CN110961624A

CN110961624A - Filling degreasing and compaction sintering method for three-dimensional printed powder bonding blank

Info

Publication number: CN110961624A
Application number: CN201910305479.2A
Authority: CN
Inventors: 吴小平; 罗天珍
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-04-26
Filing date: 2019-04-16
Publication date: 2020-04-07

Abstract

A filling degreasing and compacting sintering method for a three-dimensional printed powder bonding blank belongs to the technical field of machinery and heat treatment, and can be used independently; filling and degreasing to perform shape preservation and degreasing on the object; the compaction and sintering process needs pre-stretching treatment of linear stretching and amplifying in the axial direction on a blank (workpiece) in advance: the transverse displacement is a unique displacement solution in the direction perpendicular to the axis due to the volume compression ratio difference of the blank and the sand body, and the predictability allows pre-displacement treatment; that is, when the blank is manufactured, in addition to the pre-stretching treatment in the axial direction, the pre-displacement treatment is performed along the transverse direction, the blank subjected to the pre-stretching and pre-displacement treatment already deviates from the shape of the target object, when the compression displacement of the piston along the axial direction is equal to the pre-stretching displacement, the pre-displacement is also restored reversely, and the size of the blank is compressed and restored to the required size.

Description

Filling degreasing and compaction sintering method for three-dimensional printed powder bonding blank

[ technical field ]

The invention belongs to the technical field of machining and heat treatment, and particularly relates to a method for obtaining a compact object by filling, degreasing, compacting and sintering a prefabricated part (blank) bonded by low-density 3D metal or ceramic powder.

[ background art ]

The current three-dimensional printing technology can perform 3D molding on metal powder or wire-shaped materials mixed by metal and resin. There are 3D forming techniques: SLS laser powder sintering technology, post-sintering FDM technology and post-sintering powder filling molding technology.

SLS laser sintering technical introduction:

the Selective Laser Sintering (SLS) technique uses a laser as an energy source to uniformly sinter powder on a processing plane by a laser beam. A layer of very thin (submillimeter-level) powder is uniformly spread on a workbench to serve as a raw material, and a laser beam is scanned by a scanner at a certain speed and energy density according to two-dimensional data of a layered surface under the control of a computer. After the laser beam is scanned, the powder at the corresponding position is sintered into a solid sheet layer with a certain thickness, and the non-scanned position still keeps loose powder. This layer is scanned and the next layer is scanned. Repeating the steps until all layers are scanned. Removing the redundant powder, and carrying out appropriate post-treatment such as grinding, drying and the like to obtain the part. SLS processable raw materials include plastic powders (nylon, polystyrene, polycarbonate, etc., direct laser sintering), metal powders (direct, indirect and two-component processes), ceramic powders (requiring the use of binders including inorganic, organic and metallic binders). SLS has been successfully applied in many industries, such as automotive, shipbuilding, aerospace, and aviation. In addition to the company DTM, the company EOS in germany also developed a corresponding series of molding apparatuses. In China, such as the university of science and technology in Huazhong, the university of Nanjing aerospace, the university of northwest industry, the North China institute of Industrial science, and Beijing Longyuan automatic molding Co., Ltd, and the like, a lot of important achievements are also obtained, such as RAP-I type laser sintering rapid molding system developed by the university of Nanjing aerospace, AFS-300 laser rapid molding equipment developed by the Beijing Longyuan automatic molding Co., Ltd, and the like. SLS has been successfully applied to various industries such as automobile, shipbuilding, aerospace, aviation, and the like, and mainly relates to links such as rapid prototyping, rapid mold and tool manufacturing, small-batch production, and the like.

Introduction of post-sintered FDM technique:

the method is characterized in that the Chinese Zhuhai Tianwei company combines an FDM post-sintering technology, firstly pushes an FDM-3D metal economical printer, extrudes metal composite material wires from a low-temperature (200-plus-300 ℃) spray head by heating, and prints, piles and forms layer by layer. Removing the binder through a medium-temperature (400 ℃) degreasing process, and finally sintering and molding the iron-based metal in a high-temperature 1200 ℃ environment. The metal material is diversified, such as titanium alloy, alumina and zirconia.

