High-speed machining is widely used internationally in aerospace manufacturing, mold manufacturing, auto parts processing and precision parts processing and other industries, and has become a technological direction for enterprises to tackle key problems.
Advantages of high-speed cutting process
High-speed cutting is not only an increase in cutting speed, but also requires major advances in driving, tool materials, coatings, tools, testing, and safety based on comprehensive advances in manufacturing technology and further innovations to achieve cutting speed and advancement. only by doubling the speed can the overall cutting efficiency of the manufacturing industry be significantly improved. The advantages of high-speed cutting technology are as follows:
1. Shorten production time
Using high-speed cutting, the cutting speed and feed rate are doubled, the overall cutting efficiency is significantly improved, and the processing time is significantly shortened.
2. Reduce manufacturing costs
Higher productivity levels will inevitably lead to a decrease in manufacturing costs. The use of high-speed cutting equipment and tools can achieve the lowest manufacturing cost under mass production.
3. High-speed cutting absorbs energy
The use of high-speed cutting processing, on the one hand, reduces the heat generation of the workpiece during processing, especially in milling processing. Due to the reduction of heat generation, the workpiece heats up less, the machining size is stable, and the damage to the tools and equipment is also small; on the other hand, high-speed cutting can process hard materials, which is an advantage that ordinary machine tools cannot match.
4. Improve the processing quality of the workpiece
Using high-speed machining, the machining accuracy and the quality of the cutting surface can be greatly improved, and the surface roughness of the parts can reach the micron level, reducing and eliminating auxiliary work hours such as grinding and polishing.
High-speed machining in engine manufacturing
Nowadays, with the continuous adoption of new technology, the continuous development of superhard material cutting tools, coating cutting tools and alloy material cutting tools, high-speed machining has become more and more important in ordinary machining. Applications such as high-speed machining centers, high-speed external milling and high-speed grinding of CBN wheels in engine manufacturing are very common.
In the application of high-speed machining in the engine manufacturing industry, the main features are the electric spindle to achieve the high speed of the spindle and the linear motor to achieve the high linear movement speed. The purpose is to replace the multi-spindle machining center with a single-spindle machining center with high spindle speed and high-speed linear feed motion. It is difficult to realize a combined machine tool with high spindle speed and high-speed feed. The maximum speed of the spindle is generally up to 60000r/min, and the maximum feed speed is about 100m/min. The electric spindle incorporates many cutting-edge technologies, such as high-speed bearings that generally use composite ceramic materials or electromagnetic suspension, high-speed motor technology, fixed and quantitative oil and gas lubrication, and automatic tool change devices. In order to reduce costs, some companies do not use linear motors, but use ball screws with hollow coolant, enlarged diameter and enlarged lead.
SAIC-GM-Wuling engine plant uses high-performance machine tools such as high-speed machining centers and CBN grinding wheels to achieve high-speed milling and grinding.
At present, the machining of large planes of cylinder blocks and cylinder heads in engines generally uses milling technology. Take the milling of a cast iron cylinder on a high-speed milling machining center as an example, using cubic boron nitride (CBN) inserts, and its cutting speed can reach 700-1500m/min.
The production efficiency of milling is greatly improved. For aluminum alloy cylinder heads, face milling cutters are used for high-speed cutting. Using PCD inserts, the diameter of the milling cutter is gradually reduced, and the development of multi-station duplex processing.
SAIC-GM-Wuling engine plant uses the EX-CELL-O high-speed milling machining center from German MAG company, and a total of 104 engines are arranged in the engine block and cylinder head line. The machining center structure, the processing range of the X axis is 0～630mm, the processing range of the Y axis is 0～630mm, the processing range of the Z axis is 0～710mm, the B axis can achieve 306° rotation, and the W axis has 20 The tool magazine of the tool position and the corresponding drill break inspection device. The spindle is a Weiss electric spindle, the speed is infinitely adjustable, the maximum is 16000r/min, the driving power is 30kW, the maintenance-free internal cooling tool holder is used, the tensioning force is up to 18000N, and the permanent magnet chip is used to track the tool life, size and compensation amount. The equipment is equipped with an automatic cooling station and a cutting waste washing and recycling device, which can eliminate mechanical failures caused by flying chips, reduce the intensity of machine tool cleaning and maintenance operations, and improve equipment operation rate.
The milling, drilling and tapping processes of the cylinder block and cylinder head line are all completed by these 104 EX-CELL-O machining centers.
SAIC-GM-Wuling engine plant employs high-speed grinding in crankshaft machining. Four cylindrical grinders manufactured by the American company LANDIS are used to grind the crankshaft main journal, connecting rod neck, oil seal and spindle. In the cylindrical grinding, the patented grinding technology of LANDIS is used, which uses a CBN grinding wheel to grind the crankshaft under the condition of clamping the workpiece at one time. LANDIS grinder has the advantages of high cutting power, high-precision workpiece geometry, uniform high-precision size and outer surface quality. After processing, the diameter tolerance can be guaranteed to be between ±6mm, and the roughness of the processed surface can be controlled within Ra0.8mm Within. LANDIS grinder can realize Marposs online measurement feedback, automatic correction, automatic grinding wheel and other functions, and the measuring head is cooled with coolant to greatly reduce the influence of temperature on the measurement, which can greatly improve processing flexibility. CBN grinding wheel can process 5000 ~10,000 crankshafts.
