CN111804918A - Powder metallurgy part and preparation method thereof - Google Patents
Powder metallurgy part and preparation method thereof Download PDFInfo
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- CN111804918A CN111804918A CN202010702860.5A CN202010702860A CN111804918A CN 111804918 A CN111804918 A CN 111804918A CN 202010702860 A CN202010702860 A CN 202010702860A CN 111804918 A CN111804918 A CN 111804918A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/20—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by extruding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/24—After-treatment of workpieces or articles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/24—After-treatment of workpieces or articles
- B22F2003/241—Chemical after-treatment on the surface
- B22F2003/242—Coating
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/24—After-treatment of workpieces or articles
- B22F2003/248—Thermal after-treatment
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Abstract
The invention discloses a powder metallurgy part and a preparation method thereof, and belongs to the technical field of powder metallurgy. The preparation method of the powder metallurgy part comprises the following steps: and carrying out vibration extrusion on the surface of the powder metallurgy part preform. The method can provide uniform extrusion force, so that the surface layer metal of the powder metallurgy part prefabricated blank flows plastically and the surface layer densification is more uniform, the method is easy to process, the shape and the size precision of the powder metallurgy part can be better ensured, meanwhile, the extrusion load can be reduced, the abrasion of an extrusion die is reduced, the service life of the extrusion die is prolonged, and the processing quality and the mechanical property of the powder metallurgy part are improved. The prepared powder metallurgy part has low extrusion load, good surface quality after extrusion, small rebound quantity, more uniform densification of a dense layer, high hardness and good wear resistance.
Description
Technical Field
The invention relates to the technical field of powder metallurgy, in particular to a powder metallurgy part and a preparation method thereof.
Background
The powder metallurgy technology has the advantages of energy conservation, high production efficiency, short production flow, less pollution, near-net-shape forming and the like in the manufacturing of parts such as automobiles, machinery and the like. However, the powder metallurgy parts produced by the traditional mixing, pressing and sintering processes often have more coarse pores (low density), which seriously weakens the mechanical properties such as strength and hardness of the powder metallurgy parts and greatly limits the application range of the powder metallurgy parts. A number of engineering practices have shown that the majority of part failure occurs first at the part surface, and then the ultimate failure is initiated. The improvement of the surface mechanical property of the part can obviously improve the overall performance and the service life of the part and greatly enlarge the application range of the part. Powder metallurgy surface densification strengthening techniques have been developed for this purpose. The technology achieves the purposes of obviously improving the mechanical property and prolonging the service life of the powder metallurgy part by selectively improving the surface layer density of the powder metallurgy part, thereby expanding the application range of the powder metallurgy part.
The surface densification and strengthening technology of the powder metallurgy part firstly adopts the traditional powder metallurgy process (powder mixing-pressing forming-sintering) to manufacture a sintered blank of the powder metallurgy part with the shape and the size similar to those of the final part, and the similar sintered blank of the powder metallurgy part is generally called a prefabricated blank of the final powder metallurgy part; and then, applying certain pressure to the surface of the powder metallurgy part preform for surface layer plastic processing, so that the surface layer metal of the preform generates plastic flow, coarse pores on the surface layer of the preform are filled, the surface layer of the preform is highly densified, a highly densified layer with the thickness of about 0.1-1mm and the porosity of less than 2% is formed on the surface layer of the preform, and the shape and the size of the final part are formed, so that the high-performance and long-life powder metallurgy part is manufactured. In actual production, according to the mechanical property requirement of the part, the powder metallurgy part can be further subjected to heat treatment so as to further improve the mechanical property of the powder metallurgy part.
The existing manufacturing technology of powder metallurgy parts can be mainly divided into three types according to different surface densification processing methods of powder metallurgy part preforms: (1) surface shot blasting densification and strengthening; (2) surface rolling densification and strengthening; (3) the surface is directly pressed to densify and strengthen.
However, the current manufacturing techniques easily cause poor densification uniformity of the surface layer of the preform, affect the surface layer compactness and mechanical properties of the final powder metallurgy part, and cannot easily ensure the shape and dimensional accuracy of the final part.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a preparation method of a powder metallurgy part and the prepared powder metallurgy part so as to overcome the technical problems.
The invention is realized by the following steps:
in a first aspect, the present application provides a method of making a powder metallurgy part, comprising the steps of: and carrying out vibration extrusion on the surface of the powder metallurgy part preform.
In an alternative embodiment, the extrusion die is oscillated to extrude the surface of the preform in a reciprocating motion. Wherein, the reciprocating direction is the axial direction of the extrusion die.
In an alternative embodiment, the extrusion die may be fixed and the powder metallurgy part preform is reciprocated to perform vibratory extrusion on the surface of the powder metallurgy part preform, wherein the reciprocating direction of the powder metallurgy part preform is also the axial direction of the extrusion die.
In an alternative embodiment, the extrusion die is advanced a distance greater than the retraction distance during each reciprocation.
In an alternative embodiment, the extrusion die comprises an extrusion die or an extrusion core rod.
In an alternative embodiment, the extrusion die has a step, preferably a single step.
In an alternative embodiment, the surface of the powder metallurgy part preform comprises an outside surface of the powder metallurgy part preform and/or an inner bore surface of the powder metallurgy part preform.
In an alternative embodiment, the lubricant is filled between the extrusion die and the surface of the powder metallurgy part preform during the vibratory extrusion process.
In an alternative embodiment, the vibrational extrusion has a vibrational frequency of 0.1 to 1000Hz and an amplitude of 0.1 to 50 mm.
In an alternative embodiment, the extrusion feed amount per vibration cycle is 0.01 to 5mm, and the extrusion feed amount is a value obtained by subtracting the retreat distance from the advance distance.
In an alternative embodiment, the extrusion deformation amount perpendicular to the moving direction of the extrusion die during the vibration extrusion is 0.05 to 5 mm.
In an alternative embodiment, the step angle of the extrusion die is 1-89 °.
In an alternative embodiment, the powder metallurgy part preform is prepared by the following steps: sintering the green preform of the powder metallurgy part.
In an alternative embodiment, the sintering temperature is between 0.45 and 0.9 times the melting point of the principal component material in the green powder metallurgy part preform.
In an alternative embodiment, the sintering time is 5-150 min.
In an alternative embodiment, the green compact of the powder metallurgy part preform is mainly obtained by pressing the raw materials after being mixed according to the proportion.
In an alternative embodiment, the porosity of the green powder metallurgy part preform is less than 30%.
In an alternative embodiment, a compression deformation of 0.05 to 5mm is reserved during the pressing.
In an alternative embodiment, the method further comprises performing heat treatment after the vibration extrusion.
