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In Europe, due to the high price of gasoline and exhaust emission standards, automakers have a keen interest in the use of compacted graphite cast iron (CGI) instead of ordinary gray cast iron to make cylinders and cylinder heads for automotive engines. The CGI material can be used to manufacture thin-walled engine housings and cylinder blocks. The cylinder walls can withstand the enormous pressure generated by the pistons without expansion and deformation. This type of structure has a light weight, high horsepower, and high fuel efficiency. , exhaust emissions and other advantages. The six-cylinder, 12.6-liter new engine manufactured by Dutch truck manufacturer DAFTruckNV using CGI cast iron has a power of 530 horsepower, which is 50 horsepower higher than that of a similar engine made of gray cast iron. In North America, the engine manufactured with CGI cast iron can reach the exhaust gas emission standard of 2005. Due to the excellent resistance to expansion deformation of the CGI cylinder wall, the “leakage†phenomenon during engine operation is greatly reduced, and incomplete combustion exhaust gas can be prevented from passing through the piston ring. leakage.
Audi's flexible manufacturing unit, which is a car manufacturer, processes 10,000 CGIV8 engine casings each year. Due to the use of conventional tooling, tooling costs remain high. Since these engines are mainly used for high-end cars ($80,000 in the United States), higher tooling costs are still acceptable. However, the company will soon have to reach an annual production capacity of 200,000 CGIV6 engine housings (for other models of cars). Therefore, the high-speed processing of CGI's production efficiency and processing costs is very important.
The toughness and processability of CGI cast iron are between that of gray cast iron and malleable cast iron. The fatigue strength of CGI cast iron is 1.8 times that of gray cast iron, and the tensile strength and elastic modulus are 1.8 times and 1.4 times respectively. The graphite structure in the microstructure of CGI cast iron was worm-like or coral-like, and its cutting load was increased by 20% to 30% compared with graphite cast iron. Although conventional tools can also be used for boring and milling CGI cast iron, only low-speed, high-feed cutting methods are used, and the tool life is very short. This is for small-batch, one-off production (such as NASCAR racing engines. Processing is feasible, but for high-volume production of high-volume engines, this cutting method is obviously difficult to meet the processing requirements.
A few years ago, many machinery manufacturing experts also believed that high-speed cutting of CGI cast iron was difficult to achieve. The application of self-rotating tools provides an effective way for high-speed machining of CGI cast iron. The spin-milling concept was first proposed by Lockheed Corp., a US aircraft manufacturing giant, in the 1970s. Rotary Technologies refined the technology and applied it by UNOVA's LambTechnicon to the broaching of CGI cast iron. . The self-rotating tool is a circular rotating tool with double negative cutting angle, which can effectively reduce the friction and heat during processing. Its application opens up new ways to improve the engine design in the coming years.
A plurality of rotating tool holders are provided on the rotary trowel, and a circular blade having a diameter of about 27 mm is mounted on each tool holder. The number of tool holders/blades set on each boring tool depends on the diameter of the boring tool. For example, a cymbal with a diameter of 76.2 mm is usually provided with 4 blades, and a cutter with a diameter of 305 mm can be set with 16 blades. The material of the spin-rotating blade is generally silicon nitride ceramic, and high-speed processing of CGI cast iron can also use carbide blade. The Si3N4 ceramic inserts with a chamfer width of 0.254 mm and a chamfer angle of 10° achieve the best cutting results.
Until recently, spin tools had not attracted much attention. In the past, the design of self-rotating milling cutter holder bearings and greases made the tool system prone to overheating during processing. These problems have been gradually solved in recent years.
In the 1990s, machine tool manufacturers supplied three CNC machining centers to a European auto parts manufacturer to process CGI cast iron parts instead of gray cast iron parts. When the factory uses conventional tools to process the parameters such as the feed amount of gray cast iron and the cutting speed, the tool will soon lose its efficiency. To meet production needs, Lamb had to spend $800,000 to provide a fourth CNC machining center free of charge for manufacturers. This prompted Lamb to conduct in-depth research on CGI cast iron processing technology and tools. Soon, Lamb Company confirmed the applicability of CGI for high-speed machining of rotary tools, and constantly introduced new tool edge shapes to solve the problem of heat dissipation around the blades.
The results of the study showed that when machining with conventional tools, the wear of the tool in contact with the surface of the CGI workpiece and the friction of the chip along the rake face of the tool is severe. The temperature is about 480° C. and 150° C. higher than the shear surface temperature, respectively. Layers or uncoated conventional tool surfaces soften rapidly, causing premature failure of the tool. When using a self-rotating tool, the rotating blade can push the chips out of the cutting area, avoiding the tool and the chips to produce a large amount of cutting heat due to severe friction. Although there is still a certain amount of friction between the tool and the chips to push the blades to rotate, Friction and heat are almost negligible compared to conventional tools. When the German car manufacturer Audi Group processed conventional CGI cast iron engine housings with conventional tools (cutting speed 800m/min, cutting depth 1.5mm, feed per tooth 0.2mm), the tool quickly failed; the use of self-rotating tools with the same cutting amount When machining, the maximum wear of the insert cutting edge is only 0.15 mm after 15 minutes of cutting.
