Cutting materials and methods for difficult-to-machine materials

In recent years, the development momentum of multi-functional and high-functionality of mechanical products has been very strong, and parts must be miniaturized and miniaturized. In order to meet these requirements, the materials used must have high hardness, high toughness, and high wear resistance, and the processing of these materials with characteristics is particularly difficult, and new difficult-to-machine materials have emerged. Difficult-to-process materials have emerged with the development of the times and different fields of expertise. Their unique processing technologies have also continued to advance with the development of the times and professional fields.

On the other hand, with the advent of information society, information on cutting technology of difficult-to-machine materials can also be exchanged through the Internet. Therefore, future information on cutting processing data for difficult-to-machine materials will be more substantial, and processing efficiency will inevitably be further improved. Focusing on the cutting of difficult-to-machine materials, the development trend of this technology in recent years is introduced.

Difficult-to-machine materials for cutting

Machining, usually tool wear, includes the following two forms: (1) wear due to mechanical effects, such as chipping or abrasive wear; (2) wear due to thermal and chemical effects, such as adhesion, diffusion, Corrosion and other wear, as well as the softening of the cutting edge, melting and breaking, thermal fatigue, thermal cracking and so on.

When the hard-to-machine material is cut, the above-mentioned tool wear occurs within a short period of time. This is due to the fact that the material to be machined causes more tool wear factors. For example, most difficult-to-machine materials have low thermal conductivity characteristics, and the heat generated during cutting is difficult to diffuse. As a result, the tool tip temperature is high, and the cutting edge is extremely affected by heat. As a result of this effect, the bonding strength of the tool material adhesive at high temperature is reduced, and wc (tungsten carbide) and other particles are easily separated, thereby accelerating tool wear. In addition, some of the difficult-to-machine material components of cutting tool materials react under high-temperature conditions and appear to be analyzed, dropped off, or generate other compounds, which will accelerate tool wear such as chipping.

When cutting high-hardness, high-toughness processed materials, the cutting edge temperature is high, and tool wear similar to when cutting hard-to-machine materials occurs. For example, when cutting high-hardness steel, the cutting force is larger than that of general steel cutting. The lack of tool rigidity will cause chipping, etc., which will make the tool life unstable, and shorten the tool life, especially when machining short chipping workpiece materials. Depending on the wear of the crater near the cutting edge, tool damage may occur in a short time.

When cutting superalloys, due to the high hardness of the material at high temperatures, a large amount of stress is set at the edge of the cutting edge, which will lead to plastic deformation of the cutting edge; at the same time, the boundary wear due to work hardening is also more serious.

Due to these characteristics, when the user is required to cut a difficult-to-machine material, it is necessary to carefully select the tool type cutting conditions in order to obtain an ideal machining effect.

Difficult-to-machine materials should pay attention to the problem of cutting

Machining can be roughly divided into turning, milling, and heart-to-center cutting (drills, end mills, etc.). These cutting heat effects on the blade tip are also different. A kind of continuous cutting in turning, cutting edge bears no significant change in cutting force, cutting heat continuously acts on the cutting edge; milling is a kind of interrupted cutting, cutting force intermittently acts on the cutting edge, vibration will occur during cutting, and the cutting edge will be heated The effect is that when the cutting is not performed during heating, the cooling is alternated, and the total heat is less than that during turning.

An intermittent heating phenomenon of cutting heat during milling, the cutter tooth is cooled when it is not cut, which will facilitate the tool life extension. The Japan Institute of Physics and Chemistry made a comparative test on the life of turning milling tools. The tool used for milling was a ball end mill and the turning tool was a general turning tool. The cutting conditions were the same for both materials (due to different cutting methods, cutting depth, and feed rate). , cutting speed, etc. can only be roughly consistent) and comparative cutting tests under the same environmental conditions, the results show that milling machining is more beneficial to prolong tool life.

When a cutting tool with a heartblade (ie cutting speed = 0m/min) or a ball end mill is used for cutting, tool life near the edge of the tool often occurs, but it is still stronger than in turning.

When cutting hard-to-machine materials, the cutting edge is affected by heat and often reduces the tool life. If the cutting method is milling, the tool life will be relatively longer. However, difficult-to-machine materials cannot be completely milled from beginning to end, and there will always be times when turning or drilling is required. Therefore, corresponding technical measures should be taken for different cutting methods to improve the processing efficiency.

Cutting tool materials for difficult-to-cut materials

Cbn high-temperature hardness of the highest available tool materials, the most suitable for difficult machining materials cutting. The new coated cemented carbide is based on an ultra-fine grained alloy and is coated with a coating material with good hardness at high temperatures. This material has excellent wear resistance and can be used for cutting hard tooling materials.

