Low carbon steel is a kind of material with low hardness and high viscosity, so its cutting performance is poor. In order to make the surface roughness of the processed hole reach Ra=1.6 m after finishing, most of the high speed steel reamer is used, and the low speed reamer is selected, and the hole is finished by drilling, expanding and reaming three processes. Although this process can meet the requirements of machining accuracy, but the production efficiency is low, the tool life is short. In the process of reaming, if there is a little debris on the front surface of the cutting edge of the reamer, the hole wall will be drawn and scratched, and the surface quality of the hole will be affected. In order to solve the above disadvantages caused by the common technology, high-speed reaming experiments on the finishing of the hole with carbide reamer have been carried out, and satisfactory results have been obtained.
Carbide reamer
(1) the geometric Angle of the cutter. High speed steel reamer and carbide reamer (sees attached figure) the cutting principle is different, high speed steel reamer relies mainly on the cutting edge sharp to obtain lower surface roughness value, and the carbide reamer is heavily dependent on squeeze cut to obtain lower surface roughness value, so the tool geometric angles are different requirements and common high speed steel reamer. According to the cutting principle, when cutting sticky and soft low carbon steel reamer, the cutting edge is required to be sharp, so the positive rake Angle and large rear Angle are selected. This can reduce the cutting resistance, but in order to increase the strength of the tool tip, it is not easy to break the edge, we set the tool rake Angle γ0=3 °, blade Angle λs=20 °, back Angle α0=20 °, blade bandwidth BA1 =0.5~0.6mm (reamer φ20~ 25mm), can get a better cutting effect. At this time, the surface roughness of the hinged hole Ra=3.2~1.6 μm, and the tool also has a higher life.
(2) the determination of cutting tool materials. The material of the blade has a direct effect on the life of the tool. After making reamer with blades of YT15, YA6, YW1, YT5 and YW2 with different materials, the results are also different. The reamer made of YT15 material has a low surface roughness, but the cutting edge area is easy to collapse in the cutting process. The reamer made of YT5 and YA6 material has a surface roughness of Ra=3.2~1.6 m after reaming, but the tool has a fast wear and low service life compared with other blade materials. For the reamer of YW1 material, the surface roughness of the reamer after reaming is Ra= 1.6μm. However, due to the low bending strength of the blade, the edge collapse often occurs. YW2 manufactured reamer, relative to the above various grades of reamer, in the processing of low carbon steel, reaming after the surface roughness value is low (Ra=1.6 m), and the tool life is high.
(3)the improvement of tool structure. In order to overcome the characteristics of soft hardness and high viscosity of low carbon steel, the head of reamer is designed and manufactured into a guide head with a certain Angle. This kind of guide head can not only play a leading role in the cutting edge of the tool, so that the hole machining to obtain better straightness; And the residual chips can be pushed to the front of the hole, will not make it difficult to discharge the chips, chips crowded in the reamer groove, resulting in more debris pull hole wall, destroy the surface quality of the hole. The cutter structure adopts a large blade Angle, which can not only make the reamer cut smoothly, but also the chip can be discharged smoothly. At the same time, in order to make the chip have enough chip space, so the number of cutter teeth should be appropriately reduced compared with the standard reamer.
Improvement of processing technology and selection of cutting amount
Whether the processing technology is reasonable or not directly affects the cutting effect. In the cutting of low carbon steel, the original three processes of drilling, expanding and reaming can be changed into two processes of drilling and reaming. Because the characteristics of cemented carbide reamer hinge is extrusion, so in the hinge before leaving the hinge allowance is very important, the allowance is too small to play the role of the hinge, the allowance is not enough will cause the hinge not up, may lead to the hole is too large and the surface of the hole with a drilling marks; Allowance left too large will increase the cutting resistance, and make the tool bar distortion deformation, while the tool life will be significantly reduced, and even produce a large number of chips, pull hole surface. Taking φ20~φ25mm reamer as an example, the reamer allowance is generally 0.20~0.25mm.
The selection of reasonable cutting allowance has a great influence on the quality of the holes in the hinged low carbon steel material. Low speed hinging (Vc < 5m/min) with carbide reamer can obtain a lower surface roughness, but the cutting efficiency is too low. The medium speed cutting is easy to produce chip nodules and affect the surface quality of the hole. High speed cutting is ideal, which not only greatly improves productivity, but also achieves good machining quality. If the cutting fluid is suitable, the tool life can be improved (extreme pressure cutting fluid is preferred).
The test results show that the cutting amount of articulated low carbon steel material is as follows: cutting speed Vc =50~60m/min, feed F =0.5~0.6mm/r is the most suitable.
The conclusion
For low carbon steel high speed reaming, practice proves that as long as the choice of rational cutting tool structure, geometry angles, cutting tool material, cutting dosage and correct operation, can obtain good cutting effect, not only can remove the original reaming process, at the same time, the production efficiency is 15 ~ 20 times higher when using high speed steel cutter, tool life has improved greatly, The size of the hole is also relatively stable in batch production, and the surface roughness can be basically guaranteed to reach Ra=1.6 μm.
