阅读说明：本技术 一种直齿轮成形方法和装置 (Straight gear forming method and device ) 是由 李振红 朱秋芬 袁德虎 查光成 谢斌 赵伟 王安哲 张晨星 于 2020-12-18 设计创作，主要内容包括：本发明公开了一种直齿轮成形方法和装置,属于金属塑性成形技术领域,包括如下步骤：对圆柱形坯料进行预处理,所述预处理包括润滑、软化退火或加热；将经预处理的所述坯料置入预成形模具中进行径向挤压获得预成形件,所述预成形件轴向横截面的根圆直径小于最终待获取直齿轮的根圆直径；利用包含多个齿形型腔块的终锻模具对所述预成形件的齿形部位进行径向镦挤成形,获取具有完整齿形的直齿轮精锻件。本发明能够提高直齿轮的预成形件各齿部位金属流动的均匀性和同时性,减少坯料体积波动和预成形件定位精度对终锻时金属流动的影响,降低终锻模具受力,避免开裂,减少金属流动,降低模具磨损。(The invention discloses a straight gear forming method and a straight gear forming device, which belong to the technical field of metal plastic forming and comprise the following steps: pre-treating the cylindrical blank, wherein the pre-treatment comprises lubrication, softening annealing or heating; placing the pretreated blank into a preforming die for radial extrusion to obtain a preformed piece, wherein the root circle diameter of the axial cross section of the preformed piece is smaller than that of the straight gear to be finally obtained; and carrying out radial upsetting extrusion forming on the tooth-shaped part of the pre-forming piece by using a finish forging die comprising a plurality of tooth-shaped cavity blocks to obtain a straight gear finish forging piece with a complete tooth shape. The method can improve the uniformity and the simultaneity of metal flow of each tooth part of the preformed piece of the straight gear, reduce the influence of blank volume fluctuation and preformed piece positioning precision on the metal flow during finish forging, reduce the stress of a finish forging die, avoid cracking, reduce the metal flow and reduce the die abrasion.)

1. A spur gear forming method, characterized by comprising the steps of:

pre-treating the cylindrical blank, wherein the pre-treatment comprises lubrication, softening annealing or heating;

placing the pretreated blank into a preforming die for radial extrusion to obtain a preformed piece, wherein the root circle diameter of the axial cross section of the preformed piece is smaller than that of the straight gear to be finally obtained;

and carrying out radial upsetting extrusion forming on the tooth-shaped part of the pre-forming piece by using a finish forging die comprising a plurality of tooth-shaped cavity blocks to obtain a straight gear finish forging piece with a complete tooth shape.

2. The spur gear forming method according to claim 1, wherein the method of determining the shape of the preform includes the steps of:

calculating and obtaining the corrected tooth number of the pre-formed piece, the axial cross section area of the pre-formed piece, the trapezoidal tooth width of the pre-formed piece and the root circle diameter of the axial cross section of the pre-formed piece according to the tooth number and the modulus of a pre-given involute straight gear, the inclination of the trapezoidal tooth of the pre-formed piece and the root circle diameter variation of the axial cross section of the pre-formed piece;

and calculating the height of the trapezoidal teeth of the preformed piece according to the principle that the axial sectional areas of the preformed piece and the straight gear are consistent.

3. A method for forming a spur gear according to claim 2, wherein the preform axial cross-section has a root circle diameter variation of a pitch between the root circle diameter of the spur gear axial cross-section and the root circle diameter of the preform axial cross-section, as expressed in the following:

d_f1＝d_f-Δ

wherein Δ represents the variation of the root diameter of the axial cross section of the preform, d_f1Indicating the root diameter, d, of the spur gear precision forging_fThe root diameter of the axial cross section of the preform is indicated.

4. The spur gear forming method according to claim 3, wherein the trapezoidal tooth width S of the preform₁The radial dimension is the size of the reference circle position of the straight gear, and the width S of the trapezoidal teeth₁Taking three quarters of the tooth thickness s of the involute tooth profile of the straight gear, the formula is as follows:

in the formula, m represents the modulus of the spur gear.

5. The spur gear forming method according to claim 4, wherein a pitch α of the trapezoidal teeth of the preform ranges from 1 ° to 3 °.