In an alternative embodiment, the heat treatment comprises a quenching treatment and a low temperature tempering treatment.
In an alternative embodiment, the quenching process comprises high frequency induction hardening or carburizing quenching.
In an alternative embodiment, the carburizing and quenching is to perform carburizing treatment for 20-200min at the temperature of 800-1000 ℃ and then quench; preferably, the carburizing is performed at 920 ℃ for 120 min.
In an alternative embodiment, the temperature of the low temperature tempering treatment is 100-250 ℃, preferably 200 ℃.
In a second aspect, the present application provides a powder metallurgy part prepared by the preparation method as described above.
The beneficial effects of the invention include:
the vibration extrusion mode that this application is related to can provide even extrusion force for the surface of prefabricated base, makes the superficial layer metal plastic flow of powder metallurgy part prefabricated base and superficial layer densification more even to, this method processing is easy, can guarantee the shape and the size precision of powder metallurgy part betterly, simultaneously, can also reduce extrusion load, reduces extrusion die's wearing and tearing, extension extrusion die life improves the processingquality and the mechanical properties of powder metallurgy part. The prepared powder metallurgy part has low extrusion load, good surface quality after extrusion, small rebound quantity, more uniform densification of a dense layer, high hardness and good wear resistance.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings that are required to be used in the present application will be briefly described below, it being understood that the following drawings only illustrate certain embodiments of the present invention and the content of the description, and therefore should not be considered as limiting the scope, and that for a person skilled in the art, other related drawings may be obtained from these drawings without inventive effort.
FIG. 1 is a schematic diagram of a method of surface shot peening densification;
FIG. 2 is a schematic diagram of a surface roll densification forming process;
FIG. 3 is a schematic diagram of a one-time direct extrusion densification forming method for the surface of a multi-stage reducing combined extrusion die;
FIG. 4 is a schematic diagram of a one-time direct extrusion densification forming method of a single or multi-step variable cross-section integral extrusion female die surface;
FIG. 5 is a schematic diagram of a one-time direct extrusion densification forming method for the surface of a single-step or multi-step variable cross-section integral extrusion core rod;
FIG. 6 is a schematic diagram of a vibration compaction-densification forming process for the outer surface of a surface-densified powder metallurgy part;
FIG. 7 is a schematic diagram of a vibration compaction-densification forming process for the surface of an inner hole of a surface-densified powder metallurgy part;
FIG. 8 is a graph of extrusion die displacement versus time during surface oscillation extrusion of a powder metallurgy part preform;
FIGS. 9(a) to 9(c) are photographs showing the appearance of the powder metallurgy wear-resistant rings obtained in comparative group 1, comparative group 2 and example 1, respectively;
FIG. 10 is a graph comparing the load-displacement curves during extrusion for the preforms of control 2 and example 1;
FIGS. 11-13 are photographs of the micro-porosity profile of the outer surface of the powder metallurgy wear ring obtained in control 1, control 2, and example 1, respectively;
FIG. 14 is a graph comparing the inside diameter of a vibrating extrusion die used in the manufacturing process and the outside diameter dimensions of powder metallurgy wear rings obtained in control 2 and example 1;
FIG. 15 is a graph comparing hardness of the outer surface of the powder metallurgy wear ring obtained in comparative group 1 and comparative group 2 and in example 1;
FIG. 16 is a graph comparing the amount of wear on the outer surfaces of the powder metallurgy wear rings obtained in control 1, control 2 and example 1 under the same wear conditions;
FIGS. 17 and 18 are photographs of the micro-pore morphology of the inner bore surface of the powder metallurgy wear ring obtained in control 3 and example 2, respectively;
FIG. 19 is a microscopic pore morphology photograph of the tooth surface of the surface vibration pressed powder metallurgy gear obtained in example 3.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The powder metallurgy part and the preparation method thereof provided by the application are specifically explained below.
At present, the surface densification forming processing method of the powder metallurgy part mainly comprises a powder metallurgy part surface shot blasting densification strengthening technology, a powder metallurgy part surface rolling densification strengthening technology and a powder metallurgy part surface direct pressing densification strengthening technology. The surface extrusion densification strengthening technology for the powder metallurgy parts is mainly divided into a surface direct extrusion densification strengthening technology for a multi-stage reducing combined extrusion die and a surface direct extrusion densification strengthening technology for a single (multi) step variable cross-section integral extrusion die.
The principle of the surface shot peening technique in the above-described machining method is shown in fig. 1. Specifically, a large amount of steel shots are blown out of a shot blasting gun through high-pressure gas, the blown high-speed steel shots are used for continuously impacting the surface of a prefabricated blank of the powder metallurgy part, original coarse pores on the surface layer of the prefabricated blank are compressed and closed under the impact force of the steel shots, and a high-density layer with only a small amount of fine micropores left is formed on the surface of the prefabricated blank, so that the powder metallurgy part with high surface mechanical property, a final shape and a final size is manufactured. During the surface shot peening strengthening process, the spray gun and the powder metallurgy part preform are moved relatively: the prefabricated blank is fixed, and the spray gun moves around the prefabricated blank; or the spray gun is fixed, and the preform rotates to complete the shot peening strengthening processing of the surface of the preform.
The principle of the surface rolling densification strengthening technique is shown in fig. 2. Specifically, the powder metallurgy part prefabricated blank is placed between two driving (driving) rollers and driven (driven) rollers with the same shape characteristics for repeated rolling, so that original coarse pores on the surface layer of the prefabricated blank are compressed and closed under the rolling force of the rollers, and a high-compactness layer with only a few residual fine micropores is formed on the surface of the prefabricated blank, so that the powder metallurgy part with high surface mechanical property, final shape and size is rolled. Before the surface rolling is started, the two rollers are firstly separated and then loaded into a powder metallurgy part prefabricated blank; then, the driving roller repeatedly rolls the preformed blank at a certain rotating speed and a certain feeding amount until the total rolling amount of the surface of the preformed blank reaches a preset value, so that the surface rolling densification and strengthening of the preformed blank are realized, and the required shape and size of the final part are obtained; and finally, separating the two rollers, taking out the rolled prefabricated blank to obtain the powder metallurgy part with the densified and strengthened surface, and finishing the rolling process.
The principle of the surface direct extrusion densification strengthening technology is as follows: the method is characterized in that a pre-formed blank of the powder metallurgy part is directly extruded out from an extrusion die with variable size at one time, so that coarse pores on the surface layer of the pre-formed blank are forced to be compressed and closed under the action of lateral pressure, and a high-compactness layer with only a few residual fine micropores is formed on the surface of the pre-formed blank, thereby extruding the powder metallurgy part with high surface mechanical property, final shape and size.
