CN113172731B - Quasi-temperature isostatic pressing method and die - Google Patents

Abstract

The invention discloses a quasi-temperature isostatic pressing forming method and a die, wherein an outer die comprises a female die and male dies arranged at two ends of the female die, the female die is of a hollow cylinder structure, exhaust holes are uniformly and symmetrically formed in the wall surface of the female die, and the inner die is filled in a cavity enclosed by the female die and the male dies; the inside of centre form is equipped with the first cavity that is used for placing the sample, and the shape of first cavity is the cuboid, and the centre form includes a plurality of interior modules, and interior module is including the interior module of contact and support, and the orthographic projection scope of every face of first cavity to the internal face of external mold is equallyd divide do not be equipped with be used for with the contact interior module of sample surface contact, and the module size is the same in the contact of two just right face correspondences in the first cavity, and the region outside the module fills the support interior module in the inner chamber of external mold in the contact. The invention realizes the uniform and compact molding of the blank body by reasonably arranging the component structure, is suitable for both the discharge of gas products and the discharge of gas products in the molding process, and has wide application range.

Description

Quasi-temperature isostatic pressing method and die

Technical Field

The invention belongs to the field of new material molds, and particularly relates to a quasi-temperature isostatic pressing method and a mold.

Background

The isostatic pressing technique is an advanced technique for molding a product in a closed high-pressure container under an isotropic high-pressure state. Isostatic pressing has a number of advantages over unidirectional or bidirectional pressure forming. The density of the isostatic pressing formed product is high, and is generally 5 to l5 percent higher than that of unidirectional and bidirectional compression molding; in addition, the density of the isostatic-pressed green compacts is uniform, and the density distribution of the green compacts is not uniform in both one-way and two-way pressing in the compression molding.

The traditional isostatic pressure working principle is the pascal principle, and in a sealed container, the static pressure generated by the external force acting on static liquid or gas is uniformly transmitted in all directions, and the pressure on the acting surface area is in direct proportion to the surface area. The dies used in conventional hot isostatic pressing are typically soft, thin walled envelopes. Under the action of high temperature and high pressure, the sheath in the hot isostatic pressing furnace is softened and shrunk, and the powder in the hot isostatic pressing furnace is extruded to shrink together with the powder. After the powder is filled in the sheath, the sheath is vacuumized and sealed, and then isostatic pressing is carried out on the sheath by adopting a liquid medium or a gas medium. This is because the hot isostatic pressing process consolidates the powder and material being formed by a pressure differential, and if the capsule is not evacuated or not tightly sealed, the gaseous medium will enter the capsule, which reduces the pressure differential and thus prevents densification of the powder. Therefore, the vacuum sealing sheath is not suitable for the material blank which has physical and chemical reactions in the hot press molding process and continuously exhausts gas, and not only can damage a mold, but also influences the molding quality of a sample.

Disclosure of Invention

In order to solve the problems in the prior art, the invention aims to provide a quasi-temperature isostatic pressing method and a die, which can avoid the problems that the die is damaged and the sample forming quality is influenced due to the existence of gas in a sample raw material or the generation of gas in the forming process.

The technical scheme adopted by the invention is as follows:

a quasi-temperature isostatic pressing forming die comprises a rigid outer die and an inner die made of silica gel, wherein the outer die comprises a female die and male dies arranged at two ends of the female die, the female die is of a hollow cylinder structure, exhaust holes are uniformly and symmetrically formed in the wall surface of the female die, and the inner die is filled in a cavity defined by the female die and the male dies; the centre form divide into, in, three-layer down, the intermediate level central authorities of centre form are equipped with the first cavity that is used for placing the sample, the shape of first cavity is the cuboid, the centre form includes a plurality of interior modules, the surface of interior module is equipped with the lubricant film, interior module is including the interior module of contact and support interior module, the orthographic projection scope of every face of first cavity to the internal face of external mold is equallyd divide and is do not be equipped with the contact interior module that is used for with sample surface contact, the module size is the same in the contact of two just right faces correspondence in the first cavity, the regional packing outside the module has the support interior module in the inner chamber of external mold in the contact.

Preferably, the male die comprises a male die base plate and a male die boss arranged on the male die base plate, the male die base plate and the male die boss are both cuboids, the male die boss can extend into the female die and is in clearance fit with the female die, the clearance is 0.5-1 mm, and the male die boss can be smoothly inserted into the female die cavity only if the clearance is excessive. The length and width dimensions of the male mould chassis are respectively the same as those of the female mould outer wall.

Preferably, each surface of the first cavity is a first plane, a second plane, a third plane, a fourth plane, a fifth plane and a sixth plane, respectively, where the first plane and the second plane are a set of opposite surfaces in the height direction, the third plane and the fourth plane are a set of opposite surfaces in the length direction, the fifth plane and the sixth plane are a set of opposite surfaces in the width direction, and the height of the first plane and the second plane, which is in contact with the inner module, is (height of the preform body-height)/linear expansion rate of the silicone gel/quasi-temperature isostatic pressing temperature/2; the length of the contact inner module corresponding to the third plane and the fourth plane is (length of the preformed body-length of the formed body)/linear expansion rate of the silica gel/quasi-temperature isostatic pressing temperature/2; the widths of the contact inner modules corresponding to the fifth plane and the sixth plane are (preform width-molded body width)/linear expansion rate of silicone rubber/isothermal isostatic pressing temperature/2. The preform in the present invention means a block sample prepared for the isothermal isostatic pressing, the block sample is a block having a regular shape preliminarily formed in some way, and the molded body means a final product obtained by the isothermal isostatic pressing.

Preferably, the true volume of the shaped body is the sum of the true volume of the preform (mass of each phase to be weightless in the preform x theoretical weightlessness ratio for that phase/theoretical density before weightlessness for that phase); the true volume refers to the volume without taking into account porosity, i.e. the volume at which the sample reaches full density.

Wherein the true volume of the preform is the sum of (the mass of each phase without weight loss in the preform/the theoretical density corresponding to that phase) + (the mass of each phase to be weight loss in the preform/the theoretical density before weight loss corresponding to that phase);

theoretical density of the shaped body ═ mass of each phase without weight loss in the preform + mass of each phase to be weight loss in the preform x (100% to theoretical weight loss ratio for the phase) ]/true volume of the shaped body. The preform includes a phase that will undergo a physicochemical change without weight loss during warm isostatic pressing and a phase that will not undergo a physicochemical change without weight loss.

