阅读说明：本技术 一种粉末冶金零件的成型方法及成型装置 (Forming method and forming device for powder metallurgy part ) 是由 刘爱强 江凌燕 贺蕊 刘敏 于 2019-12-09 设计创作，主要内容包括：本发明公开了一种粉末冶金零件的成型方法及成型装置,方法包括：首次压制、末次压制、出模、烧结的步骤,成型装置包括上模冲、阴模和下模冲,阴模设有用于装粉末的阴模型腔,上模冲包括上模座和上模冲压制件,下模冲包括下模座和下模冲压制件,上模冲压制件和下模冲压制件可穿入阴模型腔对粉末进行压制。采用本发明方法和装置加工出来的粉末零件致密性好,有效的增加了中间的初始密度,整体的密度增加,相对密度差值变小,整体生坯性能提升。(The invention discloses a forming method and a forming device of powder metallurgy parts, wherein the method comprises the following steps: the forming device comprises an upper punch, a female die and a lower punch, the female die is provided with a female die cavity for containing powder, the upper punch comprises an upper die base and an upper die stamping part, the lower punch comprises a lower die base and a lower die stamping part, and the upper die stamping part and the lower die stamping part can penetrate into the female die cavity to press the powder. The powder parts processed by the method and the device have good compactness, the intermediate initial density is effectively increased, the overall density is increased, the relative density difference is reduced, and the performance of the overall green body is improved.)

1. A forming method of a powder metallurgy part is characterized by comprising the following steps:

s1, first pressing: the upper punch (1) moves upwards to leave a female die cavity (201) of the female die (2), the lower punch (3) moves downwards and is kept in the female die cavity (201), powder is sent into the female die cavity (201), the height of filler is lower than that of the female die cavity (201), then the upper punch (1) moves downwards to press the powder in the female die cavity (201), the lower punch (3) is kept still, and when the upper punch (1) moves downwards to a designated position, pressing is completed;

s2, last pressing: the upper punch (1) moves upwards to leave the female die cavity (201), the lower punch (3) moves downwards to a designated position and is kept in the female die cavity (201), powder is sent into the female die cavity (201) and is filled, and then the upper punch (1) moves downwards while the lower punch (3) moves upwards to press the powder in the female die cavity (201) together;

s3, demolding: the upper punch (1) moves upwards to leave the female die cavity (201), and the lower punch (3) moves upwards to eject a pressed green body (4);

s4, sintering: and sintering and forming the pressed green body (4).

2. The method of forming a powder metallurgy part according to claim 1, wherein: at least one intermediate pressing is further included between the first pressing in step S1 and the last pressing in step S2, and when the intermediate pressing is one, the method of the first pressing or the method of the last pressing is adopted; when the intermediate compression is performed a plurality of times, the method of the first compression, or the method of the last compression, or the method in which the first compression is used in combination with the last compression is employed.

3. The method of forming a powder metallurgy part according to claim 1, wherein: the sintered green body (4) is a bar with a large length-diameter ratio.

4. The method of forming a powder metallurgy part according to claim 2, wherein: the length of the upper punch (1) which can enter the cavity (201) of the female die is larger than the sum of the pressing amount of each time in the process of pressing in multiple times.

5. A molding apparatus based on the molding method of powder metallurgy parts according to any one of claims 1 to 4, characterized in that: including last mould towards (1), bed die (2) and lower mould towards (3), bed die (2) are equipped with bed die cavity (201) that is used for adorning the powder, go up mould towards (1) including upper die base (11) and go up mould punching press finished piece, lower mould towards (3) including die holder (31) and lower mould punching press finished piece, it can penetrate bed die cavity (201) and suppress the powder to go up mould punching press finished piece and lower mould punching press finished piece.

6. The molding apparatus of the molding method of powder metallurgy parts according to claim 5, wherein: the female die cavity (201) is set to be more than two, and the upper die stamping part and the lower die stamping part are correspondingly set to be more than two.

7. The molding apparatus of the molding method of powder metallurgy parts according to claim 5, wherein: the female die cavity (201) is a cylindrical cavity with a large length-diameter ratio, and the upper die stamping part and the lower die stamping part are correspondingly arranged into an upper die stamping forming rod (12) and a lower die stamping forming rod (32).

8. The molding apparatus for the molding method of a powder metallurgy part according to claim 5, wherein the female cavity (201) has a draft α for facilitating demolding, 0.5 ° ≦ α ≦ 2 °.