Turn-turn-turn and high-speed external milling
The crankshaft turning-turning process combines turning and turning process to increase the flexibility of processing. Not only can the main journal, connecting rod journal, flange and pulley journal of the crankshaft be processed, but also the external shoulder, fillet and edge cut of the journal can be processed at the same time. Combined with the high-speed external milling of the crankshaft, machining time can be greatly saved. SAIC-GM-Wuling engine plant uses 5 trolley-lathes from the world's leading German BOEHRINGER company for crankshaft machining to realize the machining of crankshaft main journals, connecting rod necks and flanges. The BOEHRINGER lathe-lathe-broaching machine uses a double-spindle and double-cutterhead structure, which improves the processing speed and production efficiency while ensuring the processing accuracy.
In the engine production process, the proportion of hole processing is also relatively high, especially the amount of hole processing for cylinder heads and cylinder blocks. Among them, drilling processing accounts for about 60%, followed by boring processing and tapping processing.
The drilling process of the engine block and cylinder head of SAIC-GM-Wuling Engine Plant is done using EX-CELL-O machining center, while the machining content such as the inclined oil hole of the crankshaft, the threaded hole of the flange end and the positioning hole at both ends, etc., use the Japanese HORKOS The machining center is completed. The crankshaft production line uses a total of 10 HORKOS machining centers, including two OP10, four OP50, three OP60 and one OP100. The main difficulty in high-speed drilling is how to improve chip removal performance, increase tool rigidity, prevent overheating of the drill tip and rotation balance. With its excellent performance, the HORKOS machining center, coupled with high-quality internal cooling tools, successfully solved these common problems in high-speed drilling.
Application of high-speed cutting tools
The history of the development of high-speed machining is the history of continuous advancement of tool materials. Most of the tools used in the initial SOP of SAIC-GM-Wuling Engine Factory are imported, and breakthroughs have been made in localization. Now the more commonly used tools include CBN and PCD tools, coated carbide tools, and ceramic tools. In addition, major breakthroughs have been made in the localization of quilting tools.
1. CBN and PCD tools
The representative tool materials for high-speed cutting are CBN and PCD. When using CBN tools for face milling, the cutting speed can reach 5000m/min. Machining the inner hole of 20CrMo5 hardened gear (60HRC) with CBN tool, the surface roughness can reach 0.22μm, which has become a new technology promoted by the automobile industry at home and abroad. Camshafts and crankshafts also use CBN grinding wheels for high-speed grinding; PCD tools are widely used in the milling of cylinder blocks and cylinder head aluminum alloy materials. Considering that high-speed rotation will generate a large centrifugal force, the tool body uses high strength Made of aluminum alloy material.
It is alumina grinding wheel. Because alumina base has high chemical stability and favorable thermal characteristics, considering practicability and economy, it is mainly used in cylindrical grinders with large grinding capacity, while high-end grinding tools The representative CBN grinding wheel (see Figure 7) is used in crankshaft connecting rod neck cylindrical grinders with higher follow-up requirements.
2. Carbide tool
Hard parts cutting is an important application field of high-speed cutting technology. That is, single-edge or multi-edge tools are used to process hardened parts. It is more efficient than traditional grinding, and simplifies the process and links, which not only saves costs, but also More flexible.
In drilling and milling processing, ultra-fine grained cemented carbide is suitable for most applications. They also have high toughness and excellent heat resistance, which can combine favorable cutting edge geometries with large rake angles. And the clearance angle is integrated, the direct reflection of these features is to reduce the cutting force and cutting temperature; when tapping, particularly high torque and elevated temperature at higher cutting speeds require very tough and high heat resistance Cutting materials.
SAIC-GM-Wuling engine plant uses internally cooled carbide drills instead of high-speed steel drills for hole processing. Tapping also uses cemented carbide taps to increase speed, and cylinder head tapping even uses non-cutting extrusion taps. The machining of crankshaft journals is now replaced by hard parts machining, with grinding and polishing to meet the surface roughness requirements.
3. Tool coating technology
In order to make cutting tools with low price and excellent performance, which can effectively reduce the processing cost, coating technology is currently the first choice.
The function of the tool coating: it can improve the wear resistance, increase the tool life, and improve the cutting performance; the existence of the coating reduces the friction between the tool and the chip, thereby increasing the drilling depth.
Reduce cutting force; bright coating appearance (golden yellow, fiery red, etc.), easy to observe the wear of the tool; coating on the surface of the tool can reduce cutting heat and reduce the interaction of heat between the tool and the workpiece (coating isolation The tool and the workpiece are free from chemical reactions; the thermal conductivity difference between the coating and the tool can reduce the accumulation of heat on the tool); the high-quality coating can improve the performance of the tool and reduce the formation of built-up edges and crescent craters.
Comprehensive analysis of the economics and performance of the coating, the end mills used in high-speed processing at SAIC-GM-Wuling engine plant are mostly treated with TiAlN-based composite multi-layer coating technology, and the life of the bit with different coatings.
In the context of the large-scale use of high-speed machining tools, along with the use of high-speed cutting tools, the wide application of modern high-speed machining technology has guaranteed the annual production capacity of 350,000 engines at SAIC-GM-Wuling Engine Plant. These high-speed machining technologies have not only processed a large number of engine parts for SAIC-GM-Wuling engine plant to meet market demand, but also helped SAIC-GM-Wuling maintain its lead in the fierce market competition due to the stability and reliability of the processing quality of high-speed processing machine tools. Provide quality assurance.