1 honing technology introduction
1.1 Introduction to honing technology application
As a new process for the cylinder hole or cylinder liner finishing of internal combustion engine, the boring technology of cylinder bore platform is mainly used for diesel engines with high compression ratio. It has been further developed in recent years and has been widely used in gasoline engines. The platform honing technique creates a special structure on the surface of the cylinder bore or cylinder liner that consists of a deep bearing platform surface with a deep groove between the oil reservoir and a deep groove. The surface of a typical platform honing is shown in the figure.
Mesh topography This surface structure has the following advantages: â— good surface wear resistance; â— good oil film storage, can use low friction piston rings; â— reduce oil consumption; â— reduce running-in time (almost can be saved ).
In order to form the honing surface of the platform, it is generally necessary to carry out roughing and fine boring twice in mass production. The functions are as follows: â— rough ç©: pre-twisting stage, mainly to form a cylindrical hole with correct geometric shape and suitable for subsequent The basic surface roughness of the process. â— Fine boring: The base platform honing stage forms a uniform cross-web pattern to form a platform section.
In order to obtain the ideal surface platform mesh structure, the requirements for the front and rear rough and fine coaxiality are very high, so it is more reasonable to combine the two stages into one processing, which is designed to have double feed device and thick The honing heads of the two types of honing sticks can achieve rough and fine boring in one clamping, eliminating the influence of repeated positioning errors, reducing the pressure of the pre-processing and the requirement for high precision of the machine tool.
1.2 Evaluation method for platform honing surface quality
Since the parameters such as Ra and Rz in the international standard are not sufficient to accurately represent and measure the surface of the platform honing, engine manufacturers have developed their own platform honing surface standards. After several years of practice and development, it has become more and more perfect, but so far there is no unified platform to honing technical specifications. Since Dongfeng Automobile Pump Co., Ltd. adopts German equipment and German standards, it mainly introduces several parameters and corresponding parameters used by Germany to evaluate the honing surface quality of the platform. standard.
1.2.1 mean peak-to-valley height Rz (DIN) (Mean peak-to-valley height)
The arithmetic mean of the local peak-to-valley height Zi over the range of five sample lengths connected to each other of the filtered profile. The local peak-to-valley height Z is the distance between two parallel lines that are parallel to the center line and pass through the highest and lowest points of the contour within the length of the sample. It is worth noting that Rz (DIN) is different from Rz (microscopic unevenness of ten points) in international standards.
1.2.2 Tow Wt (Total waviness height)
The waviness is the maximum peak-to-valley height in the horizontal direction of the filtered profile.
1.2.3 Core roughness depth RK (Core roughness depth)
The series parameters RK (Core roughness depth) series parameters include core profile depth RK, peak height Rpk (Reduced peak height), groove depth Rmk (Reduced valley depth), peak material ratio Mr1 (Peak material ratio), The groove material ratio is Mr2 (Valley material ratio) or the like.
2The use of honing technology in Dongfeng Motor Pump Company
2.1 Application of platform honing in the processing of air cylinder bore
When the air compressor of Dongfeng Motor Pump Co., Ltd. was originally introduced from German Green Company and Far East Company, the double-axis single-feed honing machine was honed by ordinary honing bar, first rough honing, fine honing, and separate honing. Repeated positioning of the equipment index, only Ra0.2 ~ 0.4 for the surface roughness of the cylinder bore. Due to the large amount of honing, the long honing time, and the poor geometry of the cylinder bore, it is unable to meet the requirements of subsequent products and customers. To this end, we have carried out several process improvements.
The first process improvement is the use of diamond honing bars for coarse and fine boring to improve the efficiency of honing and the surface quality is still uncontrollable. In order to completely solve the problem of high oil squeezing of air compressors, combined with the consultation results of engine manufacturers and honing machine manufacturers, we made further technological improvements in 2006, and purchased the cylinder honing machine from Nagel, Germany. The double-feeding of the shaft, the positioning of the coarse and fine at the same time honing the machining of the cylinder bore, realizing the platform netting honing in the true sense.