9. The molding apparatus of the molding method of powder metallurgy parts according to claim 7, wherein: the minimum clearance L1 between the upper die stamping forming rod (12) and the female die cavity (201) is larger than the clearance L2 between the lower die stamping forming rod (32) and the female die cavity (201).

10. The molding apparatus of the molding method of powder metallurgy parts according to claim 5, wherein: the female die (2) comprises a female die outer sleeve (21) and a female die inner sleeve (22), the female die outer sleeve (21) is a steel outer sleeve, and the female die inner sleeve (22) is a hard alloy inner sleeve.

Technical Field

The invention relates to a powder metallurgy technology, in particular to a forming method and a forming device of powder metallurgy parts.

Background

Powder metallurgy is a process of manufacturing metal materials, composite materials and various types of products by forming and sintering using metal powder or a mixture of metal powder and non-metal powder as a raw material. The characteristics of high efficiency, environmental protection and less waste enable the application range and deep application expansion of the technology in industry to be continuously extended, and the technology is continuously improved. The shadow can be seen in the body shadow of powder metallurgy parts in the automobile industry, the military industry, the aerospace industry, the computer industry, the nuclear power industry and other industries.

When a powder metallurgy part with a large length-diameter ratio (L/D >3) is pressed, a neutral zone exists, so that the waist size is smaller. The powder metallurgy compaction process determines the density distribution and degree of densification of the green body. The density of the green body can further affect the dimensional accuracy and physical properties of the part. At present, the research on improving the densification degree is more, the forming method comprises warm pressing, high pressing, vibration pressing and the like which can improve the densification degree, and the method for improving the density uniformity in the pressing process comprises the methods of optimizing feeding, improving the surface roughness of a die, increasing the lubrication of the die and the like. For ISO numerical control blade production, the surface roughness of the die reaches Ra0.04 at present, the mirror surface level is reached, the machining roughness is improved, and the economy is low. However, the above method cannot solve the problem of dimensional accuracy of the powder metallurgy part with a large length-diameter ratio due to the decrease of density in the neutral region and the thin middle part and thick two ends.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a forming method and a forming device for powder metallurgy parts, which have the advantages of simple structure and convenient operation, can reduce uneven density distribution, can improve the densification degree of the powder metallurgy parts and further improve the precision of the powder metallurgy parts.

In order to solve the technical problems, the invention adopts the following technical scheme:

a forming method of a powder metallurgy part comprises the following steps:

s1, first pressing: the upper punch moves upwards to leave a female die cavity of the female die, the lower punch moves downwards and is kept in the female die cavity, powder is sent into the female die cavity, the height of the filler is lower than that of the female die cavity, then the upper punch moves downwards to press the powder in the female die cavity, the lower punch remains stationary, and pressing is completed when the upper punch moves downwards to a specified position;

s2, last pressing: the upper punch moves upwards to leave the female die cavity, the lower punch moves downwards to a specified position and is kept in the female die cavity, powder is sent into the female die cavity and is filled in the female die cavity, and then the upper punch moves downwards and the lower punch moves upwards simultaneously to press the powder in the female die cavity together;

s3, demolding: the upper punch moves upwards to leave the cavity of the female die, and the lower punch moves upwards to eject the pressed green body;

s4, sintering: and sintering and forming the pressed green body.

As a further improvement of the above technical solution:

at least one intermediate pressing is further included between the first pressing in step S1 and the last pressing in step S2, and when the intermediate pressing is one, the method of the first pressing or the method of the last pressing is adopted; when the intermediate compression is performed a plurality of times, the method of the first compression, or the method of the last compression, or the method in which the first compression is used in combination with the last compression is employed.

The sintered green body is a bar with a large length-diameter ratio.

The length of the upper punch which can enter the cavity of the female die is larger than the sum of the pressing amount of each time in the fractional pressing process.

The utility model provides a forming device based on foretell powder metallurgy part's forming method, includes that punch, bed die and lower mould are towards, the bed die is equipped with the bed die cavity that is used for adorning the powder, go up the punch including the upper die base and go up mould punching press finished piece, the lower mould is towards including die holder and lower mould punching press finished piece, it can penetrate the bed die cavity and suppress the powder to go up mould punching press finished piece and lower mould punching press finished piece.

As a further improvement of the above technical solution:

the female die cavity is set to be more than two, and the upper die stamping part and the lower die stamping part are correspondingly set to be more than two.

