KR20230138750A - Cold Forging Die for Helical gear shaft and Helical gear shaft Manufacturing Method Using it - Google Patents

Abstract

The cold forging mold for a helical gear shaft of the present invention includes a cutting DIE and knife mold that is attached to a cold former facility and automatically cuts the supplied wire rod; A helical gear forming mold that is formed in multiple stages and sequentially molds the wires cut by the cutting die and knife mold, and performs chamfering, outer diameter processing, and tooth processing of the helical gear by cold forging; It includes a tab processing part that performs tapping processing on the helical gear formed by the helical gear molding mold.

Description

Cold forging die for helical gear shaft and helical gear shaft manufacturing method {Cold Forging Die for Helical gear shaft and Helical gear shaft Manufacturing Method Using it}

The present invention relates to a cold forging mold for a helical gear shaft that allows a helical gear shaft to be manufactured by cold forging, and a helical gear shaft manufacturing method that reduces manufacturing costs and improves productivity by reducing the helical gear shaft manufacturing process.

In general, a helical gear is a cylindrical gear whose tooth stems are inclined at an angle and have a spiral curve.

Recently, the application of helical gears has been expanding to improve the performance of automobile transmissions.

Helical gears have a longer contact line than spur gears, so their contact efficiency is high, so the thickness of the gear can be reduced and large forces can be transmitted. Since they rotate smoothly, they make less noise, so they are mainly used in transmissions and reducers of high-end vehicles, etc. It is widely used.

In the case of the existing traditional gear production method consisting of hobbing, deburring, and shaving, considerable processing time and expensive equipment and tools are required, so efforts are being made to produce gears more efficiently. come.

In particular, the forging process has been attracting attention as an efficient gear production method that can replace existing cutting methods.

Through consistent research in Korea, significant results have been achieved in the case of spur gears and bevel gears, and gear forming technology at the field level has been secured. However, in the case of helical gears, sufficient forging technology has not yet been secured.

Conventionally, when manufacturing a helical gear, it goes through raw materials - cutting - chamfering - external processing - forging - tapping processing, and the method of producing helical gear parts using forging involves forming an asymmetrical gear mountain using a single PRESS forging method after a multi-stage forming process. It is produced in a way.

This processing method has many problems in improving the manufacturing productivity of automobile parts, so measures are urgently needed.

In addition, the existing helical gear production method has problems such as handling heavy raw materials and semi-finished products, excessive tool wear, and product shipment volume restrictions due to reaching productivity limits.

The present invention was created to solve the above problems, and the purpose of the present invention is to manufacture a helical gear shaft through forging raw materials, thereby eliminating the need for cutting, chamfering, and external processing, thereby improving the manufacturing process. The aim is to provide a cold forging mold for a helical gear shaft that can be reduced and a helical gear shaft manufacturing method.

The cold forging mold for the helical gear shaft of the present invention to achieve the above object is attached to the cold former equipment, and includes a cutting DIE and knife mold that automatically cuts the supplied wire rod; A helical gear forming mold that is formed in multiple stages and sequentially molds the wires cut by the cutting die and knife mold, and performs chamfering, outer diameter processing, and tooth processing of the helical gear by cold forging; It is characterized in that it comprises a; tab processing part for performing tapping processing on the helical gear formed by the helical gear forming mold.

In addition, the mold for forming helical gears is characterized in that it is formed by being divided radially at a certain angle.

In addition, the helical gear shaft manufacturing method of the present invention includes the steps of cutting a wire rod to a certain size; Back extruding the cut wire to form the outer diameter of the gear; Forming the extrusion blank by piercing so that the center of the gear whose outer diameter is formed by rearward extrusion is hollow; It is characterized by comprising the step of forming the extrusion blank by piercing and forming it by forward extrusion so that helical teeth are formed in the formed gear.

In addition, in the front extrusion molding step, a helical tooth shape is formed by inserting a mandrel into the inner diameter of the molded extrusion blank and punching it.

When a helical gear shaft is manufactured using the cold forging mold for a helical gear shaft of the present invention according to the above configuration, the cost is reduced due to cost reduction, and the dimensional accuracy of the product is good, so machining in the post-process is carried out. This unnecessary processing time can be greatly reduced.

In addition, as the surface finishing layer improves the quality, there is no smooth phase scale or decarburization layer, so processing is unnecessary or processing man-hours are reduced.

In addition, because mechanical properties are improved through work hardening during plastic deformation, there is an advantage that the material can be used without heat treatment.

In addition, by developing mold design techniques and mold prototypes for helical gear parts, problems that occur during forging (PIN damage, etc.) can be corrected and the lifespan of the mold can be improved.