Preferably, after the outer mold is assembled:

the height of the space in the cavity of the female die is equal to the thickness of the silica gel contacted above or below the sample in a free state multiplied by 2+ the thickness of the preformed body;

the width of the space in the cavity of the female die is equal to the width of the sample in a front or rear contact silica gel free state multiplied by 2+ width of the preformed body;

the length of the space in the cavity of the female die is equal to the length of the silicone gel in the free state in contact to the left or right of the sample x 2+ the length of the preform.

Preferably, in the contact inner modules corresponding to the first cavity, the contact inner modules in the length direction of the first cavity are all embedded into the space between the contact inner modules in the width direction of the first cavity, and the embedding distance is 1-2 mm; in the space between the module in the module embedding first cavity width direction and length direction's the contact in the below contact of first cavity direction of height, the embedding distance is 1~2 mm.

In the inner modules at the lower side of the first cavity, the upper surfaces of all the supporting inner modules are provided with first compensation layers with the same area as the upper surfaces of the supporting inner modules, and the first compensation layers are made of compressible materials; the initial thickness of the first compensation layer is equal to the compression distance of the first compensation layer plus the thickness of the first compensation layer after compression, and the compression distance of the first compensation layer is equal to the thickness of the preform body-the thickness of the molded body;

in the middle layer inner module where the first cavity is located, second compensation layers are filled between all the supporting inner modules and the contact inner modules on the front side and the rear side of the first cavity, and the second compensation layers are made of compressible materials; the initial thickness of the second compensation layer is equal to the compressed distance of the second compensation layer + the compressed thickness of the second compensation layer, and the compressed distance of the second compensation layer is equal to (preform length-molding length)/2.

Preferably, the vent hole is a circular vent hole with the diameter of 3-5 mm.

Preferably, the lubricating layer adopts a graphite powder layer and plays a role of a heat conducting layer.

Preferably, the female and male dies are both steel.

The invention also provides a quasi-temperature isostatic pressing method, which is carried out by using the quasi-temperature isostatic pressing mould, and comprises the following processes:

before the quasi-temperature isostatic pressing forming, placing the quasi-temperature isostatic pressing forming die provided with the sample in a hot press for prepressing to expand the inner die made of silica gel and apply prepressing to the sample, and releasing gas in sample pores;

and taking the quasi-temperature isostatic pressing mould down, heating the hot press to the quasi-temperature isostatic pressing temperature, putting the quasi-temperature isostatic pressing mould on the hot press again, applying preset pressure, and preserving heat and pressure for preset time to obtain a final sample.

Preferably, during prepressing, the prepressing temperature is 70-90 ℃, the applied pressure is 3-5 MPa, and the heat preservation and pressure maintaining time is 0.5-1.5 h;

the quasi-temperature isostatic pressing temperature is 180-220 ℃, the pressure is 20-30 MPa, and the heat preservation and pressure maintaining time is 3-4 h;

taking down the quasi-temperature isostatic pressing mould, quickly heating the hot press to the quasi-temperature isostatic pressing temperature, and putting the quasi-temperature isostatic pressing mould on the hot press again, wherein the time is not more than 30min, and the temperature of the quasi-temperature isostatic pressing mould is not less than 55 ℃.

The invention has the following beneficial effects:

(1) the quasi-temperature isostatic compaction die comprises a rigid outer die and a silica gel inner die, wherein the silica gel has proper flexibility (Shore hardness of 55A) and obvious expansion (expansion coefficient of 5.9-7.9) multiplied by 10) during heating^-4/° c); the outer die is rigid, and the thermal expansion coefficient of the outer die is small so as to limit the outer expansion of the inner die, so that the inner die can only expand inwards, and extrusion force is applied to a blank sample placed in the first cavity. The soft silica gel mold avoids the damage to the sample when the sample is extruded due to the soft silica gel mold.

(2) The silica gel soft mold has poor thermal conductivity, and the sample can reach even temperature under the condition that the thermal conductivity of the sample is greater than that of the silica gel soft mold, so that the temperature gradient inside the sample is avoided, the thermal expansion of the sample is gradually increased due to the poor thermal conductivity of the silica gel, the extrusion force of the sample is also gradually increased, the discharge process of gas inside the sample is eased, and the overlarge internal stress caused by too fast gas discharge in the sample is avoided. The gas permeability of centre form silica gel is good, and the bed die wall evenly symmetric distribution of external mold has circular exhaust hole for the gas that produces can in time discharge, avoids the damage of mould and to the influence of sample quality.

(3) The orthographic projection range from each surface of the first cavity to the inner wall surface of the outer die is respectively provided with an inner module for contacting the surface of the sample, and the six contact inner modules can be used for applying pressure to each surface of the sample to carry out molding; the sizes of the inner modules which are used for being in contact with the samples and correspond to the two opposite surfaces in the first cavity are the same, so that the extrusion force of the samples in the opposite direction of each group is the same, the samples can be fixed in relative positions with the mold in the molding process, and the molding quality is further ensured; the inner cavity of the outer die is filled with the inner modules in the areas outside the inner modules which are used for being in contact with the samples, and the inner modules can provide good support for the six inner modules and ensure that the six modules apply extrusion force to the samples from different directions; the contact surface between the inner die block and the inner die block is provided with a lubricating layer, and the lubricating layer is used for increasing the lubricating property, so that the inner die blocks can move relatively during thermal expansion, and the blank sample can be well pressed.

(4) The thermal conductivity of the silica gel is low, and when the thermal conductivity of the sample is higher than that of the silica gel inner mold, uniform temperature distribution can be obtained in the sample, and no temperature gradient exists. Furthermore, the lubricating layer adopts the graphite powder layer, so that the defect that the working efficiency is low due to too low thermal conductivity of the silica gel inner die can be properly overcome, the conduction rate of heat in the inner die can be increased by utilizing the graphite powder layer, the heating rate and the working efficiency are further improved, and the speed of homogenizing the temperature in the silica gel soft die is accelerated.