The female die cavity is a cylindrical cavity with a large length-diameter ratio, and the upper die stamping part and the lower die stamping part are correspondingly arranged into an upper die stamping forming rod and a lower die stamping forming rod.

The female die cavity is provided with a draft angle α convenient for demoulding, and α is more than or equal to 0.5 degrees and less than or equal to 2 degrees.

The female die comprises a female die outer sleeve and a female die inner sleeve, the female die outer sleeve is a steel outer sleeve, and the female die inner sleeve is a hard alloy inner sleeve.

And the minimum clearance L1 between the upper die punching forming rod and the female die cavity is larger than the clearance L2 between the lower die punching forming rod and the female die cavity.

Compared with the prior art, the invention has the advantages that:

Drawings

FIG. 1 is a schematic process diagram of a method for molding a powder metallurgy part according to embodiment 1 of the present invention.

FIG. 2 is a graph comparing the results of the forming process of example 1 of the present invention with those of a green body obtained by a forming process of the prior art.

FIG. 3 is a schematic configuration diagram of a powder metallurgy part molding apparatus according to embodiment 1 of the present invention.

FIG. 4 is an exploded view of a part of the powder metallurgy part molding apparatus according to embodiment 1 of the present invention.

Fig. 5 is a schematic view of a gap formed between the upper and lower punch bars and the female mold cavity in example 1 of the present invention.

Fig. 6 is a schematic view showing the positional relationship between two female mold cavities in embodiment 1 of the present invention.

The reference numerals in the figures denote:

1. punching by an upper die; 11. an upper die holder; 12. punching the upper die into a rod; 2. a female die; 201. a female die cavity; 21. sleeving a female die; 22. sleeving a female die; 3. punching a lower die; 31. a lower die holder; 32. punching the lower die into a rod; 4. and (4) green pressing.

Detailed Description

The invention is described in further detail below with reference to the figures and specific examples of the specification.

As shown in fig. 1 and 2, the method for forming a powder metallurgy part according to the embodiment includes the following steps:

s1, first pressing: the upper punch 1 moves upwards to leave the female die cavity 201 of the female die 2, the lower punch 3 moves downwards and is kept in the female die cavity 201, powder is sent into the female die cavity 201, the height of filler is lower than that of the female die cavity 201, then the upper punch 1 moves downwards to press the powder in the female die cavity 201, the lower punch 3 is kept still, and when the upper punch 1 moves downwards to a specified position, pressing is completed;

s2, last pressing: the upper punch 1 moves upwards to leave the female die cavity 201, the lower punch 3 moves downwards to a designated position and is kept in the female die cavity 201, powder is sent into the female die cavity 201 and is filled, and then the upper punch 1 moves downwards while the lower punch 3 moves upwards to press the powder in the female die cavity 201 together;

s3, demolding: the upper punch 1 moves upwards to leave the female die cavity 201, and the lower punch 3 moves upwards to eject the pressed green body 4;

s4, sintering: and sintering and forming the pressed green body 4.

The method takes two pressing steps as an example, the first pressing step is one-way pressing of the upper punch 1, the powder after the first pressing step is not the complete green body 4 but a part of the green body 4a of the green body 4, the upper end of the green body 4a is the middle part of the green body 4, the upper end of the green body 4a is pressed and compacted in one way through the upper punch 1, and the process of the first pressing step is shown in parts I and II in fig. 1. III IV VI, then filling, forming another part of green body 4b of the green body 4 by the later filled powder, performing final pressing, namely, descending the upper punch 1 and ascending the lower punch 3 simultaneously, pressing the powder together to form a complete green body 4, wherein the final pressing process refers to the parts III, IV, V and VI in the figure 1, so that the green body 4 processed by segmented pressing has more uniform density, the influence of a neutral zone is reduced, and the position with the lowest intermediate density can be adjusted by the method. Referring to fig. 2, a portion a shows a green compact 4 processed by a forming method of the prior art, and a portion b shows a green compact 4 processed by the method of this embodiment, it can be understood that the green compact 4 processed by the method of this embodiment has good compactness, and the density ρ of the middle portion is not much different from the density ρ of the two end portions.

In this embodiment, the length of the upper punch 1 that can enter the cavity 201 of the female die is greater than the sum of the pressing amount of each time in the divided pressing process.

