The trouble shooting of machining operation is a difficult task, especially in the processes of drilling. The reasons are as follows: when machining for the external part, you can see the causes of tool failure: however, when the tool is hidden in the hole for drilling, you can not see the specific conditions of the tool during machining.
If you have done any drilling and machining, especially when drilling holes with carbide drill bits, you may have the experience that the drill pipe is arranged at the center line of the hole or slightly above the center line of the hole, and the diameter of the drill pipe is required to be no more than the hole diameter. It looks good. The program check passed. You think the setting is right. You press the start button. The coolant starts to spray everywhere, and you don’t notice anything unusual before the drill pipe holder leaves the workpiece. At that time, your biggest worry happened – the end of the drill was missing
When this happens, the usual reason is that the machining chips or drill pipe try to drill into the end of the blind hole. After inspection, if the top part of the drill pipe remains in the hole and is difficult to remove, then the hole is likely to be filled with chips, and you will find the cause of the catastrophic failure. In this case, the setting of cutting parameters, such as cutting depth and feed rate, resulted in more chips that could not be discharged in time. The solution is to use a smaller diameter drill pipe if possible. Otherwise, the cutting parameters must be reduced to reduce the amount of chips produced. If the end of the broken drill pipe is not in the hole, or has become loose in the hole, and is restricted in the hole so that the drill pipe cannot be withdrawn, you can try to drill the drill pipe deeper. It is impossible to complete such drilling operation with a drill pipe at this time!
After making the necessary adjustments, the drill pipe can finish the hole processing without catastrophic failure, but if you plan the number of products to be processed in each processing shift, it is unacceptable. Because you think the drill pipe changes too often. After checking the drill pipe, it is determined that the wear of the cutting edge is increased.
However, the cause of rapid wear is easily misjudged. In general, with the process of machining, intermittent cutting or chattering will lead to the formation of small pits on the edge similar to the wear of the back face. In addition, the wear of the back cutter surface may start from the combined edge of the top surface of the drill pipe. This is due to the heat and pressure generated in the chip formation process that causes the workpiece to be welded to the top surface of the drill pipe. In addition, in some cases, the welding effect will be intensified due to small pieces of carbide chips separated from the drill pipe. In order to determine if there is a condition for side wear of the drill pipe, one or two holes can be drilled and then checked for swarf or chips. Pressure or heat must be reduced in order to reduce swarf. The reason of pressure is too high cutting depth and feeding rate. Reducing the amount of cutting reduces pressure and heat, but also productivity. A more practical change is the application of coated tools. The coating can reduce the heat generated by the tool moving on the cutting surface. For thin coatings, physical vapor deposition is more effective than chemical vapor deposition, which makes the edge of tool worse.
In general, users are used to reducing heat by using coolant. For outer diameter machining, it is a common and simple cooling method. But drilling a small hole can be difficult, because the hole is partially filled with drill pipe and hot metal chips, which need to be cooled. Since the coolant line near the hole is often blocked, the best way is to supply the coolant through the drill pipe rack. It is ideal to supply enough coolant around the circumference of the drill pipe to minimize the resistance of the coolant through the path and to enter the bottom of the hole.
Generally, this requires locating several coolant paths, such as one on one side of the edge of the cutting edge, the other on the top of the drill pipe, and the other on the back opposite to the cutting edge. For adequate cooling. Scientific cutting tools use the handle of the cooling ring technology to make the coolant be used in the peripheral direction of the drill pipe, which also includes the “tube” type coolant.
If the tool breaks after drilling several parts, the most likely cause is the interruption of the machining process, such as when machining cross holes or keyways. In order to avoid the interruption of drilling process, it is necessary for the tool to have the radius of the tip fillet or cutting edge, or both.
If the cause of the crack is not the interruption of the processing process, then the most likely culprit is vibration. Vibration is similar to machining interruptions in that when the tool is bent it moves down and then up while the tool is relaxed. So as to make a middle strike on the cutting edge. The possible solution is to increase the feed rate. If the feed speed is increased by 10%, the pressure can be fully increased, so that the tool is in the deflection state, to prevent loosening and vibration.
After the diagnosis and determination of the back face wear, a large number of studies on the back face wear have come to the conclusion that a small decrease in the cutting speed will cause a significant change in the service life of the tool, so as to avoid affecting the normal use of the tool due to the excessive wear of the back face. For example, when the cutting speed is reduced from 400ft / min to 300ft / min, the tool life will be extended from 12 minutes to 40 minutes. To solve production problems, we should always attach great importance to and deal with them in time. But don’t judge the failure mode too quickly. Wrong judgment may have the opposite effect, or even make the problem worse.