(5) In the quasi-temperature isostatic pressing method, the internal mold can expand a small amount by prepressing, the prepressing is carried out on the sample, the gas in the pores of the sample is released, particularly for resin-based composite materials, the prepressing can solidify the resin in a small amount to have proper strong hardness, and the change of component distribution in an original blank due to excessive flowing of the resin under the extrusion action because of over-softness in the subsequent quasi-temperature isostatic pressing process is avoided. During the isothermal isostatic compaction, under high temperature, the expansion of the internal mold is gradually increased, and under the limitation of the external mold, the extrusion force of the internal mold to the sample is increasingly large, and the sample is gradually compacted under the extrusion action in all directions around, so that the forming is realized.

(6) The forming die has the advantages of simple structure, low manufacturing cost and simple and convenient operation.

Drawings

FIG. 1a is a front half cross-sectional view of the female mold of the outer mold of the present invention;

FIG. 1b is a left side half sectional view of the female mold of the outer mold of the present invention;

FIG. 1c is a top view of the female mold of the outer mold of the present invention;

FIG. 1d is a front half cross-sectional view of the male mold of the outer mold of the present invention;

FIG. 1e is a top view of the male mold of the outer mold of the present invention;

FIG. 2a is a top cross-sectional view of an assembled view of a quasi-temperature isostatic pressing mold according to the present invention (cut horizontally through a sample, with a compensation layer disposed thereon);

FIG. 2b is a top cross-sectional view of the assembled view of the isothermal isostatic pressing mold of the present invention (cut horizontally through the inner mold on the upper or lower side of the sample);

FIG. 2c is a left side cross sectional view of an assembled view of a quasi-temperature isostatic pressing mold according to an embodiment of the present invention (a sample is longitudinally cut in the width direction, and a compensation layer is disposed thereon);

FIG. 2d is a left side cross sectional view of the assembled view of the isothermal isostatic pressing mold of the present invention (the inner mold passing through the left or right side of the sample is longitudinally cut along the width direction, and a compensation layer is disposed thereon);

FIG. 2e is an elevational cross-sectional view of an assembled view of the isothermal isostatic mold of the present invention (with a compensation layer disposed thereon, taken longitudinally along the length of the sample);

FIG. 2f is a front cross-sectional view of an assembled view of the isothermal isostatic pressing mold of the present invention (the inner mold passing through the front or back side of the sample is longitudinally cut along the length direction, and a compensation layer is disposed thereon);

FIG. 3a is a front view of a macro topography of a 3D self-closed layered CNT/resin based composite material after being cured and molded by isostatic pressing at a temperature in an embodiment of the invention; FIG. 3b is a side view of a macro topography of the 3D self-enclosed layered CNT/resin based composite material after being cured and molded by isostatic pressing at a temperature in an embodiment of the invention; FIG. 3c is a longitudinal cutting view, along the thickness direction, of a macro topography after warm isostatic pressing curing molding of the 3D self-sealing layered CNT/resin-based composite material in the embodiment of the invention;

FIG. 4 is a microscopic topography of the 3D self-closed layered CNT paper/resin-based composite material after being cured and molded by isostatic pressing;

the invention is described in detail below with reference to the drawings and the detailed description.

In the figures, the reference numerals denote: 1 outer die, 1-1 female die, 1-1-1 female die wall surface, 1-1-2 exhaust holes, 1-2 male die, 1-2-1 male die chassis and 1-2-2 male die boss; 2 inner mould, 2-1 contact inner mould, 2-2 support inner mould; 3 compensating layers, 3-1 first compensating layers and 3-2 second compensating layers; 4 samples.

Detailed Description

The invention is further described below with reference to the accompanying drawings and examples. It should be understood that the detailed description and specific examples, while indicating the present disclosure, are given by way of illustration and explanation only, not limitation.

In the present disclosure, unless otherwise specified, the use of directional words such as "upper, lower, left, right, front, rear" generally corresponds to the upper, lower, left, right, front, rear of a product, wherein "upper, lower" corresponds to the vertical or height direction; "left and right" correspond to a transverse direction of the horizontal direction, or a length direction; "front and rear" correspond to the horizontal direction perpendicular to the lateral direction, or width direction. Wherein "raising and lowering" refers to the movement of the respective components upward or downward in the vertical direction. The foregoing directional terms are used only to explain and illustrate the present disclosure and are not meant to be limiting.

With reference to fig. 1 a-1 e and fig. 2 a-2 f, the quasi-temperature isostatic pressing mold of the present invention comprises an outer mold 1 and an inner mold 2, wherein the inner mold 1-1 is made of stainless steel (with a thermal expansion coefficient of 9.2-11.8) × 10^-6/° c)) which is a hollow cylinder structure, and the wall surface 1-1-1 of the female die is provided with an exhaust hole 1-1-2. The hollow cylinder structure is closed by a cylinder body and is axially hollow inside. 2 male dies 1-2 and bosses 1-2-2 are respectively inserted into the cavities of the female dies 1-1. A plurality of vent holes 1-1-2 are formed in the wall surface 1-1-1 of the female die, the vent holes 1-1-2 are uniformly and symmetrically distributed on the wall surface 1-1-1 of the female die, and the vent holes 1-1-2 are circular vent holes with the diameter of 3-5 mm. The inner mold 2 is a silica gel soft mold. The silica gel soft mold (namely the inner mold 2) is divided into an upper layer, a middle layer and a lower layer, wherein the upper layer and the lower layer are thicker, and the middle layer is thinner (slightly smaller than or equal to the thickness of the preformed body). The size of the combined silica gel soft mold is equal to the size of the female mold cavity after the stainless steel mold is assembled. If the inner and outer dies are rigid hard dies, the tolerances between the dimensions of the outer die cavity and the inner die must be taken into account during assembly so that the inner die can be loaded into the outer die cavity. However, because the inner silica gel mold is soft, in order to clamp the inner silica gel mold in the outer mold cavity, the surplus of the size of the outer mold cavity is not considered. In fact, after the soft silica gel mold is arranged in the stainless steel mold, due to extrusion of the stainless steel outer mold, a sample cavity in the center of the soft silica gel mold is slightly smaller than the size of the initially reserved sample cavity (the size of the sample cavity is smaller than the bottom of the sample cavity, which is determined according to the size of each block of the inner silica gel mold, and after the mold is assembled, the length, width and height of the sample cavity are respectively smaller than the initially reserved size by 0.5-2.0 mm). To resin matrix combined material's solidification shaping, interior back of the assembly of external mold, soft silica gel centre form chucking can realize sample chamber (first cavity promptly) each face seamless connection in the outer die cavity of rigid stainless steel, has avoided the resin to spill over at the initial stage of hot pressing solidification process like this, and then along with the temperature risees, the expansion of silica gel centre form can make each face extrusion degree increase in sample chamber, seamless connection more between each face, and the resin can not spill over.

