Precision machining of large transmission parts in the reloading industry

Zhao Hong, Technical Director and Senior Engineer, Transmission Equipment Branch, Northern Heavy Industry Group Co., Ltd.

With the continuous development of the equipment manufacturing industry, in the industries of mining, metallurgy, coal, electric power, military industry and building materials, the precision requirements for transmission components in mechanical equipment are increasing. The transmission equipment introduced in this paper is applied to heavy equipment manufacturing, products. It includes heavy-duty gearboxes of various specifications in rolling equipment, stacking and reclaiming equipment, grinding equipment and wind power equipment, as well as large-diameter ring gears used in grinding and calcining equipment. Transmission components are usually important components in mechanical equipment, and their operation accuracy directly affects the stability of the entire system. Therefore, in the increasing product quality, under the trend of promoting energy conservation and emission reduction and increasing equipment scale, the industry And the market demand for product precision is also increasing, from the original large and crude product quality gradually changed to fine, fine, to adapt to the development of equipment manufacturing, which is also the old industrial base in the northeast of Nirvana rebirth from extensive to sophisticated The general trend of transformation.

1. Precision Machining of large ring gear:

Large diameter gears are mainly used in large mining mills and coal mills. Some medium and small diameter ring gears are used in high-precision machine tools and military products. In the 20th century, precision requirements for such products are not high. However, the problems that followed have also appeared one after another, such as the reduction of the life of the ring gear, the increase of the vibration of the gear pair, and the frequent shutdown and maintenance of the equipment. Therefore, in the products manufactured in recent years, the transmissions in such products are The precision of the parts is improved, and the large ring gear is improved from the original ISO9 level accuracy to ISO7 level or even ISO6 level. The surface roughness value of the tooth surface is increased from the original Ra=6.3 μm to Ra=1.6-0.8 μm (see Figure 1). ). For large diameter ring gears, this accuracy requirement is a big breakthrough in terms of manufacturing equipment, manufacturing processes or inspection methods. In the production process, the material of the large-diameter ring gear is mostly steel casting, which is easy to generate stress deformation during the machining process. In order to reduce the accuracy of the ring gear affected by the deformation, the manufacturing process of the large ring gear has been improved several times, and finally adopted. 3 times of 镗, 3 times of car, 2 times of heat treatment, 2 times of milling process, in the roughing process before the tooth finishing process to release the internal stress of the steel casting blank to achieve the minimum deformation of the product, The effect of deformation on the accuracy of the ring gear is greatly reduced. Russian and German imported hobbing machines are used on the processing equipment, with a maximum machining diameter of 14 m.

Figure 1 MSZ8848 self-grinding machine (tooth ring diameter 11.6 m, accuracy class ISO8)

In order to further improve the precision of the product, we are investigating the introduction of 16 m CNC six-axis gear hobbing machine with a maximum machining diameter of 16 m. The main drive gear of the machine tool adopts DIN2 grade grinding gear. The precision of the product can reach AGMA10, and it is powered by German Heath Company. Knife-integrated tool holder. At present, our two 13.3 m large ring gears are being machined on this machine to be introduced to test the performance of the machine when machining oversized ring gears. The ring gear accuracy requires AGMA10 and the surface of the tooth surface is rough. The degree of Ra = 1.6 μm. For the ring gear of this specification, the accuracy requirement is already very strict, and it is rarely realized in China at present. This ring gear adopts a new process of grooving and tempering, that is, quenching and tempering after rough roughing and rough milling, which can more fully release the internal stress of the steel casting blank and make the finished ring gear smaller and accurate. Higher and effectively increase the hardness of the tooth surface. At the same time, the German GAGE ​​MASTER portable gear detector will be introduced to test the accuracy of the ring gear.

Among our partners, there are 5 m large CNC gear grinding machines for manufacturing high-precision large ring gears or heavy-duty hard-toothed gear shafts. On the hobbing tools, we use domestic tool factories such as Harbin Tool Factory and Hanjiang. AA grade gear hobs produced by tool factories and Ingersoll carbide tools.

For testing, we purchased the 2.5 m×4 m×4 m large three-coordinate testing center produced by Xi'an Edward Measuring Equipment Co., Ltd. to detect the accuracy of tooth profile and tooth direction, and cooperated with Beijing University of Technology and Harbin Measuring Tool Factory. Developed a large-scale ring gear laser tracking in-position measurement system. The highest detection level of the system can reach ISO4 level, which can detect any diameter ring gear. It is an important detection method for our large ring gear products.

2. Heavy duty gearbox precision machining:

In all types of gearboxes, the accuracy of the gears affects the service life of the gearbox and affects the stability of the system throughout the gearbox.

The gears used in our gearboxes include involute inner and outer cylindrical gears, circular arc gears and bevel gears. The gear accuracy grades in high-precision gearboxes are mostly above ISO6, and the surface roughness of the tooth surface. A hard-toothed gear having a value of Ra = 0.8 μm or less is usually manufactured by grinding and scraping in manufacturing. Our cylindrical gear grinding equipment is mainly based on the German HOFLER gear grinding machine. The maximum grinding gear diameter is 1.5 m, the maximum grinding gear module M25, and the corresponding 1.6 m gear detector. The highest detection accuracy is ISO4.

In the key product LMX series vertical grinding planetary reducer (see Figure 2), the accuracy of the spiral bevel gear pair of the first-stage transmission is very high. The spiral bevel gear pair we use is Klingenberg gear system. The carbon quenching process achieves a high-hardness tooth surface, but the spiral bevel gear is easily deformed after quenching, causing the gear position to shift when the gear pair is installed, which reduces the contact area, reduces the transmission accuracy, and vibrates during use. The noise is increased, the life of the gear is shortened, and the use of the whole equipment is seriously affected. Therefore, it is necessary to increase the tooth surface finishing process after carburizing and quenching, to perform the tooth surface finishing by the scraping method, and to detect the gear pair by the gear pair. To achieve high precision requirements.

Figure 2 LMX series vertical mill reducer

High-precision product quality requirements cannot rely solely on advanced manufacturing equipment and advanced testing methods, but also rely on advanced management methods. With advanced management methods, we can more closely combine various factors such as manpower, materials, equipment and methods to maximize the production system and maximize the equipment and manpower. Our company introduced “7S” and “lean production” in management.

Such advanced management concepts have enabled “all things to use” and “people to do their best”, which has promoted the company's good, steady and rapid development. This is also an important force to enhance the competitiveness of enterprises in the rapidly developing equipment manufacturing industry.