The CoLiDo AMSS 3D metal printing technology was just honored by the union of the Innovation technologies and technologies of hong Kong and the manufacturing industry to issue the silver prize of the seventh Innovation technology achievement competition of hong Kong, and Tianwei will continuously strive to realize continuous innovation and make contribution to the industry through product innovation.

Introduction to post-sinter powder filling technology:

a pioneer company Iro3D in the united states announced the introduction of a desktop grade metal 3D printer that sells only $ 5000 (about 3.2 ten thousand renminbi). The minimum layer thickness measured 0.3mm, the diameter of the jet was 1mm, and the volume required for printing at 1000CC was about 24 hours.

The sand and the metal powder are required to be paved in a metal container or a crucible layer by layer, the metal powder spray head sprays iron powder, the sand spray head sprays supporting materials to fix the shape of the iron powder, finally, a 3-dimensional object made of the iron powder taking the sand as a support is formed in the metal container or the crucible container, and after the sand powder is removed through firing, the firm steel object is manufactured.

The above three 3D forming techniques have drawbacks:

SLS laser sintering technology defect: a more serious drawback than being more costly is that high metal densification during laser sintering cannot be achieved.

And the defect of the post-sintering FDM technology: although the cost is only 5% of that of SLS technology, the method is not free from the defect of obtaining high metal compactness in subsequent sintering.

Introduction to post-sinter powder filling technology: although the cost is close to that of the FDM technology, the precision is far lower than , and the compactness of post sintering cannot be obtained.

The above 3 powder metallurgy methods can not obtain higher density, so that the strength of the metal member is not high. The density of the iron-based object is only 4-5 kg/cubic decimeter, and the compactness of more than 6.5 is far not achieved.

[ summary of the invention ]

The purpose of the invention is as follows:

the method aims to overcome the defects of soft texture and low density of the three-dimensional printing bonding metal powder blank, and seeks a technical means before sintering to compact the printed metal blank, obtain higher compactness and increase the strength of a workpiece; more important, the deformation of the blank before compaction during degreasing is overcome, and the degreased geometric shape is kept.

The invention has the characteristics that:

the process has strong operability and simple structure, and sand can be recycled.

The method comprises the following steps:

the filling degreasing and compacting sintering method is two independent processes which are respectively detailed as follows:

the filling degreasing method comprises the following steps:

the necessary condition for realizing the process is to rely on a forming cylinder body, and the structure of the forming cylinder body comprises: the container having an upper opening may be provided with a lid for closing the opening or may be left open.

The 3D molded object to be degreased is placed into the molding cylinder together with the sand to ensure that the sand fills the internal cavity of the molded object.

Then, the molding cylinder filled with sand and 3D molding object is placed in high temperature environment, generally 200 ℃ and 700 ℃, to degrease, resin (containing plastic, etc.) as adhesive is gasified and emitted at high temperature, and the object loses the components, and then space is left.

In order to make the sand better support the 3D shaped article, the upper opening of the shaped cylinder container can be initially pressure compacted, requiring a low pressure of tens of atmospheres.

The method can be used independently, and can also be used as a previous process of a compaction sintering method.

The compacting and sintering method comprises the following steps:

the necessary condition for realizing the process is to rely on a compression chamber or a forming cylinder, the structure of which comprises: the columnar cylinder body, the bottom plate and the piston form a closed space, the columnar cylinder body and the bottom plate are in rigid connection or detachable (the piston is convenient to push materials out), when the piston moves along the axis direction of the cylinder, the inner volume of the columnar cylinder body is changed, and inner materials are compressed.

During compression, the blank and the sand powder are put into a compression chamber (a bottom plate is added or a piston is used for replacing the bottom plate) from an upper hole of the compression chamber with the lower end sealed, the sand powder is completely filled in the gap of the blank through the natural action of gravity, or the compression chamber is vibrated or accompanied with vacuum extraction means (swinging, overturning and the like in a vacuum vessel), then the piston is covered, and the blank and the sand powder are compressed under a press machine.

