In the CNC machining process, leaving machining allowance for parts is a key step. Machining allowance refers to a certain thickness of material reserved on the blank or semi-finished product to avoid errors or defects during the machining process. Why should we leave machining allowance for CNC machining parts? The main reason is to ensure machining accuracy, improve machining efficiency, extend tool life and reduce scrap rate. In actual production, it is of great significance to improve the machining quality of parts to set machining allowance reasonably.
I. Definition and importance of machining allowance
The main function of machining allowance is to compensate for errors that may occur during the machining process and provide sufficient material for subsequent finishing. In CNC machining, blank materials are not always perfect. They may have dimensional errors, uneven surfaces and other problems. By reserving a certain amount of machining allowance, it can be ensured that these problems will not affect the final machining accuracy.
For example, if the final size requirements of a part are very strict, but the surface of the blank is uneven, direct finishing may cause the final part to fail to meet the size requirements or have surface defects. By leaving a machining allowance, removing the irregular parts of the blank surface initially, and then finishing, it can be ensured that the parts meet the high precision requirements.
II. Reasonable setting of machining allowance
- Initial machining allowance
The initial machining allowance refers to the material thickness reserved during the initial machining. The main purpose of machining at this stage is rough machining to remove the irregular parts of the blank surface. For parts of different materials, the setting of machining allowance will also be different. Usually, the machining allowance of steel can be set to 2-4 mm, and the allowance of aluminum alloy can be smaller, about 1-2 mm.
- Finishing allowance
After rough machining, the finishing allowance left is used to ensure the surface finish and dimensional accuracy of the parts. This part of the allowance is usually relatively small, the purpose is to avoid the influence of factors such as cutting force and tool wear on finishing. The finishing allowance is generally around 0.1 mm, and the specific value depends on the tolerance requirements and material properties of the parts.
- Adjustment of dynamic machining allowance
With the development of CNC machining technology, more and more production equipment has the function of dynamically adjusting machining allowance. This can fine-tune the machining allowance according to real-time factors such as tool wear and temperature changes during machining to ensure machining accuracy.
III. The impact of machining allowance on machining accuracy
- Improve dimensional accuracy
In CNC machining, dimensional accuracy is one of the key indicators for measuring part machining quality. By setting the machining allowance reasonably, it is possible to avoid the dimensional error of the blank affecting the dimensional accuracy of the final part. For example, when the surface of the blank has a large roughness, direct finishing may lead to inaccurate dimensions. By reserving machining allowance for rough machining first, the dimensional accuracy of the final part can be effectively improved.
- Improve surface quality
The setting of machining allowance also has a direct impact on the surface quality of the part. In the initial machining stage, a large allowance is used to remove the rough part of the surface, while in the finishing stage, a relatively smooth surface can be obtained by leaving a small amount of allowance for detailed surface treatment. For example, in high-precision part machining, the surface roughness can reach Ra0.4-0.8μm by setting the finishing allowance reasonably.
IV. Relationship between machining allowance and tool life
Tool life is one of the key factors to be considered in CNC machining. Reasonable machining allowance helps to extend the tool life. The tool bears a large force during the cutting process. If the allowance is too large, it will increase the cutting force, which will accelerate the wear of the tool. On the contrary, appropriate machining allowance can reduce the tool load and extend its service life.
For example, when machining hard steel, if the initial machining allowance is set too small, the tool may need to feed multiple times to remove excess material, which will greatly increase the tool wear rate. By setting the machining allowance reasonably, the tool can remove a large amount of material at one time, thereby reducing the number of feeds and reducing the wear rate.
V. Economic benefits of machining allowance
- Reduce scrap rate
Reasonable setting of machining allowance can effectively reduce the scrap rate. In actual production, if no machining allowance is left, the error in the initial machining will be directly transferred to the finishing stage, resulting in uncompensated dimensional deviations. By leaving enough machining allowance, finishing can be carried out under guaranteed conditions, greatly reducing the scrap rate.
- Improve production efficiency
By setting the machining allowance reasonably, the division of labor between roughing and finishing can be clearer. Roughing can remove most of the material at a faster speed, while finishing focuses on dimensional accuracy and surface quality. In this way, the processing efficiency is greatly improved and the overall production cycle is shortened. For example, in the mass production of automotive parts, the production efficiency can be improved by 10%-20% through reasonable machining allowance setting.
VI. Summary
Leaving machining allowance for CNC machined parts is of great significance for improving the machining accuracy of parts, ensuring surface quality, extending tool life and improving production efficiency. Reasonable machining allowance setting can not only reduce machining errors, but also effectively reduce scrap rate and improve economic benefits. Therefore, in actual production, understanding and mastering the setting principles of machining allowance plays an important role in improving CNC machining quality.
The reasonable setting of machining allowance is not only to avoid errors, but also a strategy to improve machining efficiency and reduce costs. Through scientific allowance reservation, enterprises can optimize production processes while improving product quality and enhance market competitiveness.