Difficult-to-machine materials Titanium and titanium alloys can be machined using diamond tools because of their high chemical activity and low thermal conductivity. Cbn sintered cutters are suitable for cutting materials such as high hardness steel and cast iron. The higher the cbn content, the longer the tool life, and the amount of cutting can be increased accordingly. It has been reported that no cbn sintered body has been developed at present.

Diamond sintered cutters are suitable for cutting materials such as aluminum alloy and pure copper. Diamond cutting tools have sharp cutting edges, high thermal conductivity, and low heat retention at the edge of the cutting edge. They can control the accumulation of built-up edge material and other adherents to a minimum. When cutting pure titanium-titanium alloy, the use of single-crystal diamond tools is relatively stable and can prolong tool life. 

Coated carbide tools are suitable for almost all kinds of difficult-to-machine materials, but the coating properties (single-layer composite coating) vary greatly. Therefore, suitable coated tool materials should be selected according to different processing objects. According to reports, diamond-coated carbide-like dlc (diamondlike carbon)-coated carbide has recently been developed, which has further expanded the range of coating tool applications and has been used in the field of high-speed machining.

Cutting difficult tool shape

When cutting difficult-to-machine materials, tool shape optimization can give full play to tool material properties. Choosing and adapting to the characteristics of difficult-to-machine materials The tool geometry such as rake angle, relief angle, and cutting-in angle can properly handle the cutting edge, which has a great influence on improving the cutting accuracy and prolonging the tool life. Therefore, the tool shape must not be taken lightly. However, with the popularization and application of high-speed milling technology, recently the small depth of cut has been gradually adopted to reduce the load on the cutting teeth, and the up-cut milling has been used to increase the feed speed. Therefore, the design concept of the cutting edge shape has also been changed.

When drilling difficult-to-machine materials, increase the drill angle and perform cross-cut grinding to reduce the thermal efficiency of the torque cutting process. It can control the contact area of ​​the cutting and cutting surfaces within the minimum range, which increases tool life and tool life. Cutting conditions are very favorable. When the drill bit is drilled, the cutting heat is likely to be trapped near the cutting edge, and chip evacuation is also difficult. When cutting difficult-to-process materials, these problems are more prominent and must be given enough attention.

In order to facilitate chip evacuation, a coolant discharge port is usually provided on the rear side of the cutting edge of the drill to provide sufficient water-soluble coolant or mist-like coolant to make chip removal smoother. This way also has a cooling effect on the cutting edge. Very ideal. In recent years, some coating materials with good lubricating properties have been developed. After these materials are coated on the surface of the drill, 3 to 5 d of shallow holes can be processed by using dry drilling.

Hole finishing has traditionally used boring methods, but recently it has gradually changed from conventional continuous cutting methods to the use of contour cutting to discontinuous cutting methods. This method is more favorable for improving chip removal performance and extending tool life. Therefore, after the design of the boring tool for intermittent cutting, it was immediately applied to the cutting of automotive components. For screw hole machining, spiral cutting interpolation is also used at present, and end mills for thread cutting have been put on the market.

As mentioned above, this conversion from the original continuous cutting to interrupted cutting, with the deepening understanding of the CNC cutting, is a gradual process. When cutting a difficult-to-machine material using such a cutting method, the cutting stability can be maintained and the tool life can be prolonged.

Difficult to machine material cutting conditions

The cutting conditions of difficult-to-machine materials have historically been set to be relatively low. With the improvement of tool performance, the emergence of high-speed and high-precision CNC machine tools, and the introduction of high-speed milling methods, etc. Currently, difficult-to-cut materials have entered the period of high-speed machining and long tool life.

Now, the use of small depth of cut to reduce the tool cutting edge load, which can improve the cutting speed feed rate processing, has become the best way to cut difficult to machine materials. Of course, it is also very important to choose the tool geometry of the tool material to meet the unique properties of difficult-to-machine materials, and to optimize the cutting path of the tool. For example, when drilling materials such as stainless steel, due to the low thermal conductivity of the material, a large amount of cutting heat must be prevented from remaining on the cutting edge. For this reason, intermittent cutting should be used as much as possible to avoid frictional heat generation on the cutting surface of the cutting edge. Helps extend tool life to ensure stable cutting. When using ball end mills for rough machining of difficult-to-machine materials, tool shape fixtures should be well-matched, which can improve the clamping rigidity of the tool cutting part's run-out precision, so that the feed per tooth can be increased under high-speed rotation conditions. To the maximum, but also can extend the tool life.