CN115839399A - Harmonic speed reducer rigid gear and preparation method and application thereof - Google Patents
Harmonic speed reducer rigid gear and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a harmonic speed reducer rigid wheel and a preparation method and application thereof. According to the harmonic reducer rigid gear, the base material is the nodular cast iron, and the nodular cast iron is treated through spheroidization and inoculation, so that carbon is separated out in the form of spheroidal graphite, more granular graphite is obtained, and the lubricating property is better, so that the harmonic reducer rigid gear has good castability, wear resistance and cutting processability. Compared with the existing materials, the harmonic speed reducer rigid wheel provided by the invention has excellent mechanical properties and machining process properties under a specific raw material proportion, and can further improve the mechanical properties through heat treatment, so that the harmonic speed reducer rigid wheel is ensured to have good mechanical properties. The invention also provides a preparation method and application of the harmonic speed reducer rigid wheel.
Description
Technical Field
The invention belongs to the technical field of speed reducers, and particularly relates to a harmonic speed reducer rigid gear, and a preparation method and application thereof.
Background
The harmonic reducer has the advantages of compact structure, small volume, light weight, large transmission ratio and bearing capacity, high transmission precision and the like, and is widely applied to the industries of electronics, aerospace, robots, automation and the like. The main structure of the harmonic speed reducer comprises three basic components, namely a wave generator, a flexible gear and a rigid gear. Wherein, the wave generator comprises flexible bearing and cam. The flexible gear is a flexible external gear, and the rigid gear is a rigid internal gear ring.
Harmonic reducers transmit motion through tooth-to-tooth meshing. In the whole movement process, the meshing area of the inner teeth and the outer teeth is large, the meshing tooth pair number accounts for about 30%, the inner teeth of the rigid gear are meshed with the outer teeth of the flexible gear, the meshing number of the teeth is related to the working condition, the larger the torque is, the more the number of the meshed teeth is, the flexible gear is of a thin-wall structure and presents the same shape as the cam after the wave generator is assembled, the end face of the flexible gear presents a periodic bell mouth deformation form in the operation process of the wave generator, the end face of the flexible gear is a curved surface, the tooth face of the flexible gear and the tooth face of the rigid gear have meshing relative movement, namely tangential relative movement and tooth direction movement caused by deformation of the flexible gear, the meshing bearing of the teeth of the flexible gear and the teeth of the rigid gear realizes the transmission of the force and the movement of the harmonic reducer, the contact between the teeth is similar to linear contact, experiments show that the lubricating state between the teeth of the rigid gear and the flexible gear is mixed lubrication, and therefore the rigid gear and the flexible gear are required to have high wear resistance. In the related art, the wear resistance of the rigid wheel is not ideal.
Disclosure of Invention
The present invention is directed to solving at least one of the above problems in the prior art. Therefore, the harmonic reducer rigid gear has high wear resistance and mechanical strength through the ball-milling cast iron with the specific raw material proportion.
The invention also provides a method for preparing the rigid wheel of the harmonic speed reducer.
The invention also provides a harmonic speed reducer.
The invention also provides an industrial robot.
The invention provides a harmonic reducer rigid gear, wherein a base material of the harmonic reducer rigid gear is nodular cast iron, and the nodular cast iron is prepared from the following raw materials in percentage by mass:
C：3.0％～4.0％，
Si：2.0％～3.0％，
Cu：0.5％～1.0％，
Mn：≤1.0％，
Cr：≤0.1％，
P：≤0.1％，
S：≤0.06％，
in the nodular cast iron, the graphite spheroidization rate of a metallographic structure is more than or equal to 95 percent.
The invention relates to a technical scheme of a rigid wheel of a harmonic speed reducer, which at least has the following beneficial effects:
according to the rigid gear of the harmonic reducer, the base material is nodular cast iron, and the graphite spheroidization rate of a metallographic structure in the nodular cast iron is more than or equal to 95%, so that the rigid gear meets the primary spheroidization standard specified in GB/T9441-2009. The nodular cast iron is cast iron with carbon precipitated as spheroidal graphite and obtained through spheroidization and inoculation, and has good castability, wear resistance and machinability. The harmonic speed reducer rigid wheel has excellent mechanical property and process property under the condition of specific raw material proportion, and can further improve the mechanical property through heat treatment, so the nodular cast iron can be used for manufacturing parts with larger load and more complex stress, such as crankshafts, connecting rods, gears, machine tool spindles and the like, and is particularly suitable for the harmonic speed reducer rigid wheel.
The base material of the harmonic reducer rigid wheel is nodular cast iron, carbon is an element for crystallizing and separating out the spheroidal graphite in the preparation raw materials, and the content of the carbon in the range of 3.0-4.0% enables the spheroidal graphite to be crystallized and separated out. Silicon is also an element for crystallizing spherical graphite, and the silicon content in the range of 2.0% to 3.0% is advantageous for crystallizing spherical graphite and can suppress generation of dross defects and floating of graphite. Copper can inhibit carbide, and is beneficial to obtaining spherical graphite. Manganese is an element which makes graphite fine and strengthens a pearlite structure, and the range of manganese of not more than 1.0% is advantageous for exerting its effect. The chromium has the functions of promoting the growth of pearlite, improving the toughness and refining a matrix. Phosphorus and sulfur are inevitable impurities in the nodular cast iron, and the content of the phosphorus and the sulfur can be reduced as much as possible.
According to some embodiments of the invention, the ductile iron comprises 3.2 to 4.0% by mass of carbon.
According to some embodiments of the invention, the ductile iron comprises 3.5 to 4.0% by mass of carbon.
According to some embodiments of the invention, the ductile iron comprises carbon in an amount of 3.8 to 4.0% by mass.
According to some embodiments of the invention, the silicon content of the nodular cast iron is 2.2% to 3.0% by mass.
According to some embodiments of the invention, the silicon content of the nodular cast iron is 2.5% to 3.0% by mass.
