Failure modes and Countermeasures of the hottest c

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Failure modes and Countermeasures of tools

failure modes of tools are different. When the same cutting edge is applied to two different processes, two completely different failure types may occur. Although tool suppliers have done a lot of research on various tool failure modes, the knowledge about tool failure modes should be really related to actual production. For the users of cutting tools, they are most interested in knowing when the cutting tools will fail and how to correctly determine the failure of the cutting tools

ingersoll cutting tools' tool experts believe that it is very useful to understand the failure mode of a specific tool in a processing process that produces pointer zero instability. One of the advantages is that by diagnosing some wear types of tools, some machining problems can be revealed, and how to improve the tools or processes can be guided, so as to prolong the tool life and improve the cutting performance. Another benefit relates to consistency. Tool failure has different basic mechanisms, including wear, thermal shock, mechanical shock and chemical action. These mechanisms lead to different tool failure modes. However, one mechanism and its related tool failure mode are better than all other modes, and this failure mode is abrasive wear. This type of wear indicates that the machining process is stable and reliable. The gradual and predictable wear of abrasive particles can often play a leverage role in improving machining efficiency

it is not very difficult to determine the failure mode of the tool - just remove the tool (especially when the tool is currently estimated to be about 30% and 70% of its life), detect the cutting edge condition in this processing stage, and compare it with the tool wear photos given in this paper and the description of the failure mode

1 abrasive wear of tools

repeat, abrasive wear is an ideal failure mode. Abrasive wear is caused by the friction of workpiece material across the main flank of the tool. In a given processing, for a certain number of blades provided by a specific tool manufacturer, the abrasive wear tends to be repetitive, so it is also predictable

Another reason why abrasive wear has become the preferred failure mode is that it can show the development process of wear. Usually, some phenomena in cutting can indicate that abrasive wear is increasing. Some of these phenomena can be observed (such as burrs on the workpiece, changes in the finish of the machined surface, etc.) and some can be heard (such as gradual changes in cutting noise, etc.). Through these processing phenomena, it is easy to determine when the blade needs to be replaced

since abrasive wear is an ideal form of wear, it is usually unnecessary to change the processing technology when abrasive wear occurs to the tool during processing. Of course, some tool brands and coatings can indeed provide higher wear resistance (especially in high-speed cutting). If the tool has abrasive wear, using these tool brands or coatings can prolong the tool life

2 tool crater wear

generally speaking, the generation of craters may be related to any form of wear caused by the interaction between the workpiece material and the rake face of the blade. The most common crater wear is caused by the chemical interaction between steel workpiece and cemented carbide tool (that is, the carbon exuded from the front face of the tool dissolves into the chip). However, the crater wear may also be caused by the abrasion of chips across the rake face of the tool when cutting cast iron at high speed

the danger of crescent wear is that the cutting edge is usually still intact, and the tool can maintain a relatively normal cutting state until the tool suddenly fails unexpectedly

in order to protect the rake face of the tool from crescent wear, the countermeasures that can be taken include:

· reduce the cutting speed to reduce the cutting edge temperature

· reduce the feed rate to reduce the stress on the blade

· select coated tool brand to strengthen the protection of the rake face

· improve the geometric shape of the tool to reduce the cutting force directly acting on the rake face

3 groove wear of tools

groove wear of tools is usually caused by the deterioration of the cutting conditions on the surface of the workpiece under the condition of full cutting depth compared with the rest. The reason for the difference of cutting conditions on the workpiece surface may be related to the peeling of the workpiece surface; It may also be caused by cold work stress or work hardening; It may also be related to some seemingly insignificant factors, such as paint. The paint on the surface of the workpiece may have a quenching effect on the cutting edge that cuts into the workpiece not too deep

for the groove wear of the tool, what countermeasures should be taken is related to whether the groove wear is caused by the broken edge or abrasive wear. According to the type of wear, you can change a blade brand with higher mechanical impact resistance or higher wear resistance. Another alternative solution is to increase the residual angle of the tool to increase the shear effect and reduce the chip of the development history of Jinan assay testing machine; Or increase the passivation size of the cutting edge to increase the strength of the cutting edge. Another solution is not to change the tool, but to use different cutting depths during each cutting, so that the wear acts on different parts of the cutting edge

