RU2176174C1 - Method of casting with crystallization under pressure - Google Patents

Abstract

FIELD: foundry; applicable in casting of metals and alloys with crystallization under pressure. SUBSTANCE: method includes application of coat to press mold, pouring of melt into female die and lowering of male die. Casting is formed under high pressure. After stopping of male die lowering, supplied to its channels is cooling agent in the form of water-air mixture. Before male die withdrawal, pressing pressure is reduced to below yield point of alloy fluidity under pressure for high temperatures. It is necessary for provision of conditions of growing of linear shrinkage of casting and male die. In this case, a gap is formed between male die and casting sufficient for hoisting the male die with no damage to casting surface. Time of holding and cooling of casting and male die in closed press mold is determined by formula in which maximum height of male die surface irregularities is taken into account. After withdrawal of male die, supplied into female die, over perimeter of casting is lubricant-coolant. Time of lubricant-coolant supply is determined by formula taking into consideration of maximum height of female surface irregularities. Casting is removed fully without scores on its surface and gas-filled porosity. EFFECT: higher quality of casting surfaces; increased process productivity. 1 dwg, 4 ex

Description

 The invention relates to the field of foundry and can be used for casting metals and alloys with crystallization under pressure.

 Known methods of cooling molds for injection molding with crystallization under pressure (LCD) water using cooling channels.

 A device is known - a mold for injection molding with crystallization under pressure, patent RU N 2043854, B 22 D 18/02, which implements a method of water cooling of the central insert in the matrix of the LCD mold, which allows casting without nadira on the side surface of the hole due to differences of shrinkage of the cooled central insert of the matrix and casting.

However, the implementation of the cooling channels significantly weakens the design of the mold matrix, and with a developed surface and complex geometry of the matrix inserts, it becomes problematic to perform cooling channels. As the operating practice shows, the inner surface of the cooling channels is quickly covered with a layer of scale, which significantly reduces heat transfer during water cooling, and the maximum temperature drops, more than 200 ^o C, observed on the walls of the molding surfaces of the mold under cyclic thermal loads, lead to the destruction of the press -forms.

 Known methods of LCD, in which the cooling of the molds is carried out by spraying with water or applying water-based lubricants to the working surface. They allow you to protect the LCD mold from premature destruction due to a milder cooling mode.

 There is also a known method of casting with crystallization under pressure of aluminum alloys, patent SU N 1787066, B 22 D 18/02, which allows casting without nadira on the side surface formed by the matrix, due to the difference in shrinkage of the cooled casting and matrix. This method is the closest analogue.

где τ - время, с;
m - масса отливки, г;
0,6 - коэффициент.In the method, the main attention is paid to the supply of cutting fluid under pressure on the surface of the casting and the die after the removal of the punch, which is determined from the ratio

where τ is the time, s;
m is the mass of the casting, g;
0.6 - coefficient.

 The main disadvantage of this method is that for castings obtained by LCD at the final stage of solidification, the pressing pressure is greater than the yield strength of the material (alloy) during compression, i.e. according to the theory of plastic deformation, deformation of the solid phase takes place and shrinkage does not begin until this condition is met, which leads to the appearance of nadirs on the surface formed on the cast by the punch.

 A disadvantage is also the fact that when casting with crystallization under pressure, a pressure of the order of several hundred million Pascals acts on the casting, and with a roughness of the forming surfaces of the mold 0.2 - 0.63 μm, lubricant is extruded, nadira is formed on the outer surfaces of the casting , which are the result of deformation braking of the casting material on the surface of the mold during the separation of the punch and the expulsion of the casting from the matrix.

 A further disadvantage of this method is that the time for supplying lubricant to cool the casting in the matrix after the punch is removed does not provide an optimal correspondence between the thermal regime of the casting, the size of the gap, and the optimal amount of lubricant applied to the side surface of the matrix during cooling. In this ratio, the supply time of the cutting fluid (coolant) is not associated with the amount of coolant, nor with its cooling ability, nor with the size of the gap between the casting and the matrix formed during cooling, or with the geometric dimensions of the casting.