According to some embodiments of the invention, the silicon content of the nodular cast iron is 2.7% to 3.0% by mass.
According to some embodiments of the invention, the nodular cast iron comprises 0.6 to 1.0% by mass of copper.
According to some embodiments of the invention, the nodular cast iron comprises 0.7 to 1.0% by mass of copper.
According to some embodiments of the invention, the nodular cast iron comprises manganese in an amount of 1.0% by mass or less.
According to some embodiments of the present invention, the nodular cast iron may have a manganese content of 0.7% by mass.
According to some embodiments of the present invention, the nodular cast iron may have a manganese content of 0.5% by mass.
According to some embodiments of the present invention, the nodular cast iron may have a manganese content of 0.2% by mass.
According to some embodiments of the invention, the nodular cast iron comprises 0.03 to 0.06% by mass of chromium.
According to some embodiments of the present invention, the nodular cast iron may have a chromium content of 0.05% by mass.
According to some embodiments of the present invention, the nodular cast iron may have a chromium content of 0.04% by mass.
According to some embodiments of the invention, the nodular cast iron has a composition of P: less than or equal to 0.1 percent, and phosphorus is an inevitable impurity in the nodular cast iron, and the content of the phosphorus can be reduced as much as possible.
According to some embodiments of the invention, in the spheroidal graphite cast iron, S: less than or equal to 0.06 percent, and sulfur is an inevitable impurity in the nodular cast iron, and the content of the sulfur can be reduced as much as possible.
The proportioning range is the proportioning range of the raw materials for preparing the proper nodular cast iron.
According to some embodiments of the invention, the metallographic structure in the spheroidal graphite cast iron comprises cementite and a phosphorus eutectic.
Cementite is a metal compound formed by iron and carbon, has a complex orthorhombic crystal structure, is a main strengthening phase in nodular cast iron, and the shape and distribution of the cementite have great influence on the performance of steel. In nodular cast iron, cementite appears in the structure in crystals of different shapes and sizes, and has great influence on the mechanical properties of the nodular cast iron.
In general cast iron, phosphorus eutectic with carbon and iron increases brittleness of cast iron, and thus phosphorus is treated as an impurity element. However, in wear-resistant cast iron, the phosphorus eutectic is beneficial to improving the wear resistance of the cast iron under certain conditions.
According to some embodiments of the invention, the cementite comprises free cementite.
Free cementite means cementite existing as a separate phase from a mechanical mixture (structure) such as ledeburite (eutectic structure) after dissociating in pearlite (eutectoid structure). Free cementite has a negative effect on the material properties and the content of free cementite needs to be controlled by controlling the cooling rate. The free cementite in the present invention mainly refers to primary cementite.
According to some embodiments of the invention, the tensile strength of the ductile iron is 1100MPa or more.
The tensile strength of the nodular cast iron is more than or equal to 1100MPa, and the higher mechanical strength of the rigid gear of the harmonic speed reducer is ensured.
The second aspect of the invention provides a method for preparing the rigid wheel of the harmonic speed reducer, which comprises the following steps:
s1: carrying out rough machining on the nodular cast iron base material to obtain a semi-finished rigid wheel;
s2: and carrying out heat treatment on the semi-finished rigid wheel, and then carrying out finish machining to obtain the harmonic speed reducer rigid wheel.
The invention relates to a technical scheme in a preparation method of a harmonic reducer rigid gear, which at least has the following beneficial effects:
according to the preparation method of the harmonic speed reducer rigid wheel, firstly, the ball-milling cast iron base material is subjected to rough machining to obtain a rigid wheel semi-finished product, then, after the rigid wheel semi-finished product is subjected to heat treatment, the nodular cast iron base material is strengthened, the base material has better toughness, and finally, the fine machining is performed, so that the harmonic speed reducer rigid wheel with composite requirements on performance and precision can be obtained. The heat treatment process is a key process in the preparation of the harmonic reducer, and the hardness after heat treatment directly influences the wear resistance of the rigid wheel.
The preparation method of the harmonic reducer rigid wheel does not need expensive equipment and complex process control, and the preparation process is relatively simple and easy to control.
According to the preparation method of the harmonic reducer rigid gear, firstly, the ball-milling cast iron base material is subjected to rough machining, and then is subjected to finish machining after heat treatment, so that on one hand, the possible dimensional change of the rigid gear precision in the heat treatment process is avoided; on the other hand, the finally prepared rigid gear of the harmonic speed reducer has more excellent performance through a mode of combining rough machining and finish machining.
According to some embodiments of the invention, the metallographic structure in the semi-finished rigid wheel comprises spheroidal graphite, pearlite and ferrite.
The spherical graphite can reduce the cracking effect on the cast iron matrix to the minimum, so that the stress concentration effect in the cast iron is the minimum, and the strength of the nodular cast iron is very high and can be compared favorably with medium carbon steel. The nodular cast iron is used as a base material and can be used for manufacturing workpieces with high toughness requirements and complex shapes. When the method is used for processing the harmonic speed reducer rigid wheel, the performance of the nodular cast iron matrix can be fully exerted, so that the prepared harmonic speed reducer rigid wheel has certain plasticity and good toughness.
Under casting conditions, the ductile iron undergoes solid-state phase transformation in a eutectoid transformation stage according to a stable system and a metastable system, and nucleation and growth of ferrite and pearlite occur.
According to some embodiments of the invention, the ductile iron substrate may be self-prepared. The preparation method comprises the following steps: according to the proportion, melting the metal raw materials, and then carrying out spheroidization on the molten metal. Wherein, the spheroidizing treatment has the functions of making the graphite into a spherical shape during the crystal growth, more granular graphite and better lubricating property, and improving the mechanical property of the casting.
According to some embodiments of the present invention, the spheroidizing agent comprises 30 to 70% of metallic magnesium powder, 18 to 60% of MgO, and 10 to 12% of a binder (e.g., phenolic resin). Wherein the particle size of the metal magnesium powder is 0.05 mm-0.145 mm.
