CBN grinding wheel with high efficiency, high precision, low cost and other significant advantages, camshaft grinding technology development trend. Based on years of experimental research results and related technical literature, the article pointed out that the domestic CBN in the camshaft grinding process technology to market major constraint and made a positive recommendation to the camshaft is widely used in processing CBN grinding technology, processing technology to improve the overall level of the engine.
As a key part of the engine camshaft, one of its processing quality directly affects the engine power characteristics; Meanwhile, the camshaft is also a non-circular grinding of the workpiece, the allowance is large and difficult to grind materials for grinding cutting accuracy and production efficiency requirements are high, processing more difficult. Thus, camshaft grinding technology has been the focus of the industry. How to improve the grinding efficiency and processing quality is camshaft grinding urgent problem should primarily consider the following factors:
● The machine features;
● cam contour grinding shaping the way;
● grinding performance and cooling liquid;
● grinding process, including the dressing tool and finishing processes.
Camshaft grinding technology development status at home and abroad
Currently, the majority of domestic car production line OEMs and professional production camshaft camshaft manufacturers have introduced a CBN grinding technology, but there are still a lot of trucks, diesel and motorcycle engine cam is still using the traditional corundum grinding wheel, by imitating shaped grinding process. Coarse grinding process using a homemade low-speed grinder (35m / s less), some manufacturers use imported grinding grinding process, but are in the use of speed 60m / s or less, a single-point diamond dressing tools pen mostly import grinder and a few domestic use of diamond grinding wheel dressing. This traditional approach to the problems posed by the camshaft grinding is mainly reflected in the following aspects:
● cam profile accuracy is low and it is difficult to improve
Grinding using the master plate cam contour shape the smallest error can only be controlled within ± 0.03mm range, and no CNC cam grinding can be controlled within ± 0.01mm. Furthermore, in use of abrasive wheel, outside diameter range (80 ~ 100mm), and the wheel diameter changes every 1mm 0.007mm generated will cause the cam profile changes, it is difficult to further improve the accuracy of the cam profile.
● cam surface is easy to produce burns, cracks and other defects, it is difficult to improve production efficiency
Since the cam grinding allowance is large and difficult to grind materials, ordinary abrasive performance is difficult to adapt, grinding both quality and production efficiency are often not taken into account.
● overall economic efficiency is not high
Ordinary abrasive durability and low life, need frequent repair or replacement of the dressing tool loss accelerated, auxiliary time and labor intensity increases, it will affect the efficiency of production, but also increased the cost of production. In addition, a large amount of wheel, its quality fluctuations also affect the stability of the grinding process, because a lot of grinding residue generation, increasing the amount of grinding fluid filter cleaning, some pollution caused to the environment.
CBN grinding technology, the traditional camshaft grinding process problems solved. Ten years ago, about using CBN grinding wheel camshaft reported only in limited foreign literature seen. In large-scale industrial production, the use of special CNC Camshaft Grinding CBN camshaft technology in some Western countries have just entered the practical stage. Closely follow the world trend of development of advanced manufacturing technology, Suzhou in the early 1990s, research and development in the domestic automotive camshaft for vitrified CBN grinding wheel, in the domestic ordinary high-speed (60m / s) strongly Camshaft Grinder on coarse chilled cast iron camshaft, made good use of effects. However, due to the time machine grinding wheel manufacturing conditions and technical constraints, have not been able to achieve better results. To the mid-1990s, the majority of car manufacturers in industrialized countries have adopted a CBN grinding wheel camshaft, major domestic car production line also have introduced this technology. It is based on CBN dedicated CNC CNC camshaft grinding machines, high-speed and high-performance ceramic CBN grinding wheel, special grinding fluid, dressing roller and grinding process technology in the form of the introduction of the package. The main features of this technology are: high speed grinding wheel (80 ~ 125m / s), high processing efficiency (the workpiece from the rough coarse grinding once completed, the efficiency of an ordinary wheel 2 to 3 times). With camshaft grinder CBN grinding technology and its continuous introduction of dedicated domestic research dedicated high-speed CNC camshaft grinding CBN will soon enter the market. In this regard, in improving the domestic coarse grinding with CBN grinding wheel camshaft technology, and actively study camshaft grinding with CBN grinding wheels at the same time, Suzhou began to develop as a dedicated CNC camshaft grinding machine imported CBN supporting high-speed, high performance ceramic CBN grinding wheel, and has achieved certain results. Developed using wheel speed 80m / s, durability and longevity of imports wheel, the wheel and the price of imports only 1/3. Developed ceramic CBN grinding wheel, compared with similar imported, the main difference lies in durability, longevity and stability of product quality is low, can not entirely replace the camshaft wheel production line imported continuous use. In order to catch up with the rapid development of this level of technology, research and development in recent years has successfully used a speed of 125m / s camshaft ceramic CBN grinding wheel, and its use of speed, grinding efficiency, grinding quality have reached the level of similar imported products, with a very high price, product quality is stable quality, can replace imported. All these indicate that our CBN grinding wheel manufacturing and application technology has reached a new level.