Figure 1 is an exploded perspective view showing a cold forging mold for a helical gear shaft of the present invention.
Figure 2 is a diagram showing the forging forming process of a helical gear.
Figure 3 is a graph showing stress-strain.
Figure 4 is a graph showing the molding load distribution.
Figure 5 is a diagram showing the cold front extrusion process of a helical gear.
Figure 6 is a diagram showing the effective strain and deformed shape when a mandrel is not used.
Figure 7 is a diagram showing a state in which the mandrel is inserted into the inner diameter portion of the blank.
Figure 8 is a diagram showing the effective strain and deformed shape when a mandrel is used.
Figure 9 is a diagram showing the deformed shape of the material on the mold teeth when a mandrel is used.
Figure 10 is a photograph showing the lower assembly of the mold and the entire mold set installed on the press.
Figure 11 is a photograph showing a prototype of a molded helical gear.
Figure 12 is a diagram showing a gear tooth profile obtained by three-dimensional gear measurement.
Figure 13 is a photograph showing a tooth bending strength tester of a helical gear.
Figure 14 is a graph showing the results of the tooth bending strength test.

Hereinafter, the cold forging mold for a helical gear shaft and the method for manufacturing a helical gear shaft of the present invention will be described in detail with reference to the drawings.

Figure 1 is an exploded perspective view showing a cold forging mold for a helical gear shaft of the present invention, Figure 2 is a diagram showing the forging forming process of a helical gear, Figure 3 is a graph showing stress-strain, and Figure 4 is a forming load distribution. is a graph showing, Figure 5 is a diagram showing the cold forward extrusion process of a helical gear, Figure 6 is a diagram showing the effective strain and deformed shape when a mandrel is not used, and Figure 7 is a diagram showing the mandrel of the blank. It is a drawing showing the state inserted into the inner diameter part, Figure 8 is a drawing showing the effective strain rate and deformed shape when a mandrel is used, and Figure 9 is a drawing showing the deformed shape of the material for the mold teeth when a mandrel is used. Figure 10 is a photograph showing the lower assembly of the mold and the entire mold set installed on the press, Figure 11 is a photograph showing a prototype of a molded helical gear, and Figure 12 is a gear tooth profile obtained by three-dimensional gear measurement. Figure 13 is a photograph showing a tooth bending strength tester of a helical gear, and Figure 14 is a graph showing the results of a tooth bending strength test.

The cold forging mold for a helical gear shaft according to the present invention includes a cutting DIE and knife mold that is attached to a cold former facility and automatically cuts the supplied wire rod; A helical gear forming mold that is formed in multiple stages and sequentially molds the wires cut by the cutting die and knife mold, and performs chamfering, outer diameter processing, and tooth processing of the helical gear by cold forging; It includes a tab processing part that performs tapping processing on the helical gear formed by the helical gear molding mold.

At this time, it is preferable that the mold for forming the helical gear is formed by dividing it radially at a certain angle.

The helical gear shaft manufacturing method according to the present invention includes the steps of cutting a wire rod to a certain size; Back extruding the cut wire to form the outer diameter of the gear; Forming the extrusion blank by piercing so that the center of the gear whose outer diameter is formed by rearward extrusion is hollow; It includes the step of forming the extrusion blank by piercing and forming it by forward extrusion so that helical teeth are formed in the formed gear.

At this time, in the front extrusion furnace forming step, it is preferable to insert a mandrel into the inner diameter of the formed extrusion blank and punch it to form a helical tooth shape.

The press-fitting sequence of the integrated forging mold is as follows.

Carbide (WC-Co) ⇒ Reinforced ring case (RING-CASE) ⇒ Primary press-fit (cold) ⇒ Carbide mold (WC-Co_DIE) ⇒ Mold case (DIE-CASE) ⇒ Secondary press-fit (cold) ⇒ Mold support (FEELER_DIE) ) ⇒ 2nd pressing (cold) ⇒ Production completed

① WC-Co_DIE, RING CASE, FEELER, CASE, etc. are press-fitted to complete #1DIE

② Carbide (WC-Co): Machining the inner diameter, outer diameter, and plane of the carbide sintered body with an outer diameter of Φ50 * length of 60mm through a polishing process.

③ RING CASE: In the first processing, HOLE (inner diameter), outer diameter, and flat section are processed using CNC automatic lathe equipment. At this time, an extra dimension of +2mm is left unprocessed for secondary processing tolerance. A technology that improves the properties of industrial materials by using heat treatment (heating and cooling) to increase the hardness (HRC) of 61 types of SKD high-speed tool steel before secondary lathe processing. When the material is heated or cooled, the internal structure changes. After the process (the properties are significantly improved), the press-fit tolerance is processed to about 70% (0.07mm) through lathe processing.

④ First pressing (cold): Heating the processed RING_CASE in an electric furnace at a temperature of about 280~320˚C for 2~3 hours and then press fitting the processed carbide.