According to some embodiments of the invention, roughing includes pouring the molten metal into a mold, inoculating with an inoculant, wherein the purpose of the inoculation is to eliminate white notches, increase eutectic clusters, graphite nodules and refining, eliminate segregation, eliminate the tendency to undercooling, and the like. The inoculant can be Si-Fe and the like. And obtaining a semi-finished rigid wheel from the casting mould after cooling.
Before heat treatment, the metallographic structure of the semi-finished rigid wheel consists of spherical graphite and a matrix structure. Wherein the matrix structure comprises pearlite and ferrite. Ferrite is a single-phase structure, is an interstitial solid solution formed by dissolving carbon in alpha-Fe, and has low strength and hardness, but good plasticity and toughness. Pearlite is a two-phase structure, a mechanical mixture of ferrite and cementite, which is a metal compound formed by iron and carbon and has the chemical formula of Fe 3 And C, the pearlite strength and the hardness are high. The semi-finished steel wheel with the above-described metallographic structure can balance strength and plasticity by ferrite and pearlite.
According to some embodiments of the invention, the graphite spheroidization rate of the metallographic structure in the semi-finished rigid wheel is more than or equal to 70%.
According to some embodiments of the invention, the metallographic structure of the semi-finished rigid wheel before the heat treatment comprises spheroidal graphite, bovine eyeball structure and ferrite. Wherein, the graphite spheroidization rate is more than 80 percent, and the ferrite content is less than 25 percent. The bullseye structure is a structure similar to the bullseye shape formed by surrounding ferrite around spherical graphite and pearlite around the periphery of the ferrite, the ferrite content in the bullseye structure is below 25 percent, and the ferrite content in the whole metallographic structure is below 25 percent. The semi-finished rigid wheel with the metallographic structure before heat treatment has good strength and hardness performance, is favorable for preparing a wear-resistant rigid wheel, and is particularly suitable for a rigid wheel for a harmonic reducer.
In the semi-finished product of the rigid wheel, the graphite spheroidization rate of a metallographic structure is more than or equal to 70%, the mechanical property of the finished harmonic reducer rigid wheel is ensured, and particularly, the impact strength, the fatigue property, the corrosion resistance and the wear resistance of the nodular cast iron are improved.
According to some embodiments of the invention, the heat treatment comprises a normalizing treatment.
According to some embodiments of the invention, the normalizing process comprises: firstly, heating a semi-finished product of the rigid wheel to a certain temperature above eutectoid temperature, and preserving heat for a period of time, wherein the nodular cast iron base material is austenitized; then cooling to a bainite transformation region in a cooling chamber at a cooling speed higher than that of pearlite formation for isothermal treatment, wherein an austenitizing part is transformed into bainite at the time, and the strength and the toughness of the bainite are higher. The cooling mode can be water quenching.
According to some embodiments of the invention, the quenching temperature of the normalizing treatment is 830 ℃ to 950 ℃, which is a temperature range "above the eutectoid temperature".
According to some embodiments of the invention, the quenching temperature of the normalizing treatment is 870 ℃ to 950 ℃.
According to some embodiments of the invention, the quenching temperature of the normalizing treatment is 900 ℃ to 950 ℃.
According to some embodiments of the invention, the holding time for the normalizing treatment is 1h to 4h.
According to some embodiments of the invention, the holding time for the normalizing treatment is 2h to 4h.
According to some embodiments of the invention, the holding time for the normalizing treatment is 3h to 4h.
After the ductile cast iron is subjected to the normalizing treatment process, the strength, the hardness and the wear resistance are improved.
After the ductile cast iron is subjected to the normalizing treatment process, the surface hardness of the semi-finished rigid wheel is 330 HBW-360 HBW.
After the ductile cast iron is subjected to the normalizing treatment process, the surface hardness of the semi-finished rigid wheel is 340 HBW-360 HBW.
After the ductile cast iron is subjected to the normalizing treatment process, the surface hardness of the semi-finished rigid wheel is 350 HBW-360 HBW.
After the ductile cast iron is subjected to the normalizing treatment process, the tensile strength of the semi-finished rigid gear is more than or equal to 1100MPa.
The hardness and tensile strength show that the semi-finished rigid wheel after heat treatment has better wear resistance.
When the semi-finished product of the rigid wheel after heat treatment is subjected to a thermal deformation test under the condition of keeping the temperature at 170 ℃ for 24 hours, the measured dimensional change is below 0.01 percent, which shows that the semi-finished product of the rigid wheel obtained after heat treatment and before finish machining has higher thermal stability.
According to some embodiments of the invention, the finishing comprises grinding the heat-treated semi-finished rigid wheel to form the finished rigid wheel.
A third aspect of the present invention provides a harmonic speed reducer in which the harmonic speed reducer rigid gear of the present invention is provided.
The invention relates to a technical scheme of a harmonic speed reducer, which at least has the following beneficial effects:
the main structure of the harmonic speed reducer comprises three basic components, namely a wave generator, a flexible gear and a rigid gear. In the harmonic reducer, the rigid wheel is made of the ball-milling cast iron with a specific raw material ratio, so that the harmonic reducer has high wear resistance and mechanical strength and is more durable, and the service life, stability and reliability of the harmonic reducer are prolonged.
A fourth aspect of the present invention provides an industrial robot in which the harmonic reducer rigid gear of the present invention or the harmonic reducer of the present invention is disposed.
The invention relates to a technical scheme of an industrial robot, which at least has the following beneficial effects:
industrial robots are multi-joint manipulators or multi-degree-of-freedom machine devices widely used in the industrial field, have a certain degree of automation, and can realize various industrial processing and manufacturing functions depending on the power energy and control capability of the industrial robots. Industrial robots are widely used in various industrial fields such as electronics, logistics, and chemical industry. The speed reducer is one of important parts of the industrial robot, and the harmonic speed reducer rigid wheel is assembled in the speed reducer, so that the comprehensive performance is better, the service life of the speed reducer is directly prolonged, and the fault rate of the industrial robot is also reduced.
