When formulating project work, it is often necessary to make an estimate of the tool’s lifespan as a reference for budgeting and planning. Usually, we need to study and understand the consumption of tools of similar processing forms in the same industry and product. Based on this, we can establish a predetermined value for the corresponding tool life of our company after evaluating maturity and accuracy. However, for various reasons, it is often desired to obtain tool life data in a more direct form.
Taylor formula
In the theoretical discipline of machining, Taylor’s formula (FWTaylor) is generally used to express the relationship between tool durability (T) and linear speed (V). VTm=C1, called TV relationship Different workpiece materials, different tool materials and different cutting conditions have different coefficients and exponents. Different tool durability relationship graphs can be drawn in the hyperbolic coordinate system, called TV graphs. Similarly, there are also expressions and relationship graphs between T, f (feed) and ap (cutting depth).
The Taylor formula is used in classrooms and laboratories, but rarely in factories. Factories are accustomed to using estimation methods to obtain tool durability, or tool life. Generally, there are several estimation methods:
1. According to cutting time:
In the metal cutting tool industry, linear cutting speed is recommended based on a tool life of 15 minutes. In actual use, 75% of the tool brand manufacturer’s recommended value is typically used. Currently, the tool life is about 60 minutes.
The number of parts that can be processed by a blade can be estimated as follows:
N=(19100XVXf)/(DXh)
N – Tool life, number of parts that can be processed, unit: parts
V – Tool selection linear cutting speed, unit: m/min
f – feed quantity during processing, unit: mm/rev
D – Diameter of the workpiece, unit: mm
h – processing length, mm
Example: Turning a part with a diameter of 50 mm and a length of 100 mm. The tool manufacturer recommends a linear speed of 200 m/min. The programmed cutting time and tool life T = 60 minutes. /min and the feed rate is 0.1 mm/min. Turn to estimate tool life:
N=(19100X150X0.1)/(50X100)=57.3
That is, based on the above conditions, each edge can process 57 pieces.
2. In terms of cutting distance:
Cutting distance refers to the fact that assuming a cutting edge continually cuts at a certain speed on a very large workpiece, the total distance traveled by the tool from start to failure is called the tool life of the cutting distance. Represented by L.
The number of parts that can be processed by a blade can be estimated as follows:
N=(318300XLXf)/(DXh)
N – Tool life, number of parts that can be processed, unit: parts
L – Cutting distance and expected life, unit: kilometers
f – feed quantity during processing, unit: mm/rev
D – Diameter of the workpiece, unit: mm
h – processing length, mm
Example: For turning a part with a diameter of 50 mm, a length of 100 mm, a feed rate of 0.1 mm/revolution and a cutting life of 10 kilometers introduced by the tool manufacturer, the estimated tool life is:
N=(318300X10X0.1)/(50X100)=63.66
That is, based on the above conditions, each edge can process 63 pieces.
3. Based on experience value:
Experienced practitioners have accumulated rich experience in the service life of some materials and tools commonly used in processing parts made of a certain type of material, and can directly estimate the service life of tools.
For example, for coated carbide drill bits with a diameter between Ф25 and Ф30, the total drilling length when processing ordinary carbon steel is about 20-30 meters. When processing cast iron, the total overall length is generally 80 to 100 meters.
The three estimation methods mentioned above are only rough estimates under normal circumstances. Whether calculated in terms of cutting time or cutting distance, they are both relatively conservative. Because few tool manufacturers provide this data. Even if this is provided, it is only a particular case of the supplier under specific environmental conditions in the laboratory and does not necessarily have a general meaning.
Estimation based on empirical values has considerable limitations, does not necessarily have universal commonalities, and can only be roughly estimated under basically the same conditions. But for the processing of certain types of materials by a certain brand of certain tools, this estimation method is closer to reality. Under the same or similar conditions, it can be used as a reference.