But also because the silicone is soft, the preform sample can fit into the sample cavity (into which the sample is clamped), and particularly for uncured resin-based composite samples, the sample itself is soft and compressible, making it easier to fit into the sample cavity. The invention designs the die set which is mainly used for hot-pressing curing molding of resin matrix composite materials, wherein a preforming body sample is in a spiral laminated shapeThe length of the reserved sample cavity is 1-2 mm smaller than the length of the preformed body, and the product of the width and the height of the sample cavity after the die is assembled is 0.25-1 mm smaller than the area of the cross section of the cylindrical sample². When the sample is loaded, the length direction of the sample is slightly bent, two ends of the sample are firstly placed in the sample cavity, then the middle part of the sample is lightly tapped into the sample cavity by the rubber hammer, and the rubber hammer has a densification effect on the sample in the process of lightly tapping the sample, so that the sample can completely enter the sample cavity and is intact. The original size of the sample to be pressed is slightly larger than the size of the sample cavity, so that the sample to be pressed is clamped in the first cavity, namely, the sample is connected with the first cavity in a seamless mode, and the sample can be pressed more compactly. The silica gel soft mold has good air permeability, and the vent holes 1-1-2 are uniformly and symmetrically distributed on the wall surface 1-1-1 of the female mold of the outer mold 1, so that the smooth air exhaust of a sample in the molding process can be realized, and the defects of sample lamination crack, over-high porosity and the like are avoided.

The silica gel soft mold is divided into 3 layers, and the upper layer and the lower layer are vertically and symmetrically distributed by taking the middle layer as a boundary. Integrally pouring the silica gel soft mold of each layer, demolding after curing, cutting the upper layer and the lower layer into 5 blocks (as shown in figure 2b), wherein one piece of silica gel at the center of the upper layer and the lower layer is directly opposite to the upper surface and the lower surface of the sample block to be pressed and formed, namely, is contacted with the inner module (as shown in figure 2 c); the 4 pieces of silicone around it are each pressed against the silicone in the middle layer, i.e. supporting the inner module (if 2d shows). The middle layer was cut into 9 pieces and the center most silicone rubber was removed to form a first cavity for placement of a sample piece to be compression molded (as shown in fig. 2 a). The graphite is coated on the two opposite surfaces of each silica gel, so that the frictional resistance between the silica gels is reduced, and the silica gels can slide relatively to each other to better press a sample; moreover, silica gel has poor thermal conductivity, and graphite can also increase the thermal conductivity of silica gel appropriately, shortening the time for silica gel to reach the target temperature.

Because the sample is in the center of the silica gel soft mold, the upper and lower, left and right, front and back of the sample are all surrounded by the silica gel soft mold in all directions, the silica gel expands after being heated to extrude the sample from all directions, and the silica gel in two opposite directions has the same size or is very close to each other, under the limitation of the stainless steel outer mold, the silica gel in the opposite directions expands in the opposite directions in the same degree after being heated, therefore, the extrusion forces of the front and back directions, the left and right directions, the up and down directions of the sample on the sample act on a straight line respectively, and the extrusion forces are equal in size and opposite in direction, thus the sample can be ensured to become dense and not deform gradually in the extrusion process. Moreover, the silica gel is soft, and does not damage the sample while squeezing the sample. Moreover, because the supporting silica gel (i.e. the supporting inner module 2-2) around the contact silica gel (i.e. the contacting inner module 2-1) is also expanded, and the supporting silica gel around the contact silica gel is also symmetrically distributed, that is, 6 supporting silica gel blocks around the sample are contacted, after being heated, two supporting silica gels are arranged around each block, the two supporting silica gels have the same size and opposite directions and act on the extrusion force on a straight line, so that the supporting silica gel has larger expansion towards the sample direction, and the two opposite surfaces of the adjacent silica gels are coated with graphite powder and can slide relatively, thereby forming larger extrusion force on the sample. As the silica gels are expanded and mutually extruded, the silica gels form seamless connection around the sample, and the resin can be completely prevented from being extruded from the sample to cause loss in the curing process of the resin-based composite material. And after the mold is cooled, the silica gel shrinks to the initial size, the size of the sample is reduced, and the silica gel contains lubricants such as paraffin, silicone oil and the like, so that the silica gel is not adhered to the sample and can be easily demoulded. Particularly for resin-based composite materials, the fluidity of resin is increased when the resin is heated before curing, the resin is easy to lose when being heated and pressed, other components in a sample can be brought out when the resin is lost, and the resin flowing out is easy to stick to a mold, so that the demolding is difficult. Because the silica gel internal mold extrudes the preformed body sample from all directions in an all-round way and forms seamless connection around the preformed body sample, resin loss can be completely avoided and a compact formed body can be obtained.

The silica gel has good air permeability, and if the sample is exhausted due to physicochemical change in the molding process, the gas can be exhausted through the silica gel layer. Silica gel is the heat conduction medium between stainless steel mould and the sample, because silica gel heat conduction is slow, so the temperature of sample also rises step by step, has slowed down the physical chemistry reaction process, therefore has also slowed down the exhaust process. Moreover, the extrusion and protection of the silica gel also slow down the gas discharge process. Slowing the venting process may reduce the generation of stress and thus reduce damage to the sample. Particularly for the curing and forming process of a resin-based composite material sample, the silica gel can reduce the discharge of small molecular gas by pressing the sample, which is beneficial to the conversion of a chain structure of the resin to a net structure, and more carbon atoms enter the net structure instead of being changed into the small molecular gas to be discharged, thereby reducing the curing weight loss rate. Moreover, as long as the thermal conductivity of the sample is higher than that of silica gel, a uniform distribution of temperature is formed in the sample, no temperature gradient is generated, which is very advantageous for uniform densification of the sample.