In the technology, the principle and the process of the method for manufacturing the powder metallurgy part with high surface mechanical property, final shape and size by directly extruding the surface of the prefabricated blank of the powder metallurgy part by using the multi-stage reducing combined extrusion die are shown in figure 3. Specifically, the powder metallurgy part preform passes through a multi-stage reducing combined extrusion die to perform a process of one-time direct extrusion densification of the surface: the extrusion head pushes the preformed blank of the powder metallurgy part to extrude from a combined extrusion die (the variable diameter die plates are fastened by pressing plates, bolts and the like without relative sliding) formed by combining the multi-stage die plates with gradually reduced inner diameters, the outer diameter of the preformed blank is forced to be reduced, the surface layer metal is subjected to plastic deformation, thick pores on the surface layer of the preformed blank are compressed and closed under the action of lateral pressure, and a high-compactness layer with only a few residual fine micropores is formed on the surface of the preformed blank, so that the powder metallurgy part with high surface mechanical property, final shape and size is extruded.
The other method is to directly extrude the surface of a prefabricated blank of the powder metallurgy part by using a single-step or multi-step variable cross section integral extrusion die to manufacture the powder metallurgy part with high surface mechanical property, final shape and size, and the principle of the method is shown in figures 4 and 5. The surface direct compression densification method can be used for extruding the outer side surface of the powder metallurgy part preform (for example, a multi-step variable cross section integral compression female die is shown in figure 4) and can also be used for extruding the inner hole surface of the powder metallurgy part preform (for example, a multi-step variable cross section integral compression core rod is shown in figure 5).
FIG. 4 shows that the preform of the powder metallurgy part passes through a single or multi-step variable cross-section integral extrusion female die, and the surface is densified by one-time direct extrusion: the extrusion head pushes the preformed blank of the powder metallurgy part to extrude from the integral extrusion female die with the single or multi-step variable cross section, the outer diameter of the preformed blank is forced to be reduced, the metal of the outer side surface layer is subjected to plastic deformation, the thick pore of the outer side surface layer of the preformed blank is compressed and closed under the action of lateral pressure, and a high-compactness layer only with a small number of residual fine micropores is formed on the outer side surface of the preformed blank, so that the powder metallurgy part with high surface mechanical property, final shape and size is extruded.
FIG. 5 shows that the preform of the powder metallurgy part is densified by one-step direct extrusion through a single or multi-step variable cross-section integral extrusion core rod, and the process of carrying out one-step direct extrusion densification on the surface comprises the following steps: the extrusion head pushes the preformed blank of the powder metallurgy part to extrude from the periphery of the single-step or multi-step variable-cross-section integral extrusion core rod, so that the inner hole of the preformed blank is forced to be enlarged, the metal on the surface layer of the inner hole is subjected to plastic deformation, the thick pore of the surface layer of the inner hole of the preformed blank is compressed and closed under the action of lateral pressure, and a high-compactness layer with only a small amount of fine micropores left is formed on the surface layer of the inner hole of the preformed blank, so that the powder metallurgy part with high surface mechanical property, final shape.
The inventors have found that the above-mentioned various processing methods for surface densification have the following defects by conducting studies on the above-mentioned various processing methods for surface densification, and have given the causes of these defects accordingly.
The surface shot blasting densification strengthening technology continuously impacts the surface of a prefabricated blank of the powder metallurgy part by using high-speed steel shots to enable the metal on the surface layer of the prefabricated blank to generate plastic deformation and promote the compression and closure of coarse pores on the surface layer to achieve densification. The method has the following disadvantages:
a. densification of the small and deep internal bore surfaces of preforms (powder metallurgy mechanical parts are usually less than a few kilograms, the internal bore being small and deep) cannot be accomplished due to the space constraints of the shot blasting operation.
b. In the shot blasting process, steel shots blown out by high-pressure gas randomly and discretely impact the surface of a powder metallurgy part prefabricated blank, the densification uniformity of a compact layer formed on the surface of the prefabricated blank under the action of dispersed and uneven impact force is poor, coarse pores are still remained in the compact layer, the dimensional accuracy of the shot blasting part cannot be guaranteed, the surface is very rough, and even small pits or edge scraps occur.
The surface rolling densification strengthening technology repeatedly rolls the surface of a preform of the powder metallurgy part through two rollers with the same shape characteristics, so that the surface metal of the preform is subjected to plastic deformation, and coarse pores on the surface are compressed and closed to densify. The method has the following disadvantages:
a. in the rolling process, the surface layer rolling densification of the prefabricated blank can be finished only by accurately regulating and controlling the position, the rotating speed, the feeding amount and the like of the two pairs of rollers, the shape and the size precision of a final part are obtained, the requirements on the manufacturing and control precision of rolling equipment are high, and the equipment is complex.
b. In the rolling process, the powder metallurgy part preform is respectively subjected to two opposite lateral rolling forces exerted by the driving roller and the driven roller at the same time, the two opposite lateral rolling forces are not equal, the densification of a rolling layer on the surface of the preform is easy to be uneven, and the mechanical property and the dimensional accuracy of the rolled part are directly influenced.
c. When the prefabricated blank of the powder metallurgy part is rolled, two pairs of rollers are separated, the rolled part is withdrawn, then the next prefabricated blank to be rolled is loaded, then the two pairs of rollers are matched with the prefabricated blank to be rolled, finally surface rolling is carried out, and the operations are repeated, so that the surface rolling densification forming processing of the parts is completed one by one. The continuous processing of the surfaces of a plurality of powder metallurgy part preformed blanks can not be realized, the processing efficiency is influenced, and when one preformed blank is rolled, two pairs of rollers are opened and closed respectively once, and the requirement on the automatic reset control precision of rolling equipment is high.
d. The surface rolling densification strengthening method is only suitable for the rolling densification forming processing of the outer surface of the preformed blank of the axisymmetric solid of revolution part and can not finish the surface rolling densification forming processing of the preformed blank of the non-axisymmetric solid of revolution part or the inner hole of the preformed blank of the axisymmetric solid of revolution part.