When establishing actual estimates, the following conditions should also be taken into account:
1) Determination of the failure limit, i.e. under what circumstances the tool can no longer be used. Except extreme situations such as edge chipping and breakage. Mainly refers to wear, especially during finishing. It is generally considered normal when wear on the surface of the sides of the finishing insert is less than 0.2 mm. Tihao Machinery is the company’s main products with rotating center, lead screw, machine tool spindle, shaft processing, high precision tool holder, tool holder, elastic chuck, non-standard parts processing and adapter machine tool! However, if it is a fixed diameter tool, wear of the flank surface will cause the diameter of the workpiece to change. Once the radial size change reaches a dangerous situation, the tool should be replaced. For another example, if there are special requirements for surface roughness, the tool should be replaced if the tool is slightly worn or the surface roughness decreases slightly and cannot meet the requirements. When estimating, the estimated value must be reduced by a certain proportion. If the radial dimensions are adjusted or compensated and the surface roughness requirements are relatively low, the estimated value can be increased proportionally.
2) Cutting speed has a considerable impact on tool wear. Generally speaking, the faster the linear speed, the shorter the tool life. However, if the linear speed is too low, it will affect the processing efficiency on the one hand, and on the other hand. is not necessarily beneficial to the life of the tool, so the choice of cutting speed should refer to the cutting parameters provided by the tool manufacturer, and then determine the most reasonable speed according to the conditions on site.
3) The material of the workpiece also has a considerable impact on the tool life. Although seemingly the same material contains slightly different proportions of components, the cutting performance can be very different. Even if the materials are exactly the same, different component structures, different casting methods, different heat treatment equipment or processes, and different processing tools in the previous process will cause significant differences in tool life. Tihao Machinery is the company’s main products with rotating center, lead screw, machine tool spindle, shaft processing, high precision tool holder, tool holder, elastic chuck, non-standard parts processing and adapter machine tool! For example, when processing stainless steel parts, if the roughing tool in the previous process is not sharp, a hardened layer will form on the surface of the part due to the cold work hardening effect. , causing heavy wear of the finishing tool in the later process, causing serious damage to the life of the finishing tool.
4) Reasonable and accurate use of cutting fluid can significantly improve tool life. First of all, the cutting fluid must be accurate, clean, sufficient and effective. Different tool materials, different workpieces and different processing forms need to be filled with different cutting fluids according to the requirements of the purpose, such as cooling during rough machining and lubrication during finishing.
5) The foundation, machine tools, fixtures, parts, tools, etc. all form a system, and the rigidity of the whole system has a great impact on the life of the tool. Since tiny vibrations cause abnormal micro-displacements between the tool and the workpiece, the tool unnecessarily increases ineffective friction, ultimately leading to tool wear and rapid decrease in tool life. . Improving system rigidity is an important measure and means to improve tool life. However, to effectively improve the rigidity of the system, detailed and complex investigation, analysis and research work must be carried out continuously. Many people think that changing a certain local structure will cost a lot of money. In reality, this is not the case. A one-time investment in human and material resources can result in a long-term reduction in consumable costs for many. years, or even more than ten years.
What is mentioned above is about turning and boring. It can also refer to the processing of drilling, enlarging, reaming, etc. The milling process is very different:
1. Milling is intermittent cutting, and the tool edge material should be impact resistant, with relatively good toughness, relatively low hardness and relatively low wear resistance.
2. Milling is an intermittent process, and the actual cutting time of the blade is only 30%-50% of the total processing time, which is beneficial to the heat dissipation of the blade and can effectively extend the service life of the tool.
3. During the processing process, different forms of processing, such as end milling, circumferential milling, face milling, groove milling; different workpieces such as main cutting edge, different processing requirements, such as rough milling, fine milling, etc. ; . Failure modes vary widely. The situation of tool life is also different.
4. Milling cutters are multi-edged tools and the above formula cannot simply be applied when calculating. Generally, we can only analyze and borrow according to the actual situation and make rough estimates.
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