Drawings
Fig. 1 is a schematic structural diagram of a rigid wheel of a harmonic reducer.
Fig. 2 is a flow chart of the preparation of a rigid wheel of a harmonic reducer.
Fig. 3 is a metallographic structure diagram of a rigid gear of a harmonic reducer prepared in the example.
FIG. 4 is a schematic representation of the surface of a rigid wheel prepared in accordance with an example prior to tooth flank wear.
FIG. 5 is a schematic surface view of a worn gear face of a rigid wheel prepared in accordance with an example.
Fig. 6 is a schematic surface view of a tooth surface of a steel wheel prepared in comparative example before being worn.
Fig. 7 is a schematic surface view of a gear tooth surface of a steel wheel prepared in comparative example after being worn.
Detailed Description
The following are specific examples of the present invention, and the technical solutions of the present invention will be further described with reference to the examples, but the present invention is not limited to the examples.
In some embodiments of the present invention, the present invention provides a rigid gear of a harmonic reducer, wherein a base material of the rigid gear of the harmonic reducer is nodular cast iron, and the nodular cast iron is prepared from Fe and the following components, by mass:
C：3.0％～4.0％，
Si：2.0％～3.0％，
Cu：0.5％～1.0％，
Mn：≤1.0％，
Cr：≤0.1％，
P：≤0.1％，
S：≤0.06％，
in the nodular cast iron, the graphite spheroidization rate of a metallographic structure is more than or equal to 95 percent.
The base material of the harmonic reducer rigid wheel is nodular cast iron. The spheroidal graphite cast iron is cast iron in which carbon obtained through spheroidization and inoculation is precipitated as spheroidal graphite, and has good castability, wear resistance and machinability. The harmonic reducer rigid gear has excellent mechanical property and technological property under the condition of specific raw material proportion, and the mechanical property of the harmonic reducer rigid gear can be further improved through heat treatment, so that the nodular cast iron can be used for manufacturing parts with larger load and more complex stress, such as crankshafts, connecting rods, gears, machine tool spindles and the like, and is particularly suitable for the harmonic reducer rigid gear.
It can be understood that the base material of the harmonic reducer rigid gear of the invention is nodular cast iron, carbon is an element required for the crystallization and precipitation of the spheroidal graphite in the preparation raw materials, and the carbon content in the range of 3.0-4.0% enables the spheroidal graphite to be crystallized and precipitated. Silicon is an element necessary for crystallization of spherical graphite, and the silicon content in the range of 2.0% to 3.0% is advantageous for crystallization of spherical graphite and can suppress generation of scum defects and floating of graphite. Copper can inhibit carbide, and is beneficial to obtaining spherical graphite. Manganese is an element that has the function of making graphite fine and strengthening the pearlite structure, and the above range of 1.0% or less is advantageous for exerting its function. The chromium has the functions of promoting the growth of pearlite, improving the toughness and refining a matrix. Phosphorus and sulfur are inevitable impurities in the nodular cast iron, and the content of the phosphorus and the sulfur can be reduced as much as possible.
In some embodiments of the invention, the ductile iron comprises 3.2 to 4.0% by mass of carbon.
Further, in some embodiments of the present invention, the ductile iron contains 3.5 to 4.0% by mass of carbon.
Further, in some embodiments of the present invention, the ductile iron contains 3.8% to 4.0% by mass of carbon.
In some embodiments of the invention, the silicon is present in the ductile iron in an amount of 2.2% to 3.0% by mass.
Further, in some embodiments of the present invention, the nodular cast iron has a silicon content of 2.5 to 3.0% by mass.
Further, in some embodiments of the present invention, the nodular cast iron has a silicon content of 2.7% to 3.0% by mass.
In some embodiments of the invention, the ductile iron comprises 0.6 to 1.0% by weight of copper.
Further, in some embodiments of the present invention, the nodular cast iron has a copper content of 0.7 to 1.0% by mass.
In some embodiments of the invention, the ductile iron comprises manganese in an amount of 1.0% by mass or less.
Further, in some embodiments of the present invention, the mass percentage of manganese in the ductile iron may be 0.7%.
Further, in some embodiments of the present invention, the mass percentage of manganese in the ductile iron may be 0.5%.
Further, in some embodiments of the present invention, the mass percentage of manganese in the ductile iron may be 0.2%.
In some embodiments of the invention, the nodular cast iron comprises 0.03 to 0.06 mass% chromium.
Further, in some embodiments of the present invention, the nodular cast iron may have a chromium content of 0.05% by mass.
Further, in some embodiments of the present invention, the nodular cast iron may have a chromium content of 0.04% by mass.
The proportioning range is the proportioning range of the raw materials for preparing the proper nodular cast iron.
In some embodiments of the invention, the metallographic structure in spheroidal graphite cast iron comprises cementite and a phosphorus eutectic.
It can be understood that cementite is a metal compound formed by iron and carbon, has a complex orthorhombic crystal structure, is a main strengthening phase in nodular cast iron, and the shape and distribution of the cementite have great influence on the performance of steel. In nodular cast iron, cementite appears in the structure in crystals of different shapes and sizes, and has a great influence on the mechanical properties of the nodular cast iron.
In general cast iron, phosphorus eutectic with carbon and iron increases brittleness of cast iron, and thus phosphorus is treated as an impurity element. However, in wear-resistant cast iron, the phosphorus eutectic is beneficial to improving the wear resistance of the cast iron under certain conditions.
In some embodiments of the invention, the cementite comprises free cementite.
Specifically, free cementite means cementite existing as a separate phase other than a mechanical mixture (structure) such as ledeburite (eutectic structure) after dissociating in pearlite (eutectoid structure). Free cementite has a negative effect on the material properties and the content of free cementite needs to be controlled by controlling the cooling rate. The free cementite in the present invention mainly refers to primary cementite.
In some embodiments of the invention, the tensile strength of the ductile iron is 1100MPa or greater.