Although the engine plant of DaimlerChrysler Corp. in Trenton, Michigan, USA, does not produce CGI cast iron engine housings, they have also achieved very good results by using self-rotating tools to machine the grey cast iron engine housing. The plant uses dry milling cutters to dry mill the top and bottom surfaces of the engine housing on a production line with an annual output of 500,000 engine housings (for Chrysler minivans) (currently in front of and behind the test engine housing) The cutting speed is about 625m/min, and the feed rate is 3073mm/min. With the use of a self-rotating tool, the number of tool changes has been reduced from 697 previously to 46 times per year. The only inconvenience of using this tool is that it is necessary to adjust the blade diameter of the self-rotating tool in the original tool changing station. In addition, the structural design of many existing processing equipment is not entirely compatible with the use of self-rotating tools. For this reason, it is necessary to modify and adjust the existing production line, although this requires a certain amount of time and money, plus the cost of the self-rotating tool itself. It's not low ($40 blade, $225 tool holder), but it's worth it compared to the benefits of using a spin tool. Now the processing life of each tool has been increased from about 500 to 5,000 to 7,000.
The DaimlerChrysler engine plant began using spin tools in early 2000. Prior to this, the plant had conducted several years of testing and evaluation of the tool. For many years, the problem of heating and lubrication of the tool holder bearing of the rotary tool has been plaguing technicians. With the appearance of new tool holder bearing materials and grease, the problem of knife holder heating when processing grey cast iron has been better solved, but there is still a small amount of knife holder heating phenomenon in the processing of CGI cast iron, and the use of the reverse milling method can be compared Good solution to this problem. For up-cut milling, the tool enters the cut with a small cut-in angle (eg, 15°). During the cutting process, the chip thickness gradually increases from zero to maximum, which is the exact opposite of the straight-milling method commonly used for machining engine casing. The cut-in angle is larger (eg, 90°). The depth of cut is greatest when cutting in, and the chip thickness is gradually reduced to zero during cutting. For conventional tools, the reverse milling method is unfavorable to the life of the tool. Because the tool moves forward and rotates, the bottom of the insert always rubs against the workpiece, causing heat and wear. However, the up-cut milling is more advantageous for self-rotating tools because it can extend the life of the toolholder bearing. In addition, the up-cut milling is also beneficial to the complex surface of the engine housing (including the thin-walled cross-section). Reduce the impact vibration of the workpiece, so as to obtain a better surface roughness. Smaller cut-in angles are also important because Si3N4 ceramic inserts, which are the most commonly used spin tools, are more susceptible to damage than carbide inserts due to the impact of cutting.
Currently, Lamb's technicians are working to reduce the size of the tool holder for rotary tools. A new type of tool holder has been preliminarily designed to reduce the diameter to approximately 15.24 mm. This small-size tool holder can be allowed to More blades are placed on the body. According to the original rotary boring tool and its tool holder design, the smallest hole diameter that can be machined is 76.3mm, which is difficult to use for boring other machining operations outside the cylinder hole. After the tool holder is reduced in size, the smaller aperture can be realized. Cutting. For the self-rotating milling cutter, the newly designed tool holder is only about half the size of the original tool holder, so the number of inserts can be increased on the same diameter of the tool body, thereby increasing the feed rate of the cutting workpiece. The development of this new tool holder can greatly expand the application of self-rotating tools. In the aerospace industry, a large number of titanium alloy parts need to be machined, and more end mills are used. By developing small-diameter tool holders, small-diameter, self-rotating end mills as small as 38 mm can be designed. By further developing a self-rotating tool with a positive rake angle or a positive/negative rake angle, it is also possible to extend the application range of the self-rotating tool to high-speed machining of steel and aluminum alloy workpieces.
Many people think that the use, maintenance and repair of spin tools are time-consuming and laborious, but it is not. In addition to cleaning the tool holder, it does not require a lot of maintenance work. After replacing the blade and cleaning the tool holder, grease can only be added through the small hole behind the tool. It took less than half an hour to install a 254mm diameter 13- tooth self-aligning milling cutter.
Lamb said that it will further improve the structural design of the spin tool system. For example, the new structure will eliminate the need to add grease to toolholder bearings. In addition, the company will conduct in-depth studies on the microcracks generated by the thermal shock of the blades when high-speed milling of CGI cast iron. When the milling insert cuts into the workpiece material at room temperature, its temperature rises rapidly to about 480°C, and then it rapidly cools under the action of air and cutting fluid. At this time, the blades are prone to hot cracks. Although blade manufacturers have developed high-temperature-resistant carbide and Si3N4 ceramic inserts, hot cracking may still occur when using high-speed cutting tough CGI cast irons with high-speed cutting.
