Failure analysis of boring cutter with hard alloy

27 April 2021

the boring bar, allowing For boring, especially with a monolithic alloy boring bar machining holes, you may experience the following conditions: the boring bar is adjusted at or slightly above the center line, the diameter of the boring bar is smaller than the aperture, the machining condition appears to be good, and the processing program is checked correctly. After the adjustment is completed and satisfied, press the start button to start processing, and the coolant splashes everywhere; Nothing is observed until the boring bar is retracted from the part. The boring head was found to be missing after boring was completed.
The cause of this situation is usually chip accumulation or boring tool trying to pass through the bottom of the blind hole. If the boring bar head is found by inspection to be still in the hole and difficult to remove, the most likely reason for this catastrophic failure is the accumulation of chips in the hole. The reason for this is that the material removal rate is greater than the chip removal capacity due to excessive cutting parameters such as cutting depth and feed rate. One of the solutions is to use a smaller diameter boring bar. If a smaller diameter boring bar cannot be used, the cutting parameters must be reduced to reduce the metal removal rate. If it is found that the broken boring bar is not in the hole or is very loose in the hole and is difficult to take out, the possible reason is that the depth of the boring feed is greater than the depth of the existing hole on the part and the boring bar is broken. Remember that a boring cutter does not drill like a drill.


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The cause of wear of boring tool rear surface was misjudged.


Tool wear

When the boring tool is adjusted correctly and there is no catastrophic machining failure, the low production efficiency caused by frequent tool change is unacceptable. Excessive wear on the back face of the cutting edge was found on inspection. However, excessive or rapid wear of the posterior surface can be misdiagnosed. Usually, the cutting time is too long, intermittent cutting or cutting vibration will cause the cutting edge edge collapse and is regarded as after the tool face wear. Rank surface wear may be caused by chip buildup on the front surface in the first place. This is because the cutting heat and cutting pressure will weld chip buildup on the front surface of the tool. At some point during cutting, chip buildup will take away the chip buildup, along with alloy material on the front surface of the tool.


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Cuttings can be misdiagnosed as wear on the back surface when the chip carries off the chip and the alloy material on the tool.


In order to determine the real cause of tool surface wear, can be in the boring tool after machining one or two holes to check whether there is debris or chipped edge existence. Cutting pressure, which is dependent on cutting depth and feed rate, can be reduced by reducing cutting pressure and cutting heat. Reducing the cutting depth and feed rate can reduce the cutting pressure and cutting heat, but also reduce the production efficiency. One way to improve production efficiency is to use coated tools. Coating reduces cutting heat as chip flow passes through the cutting surface of the tool. Altin PVD film coatings are more effective than CVD film coatings because too thick coatings deteriorate the cutting performance of the cutting edge.

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Boring cutter with carbide


Cutting cooling

Coolant is usually used to reduce the cutting heat. This is simple and easy for turning the outer circle, but difficult for boring the inner hole, which contains the boring bar and chips that need to be cooled. Placing the coolant nozzle close to the orifice will prevent cutting. Therefore, the best way is to provide internal coolant through the boring bar. It is an ideal solution to provide sufficient flow of coolant along the circumference of the boring bar to minimize the coolant resistance and reach the bottom of the boring hole. This usually requires placing the coolant nozzle in multiple places, such as in the main after the cutter face, the front cutter face and the secondary after the cutter face. In response to the need for adequate coolant, Scientific Cutting Tools provides a tool bar with cooling ring technology that allows the coolant to be applied circumferential tothe coolant to wrap around the boring bar.
After machining several parts, the most likely cause of a chipped edge is encountered in intermittent cutting, such as cross holes or keyways. In this case, the need to choose the edge of the tool to strengthen.
If the breaking edge is not caused by intermittent cutting, cutting vibration may be the cause. As with intermittent cutting, cutting vibration will make the cutting tool bend downward, and then rebound with the disappearance of the force, thus causing impact on the cutting edge. One possible solution is to increase the feed speed, the feed speed increases by 10%, can fully increase the cutting pressure to keep the cutter under pressure, in order to avoid rebound impact on the edge.

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