The surface of the combined extrusion die with multiple reducing diameters in the surface direct extrusion densification strengthening technology is subjected to one-step direct extrusion densification forming, a prefabricated blank of a powder metallurgy part is pushed by an extrusion head and extruded from an extrusion die combined by templates with multiple gradually reduced pore diameters, so that the outer diameter of the prefabricated blank is reduced, surface layer metal is subjected to plastic deformation, and large pores on the surface layer are compressed and closed to densify. The method has the following disadvantages:
a. the method has high requirement on the matching precision between the variable-diameter templates of the adopted multistage variable-diameter combined extrusion die, the combined structure of the extrusion die is complex, the processing difficulty is high, the manufacturing cost is high, and the processing cost of the surface densified powder metallurgy part is increased.
b. In the extrusion process, the prefabricated blank of the powder metallurgy part is simultaneously extruded by each reducing template, the surface layers of the prefabricated blank are simultaneously subjected to plastic deformation, higher extrusion load is caused, the higher extrusion load accelerates the wear failure of the combined extrusion die, the service life of the combined extrusion die is shortened, and meanwhile, the processing cost of the surface densified powder metallurgy part is further increased.
c. The higher extrusion load can aggravate the elastic deformation and even overload failure of the combined extrusion die, and the size precision of the extruded powder metallurgy part is influenced.
d. The powder metallurgy part prefabricated blank is extruded by each reducing template of the extrusion die for many times, the lubrication of the contact surface between the surface of the prefabricated blank and the reducing template is increasingly poor, the friction resistance of the contact surface is large, the abrasion failure of the extrusion die is further accelerated, and the surface densification effect (surface layer compactness), the mechanical property and the surface quality (surface roughness) of the extruded powder metallurgy part are influenced.
In the surface one-time direct extrusion densification forming method of the single-step or multi-step variable cross-section integral extrusion die in the surface direct extrusion densification strengthening technology, the multi-step variable cross-section integral extrusion die is used for extruding the preform of the powder metallurgy part, and the defects similar to the defects of the method that the multistage variable diameter combined extrusion die is used for extruding the preform of the powder metallurgy part exist:
a. the multi-step variable cross-section integral extrusion die is also complex in structure, high in processing difficulty and high in manufacturing cost, and the processing cost of the surface densified powder metallurgy part is increased.
b. In the extrusion process, the powder metallurgy part preform is simultaneously extruded by each step surface of the extrusion die, so that high extrusion load is caused, the high extrusion load accelerates the wear failure of each step surface of the extrusion die, the service life of the extrusion die is shortened, and the processing cost of the surface densified powder metallurgy part is further increased.
c. The high extrusion load can aggravate the elastic deformation and even overload failure of the extrusion die, and the dimensional accuracy of the extruded powder metallurgy part is influenced.
d. The powder metallurgy part prefabricated blank is extruded for many times by each step surface of the extrusion die, the lubrication between the surface of the prefabricated blank and the step surface is increasingly poor, the friction resistance is large, the abrasion failure of the extrusion die is further accelerated, and the surface densification effect (surface layer compactness), the mechanical property and the surface quality (surface roughness) of the extruded powder metallurgy part are influenced.
The single-step variable-cross-section integral extrusion die is adopted, and when the powder metallurgy part prefabricated blank is directly extruded at one time, the die is relatively simple in structure and easy to process. However, the following disadvantages also exist:
a. the powder metallurgy part prefabricated blank is only extruded once by a step surface in the extrusion process, the plastic flow of metal on the surface layer of the prefabricated blank is insufficient, large pores on the surface layer cannot be completely compressed and closed, and large pores are easily remained, so that the densification uniformity of the surface layer of the prefabricated blank is poor, and the surface densification effect (surface layer compactness) and the mechanical property of the powder metallurgy part after extrusion are influenced.
b. The pre-formed blank of the powder metallurgy part is directly extruded once through the single-step integral extrusion die to complete the preset extrusion deformation, the metal on the surface layer of the pre-formed blank is greatly deformed at the same moment, and the large elastic deformation is gathered, so that the rebound quantity of the pre-formed blank after being demoulded is large, and the size precision of the part after extrusion is influenced.
Therefore, the existing surface densification forming processing method of the powder metallurgy part has more or less adverse effects on the processing quality, the mechanical property and the like of the powder metallurgy part. In view of the above, the inventors have creatively proposed a new method for preparing powder metallurgy parts, i.e. surface vibration compaction densification strengthening technology, which relates to powder metallurgy parts including, but not limited to, powder metallurgy wear-resistant rings, powder metallurgy gears and powder metallurgy sprockets. Meanwhile, the method can also be applied to surface densification processing of non-iron-based powder metallurgy parts such as aluminum, titanium, copper, magnesium, lithium and the like.
The technology mainly comprises the following steps: and carrying out vibration extrusion on the surface of the powder metallurgy part preform.
In alternative embodiments, the extrusion die is oscillated to extrude the surface of the preform in a reciprocating motion or the die is fixed and the powder metallurgy part preform is reciprocated to oscillate and extrude the surface thereof. The reciprocating directions in the two modes are the axial directions of the extrusion die. The advancing distance of the extrusion die (defined as S) during each reciprocating motion1) Greater than the backoff distance (defined as S)2)。
Through the mode, the extrusion process that once directly extrudees at present surface is replaced to the gradual extrusion process with a plurality of little increments, make the prefabricated base top layer of single reciprocal extrusion cycle receive the region of extrusion load effect little, and surface layer metal is under the reciprocal stress effect, deformation resistance reduces, surface layer metal plastic flow is more abundant, the densification of the surface compact layer that forms is more even, show simultaneously and reduce the extrusion load, reduce the wearing and tearing of extrusion die, the extension extrusion die life-span, the processingquality and the mechanical properties of the powder metallurgy part of improvement surface densification.
Meanwhile, in the process of returning metal on the surface layer of the powder metallurgy part preform in each extrusion period of the extrusion female die or the extrusion core rod, stress is continuously released, so that the accumulated elastic deformation of the surface layer of the preform is obviously reduced, the rebound quantity of the powder metallurgy part after surface vibration extrusion is reduced, and the shape and size precision of the surface densified powder metallurgy part are better ensured.
In an alternative embodiment, the extrusion die may include a female extrusion die or a core extrusion rod, and the structure of the female extrusion die and the core extrusion rod may refer to the prior art, which is not described in detail herein.
In an alternative embodiment, the extrusion die has a step, such as a single step or a multi-step, wherein the multi-step comprises two or more steps. In a preferred embodiment, the extrusion die has a single step, and the structure of the vibration extrusion die with the single step is simpler than that of a combined extrusion die with multi-step reducing and an integral extrusion die with multi-step variable cross section, so that the vibration extrusion die is easier to process, has smaller extrusion load, is easier to ensure the precision and has lower die manufacturing cost. In an alternative embodiment, the surface of the powder metallurgy part preform comprises an outside surface of the powder metallurgy part preform and/or an inner bore surface of the powder metallurgy part preform.
In an alternative embodiment, the lubricant is filled between the extrusion die and the surface of the powder metallurgy part preform during the vibratory extrusion process. Therefore, the lubricant can enter the interface between the powder metallurgy part prefabricated blank and the extrusion die in each return stroke process of the extrusion female die or the extrusion core rod, the lubricating effect is greatly improved, the extrusion load is further reduced, the abrasion of the extrusion die is obviously reduced, and the surface quality of the surface densified powder metallurgy part is improved.