 The disadvantage is that the LCD method provides for cooling both the matrix and castings, which leads to a decrease in the temperature of the side walls of the matrix, the excess and accumulation of lubricant (SM), which are the cause of the formation of neslitins on the side surface, shells, gas and shrinkage porosity.

It should be noted that under the most severe conditions during LCD there is a punch, the temperature of its heat-loaded sections during natural cooling is 470 - 500 ^o C, which can be achieved in 8 - 10 cycles.

где R $\genfrac{}{}{0ex}{}{\text{п}}{\text{max}}$ - наибольшая высота неровностей поверхности пуансона, м;
R_п - радиус пуасона, м;
H_п - высота пуансона, м;
K_п - коэффициент охлаждения материала пуансона;
Q_в - количество воды, находящееся в секундном расходе сжатого воздуха, кг,
а подачу смазочно-охлаждающей жидкости после отвода пуансона осуществляют по периметру отливки в течение времени, определяемого из соотношения

где R $\genfrac{}{}{0ex}{}{\text{м}}{\text{max}}$ - наибольшая высота неровностей поверхности матрицы, м;
R_о - радиус отливки, м;
m_о - масса отливки, кг;
К_о - коэффициент охлаждения смазочно-охлаждающей жидкостью материала отливки;
Q_вр - количество воды, находящееся в секундном расходе смазочно-охлаждающей жидкости распылителя, кг;
n_т - коэффициент фактического участия смазочно-охлаждающей жидкости в теплообмене, равный 0,5 - 0,6.The technical task of the invention is to obtain castings with a complex geometric configuration, increasing the productivity of the casting process and improving the quality of the outer surface. The stated technical problem is achieved by the fact that in the injection molding process with crystallization under pressure, including applying SM to the mold, pouring the melt into the die, forming the die under high pressure of the punch, withdrawing the punch, supplying the cutting fluid to the die in the die and removing the cast from the mold, the casting is cooled during its formation by feeding a water-air mixture into the punch, before pressing the punch, the pressing pressure is lowered below the yield strength of the alloy under compression for high their temperatures and cooled in the die casting and the mold closed for the time determined by the relation

where r $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ - the maximum height of the surface roughness of the punch, m;
R _p - the radius of the poisson, m;
H _p - the height of the punch, m;
K _p - coefficient of cooling of the material of the punch;
Q _in - the amount of water in the second flow rate of compressed air, kg,
and the supply of cutting fluid after the removal of the punch is carried out along the perimeter of the casting for a time determined from the ratio

where r $\genfrac{}{}{0ex}{}{\text{m}}{\text{max}}$ - the maximum height of the surface roughness of the matrix, m;
R _{about the} radius of the casting, m;
m _{about the} mass of the casting, kg;
To _about - the coefficient of cooling by the cutting fluid of the casting material;
Q _BP - the amount of water in the second flow rate of the cutting fluid, kg;
n _t is the coefficient of actual participation of the cutting fluid in heat transfer, equal to 0.5 - 0.6.

т. о. данное соотношение устанавливает зависимость между максимальной высотой неровностей поверхности пунсона, геометрическими размерами пуансона, охлаждающей способностью хладагента (например, воды) и его количеством в носителе - сжатом воздухе;
- подачу смазочно-охлаждающей жидкости на отливку по ее периметру, не охлаждая матрицу, в течение времени, определяемого из соотношения

которое устанавливает зависимость между основными параметрами теплового обмена отливки при ее охлаждении СОЖ перед выталкиванием из матрицы, качеством боковой поверхности матрицы, массой отливки и ее характерным геометрическим размером, охлаждающей способностью СОЖ и количеством хладагента, участвующего в теплообмене.Compared with the analogue, the proposed method is characterized by the presence of the following operations:
- cooling the crystallizable castings through vertical channels in the central part of the punch with refrigerant;
- lowering the pressing pressure at the end of the solidification of the casting in closed form below σ _s - the yield strength of the alloy under compression for high temperatures, which eliminates the deformation braking of the casting material in order to create a non-separating medium (lubricant) between the casting and the forming surfaces of the mold, and the growth conditions of the linear (thermal) shrinkage of the casting and punch, i.e. clearances during the time determined from the ratio

so about this ratio establishes the relationship between the maximum height of the punch surface roughness, the geometrical dimensions of the punch, the cooling ability of the refrigerant (for example, water) and its amount in the carrier - compressed air;
- the supply of cutting fluid to the casting along its perimeter, without cooling the matrix, for a time determined from the ratio

which establishes the relationship between the main parameters of the heat exchange of the casting when it is cooled by the coolant before being expelled from the matrix, the quality of the side surface of the matrix, the mass of the casting and its characteristic geometric size, cooling ability of the coolant and the amount of refrigerant involved in heat transfer.