6. The method for forming a spur gear according to claim 5, wherein the inclination α has an inverse relationship between a value of the inclination α and a value of the modulus m within a value range, specifically as follows:

when the modulus m is larger, the inclination alpha takes a smaller value in a value range, and when the modulus m is smaller, the inclination alpha takes a larger value in the value range.

7. The spur gear shaping method as set forth in claim 6 wherein the preform has an axial cross-sectional area A₁Is represented as follows:

in the formula, z₁For correcting the number of teeth, the number z of corrected teeth₁The notations of (a) are as follows:

wherein z is the number of teeth of the spur gear.

8. The method for forming a spur gear according to claim 1, wherein the method for radially upsetting-extruding the tooth-shaped portion of the preform by the finish die comprises the steps of:

each tooth-shaped cavity block matched with the tooth form of the straight gear to be obtained is distributed along the circumferential direction in a partitioning mode, when the tooth number of the straight gear is small, the tooth-shaped cavity blocks are partitioned according to the tooth number of the straight gear, each tooth-shaped cavity block corresponds to one partitioning block, and when the tooth number of the straight gear is large, a plurality of tooth-shaped cavity blocks are distributed to the same partitioning block;

and simultaneously moving each tooth-shaped cavity block along the radial direction of each tooth-shaped cavity block, so as to apply extrusion pressure to the trapezoidal teeth on the preformed piece corresponding to each tooth-shaped cavity block until each tooth-shaped cavity block is contacted with the root circle of the preformed piece.

9. A spur gear forming device is characterized by comprising the following modules:

the pretreatment module is used for pretreating the cylindrical blank, and the pretreatment comprises lubrication, softening annealing or heating;

the pre-forming module is used for placing the pre-treated blank into a pre-forming die to carry out radial extrusion to obtain a pre-formed piece, and the root circle diameter of the axial cross section of the pre-formed piece is smaller than that of the straight gear to be finally obtained;

and the forming module is used for carrying out radial upsetting extrusion forming on the tooth-shaped part of the preformed piece by using a finish forging die containing a plurality of tooth-shaped cavity blocks to obtain a straight gear finish forging piece with a complete tooth shape.

Technical Field

The invention relates to the technical field of metal plastic forming, in particular to a straight gear forming method and a straight gear forming device.

Background

The straight gear is a cylindrical gear with the tooth trace parallel to the axis direction. Because of easy processing, the gear box is widely applied to transmission systems of automobiles, machines and machine tools. The most common gear tooth form is an involute tooth form, which can be correctly meshed and is easy to process and can smoothly transmit rotary motion; as long as the size of the gear teeth is the same, one cutter can machine gears with different tooth numbers.

Machining gears by cutting is the most common gear machining process. The production process is generally divided into: gear blank processing → tooth surface processing → heat treatment process → fine processing of tooth surface. The specific procedures are as follows: forging or bar stock to form gear blank → rough machining, cutting off more allowance → semi-finishing, turning, hobbing, gear shaping, etc → heat treatment, quenching and tempering, carburizing and quenching, high frequency quenching → finishing, finishing benchmark, finishing tooth profile, etc.

The gear machined by the cutting method can reach higher precision, generally can reach 6 grades, can reach more than 5 grades after honing, and can be used in a high-speed and low-noise working environment. But the gear is produced by cutting, and the gear-by-gear forming is needed, so that the production efficiency is low, and the material utilization rate is low; and the cutting process cuts off the metal flow line of the rolled bar billet or die forging billet, reduces the fatigue resistance of the gear and prolongs the service life of the gear, and the gear body has higher failure proportion in practical application, mainly bending fatigue fracture and overload fracture.

The application of pressure to the blank by plastic forming to cause the metal to fill the tooth cavity is a relatively new forming method for obtaining gears. Because the tooth form die cavity which is consistent with the shape of the final gear is adopted, the tooth form with higher precision can be obtained. At present, the closed forging process is widely applied at home and abroad.

The flow resistance is increased rapidly in the forming process by applying the closed forging process, the stress of the die is increased, and the die is cracked in severe cases. Even if the blank does not crack, the pressure between the blank and the die surface is large, and the blank flows on the die surface to cause rapid wear of the die, so that the service life of the die is shortened.

