JPH0261863B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a spur gear in which precision die forging is performed by warm forging and a gear cutting process is omitted. The accuracy of gears used for automobiles etc. is JIS4.
High-precision spur gears of grade or higher are made from rolled material→hot forging→
Normalizing (annealing) → Machining → Gear cutting →
It was made using a manufacturing process of carburizing, quenching, tempering, and wrapping. As mentioned above, machining and gear cutting processes were required after hot forging. In the machining and gear cutting processes mentioned above, scale is generated after hot forging, so it is not possible to finish to precise dimensions by hot forging. After hot forging, it was finished to precise dimensions by machining and gear cutting. However, there was a problem in that the inclusion of these machining and gear cutting processes increased production costs, which was disadvantageous for mass production. In view of the current situation, this invention utilizes warm forging, which has the advantages of both cold forging, which has the advantage of no scale generation and high precision, and hot working, which has the advantage of obtaining high deformability under low load. This paper proposes a method for manufacturing high-precision spur gears that eliminates the gear cutting process. That is, this invention provides: (1) A round steel bar having a diameter that is 65% or more and less than 100% of the root diameter of a spur gear of module 4 or less to be manufactured is cut to a required length and scale is removed. The obtained blank is heated to a temperature range of 100 to 200°C and immersed in a water-soluble lubricant solution to form a lubricant film on the blank surface, and then heated to a temperature range of 650 to 900°C by high frequency heating to form a precision mold. A method for manufacturing spur gears, characterized by forging. (2) The method for manufacturing a spur gear according to claim 1, wherein the thickness of the lubricating film is 5 to 20 μm. (3) The method for manufacturing a spur gear according to Claims 1 and 2, characterized in that after the precision die forging, slow cooling is performed at a cooling rate lower than air cooling. It is related to. In other words, when manufacturing spur gears with complex and highly accurate tooth profiles, hot forging, which is easy to form the shape, generates a large amount of scale and large heat shrinkage, so it is difficult to manufacture spur gear teeth with good precision. The tooth profile could only be formed by cutting the teeth. In addition, when attempting to form a tooth profile by cold forging, a large load is required, resulting in breakage of the mold and various defects such as lack of thickness and non-filling in the tooth portion, making it impossible to form the tooth. However, in this invention, in spur gears with module 4 or less, the diameter of the spur gear is 65% or more and 100% of the root diameter of the spur gear.
Control the carbon lubricant film thickness by using a cylindrical blank with a diameter of less than 650℃~900℃
It was discovered that spur gears with extremely high tooth profile accuracy can be manufactured by warm forging in the atmosphere at a temperature of They discovered that this could be prevented and completed this invention. In this invention, the blank outer diameter dimension is extremely important in order to maintain the tooth profile accuracy of the spur gear. The direct diameter of the blank 1 is 100% of the root diameter of the spur gear because it is necessary to make the root diameter of the spur gear smaller in order to fit it into the hole 4 of the forging die, as shown in Figure 3.
less than However, even in this case, as a result of detailed study, the tooth profile of a spur gear having a tooth height of module 4 or more cannot be formed well. In other words, in module 4 and above, the material is cooled by the mold during the tooth profile filling process, and the temperature drops significantly below 650°C, deteriorating the deformability of the material, causing cracks at the tooth tips, and abnormally large deformation resistance. This is because the material cannot be filled up to the tooth ridges, that is, the tooth tips, if the pressure resistance of the mold is below. If the forging temperature is 900℃ or higher, it is possible to forge module 4 or higher, but
Scale occurs and tooth profile accuracy is poor. Furthermore, when the blank diameter is less than 65% of the spur gear root diameter, the blank 1 is replaced by the upper punch 2,
After being upset by the lower die 3, the material is further cooled by the mold as it fills the tooth profile, which deteriorates the deformability of the material and increases the deformation resistance, making the tooth profile of the spur gear free of underfilling 5 and cracks 6. It turned out that it could not be molded. FIG. 4 shows the relationship between the blank diameter and the area in which high-precision tooth formation is possible. This figure shows that when the blank diameter is less than 65% of the spur gear root diameter, the formable area decreases rapidly. For the above reasons, the blank diameter was limited to 65% or more and less than 100% of the root diameter of the spur gear to be manufactured. If the blank temperature when immersed in a water-soluble lubricant solution is less than 100℃, the lubricant film will not dry properly;
If the temperature exceeds 200℃, the lubricant will adhere in the form of bubbles and a sufficiently uniform film cannot be formed, so the heating temperature of the blank should be
The temperature range was 100 to 200°C. Heating during precision die forging requires rapid heating to suppress the formation of scale and to process economically, and therefore it is desirable to use high frequency heating. In addition, if the heating temperature at that time is less than 650℃, the deformability of the material will be low, cracks will occur at the tooth tip, the deformation resistance will be high, and a large forging load will be required to fill the material to the tooth tip. As a result, the pressure exceeds the pressure resistance of the mold and the mold is damaged. In addition, processing strain and residual stress remain in the product, which is undesirable. On the other hand, when the temperature exceeds 900°C, the filling of the tooth tip with material is stable, but scale formation is observed and the tooth profile accuracy of the product decreases. Therefore, the temperature range was limited to 650-900°C. Although colloidal graphite is generally used as a lubricant for warm forging, a water-soluble carbon lubricant is also used in this invention. Next, embodiments of the invention will be described. A round steel bar having a diameter of 65 to 100% of the root diameter Do of the spur gear to be manufactured is cut into the required length, subjected to shotplast or pickling to remove scale, and then used as a blank. At this time, in order to prevent the corner portions of the blank from forming folding flaws during die forging, it is better to chamfer the corner portions by grinding, cutting, or forging. Furthermore, if a round steel bar is cut using normal shear cutting, the deformation of the blank and the sagging of the end face will become large, so it is necessary to lubricate the blank and modify the shape by separately forging, etc., which ends up increasing costs. Therefore, it is desirable to perform saw cutting or constrained shear cutting. The above blank is heated to a temperature of 100 to 200°C in a heating furnace, and a water-soluble lubricant solution previously stored in a storage tank, such as White Lup (trade name of Taihei Kagaku products), Delta Forge 144 (trade name of Nippon Acheson products), is added to the blank. ) to form a lubricating film with a thickness of about 5 to 20 μm on the blank surface. If the carbon lubricant film thickness is less than 5 μm, defects such as seizure of the spur gear teeth and die, lack of thickness in the teeth, or unfilling will occur due to poor lubrication, and if it exceeds 20 μm, the corners of the die tips will not be lubricated. The agent becomes clogged, the tooth becomes thin,
It is desirable to limit the thickness of the carbon lubricant film to a range of 5 to 20 μm since underfilling occurs at the corners. Then, by high frequency heating, for example, 200℃/
The heated blank is rapidly heated to a temperature range of 650 to 900°C at a heating rate of min or more, and warm precision forging is performed by charging the heated blank into a mold set in a forging machine such as a clamp press. The molded product is removed from the mold and air cooled. In addition, if the blank is made of a material with high hardenability,
If the material is air-cooled, it will be quenched and the material will harden, which will reduce tool life in the subsequent cutting and shaving processes, so slow cooling is necessary in this case. Slow cooling is also effective in preventing grain coarsening during carburizing. Example Spur gear A shown in Fig. 1 and spur gear B shown in Fig. 2 were each made using blanks shown in Table 1,
It was finished by warm precision forging under the forging conditions shown in the same table.

