JPH0325253B2 - - Google Patents

Description

[Detailed description of the invention]

Field of Application This invention relates to a method for manufacturing high-precision spur gears, in which precision die forging is performed by warm forging, the gear cutting process is omitted, and the tooth base bending strength is improved by grain refinement carburizing treatment. Concerning the manufacturing method of precision and high strength spur gears. Background technology The accuracy of gears used in automobiles etc. is JIS4
High-precision spur gears of grade or higher are generally manufactured through the following manufacturing process: rolled material → hot forging → normalizing (annealing) → machining → gear cutting → carburizing/quenching/tempering → wrapping. There is. As mentioned above, conventional manufacturing methods have required machining and gear cutting steps after hot forging.
This machining and gear cutting process generates scale on the material after hot forging, and it is not possible to finish it to precise dimensions with hot forging. Then, after hot forging, it was finished to precise dimensions by machining and gear cutting. However, the above-mentioned machining and gear cutting processes are factors that increase production costs, resulting in poor yields and disadvantages for mass production. There were various problems such as a decrease in bending strength. Purpose of the invention The object of the present invention is to provide a method for manufacturing a spur gear that can manufacture high-precision spur gears with high yield and high efficiency, and
The objective is to create a method for manufacturing high-precision, high-strength spur gears that can omit the machining and gear cutting processes that are essential in conventional manufacturing methods, and can improve the bending strength of the tooth root. Structure and Effects of the Invention As a result of various studies aimed at omitting the machining and gear cutting processes in the manufacture of spur gears and increasing the accuracy and strength of spur gears, the present invention has been developed. By using warm forging, which combines the advantages of cold forging and hot working, which provides high deformability with low loads, the gear cutting process is omitted, and after heating and holding the steel material to its carburizing temperature, the Ar ₁ of the steel material used is It has been discovered that the bending strength at the root of the tooth can be improved by a grain-refining carburizing treatment in which the steel is cooled to below the transformation point and heated again to the quenching temperature for quenching. In other words, this invention involves cutting a round steel bar to the required length, removing scale, and performing a preliminary upsetting process with a total upsetting rate of 20% or more. heating and soaking in a water-soluble lubricant solution to form a lubricating film on the surface of the material,
The spur gear is heated to 650°C to 900°C by high frequency heating and made into a spur gear by precision die forging. Alternatively, if preliminary upsetting is not performed after the scale removal described above, preliminary upsetting is performed before the precision die forging process. After forming a spur gear by die forging, sizing or shaving the spur gear, and carburizing the spur gear,
This method of manufacturing a high-strength spur gear is characterized by cooling the gear to below the Ar ₁ transformation point and heating it again to perform quenching and tempering. This invention uses warm forging to omit the gear cutting process that was previously indispensable in the manufacturing method of high-precision spur gears, making it possible to reduce manufacturing costs, and strengthening metal flow through preliminary upsetting. , the metal flow in the cross section of the product is not cut, and the fine carburizing treatment improves the tooth base bending strength by more than 10% compared to conventional spur gears made by hot forging and gear cutting, resulting in high precision.・
High-strength spur gears can be easily manufactured with high efficiency and at low cost. Preferred Embodiment of the Invention In this invention, scale is removed after cutting the round steel bar to the required length. In order to prevent deformation of the forging material and sagging of the end face, it is preferable to cut with a saw or restraint shear, and then cut with a shot. Blasting or pickling may be performed to remove scale, and if necessary, the edges of the forging material may be chamfered to prevent folding flaws during die forging. In this invention, the reason why a round steel bar of the required length that has been pre-upset with a pre-upsetting rate of 20% or more is used as the forging material is because the metal flow is sufficiently bent at the manufacturing teeth. This is to make the gear a forged gear, and is effective in improving the bending strength of the tooth base. This total upsetting rate is the ratio of the product height when forged into a gear and the cut round bar material, and if it is less than 20%, the above strength improvement effect will be small, so a preliminary upsetting process of 20% or more is required. Moreover, the same effect can be obtained even if this preliminary upsetting is performed before tooth flank forging in the warm precision die forging process. The material temperature when the forging material is immersed in a water-soluble lubricant solution to form a lubricant film on the material surface is:
If it is less than 100℃, the drying rate of the lubricant film on the surface is poor and is undesirable, and if it exceeds 200℃, the lubricant will adhere to the material surface in the form of bubbles and a uniform and sufficient film will not be formed. The heating temperature shall be . This lubricant film functions to prevent scale generation during high-frequency heating and as a lubricant during precision die forging, and colloidal graphite is generally used, but a water-soluble carbon lubricant is also preferred in this invention. Heating during precision die forging is performed to suppress scale formation and to perform economical heat treatment, for example,
Rapid heating is required at a heating rate of 200°C/min or higher, and high-frequency heating is preferred. In addition, when the heating temperature during high-frequency heating is less than 650℃, the deformability is low.
It is undesirable because the forging load becomes high and the effect of work hardening remains on the product.On the other hand, when the temperature exceeds 900℃, scale formation is observed and the tooth profile accuracy of the product decreases, which is undesirable. Heating temperature. The forging material heated to the above temperature is charged into a mold attached to a forging machine such as a clamp press to perform warm precision forging. The molded product is taken out of the mold and cooled in air, but if the material is a highly hardenable material, slow cooling is required to facilitate cutting in the subsequent process. Slow cooling is also effective in preventing grain coarsening during carburizing. After warm die forging, sizing such as extrusion forging or shaving is performed to improve the tooth profile accuracy of spur gears.
It may be selected as appropriate depending on various conditions such as required gear accuracy and cost. In this invention, the fine carburizing treatment method involves heating to the normal carburizing temperature, holding this temperature for the required time, cooling to below the Ar ₁ transformation point, and heating again to the required quenching temperature to perform quenching and tempering. The heating temperature, holding time, cooling rate, etc. are appropriately selected depending on the material. Example Spur gears whose specifications and dimensions are shown in FIG. 1 and Table 1 were warm forged under the conditions shown in Tables 1 and 2. In other words, as-rolled round steel bars (SCr
420) to the dimensions shown in Table 2, scales were removed by shot blasting, preliminary upsetting was performed as shown in Table 2, heated to 140°C, and a water-soluble lubricant (trade name) : Deltaforge 144, manufactured by Acheson Japan Co., Ltd.) was immersed in a 2-fold diluted solution to form a lubricating film, and then subjected to high frequency heating and warm die forging using a crank press under the conditions shown in Table 1. After warm forging, it was taken out from the mold, air cooled, and shaved, and then subjected to grain refinement carburizing treatment according to the present invention and conventional carburizing treatment. For comparison, spur gears with the same specifications were manufactured using conventional hot forging and gear cutting under the conditions shown in Table 2. The root bending strength and crystal grain size of the various spur gears obtained were measured, and the results are shown in Table 2. In addition,
The tooth root bending strength test was performed by bending the tooth using a press machine, and the grain size was indicated by the ASTM grain size number. In addition, 7,000 spur gears were forged using the above method of the present invention and the tooth profile accuracy was measured, and the results shown in Table 3 were obtained. As is clear from the results in Table 2, the method of the present invention, which involves preliminary upsetting of 20% or more, warm die forging, and grain refinement carburizing treatment, produces a spur gear that has been previously hot forged and gear cut. As a result, high strength gears can be obtained, 53
% total upsetting rate is higher than that of conventional manufacturing method.
A 20% increase in strength was observed. Further, as shown in Table 3, it can be seen that the manufacturing method according to the present invention can mass-produce spur gears with JIS overall grade 4 accuracy with high efficiency without a gear cutting process.

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【table】 [Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing a spur gear.

Claims (1)

[Scope of Claims] 1 After cutting a round steel bar to a required length, removing scale and performing preliminary upsetting with a total upsetting rate of 20% or more, the forging material is heated at a temperature of 100°C to 200°C. A lubricant film is formed on the surface of the material by heating it to a temperature range of 650℃ to 900℃ by immersing it in a water-soluble lubricant solution.
The resulting spur gear is sized or shaved, and then the spur gear is carburized, cooled to below the Ar ₁ transformation point, heated again, and quenched. A method for manufacturing a high-strength spur gear, which is characterized by performing a return process. 2. After cutting the round steel bar material to the required length and removing the scale, the forging material is heated to a temperature range of 100°C to 200°C and immersed in a water-soluble lubricant solution to form a lubricating film on the surface of the material, 650℃~900℃ by high frequency heating
After heating and pre-upsetting to a total upsetting rate of 20% or more, it is made into a spur gear by precision die forging.
After sizing or shaving the obtained spur gear and carburizing the spur gear, Ar ₁
A method for manufacturing a high-strength spur gear, characterized by cooling to below a transformation point and heating again to perform quenching and tempering.