Therefore, how to quickly and efficiently design the pre-forming shape of the spur gear, reduce the influence of blank volume fluctuation and pre-forming piece positioning precision on metal flow during finish forging, reduce the stress of a finish forging die, avoid cracking, reduce metal flow and reduce die abrasion becomes a very important technical problem in practical production and application, and has important economic significance and technical value for application and popularization of a precision plastic forming process of the spur gear.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a straight gear forming method and a straight gear forming device, which can ensure the uniformity and simultaneity of metal flow of each tooth part, reduce the influence of blank volume fluctuation and pre-forming piece positioning precision on metal flow during finish forging, reduce the stress of a finish forging die, avoid cracking, reduce metal flow and reduce die abrasion.

In order to achieve the purpose, the invention is realized by adopting the following technical scheme:

in a first aspect, the present invention provides a spur gear forming method, including the steps of:

pre-treating the cylindrical blank, wherein the pre-treatment comprises lubrication, softening annealing or heating;

placing the pretreated blank into a preforming die for radial extrusion to obtain a preformed piece, wherein the root circle diameter of the axial cross section of the preformed piece is smaller than that of the straight gear to be finally obtained;

and carrying out radial upsetting extrusion forming on the tooth-shaped part of the pre-forming piece by using a finish forging die comprising a plurality of tooth-shaped cavity blocks to obtain a straight gear finish forging piece with a complete tooth shape.

Further, the method for determining the shape of the preform comprises the following steps:

calculating and obtaining the corrected tooth number of the pre-formed piece, the axial cross section area of the pre-formed piece, the trapezoidal tooth width of the pre-formed piece and the root circle diameter of the axial cross section of the pre-formed piece according to the tooth number and the modulus of a pre-given involute straight gear, the inclination of the trapezoidal tooth of the pre-formed piece and the root circle diameter variation of the axial cross section of the pre-formed piece;

and calculating the height of the trapezoidal teeth of the preformed piece according to the principle that the axial sectional areas of the preformed piece and the straight gear are consistent.

Further, the variation of the root circle diameter of the axial cross section of the preformed piece is the distance between the root circle diameter of the axial cross section of the spur gear and the root circle diameter of the axial cross section of the preformed piece, and the common expression is as follows:

d_f1＝d_f-Δ

wherein Δ represents the variation of the root diameter of the axial cross section of the preform, d_f1Indicating the root diameter, d, of the spur gear precision forging_fThe root diameter of the axial cross section of the preform is indicated.

Further, the pre-form has a trapezoidal tooth width S₁The radial dimension is the size of the reference circle position of the straight gear, and the width S of the trapezoidal teeth₁Taking three quarters of the tooth thickness s of the involute tooth profile of the straight gear, the formula is as follows:

in the formula, m represents the modulus of the spur gear.

Further, the inclination alpha of the trapezoidal teeth of the preformed piece ranges from 1 degree to 3 degrees.

Further, the inclination has an inverse relationship between the value of the inclination and the value of the modulus m within the value range, which is as follows:

and when the modulus m is larger, the inclination takes a smaller value in a value range, and when the modulus m is smaller, the inclination takes a larger value in the value range.

Further, the preform axial cross-sectional area A₁Is represented as follows:

in the formula, z₁For correcting the number of teeth, the number z of corrected teeth₁The notations of (a) are as follows:

wherein z is the number of teeth of the spur gear.

Further, the method for carrying out radial upsetting extrusion forming on the tooth-shaped part of the pre-forming piece by using the finish forging die comprises the following steps:

each tooth-shaped cavity block matched with the tooth form of the straight gear to be obtained is distributed along the circumferential direction in a partitioning mode, when the tooth number of the straight gear is small, the tooth-shaped cavity blocks are partitioned according to the tooth number of the straight gear, each tooth-shaped cavity block corresponds to one partitioning block, and when the tooth number of the straight gear is large, a plurality of tooth-shaped cavity blocks are distributed to the same partitioning block;

and simultaneously moving each tooth-shaped cavity block along the radial direction of each tooth-shaped cavity block, so as to apply extrusion pressure to the trapezoidal teeth on the preformed piece corresponding to each tooth-shaped cavity block until each tooth-shaped cavity block is contacted with the root circle of the preformed piece.