As can be understood, the tensile strength of the nodular cast iron is more than or equal to 1100MPa, and the higher mechanical strength of the rigid gear of the harmonic reducer is ensured.
In further embodiments of the present invention, the present invention provides a method for manufacturing a harmonic reducer rigid gear, comprising the steps of:
s1: carrying out rough machining on the nodular cast iron base material to obtain a semi-finished rigid wheel;
s2: and (4) performing heat treatment on the semi-finished rigid wheel, and then performing finish machining to obtain the rigid wheel of the harmonic speed reducer.
The method for preparing the harmonic speed reducer rigid wheel comprises the steps of firstly carrying out rough machining on a ball-milling cast iron base material to obtain a rigid wheel semi-finished product, then carrying out heat treatment on the rigid wheel semi-finished product to strengthen the nodular cast iron base material, wherein the base material has better toughness, and finally carrying out finish machining to obtain the harmonic speed reducer rigid wheel with the composite requirements on performance and precision. The heat treatment process is a key process in the preparation of the harmonic reducer, and the hardness after heat treatment directly influences the wear resistance of the rigid wheel.
The method for preparing the rigid wheel of the harmonic reducer does not need expensive equipment and complex process control, and the preparation process is relatively simple and easy to control.
The method for preparing the rigid wheel of the harmonic reducer comprises the steps of firstly carrying out rough machining on a ball-milling cast iron base material, and then carrying out finish machining after heat treatment, so that on one hand, the dimensional change of the rigid wheel precision possibly brought in the heat treatment process is avoided; on the other hand, the finally prepared rigid gear of the harmonic speed reducer has more excellent performance through a mode of combining rough machining and finish machining.
In some embodiments of the invention, the metallographic structure in the semi-finished steel wheel comprises spheroidal graphite, pearlite and ferrite.
In particular, spheroidal graphite minimizes the effects of cracking the cast iron matrix and thus minimizes stress concentration in the cast iron, so that spheroidal graphite iron has high strength comparable to medium carbon steel. The nodular cast iron is used as a base material and can be used for manufacturing workpieces with high toughness requirements and complex shapes. When the method is used for processing the harmonic speed reducer rigid wheel, the performance of the nodular cast iron matrix can be fully exerted, so that the prepared harmonic speed reducer rigid wheel has certain plasticity and good toughness.
Under casting conditions, the ductile iron undergoes solid-state phase transformation in a eutectoid transformation stage according to a stable system and a metastable system, and nucleation and growth of ferrite and pearlite occur.
In some embodiments of the invention, the ductile iron substrate may be self-prepared. The preparation method comprises the following steps: according to the proportion, melting the metal raw materials, and then carrying out spheroidization on the molten metal. Wherein, the spheroidizing treatment has the function of making the graphite into a spherical shape during the crystal growth so as to improve the appearance of the base material and improve the mechanical property of the casting.
In some embodiments of the invention, the spheroidizing agent comprises 30 to 70% magnesium metal powder, 18 to 60% MgO, and 10 to 12% binder (e.g., phenolic resin). Wherein the particle size of the metal magnesium powder is 0.05 mm-0.145 mm.
In some embodiments of the invention, roughing includes pouring the molten metal into a mold, inoculating with an inoculant, wherein the purpose of the inoculation is to eliminate white cast, increase eutectic clusters, graphite nodules and refining, eliminate segregation, eliminate tendency to undercooling of the crystals, and the like. The inoculant can be Si-Fe and the like. And cooling and obtaining a semi-finished rigid wheel from the casting mould.
Specifically, before heat treatment, the metallographic structure of the semi-finished rigid wheel consists of spherical graphite and a matrix structure. Wherein the matrix structure comprises pearlite and ferrite. Ferrite is a single-phase structure, is an interstitial solid solution formed by dissolving carbon in alpha-Fe, and has low strength and hardness, but good plasticity and toughness. Pearlite is a two-phase structure, a mechanical mixture of ferrite and cementite, which is a metal compound formed by iron and carbon and has the chemical formula of Fe 3 C, pearliteHigh strength and hardness. The semi-finished steel wheel with the above-described metallographic structure can balance strength and plasticity by ferrite and pearlite.
In some embodiments of the present invention, the metallographic structure of the semi-finished rigid wheel has a graphite spheroidization rate of 70% or more.
In some embodiments of the present invention, the metallographic structure of the semi-finished rigid wheel before the heat treatment comprises spherical graphite, bullseye structure and ferrite. Wherein, the graphite spheroidization rate is more than 80 percent, and the ferrite content is less than 25 percent. The bullseye structure is a structure similar to the bullseye shape formed by surrounding ferrite around spherical graphite and pearlite around the periphery of the ferrite, the ferrite content in the bullseye structure is below 25 percent, and the ferrite content in the whole metallographic structure is below 25 percent. The semi-finished rigid wheel with the metallographic structure before heat treatment has good strength and hardness performance, is favorable for preparing a wear-resistant rigid wheel, and is particularly suitable for a rigid wheel for a harmonic reducer.
The graphite spheroidization rate of a metallographic structure in the semi-finished rigid wheel is more than or equal to 70%, the mechanical property of the finished harmonic reducer rigid wheel is ensured, and the impact strength, the fatigue property, the corrosion resistance and the wear resistance of the nodular cast iron can be improved.
In some embodiments of the invention, the heat treatment comprises a normalizing treatment.
In some embodiments of the invention, the normalizing process comprises: firstly, heating a semi-finished product of the rigid wheel to a certain temperature above a eutectoid temperature, and preserving heat for a period of time, wherein the nodular cast iron base material is austenitized; then cooling to a bainite transformation region in a cooling chamber at a cooling speed higher than that of pearlite formation for isothermal treatment, wherein an austenitizing part is transformed into bainite at the time, and the strength and the toughness of the bainite are higher.
In some embodiments of the invention, the quenching temperature of the normalizing treatment is 830 ℃ to 950 ℃, i.e. the heating to a temperature above the eutectoid temperature during the above process.
