There are various processes such as gear hobbing, milling, gear shaping, etc., but there is also a gear that is pressed out of metal powder, that is, powder metallurgy process. Let's start with a video to see what the difference is:
Part.1
Detailed explanation of powder metallurgy process
Powder metallurgy gears are commonly used in all kinds of automobile engines, and although they are very economical and practical in the case of large quantities, there are other areas that need to be improved.
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Analysis of the 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 to manufacture metal materials, composite materials and various types of products through forming and sintering.
Merit:
1. The general powder metallurgy gear manufacturing process is less.
2. When manufacturing gears by powder metallurgy method, the material utilization rate can reach more than 95%.
3. The repeatability of powder metallurgy gears is very good. Because powder metallurgy gears are pressed into shape by molds, under normal use conditions, a pair of molds can press tens of thousands to hundreds of thousands of gear blanks.
4. The powder metallurgy method can integrate several parts into manufacturing.
5. The material density of powder metallurgy gears is controllable.
6. In powder metallurgy production, in order to facilitate the removal of the blank from the die after forming, the roughness of the die working surface is very good.
Shortcoming:
1. It must be mass-produced, generally speaking, the batch of more than 5000 pieces is more suitable for powder metallurgy production;
2. The size is limited by the pressing capacity of the press. THE PRESS IS GENERALLY A FEW TONS TO HUNDREDS OF TONS OF PRESSURE, AND THE DIAMETER IS BASICALLY WITHIN 110MM, WHICH 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°. Helical gears are generally recommended to be designed within 15°;
4. The thickness of powder metallurgy gears is limited. The cavity depth and press stroke must be 2~2.5 times of the gear thickness, and considering the uniformity of the longitudinal density of the gear height, the thickness of the powder metallurgy gear is also very important.
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The basic process of powder metallurgy process
1. Milling is the process of making raw materials into powder, and the commonly used milling methods include oxide reduction method and mechanical method.
2. Mixing is the process of mixing all kinds of required powders in a certain proportion and homogenizing them into billet powder. There are three types: dry, semi-dry and wet, which are used for different requirements.
3. Forming is the process of mixing evenly mixed materials, loading them into a stamper and pressing them into a parison with a certain shape, size and density. The molding method is basically divided into pressure molding and pressure molding. The most widely used in pressure molding is compression molding.
4. Sintering is a key process in the powder metallurgy process. After molding, the pressed blank is sintered to obtain the required final physical and mechanical properties. Sintering is further divided into unit sintering and multi-system sintering. In addition to ordinary sintering, there are also special sintering processes such as loose sintering, melt leaching, and hot pressing.
5. The treatment after sintering can be done in a variety of ways according to the different requirements of the product. Such as finishing, 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 have achieved better results.
Part.2
Clamping systems in common gear machining methods
Powder metallurgy is a method of making gears in large quantities, and common processes such as hobbing and shaping seem to be better able to meet the needs of multiple varieties and small batches, so their clamping systems are very particular.
From general turning→ hobbing→ shaping→ shaving→ hard turning→ gear grinding→ honing→ drilling→ internal grinding→ welding → measurement, it is important to have the right clamping system for this process.
1. Ordinary lathe processing
In general turning, gear blanks are usually clamped on a vertical or horizontal turning machine. For automatic clamping, most of them do not require an auxiliary stabilisation device on the other side of the spindle.
2. Hobbing processing
Due to its outstanding economy, gear hobbing is a cutting process used in the production of external gears and cylindrical gears. Gear hobbing is widely used not only in the automotive industry, but also in the manufacture of large industrial transmissions, but only if it is not limited by the outer contour of the workpiece to be processed.
3. Gear shaping processing
Gear shaping, a process for processing gears, is mainly used in the case that gear hobbing is not possible. This machining method is mainly suitable for the internal tooth machining of gears, as well as the external tooth machining of some gears that are disturbed by the structure.
4. Shaving processing
Shaving is a finishing process for gears that are cut with a blade corresponding to the tooth profile of the gear. This process is highly economical and therefore has been widely used in industry.
5. Hard turning
Hard turning makes it possible to replace expensive grinding processes. In order for it to function properly, the various parts of the system and the machining part are connected together accordingly. The selection of the right machine tools, fixtures, and cutting tools determines the quality of the turning results.
6. Gear grinding processing
In order to successfully achieve the precision necessary in gear production today, hard finishing of the tooth flanks is in many cases essential. In mass production, it is a very cost-effective way to process. On the other hand, similar to sample machining, gear grinding shows greater flexibility when an adjustable grinding tool is used.
7. Honing processing
Honing is the process of final finishing of hard gears using amorphous cutting angles. Honing is not only highly economical, but also gives the gears to be machined a smooth surface with low noise. Compared to grinding, honing has a very low cutting speed (0.5 to 10 m/s) and thus avoids damage to gear machining due to cutting heat. More precisely, the internal stress generated on the tooth surface to be processed has a certain positive effect on the bearing capacity of the equipment.
Examples of honing using flanged clamps:
8. Drilling
Drilling is a rotational cutting process. The axis of the tool and the center of the hole to be machined are exactly the same as the direction of feed of the tool in the axial direction. The spindle of the cutting motion should be consistent with the tool, regardless of the direction of the feed movement.
Examples of drilling with the SG fixture system:
9. Inner hole grinding
Internal grinding is a machining process with amorphous cutting angles. Compared with other cutting processes, grinding has the advantages of high dimensional and forming accuracy, dimensional accuracy (IT 5-6), small shock marks and high-quality surface accuracy (Rz = 1-3μm) for hard metals.
Example of internal bore grinding using the film clamping SM system:
10. Capacitor discharge welding
Capacitor discharge welding is a resistance welding process. Capacitive discharge welding is achieved by a very fast current increase, a fairly short welding time, and a very high welding current. Therefore, capacitor discharge welding has many advantages. In the face of increasing energy prices, the economy and efficiency of capacitor discharge welding are particularly important.
Example of capacitive discharge welding using a welding fixture system:
11. Measurements
The inspection of gears is very extensive, which must be adjusted according to the different forms of gears. In the measurement of gears, the different important parameters of the gears are determined by the measurement of length, angle, and special gear process.
Example of measurement using a flanged SP fixture system:
The above is a demonstration of powder metallurgy processing of gears, as well as an example of the fixture system under the processing methods such as gear shaping and gear hobbing.