 Thus, the claimed method meets the criterion of "novelty."

 Comparison of the proposed method with other well-known authors of the LCD methods allows us to conclude that this method meets the criterion of "inventive step". Confirmation of this is that the claimed method allowed to resolve the technical contradiction between the need to increase the productivity of the casting process and the limited possibilities of improving the quality of the outer surfaces of castings of complex geometric configurations obtained by the LCD method, by creating gaps between the punch and the casting, die and casting, larger than the largest the height of the surface roughness of the mold involved in the molding of the casting, while increasing flax of the casting process.

 The drawing shows a device that implements the inventive method, which consists of a punch 1 with a base 2 connected to a plate 3, in the central part of the punch 1 and the base 2 there are vertical cooling channels 4, with a cooling system consisting of tubes 5, a manifold 6 and nozzles 7, inlet refrigerant; and also the mold consists of a matrix 8 with a plate 9, a pushing system 10, a casting 11 and a spray 12.

 The casting with crystallization under pressure is carried out as follows: after heating the mold with gas or 3-4 portions of the melt, lubrication and blowing with compressed air using a spray gun 12, a measured portion of the melt is poured into the matrix 8 and, at the end of pouring, the punch 1 is quickly lowered to the moment closures with the matrix 8. When switching to a stroke, a casting 11 is formed in the matrix 8 with a punch 1.

 After stopping the punch 6 when its temperature rises above a predetermined initial value, the supply of refrigerant (for example, compressed air or air-water mixture) to the cooling channels 4 is turned on.

At the end of the complete crystallization of the casting, before pressing the punch 1, the pressing pressure is relieved below the σ _{s of the} yield strength of the alloy under compression for high temperatures (approximately 300 - 350 ^o C), to create conditions for the growth of linear (thermal) shrinkage of the casting 11 and punch 1 in a closed mold. This mode is necessary to create gaps between the punch and the casting, because if there is pressure above the specified value, the solid phase of the casting is deformed and shrinkage will not start, which will ultimately affect the quality of the surface of the casting formed by the punch.

 After this, a time delay is established for cooling the casting and the punch in a closed mold so that a gap is created between the casting and the punch, which is necessary and sufficient for the punch to be lifted freely without disturbing the surface of the casting.

After the expiration of the time, the punch 1 is lifted and before removing the workpiece from the matrix 8 using a spray gun 12, the casting 11 is cooled by the air-air mixture of lubricant along its perimeter until the gap becomes greater than or equal to the highest height of the irregularities on the side surface of the matrix, i.e. Δ ≥ R $\genfrac{}{}{0ex}{}{\text{M}}{\text{max}}$ .

 After extraction of the casting 11 from the matrix 8, lubricant is applied to the punch 1, the matrix 8, pushers 10, blown with a water-air mixture of the lubricant, then compressed air, and when the temperature of the punch 1 and the specified operating range are entered, the next portion of the molten metal is poured before pressing.

 Example 1 (analogue method).

The stator case casting was made of AK7ch aluminum alloy with a size of ⌀ 200x75 and a mass of 2.7 kg by piston-piston pressing on an EPR-34A non-specialized hydraulic press with a pressing force of 2500 kN. The pouring temperature is 710 - 720 ^o C, the mold temperature is 150 - 250 ^o C, the melt holding time in the matrix until the pressure is applied is no more than 10 seconds, the holding time under pressure is 60 seconds.