The compaction sintering process needs to amplify the actual size of a workpiece (to manufacture a larger blank) in advance before manufacturing the blank, namely, pre-stretching amplification treatment and transverse pre-displacement treatment which are used for carrying out linear stretching amplification in the axial direction (a target workpiece: a finally finished workpiece) in advance; the pre-stretching amplification treatment is to perform linear one-dimensional amplification treatment on the size of the generated blank along the axial direction (the direction of piston movement), and a blank larger than the target workpiece is produced, and the transverse pre-displacement is produced by the volume compression ratio difference of the blank and the sand body, which causes the transverse displacement and deformation of the shape of the blank on the transverse slice in the compression chamber, because of the rigid boundary condition of the cylindrical cylinder body and the constraint condition of consistency of volume compression ratio of the raw materials, the transverse displacement is determined to be a unique mathematical solution, and the predictability allows for pre-displacement treatment (due to the difference of volume shrinkage rates of 2 materials, geometric displacement in the blank compression process is caused, the magnitude of the pre-displacement is far smaller than that of pre-stretching, when the volume compression ratio of the blank and the sand body is completely consistent, the pre-displacement is 0, and the pre-stretching is completely linear); the blank subjected to the pre-stretching and pre-displacement treatment deviates from the shape of a target object (the directions of the pre-stretching and the pre-displacement are opposite to the displacement direction of the actual compression, the magnitudes are equal, and the displacement is finally completely offset), but is larger; the process comprises the following operation steps: the blank and sand powder are filled in a compression chamber, the blank is put into the compression chamber from an upper hole of the compression chamber with the lower end sealed, the pre-stretching direction of the blank is parallel to the axial direction, the periphery of the blank is not in contact with the inner wall of the compression chamber, the sand powder is continuously filled in the compression chamber, the sand powder completely fills the gap of the blank through the natural action of gravity, or the vibration is carried out on the compression chamber, or a vacuum pumping means is carried out, then a piston is covered, so when the piston compresses the volume of the columnar cylinder along the axial direction, the inner space of the columnar cylinder is compressed in one dimension, and when the displacement generated by the compression, the pre-stretching, the pre-positioning phase shift and the like are opposite, the size of the blank is compressed and is recovered to the size required by a target workpiece.

In summary, the basic process operations are divided into: a filling process of the compression chamber, a compacting process of the filling material and a sintering process.

The filling process of the compression chamber is as follows: the blank and the sand powder are filled in the compression chamber, the blank is placed in the compression chamber from the upper hole of the compression chamber with the lower end sealed, the pre-stretching direction of the blank is parallel to the axial direction, the periphery of the blank is not in contact with the inner wall of the compression chamber, the sand powder is continuously filled in the compression chamber, the sand powder completely fills the gap of the blank through the natural action of gravity, or the vibration is carried out on the compression chamber, or the vacuum extraction means is carried out, and the sand powder is filled between the blank and the inner wall of the compression chamber to avoid the contact with the wall.

The compaction process of the filler is as follows: the press presses the piston to make the piston compress the compression chamber along the axis direction one-dimensionally, which will generate the compression deformation opposite to the pre-stretching displacement to the blank, and the sand around the blank is compressed equally, as a result, the pre-stretching and the pre-displacement will also be offset by the reverse recovery, the size of the blank is compressed and restored to the size needed by the target workpiece, and in addition, the bottom plate is a fixed or detachable bottom plate or a piston is also used.

The sintering process of the filler is as follows: the sintering process comprises pressureless sintering and pressure sintering, wherein the pressure sintering refers to maintaining the pressure inside the cylindrical cylinder body through mechanical clamping in the sintering process; or sintering together with the inside of the forming cylinder and then taking out the sintered blank, or directly taking out the blank and sintering separately; or pre-sintering at medium and low temperature and then taking out for high-temperature sintering. The high-temperature sintering (following the principle of equivalent compression ratio: the compression ratio of the compression space of the whole compression chamber is equal to the pre-compression ratio of the blank) is to take out the fired blank after sintering together with the inside of the forming cylinder or take out the blank for sintering separately; or pre-sintering at the medium and low temperature (200-.

