Can the inner hole rolling meet the requirements
2021-11-29

Can the inner hole rolling meet the requirements?

Rolling

Rolling processing is a kind of plastic processing method in which a high hardness and smooth roller is rolled into contact with a metal surface to cause a small amount of plastic deformation on the surface layer to improve the surface roughness.


We often see that when the road is paved, the road rolling machine presses the uneven road very smoothly. The same is true for the processing principle of rolling tools. Rollers are used to roll the metal surface, and the convex parts of the surface are flattened, and the concave parts are raised and processed into a smooth mirror-like surface. Different from cutting processing, it is a kind of plastic processing.


The surface roughness of the rolled workpiece can reach Ry0.1-0.8μm in an instant, but the wear resistance of the processed surface is improved after hardening, and the fatigue strength is also increased by 30%. It has advantages that cannot be obtained in cutting processing.


Because ultra-precision machining of parts can be performed easily and at a low cost, rolling machining is increasingly being widely used in precision machinery, chemicals, and home appliances, led by the automotive industry, and has exerted great advantages.


Processing conditions

1. Surface before processing


Since rolling is a processing method using roller rolling, the surface roughness after processing is affected by the height and shape of the raised part (that is, the state before processing).


If the surface is rough before processing (high convex part and deep concave part), the convex part cannot be completely buried in the concave part, resulting in a rough surface.


In addition, the shape of the raised portion also affects the processed surface. When the regular uneven shape is cut by a lathe or a boring sheet and the height is easy to roll, the ideal surface can be obtained. Generally, the better the surface condition before processing, the better the surface condition after processing, and the wear of the rolling head are also less. If necessary, a process can be added.


2. Dimensions before processing

Since rolling is a processing method using rollers, the diameter of the workpiece before and after processing will change (the inner diameter will be enlarged, and the outer diameter will be reduced). To process within the dimensional tolerance range, this change should be considered to determine the size of the previous process. The amount of change in diameter is related to the workpiece's material, hardness, and rolling amount, so the size is determined after 2 to 3 trial machining is performed initially.


3. Drive machinery

The standard model of the rolling head has Morse taper mounting part and a parallel mounting part. Rolling processing is different from cutting processing. It does not require high torque and can also be used on low-power machine tools. It can be installed on drilling machines, lathes, hexagonal lathes, boring machines, drills, and other equipment for processing without special equipment.


4. Lubrication and cleaning

Fine dust will be generated since the rolling process is processed by roller rolling. Dust affects the surface quality and accelerates the wear of the rolling head, so it is necessary to inject a large amount of cutting fluid to remove the dust. The cutting fluid with low viscosity should be used when rolling. Although cutting fluid with high viscosity has good lubricity, it has poor cleaning performance and is unsuitable for rolling processing. The company has special rolling lubricants for rolling processing. As long as 5% of the rolling lubricants are mixed with low-viscosity cutting fluids, its outstanding performance can be exerted.


5. The wall thickness of the processed part

Rolling is to use rollers to roll the surface of the processed part to densify it. Therefore, the part being processed should have a sufficient wall thickness (20% of the inner diameter) to withstand the processing pressure. When the wall thickness is too thin or partly thin, undulations or a decrease in roundness will occur after processing.

The following methods usually solve this problem:

 ①Reduce the amount of rolling; 

②Use a clamp to support the outer periphery; 

③To implement rolling processing before thinning the wall thickness.


6. Hardness of the processed part

The upper limit of the hardness of the workpiece that the rolling head can process is 40HRC, but the rolling head is also specially designed for processing high-hardness workpieces (the upper limit of hardness is 55HRC). When rolling high-hardness workpieces, the machining part is subjected to high pressure, and the tool life is shortened. Therefore, to obtain the required precision of the machined surface, the main measure is to reduce the amount of rolling.


7. Speed and feed

Rotate the rolling head to the right for rolling processing; the rolling head can also be fixed, and the same result can be obtained by rotating the workpiece. The speed and feed rate varies according to the machining diameter.


8. The part that cannot be rolled

When rolling blind holes and stepped shafts with a rolling head, there are the following parts that cannot be processed:

①The arc part of the front end of the roller

②The distance from the front end of the roller to the front end of the bracket

③The gap between the front end of the bracket and the end surface of the processed part

To minimize the part that cannot be rolled, after the tool diameter is set, the mandrel at the front end of the roller will be ground off, or the protrusion of the head will be kept at the same position as the front end of the roller.




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