In a second aspect, the present invention provides a spur gear forming apparatus, including the following modules:

the pretreatment module is used for pretreating the cylindrical blank, and the pretreatment comprises lubrication, softening annealing or heating;

the pre-forming module is used for placing the pre-treated blank into a pre-forming die to carry out radial extrusion to obtain a pre-formed piece, and the root circle diameter of the axial cross section of the pre-formed piece is smaller than that of the straight gear to be finally obtained;

and the forming module is used for carrying out radial upsetting extrusion forming on the tooth-shaped part of the preformed piece by using a finish forging die containing a plurality of tooth-shaped cavity blocks to obtain a straight gear finish forging piece with a complete tooth shape.

Compared with the prior art, the invention has the following beneficial effects:

1) according to the forming method and the forming device, the preformed piece is manufactured through the preforming die, the metal material required by processing is pre-distributed, the metal flow amount required by direct finish forging is reduced, the difficulty of finish forging filling is reduced, the stress of the die and the abrasion of the metal to the die are reduced, and the service life of the finish forging die is prolonged;

2) during finish forging, the plurality of tooth-shaped cavity blocks move along the radial direction of the tooth-shaped cavity blocks simultaneously, so that a preformed piece with inaccurate positioning can automatically move to the middle of the tooth-shaped cavity blocks, the forming precision is ensured, and the influence of the inaccurate positioning of the preformed piece on the flow uniformity and simultaneity of finish forging metal is avoided;

3) when a plurality of tooth-shaped cavity blocks move along the radial direction during the finish forging radial upsetting extrusion, the upper end surface of the preformed tooth-shaped piece is not limited by a die, and redundant metal can flow to the upper end surface along the axial direction at a tooth-shaped part, so that the volume of a blank can be slightly larger than that of a gear precision forging piece, and the problems of insufficient tooth-shaped filling caused by insufficient volume during closed forging, overlarge die stress caused by overlarge volume and the like are avoided;

4) in the design of the axial cross section of the preformed piece, the corrected tooth number of the preformed piece, the area of the axial cross section of the preformed piece, the width of the preformed trapezoidal tooth, the diameter of the root circle of the axial cross section of the preformed piece and the height of the trapezoidal tooth of the preformed piece can be calculated and obtained according to the tooth number and the modulus of a given involute straight gear, the inclination of the preformed trapezoidal tooth and the variation of the diameter of the root circle of the axial cross section of the preformed piece; the area of the axial cross section of the preformed piece calculated by adopting the corrected tooth number given by the forming method provided by the invention is more accurate, and the error with the actual sectional area is within 0.1%;

5) the forming method and the forming device provided by the invention can be applied to various scenes, such as forming of the revolving body parts with radial regular characteristics.

Drawings

Fig. 1 is a flowchart of a spur gear forming method according to an embodiment of the present invention;

fig. 2 is a schematic view of a finish forged part of a spur gear according to an embodiment of the present invention;

fig. 3 is a schematic design parameter diagram of trapezoidal teeth of a spur gear preform according to an embodiment of the present invention;

fig. 4 is a schematic structural diagram of a spur gear preform according to an embodiment of the present invention;

FIG. 5 is a top view of a preform mold according to an embodiment of the present invention;

FIG. 6 is a schematic view of the structure of section A-A in FIG. 5;

FIG. 7 is a schematic illustration of the positioning of a plurality of tooth cavity blocks and preforms prior to the start of finish forging according to an embodiment of the present invention;

FIG. 8 is a schematic position diagram of a plurality of tooth-shaped cavity blocks and a finish forged piece at the end of finish forging according to an embodiment of the present invention;

in the figure:

1. a spur gear; 2. a preform; 3. performing a mold; 4. a tooth-shaped cavity block; 31. an upper male die sleeve; 32. a lower punch sleeve; 33. a lower male die; 34. a female die; 35. an upper male die; 36. a cylindrical blank.

Detailed Description

The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention. Furthermore, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art through specific situations.