In alternative embodiments, the vibrational frequency of the vibrational extrusion provided herein can be 0.1 to 1000Hz, such as 0.1Hz, 1Hz, 10Hz, 50Hz, 100Hz, 200Hz, 500Hz, 800Hz, 1000Hz, or the like, and the amplitude can be 0.1 to 50mm, such as 0.1mm, 1mm, 5mm, 10mm, 20mm, 40mm, or 50mm, or the like. According to the method, the vibration frequency and the vibration amplitude are set to be in the ranges, the vibration frequency and the vibration amplitude are reasonably selected according to the specific conditions of the powder metallurgy part, the surface vibration, extrusion and densification processing of the powder metallurgy part can be completed, and the qualified surface densification reinforced powder metallurgy part is manufactured; if the range is exceeded, the surface densification of the part is insufficient, the surface layer densification is uneven, the processing quality is affected, and even the part preform is damaged and cracked in the vibration extrusion process, or the extrusion load is too large, so that the extrusion die is damaged.
In alternative embodiments, the extrusion feed per oscillation cycle may be 0.01-5mm, such as 0.01mm, 0.05mm, 0.1mm, 0.5mm, 1mm, 2mm, or 5mm, etc. The extrusion feed amount is a value obtained by subtracting the retreat distance from the advance distance. The method has the advantages that the extrusion feed amount in each vibration period is set to be within the range, the extrusion feed amount is reasonably selected according to the specific conditions of the powder metallurgy parts, the surface vibration extrusion densification processing of the powder metallurgy parts can be completed, and qualified surface densification reinforced powder metallurgy parts are manufactured; if the feeding amount exceeds the range, the feeding amount is too small, so that the machining efficiency is reduced, and the surface densification effect of the part is weakened; too large a feed amount will also impair the surface densification effect of the part and degrade the processing quality of the part, even causing metal accumulation, scratches or cracks on the surface of the part and leading to too high a pressing load or rendering the vibration pressing process unable to proceed smoothly.
In an alternative embodiment, the extrusion deformation perpendicular to the direction of movement of the extrusion die (which may also be understood as perpendicular to the extrusion direction) during the vibratory extrusion process may be 0.05-5mm, such as 0.05mm, 0.1mm, 0.5mm, 1mm, 2mm, or 5mm, etc. The extrusion deformation amount perpendicular to the movement direction of the extrusion die is set to be within the range, the extrusion deformation amount is reasonably selected according to the specific conditions of the powder metallurgy part, the surface vibration extrusion densification processing of the powder metallurgy part can be completed, and the qualified surface densification reinforced powder metallurgy part is manufactured; if the extrusion deformation amount is too small, the surface densification effect of the part is weakened, and even the required depth of a dense layer cannot be obtained; the extrusion deformation is too large, which easily causes large deformation of part local parts, affects the processing quality of the parts, even causes the part prefabricated blank to crack in the extrusion process, generates too high extrusion load, causes the vibration extrusion process not to be smoothly carried out, and damages the extrusion die.
In alternative embodiments, the step angle (noted α) of the extrusion die may be 1-89 °, such as 1 °, 5 °, 10 °, 20 °, 50 °, 80 °, or 89 °, and the like. The step angle is set to be within the range, the step angle of the extrusion die is reasonably determined according to the specific condition of the powder metallurgy part, the surface vibration extrusion densification processing of the powder metallurgy part can be completed, and the qualified surface densification reinforced powder metallurgy part is manufactured; if the range is exceeded, the step angle is too small, the surface densification effect of the part is weakened, and even the required depth of a dense layer cannot be obtained; the step angle is too large, which easily causes the local part of the part to generate too large deformation concentration, even causes the local part of the part to generate metal accumulation, scratch or crack, and influences the processing quality of the part.
By reference, the powder metallurgy part preform is mainly prepared by the following steps: sintering the green preform of the powder metallurgy part.
In alternative embodiments, the sintering temperature is preferably 0.45 to 0.9 times, such as 0.45, 0.5, 0.6, 0.7, 0.8, or 0.9 times, the melting point of the principal component material in the green powder metallurgy part preform. The sintering time may be 5-150min, such as 5min, 10min, 50min, 100min, 120min or 150 min.
The green compact of the powder metallurgy part prefabricated blank is mainly obtained by pressing raw materials mixed according to the proportion.
In an alternative embodiment, the porosity of the green powder metallurgy part preform is less than 30%.
In an alternative embodiment, a compression deformation of 0.05 to 5mm is reserved during the pressing. The extrusion deformation is also perpendicular to the direction of movement of the extrusion die.
Further, the surface vibration extrusion densification strengthening technology provided by the application also comprises a heat treatment after the vibration extrusion.
As a reference, the heat treatment may include a quenching process and a low temperature tempering process. Wherein the quenching treatment may include induction hardening or carburizing and quenching.
In an alternative embodiment, the carburizing and quenching can be performed for 20-200min at 800-1000 ℃, and then quenching is performed; preferably, the carburizing may be performed at 920 ℃ for 120 min.
In an alternative embodiment, the temperature of the low temperature tempering treatment may be 100-.
In summary, the general process of the surface vibration pressing densification strengthening technology includes: powder weighing, powder mixing, preform pressing and forming, preform sintering, preform surface vibration extrusion densification forming processing and surface vibration extrusion densification powder metallurgy part heat treatment.
Reference may be made specifically to: firstly, weighing a certain weight of metal and nonmetal powder according to the material composition and manufacturing process requirements of the powder metallurgy part, and uniformly mixing in a mixer; then, putting the mixed powder into a powder forming die, and pressing to form a pre-formed blank with the shape and the size similar to those of the final powder metallurgy part; then, placing the green body of the prefabricated blank in a sintering furnace for sintering, so that powder particles in the green body are metallurgically bonded to form a proper metallurgical structure, and obtaining the prefabricated blank of the powder metallurgy part with a certain processing allowance; then, carrying out surface vibration extrusion processing on the outer side surface or the inner hole surface of the powder metallurgy part prefabricated blank, respectively forming a high-density layer on the outer side surface layer or the inner hole surface layer of the prefabricated blank, and simultaneously forming the surface-densified powder metallurgy part with high dimensional precision and high surface quality, thereby realizing the surface vibration extrusion densification forming processing of the powder metallurgy part with high dimensional precision and high surface quality; and finally, carrying out heat treatment according to the performance requirements of the surface densified powder metallurgy part so as to meet the structure and performance requirements of the finished part.