CBN camshaft grinding technology elements
Industrialized countries in the development of a CBN grinding technology notable feature is the CBN abrasive, abrasive, grinding and grinding process as a system to carry out the project. Such as the United States in the early 1990s, to address the camshaft CBN grinding technology, the joint GE's (CBN abrasives), Norton Company (abrasive) and Landis Company (grinder) three of the industry's top companies jointly research. They eventually a high speed CBN grinding wheels, high-speed CNC grinding and CBN CBN grinding dedicated set of technologies available to the market.
The camshaft grinding system, you must also take into account the CBN grinding wheel manufacturing and application technology involved in all aspects of the influencing factors, will finally get a satisfactory grinding result. Camshaft CBN grinding technology of the important factors are:
● CBN grinding wheel
The superior performance of the grinding wheel must also have sharp, good self-sharpening and durability and other features. In the manufacture of the main consideration and selection wheel binders, abrasives, grinding wheels and abrasive hardness concentration.
1, binders
In the four CBN abrasive binder (resin, ceramic, metal plating) in order vitrified bond CBN abrasive fastest. Worldwide, the proportion of ceramic CBN abrasive 1980s by 4% to over 50% now, the rapid growth. As the ceramic CBN abrasive grinding with high efficiency, good shape retention and durability, easy trimming, abrasives high utilization (75% or more, other types of binding agent is 50 to 60%), long life and other advantages wheel , and thus become efficient, high-precision grinding preferred abrasive. Currently, CBN grinding wheel for camshaft used in all vitrified.
2, abrasives
In grinding, the abrasive is abrasive in the main, its performance directly affects the grinding effect. Compared with corundum abrasives CBN abrasives, has a higher hardness and strength (see Table 4), thus cutting sharpness and wear. In the camshaft grinding such high strength case, CBN abrasives is the best choice. CBN abrasives different grades, different due to manufacturing process, the crystal morphology, particle shape is also different, which each have a different strength, thermal stability, chemical resistance and breaking properties. Should be based on the type of binder, grinding the workpiece and the grinding of different ways, choose different grades of abrasive. It is noted that, CBN abrasive with water under high temperature and chemical reaction of alkaline oxide and its structure is damaged, it is the choice of the type of grinding fluid, pressure and flow factors must be considered.
3, the concentration
Wheel indicates the level of concentration per unit area of the grinding wheel face participate on how much the number of grinding grains, high concentrations can bring high grinding ratio, 200% concentration of less than 100% density wheel life length of 4 to 5 times . Currently, high-speed, efficient grinding wheel are made of high density, such as import camshaft grinder grinding ceramic CBN wheels supporting concentrations in general are 200%.
4, the hardness
Hardness grade abrasive abrasive binders on said gripping force size, which is an important process control manufacturers indicator, is also user-selected abrasive performance of the main parameters. Wheel hardness uniformity and stability and hardness of the level of rational choice is an important prerequisite to ensure the quality of grinding. Foreign ceramic CBN wheels are generally 3 to 7 hardness levels to choose from, yet formulate domestic CBN wheel (including diamond abrasive) hardness test, the manufacturer only recipe hardness control.
● grinder
As with grinding wheel grinding system as the center of an attachment, only through the grinder has the excellent properties and optimize various grinding parameters, in order to maximize the advantages of the CBN grinding is especially true.