Example one

As shown in fig. 1, an embodiment of the present invention provides a spur gear forming method, which can realize precise plastic forming of a spur gear 1, and the method includes the following steps:

the method comprises the following steps: and (3) performing pretreatment on the cylindrical blank, wherein the pretreatment comprises lubrication, softening annealing or heating, specifically, peeling the surface of the bar stock, and blanking by sawing according to the volume of the preformed piece 2 to obtain the cylindrical blank with the required specification. Then, lubricating, softening annealing (cold forming) or heating (warm and hot forming) is carried out according to the requirement;

step two: putting the pretreated blank into a preforming die 3 for radial extrusion to obtain a preformed piece 2, wherein the root circle diameter of the axial cross section of the preformed piece 2 is smaller than that of the straight gear 1 to be finally obtained, and the difference between the two diameters is the root circle diameter variation of the axial cross section of the preformed piece 2;

step three: and (3) carrying out radial upsetting extrusion forming on the tooth-shaped part of the preformed piece 2 by using a finish forging die comprising a plurality of tooth-shaped cavity blocks 4 to obtain a straight gear 1 finish forging piece with a complete tooth shape.

In an embodiment of the present invention, after step three, a post-forging process is further included, i.e., the finish forged piece of the spur gear 1 is ground and heat treated as necessary.

In step two, a method for determining the shape of the preform 2 is also included, and the specific operation comprises the following steps:

calculating and obtaining the corrected tooth number of the preformed piece 2, the area of the axial cross section of the preformed piece 2, the width of the trapezoidal tooth of the preformed piece 2 and the diameter of the root circle of the axial cross section of the preformed piece 2 according to the tooth number and the modulus of the preset involute straight gear 1, the inclination of the trapezoidal tooth of the specified preformed piece 2 and the diameter variation of the root circle of the axial cross section of the preformed piece 2;

and calculating to obtain the height of the trapezoidal teeth of the preformed piece 2 according to the principle that the preformed piece 2 is consistent with the axial sectional area of the straight gear 1.

The root and the top of the preformed piece 2 are provided with fillets, the fillets at the root are convenient for metal flowing, and the fillets at the top are used for ensuring the strength of the die. The radius of the partial curve can be obtained by adopting the measuring function of three-dimensional modeling software during design, other parameters of the preformed piece 2 are firstly determined, and then the height of the teeth of the preformed piece 2 is adjusted according to the principle that the sectional areas are equal.

It should be noted that, different gear fillets are different in size, the smaller the fillet is, the harder the metal flows, and the higher the corresponding height is; the fillet must not be too large, which would prevent the tooth-shaped cavity block 4 from closing during the finish forging.

The preform 2 obtained by the above-described method for determining the preform 2 has the following features:

(a) root diameter d of axial cross section of preform 2 of spur gear 1_f1Root diameter d of precision forged part of gear_fSmall Δ, expressed by the formula:

d_f1＝d_f-△

wherein, delta represents the root diameter variation of the axial cross section of the preformed piece 2, the value range of delta is 0.2 mm-1 mm, the preformed piece 2 can be ensured to be placed in a finish forging die used for radial upsetting extrusion of finish forging, and the positioning precision is higher. The larger the diameter of the spur gear 1 is, the larger the value of the variation Δ can be taken.

(b) In the embodiment of the invention, the tooth form of the preformed part 2 is simplified because the tooth form is different from the involute tooth form of the gear precision forging, and the tooth form of the preformed part 2 is changed into a small-slope trapezoid.

Wherein the trapezoidal tooth height h of the preform 2₁The tooth height h is higher than that of a precision forging piece of the spur gear 1; the bottom length of the trapezoidal teeth is smaller than the thickness of the root circle of the final straight gear 1; preformed trapezoidal tooth width s₁3/4 of the involute tooth profile tooth thickness s of the finish forged piece of the spur gear 1 at the reference circle position d which is the finish forged piece of the final spur gear 1 in the radial direction is expressed as:

wherein m is the modulus of the spur gear.

(c) In the present embodiment, the inclination α of the trapezoidal teeth of the preform 2 is 1 to 3 °.

Specifically, the smaller the modulus is, the closer the involute of the tooth profile is to a straight line, and the tooth profile width changes violently; the larger the modulus, the more obvious the involute, the enough tooth width and the smaller the inclination. The value of the inclination alpha in the value range is in an inverse relation with the value of the modulus m, and the method specifically comprises the following steps:

when the modulus m is larger, the inclination alpha takes a smaller value in a value range, and when the modulus is smaller, the inclination alpha takes a larger value in the value range.

(d) In the present embodiment, the axial cross-sectional area of the preform 2 of the spur gear 1 is expressed by the following formula:

in the formula, z₁Expressed as the number of modified teeth used for the cross-sectional area calculation, the value of which is expressed as:

wherein z is the number of teeth of the spur gear.

