8 260 405 11 120 20 Freezing in the air 5 MPa 410 460 85 250 400 12 260 410 15 130 Freezing in the value 10 MPa 440 490 100 260 420 15 260 420 18 140 25

The improvement of all measured characteristics and in particular the increased fatigue strength are noted.

II.

Claims (3)

921 62 1. A method may cast pieces of aluminum and its alloys according to the low chlorine foam method and under pressure, when a molding of organic foam is cast from the molding in a mold, the walls of the spring are bounded by dry mold sand without any binder, filling the metal-liquid form that replaces the foams and from one to the other solidifies and applies a traveling isostatic gas pressure simultaneously to the mold and to the metal as soon as possible at the end of the filling, characterized by the fact that in order to increase the fatigue stress (F) of said metal pieces, the exerted pressure is raised to a care of between> 1.5 and 10 MPa, a care that is reached before the amount of solidified metal exceeds 90% by weight. 92162 1. Menetelmå metallikappaleiden, erityisesti alumiinia ja sen seoksia olevien metallikappaleiden, valamiseksi paineen alia hoviåvån mallin technikaikaa kåyttåen, jossa valettavan 5 kappaleen organaanista vaahtoa oleva valumalli upotetaan muot-tiin metallilla, joka korvaa vaahdon ja jåhmettyy asteittain, ja kohdistetaan kasvava isostaattinen kaasunpaine samanaikai-10 sesti valumuottiin ja metalliin mahdollisimman pian tåyttå-misen lopussa, tunnettu siitå, etå mainittujen 5 yes s 10 MPa, joka arvo saavutetaan and kuin jåhmettyneen metallin must yearly 15 ylittoo 90 paino%. Process according to claim 1, characterized in that the exerted pressure is raised to a value of between 5 and 10 mPa. 2. Patenttivaatimuksen 1 mukainen menelelmå, tunnettu siitå, etå kåytetty paine nostetaan vålillå 5-10 MPa olevaan arvoon. 20 3. Patenttivaatimuksen 1 mukainen menelelmå, tunnettu siitå, one paine kohdistetaan viimeiståån, only jåhmettyneen metallin may year on 40 paino%. 25 Patent claims Process according to claim 1, characterized in that the pressure is applied at the latest when the amount of solidified metal amounts to 40% by weight. II