Automotive design engineers have fully understood that the use of intensive processes can significantly extend the safe life of transmission components. In general, reinforcement is seen as a heat-treated process. For some key components, such as ring gears, planetary gears, reinforcement is the last important step in the production process.
The principle of strengthening is that the metal surface is subjected to continuous slamming of the high-speed metal particle beam, that is, a compressive stress is introduced on the surface thereof. Based on this mechanism, it seems that it is not difficult to find a machine that can be strengthened. Then, it turned out that premature transmission failure and product returns made many gear manufacturers have to re-examine this seemingly simple process.
Mechanism and effect of shot peening
The continuous impact of the metal medium (steel or shredded pill) causes plastic deformation of the surface of the part. This effect extends to the area below the surface layer that forms the compressive stress, counteracting the original tensile stress there. The residual compressive stress delays the formation of fatigue cracks, thereby improving the fatigue strength of the parts and prolonging the fatigue life.
After heat treatment, the surface of the gear is subjected to a slamming of the continuous strengthening medium to convert the retained austenite into martensite. This can increase the hardness of the material.
In the case of gears, the maximum shear stress occurs at the root and transition fillet. The gear drive face and the flank edge are subject to ever-increasing loads. Therefore, the key part of gear strengthening is
- Drive surface
- Toothed edge
- Root portion
For each type of gear, the required strength and coverage are not the same, depending on the application. Coverage is a visual process, and reinforcement strength is measured by a special spring steel test piece called the Almen test piece.
Strength test
The Part Calibration Tool (PVT) is designed to hold the test piece in a specific position. When the test piece is in these positions, it is possible to simulate the area where the part needs to be measured for strength.
Depending on the application, the intensity range is from 0.015 to 0.030 ("A" Scale) and the coverage can range from 100% to 200%.
The gear enhancement effect can be achieved in several different ways, each with its own advantages.
- Centrifugal force throwing shot peening
- Compressed air nozzle type shot peening
- Mixed (shot blast + shot peening)
Media ejection type
If the output is the main consideration, the centrifugal force throwing method is the most ideal. The media stream produced by the throwing jet can cover a large area per unit time. The process is then limited by the gear size. For smaller gears, where the root of the tooth is narrow, it is necessary to use multiple throwing heads and fix them at different angles to achieve the required coverage.
Alternatively, multiple pressure nozzles can be used to directly and more accurately inject specific root regions to achieve the desired coverage.
Both of these enhancement methods are commonly used in gear production. Relatively speaking, shot peening is more widely used because of its superiority in terms of technology and precision.
The third type of shot peening and shot blasting reinforcement system, although its application is less common, its advantage lies in the same machine, which can not only use the throwing head to ensure high productivity, but also can use a pressure nozzle. Concentrated and more precise shot peening in specific areas.
Process parameters
Regardless of which reinforcement technology is used, their ultimate goal is to achieve the desired strength in a sustained, constant, and highly reproducible manner. Therefore, it is important to fully understand which key parameters affect the final enhancement. These parameters include
Centrifugal head expansion:
- throwing the head
- Head power
- Blade speed
- Projection angle
- Head position
- Directional sleeve movement
Next page
Escalator,Flat Escalator,Escalator Stairs,Escalator Lift
MAURER TECHNOLOGIES CO., LTD. , https://www.maurer-elevator.com