During the cutting process of cemented carbide end mills, the tool tip first comes into contact with the cutting material, and the cutting force acts on the tool tip first, which easily causes chipping of the tool tip. Therefore, enhancing tool tip protection can increase the bearing area of the cutting force, thereby protecting the tool tip and improving the tool life (see Figure 1).

The quality of the tool edge determines its service life and cutting performance. Although the performance of CNC grinding machines is quite good, unreasonable selection of grinding wheel process parameters during production will still lead to varying degrees of processing defects, among which the most common defect is edge serration. This is because the thickness of the cutting edge gradually decreases with the progress of grinding, and its strength also decreases accordingly. When the abrasive cutting force is too large, the surface of the cutting edge exhibits uneven serrated damage, which is known as edge serration.

When Meetyou Cemented Carbide Co., Ltd. (hereinafter referred to as “the Company”) processed a micro-diameter end mill with ultra-fine grain cemented carbide (grain size: 0.2 μm) as the tool material and a matrix diameter of 0.55 mm, it was found that serrated defects easily occurred at the edge of the tool tip protection. The finer the WC grains, the higher the material hardness and the lower the fracture toughness. A study on the material removal mechanism of ultra-fine grain cemented carbide grinding shows that due to the high hardness and brittleness of ultra-fine grain cemented carbide, defects such as cracks and fractures are more likely to occur on its grinding surface under the same grinding conditions.

In order to obtain better tool edge quality, domestic and foreign scholars have conducted extensive research. Experiments have found that reducing the rigidity of the grinding wheel within a certain range can improve its grinding performance and the processing quality of the tool.

Taking the grinding process of solid end mills as the research object, grinding was carried out by changing the feed rate and linear speed of the grinding wheel, and the conclusion was drawn that reducing the feed rate and linear speed of the grinding wheel has a significant effect on improving the tool edge quality. The main factors affecting the production efficiency and product quality of grinding grooves are grinding wheel grain size, feed rate, and linear speed.

Experiments have proved that the grinding wheel grain size has the greatest impact on the groove surface roughness, and the optimal processing parameters have been obtained, significantly improving the processing efficiency.

Experimental analysis was conducted on the excessive serration problem during the grinding of solid cemented carbide tools by changing the grinding process parameters. The results show that lower grinding wheel grain size, lower feed rate within a certain range, reasonable process sequence, and higher tool path density can effectively improve the excessive serration and obtain good edge quality of solid cemented carbide tools.

Existing studies mainly focus on the edge quality of cemented carbide tools with larger grains, while there are few studies on ultra-fine grain micro-diameter end mills.

Therefore, this paper conducts experimental analysis on the serration problem at the tool tip protection during the grinding of micro-diameter end mills with a cutting edge diameter of 0.55 mm, and studies the effects of grinding wheel grain size, feed rate, and rotation direction on the serration phenomenon, which is of great significance for improving the tool processing quality.

By analyzing the grinding damage mechanism of the cemented carbide end mill edge, it is found that the main influencing factors are material properties and grinding behavior. For the micro-morphology of ultra-fine grain cemented carbide materials, problems such as excessive porosity in the binder phase and uneven grain size will lead to edge defects of the cutting edge.

Grinding behavior mainly affects factors such as grinding heat and grinding force. Excessive grinding heat will cause plastic deformation of the binder phase material under grinding conditions, resulting in cracks. At the same time, under the action of grinding force, the cracks will gradually release energy in the direction of fracture shrinkage, eventually forming grinding damage to the cutting edge. The grinding force is mainly affected by the maximum undeformed cutting thickness, and the process parameters are the key factors determining the maximum undeformed thickness.

This paper studies and analyzes the effects of different grinding process parameters on the serration amount at the tool tip protection of micro-diameter end mills. Serrations are generated at the edge where different tool planes intersect. The serration amount comprehensively characterizes the surface micro-morphology of the edge by the length and depth of the serrations.

To measure the surface micro-morphology at the tool tip protection, a Keyence 1000x lens was used in this paper to measure the serration amount at the tool tip protection. The dimension parallel to the intersection line of the planes is the serration length, and the dimension normal to the intersection line of the planes is the serration depth.

The tool tip protection is formed during the chip flute processing, and the grinding process parameters of the chip flute directly affect the quality of the tool tip protection. Therefore, this experimental scheme only analyzes the grinding process parameters of the chip flute. A ROLLOMATIC 5-axis machine tool was used for the grinding test, and a diamond grinding wheel with resin bond was adopted. The experimental process parameters are shown in Table 1.

The effect of different grinding wheel grain sizes on the serration amount at the tool tip protection of double-edged end mills was measured under the same grinding wheel speed and rotation direction. The serration amount is shown in Figure 2.

It can be seen from Figure 2 that when the grinding wheel grain size is D15, there are obvious serrations at the tool tip protection, with the maximum serration length of about 12 μm; when the grinding wheel grain size is D20, the serration amount at the tool tip protection is significantly reduced, and the edge quality is better, with the maximum serration length of about 4.4 μm; when the grinding wheel grain size is D25, due to the increased grain size and poor grinding quality, the serration amount at the tool tip protection increases significantly.

The analysis shows that as the grinding wheel grain size increases, the serration amount at the tool tip protection first decreases and then increases, and the edge quality is the best when the grinding wheel grain size is D20.

The serration amount at the tool tip protection of double-edged end mills under different grinding wheel speeds was measured under the same grinding wheel grain size and rotation direction. The experimental results are shown in Figure 3.

It can be seen from Figure 3 that when the grinding wheel rotation speed is 20 m/s, the surface morphology of the tool tip protection is better, and the serration amount is smaller; with the increase of rotation speed, the serration amount at the tool tip protection increases significantly; when the rotation speed is 30 m/s, chipping even occurs at the tool tip. The above situation indicates that the edge quality is the best when the grinding wheel rotation speed is 20 m/s.

The serration amount at the tool tip protection of double-edged end mills under different grinding wheel rotation directions was measured under the same grinding wheel grain size and rotation speed. The experimental results are shown in Figure 4.

It can be seen from Figure 4 that when the grinding wheel rotates forward, the surface morphology of the tool tip protection is better, with the maximum serration length of about 2 μm and depth of about 0.3 μm. When the grinding wheel rotates in the reverse direction, the serration amount at the tool tip protection increases significantly, and even chipping occurs at the tool tip. This proves that the grinding wheel should not rotate in the reverse direction during chip flute grinding, as it is not conducive to improving the edge quality.

Through grinding tests, this paper studies and analyzes the effects of different grinding wheel speeds, grain sizes, and rotation directions on the serration amount at the tool tip protection of solid cemented carbide double-edged end mills, and draws the following conclusions:

(1) For different grinding wheel grain sizes, the serration amount at the tool tip protection varies. However, smaller grinding wheel grain size does not mean better edge quality, so the grinding wheel grain size should be selected reasonably during grinding. In the grinding test of this paper, the edge serration amount at the tool tip protection is the lowest when the grinding wheel grain size is D20.

(2) With the increase of grinding wheel speed, the quality of tool tip protection gradually decreases. When the speed increases to 30 m/s, chipping occurs at the tool tip. Therefore, during the grinding of chip flutes, a lower grinding wheel speed should be selected as much as possible to improve the edge quality.

(3) During the grinding of chip flutes, the forward rotation direction of the grinding wheel can effectively reduce the serration amount at the tool tip protection and improve the edge quality.