1, high-speed
Increase working speed wheel can significantly improve the grinding efficiency and the grinding ratio, lower grinding forces, thereby reducing the cost of the grinding. If using a ceramic CBN grinding wheel camshaft, when wheel speed from 80m / s up to 160m / s, the grinding time of the same, dressing interval (durability) increased by 2-fold; when the wheel speed 35m / s to 60m increased / s, the metal removal rate in different units (Q'w) case, the normal grinding force (F'n) are reduced by 1/3. CBN grinding wheel CBN abrasives its structural characteristics and the characteristics of high-speed, ultra-high speed grinding possible. 80 ~ 125m / s the use of speed has become the domestic import CBN special camshaft grinder basic characteristics. When conditions permit, to use the highest possible speed CBN grinding is to improve the technical and economic important prerequisite.
2, high machine rigidity and shock resistance
High-speed grinding and CBN grinding wheel characteristics and requirements, and overall to the machine spindle with high rigidity and excellent shock resistance, thus ensuring the accuracy of the workpiece and the grinding surface quality, which is CBN high-speed grinding technology for grinder basic requirements. Without these conditions, the use of CBN grinding wheel, in order to obtain higher metal removal rate, workpiece geometrical accuracy and surface quality will deteriorate. Corrugated surface is a common quality defects, which is generated by the vibration. Vibration caused by a variety of reasons, including machine rigidity is low, poor shock resistance, machine design parameters resonance caused by the irrational or grinding wheel grinding force too big. Data shows: the stiffness of the machine should not be less than 100N/0.001mm of magnitude as well.
● Dressing
Using a diamond wheel dresser, dressing can not only improve the efficiency, and more importantly, can achieve better wheel topography. Use other dressing tools, it is difficult to complete the dressing wheel surface with high hardness. Trimming device feeding accuracy is higher, the amount of each feed should be mm level, excessive trimming affects both the quality will greatly reduce the grinding wheel life. Trimming ratio Vr / Vc dressing process is an important parameter, which causes the wheel surface changes in a significant change in morphology, and ultimately affect the surface quality.
● Coolant
In the grinding process, 90% of the energy is converted into heat, which heat must be cooled maximize the absorption of fluid, or the workpiece will be burned. The CBN grinding wheel is concerned, but also consider the CBN abrasive with water at high temperatures generated by the chemical reaction for abrasive damage. Select the correct type of coolant and cooling process parameters, tend to have a multiplier effect. Different coolant, make grinding wheel several times or even ten times than the difference. Table 5 for the cooling fluid of the CBN grinding wheel, the results show that the grinding wheel in the process of mechanical wear, chemical attack and thermal damage is closely related to the degree of cooling effect.
Questions and suggestions
At present, the domestic CBN in the camshaft grinding process technology to market constraints mainly reflected in the following aspects:
1, imported matching CBN grinding wheel grinder and expensive, the price is the common camshaft grinder grinding machine about 10 times, is the development of similar grinder 3 to 4 times; imports CBN grinding wheel price is the same 3-5 times, making the further promotion in the domestic market by cost constraints.
2, made most of the camshaft grinder processing speed is low, its accuracy, rigidity, vibration resistance, finishing, cooling and other conditions are not met the requirements to use CBN grinding wheel. Therefore, when using CBN grinding wheel, it is often not the desired effect.
3, the main domestic CBN grinding wheel performance has reached the level of similar foreign products, but the wheel durability, service life and stable quality, adaptability is slightly lower, but the price is low, and thus has a higher cost, its technical and economy has many domestic automobile OEMs and supporting plants recognized, but still need to further improve the level of manufacturing technology CBN wheels.
4, the new technology is not enough publicity, some companies follow the beaten track, the demand for new technology is not strong, to improve production efficiency and processing quality is not paying attention to is the technology to promote external constraints.
To do this, make the following recommendations:
1, accelerate the development of domestic high-speed CNC camshaft grinding CBN dedicated, focused on solving its rigidity and vibration resistance of the key technologies, first make 80m / s grinders on the market as soon as possible, so that most of the technical and economic performance to meet the needs of SMEs. On this basis, further development speed, higher performance and better products.
2, CBN grinding wheel studies should be based on improved performance, improved technology, stable quality and mass production. Should strengthen basic research and the development of special equipment. By supporting the grinding wheel for the import of the development of key technologies to solve their manufacture, import wheel meet domestic needs. At the same time, given the current state of technology of domestic camshaft grinder, CBN grinding wheel manufacturing technology parameters in the design of this part of the effort to meet the requirements of grinding using CBN grinding wheel, CBN grinding the maximum possible effect.
3, in the grinder, abrasive manufacturers and users to build closer ties, strengthen communication and coordination to jointly promote CBN grinding technology continues to improve.