In some embodiments of the invention, the quenching temperature of the normalizing treatment is 870 ℃ to 950 ℃.
Further, in some embodiments of the present invention, the quenching temperature of the normalizing treatment is 900 ℃ to 950 ℃.
In some embodiments of the invention, the holding time for the normalizing treatment is 1h to 4h.
Further, in some embodiments of the present invention, the holding time for the normalizing treatment is 2 to 4 hours.
Further, in some embodiments of the present invention, the holding time for the normalizing treatment is 3 to 4 hours.
After the ductile cast iron is subjected to the normalizing treatment process, the strength, the hardness and the wear resistance are improved.
After the ductile cast iron is subjected to the normalizing treatment process, the surface hardness of the semi-finished rigid wheel is 330 HBW-360 HBW.
Further, after the nodular cast iron is subjected to normalizing treatment, the surface hardness of the semi-finished rigid wheel is 340 HBW-360 HBW.
Further, after the ductile cast iron is subjected to normalizing treatment, the surface hardness of the semi-finished rigid wheel is 350 HBW-360 HBW.
After the ductile cast iron is subjected to the normalizing treatment process, the tensile strength of the semi-finished rigid gear is more than or equal to 1100MPa.
It will be appreciated that the hardness and tensile strength indicated above indicate that the wear resistance of the semi-finished steel wheel after heat treatment is better.
When the semi-finished product of the rigid wheel after heat treatment is subjected to a thermal deformation test under the condition of keeping the temperature at 170 ℃ for 24 hours, the measured dimensional change is below 0.01 percent, which shows that the semi-finished product of the rigid wheel obtained after heat treatment and before finish machining has higher thermal stability.
In some embodiments of the present invention, finishing comprises grinding the heat-treated semi-finished rigid gear to form a finished rigid gear.
In other embodiments of the present invention, the present invention provides a harmonic reducer in which the harmonic reducer rigid gear of the present invention is provided.
It can be understood that the main structure of the harmonic reducer comprises three basic components of a wave generator, a flexible gear and a rigid gear. In the harmonic reducer, the rigid wheel is made of the ball-milling cast iron with a specific raw material ratio, so that the harmonic reducer has high wear resistance and mechanical strength and is more durable, and the service life, stability and reliability of the harmonic reducer are prolonged.
Specifically, the harmonic speed reducer is a precision transmission part and mainly comprises a cam, a flexible bearing, a flexible gear, a rigid gear and a crossed roller bearing, the transmission principle of the harmonic speed reducer is small tooth difference transmission, and the harmonic speed reducer can be used as a speed-reducing and moment-increasing or speed-increasing and moment-reducing device. The harmonic speed reducer is assembled in such a way that a hat-shaped harmonic speed reducer is taken as an example, a cam is assembled on a flexible bearing in a small interference manner to form a wave generator, the wave generator can be used as an input end, a flexible gear is assembled on an outer ring of a crossed roller bearing, the wave generator is assembled on an inner wall of the flexible gear, the inner wall of the flexible gear and the outer ring of the flexible bearing are mutually friction pairs, a rigid gear is assembled on an inner ring of the crossed roller bearing, relative motion exists between partial teeth of the rigid gear and the flexible gear and is mutually friction pairs, the tooth meshing rate is related to a working condition, the rigid gear is fixed, the flexible gear can be used as an output end, and the reduction ratio i = (flexible gear tooth number-rigid gear tooth number)/flexible gear tooth number is adopted. The tooth surface of a flexible gear of the harmonic speed reducer and the tooth surface of a rigid gear are in line contact friction pairs, relative motion between the tooth surfaces is tangential meshing and tooth direction rotation, wherein the meshing speed is related to the rotating speed of an output end and the size of the flexible gear, the axial relative speed is related to the rotating speed of an input end, torque and the rigidity of the flexible gear, the axial movement is caused by the periodic buckling deformation of the flexible gear, and the lubrication state of the tooth surface friction pairs is mixed lubrication.
In further embodiments of the present invention, the present invention provides an industrial robot in which the harmonic reducer rigid gear of the present invention or the harmonic reducer of the present invention is disposed.
It can be understood that an industrial robot is a multi-joint manipulator or a multi-degree-of-freedom machine device widely used in the industrial field, has certain automation, and can realize various industrial processing and manufacturing functions by means of the power energy and control capability of the industrial robot. Industrial robots are widely used in various industrial fields such as electronics, logistics, and chemical industry. The speed reducer is one of important parts of the industrial robot, and the harmonic speed reducer rigid wheel is assembled in the speed reducer, so that the comprehensive performance is better, the service life of the speed reducer is directly prolonged, and the fault rate of the industrial robot is also reduced.
The technical scheme of the invention is better understood by combining the specific embodiments.
Examples
This embodiment prepares a rigid gear of a harmonic reducer, and the structure of the rigid gear of the harmonic reducer is shown in fig. 1. The base material of the harmonic speed reducer rigid wheel is nodular cast iron, and the preparation raw materials of the nodular cast iron comprise Fe and the following components in percentage by mass:
C：3.9％，
Si：2.5％，
Cu：0.7％，
Mn：0.8％，
Cr：0.1％，
P：0.1％，
S：0.03％。
the nodular cast iron base material is prepared by itself. The preparation method comprises the following steps: according to the proportion, the metal raw materials are melted, and then the molten metal is spheroidized. The spheroidizing agent used for spheroidizing was composed of 50% of metal magnesium powder, 39% of MgO and 11% of phenolic resin. Wherein the particle size of the metal magnesium powder is about 0.1 mm.
Referring to fig. 2, a preparation process of a rigid gear of a harmonic reducer is specifically as follows:
s1: carrying out rough machining on the nodular cast iron base material to obtain a semi-finished rigid wheel;
s2: and (4) performing heat treatment on the semi-finished rigid wheel, and then performing finish machining to obtain the rigid wheel of the harmonic speed reducer.
