GY800 rolling special machine tool is a specialized machine tool for rolling processing, which is a chip free processing that applies pressure to the surface of the workpiece through a formal rolling tool. By utilizing the plastic deformation of metals at room temperature, the micro roughness of the workpiece surface is flattened to achieve the goal of changing the surface structure, mechanical properties, shape, and size. Therefore, this method can achieve both finishing and strengthening purposes simultaneously.

Rolling processing is a plastic processing method that rolls high hardness and smooth rollers into contact with the metal surface, causing local micro plastic deformation of the surface layer and resulting in surface roughness. We often see that when laying roads, the rolling mill flattens the uneven road surface. The principle of rolling processing is also the same. Use a roller to roll the metal surface, flatten the raised parts of the surface, and make the depressed parts rise, processing it into a smooth mirror like surface. Unlike cutting, it is a type of plastic machining. The workpiece processed by rolling can not only achieve a surface roughness of Ry0.1-0.8 μ m in an instant, but also have advantages that cannot be achieved in cutting, such as an increase in fatigue strength by 30% while improving its properties after surface hardening. Due to the easy and low-cost ultra processing of components, it is increasingly being widely adopted by industries such as machinery, chemistry, and home appliances, led by the automotive industry, and has played a significant advantage.

Processing conditions:

Surface before processing

Due to the use of roller rolling in rolling processing, the surface roughness after processing is affected by the height and shape of the raised parts (i.e. the pre processing state).

If the surface is rough before processing (with high protrusions and deep depressions), the protrusions cannot be completely buried in the depressions, resulting in a rough processing surface.

In addition, the shape of the protruding part also affects the surface after processing. When the regular concave convex shape is cut by a lathe or boring machine at a single point, and it is at a height that is easy to crush, it can achieve an ideal surface. The better the surface condition before processing, the better the surface condition after processing, and the less wear on the rolling head. If necessary, an additional process can be added.

Dimensions before rolling processing

Due to the use of roller rolling in rolling processing, the diameter of the workpiece will change before and after processing (the inner diameter will increase and the outer diameter will decrease). In order to process within the dimensional tolerance range, the variation should be considered to determine the dimensions of the previous process. The change in diameter is related to the material, hardness, and rolling amount of the workpiece, so its size is determined after 2-3 trial runs.

Rolling processing driven machinery

The standard models of rolling heads include Morse cone mounting parts and parallel mounting parts. Rolling processing is different from cutting processing, as it does not require high torque and can be used with low-power machine tools. It can be installed on drilling machines, lathes, hexagonal lathes, boring machines, drills, and other equipment for processing, without the need for special equipment.

Rolling processing lubrication and cleaning

Due to the use of roller rolling for processing, fine dust will be generated. Dust not only affects surface quality, but also accelerates the wear of the rolling head, so a large amount of cutting fluid is injected to remove dust. Low viscosity cutting fluid should be used during rolling processing. Although cutting fluids with high viscosity have good lubricity, their cleaning performance is poor and they are not suitable for rolling processing. Our company has special rolling lubricating oil for rolling processing. As long as 5% of rolling lubricating oil is added to low viscosity cutting fluid, its outstanding performance can be achieved.

Wall thickness of the rolling processing part

Rolling processing is the process of using rollers to press and compact the surface of a part. So, in order to withstand processing pressure, the part to be processed should have sufficient wall thickness (20% of the inner diameter). When the wall thickness is too thin or partially thin, there will be fluctuations or a decrease in roundness after processing.

Usually, the following methods are used to solve this problem: ① reduce the amount of rolling; ② Use fixtures to support the periphery; ③ Implement rolling processing before cutting thin and thick walls.

Rolling processing speed and feed rate

Rotate the rolling head to the right for rolling processing; The rolling head can also be fixed, and the same result can be achieved when the workpiece rotates. The rotational speed and feed rate vary depending on the machining diameter.

Parts that cannot be processed by rolling

When using a rolling head to roll blind holes and step shafts, there are the following parts that cannot be processed: ① the circular arc at the front end of the roller; ② The distance from the front end of the roller to the front end of the bracket; ③ The gap from the front end of the bracket to the end face of the processing part; In order to make the parts that cannot be rolled smaller, after determining the tool diameter, grind off the spindle at the front end of the roller or keep the protrusion of the head in the same position as the front end of the roller.