[Table] Using the above manufacturing method, the tooth profile accuracy was measured when 500 pieces were forged and when 7000 pieces were forged. The results are shown in Tables 2 and 3.

【table】

[Table] From Table 2 above, it can be seen that when 500 pieces were forged, all of them achieved good results of grade 4 or higher in terms of JIS overall accuracy. Also, according to Table 3, the tooth profile accuracy when forging 7000 pieces is slightly inferior to when forging 500 pieces, but by shaving it can easily maintain high accuracy of JIS class 4 or higher. As described above, by performing warm forging, this invention can mass-produce spur gears with high tooth profile accuracy, and can significantly reduce production costs by omitting the gear cutting process.

[Brief explanation of drawings]

Figures 1 and 2 are longitudinal cross-sectional views of spur gears manufactured according to the present invention, and Figure 3 shows the main parts of the forging die, with the left half showing the state before forging and the right half showing the state after forging. The explanatory diagram shown in FIG. 4 is a graph showing the relationship between the blank diameter and the area in which high-precision tooth formation is possible. D...outer diameter, Do...trough diameter, T...thickness.

Claims (1)

[Claims] 1. Obtained by cutting a round steel bar material having a diameter of 65% or more and less than 100% of the root diameter of a spur gear of module 4 or less to be manufactured into a required length and removing scale. The blank is heated to a temperature range of 100 to 200℃ and immersed in a water-soluble lubricant solution to form a lubricant film on the blank surface, and then heated to a temperature of 650 to 900℃ by high-frequency heating.
A method for manufacturing spur gears, characterized by precision die forging by heating to a temperature range of ℃. 2. The method of manufacturing a spur gear according to claim 1, wherein the lubricating film has a thickness of 5 to 20 μm. 3. The method for manufacturing a spur gear according to claim 1, wherein after the precision forging, slow cooling is performed at a cooling rate lower than air cooling.