Before quasi-temperature isostatic pressing, the whole die with the sample is placed in a hot press for prepressing at the temperature of 70-90 ℃, the applied pressure is 3-5 MPa, an upper pressure head of the hot press moves downwards to press a male die base plate 1-2-1 at the upper part of an outer die, the upper male die base plate 1-2-1 of the outer die is made to cling to the wall surface 1-1-1 of a female die, and the heat preservation and pressure maintaining time is 0.5-1.5 hours. And the silica gel expands a little at 70-90 ℃, prepressing the sample, releasing gas in pores of the sample, and curing the resin-based composite material a little so as to properly reduce the fluidity of the resin. And then taking down the whole die, rapidly heating the hot press to 180-220 ℃, wherein the time does not exceed 30min and the temperature of the quasi-temperature isostatic pressing die is not lower than 55 ℃, putting the whole die on the hot press again, applying the pressure of 20-30 MPa, and moving an upper pressure head of the hot press downwards to press an upper male die base plate 1-2-1 of the outer die 1, so that the upper male die base plate 1-2-1 of the outer die 1 is tightly attached to the wall surface 1-1-1 of the female die, and keeping the temperature and the pressure for 3-4 h. Under high temperature, the expansion of the silica gel is gradually increased, and under the limitation of the outer die 1, the extrusion force of the silica gel inner die 2 to the sample is increasingly larger, and the sample is gradually compacted under the extrusion action in all directions around.

Calculation of die dimensions

Accurate calculation of the size of the die is of great importance to the implementation effect of the quasi-temperature isostatic pressing.

The sample is subjected to warm isostatic pressing to reach a fully compact theoretical volume, namely the true volume.

The preform includes a phase that is to undergo a physicochemical change without weight loss during warm isostatic pressing and a phase that is to undergo no physicochemical change without weight loss.

The true volume of the molded article (1) is the sum of the true volume of the preform (mass of each phase to be reduced in weight in the preform X theoretical weight loss ratio for the phase/theoretical density before weight loss for the phase)

The sum of the true volume of the preform (mass of each phase without weight loss in the preform/theoretical density for that phase) + (mass of each phase with weight loss in the preform/theoretical density before weight loss for that phase) (2)

Theoretical density of the molded article ═ mass of each phase without weight loss in the preform + mass of each phase to be weight loss in the preform × (100% to theoretical weight loss ratio for each phase) ]/true volume of the molded article (3)

And according to the initial three-dimensional size of the preformed sample and the calculated true volume of the formed body, assuming the size of the formed body in two-dimensional directions, the size of the other dimension can be calculated. For example, assuming a width and a height (which may be assumed to be equal), then

Length of molded article (true volume of molded article/(width of molded article × height of molded article) (4)

Thickness of contact silica gel above or below the sample (preform thickness-thickness of molded body)/linear expansion rate of silica gel/temperature of isothermal isostatic pressing/2 (5)

If the first compensation layer is provided, then

Thickness of contact silica gel under sample ═ (preform thickness-molded body thickness)/linear expansion rate of silica gel/quasi-temperature isostatic pressing temperature/2 + initial thickness of first compensation layer (6)

Width of contact silica gel before or after sample (preform width-molded body width)/linear expansion rate of silica gel/isothermal isostatic pressing temperature/2 (7)

Length of contact silica gel on left or right of sample (preform length-molding length)/linear expansion rate of silica gel/quasi-warm isostatic pressing temperature/2 (8)

After the stainless steel outer mold is assembled, the height of the space in the cavity of the female mold is equal to the thickness of the silica gel contacting the upper part or the lower part of the sample multiplied by 2+ the thickness of the preformed body (9)

After the stainless steel outer mold is assembled, the space width in the cavity of the female mold is equal to the width of silica gel contacted with the front or the back of the sample multiplied by 2+ the width of the preformed body (10)

After the stainless steel outer mold is assembled, the length of the space in the cavity of the female mold is equal to the length of the silica gel contacted on the left or right of the sample multiplied by 2+ the length of the preformed body (11)

In all the calculation formulas, the orientation is specified: in front of the sample, the front-back direction is the width, the left-right direction is the length, and the up-down direction is the thickness (or height).

Referring to fig. 2a, the length of the contact silica gel in front of or behind the sample is equal to the length of the preformed body plus (2-4) mm, the preformed body sample is placed in the center, and the left end and the right end of the front silica gel or the rear silica gel are 1-2 mm longer than the preformed body; the thickness of the silica gel contact device is equal to the thickness of the preformed body plus (1-2) mm, the width of the silica gel contact device on the left or right of the sample is equal to the width of the preformed body, the thickness of the silica gel contact device is equal to the thickness of the preformed body plus (1-2) mm, and the silica gel contact device on the left/right of the sample enters the space surrounded by the silica gel contact device on the front/back of the sample by 1-2 mm. The length of the contact silica gel above or below the sample is equal to the length of the preformed body (figure 2b), the width of the contact silica gel is equal to the width of the preformed body (figure 2d), and the contact silica gel below enters a space enclosed by the contact silica gel at the front/rear part and the contact silica gel at the left/right part by 1-2 mm; the contact silica gel on the upper/lower part of the sample, the contact silica gel on the left/right part and the contact silica gel on the front/rear part jointly enclose a first cavity as a sample chamber.

The upper contact silica gel in the height direction of the first cavity is not embedded into a space surrounded by the four contact silica gels in the middle layer, but is flush with the surrounding support silica gel. This is for the convenience of assembling the silica gel inner mold 2. The upper layer silica gel and the lower layer silica gel with large thickness are integrally assembled into a rigid outer die cavity, and the middle layer with thin thickness can be assembled piece by piece. When the die is assembled, the lower layer silica gel (composed of five pieces of silica gel) is integrally assembled into the female die cavity of the rigid outer die 1, the five pieces of silica gel on the surface of the lower layer silica gel, which is close to the boss 1-2-2 of the lower male die, are flush, and the central contact silica gel on the surface close to the middle layer protrudes 1-2 mm more than the surrounding support silica gel. Then sequentially assembling the thin silica gel (eight blocks) of the middle layer into the female die cavity block by block, and enabling the two contact silica gels in the length direction of the middle layer to be embedded into a space surrounded by the two contact silica gels in the width direction for 1-2 mm; and the contact silica gel in the center of the lower layer silica gel is embedded into a space surrounded by the four pieces of contact silica gel in the middle layer by 1-2 mm. The assembly of the lower layer silica gel and the middle layer silica gel can be observed while the assembly is carried out, but when the upper layer silica gel is integrally assembled, only one surface close to the boss 1-2-2 of the upper male die can be observed while the upper layer is assembled, and the other surface cannot be observed, so that the central contact silica gel cannot be ensured to be embedded into a space surrounded by four contact silica gels in the middle layer. Therefore, the five pieces of silica gel on the upper layer are arranged above the middle layer in a flush manner.