Wherein, the rough machining method comprises the following steps: pouring the molten nodular cast iron base material into a casting mold, adding an inoculant for inoculation, wherein the inoculant is commercially available Si-Fe, and obtaining a semi-finished rigid wheel from the casting mold after cooling.
The normalizing treatment process comprises the following steps: firstly, heating the semi-finished product of the rigid wheel to over 860 ℃, and preserving heat for about 2.5 hours, wherein the nodular cast iron base material is austenitized; then cooling to a bainite transformation region in a cooling chamber at a cooling rate larger than that for forming pearlite, and carrying out isothermal treatment at about 340 ℃, wherein an austenitized part is transformed into bainite.
The quenching temperature of the normalizing treatment is about 890 ℃.
The heat preservation time of the normalizing treatment is 3h.
After the ductile cast iron is subjected to the normalizing treatment process, the surface hardness of the semi-finished rigid wheel is 345HBW.
After the ductile cast iron is subjected to the normalizing treatment process, the tensile strength of the semi-finished product of the rigid gear is more than or equal to 1100MPa.
When the semi-finished product of the rigid wheel after heat treatment is subjected to a thermal deformation test under the condition of keeping the temperature at 170 ℃ for 24 hours, the measured dimensional change is below 0.01 percent, which shows that the semi-finished product of the rigid wheel obtained after heat treatment and before finish machining has higher thermal stability.
And finally, polishing the semi-finished rigid wheel after heat treatment through finish machining to obtain a rigid wheel finished product.
Comparative example
This comparative example prepared a harmonic reducer rigid gear, the structure of which is shown with reference to fig. 1. The base material of the harmonic speed reducer rigid wheel is nodular cast iron, and the preparation raw materials of the nodular cast iron comprise Fe and the following components in percentage by mass:
C：3.9％，
Si：2.5％，
Mn：0.8％，
P：0.1％，
S：0.03％。
the nodular cast iron base material is prepared by itself. The preparation method comprises the following steps: according to the proportion, melting the metal raw materials, and then carrying out spheroidization on the molten metal. The spheroidizing agent used for spheroidizing was composed of 50% of metal magnesium powder, 39% of MgO and 11% of phenolic resin. Wherein the particle size of the metal magnesium powder is about 0.1 mm.
The preparation flow of the rigid wheel of the harmonic reducer is shown in fig. 2. The preparation method comprises the following steps:
s1: carrying out rough machining on the nodular cast iron base material to obtain a semi-finished rigid wheel;
s2: and (4) performing heat treatment on the semi-finished rigid wheel, and then performing finish machining to obtain the rigid wheel of the harmonic speed reducer.
Wherein, the rough machining method comprises the following steps: pouring the molten nodular cast iron base material into a casting mold, adding an inoculant for inoculation, wherein the inoculant is commercially available Si-Fe, and obtaining a semi-finished rigid wheel from the casting mold after cooling.
The normalizing treatment process comprises the following steps: firstly, heating the semi-finished product of the steel wheel to over 860 ℃, and preserving heat for about 2.5 hours, so that the nodular cast iron base material austenitizes; then cooling to a bainite transformation region in a cooling chamber at a cooling rate larger than that for forming pearlite, and carrying out isothermal treatment at about 340 ℃, wherein an austenitized part is transformed into bainite.
The quenching temperature of the normalizing treatment is about 890 ℃.
The heat preservation time of the normalizing treatment is 3h.
When the semi-finished product of the rigid wheel after heat treatment is subjected to a thermal deformation test under the condition of keeping the temperature at 170 ℃ for 24 hours, the measured dimensional change is below 0.01 percent, which shows that the semi-finished product of the rigid wheel obtained after heat treatment and before finish machining has higher thermal stability.
And finally, polishing the semi-finished rigid wheel after heat treatment through finish machining to obtain a rigid wheel finished product.
Test example
The metallographic structure of the rigid wheel prepared in the examples was observed according to GB/T9441-2009 national standard for metallographic examination of nodular cast iron, as shown in FIG. 3. In fig. 3, the black spheres are graphite, the maximum size is 48.1 μm, the average size is 11.7 μm, the spheroidization rate is greater than or equal to 95%, specifically 99.3%, and the black spheres meet the national standard level 1 standard, and the pearlite proportion is greater than 95%.
According to GB/T230.1-2018 part 1 of Rockwell hardness test of metal materials: test method the surface hardness of the rigid wheels prepared in examples and comparative examples was tested. The surface hardness of the rigid wheel prepared in the embodiment is 330 HBW-360 HBW. The surface hardness of the steel wheel prepared by the comparative example is about 280 HBW.
According to GB/T228.1-2021 part 1 of the tensile test of metallic materials: the tensile strength of the steel wheels prepared in examples and comparative examples was tested by room temperature test method. Wherein, the tensile strength of the rigid wheel prepared in the example reaches 1120MPa. The tensile strength of the steel wheel prepared by the comparative example is about 900MPa.
Further, the surface states before and after the tooth surfaces of the steel wheels prepared in examples and comparative examples were worn were also observed. The rigid wheel prepared in the examples and the comparative examples is used in a top hat type harmonic speed reducer (25 models, 80 reduction ratios), the speed reducer is operated for 500 hours under the rated working condition, and the abrasion condition of the tooth surface of the rigid wheel is observed. As shown in fig. 4-7. FIG. 4 is a schematic representation of the surface of a prior-to-wear steel wheel prepared in accordance with an example, and FIG. 5 is a schematic representation of the surface of a prior-to-wear steel wheel prepared in accordance with an example. Fig. 6 is a schematic view of the surface of a steel wheel prepared in comparative example before being abraded, and fig. 7 is a schematic view of the surface of a steel wheel prepared in comparative example after being abraded. As can be seen from comparison of fig. 4 to 7, the steel wheel prepared in the examples has no significant change before and after the tooth surface is worn, and no defect such as chipping is observed. In contrast, in the case of the steel wheel prepared in the comparative example, the tooth surface was cracked after being worn.