⑤ CASE & FEELER: The CASE is press-fitted in a shape that surrounds and covers the WC-CO_DIE in which carbide and RING_CASE are press-fitted. At this time, the tolerance is about 50% for cold pressing.

⑥ 2nd press fit (cold): Simultaneous press fit of RING_CASE and FEELER_DIE, which acts as a stand, using a 200 ton press.

⑦ Precision processing: The mold after secondary press fitting is completed through processes such as lathe, CNC lathe, discharge, polishing, and surface treatment.

(Example)

The subject of the present invention is a helical gear with a pitch circle diameter of 43.5 mm and a helical angle of 18.4o for an automobile transmission. For tooth forming of helical gears, it is possible to design a closed forging or forward extrusion type process, but the target product of the present invention is a helical gear with a relatively small diameter, and it was judged appropriate to apply the forward extrusion type process. In the present invention, the material flow and tooth formation trends of forward extrusion type gear molding were identified through CAE analysis, and a prototype was manufactured through molding experiments. In addition, through 3D gear measurement and tooth bending strength tests on the manufactured prototype, it was confirmed that the tooth shape precision and mechanical properties are applicable to automobile transmissions.

1. Product analysis and process design

The shape conditions of the helical gear targeted in the present invention are shown in the table below. As a helical gear used in automobile transmissions, it is a relatively small product with a gear thickness of 16.8mm and a pitch circle diameter of 43.5mm, and the helical angle is 18.4 degrees, which is gentle. The material used was SCM920HVSI, a carburized steel for automobile gears, and carburizing heat treatment is performed after cutting or forging.

In general, the forging process of a helical gear is a closed forging process in which teeth are created in the lateral direction by pressing the top and bottom of the material in a closed mold, as shown in Figure 2 (a), and the material is formed as shown in Figure 2 (b). It is divided into a forward extrusion process in which a load is applied to the upper surface of the machine to create a tooth shape in the longitudinal direction and then extracted in the downward direction.

In the present invention, CAE analysis was performed using Deform-3D, a commercial software, to select the forging process appropriate for the target product among the two processes. The stress-strain diagram of the material used in the analysis is as shown in Figure 3, and the friction constant was 0.08. The shape model for analysis was constructed using tetrahedral elements, with approximately 180,000 and 330,000 grids for the closed forging process and forward extrusion process, respectively. In addition, in both processes, the mold was assumed to be a rigid body, and the pressing speed was set at 70 mm/sec in consideration of the specifications of the molding equipment to be actually used.

The forming load distribution of the two processes obtained from the CAE analysis is shown in Figure 4. In the case of the forward extrusion process, the load increases rapidly at the beginning of forming as shown in Figure 4 (a), but, similar to the general forward extrusion process, it remains in a steady state (Figure 4). It was found that once the Steady State was reached, the forming load was maintained at a constant level of about 120 tons. However, in the case of the closed forging process, as shown in Figure 4 (b), as the shape of the gear teeth became clearer, the load increased rapidly, and it was observed that an even tooth shape was formed only when a load of 500 tons or more was supplied.

In the case of this product, since it is a relatively small product with a pitch circle diameter of 43.5 mm, heating of the material was not considered. If a closed forging process is used, it will be difficult to obtain the required tooth shape precision if sufficient forming load is not supplied. It was judged. In addition, in the case of the forward extrusion process, the product can be naturally discharged downward from the mold after molding is completed, but in the case of the closed forging process, a more complex mold structure is expected to be required because the mold or material must be rotated to eject the product. It was predicted. Therefore, in the case of small-diameter helical gears such as this product, it was judged to be more efficient to apply the front extrusion process. As shown in Figure 5, the extrusion blank is formed by rear extrusion and piercing, and finally the front extrusion is applied in three steps. The process was designed.

2. Analysis of molding characteristics through CAE analysis

go. Freeform extrusion without mandrel

Forward extrusion of hollow products can be divided into a constrained type, which performs molding by inserting a mandrel into the inner diameter, and a free type, which does not use a mandrel. However, in the case of a hollow mold with an empty inner diameter area like this product, if a mandrel is not used, it is expected that the material will separate from the mold surface due to radial compression force, making it difficult to secure the precision of the tooth shape. As shown in Figure 6 (a), in the case of free-form forward extrusion, a difference occurs in the effective strain in the longitudinal direction of the blank, and as indicated by 'A' in Figure 6 (b), the material is exposed to the teeth of the mold during molding. It was confirmed through CAE analysis that the required dimensional accuracy could not be satisfied due to deviation from .

me. Mandrel-applied constrained extrusion

As mentioned above, if the mandrel is not used, it was determined that the tooth shape precision of the molded product cannot be secured due to the material flow in the inner diameter direction. Therefore, in order to improve tooth shape precision, CAE analysis was performed by inserting a mandrel into the inner diameter of the blank as shown in Figure 7. At this time, the introduction angle of the tooth forming part was set to 65 degrees, and the length of the land part was set to 10 mm.

