Because of the small module, small number of teeth, lar […]
Because of the small module, small number of teeth, large production batch and high precision requirement, it is difficult to use the traditional shaving, honing and grinding process, and the economy is poor. In this context, it is very urgent to innovate the traditional processing methods and adopt high-speed, efficient and high-precision processing equipment and technology.
According to our understanding of the customer's processing requirements, we have innovated the traditional processing technology, made a series of improvements on the user's process path, processing equipment, tool selection and other aspects, and obtained superior process performance. Over the past few years, we have been learning from advanced foreign experience, combining with the actual situation of users, making a series of innovations and accumulating some experience. In this paper, only from the perspective of new process practice and new equipment improvement, combined with the user's examples, an overview is given.
Take a customer's product as an example (Figure 1): this part is a motor shaft of new energy vehicles. The length of the end spline is 35.8mm, the modulus is 1.5, the number of teeth is 21, the pressure angle is 30. After carburizing and quenching, the surface hardness is hrc56-62. The surface roughness is above 3.2, and the accuracy requirement is level 6. The solution is provided by high speed dry cutting hobbing technology. Around this goal, we make a comprehensive comparison of each process link:
1、 Cutting tool
The performance of hob for high-speed dry cutting hobbing mainly depends on the following three aspects: tool material, surface coating, design and manufacture of hob parameters and structure. There are four kinds of materials for cutting tools: cemented carbide, ceramics, high speed steel of powder metallurgy and high performance high speed steel. Ceramic materials have been widely used as turning tool blades for a long time. As a complex gear cutting tool, it can not be realized at present. However, some excellent properties of ceramic materials should be the most needed for high-speed dry cutting process. Therefore, the application of ceramic materials in the high-speed dry cutting hob will also be an inevitable trend, especially in the hard tooth surface scraping tool. At present, the hob material used for high-speed dry cutting of hard tooth surface is mainly cemented carbide, while the hob material used for high-speed dry cutting of soft tooth surface is mainly high-speed steel, and cemented carbide is also used.
Using high-speed dry cutting, if only using the existing tool materials with good thermal stability to optimize the tool geometry, still can not achieve good results. Therefore, the tool surface is coated with a hard coating with good thermal insulation, which has a soft coating with solid lubrication performance, so that the tool can withstand higher cutting temperature.
The coating has two main functions: first, it provides a low friction layer, reduces the friction and adhesion between the tool and the workpiece surface, which is equivalent to the lubrication effect of cutting fluid; second, it plays a role of heat insulation between tool cutting, prevents the transmission of cutting heat to the tool, which is equivalent to the cooling effect of cutting fluid.
The core problem of high-speed dry cutting is the tool wear. Therefore, pay close attention to the tool wear in the cutting process. In addition to the tooth profile inspection of the workpiece, we can also combine the traditional tool wear inspection to take a better feeding mode and determine a reasonable regrinding time. It is very important to adjust the technology in time according to the tool wear, which can improve the machining accuracy and implement the high-speed dry cutting hobbing technology. For the selection of cutting speed, feed rate and cutting depth, we have made a comprehensive comparison, and finally we choose the P / M alloy steel hob with high cost performance as the solution.
2、 Cooling mode
The cooling mode of high-speed dry cutting technology is mainly air cooling. The cooling system of wet cutting hobbing machine is replaced by compressed air cooling system. On the basis of air cooling, add micro lubrication device, so that the service life and surface cutting quality of the tool can be greatly improved.
The principle of micro lubrication is to spray a small amount of lubricant onto the cutting edge for lubrication through the precise tut device, which is mostly carried out by compressed air. There are essential differences between micro lubrication and traditional oil lubrication. The traditional oil lubrication has three functions of washing, cooling and lubrication. The amount of oil is very large. When cutting, the lubricating oil based on mineral oil added with extreme pressure and antiwear agent is harmful to workers and environment. Micro lubrication only plays the role of lubrication, the rest of the functions are undertaken by compressed air. The lubricant used in micro lubrication is a kind of pure natural environment-friendly, safe and biodegradable lubricant extracted from plants, which does not cause harm to people and the environment. The product is composed of refined base oil compounded with different proportions of sulfurized lard, sulfurized fatty acid ester, extreme pressure antiwear agent, lubricant, antirust agent, mould proof bactericide, antioxidant, refrigerant and other additives. Therefore, the product has excellent complete protection performance for CNC machine tool itself, cutting tools and workpieces. Cutting oil has super lubricating extreme pressure effect, which can effectively protect the tool and extend its service life, and can obtain high workpiece precision and surface finish. The installation, adjustment and control of the micro lubrication device are simple, and the one-time investment is not high, but the effect is certain.
3、 Processing equipment
Modern machine tool is a complex of modern manufacturing theory and technology, and it also has many influences on high-speed dry cutting hobbing process, such as reasonable motion parameters, overall rigidity, vibration resistance, etc., which should be considered comprehensively when selecting equipment. Under the condition that the high-performance CNC gear hobbing machine can not be popularized in our country, many manufacturers have implemented the high-speed dry cutting gear hobbing process by adjusting the transmission accuracy of the ordinary gear hobbing machine and improving the overall rigidity, and achieved good results