2.2 Process of air compressor cylinder hole machining
The bore of the cylinder bore of the air compressor is divided into rough, semi-precision and fine boring; the honing is divided into rough and fine boring, and the coarse honing is realized by two separate feedings at the same station. Since the cylinder line of Dongfeng Motor Pump Co., Ltd. adopts mixed flow production and has a wide variety of production, the typical 3509DC2-015/016 processing is taken as an example. The dimensions and surface quality requirements of each step are as follows: â— Rough hole of cylinder bore: Φ68.5～69mm Ra3.2 semi-fine cylinder bore: φ69.3～69.5mm Ra1.6 fine boring cylinder bore: φ69.94～69.97mm Ra0.8â— honing cylinder bore rough boring cylinder bore: φ69.97～ 70mm fine ç©: φ70～70.03mm cylinder bore cylindricity: 0.015mm mesh angle (along the axis) 145°±10° â— honing surface quality parameter roughness Ra=0.4-0.8, average peak-to-valley height Rz=4 -7, core profile depth Rk=0.2-0.8 reduced peak height Rvk=1.5-2.0, reduced groove depth Rpk=0.3-0.38, peak material ratio Mr1=5%-20%, groove material ratio Mr2=75 %-95% third highest peak to trough average height R3z=2.8-6.0 2.3 air compressor cylinder hole honing process
Dongfeng Automobile Pump Co., Ltd. introduced a cylinder honing machine from Nagel, Germany, in 2006 for honing processing of air compressor cylinder bores. The processing process and characteristics are as follows: The equipment consists of 2 stations. The equipment realizes one-time loading, and can automatically honing two cylinder holes at the same time, from the initial position, returning to the initial position after honing, which is convenient for the worker's operation, and automatically detects and performs compensation processing during the honing process. At the same time, the fixture adopts lightweight design, which effectively reduces the switching time of the variety.
The platform honing of the cylinder bore is achieved by two honing operations, namely rough honing and fine honing. The entire honing process of the cylinder is as follows: the finished cylinder is installed by the worker to the initial position of the fixture, and then the equipment is automatically transported to the fixture through the guide rail. Honing station.
The machine tool performs rough honing of the cylinder bore at the honing station. The feed of the rough honing diamond honing stick is controlled by a stepping motor. The feed speed of the honing stick and the size of the honing head and the stroke of the honing head are all set by a preset program. To control, the above values ​​can be adjusted by simply changing the corresponding parameters in the program. The machine tool can automatically correct the shape error of the cylinder bore according to the measurement result during the honing process.
Fine boring is carried out immediately after rough honing. The rough honing and fine honing of the cylinder bore are realized by two knives at the same station, eliminating the repeated positioning error and obtaining a more ideal surface texture structure. Since the on-line measurement technology is adopted in the honing process of the cylinder bore, the machine tool can automatically correct the shape of the cylinder bore according to the measurement result to ensure the machining accuracy of the cylinder bore. The cylinder bore has a cylindricity of 0.008 mm and a diameter dimensional accuracy of ±0.005 mm.
The cylinder bore honing adopts the diamond honing strip. The cylinder bore honing strip can generally process more than 3,000 pieces of life, and the bream strip is replaced less frequently, which ensures the consistency of processing and the auxiliary time is also relatively reduced.
The honing machine honing liquid has a temperature relative control device to ensure that the honing liquid temperature is lower than the ambient temperature by 2 to 6 ° C, which reduces the influence of the honing temperature on the workpiece, and is beneficial to improving the machining precision of the cylinder bore. At the same time, due to the fully enclosed structure of the machine tool, the loss due to atomization and evaporation of the honing liquid is reduced, and the environmental pollution is also reduced.
