Gear manufacturing has various processes such as hobbing, milling, and gear shaping, but there is also a gear that is pressed out of metal powder, which is the powder metallurgy process.
Detailed explanation of powder metallurgy process
Powder metallurgy gears are commonly used in various automobile engines. Although they are very economical and practical in large quantities, there are still room for improvement in other aspects.
Analysis of Advantages and Disadvantages of Powder Metallurgy Process
Powder metallurgy is a process technology that uses metal powder (or a mixture of metal powder and non-metal powder) as raw material, after forming and sintering, to manufacture metal materials, composite materials and various types of products.
advantage
1. General powder metallurgy gear manufacturing process is less.
2. When the gear is manufactured by powder metallurgy, the material utilization rate can reach more than 95%.
3. The repeatability of powder metallurgy gear is very good. Because powder metallurgy gears are formed by pressing with molds, under normal use conditions, a pair of molds can press tens of thousands to hundreds of thousands of gear compacts.
4. The powder metallurgy method can integrate several parts into one.
5. The material density of powder metallurgy gears is controllable.
6. In powder metallurgy production, in order to facilitate the release of the compact from the die after forming, the roughness of the working surface of the die is very good.
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shortcoming
1. It must be produced in batches. Generally speaking, a batch of more than 5,000 pieces is more suitable for powder metallurgy production;
2. The size is limited by the pressing capacity of the press. The press generally has a pressure of several tons to several hundred tons, and the diameter is basically within 110mm and can be made into powder metallurgy;
3. Powder metallurgy gears are limited by structure. Due to pressing and mold reasons, it is generally not suitable for the production of worm gears, herringbone gears and helical gears with a helix angle greater than 35°. For helical gears, it is generally recommended to design the helical teeth within 15°;
4. The thickness of powder metallurgy gears is limited. The depth of the mold cavity and the stroke of the press must be 2 to 2.5 times the thickness of the gear. At the same time, the uniformity of the longitudinal density of the gear height is considered, so the thickness of the powder metallurgy gear is also very important.
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Basic process of powder metallurgy process
1. Milling is the process of making raw materials into powder. Commonly used milling methods include oxide reduction method and mechanical method.
2. Mixing is the process of mixing various required powders in a certain proportion and homogenizing them to make green powder. It is divided into three types: dry type, semi-dry type and wet type, which are used for different requirements.
3. Molding is the process of putting the uniformly mixed material into the die and pressing it into a parison with a certain shape, size and density. The molding method is basically divided into pressure molding and non-pressure molding. Compression molding is the most widely used in compression molding.
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4. Sintering is a key process in the powder metallurgy process. The formed compact is sintered to obtain the required final physical and mechanical properties. Sintering is divided into unit system sintering and multi-system sintering. In addition to ordinary sintering, there are also special sintering processes such as loose packing sintering, immersion immersion method, and hot pressing method.
5. The treatment after sintering can be done in various ways according to different product requirements. Such as finishing, oil immersion, machining, heat treatment and electroplating. In addition, in recent years, some new processes such as rolling and forging have also been applied to the processing of powder metallurgy materials after sintering, and achieved better results.
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Clamping system in common gear processing methods
Powder metallurgy is a method of manufacturing gears in large quantities, and the common processes such as gear hobbing and gear shaping seem to be able to better meet the needs of multiple varieties and small batches. At this time, their clamping systems are very particular.
From ordinary turning→hobbing→shaping→shaving→hard turning→grinding→honing→drilling→inner hole grinding→welding→measurement, configuring a suitable clamping system for this process is very important. Particularly important.
1. Ordinary car processing
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In conventional turning, the gear blank is usually clamped on a vertical or horizontal turning machine. For automatic clamping fixtures, most of them do not need to install auxiliary stabilizing devices on the other side of the main shaft.
2. Hobbing
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Gear hobbing is a cutting process used for the production of external gears, spur gears because of its outstanding economy. Gear hobbing is widely used not only in the automotive industry, but also in the manufacture of large industrial transmissions, provided that it is not limited by the outer contour of the workpiece to be machined.
3. Shaping processing
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Gear shaping, a process for processing gears, is mainly used when gear hobbing is not possible. This processing method is mainly applied to the processing of internal teeth of gears and the processing of external teeth of some gears subject to structural interference.
4. Shaving processing
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Gear shaving is a finishing process for gears that is cut with a blade that corresponds to the tooth shape of the gear. This process has a high production economy, so it has been widely used in industry.
5. Hard turning
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Hard turning makes it possible to replace expensive grinding processes. In order to make it work properly, the various parts of the system and the processing parts are connected together correspondingly. Selecting the correct machine tools, fixtures, and cutting tools determines the quality of the turning effect.
6. Grinding processing
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Hard finishing of the tooth flanks is in many cases essential in order to successfully achieve the precision necessary in today's gear production. In mass production, it is a very cost-effective processing method. On the other hand, similar to prototyping, gear grinding offers greater flexibility when using adjustable grinding tools.
7. Honing processing
Honing is the final finishing process of hard gears using an amorphous cutting angle. Honing not only has high economic efficiency, but also can make the processed gear have a smooth surface with low noise. Compared with grinding, the cutting speed of honing is very low (0.5-10m/s), thus avoiding the damage of cutting heat to gear processing. More precisely, the internal stress generated on the machined tooth surface has a certain positive effect on the bearing capacity of the equipment.
8. Drilling
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Drilling is a rotary cutting process. The axis of rotation of the tool and the center of the hole to be processed are completely consistent in the axial direction, and are consistent with the axial feeding direction of the tool. The main axis of the cutting motion should be consistent with the tool, regardless of the direction of the feed motion.
9. Inner hole grinding
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Bore grinding is a machining process with an amorphous cutting angle. Compared with other cutting processes, grinding has the advantages of high dimensional and forming accuracy for hard metals, dimensional accuracy (IT5-6), small vibration marks and high-quality surface accuracy (Rz=1-3μm), etc.
10. Capacitor discharge welding
Capacitor discharge welding belongs to the resistance welding process. Capacitor discharge welding is achieved by very fast current build-up, relatively short welding times, and very high welding currents. Therefore, capacitor discharge welding has many advantages. In view of the increasing energy price, the economy and high efficiency of capacitor discharge welding are all the more important.
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11. Measurement
The detection of gears is very extensive, and it must be adjusted according to different forms of gears. In the measurement of gears, various important parameters of gears are determined through length, angle measurement, and special gear process measurement.
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The above is a demonstration of powder metallurgy processing of gears, and an example of fixture system under processing methods such as gear shaping and hobbing. In addition to the batch size, the specific selection should also be combined with actual and reasonable analysis to facilitate the realization of the manufacturing process.