где m - масса отливки в граммах (для отливки массой m = 2700 г, τ = 31,2 сек). Затем производили выталкивание и съем отливки. Технологический цикл осуществлялся в течение 250 - 300 сек.The technology consists in the following: after applying SM to the punch and die for 10 seconds, the punch and die were cooled for 120 seconds using a spray gun of E13M1C or E77 Elitol water-soluble lubricant with a dilution ratio of 1:20; 1:25. For 70 seconds, casting, pressing and crystallization were performed under a pressure of 80-100 MPa. After removal of the punch, the die casting was cooled using a manual spray gun with a water-air mixture of coolant over time

where m is the mass of the casting in grams (for casting weighing m = 2700 g, τ = 31.2 sec). Then made the extrusion and removal of the casting. The technological cycle was carried out for 250 - 300 seconds.

There were casting defects on castings:
- nadir on the lateral surfaces formed by a punch and a matrix;
- non-slit, gas porosity, patterns associated with excess and uneven lubrication;
- leakage of machined parts with a reject rate of up to 15% and higher.

 Example 2 (by the present method).

The stator case casting was made of AK7ch aluminum alloy with a size of ⌀ 200x75 and a mass of 2.7 kg by piston-piston pressing on an EPR-34A non-specialized hydraulic press with a pressing force of 2500 kN. The pouring temperature is 710 - 720 ^o C, the temperature is 150 - 250 ^o C, the exposure time of the melt in the matrix until the pressure is applied is no more than 10 seconds, the exposure time under pressure is 60 seconds.

(~ 15 сек) осуществляли выдержку без давления в закрытой форме, производили подъем пуансона ~ 5 сек и охлаждение отливки в матрице смесью СОЖ в течение

(~ 11 сек) выталкивание и съем отливки - 10 сек, нанесение противозадирной смазки на выталкиватели - 10 сек.After applying the SM to the punch and the matrix for ~ 10 sec, the mixture was cooled with a coolant mixture with a dilution ratio of 1: 150; 1: 200 and blowing with compressed air for ~ 20 sec. Within 70 seconds, the melt was poured, pressed, crystallized under pressure, then for

(~ 15 sec), holding without pressure in a closed form was carried out, the punch was lifted ~ 5 sec and the casting in the matrix was cooled with a coolant mixture for

(~ 11 sec) ejection and removal of the casting - 10 sec, applying anti-seize lubricant to the ejectors - 10 sec.

Example 3 calculation of the cooling time of the casting and punch according to the formula
τ _p = R $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ • R _p • H _p • K _p / Q _c
The calculation formula for the cooling time of the casting and the punch before it is withdrawn in a closed mold is obtained from the solution of the system of equations of heat balance of the mold, linear (thermal) shrinkage of the punch and casting, provided there is no deformation braking during the separation of the punch, when the height of the unevenness of the mold and casting do not touch each other, i.e. clearance Δ ≥ R $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ .
K _p - coefficient of cooling of the material of the punch, for interacting substances (steel-water) - the value is constant and dimensionless, because includes only the thermophysical characteristics of these materials, equal to ≈ 680000.

Пример 4 расчета времени подачи СОЖ на отливку после отвода пуансона по формуле
τ_o= R $\genfrac{}{}{0ex}{}{\text{п}}{\text{max}}$ •m_o•K/R_o•Q_вр•n_т.
Расчетная формула времени для подачи СОЖ на отливку в матрице после отвода пуансона определяется также из системы уравнений теплового баланса отливки, линейной (тепловой) усадки отливки и матрицы при условии отсутствия деформационного торможения материала отливки во время ее выталкивания, когда наибольшие высоты неровностей боковой поверхности матрицы и отливки не касаются друг друга, т.е. зазор Δ ≥ R $\genfrac{}{}{0ex}{}{\text{п}}{\text{max}}$ .
К_о - коэффициент охлаждения материала отливки СОЖ, для взаимодействующих веществ (AL - сплав-вода) - величина постоянная и безразмерная, т.к. включает только теплофизические характеристики этих материалов, равен ≈ 26. Так, при изготовлении отливки, например, массой m_о - 2,7 кг, с радиусом отливок R_о - 0,1 м при наибольшей высоте неровностей матрицы. R $\genfrac{}{}{0ex}{}{\text{M}}{\text{max/}}$ - 0,0001 м, коэффициенте охлаждения СОЖ материала отливки из сплава АК7ч К_о = 26 и секундном расходе СОЖ Q_вр - 0,01 кг, коэффициенте n_т- 0,5 время для подачи СОЖ на отливку в матрице после отвода пуансона составит