As shown in fig. 3 to 6, the device used in the method for forming a powder metallurgy part according to this embodiment includes an upper punch 1, a female die 2, and a lower punch 3, where the female die 2 is provided with a female die cavity 201 for containing powder, the upper punch 1 includes an upper die holder 11 and an upper punch part, the lower punch 3 includes a lower die holder 31 and a lower punch part, and the upper punch part and the lower punch part can penetrate into the female die cavity 201 to press the powder.

In this embodiment, the number of the female mold cavities 201 is two, and the number of the upper mold punching part and the number of the lower mold punching part are correspondingly two. The roughness of the inner wall surface of each female die cavity 201 needs to be consistent, otherwise, the imagination that the heights of the green bodies 4 pressed in each die cavity are different for multiple times is easy to occur.

In this embodiment, the molding is performed on a rod with a large length-diameter ratio, so the female die cavity 201 is a cylindrical cavity with a large length-diameter ratio, and the upper die stamping product and the lower die stamping product are correspondingly set as the upper die stamping rod 12 and the lower die stamping rod 32. In this structure, the upper die punch forming bar 12 and the lower die punch forming bar 32 are used for controlling the stroke, respectively, to prevent excessive pressing, and operate in the cavity 201 of the female die to complete powder pressing in cooperation with the female die 2. Because the intermediate density is continuously increased in the early stage by the sectional forming, the influence of a neutral zone is effectively reduced, the radial size value is effectively reduced in a mixture system with higher friction coefficient, a product with larger length-diameter ratio or height-diameter ratio can be effectively formed, the crack risk is avoided, the structure is simple, the phenomenon of uneven distribution of axial density of a green body is effectively reduced, and the size precision of press forming is greatly improved. The length of the upper punch forming rod 12 which can enter the female die cavity 201 is larger than the sum of the pressing amount of each time in the process of pressing in multiple times.

In this embodiment, the female die cavity 201 has a draft α value convenient for demolding of 0.5 ° to α ° to 2 °, in this embodiment, α is preferably 0.5 °, the draft (inclination angle) is set to 0.5 °, on one hand, the green compact 4 is conveniently ejected upward from the female die 2 during demolding, on the other hand, both end faces of the product are not inclined too much after sintering, the draft α is related to the number of segmentation, the larger the angle, the distance of the draft is controlled to be not less than the elastic aftereffect of the powder-metallurgy part, compared with the conventional forming die, the inner wall face of the female die cavity 201 of the forming device is divided into two types, the straight face of the portion with an angle of 0 ° and the forming inclined face (demolding portion) with a draft angle, i.e., the distance of the portion of the green compact 4 is formed, which ensures smooth demolding, when the elastic aftereffect is ejected from the lower die 4 after the upper die 1 is retracted, the elastic aftereffect obtains a release space, and ensures that the green compact 4 does not have a lateral crack.

In the embodiment, the minimum clearance L1 between the upper die stamping rod 12 and the female die cavity 201 is larger than the clearance L2 between the lower die stamping rod 32 and the female die cavity 201, the arrangement is such that the distance between the upper die stamping rod 12 and the demoulding part (part with the draft angle) of the female die cavity 201 is not too large, abnormal burr of the stroke is avoided, and the green body 3 is prevented from generating abnormal wide burr to cause easy damage, wherein, the height of the forming inclined plane of the female die 2 with the draft angle is H, and the relationship between the draft angles α, H, L1 and L2 is α -arctan ((L1-L2)/H).

In this embodiment, the female die 2 includes a female die outer sleeve 21 and a female die inner sleeve 22, the female die outer sleeve 21 is a steel outer sleeve, and the female die inner sleeve 22 is a hard alloy inner sleeve. The hard alloy inner sleeve has the characteristic of high hardness, and the powder is filled in the female die inner sleeve 22 for pressing, so that the stability is good. The outer sleeve does not need high hardness, and only needs common steel, so that the cost can be reduced, the economy and the economy are realized, and the practicability is good.

In this embodiment, the upper die punch forming rod 12 is closely matched with powder filling, and each time powder is refilled, the upper die punch forming rod 12 needs to move up to a height higher than a filling vessel for filling to avoid collision; but can not move upwards too high to ensure that the upper punch does not need to move too much idle stroke in the subsequent secondary pressing so as to ensure the pressing efficiency.

In this embodiment, the effective loading height of the female die 2 is within the range of 10mm to 20 mm. The powder bulk density can be increased a little under a powder system with stable powder bulk density, and a larger value needs to be increased under the condition of unstable powder system precision so as to ensure that powder with certain weight is effectively filled.