2.4 Key Problems in the Honing Process of 2.4 Cylinder Platform
2.4.1 Determination of surface quality parameters
The surface quality parameters of the cylinder bore are usually given by the designer during the product design process. In the past, since the surface quality was generally evaluated only by the surface roughness Ra, the product has less requirements on the process. After adopting the platform honing standard, the surface parameters and evaluation criteria will determine the process method, including equipment structure, honing bar type, testing equipment, etc., such as: German Volkswagen adopts Rk series parameters, British Perkins uses R3z, Skew and other parameters, and The testing equipment has clear requirements. Therefore, it can be said that the determination of the surface quality parameters of the cylinder bore platform is a process of combining the product and the process, especially the improvement of the old product process. The surface parameters of the engine cylinder hole platform mesh of the second engine plant of FAW Car Co., Ltd. were determined on the basis of the process test (completed by Nagel, Germany), combined with Porsche's consulting results and road tests.
2.4.2 Honing process
In the past, it was generally believed that both honing and three honing could achieve the surface structure of the platform. With the improvement of the technological level, it is generally believed that the rough honing and fine honing are performed once at the same station to obtain a precise platform surface structure.
During the two honing processes, the margin for coarse honing removal is 0.03-0.05 mm, and the margin for fine honing removal is 0.01-0.03 mm. In the rough honing, the main part is removed, the knife marks of the fine processing are eliminated, and the conditions for honing the netting are created; the fine boring forms the deep groove and the platform of the netting.
Due to the small amount of fine honing, the number of machining strokes is only 10 to 12 times. If the rough honing and fine honing are performed by independent spindle machining, the honing is completed before the honing head does not eliminate the repeated positioning error, resulting in a false platform. The roughing and honing is done once, that is, roughing and honing on one spindle. When the rough grinding is increased, the fine grinding does not increase the knife. When the rough grinding completes the retracting, the fine grinding knife is processed, which can eliminate the influence of repeated positioning error.
2.4.3 Spindle rotation direction during honing
When using a diamond honing stick, in order to avoid the influence of metal fragments caused by the high pressure of the honing stick on the wall of the hole, the direction of rotation of each processing should be reversed.
2.4.4 Tracking measurement and taper compensation during honing
In the honing process, the control program can compensate the taper of the cylinder hole by adjusting the overtravel amount of the sand bar according to the tracking detection result, and finally the taper correction can be performed by local short stroke honing.
2.4.5 Selection and initial dressing of the honing stick
From the point of view of honing efficiency and honing strip life, diamond honing bars are generally used for both rough honing and fine honing. When the diamond sand strip is used, it should be installed on the ruler before the bonding is completed for out-of-line trimming to adapt to the shape of the cylinder bore.
2.5 Comparison of the quality of platform honing and general honing processing
The surface structure of the honing of the platform has a significant improvement compared with the surface structure of the conventional honing, forming a platform with both a high bearing ratio and a deep groove structure for oil storage.
The improvement of the precision of the equipment and the improvement of the process have significantly improved the dimensional accuracy and geometric accuracy of the cylinder bore. The cylinder bore has a cylindricity of 0.005 mm and a diameter dimension accuracy of ±0.005 mm.
2.5.1 Practical application effect on air compressor
After the bench test, the air compressor using the platform netting honing process has made great progress in the following aspects compared with the air compressor not using this process: a.
Improve the service life of the cylinder block, piston and piston ring.
The platform netting honing process enhances the oil storage and carrying capacity of the cylinder wall, and improves the shape accuracy of the cylinder bore, thereby improving the lubrication condition between the cylinder wall and the piston and the piston ring, so that the cylinder wall, the piston and the piston ring are The wear rate is significantly slowed down, greatly improving the service life of the cylinder block, piston and piston ring.
b.
Reduce the amount of oil in the air compressor.
Due to the geometric accuracy of the cylinder bore and the improvement of the surface quality, coupled with the improvement of the piston ring structure, the air compressor oil is reduced from 0.25% to 0.50% to 0.15%.
3 Discussion and analysis of the problems faced by localization of honing head
3.1 Technical requirements and difficult points of honing head in honing technology
Due to the wide variety of air compressors in the pump industry, in the process of product design and process planning, each product must be serialized, and the serialized varieties of each series should be honed.