The process and principle are shown in fig. 6 and 7: the vibration exciter drives the extrusion female die or extrusion core rod with a single step to make a forward distance S with a certain frequency and amplitude1Greater than the back-off distance S2The reciprocating motion of the extrusion die is shown in figure 8, the outer side surface or the inner hole surface of the powder metallurgy part preform is extruded under the lubricating condition of the lubricant (c), so that the metal of the outer side surface layer or the inner hole surface layer of the preform is plastically deformedAnd (4) pressing and closing the original coarse pores (IV) of the outer surface layer or the inner hole surface layer of the preformed blank, forming a high-density layer with only a few residual micropores (V) on the outer surface layer or the inner hole surface layer of the preformed blank, and forming the surface-densified powder metallurgy part (VI) with high dimensional precision and high surface quality.
It should be noted that the surface vibration pressing densification strengthening technique provided by the present application has at least the following advantages over the currently common surface densification forming processing method:
A. compared with the surface shot blasting densification strengthening technology:
the application provides a surface vibration extrusion densification intensification technique can be through the outside surface of extrusion die vibration extrusion powder metallurgy part prefabricated base, also can be through the hole surface of extrusion core rod vibration extrusion powder metallurgy part prefabricated base, can accomplish the densification of powder metallurgy part outside surface and hole surface and strengthen. In the vibration extrusion process, the whole outside surface layer metal or the whole inner hole surface layer metal of the powder metallurgy part prefabricated blank is subjected to progressive approximate equal pressure extrusion of an extrusion female die or an extrusion core rod respectively, random discrete impact of high-speed steel shots when shot blasting is compared, extrusion force is more uniform, the surface layer metal plastic flow of the powder metallurgy part prefabricated blank is more uniform, and surface layer densification is more uniform. The method adopts an extrusion female die or an extrusion core rod to carry out rigid constraint extrusion on a prefabricated blank of the powder metallurgy part, and can form the surface densified powder metallurgy part with high dimensional precision and high surface quality while finishing the surface vibration extrusion densification strengthening of the powder metallurgy part.
B. Compared with the surface rolling densification strengthening technology:
the surface vibration extrusion densification strengthening technology provided by the application controls the densification effect and the shape and size precision of the surface densification powder metallurgy part through the rigid constraint of an extrusion die (an extrusion female die, an extrusion core rod and the like), more easily ensures the surface densification forming processing effect of the powder metallurgy part, and has lower requirements on vibration extrusion equipment. In the vibration extrusion process, the outer side surface or the inner hole surface of the powder metallurgy part prefabricated blank is subjected to extrusion force in the whole circumferential direction, the prefabricated blank is more uniformly stressed, the plastic flow of surface layer metal is more uniform, the densification is more uniform, and the densification effect and the shape and size precision of the final part are ensured.
The extrusion die can carry out continuous surface vibration extrusion processing on a plurality of powder metallurgy part prefabricated blanks along the axial direction of the powder metallurgy part prefabricated blanks, can realize the continuous production of the surface vibration extrusion of the powder metallurgy part prefabricated blanks, reduces the clamping times of the prefabricated blanks and improves the processing efficiency. Meanwhile, the adopted integral rigid die can more easily ensure the extrusion deformation of the powder metallurgy part prefabricated blank in batch production, avoid repeated assembly errors of the extrusion die in the extrusion process and process the surface densified powder metallurgy part with better consistency.
In addition, the surface vibration extrusion densification strengthening technology provided by the application not only can finish the surface densification forming processing of the axisymmetric powder metallurgy part preform, but also can finish the surface densification forming processing of the non-axisymmetric powder metallurgy part preform and the surface densification forming processing of the inner hole of the axisymmetric or non-axisymmetric powder metallurgy part preform.
C. Compared with the surface one-time direct extrusion densification strengthening technology:
the application provides an extrusion die or extrusion plug can process into single step or multistage step among the surface vibration extrusion densification strengthening technique, compare in the whole extrusion die of the used multistage reducing of the once direct extrusion densification processing of current surface's combination extrusion die and many steps variable cross sections, vibration extrusion die's structure is simpler, and processing is easier, and the precision also guarantees more easily, and mould manufacturing cost is lower.
Through the extrusion die of vibration or extrusion plug with certain frequency and amplitude, reciprocal outside surface or the hole surface of extrusion powder metallurgy part preformed blank, replace the extrusion process of the once direct extrusion of current surface with the gradual extrusion process of a plurality of little increments, make the area that the preformed blank top layer received extrusion load effect in single reciprocal extrusion cycle little, and surface metal is under the reciprocal stress action, the deformation resistance reduces, surface metal plastic flow is more abundant, the densification of the surperficial compact layer of formation is more even, show simultaneously and reduce extrusion load, reduce extrusion die's wearing and tearing, the life of extension extrusion die, the processingquality and the mechanical properties of the powder metallurgy part of improvement surface densification. The surface layer metal of the powder metallurgy part preform continuously releases stress in the retraction process of each extrusion period of the extrusion female die or the extrusion core rod, so that the accumulated elastic deformation of the surface layer of the preform is obviously reduced, the rebound quantity of the powder metallurgy part after surface vibration extrusion is reduced, and the shape and the size precision of the surface densified powder metallurgy part are better ensured.
In addition, during each return stroke of the extrusion die or the extrusion core rod, lubricant can enter the interface between the powder metallurgy part preform and the extrusion die, so that the lubricating effect is greatly improved, the extrusion load is further reduced, the abrasion of the extrusion die is obviously reduced, and the surface quality (shape tolerance, smoothness and the like) of the surface densified powder metallurgy part is improved.
Furthermore, the application also relates to a powder metallurgy part which is prepared by the preparation method. The powder metallurgy part has low extrusion load, good surface quality after extrusion, small rebound quantity, more uniform densification of a dense layer, high hardness and good wear resistance.
In alternative embodiments, the powder metallurgy part has a porosity of less than 2% and a dense layer depth of 0.1 to 1.0mm, such as 0.1mm, 0.2mm, 0.3mm, 0.5mm, or 1.0mm, and the like. Furthermore, in other alternative embodiments, the depth of the dense layer with a porosity of less than 2% may also exceed 1.0 mm.