Because the surplus of the size of the outer mold cavity is not considered, for thick upper layer silica gel and thick lower layer silica gel, if the thick upper layer silica gel and the thick lower layer silica gel are sequentially assembled into the rigid outer mold cavity one by one, when only the last silica gel is left to be unassembled, the volume of a cavity formed by combining the four silica gels assembled previously is smaller than that of the last silica gel, the silica gel is soft but incompressible, the friction resistance of the last silica gel during assembly is very large due to extrusion of the surrounding silica gel, and the last thick silica gel is difficult to insert into a space smaller than the volume of the last silica gel. However, if five pieces of silica gel are integrally assembled into the rigid outer mold cavity, the combined bottom area of the 5 pieces of silica gel is just equal to the bottom area of the female mold cavity of the rigid outer mold 1, and the silica gel assembly can smoothly enter the female mold cavity by lightly tapping with a hammer. The thin middle layer silica gel has small thickness and short sliding distance during assembly, so that the thin middle layer silica gel can overcome the frictional resistance with the surrounding silica gel and be assembled in sequence block by block.

The contact silicone rubber above and below the preform, the contact silicone rubber in front and behind, and the contact silicone rubber in left and right divide the space in the cavity of the assembled outer mold 1 into different spaces. These spaces are filled with supporting silicone gel, respectively, which matches the size of these spaces. After the external die 1 of the die is assembled, the compensation layers 3 can be arranged in the length direction, the width direction and the height direction of the female die cavity, and the compensation layers are not required to be arranged. In the embodiment of the invention, the size of the female die cavity in the thickness direction and the length direction is larger than that in the width direction, and in order to compensate the contradiction between the expansion of the edge supporting silica gel and the contraction of the central sample in the two directions in the heating forming process, the compensation layers 3 are arranged in the two directions, while the size of the female die cavity in the width direction is smaller, the expansion of the supporting silica gel filled in the direction is limited, and the compensation layers are not required to be arranged. If the compensation layer is not arranged, the stress generated by the expansion of the supporting silica gel is completely borne by the outer die, one part of the stress generated by the expansion of the contacting silica gel is used for extruding the preformed body to enable the preformed body to contract and densify, and the other part of the stress generated by the expansion of the contacting silica gel is borne by the outer die, so that different parts of the outer die are stressed to different degrees, and the outer die can deform after being used for a long time. The first compensation layer 3-1 in the thickness direction is formed by four compressible and flexible porous nets (for example, a single-layer stainless steel net is folded into multiple layers) with equal thickness, that is, the first compensation layers with equal areas are respectively laid on the upper surfaces of the rest four supporting silica gels (fig. 2c and 2d) on the lower layer except the contact silica gel right below the preform sample 4. Meanwhile, a second compensation layer 3-2 is also arranged in the length direction and is formed by four compressible flexible porous nets with equal thickness (for example, a single-layer stainless steel wire net is folded into multiple layers). In the middle layer where the preform sample 4 is located, four second compensation layers are respectively placed between the four supporting silica gels at the edge and the two contact silica gels in the middle in a side-standing manner (fig. 2 a). The second compensation layer 3-2 in the length direction is turned with respect to the orientation of the entire mold because it is placed on its side, that is, the thickness direction of the second compensation layer 3-2 is the length direction of the entire mold.

Because the total size of the silica gel inner mold in the free state is the same as the size of the inner space of the cavity of the female mold after the outer mold 1 is assembled, the size of the first cavity reserved in the center of the middle layer after the soft silica gel inner mold is assembled is 0.5-2 mm smaller than the preset size in the three-dimensional (3D) direction, and therefore the preformed body sample 4 placed in the center of the silica gel inner mold is in an initial extrusion state after the whole mold is assembled.

Examples

The assembly and use of the mold will be described by taking the example of the quasi-warm isostatic pressing of a 3D self-closing layered CNT paper/resin-based composite material (see patent 201910114419.2 for the preparation technique of a preform sample of the composite material).

(1) Assembling die

With reference to fig. 1a to 1e and fig. 2a to 2f, the mold is assembled. The lower layer of the inner mold 2 is fitted into the female mold cavity from the lower surface of the female mold 1-1 of the outer mold 1. The lower layer silica gel is laid with the first compensation layer 3-1 (as shown in fig. 2c and 2d) with the same area as the central silica gel on the upper surfaces of the other 4 pieces of silica gel except the central silica gel. And then the middle layer of the inner mold 2 is filled, the middle layer is divided into 9 silica gel blocks, one silica gel block in the center is taken out, 4 contact silica gel blocks in the other 8 silica gel blocks surround a first cavity, and the other 4 support silica gel blocks are respectively filled in gaps between the contact silica gel blocks and the wall surface 1-1-1 of the outer mold. The left/right contact silica gel of the middle layer is embedded into the space surrounded by the front/back contact silica gel with the depth of 1mm (as shown in fig. 2a), and the central contact silica gel of the lower layer enters the space surrounded by the 4 contact silica gels of the middle layer with the depth of 1mm (as shown in fig. 2 c). A second compensation layer 3-2 is inserted between the 4 pieces of supporting silica gel and the 2 pieces of contact silica gel in the middle layer (as shown in fig. 2 a). Sample 4 was then packed into the central first cavity of the middle layer. Then, the upper layer silicone rubber of the inner mold 2 is loaded into the female mold cavity from the upper surface of the female mold 1-1 of the outer mold 1. Graphite powder is coated on the two opposite surfaces of any two adjacent silica gels. Finally, the two male die bosses 1-2-2 of the outer die 1 are inserted into the female die cavity.

(2) Pre-hot pressing

And (3) after the temperature of the hot press is raised to 70 ℃, putting the whole assembled die on the hot press, and applying pressure of 3MPa by an upper pressure head of the hot press to contact an upper male die base plate 1-2-1 of the outer die 1. And (5) after heat preservation and pressure maintaining are carried out for 1.5h, lifting the upper pressure head of the hot press, and taking down the whole die. The preheating and prepressing process can ensure that the resin in the resin-based composite material preformed body has small curing degree, so that the fluidity is reduced moderately.

