Gear manufacturing includes various processes such as gear hobbing, gear milling and gear shaping, but there is also a type of gear pressed from metal powder, which is the metallurgy process powders.
Part.1
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, they still need improvement in other aspects.
Analysis of the advantages and disadvantages of powder metallurgy process
Powder metallurgy is a processing technology that uses metal powder (or a mixture of metal powder and non-metallic powder) as a raw material to manufacture metal materials, composite materials and various types of products by shaping and sintering.
advantage:
1. Generally, there are few powder metallurgy gear manufacturing processes.
2. When using powder metallurgy to make gears, the material utilization rate can reach more than 95%.
3. The repeatability of powder metallurgy gears is very good. Since powder metallurgy gears are pressed and formed using molds, under normal use, a pair of molds can press tens or even hundreds of thousands of compact gears.
4. Powder metallurgy can integrate multiple parts into one part.
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 die working surface should be very good.
default:
1. Mass production is required. Generally speaking, powder metallurgy production is more suitable for batches of 5,000 parts or more.
2. The size is limited by the pressing capacity of the press. The presses generally have a pressure of several tons to hundreds of tons, and the diameter is basically less than 110mm, and can be used to produce powder metallurgy.
3. Powder metallurgy gears are subject to structural limitations. For pressing and molding reasons, it is generally not suitable for the production of worm gears, herringbone gears and helical gears with 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 mold cavity depth and press stroke should be 2-2.5 times the gear thickness. Considering the uniformity of gear height and longitudinal density, the thickness of powder metallurgy gear is also very important.
Basic flow of powder metallurgy process
1. Powder coating is the process of transforming raw materials into powder. Commonly used powder coating methods include the oxide reduction method and the mechanical method.
2. Mixing is the process of mixing various required powders in a certain proportion and homogenizing them to form green powder. It is divided into three types: dry type, semi-dry type and wet type, which are used for different requirements.
3. Forming is the process of placing uniformly mixed materials into a die and pressing them into a parison of a certain shape, size and density. Casting methods are basically divided into pressure casting and non-pressure casting. The most commonly used type of die casting is compression casting.
4. Sintering is a key process in powder metallurgy process. The formed compact is then 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 free sintering, immersion method and hot pressing method.
5. Post-sintering processing can be carried out in different 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 used in the processing of powder metallurgy materials after sintering, thereby achieving ideal results.
Part.2
Clamping system in common gear processing methods
Powder metallurgy is a method of manufacturing gears in large quantities, and common processes such as gear hobbing and shaping appear better able to meet the needs of multiple varieties and small batches. Currently, their clamping systems are very particular.
From ordinary turning processing → hobbing processing → gear shaping processing → gear shaving processing → hard turning processing → gear grinding processing → sharpening processing → drilling → inner hole grinding → welding → measurement, it is obvious to configure a suitable clamping system for this process. Particularly important.
1. Ordinary automobile treatment
In ordinary turning, the gear blank is usually clamped on a vertical or horizontal lathe. For automatic workholding devices, most do not need to install an auxiliary stabilizing device on the other side of the spindle.
2. Gear cutting
Due to its exceptional economy, gear hobbing is a cutting process used to produce external gears and spur gears. Gear hobbing is widely used not only in the automobile industry, but also in large-scale industrial transmission manufacturing, but the principle is that it is not limited by the outer contour of the workpiece.
3. Gear shaping processing
Gear shaping, a gear processing process, is mainly used when gear sizing cannot be achieved. This processing method is mainly suitable for processing the internal teeth of gears, as well as the processing of the external teeth of some gears affected by structural interference.
4. Teeth Shaving Treatment
Gear shaving is a process of finishing gears, with a blade matching the profile of the gear teeth when cutting. This process has high production economy and has therefore been widely used in industry.
5. Hard turning treatment
Hard turning can replace expensive grinding processes. To make it work properly, each part of the system and the processing part are connected together accordingly. The selection of appropriate machine tools, fixtures and cutting tools determines the quality of the turning effect.
6. Gear grinding processing
In order to achieve the necessary precision in gear production today, a hard finish of the tooth flanks is in many cases essential. In mass production, it is a very economical and efficient processing method. On the other hand, like sample machining, gear grinding offers greater flexibility when adjustable grinding tools are used.
7. Sharpening process
Sharpening is a process that uses amorphous cutting angles to achieve the final finish of hard gears. The sharpening treatment is not only very economical, but also makes the machined gear have a smooth surface with low noise. Compared with grinding, the cutting speed of lapping is very low (0.5~10m/s), avoiding damage to gear processing caused by cutting heat. To be more precise, the internal stress generated on the treated tooth surface has a certain positive effect on the bearing capacity of the equipment.
8. Drilling
Drilling is a rotary cutting process. The rotation axis 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 feed direction of the tool. The main axis of the cutting movement must be consistent with the tool, regardless of the direction of the feed movement.
9. Grinding the inner hole
Bore grinding is a machining process with amorphous rake angles. Compared with other cutting processes, grinding has the advantages of high dimensional and forming accuracy for hard metals, dimensional accuracy (IT 5~6), very small vibration marks and high quality surface precision (Rz=1~3μm).
10. Capacitor discharge welding
Capacitor discharge welding is a resistance welding process. Capacitor discharge welding is achieved by a very rapid increase in current, a relatively short welding time and a very high welding current. Therefore, capacitor discharge welding has many advantages. With the increase in energy prices, the economy and efficiency of capacitor discharge welding are particularly important.
11. Measurement
Gear inspection is very thorough and needs to be adjusted according to different gear shapes. When measuring gears, various important parameters of gears are determined by measuring the length, angle and special measurements of the gear process.
The above is a demonstration of powder metallurgy gear processing, as well as examples of fixture systems in gear shaping, hobbing and other processing methods. In addition to batch size, the specific selection should also be based on real and reasonable analysis to facilitate. the implementation of the manufacturing process.
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