In an alternative embodiment, the hardened layer depth of the powder metallurgy part is not less than the densified layer depth.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The embodiment provides an outside surface vibration pressing densification powder metallurgy wear-resistant ring, which mainly comprises the following preparation processes:
according to the components of the powder metallurgy wear-resistant ring: fe-0.5Mo-2Cu-0.6C (wt%), weighing Fe-Mo prealloying powder, copper powder, graphite powder and lubricant according to the proportion, and uniformly mixing in a mixer;
placing the mixed powder into a powder forming die, and pressing to form a pre-blank of the powder metallurgy wear-resistant ring, wherein the shape and the size of the pre-blank are similar to those of the final powder metallurgy wear-resistant ring, and the porosity of the pre-blank is about 10%;
thirdly, sintering the pressed green compact of the prefabricated blank in a sintering furnace at 1150 ℃ for 60min to prepare the prefabricated blank of the powder metallurgy wear-resistant ring;
and fourthly, placing the prefabricated blank of the powder metallurgy wear-resistant ring in a surface vibration extrusion die with a step angle alpha of 5 degrees, and performing vibration extrusion on the outer side surface of the prefabricated blank of the wear-resistant ring under the conditions that the frequency is 20Hz, the amplitude is 1mm and the extrusion feed amount of one vibration period is 0.4mm, wherein the radial extrusion amount is 0.3mm, so as to obtain the powder metallurgy wear-resistant ring densified by vibration extrusion on the outer side surface.
The photograph of the outer surface of the powder metallurgy wear-resistant ring densified by vibration compaction on the outer surface obtained in this example is shown in fig. 9 (c).
Further, control 1 and control 2 were provided, and control 1 was different from example 1 in that: no extrusion is carried out; control 2 differs from example 1 in that: the preform is directly extruded once using the same extrusion die.
The photograph of the appearance of the powder metallurgy wear-resistant ring obtained by non-pressing of the control group 1 is shown in fig. 9(a), and the photograph of the appearance of the powder metallurgy wear-resistant ring obtained by directly pressing the surface of the control group 2 once is shown in fig. 9 (b).
Further, the load-displacement relationship during the extrusion of the preforms of the control group 2 and example 1 was examined, and the results (load-displacement graph) are shown in fig. 10.
The micro-pore morphology of the outer side surface of the powder metallurgy wear-resistant ring obtained in the control group 1, the control group 2 and the example 1 is compared, and the corresponding photos of the micro-pore morphology are shown in fig. 11 to 13.
The pair of the inner diameter of the vibrating extrusion die used in the preparation process and the outer diameter of the powder metallurgy wear-resistant ring obtained in the comparison group 2 and the example 1 is shown in FIG. 14.
The hardness ratio of the outer surface of the powder metallurgy wear-resistant ring obtained in comparison 1, comparison 2 and example 1 is shown in fig. 15.
The wear amounts (wear resistances) of the outer side surfaces of the powder metallurgy wear-resistant rings obtained in the control 1, the control 2 and the example 1 under the same wear test conditions are shown in fig. 16.
It can be seen from the above photographs and diagrams that the surface vibration extrusion mode significantly improves the surface quality, surface layer density, surface layer hardness and wear resistance of the powder metallurgy wear-resistant ring compared with the non-extrusion mode or the one-time direct extrusion mode. And compared with the one-time direct extrusion of the surface, the extrusion load of the powder metallurgy wear-resistant ring extruded by surface vibration is lower, the surface quality is better after extrusion, the rebound quantity is smaller, the densification of the dense layer is more uniform, the hardness is higher, and the wear resistance is better.
Example 2
The embodiment provides a powder metallurgy wear-resistant ring densified by inner hole surface vibration and extrusion, which mainly comprises the following steps:
firstly, according to the components of a powder metallurgy wear-resistant ring: fe-2Cu-0.6C (wt%), weighing iron powder, copper powder, graphite powder and a small amount of lubricant according to the proportion, and uniformly mixing in a mixer;
placing the mixed powder into a powder forming die, and pressing to form a pre-blank of the powder metallurgy wear-resistant ring, wherein the shape and the size of the pre-blank are similar to those of the final powder metallurgy wear-resistant ring, and the porosity of the pre-blank is about 10%;
thirdly, sintering the pressed green body of the prefabricated blank in a sintering furnace at 1200 ℃ for 30min to obtain the prefabricated blank of the powder metallurgy wear-resistant ring.
And fourthly, placing the prefabricated blank of the powder metallurgy wear-resistant ring in a surface vibration extrusion die with a step angle of 60 degrees, and performing vibration extrusion on the inner hole surface of the prefabricated blank of the wear-resistant ring under the conditions that the frequency is 35Hz, the amplitude is 2.5mm and the extrusion feeding amount in one vibration period is 0.5mm, wherein the radial extrusion amount is 0.2 mm.
Furthermore, a control group 3 was provided, and the control group 3 was different from example 2 in that: no extrusion was performed. The photograph of the micro-pore morphology of the inner bore surface of the powder metallurgy wear-resistant ring obtained by non-pressing in the control group 3 is shown in fig. 17, and the photograph of the micro-pore morphology of the inner bore surface of the powder metallurgy wear-resistant ring obtained by vibration pressing densification of the inner bore surface in the embodiment is shown in fig. 18.
As can be seen from FIGS. 17 and 18, the surface vibration extrusion obviously improves the compactness of the inner hole surface of the powder metallurgy wear-resistant ring, and the depth of the compact layer with the porosity lower than 2 percent is about 0.5 mm.
Example 3
The embodiment provides a tooth surface vibration pressing densification powder metallurgy gear, and the preparation process mainly comprises the following steps:
according to the components of the powder metallurgy gear: fe-2Cu-0.6C (wt%), weighing iron powder, copper powder, graphite powder and lubricant according to the proportion, and uniformly mixing in a mixer;
placing the mixed powder into a powder forming die, and pressing to form a pre-blank of the powder metallurgy gear, wherein the shape and the size of the pre-blank are similar to those of the final powder metallurgy gear, and the porosity of the pre-blank is about 10%;
thirdly, sintering the pressed green compact of the prefabricated blank in a sintering furnace at 1120 ℃ for 45min to prepare the prefabricated blank of the powder metallurgy gear;
and fourthly, placing the prefabricated blank of the prepared powder metallurgy gear into a surface vibration extrusion die with a step angle of 30 degrees, and performing vibration extrusion on the surface of the tooth part of the prefabricated blank of the gear under the conditions that the frequency is 50Hz, the amplitude is 0.5mm and the extrusion feed amount in one vibration period is 0.2mm, wherein the radial extrusion amount is 0.5 mm.
The microscopic pore morphology photograph of the surface vibration pressing powder metallurgy gear tooth surface obtained in this example is shown in fig. 19.
As can be seen from the figure, the surface vibration pressing can make the tooth surface of the powder metallurgy gear have higher compactness. In addition, the porosity of the powder metallurgy gear obtained in the embodiment is lower than 2% and the depth of the dense layer is about 0.3-0.4 mm.