(3) Quasi-temperature isostatic pressing solidification forming

And the temperature of the hot press is continuously increased to 200 ℃, the whole die is placed on the hot press, the upper pressure head of the hot press is contacted with the upper male die base plate 1-2-1 of the outer die 1, and the applied pressure is 20 MPa. And (4) after heat preservation and pressure maintaining are carried out for 4 hours, the upper pressure head of the hot press is lifted, and the whole die is taken down.

(4) Demoulding

And taking the upper and lower male dies 1-2 of the outer die 1 down. Because the whole silica gel inner die 2 has larger thickness, the silica gel inner die is difficult to extrude from one end, and a sample is easily damaged by adopting a knocking mode, so the silica gel inner die 2 is removed layer by layer. When 2 drawing of patterns of silica gel centre form, with the lower surface of mould up, stab a fritter silica gel of rotten centre form 2 with knife or scissors, then other silica gels of lower floor can hand take out, and the silica gel in intermediate level is thinner relatively, can take out with the flat screwdriver in front end and tweezers piece by piece, takes out the sample. The last layer of silica gel was then knocked off.

Referring to fig. 3a and 3b, the appearance of the sample prepared in this embodiment is similar to that of the sample prepared in this embodiment, because the resin is softened during the warm isostatic pressing process due to the hot-pressing curing molding of the resin-based composite material, and the expanded graphite (with a particle size of 100-300 μm) coated on the surface of the silica gel inner mold is adhered to the surface of the sample, the surface of the sample is not smooth. From the overall macro-morphology picture of the sample, no resin flows out during the warm isostatic pressing process. Referring to fig. 3c, the sample is longitudinally cut along the thickness direction, and the section morphology (the self-sealing ring-shaped layered structure is very compact, and the expanded graphite is only adhered to the surface of the sample and does not enter the sample, so only the expanded graphite on the surface needs to be polished off, referring to fig. 4, it is shown that the self-sealing ring-shaped layered structure of the sample prepared in this embodiment is very compact, the CNT paper/resin self-sealing layered composite material sample of this embodiment is aligned before and after being subjected to quasi-temperature isostatic pressing curing molding, as shown in table 1:

TABLE 1

Sample (I)	Height/cm	Width/cm	Diameter/cm	Cross sectional area/cm2	Length/cm	Mass/g	Density/(g cm-3)
								Preform body			2	3.14	9	37.44	1.32
Shaped body	1.55	1.6		2.56	8.4	33.75	1.62

From the above, it can be seen that after the CNT paper/resin composite material is subjected to the quasi-temperature isostatic pressing, the molded blank has a flat surface, a regular shape, no resin, no bulge and no defect on the surface, the molded blank has shrinkage in the length direction, the width direction and the thickness direction, the shrinkage is close to the theoretically calculated linear expansion dimension of the contact silica gel in different directions of the blank, the air opening rate is lower than 1% by an archimedes method, and the density is not lower than 98%.

The bulk density and open porosity of the sample were measured by archimedes' drainage method using an electronic analytical balance (model AG 204) with a mass weighing device of 0.0001g, and the bulk density and open porosity of the warm isostatic-pressing cured molded body were calculated according to equations (12) and (13), respectively, and the density thereof was calculated according to equation (14).

The bulk density of the molded article (mass of the dried molded article sample in air/(mass of the saturated molded article sample immersed in water) × the density of water (12)

Open pore ratio of the molded article (mass of the molded article-saturated sample in water-mass of the molded article-dried sample in air)/(mass of the molded article-saturated sample in water-mass of the molded article-saturated sample in air) × 100% (13)

Density of warm isostatic pressing solidified formed body as measured density of warm isostatic pressing solidified formed body/theoretical density of warm isostatic pressing solidified formed body x 100% (14)

The thickness direction compensation layer is formed by arranging 4 compressible flexible porous nets with equal thickness in parallel (in the embodiment, a single layer of stainless steel net is folded into a plurality of layers). And (3) respectively paving compensation layers with the same areas as the upper surfaces of the rest 4 pieces of supporting silica gel on the lower layer except the silica gel contacted under the sample 4.

The initial thickness of the thickness direction compensation layer is equal to the compression distance of the thickness direction compensation layer + the thickness of the thickness direction compensation layer after compression (15)

The compression distance of the thickness direction compensation layer is equal to the thickness of the preform-thickness of the molded body (16)

Taking the stainless steel wire multilayer net as an example of the compensation layer,

the thickness of the compressed compensation layer in the thickness direction is equal to the thickness of a single stainless steel wire net multiplied by the number of layers (17)

The compensation layer in the length direction is composed of 4 compressible flexible porous nets (in the embodiment, a single-layer stainless steel net is folded into multiple layers) with the same length, the same width and the same thickness, and the porous nets are respectively placed between the four supporting silica gels in the middle layer and the two contact silica gels in the middle layer in a side standing mode.

The area of the length-direction compensation layer is equal to the width of the middle layer single piece supporting silica gel and the thickness of the middle layer single piece supporting silica gel (18)

The initial thickness of the longitudinal compensation layer (19) is the compressed distance of the longitudinal compensation layer + the compressed thickness of the longitudinal compensation layer

Length direction compensation layer compression distance (preform length-form length)/2 (20)

In conclusion, the invention realizes the uniform and compact molding of the blank body by reasonably setting the component structure, is suitable for both the gas product discharge and the non-gas product discharge in the molding process, has wide application range, ensures the uniform temperature in the sample in the whole warm isostatic pressing process, and gradually increases the extrusion force to the maximum value under the controllable condition, thereby not only avoiding the stress damage caused by the gas discharge, but also ensuring the high working efficiency, promoting the development of novel composite materials, having simple equipment and low cost, and breaking through the defects that the traditional isostatic pressing method and the mould can not realize the gas permeability and the equipment is expensive. The invention is suitable for a low-temperature (100-250 ℃) non-sealing forming die, is particularly suitable for a forming process with gas discharged under a heating condition, and is particularly favorable for a compact curing forming process of a resin matrix composite material. The composite blank is densified uniformly under the action of temperature and quasi-isostatic pressure to obtain regular shape.