The axial cross section area of the preformed piece 2 calculated by adopting the corrected tooth number given by the forming method provided by the invention is more accurate, and the error with the actual cross section area is within 0.1 percent

In the third step, the cylindrical blank of the preformed piece 2 flows in the closed cavity formed by the tooth-shaped male die and the tooth-shaped female die, the metal flows into the tooth-shaped cavity along the radial direction on the horizontal plane under the action of the pressure in the vertical direction, and the metal can reach the edge of the die at the same time by controlling the uniformity and the simultaneity of the metal flow at each tooth part in the process, so that the filling process is completed.

If the filling can not be completed at the same time, the flow of the subsequent metal is limited by the formed part firstly, so that the flow resistance is increased rapidly, the stress of the die is increased, the die is cracked seriously, or the pressure between the blank and the surface of the die is increased, the rapid abrasion of the die is caused when the blank flows on the surface of the die, and the service life of the die is shortened.

Therefore, in this embodiment, the radial upsetting operation at the time of finish forging has the following features:

each tooth-shaped cavity block 4 matched with the tooth shape of the straight gear 1 to be obtained is distributed along the circumferential direction in a partitioning manner, when the tooth number of the straight gear 1 is small, the tooth-shaped cavity blocks 4 are partitioned according to the tooth number of the straight gear 1, each tooth-shaped cavity block 4 corresponds to one partitioning block, and when the tooth number of the straight gear 1 is large, a plurality of tooth-shaped cavity blocks 4 are distributed on the same partitioning block; in this embodiment, one block is a relatively independent mold, and one tooth-shaped cavity block 4 may be allocated or a plurality of tooth-shaped cavity blocks 4 may be allocated simultaneously, and the plurality of block molds together form the finish forging mold along the circumferential direction.

And (3) enabling each tooth-shaped cavity block 4 to move along the radial direction of each tooth-shaped cavity block simultaneously, so that extrusion pressure is applied to the trapezoidal teeth on the preformed piece 2 corresponding to each tooth-shaped cavity block 4 until each tooth-shaped cavity block 4 is in contact with the root circle of the preformed piece 2.

During the final forging process of applying the extrusion pressure on the trapezoidal teeth until each tooth-shaped cavity block 4 is contacted with the root circle of the preformed piece 2, the shape of the trapezoidal teeth is changed as follows:

the height of the trapezoidal teeth gradually decreases while the cross-sectional area of the trapezoidal teeth increases near the root circle portion of the preform 2 and decreases near the addendum circle portion of the preform 2.

In the embodiment, when the plurality of tooth-shaped cavity blocks 4 move along the radial direction during the finish forging radial upsetting, the upper end surface of the preformed tooth-shaped member is not limited by a die, and the redundant metal can flow to the upper end surface along the axial direction at the tooth-shaped part, so that the volume of a blank can be slightly larger than that of a gear precision forging piece, and the problems of insufficient tooth-shaped filling caused by insufficient volume, overlarge die stress caused by overlarge volume and the like during the closed forging are solved.

Next, a method for forming the spur gear 1 according to the present invention will be described with reference to specific parameters of the spur gear 1, and the following description will be made.

As shown in fig. 2, the embodiment of the invention provides a precision forging piece of a spur gear 1, wherein the number of teeth z is 17, the modulus m is 5, the tooth width b is 20mm, and the pressure angle α is 20 °. The pressure angle α is a parameter of the gear, that is, an included angle between a force direction and a speed direction when the two gears are in meshing transmission.

In practical application, when a cylindrical blank is used for one-step finish forging forming, the tooth form is difficult to fill, and the product quality is influenced. In order to solve the technical problem, the method for precisely plastic forming the spur gear 1 provided by the embodiment of the invention is adopted, and the specific process is as follows:

(1) blanking and blank pretreatment: peeling the surface of the 40Cr round bar stock intoSawing a bar stock with the height of 29 +/-0.1 mm to obtain a cylindrical blank 36 with the required specification, and then heating the cylindrical blank to 950 ℃ by adopting induction heating.

(2) The preform 2 is shape designed, including axial cross-sectional area calculations.