Rolling precautions:

Rolling processing can solve key problems that are difficult to implement in certain process methods. For example, the processing of oversized cylinder blocks. At the same time, it is also suitable for precision machining of small holes or certain special materials.

Through experiments with different materials, we found that:

(1) Whether the selection of rolling pressure is correct has an impact on the surface roughness, size, and accuracy after rolling. In general, as the rolling force increases, the surface roughness also improves. But when the rolling force increases to a certain extent, the surface roughness no longer improves. If it continues to increase, the rolled surface begins to deteriorate and even cracks appear.

(2) Improving the surface roughness of the workpiece through rolling processing yields good results. When the pre machining roughness reaches Ra1.6, as long as the interference fit is appropriate, the roughness can reach Ra0.2 or above. But when the pre processed roughness is only Ra6.4~Ra3.2 and there are vibration and irregular cutting patterns on the processed surface, the deeper cutting patterns cannot be rolled smooth, so the only solution is to increase the interference fit and roll again. If the ellipticity and taper of the hole are too large, the above-mentioned defects will still exist after rolling, and the roughness will be high. Therefore, the pre machined surface should be smaller than Ra3.2, with geometric accuracy above level one or two, and can achieve small roughness and ideal accuracy.

(3) The material is soft, has high plasticity, and is easily rolled and polished. As plasticity decreases and hardness increases, the amount of deformation decreases accordingly. Generally speaking, the rolling effect of steel and copper is better, while the effect of cast iron is poorer. The rolling effect of malleable iron and ductile iron is better than that of gray cast iron. When rolling cast iron parts, if the material hardness of the casting is uneven, defects on the rolled surface (such as pores, sand holes, etc.) will immediately appear. Therefore, when there are many surface defects and poor quality on the casting, rolling technology should not be used.

(4) The size of the rolling interference has a significant impact on surface roughness and geometric accuracy. Through experiments, it has been found that a reasonable rolling interference amount is 0.027-0.036mm, at which point the surface roughness is small. The large interference fit is influenced by various factors, so the determination of the optimal interference fit should be determined through multiple experiments based on specific conditions.

(5) The rolling speed has little effect on surface roughness, so we can increase the rolling speed to improve production efficiency.

(6) The number of rolling should not be too many. The one-time rolling effect is significant and can reduce roughness by 2-3 levels. 2、 Three times.

(7) The size of the feed rate should be determined according to the diameter of the ball. The smaller the feed rate, the smaller the surface roughness. The optimal feed rate should be determined through experimentation.

(8) Rolling tools usually include ball bearings, cylindrical rollers, conical rollers, rollers, etc. But using ball bearings as deformation components can reduce the overall cost of rolling tools. Moreover, the precision and hardness of the ball bearings are high, and the contact surface with the workpiece is small. With smaller rolling force and smaller interference fit, higher pressure and lower roughness can be obtained. Moreover, the ball bearings have a long service life, are not easily worn, are inexpensive, and are easy to replace.

Through a period of practice, I have gained a preliminary understanding of:

(1) The rolling effect is closely related to the previous process. After turning and boring, the greater the unevenness of the workpiece, the greater the rolling force will inevitably increase, the feed rate will decrease, and the rolling effect will be poor. If a pointed cutting tool is used for precision machining with a small feed rate, and the workpiece is cleaned with gasoline and kerosene, sufficient cooling with kerosene during rolling can be achieved to obtain a surface roughness Ra ≤ 3 μ m for machining.

(2) The relationship between roller diameter, arc radius, and machining surface.

① The larger the diameter of the roller, the larger the surface area of the roller in contact with the workpiece, resulting in insufficient plastic deformation.

② When the roller diameter and arc radius are too small, they will leave indentations on the machining performance. Practice has shown that when the roller diameter is D=11-14mm and R=3-5mm, the rolling feed rate and S=0.035-0.1mm have good rolling effect. The dimensional tolerance before and after rolling can be reduced by 10-15% based on the diameter calculation.

In short, we cannot simply copy all aspects of rolling, and further exploration of experimental data is needed in the future.