The final compactness can obtain more than 6.0 and even 6.8 g/cubic centimeter, and the strength of the workpiece is increased by more than one order of magnitude.

Further: the bottom plate can be dismantled: when compaction is complete, the bottom plate is removed and the piston easily pushes the compact out.

Further: double-piston displacement compaction: the bottom plate is replaced by a piston, the cylindrical cylinder filled with the powder and the blank is placed on a press machine, and the upper piston and the lower piston of the press machine apply pressure displacement to compress the inner space.

Further: the physical property requirements of the sand powder and the iron powder are as follows: in order to minimize the deviation of the compression process from linearity, the volume compression ratio of 2 materials is required to be consistent as much as possible under the same pressure, and the difference is controlled within 50%.

Further: the supporting powder and the metal powder can be iron-based alloy powder, copper-based alloy powder, aluminum-based alloy powder or non-metal alloy powder, and the sand powder is carborundum, quartz sand and other improved high-temperature minerals and artificial sand powder.

The invention has the beneficial effects that:

the new technical route enables the metal printing to be low in cost and the compacted compact sintered part to be high in strength.

[ description of the drawings ]

The invention is further described in the following preferred embodiments with reference to the accompanying drawings in which:

FIG. 1 is a schematic view of the position of the slug and sand in the compression chamber.

Fig. 2 is a schematic diagram of the pre-stretching and pre-displacement of the blank.

FIG. 3 is one of the introduction to post-sinter powder filling technology.

FIG. 4 is one of the introduction to post-sinter powder filling technology.

Description of reference numerals:

(1) columnar cylinder

(2) Piston

(3) Fixed bottom plate

(4) Direction of compaction

(5) Sand powder

(8) Axial line

(9) Cylindrical surface bedding sand layer

(10) Upper bedding sand layer

(11) Lower bedding sand layer

(12) Compression chamber

(13) Slicing

(14) Blank

(15) Base plate

(16) Axial line

(17) Pre-displacement of

(18) Pre-stretching 1

(19) Pre-stretching 2

(20) Front view of slice

(21) Blank slicing

[ examples of embodiment ]

As shown in [ fig. 1 ]:

the right drawing is a sectional view of the compression chamber (12) after the inner space is compressed.

A blank (14) in a solid state is placed in a cylindrical cylinder body (1), sand powder (5) is arranged above, below and around the blank (14), the sand powder (5) is fully contacted with the inner surfaces of the cylindrical cylinder body (1), a piston (2) and a fixed bottom plate (3), and all spaces (including the inner space) of the cylindrical cylinder body (1) except the actual volume occupied by blank objects (14) are filled.

The pre-stretching of the blank is in the direction of the axis (8) and the pre-displacement is in the direction of a section (slice) perpendicular to the axis.

When pressure acts between the piston (2) and the fixed base plate (3), the piston (2) can displace along the axis (8) direction, such as the compaction direction (4), and the internal volume is mainly linearly compressed due to the constraint of the cylindrical cylinder body (1); and the cylindrical surface sand bedding layer (9), the upper sand bedding layer (10) and the lower sand bedding layer (11) mainly protect the blank (14) from rubbing against the inner wall of the forming cylinder.

As shown in fig. 2:

the blank in the compression chamber (12) is sliced (21) along the MN blank containing sand powder, as seen in the direction above the compacting direction (4), as shown in the front view (20) of the slice, into 2 circular cross-sections of different sizes.

From an absolute coordinate point of view, the prestretching is divided into prestretching 1(18) and prestretching 2(19), which is the sum of 2.

The condition of the pre-displacement (17) is complex, and the pre-displacement can be ignored generally only when the volume compression ratio of the sand powder and the iron powder (blank) is represented by a large difference value.

As shown in fig. 3 and 4:

is a introduction of post-sintering powder filling technology: belongs to the prior art; the corresponding structure is realized as described in the present specification (background art: page 2, line 4 to line 10 of the specification).