Claims (9)

1. A quasi-temperature isostatic pressing forming die is characterized by comprising a rigid outer die (1) and an inner die (2) made of silica gel, wherein the outer die comprises a female die (1-1) and male dies (1-2) arranged at two ends of the female die, the female die (1-1) is of a hollow cylinder structure, vent holes (1-1-2) are uniformly and symmetrically formed in the wall surface (1-1-1) of the female die (1-1), and the inner die (2) is filled in a cavity enclosed by the female die (1-1) and the male dies (1-2); the inner die (2) is divided into an upper layer, a middle layer and a lower layer, a first cavity for placing a sample is arranged in the center of the middle layer of the inner die (2), the first cavity is cuboid in shape, the inner die (2) comprises a plurality of inner modules, a lubricating layer is arranged on the surface of each inner module, each inner module comprises a contact inner module (2-1) and a support inner module (2-2), the orthographic projection range from each surface of the first cavity to the inner wall surface of the outer die (1) is respectively provided with the contact inner modules (2-1) for contacting with the surface of the sample, the contact inner modules (2-1) corresponding to two opposite surfaces in the first cavity are same in size, and the support inner modules (2-2) are filled in the region of the inner cavity of the outer die (1) except the contact inner modules (2-1);

each surface of the first cavity is respectively a first plane, a second plane, a third plane, a fourth plane, a fifth plane and a sixth plane, wherein the first plane and the second plane are a group of opposite surfaces in the height direction, the third plane and the fourth plane are a group of opposite surfaces in the length direction, the fifth plane and the sixth plane are a group of opposite surfaces in the width direction, and the heights of the first plane and the second plane which are in contact with the inner module = (the height of the preformed body is ‒)/the linear expansion rate of the silica gel/the quasi-temperature isostatic pressing temperature/2; the length of the contact inner module corresponding to the third plane and the fourth plane = (preform length ‒ molded body length)/linear expansion rate of the silicone gel/quasi-temperature isostatic pressing temperature/2; width of the contact inner mold block corresponding to the fifth plane and the sixth plane = (preform width ‒ molded body width)/linear expansion rate of silicone gel/quasi-warm isostatic pressing temperature/2.

2. The isothermal isostatic pressing mold according to claim 1, wherein the male mold (1-2) comprises a male mold base plate (1-2-1) and a male mold boss (1-2-2) arranged on the male mold base plate (1-2-1), the male mold base plate (1-2-1) and the male mold boss (1-2-2) are cuboids, the male mold boss (1-2-2) can extend into the female mold (1-1) and is in clearance fit with the female mold (1-1), the clearance is 0.5-1 mm, and the dimensions of the male mold base plate (1-2-1) in the length direction and the width direction are respectively the same as the dimensions of the outer wall of the female mold (1-1) in the length direction and the width direction.

3. A quasi-warm isostatic pressing mould as claimed in claim 2, wherein, after the outer mould (1) is assembled:

the height of the space in the female die cavity = the thickness of the contact silica gel above or below the sample in a free state x 2+ thickness of the preform;

the space width in the female die cavity is = the width of the sample in the free state of the silica gel in front of or behind the sample x 2+ the width of the preform;

the length of the space in the female mold cavity = the length of the silicone gel in the free state in contact to the left or right of the sample x 2+ preform length.

4. The isothermal isostatic pressing mold according to claim 1, wherein in the contact inner modules (2-1) corresponding to the first cavity, the contact inner modules (2-1) in the length direction of the first cavity are embedded into the space between the contact inner modules in the width direction of the first cavity, and the embedding distance is 1-2 mm; the lower contact inner module (2-1) in the height direction of the first cavity is embedded into a space between the contact inner modules in the width direction and the length direction of the first cavity, and the embedding distance is 1-2 mm;

in the inner modules at the lower side of the first cavity, the upper surfaces of all the supporting inner modules (2-2) are respectively provided with a first compensation layer (3-1) with the same area as the upper surfaces of the supporting inner modules, and the first compensation layers (3-1) are made of compressible materials; the initial thickness of the first compensation layer = the compressed distance of the first compensation layer + the compressed thickness of the first compensation layer, the compressed distance of the first compensation layer = the preform thickness ‒ shape thickness;

in the middle layer inner module where the first cavity is located, second compensation layers (3-2) are filled between all supporting inner modules (2-2) and contact inner modules (2-1) on the front side and the rear side of the first cavity, and the second compensation layers (3-2) are made of compressible materials; the initial thickness of the second compensation layer = the compressed distance of the second compensation layer + the compressed thickness of the second compensation layer, and the compressed distance of the second compensation layer = (preform length ‒ molded body length)/2.

5. The quasi-warm isostatic pressing mold according to claim 1, wherein the vent holes (1-1-2) are circular vent holes with a diameter of 3-5 mm.

6. The quasi-warm isostatic pressing mold according to claim 1, wherein said lubricating layer is a graphite powder layer.

7. A quasi-warm isostatic pressing mould as claimed in claim 1, wherein said female mould (1-1) and said male mould (1-2) are made of steel.

8. A method of forming a cold isostatic press, using the cold isostatic press according to any one of claims 1 to 7, comprising the steps of:

before the quasi-temperature isostatic pressing forming, placing the quasi-temperature isostatic pressing forming die provided with the sample in a hot press for prepressing to expand the inner die made of silica gel and apply prepressing to the sample, and releasing gas in sample pores;

and taking the quasi-temperature isostatic pressing mould down, heating the hot press to the quasi-temperature isostatic pressing temperature, putting the quasi-temperature isostatic pressing mould on the hot press again, applying preset pressure, and preserving heat and pressure for preset time to obtain a final sample.

9. The method of claim 8, wherein the hot isostatic pressing is performed at a temperature below the melting point of the molten metal,

during prepressing, the prepressing temperature is 70-90 ℃, the applied pressure is 3-5 MPa, and the heat preservation and pressure maintaining time is 0.5-1.5 h;

the quasi-temperature isostatic pressing temperature is 180-220 ℃, the pressure is 20-30 MPa, and the heat preservation and pressure maintaining time is 3-4 h;

taking down the quasi-temperature isostatic pressing mould, quickly heating the hot press to the quasi-temperature isostatic pressing temperature, and putting the quasi-temperature isostatic pressing mould on the hot press again, wherein the time is not more than 30min, and the temperature of the quasi-temperature isostatic pressing mould is not less than 55 ℃.

Images