Abstract: this paper mainly introduces the process parameters, technology and operation of rolling tool in order to improve the smoothness of products. Through the introduction of this article to explain how to improve the surface of the workpiece after rolling pressure, the surface of the workpiece is not clean, the traces of rolling, and so on.
Before the roller burnishing tool was widely used, many factories used polishing, honing, grinding and other techniques to improve the surface finish of metal products in the machining process. The honing process also has certain advantages. For some internal holes with high hardness and small bore diameter, the honing tool is used to complete the honing process, but its efficiency is much lower than that of the roller burnishing tool.
However, there are many advantages to using roller burnishing tool, but also there are many conditions that need attention in rolling process.
We introduce some problems of rolling process:
First of all, after surface rolling, the surface of metal workpiece is strengthened, the ultimate strength and yield point are increased, and the hardness can be increased by 15-30%.
Abrasion resistance increased by 15%;
Fatigue limit increased by 30%;
The dimension tolerance can be reduced by 10-15% by diameter calculation.
The surface roughness can reach above Ra0.2 if the overfill is suitable and matches with other process parameters.
Secondly, the surface micro-protuberances after rolling are smoothed, and the contact with sealing materials is smooth, which reduces the wear of sealing parts while reducing the wear of products. In terms of processing efficiency, one roll can complete the processing. High production efficiency. (finishing 100 x 300 holes in 1.5 minutes can be completed; completing 30 x 40 holes in 10 seconds can be completed).
Process parameters and requirements
1) Burnishing amount: when machining the inner hole of the workpiece with the roller burnishing tool, the tool diameter is set to be slightly larger than the previous machining size, rotating and feeding the tool (workpiece), and rolling the inner hole. The difference value between the diameter of the tool and the size of the workpiece before processing is called burnishing amount.
The burnishing amount is set according to the material and wall thickness. The setting of burnishing amount is generally 3 to 5 times of the surface roughness before processing, which is ideal. When the material is steel, the burnishing amount ranges from 0.04 to 0.07mm to obtain the most ideal surface. When the burnishing amount range of steel and cast iron parts is 0.04~0.07mm, its inner diameter will not change.
2) Preprocessing size: as the diameter size will change after rolling, the machining allowance should be left before rolling to ensure the dimensional tolerance. The variation of diameter and size is affected by the material, hardness and rolling pressure of the workpiece, etc., so the determination of machining allowance should be made on the basis of the manufacturer’s reference value after several trials. It should be noted that the inner diameter cannot be expanded to the same size as the diameter of the tool after rolling, because the enlarged inner diameter is reduced after the tool passes through due to the elastic recovery of the material.
3) The upper limit of hardness of workpiece processed by roller burnishing tool is HRC40.
4) In order to avoid the deformation of thin wall parts during rolling, the wall thickness of the machining part should reach more than 15% to 20% of the aperture.
5) The roughness of the preprocessed surface is preferably less than Ra3.2. At the same time, when the hardness of casting materials is not uniform, the surface defects of rolling pressure will be exposed immediately. Therefore, the quality of the rolled parts is good, and the surface defects should not be too many.
6) The effect of primary rolling is best, and the roughness can be reduced from 2 to 3 grades.
7) The rolling process is lubricated with clean machine oil or lubricated with diesel oil (ratio 3:7), or with special lubricating fluid provided by the manufacturer. A large amount of lubricating fluid should be used because the lubricating fluid needs to clear the small metal powder produced in the rolling process. Keep the lubricating fluid clean, pay attention to dust prevention and filtration.
8) Rolling effect is closely related to the previous process. After the current process, if the surface is too concave and convex, the rolling pressure will also increase, and the feed quantity will be reduced, so the rolling effect will not be ideal. It is recommended to pay attention to the machining precision in the process before rolling, and pay attention to cleaning at the same time to avoid the chip sticking to the inner wall of cylinder body.