Development of the hottest powder metallurgy doubl

2022-08-03
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Development of powder metallurgy double sided gear

[Key words]: powder metallurgy; Double sided gear; Mold base transformation; Bright quenching

[Abstract]: powder metallurgy double-sided gears with multi-step, complex shape and bright surface were originally produced by foreign manufacturers. The author has developed this kind of part by using fecuc material, by means of reforming the press mold base and die structure, and by using bright quenching treatment. Its hardness can reach or exceed hrc30

1 preface

powder metallurgy can form products with almost final shape. However, for parts with many steps and complex shapes, it is usually necessary to complete the product forming process through a multi-functional press and mold base. How to carry out technical transformation on the existing common press and mold base, so that it can press special-shaped multi-step parts, so as to improve the original equipment level at the temperature of 150 ℃, save investment and reduce product cost is a problem that many manufacturers are looking forward to solving. At the same time, users now have higher and higher requirements for product performance and surface quality. How to select the appropriate heat treatment process to make the product achieve both high performance and good surface quality is also a problem to be solved in actual production. Practice has proved that these problems can be solved by adopting appropriate methods [1,2]

powder metallurgy double-sided gear is a product required by foreign customers. The product shape is shown in Figure 1. The two ends of the part are symmetrical gears, the middle is an annular belt, the two ends are also provided with a concave small step, and the annular belt is drilled with two M8 screw holes. It is required that the material is fecuc, the density is greater than 6.4g/cm3, and the surface hardness of the parts after heat treatment reaches hb286 (hrc30). The gear is characterized by multi-step, complex shape, and bright surface after heat treatment. This part was originally produced by foreign manufacturers. After trial production, we successfully manufactured the product. This paper introduces the development process of the gear, which is the same as that of Johnson Matthey, an international chemical giant

2 trial production process

trial production process:

mixing - forming - sintering - drilling, tapping - heat treatment - oil immersion - finished product

mixing is carried out in the V-type powder mixer; Press on ya79125 hydraulic press; It is sintered in a pusher sintering furnace at 1100 ℃ for 90min under the protection of decomposition ammonia atmosphere. After sintering, the samples were drilled, tapped, Quenched and tempered at low temperature. Finally, soak the oil in the vacuum oiler

3 trial production results

3.1 the difficulty in forming the product is in forming. Because the shape of the product is three steps up and down, that is to say, three die punches up and down must be used during forming. The existing ya79125 hydraulic press has a single upper and lower oil cylinders. Generally, the mold base is only equipped with one die punch for the upper and lower parts, which lacks the function of forming multi-step parts. Through analysis, we simplified the die into a structure of two die punches at the top and bottom, that is, the forming concave small step and the end face were combined into one die punch. At the same time, the original common mold base is reformed to have a double punch structure. The upper punching structure has also been modified so that two die punches can be installed, and a spring floating structure is added to the outer upper punching to ensure uniform powder distribution and consistent compression ratio during pressing. In addition, a demoulding ejection mechanism is added to the inner punch. During pressing, the outer upper punch first enters the female mold, and the depth is about twice the height of the step, and the inner upper punch also enters the female mold. Then, the outer up punch floats upward relative to the inner up punch, while the outer down punch and the female die float downward, and finally the pressing is completed. During demoulding, protective demoulding shall be adopted: two upper punches shall be used to hold the blank, and the female mold, outer lower punch and core rod shall be pulled down (out) first; Then, the two upper punches rise, and the inner upper punches eject the blank from the outer upper punches by means of the ejection mechanism during the rising process

3.2 sintering is the key process to control product performance. In order to make the product reach the required performance, the sintering quality must be well controlled. One is to control the deformation and ensure the required dimensional accuracy. It is mainly to ensure that the sintering box is flat, and the products shall be arranged neatly with a gap, so as to prevent expansion and box deformation and extrusion during temperature rise, and control the temperature rise rate and temperature drop rate. The second is to control the content of combined carbon so that the products after heat treatment can meet the required structure and properties. Due to the high decarburization tendency and uneven decarburization in decomposed ammonia atmosphere, these products must be properly protected during sintering. Satisfactory results were obtained by capping and carbon sealing in the sintering box

carbon sealing effectively reduces decarburization, and makes the product structure and performance more uniform if more information is needed

3.3 heat treatment

the product has high surface quality requirements, and it is difficult to guarantee the general heat treatment methods. So we use belt type continuous bright quenching furnace for bright quenching. The heating temperature is 860 ℃, the heating speed is 50mm/min, and the decomposition ammonia atmosphere is used for protection. After heating, it is automatically quenched into bright oil, and then tempered at 200 ℃ for 2h. After treatment, the surface is bright, the hardness is uniform and the deformation is small. The results are shown in Table 2. It can be seen from table 2 that the size changes slightly after heat treatment, mainly due to swelling, which may be due to phase transformation after quenching, but can be controlled within the allowable tolerance range. At the same time, it can be seen that as long as the density is greater than 6.4g/cm3, the heat treatment hardness can be greater than hrc30

4 conclusion

(1) the powder metallurgy double-sided gear made of fecuc material with pressing density ≥ 6.4g/cm3 can reach or exceed hrc30 after bright quenching

(2) by reforming the die base and upper die punching structure of ya79125 hydraulic press, the special-shaped multi-step parts are successfully pressed

(3) the bright quenching treatment of powder metallurgy structural parts not only achieves the required performance, but also obtains the ideal surface quality

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