Качество полученных отливок
- отсутствие надиров на всех поверхностях;
- отсутствие газовой пористости на боковой поверхности;
- отсутствие дефектов, обусловленных избытком и неравномерностью нанесения смазочного материала;
- шероховатость отливки 0,63-2 мкм.So, the cooling time of the casting and punch before it is withdrawn in a closed mold after depressurizing the mold in which the casting is made weighing 2.7 kg at the highest roughness height R $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ - 0.0001 m, the radius of the punch, R _p - 0.02 m, the height of the punch H _p - 0.04 m, the coefficient of cooling of the material of the punch with moist air with a second water flow in it Q _in - 0.01 kg will be

Example 4 of the calculation of the coolant supply time for casting after the removal of the punch according to the formula
τ _o = R $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ • m _o • K / R _o • Q _bp • n _t
The estimated time formula for supplying coolant to the casting in the matrix after the punch removal is also determined from the system of equations of the heat balance of the casting, the linear (thermal) shrinkage of the casting and the matrix, provided there is no deformation braking of the casting material during its ejection, when the heights of the roughnesses of the side surface of the matrix and castings do not touch each other, i.e. clearance Δ ≥ R $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ .
To _about - the cooling coefficient of the material of the coolant casting, for interacting substances (AL - alloy-water) - the value is constant and dimensionless, because includes only the thermophysical characteristics of these materials, it is ≈ 26. So, in the manufacture of castings, for example, with a mass of m _о - 2.7 kg, with a radius of castings R _о - 0.1 m at the highest height of the unevenness of the matrix. R $\genfrac{}{}{0ex}{}{\text{M}}{\text{max /}}$ - 0.0001 m, the cooling coefficient of the coolant of the material of the AK7ch alloy casting К _о = 26 and the second coolant flow rate Q _BP - 0.01 kg, the coefficient n _t - 0.5, the time for supplying coolant to the casting in the matrix after the punch is removed

The quality of the castings
- lack of nadir on all surfaces;
- lack of gas porosity on the side surface;
- the absence of defects due to excess and uneven application of lubricant;
- the roughness of the casting of 0.63-2 microns.

 The method allows to obtain castings with high surface quality. The use of forced, controlled cooling for this purpose allows to increase the productivity of the process by reducing the solidification period and cooling of the casting before it is removed from the mold by more than 40%.

Claims (1)

A method of casting with crystallization under pressure, including applying a lubricant to the mold, pouring the melt into the die, forming a high-pressure die casting, discharging the die, supplying cutting fluid to the die in the die, and extracting the die from the mold, characterized in that in the process of forming the casting, it is cooled by feeding a water-air mixture into the punch, before removing the punch, the pressing pressure is lower than the yield strength of the alloy under compression for high temperatures and the casting is cooled and the punch in closed mold for a time determined by the relation
τ _p = R $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ • R _p • H _p • K _p / Q _c ,
where r $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ - the maximum height of the surface roughness of the punch, m;
R _p - the radius of the punch, m;
N _p - the height of the punch, m;
K _p - coefficient of cooling of the material of the punch;
Q _in - the amount of water in the second flow rate of compressed air, kg,
and the supply of cutting fluid after the removal of the punch is carried out along the perimeter of the casting for a time determined from the ratio
τ _o = R $\genfrac{}{}{0ex}{}{\text{M}}{\text{max}}$ • m _o • K _o / R _o • Q _bp • n _t
where r $\genfrac{}{}{0ex}{}{\text{M}}{\text{max}}$ - the maximum height of the surface roughness of the matrix, m;
R _{about the} radius of the casting, m;
m _{about the} mass of the casting, kg;
K _about - the cooling coefficient of the cutting fluid of the casting material;
Q _BP - the amount of water in the second flow rate of the cutting fluid, kg;
n _t - the coefficient of actual participation of the cutting fluid in heat transfer, equal to 0.5-0.6.