4 hot cracks of tools

most machine tool users associate hot cracks with coolant. When the coolant poured onto the cutting edge is uneven, the temperature of the cutting edge will fluctuate, causing the blade to expand and contract, resulting in cracks on the cutting edge

however, hot cracks may also occur when coolant is not used. For example, in dry milling, the cutting edge may also cause temperature fluctuations sufficient to produce fatigue cracks when cutting into and out of the workpiece material. For this kind of thermal crack caused by non coolant, the crack on the blade is straight and parallel; On the contrary, due to the randomness of temperature fluctuation, the non parallel cracks caused by coolant are more likely to cause edge collapse

the Countermeasures for hot cracks include:

· reduce the cutting speed to reduce the cutting edge temperature

· stop using coolant to reduce the fluctuation range of temperature

· choose the blade brand with good thermal shock resistance but more than enough for the existing n variety of experimental machine standards

· choose coating blade brand, especially PVD coating can effectively prevent the formation of cracks, because the coating used for crack resistance can exert compressive stress on the blade surface

5 tool edge collapse and fragmentation

like hot cracks, edge collapse or fragmentation is not "wear" in nature. This failure mode is because the cutting edge is too brittle to withstand cutting impact and fragment collapse occurs. It should be noted that it is related to both cutting impact and cutting edge

the measures that can be taken to deal with blade collapse and fragmentation include:

· choose a blade brand with good mechanical impact resistance (i.e. rigidity)

· increase the tool offset angle to reduce chip thickness and increase shear effect

· improve the rigidity of the process system, including improving the stability of the mechanism or the maintenance level of the machine tool

· increase the passivation size of the cutting edge to increase the strength of the cutting edge

6 cutting edge fusion welding of cutting tools

to some extent, cutting edge fusion welding is a problem that can be satisfactorily solved by improving cutting speed, which can also improve productivity

cutting edge fusion welding is caused by the workpiece material being fused to the tool. When processing, the chip temperature rises enough to make it soften and sticky, and then it cools quickly, and it will adhere to the blade. The solution is to prevent the chip from overheating, or increase the chip temperature so that it will not cool immediately before leaving the tool

in order to prevent the chips from heating to a temperature sufficient for fusion welding, try using coolant. Other possible methods include using a larger radial or axial positive rake angle to reduce the cutting force. In addition, the brand of coated blade can also be selected. The coating can reduce the friction between the tool and the workpiece and the possibility of mutual reaction

the opposite method is to raise the chip temperature further. By increasing the cutting speed and/or feed rate, the chip can be heated additionally, so as to prevent the chip from melting and welding due to softening and sticking

7 tool deformation

tool deformation refers to the softening and twisting deformation of the blade under the action of cutting heat and cutting pressure

cemented carbide, a hard tool material, will also deform. It sounds incredible, but in fact, tool deformation is increasing. There was a time when the heat resistance of cemented carbide far exceeded the performance of machine tools at that time, so that machine tools would not actually cause the danger of tool deformation under applicable processing conditions. However, with the continuous progress of machine tool performance, today's high-performance machine tools can be processed under high cutting parameters that are enough to deform cemented carbide tools, and the high stability of the machine tool is enough to prevent the fracture failure of cemented carbide tools

when there is a danger of tool deformation, the countermeasures that can be taken are as follows:

· reduce the cutting speed to reduce the cutting heat

· reduce the feed rate to reduce the cutting pressure on the tool

· select the tool brand with high heat resistance or high wear resistance

· reduce the passivation size of the cutting edge or adopt a larger positive geometric edge shape to reduce the stress and cutting heat acting on the cutting edge

· select coated tool brand, especially nitrogen aluminum titanium coating or aluminum oxide coating, either of which can effectively isolate cutting heat, so as to protect the blade from deformation

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