In the present embodiment, taking a precision forging of a spur gear 1 as shown in fig. 1 as an example, the following data are obtained by calculation according to the tooth number z being 17 and the modulus m being 5:

corrected tooth number z of preform 2₁16.82; preform 2 axial cross-sectional area A₁＝5555.7mm²And the true cross-sectional area A₀＝5553mm²Compared with the error of 0.05%; the cross-sectional area A' obtained by the straight gear 1 pitch circle method is 5674.5mm²Its error from the true axial cross-sectional area is 2.19%.

The relevant data are shown in the second row of the following table 1, and meanwhile, the table also provides error values of axial cross-sectional areas calculated by a modified tooth number method when the modulus is changed and the tooth number is changed, and the error values are all within 0.1%.

Table 1:

(3) design of the preform 2: root diameter d of gear finish forging_fThe diameter d of the root circle of the axial cross section of the preformed piece 2 can be obtained when the gear is 72.5mm and the gear is small, and the variation delta is 0.5mm_f172 mm. The inclination alpha of the preformed trapezoidal tooth is 1 degree, the tooth thickness s of the involute tooth profile of the precision forging piece of the straight gear 1 is 7.85mm, and the width s of the trapezoidal tooth of the preformed piece 2₁Calculated as 3/4 times s₁5.9 mm. Calculating to obtain the height h of the trapezoidal teeth of the preformed piece 2 according to the principle that the axial sectional areas of the preformed piece 2 and the gear precision forging are consistent₁5.9mm as shown in fig. 3. According to the above parameters and the obtained axial cross sectionThe design of the preform 2 is completed as shown in fig. 4.

(4) Preparing a preformed piece 2: designing and manufacturing a pre-forming radial extrusion die according to the shape of the pre-forming piece 2The cylindrical blank is put into a preforming die 3 corresponding to the preformed shape for radial extrusion to obtain a preformed piece 2, as shown in fig. 5 and 6, an upper male die sleeve 31, a lower male die sleeve 32, a lower male die 33, a female die 34 and an upper male die 35 jointly carry out die fixing on the cylindrical blank 36.

(5) Finish forging: dividing the tooth cavity blocks 4 into blocks along the circumferential direction to form a finish forging die, placing the preformed piece 2 into the finish forging die, and simultaneously moving each tooth cavity block 4 along the radial direction thereof, as shown in fig. 7; in the finish forging process, upsetting-extruding forming is carried out on the trapezoidal teeth of the preformed piece 2 which are higher than the straight gear 1, and a straight gear 1 finish forging piece with a complete tooth shape is obtained, as shown in fig. 8.

(6) And (3) after-forging treatment: according to the requirements, the gear precision forging piece is mechanically processed, the mechanical property of the gear precision forging piece is changed through heat treatment, a small amount of grinding processing is carried out on the tooth-shaped part, and the tooth-shaped precision is further improved.

Example two

The embodiment of the invention provides a straight gear forming device, which comprises the following modules:

the pretreatment module is used for pretreating the cylindrical blank, and the pretreatment comprises lubrication, softening annealing or heating;

the pre-forming module is used for placing the pre-treated blank into a pre-forming die 3 for radial extrusion to obtain a pre-forming piece 2, and the root circle diameter of the axial cross section of the pre-forming piece 2 is smaller than that of the straight gear 1 to be obtained finally;

and the forming module is used for carrying out radial upsetting extrusion forming on the tooth-shaped part of the preformed piece 2 by using a finish forging die containing a plurality of tooth-shaped cavity blocks 4 to obtain a straight gear 1 finish forging piece with a complete tooth shape.

To sum up, the spur gear forming method and device provided by the embodiment of the invention can be used for pre-distributing the metal material required by processing by manufacturing the preformed piece 2 through the preforming die, so that the metal flow amount required by direct finish forging is reduced, the difficulty of finish forging filling is reduced, the stress of the die and the abrasion of the metal to the die are reduced, and the service life of the finish forging die is prolonged;

during finish forging, the tooth-shaped cavity blocks 4 move along the radial direction of the tooth-shaped cavity blocks simultaneously, the preformed piece 2 with inaccurate positioning can automatically move to the middle of the center, the forming precision is ensured, and the influence of the inaccurate positioning of the preformed piece 2 on the flow uniformity and simultaneity of finish forging metal is avoided; and can be applied in a variety of scenarios, such as for the formation of parts of revolution of radially regular features.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.