In other embodiments of the present invention, the present invention further provides a harmonic reducer, in which the harmonic reducer rigid gear of the present invention is disposed.
It can be understood that the main structure of the harmonic reducer comprises three basic components of a wave generator, a flexible gear and a rigid gear. In the harmonic reducer, the rigid wheel is made of the ball-milling cast iron with a specific raw material ratio, so that the harmonic reducer has high wear resistance and mechanical strength and is more durable, and the service life, stability and reliability of the harmonic reducer are prolonged.
Specifically, the harmonic speed reducer is a precision transmission part and mainly comprises a cam, a flexible bearing, a flexible gear, a rigid gear and a crossed roller bearing, the transmission principle of the harmonic speed reducer is small tooth difference transmission, and the harmonic speed reducer can be used as a speed-reducing and moment-increasing or speed-increasing and moment-reducing device. The harmonic speed reducer is assembled in such a way that a hat-shaped harmonic speed reducer is taken as an example, a cam is assembled on a flexible bearing in a small interference manner to form a wave generator, the wave generator can be used as an input end, a flexible gear is assembled on an outer ring of a crossed roller bearing, the wave generator is assembled on an inner wall of the flexible gear, the inner wall of the flexible gear and the outer ring of the flexible bearing are mutually friction pairs, a rigid gear is assembled on an inner ring of the crossed roller bearing, relative motion exists between partial teeth of the rigid gear and the flexible gear and is mutually friction pairs, the tooth meshing rate is related to a working condition, the rigid gear is fixed, the flexible gear can be used as an output end, and the reduction ratio i = (flexible gear tooth number-rigid gear tooth number)/flexible gear tooth number is adopted. The tooth surface of a flexible gear of the harmonic speed reducer and the tooth surface of a rigid gear are in line contact friction pairs, relative motion between the tooth surfaces is tangential meshing and tooth direction rotation, wherein the meshing speed is related to the rotating speed of an output end and the size of the flexible gear, the axial relative speed is related to the rotating speed of an input end, torque and the rigidity of the flexible gear, the axial movement is caused by the periodic buckling deformation of the flexible gear, and the lubrication state of the tooth surface friction pairs is mixed lubrication.
In further embodiments of the present invention, the present invention provides an industrial robot in which the harmonic reducer rigid gear of the present invention or the harmonic reducer of the present invention is disposed.
It can be understood that an industrial robot is a multi-joint manipulator or a multi-degree-of-freedom machine device widely used in the industrial field, has certain automation, and can realize various industrial processing and manufacturing functions by means of the power energy and control capability of the industrial robot. Industrial robots are widely used in various industrial fields such as electronics, logistics, and chemical industry. The speed reducer is one of important parts of the industrial robot, and the harmonic speed reducer rigid wheel is assembled in the speed reducer, so that the comprehensive performance is better, the service life of the speed reducer is directly prolonged, and the fault rate of the industrial robot is also reduced.
The present invention has been described in detail with reference to the embodiments, but the present invention is not limited to the embodiments described above, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.
Claims (12)
1. The harmonic speed reducer rigid wheel is characterized in that a base material of the harmonic speed reducer rigid wheel is nodular cast iron, and the preparation raw materials of the nodular cast iron comprise Fe and the following components in percentage by mass:
C：3.0％～4.0％，
Si：2.0％～3.0％，
Cu：0.5％～1.0％，
Mn：≤1.0％，
Cr：≤0.1％，
P：≤0.1％，
S：≤0.06％，
in the nodular cast iron, the graphite spheroidization rate of a metallographic structure is more than or equal to 95 percent.
2. The rigid wheel of the harmonic reducer of claim 1, wherein the raw materials for preparing the ductile cast iron comprise Fe and the following components in percentage by mass:
C：3.5％～4.0％，
Si：2.5％～3.0％，
Cu：0.7％～1.0％，
Mn：≤1.0％，
Cr：≤0.1％，
P：≤0.1％，
S：≤0.06％。
3. the harmonic reducer rigid gear according to claim 1, wherein in the ductile cast iron, a metallographic structure comprises cementite and a phosphorus eutectic.
4. The rigid gear of the harmonic reducer according to any one of claims 1 to 3, wherein the tensile strength of the ductile cast iron is not less than 1100MPa.
5. A method for manufacturing a harmonic reducer rigid gear according to any one of claims 1 to 4, comprising the steps of:
s1: carrying out rough machining on the nodular cast iron base material according with the element proportion to obtain a semi-finished rigid wheel;
s2: and carrying out heat treatment on the semi-finished rigid wheel, and then carrying out finish machining to obtain the harmonic speed reducer rigid wheel.
6. The method of claim 5, wherein the roughening comprises melting the ductile iron substrate and injecting the molten ductile iron substrate into a mold, and inoculating with an inoculant.
7. The method of claim 5, wherein the metallographic structure of the semi-finished steel wheel comprises spheroidal graphite, pearlite and ferrite.
8. The method according to claim 5, wherein the graphite spheroidization rate of a metallographic structure in the semi-finished rigid wheel is more than or equal to 70%.
9. The method of claim 5, wherein the heat treatment comprises a normalizing treatment.
10. The method of claim 9, wherein the normalizing comprises heating the semi-finished steel wheel above the eutectoid temperature for holding to austenitize the ductile iron substrate, and then cooling the semi-finished steel wheel to a bainite transformation region for isothermal transformation at a cooling rate greater than that for pearlite formation to transform the austenitized portion to bainite.
11. A harmonic reducer having the harmonic reducer rigid gear according to any one of claims 1 to 4.
12. An industrial robot characterized in that the harmonic reducer rigid gear of any one of claims 1 to 4 or the harmonic reducer of claim 11 is provided therein.
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| CN110295272A (en) * | 2019-06-19 | 2019-10-01 | 东莞市卓蓝自动化设备有限公司 | A kind of firm gear heat treatment process |
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