Claims

1. The filling degreasing and compacting sintering method of the three-dimensional printed powder bonding blank is characterized by comprising the following steps of: the method comprises two independent processes of filling degreasing and compacting sintering, and comprises the following steps: the necessary condition for realizing the process is to rely on a forming cylinder body, and the structure of the forming cylinder body comprises: the container is provided with an opening at the upper part, the 3D forming object to be degreased and sand are put into the forming cylinder together, the sand is ensured to fill the inner cavity of the forming object, and then the forming cylinder filled with the sand and the 3D forming object is placed in a high-temperature environment for degreasing; in order to make the sand better support the 3D shaped article, the upper opening of the shaped cylinder container may be preliminarily pressure compacted, the filling and degreasing method being used alone or as a preceding process of the compacting and sintering method; the compaction-sintering method is detailed, and the process must be realized by using a compression chamber which is composed of: the closed space container is composed of a columnar cylinder body, a bottom plate and a piston, the columnar cylinder body and the bottom plate are in rigid connection or detachable, and when the piston moves along the axis direction of the cylinder, the internal volume of the columnar cylinder body is changed; another requirement is that: pre-stretching amplification and transverse pre-displacement treatment of linear stretching amplification in the axis direction are required to be carried out on a target workpiece in advance: the pre-stretching amplification treatment is to linearly amplify the size of the blank to be generated in one dimension along the axial direction to generate the blank longer than a target workpiece, and the pre-displacement is generated by the difference of the volume compression ratio physical characteristics of the blank and a sand body material, so that the transverse slicing of the blank in the compression chamber can be predicted displacement and deformation in the direction vertical to the axial line; the following process operations are as follows: a filling process of the compression chamber, a compacting process of the filling material and a sintering process.

2. A compression chamber filling process as defined in claim 1 in a method of filling, degreasing and compacting-sintering three-dimensionally printed powder bond blanks, characterized by: the blank and the sand powder are filled in the compression chamber, the blank is placed in the compression chamber from the upper hole of the compression chamber with the lower end sealed, the pre-stretching direction of the blank is parallel to the axial direction, the periphery of the blank is not in contact with the inner wall of the compression chamber, the sand powder is continuously filled in the compression chamber, the sand powder completely fills the gap of the blank through the natural action of gravity, or the vibration is carried out on the compression chamber, or the vacuum extraction means is carried out, and the sand powder is filled between the blank and the inner wall of the compression chamber to avoid the contact with the wall.

3. The process of filling, degreasing, compacting and sintering a three-dimensionally printed powder bond blank according to claim 1, wherein the compacting step comprises: the press presses the piston to make the piston compress the compression chamber along the axis direction one-dimensionally, which will generate the compression deformation opposite to the pre-stretching displacement to the blank, and the sand around the blank is compressed equally, as a result, the pre-stretching and the pre-displacement will also be offset by the reverse recovery, the size of the blank is compressed and restored to the size needed by the target workpiece, and in addition, the bottom plate is a fixed or detachable bottom plate or a piston is also used.

4. The sintering process as claimed in claim 1, in a method of filling, degreasing and compacting sintering of three-dimensionally printed powder-bonded blanks, characterized in that: the sintering process comprises pressureless sintering and pressure sintering, wherein the pressure sintering refers to maintaining the pressure inside the cylindrical cylinder body through mechanical clamping in the sintering process; or sintering together with the inside of the forming cylinder and then taking out the sintered blank, or directly taking out the blank and sintering separately; or pre-sintering at medium and low temperature and then taking out for high-temperature sintering.

5. The method of filling, degreasing, compacting and sintering a three-dimensionally printed powder bond blank of claim 1, wherein said blank and said sand body are selected from the group consisting of: the blank and the sand body are made of iron-based alloy powder, copper-based alloy powder, aluminum-based alloy powder or non-metal alloy powder, and the sand powder is carborundum or quartz sand.

6. The method of filling, degreasing, compacting and sintering a three-dimensionally printed powder bond blank of claim 1, wherein said blank and said sand body are selected from the group consisting of: the volume compression ratio of the blank and the 2 materials of the sand body is consistent as much as possible, and the difference value is controlled within 50 percent.

7. The filling degreasing and compacting sintering process of claim 1, wherein the two processes are separate processes and can be used independently.