Figure 8 shows the deformed shape and effective strain distribution obtained through analysis. It was confirmed that the material flow in the inner diameter direction was controlled through the insertion of the mandrel, thereby reducing the effective strain deviation in the blank length direction.

In addition, as shown in Figure 9, in order to determine the flow tendency of the material when inserting the mandrel, 3, 7, and 12 mm were cut based on the lower part of the mold and the deformed shape of the material with respect to the mold teeth was compared. saw. There was no particular difference in the material flow characteristics with respect to the longitudinal position of the blank, and comparing the deformed shape at the outlet 'Z-3.0' shown in the figure with Figure 6(b), the material flow characteristics in the inner diameter direction through mandrel insertion showed no particular difference. It was confirmed that the material flow was restricted and the contact between the material and the mold surface was maintained up to the extrusion outlet of the mold. However, despite using about 330,000 grids, the analysis model is somewhat insufficient to simulate fine tooth edges. However, when comparing the areas marked as 'A' and 'B' in Figure 6(b) and Figure 9, respectively, It was confirmed that the contact range between the deformed material and the mold surface increased.

3. Prototype production and verification

go. Prototyping

Figure 10 shows the lower combination of the manufactured mold and the entire mold set installed on the press. The length and extrusion angle of the mold land part were 10 mm and 65 degrees, respectively, identical to the conditions in the CAE analysis performed in the previous section. A 450-ton knuckle press was used in the forming experiment, and the prototype of the formed helical gear is shown in Figure 11. Utilizing the characteristics of the forward extrusion process, testing was performed by varying the length of the initial material in the range of 20 to 60 mm. The prototype shown in the picture is a case where the initial material length is 44 mm. When the forged product is cut to fit the dimensions of the final product, Two products can be obtained through one molding.

me. Verification of tooth shape precision and mechanical properties

In the forging of helical gears, the causes of various errors, such as electrode processing errors, mold discharge errors, elasticity recovery during forging forming, and deformation errors due to heat treatment, must be controlled to achieve tooth shape precision. In the present invention, dimensional accuracy was examined through three-dimensional measurements of electrodes, molds, and prototypes in each process of mold production, forging, and heat treatment. In order to secure the dimensional precision required for the product, three rounds of mold correction were performed. As shown in Figure 12, it was found that the tooth shape precision of the forged product was improved through the improvement of the precision of electrode and electric discharge machining.

Additionally, a gear tooth bending test was performed on the forged and machined helical gear using the device shown in FIG. 13. Because the upper jig had to contact the sides of the helical teeth evenly, some of the teeth were removed by cutting, as shown in the picture on the right, and then installed on the lower jig. In the present invention, heat treatment was performed after cutting and shaving the forged product. In the same way as existing machined products, the temperature was gradually raised in the range of 800 to 900°C, carburization and diffusion were performed, and then quenching and tempering heat treatment were performed. The results of the tooth bending strength test are shown in Figure 14, and it was confirmed that the prototype obtained through the forward extrusion process had greater breaking strength and elongation than the helical gear manufactured by the existing cutting method.

The technical idea of the present invention should not be interpreted as limited to the above-described embodiments. Not only is the scope of application diverse, but various modifications can be made at the level of those skilled in the art without departing from the gist of the present invention as claimed in the claims. Therefore, such improvements and changes fall within the scope of protection of the present invention as long as they are obvious to those skilled in the art.

Claims (4)

A cutting DIE and knife mold that is attached to the cold former equipment and automatically cuts the supplied wire;
A helical gear forming mold that is formed in multiple stages and sequentially molds the wires cut by the cutting die and knife mold, and performs chamfering, outer diameter processing, and tooth processing of the helical gear by cold forging;
A cold forging mold for a helical gear shaft, characterized in that it includes a tab processing portion for performing tapping processing on the helical gear formed by the helical gear molding mold. According to claim 1,
A cold forging mold for a helical gear shaft, characterized in that the mold for forming a helical gear is formed by dividing radially at a certain angle. Cutting the wire rod to a certain size;
Back extruding the cut wire to form the outer diameter of the gear;
Forming the extrusion blank by piercing so that the center of the gear whose outer diameter is formed by rearward extrusion is hollow;
A helical gear shaft manufacturing method comprising: forming an extrusion blank by piercing and forming it by forward extrusion so that helical teeth are formed on the gear formed. According to claim 3,
A helical gear shaft manufacturing method characterized in that, in the front extrusion molding step, a helical tooth shape is formed by inserting a mandrel into the inner diameter of the molded extrusion blank and punching it.