Example 4
The embodiment provides a tooth surface vibration extrusion densification and surface quenching powder metallurgy chain wheel, and the preparation process mainly comprises the following steps:
according to the components of the powder metallurgy chain wheel: fe-2Cu-0.6C (wt%), weighing iron powder, copper powder, graphite powder and lubricant according to the proportion, and uniformly mixing in a mixer;
placing the mixed powder into a powder forming die, and pressing to form a powder metallurgy chain wheel prefabricated blank with the shape and the size similar to those of the final powder metallurgy chain wheel and the porosity of about 8%;
thirdly, sintering the pressed pre-formed blank in a sintering furnace at 1200 ℃ for 30min to prepare a powder metallurgy chain wheel pre-formed blank;
and fourthly, placing the powder metallurgy chain wheel prefabricated blank in a surface vibration extrusion die with a step angle alpha of 60 degrees, and performing vibration extrusion on the tooth part surface of the chain wheel prefabricated blank under the conditions that the frequency is 25Hz, the amplitude is 2.5mm and the extrusion feed amount in one vibration period is 0.25mm, wherein the radial extrusion amount is 0.3 mm.
Fifthly, carrying out high-frequency induction heating quenching on the tooth part of the powder metallurgy chain wheel after the surface vibration extrusion densification, and then tempering at low temperature of 200 ℃.
The depth of the hardened tooth layer of the obtained powder metallurgy sprocket is about 1.2 mm.
Example 5
The embodiment provides a tooth surface vibration extrusion densification and surface carburizing quenching powder metallurgy gear, the preparation process mainly comprises:
the method comprises the following steps of: fe-0.5Mo-2Cu-0.35C (wt%), weighing Fe-Mo prealloying powder, copper powder, graphite powder and lubricant according to the proportion, and uniformly mixing in a mixer;
placing the mixed powder into a powder forming die, and pressing to form a powder metallurgy gear preformed blank with the shape and the size similar to those of the final powder metallurgy gear and the porosity of about 8%;
thirdly, sintering the pressed green compact of the prefabricated blank in a sintering furnace at 1150 ℃ for 60min to obtain a powder metallurgy gear prefabricated blank;
and fourthly, placing the powder metallurgy gear preform in a surface vibration extrusion die with a step angle alpha of 5 degrees, and performing vibration extrusion on the surface of the tooth part of the gear preform under the conditions that the frequency is 20Hz, the amplitude is 1mm and the extrusion feed amount in one vibration period is 0.2mm, wherein the radial extrusion amount is 0.3 mm.
And fifthly, performing carburizing and quenching on the powder metallurgy gear with the surface subjected to vibration extrusion densification, wherein the carburizing temperature is 920 ℃, the time is 120min, the depth of a carburized layer is about 1.0mm, quenching is performed after carburizing, and low-temperature tempering is performed at 200 ℃.
In summary, the surface vibration extrusion densification strengthening technology provided by the application can provide uniform extrusion force, so that the surface metal of the powder metallurgy part preform can flow plastically and the surface densification is more uniform, the method is easy to process, the shape and the size precision of the powder metallurgy part can be better ensured, meanwhile, the extrusion load can be reduced, the abrasion of an extrusion die is reduced, the service life of the extrusion die is prolonged, and the processing quality and the mechanical property of the powder metallurgy part are improved. The prepared powder metallurgy part has low extrusion load, good surface quality after extrusion, small rebound quantity, more uniform densification of a dense layer, high hardness and good wear resistance.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The preparation method of the powder metallurgy part is characterized by comprising the following steps: and carrying out vibration extrusion on the surface of the powder metallurgy part preform.
2. The production method according to claim 1, wherein the surface of the powder metallurgy part preform is subjected to vibration extrusion by an extrusion die in a reciprocating state, wherein the reciprocating direction of the extrusion die is the axial direction of the extrusion die;
or fixing the extrusion die, and reciprocating the powder metallurgy part preform to perform vibration extrusion on the surface of the powder metallurgy part preform, wherein the reciprocating direction of the powder metallurgy part preform is the axial direction of the extrusion die;
preferably, the advancing distance of the extrusion die is larger than the retreating distance during each reciprocating motion;
preferably, the extrusion die comprises an extrusion die or an extrusion core rod;
preferably, the extrusion die has a step, more preferably, the extrusion die has a single step;
preferably, the surface of the powder metallurgy part preform comprises an outside surface of the powder metallurgy part preform and/or an inner bore surface of the powder metallurgy part preform;
preferably, during the vibration extrusion process, a lubricant is filled between the extrusion die and the surface of the powder metallurgy part preform.
3. The production method according to claim 2, wherein the vibration frequency of the vibration extrusion is 0.1 to 1000Hz, and the amplitude is 0.1 to 50 mm.
4. The production method according to claim 2, wherein a press feed amount in each vibration cycle is 0.01 to 5mm, which is a value obtained by subtracting the retreat distance from the advance distance.
5. The production method according to claim 2, wherein an extrusion deformation amount perpendicular to a moving direction of the extrusion die during the vibration extrusion is 0.05 to 5 mm.
6. The production method according to claim 2, wherein the step angle of the extrusion die is 1 to 89 °.
7. The method according to claim 1 or 2, wherein the powder metallurgy part preform is mainly prepared by the following steps: sintering the green body of the powder metallurgy part prefabricated blank;
preferably, the sintering temperature is 0.45-0.9 times the melting point of the main component material in the green body of the powder metallurgy part prefabricated blank;
preferably, the sintering time is 5-150 min.
8. The method of claim 7, wherein the green compact of the powder metallurgy part preform is mainly prepared by pressing raw materials mixed according to the mixture ratio;
preferably, the porosity of the green compact of the powder metallurgy part preform is less than 30%;
preferably, the extrusion deformation amount of 0.05-5mm is reserved in the pressing process.
9. The production method according to claim 1 or 2, further comprising performing heat treatment after the vibration extrusion;
preferably, the heat treatment comprises quenching treatment and low-temperature tempering treatment;
preferably, the quenching treatment includes high-frequency induction hardening or carburizing and quenching;
preferably, the carburizing and quenching is to perform carburizing treatment for 20-200min at the temperature of 800-1000 ℃ and then to perform quenching; more preferably, the carburizing is carried out at 920 ℃ for 120 min;
preferably, the temperature of the low temperature tempering treatment is 100-250 ℃, more preferably 200 ℃.
10. A powder metallurgical part, characterized by being produced by the production method according to any one of claims 1 to 9.
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| CN116252035A (en) * | 2023-05-15 | 2023-06-13 | 杭州沈氏节能科技股份有限公司 | Step-by-step continuous diffusion welding equipment and diffusion welding method |
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| EP3181249A1 (en) * | 2015-12-15 | 2017-06-21 | FELSS Systems GmbH | Method and device for forming a workpiece by impact extrusion |
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