At present, the cylinder bore sizes are respectively divided into two groups for the above: mainly related to the design and manufacture of the honing head, the honing stick and the gauge.
In the design and manufacture of the honing head, the main difficulty lies in the high precision. The key point is the design of the inner mandrel and the honing seat of the honing head. The following figure: The single-axis double-height honing head structure controls the internal hydraulic pressure of the spindle of the equipment first, and then rough. Machining, the spindle ejector pushes the rough top sleeve, the thrust is transmitted to the rough mandrel, and the honing seat and the honing strip are supported by the cone surface to contact with the inner wall of the cylinder bore, and the spindle is rotated.
The internal measurement system of the spindle measures the size of the cylinder bore through the air pressure of the air nozzle, and the size of the cylinder bore is to be roughed to the fine size. The rough ejector rod is returned to the position, the honing seat is returned by the spring contraction, and the internal ejector rod is finely lapped. The rod acts to push the fine grinding seat and the fine grinding rod to act on the inner wall of the cylinder to perform fine boring and platform honing to ensure the need for the netting.
Pump companies need a variety of honing heads for many varieties. In order to effectively reduce the cost of new products and the daily cost of honing, it is necessary to localize the honing head.
3.2 Problems and analysis of the honing head in the process of localization and use
In the design process of the 3509DE2-015/016 cylinder bore air compressor cylinder, the honing head is mainly referenced by the honing head, and the requirements are put forward: a.
In the structure of the honing head, the optimized coarse and fine honing seat and the honing stone are evenly distributed on the circumference. During the honing process, the workpiece hole is evenly stressed, and the roundness and cylindricity of the workpiece hole are improved after honing; the original honing head is thick, The fine grinding bar is unevenly distributed on the circumference, so that the workpiece hole is affected by the alternating stress during the honing process, and the roundness and cylindricity of the workpiece hole after honing are poor.
The roundness and cylindricity are the key factors for the cylinder bore quality and the key factors affecting the air compressor slick.
Symmetrical structure asymmetric structure comparison diagram b.
Considering the optimization ruler on the structure of the ruler is mainly used to ensure the roundness of the cylinder hole can be pre-ground after the honing bar is welded. Therefore, the design and manufacture of the ruler is the same as the honing head design. And manufacturing 3.3 ç© grinding head domestic application and post-use maintenance
The honing process is super-finishing during the entire cylinder machining process. Therefore, the use and maintenance of the honing head is very important in daily production, especially in the process of variety switching, the main program of the design equipment is switched and the fixture, honing head, The switching of the measuring ring is particularly important.
The localization of the later honing sticks is also an important aspect. From the current situation, there is a gap between the various domestic honing sticks and the imported products, and the technical level of this part has to continue to improve.
Conclusion
In summary, the cylinder hole platform moiré honing process is one of the most advanced cylinder bore honing processes in the world, and its application has extremely important significance for the service life of the air compressor, especially for solving the early problems of air compressors. Problems such as oil quantity play a crucial role, and its process development and popularization should be an inevitable trend. The evaluation standard of the platform netting honing process is more complicated. At the same time, the realization of the process is a process of combining products and processes, and it is the combination of air compressor design, manufacturer and equipment manufacturer. The key to the mesh honing process of the cylinder bore platform lies in the control of the surface platform and the deep groove. From the technical point of view, only the coarse and fine honing is completed once at the same station, in order to realize the platform netting in the true sense. There is still a lot of research space in the technical research of honing head improvement and honing.
Equally important, the improved structure has the following advantages:
1. The improved structure is directly based on the two central holes of the mandrel, and the clamping is convenient and quick, and the adjustment is convenient. The original structure requires two large bald heads, and the top contact surface is easy to wear when the rule is rounded, thereby generating a beating, and it is difficult to ensure the accuracy of the calibration.
2. The improved structure adjustment size is very convenient and can be carried out at any time.
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