Rotary Technologies currently owns technology patents for machining non-CGI materials (including engine shells) using spin tools; Lamb, with the assistance of Rotary Technologies, is working on the application of self-rotating tool holder systems and has only one application in the world. Rotary Tools Milling and boring technology patents for CGI cast iron materials, therefore, this processing technology is currently only applied to Lamb's machine tools.
Audi's flexible manufacturing unit, which is a car manufacturer, processes 10,000 CGIV8 engine casings each year. Due to the use of conventional tooling, tooling costs remain high. Since these engines are mainly used for high-end cars ($80,000 in the United States), higher tooling costs are still acceptable. However, the company will soon have to reach an annual production capacity of 200,000 CGIV6 engine housings (for other models of cars). Therefore, the high-speed processing of CGI's production efficiency and processing costs is very important.
The toughness and processability of CGI cast iron are between that of gray cast iron and malleable cast iron. The fatigue strength of CGI cast iron is 1.8 times that of gray cast iron, and the tensile strength and elastic modulus are 1.8 times and 1.4 times respectively. The graphite structure in the microstructure of CGI cast iron was worm-like or coral-like, and its cutting load was increased by 20% to 30% compared with graphite cast iron. Although conventional tools can also be used for boring and milling CGI cast iron, only low-speed, high-feed cutting methods are used, and the tool life is very short. This is for small-batch, one-off production (such as NASCAR racing engines. Processing is feasible, but for high-volume production of high-volume engines, this cutting method is obviously difficult to meet the processing requirements.
A few years ago, many machinery manufacturing experts also believed that high-speed cutting of CGI cast iron was difficult to achieve. The application of self-rotating tools provides an effective way for high-speed machining of CGI cast iron. The spin-milling concept was first proposed by Lockheed Corp., a US aircraft manufacturing giant, in the 1970s. Rotary Technologies refined the technology and applied it by UNOVA's LambTechnicon to the broaching of CGI cast iron. . The self-rotating tool is a circular rotating tool with double negative cutting angle, which can effectively reduce the friction and heat during processing. Its application opens up new ways to improve the engine design in the coming years.
A plurality of rotating tool holders are provided on the rotary trowel, and a circular blade having a diameter of about 27 mm is mounted on each tool holder. The number of tool holders/blades set on each boring tool depends on the diameter of the boring tool. For example, a cymbal with a diameter of 76.2 mm is usually provided with 4 blades, and a cutter with a diameter of 305 mm can be set with 16 blades. The material of the spin-rotating blade is generally silicon nitride ceramic, and high-speed processing of CGI cast iron can also use carbide blade. The Si3N4 ceramic inserts with a chamfer width of 0.254 mm and a chamfer angle of 10° achieve the best cutting results.
Until recently, spin tools had not attracted much attention. In the past, the design of self-rotating milling cutter holder bearings and greases made the tool system prone to overheating during processing. These problems have been gradually solved in recent years.
In the 1990s, machine tool manufacturers supplied three CNC machining centers to a European auto parts manufacturer to process CGI cast iron parts instead of gray cast iron parts. When the factory uses conventional tools to process the parameters such as the feed amount of gray cast iron and the cutting speed, the tool will soon lose its efficiency. To meet production needs, Lamb had to spend $800,000 to provide a fourth CNC machining center free of charge for manufacturers. This prompted Lamb to conduct in-depth research on CGI cast iron processing technology and tools. Soon, Lamb Company confirmed the applicability of CGI for high-speed machining of rotary tools, and constantly introduced new tool edge shapes to solve the problem of heat dissipation around the blades.
The results of the study showed that when machining with conventional tools, the wear of the tool in contact with the surface of the CGI workpiece and the friction of the chip along the rake face of the tool is severe. The temperature is about 480° C. and 150° C. higher than the shear surface temperature, respectively. Layers or uncoated conventional tool surfaces soften rapidly, causing premature failure of the tool. When using a self-rotating tool, the rotating blade can push the chips out of the cutting area, avoiding the tool and the chips to produce a large amount of cutting heat due to severe friction. Although there is still a certain amount of friction between the tool and the chips to push the blades to rotate, Friction and heat are almost negligible compared to conventional tools. When the German car manufacturer Audi Group processed conventional CGI cast iron engine housings with conventional tools (cutting speed 800m/min, cutting depth 1.5mm, feed per tooth 0.2mm), the tool quickly failed; the use of self-rotating tools with the same cutting amount When machining, the maximum wear of the insert cutting edge is only 0.15 mm after 15 minutes of cutting.
Although the engine plant of DaimlerChrysler Corp. in Trenton, Michigan, USA, does not produce CGI cast iron engine housings, they have also achieved very good results by using self-rotating tools to machine the grey cast iron engine housing. The plant uses dry milling cutters to dry mill the top and bottom surfaces of the engine housing on a production line with an annual output of 500,000 engine housings (for Chrysler minivans) (currently in front of and behind the test engine housing) The cutting speed is about 625m/min, and the feed rate is 3073mm/min. With the use of a self-rotating tool, the number of tool changes has been reduced from 697 previously to 46 times per year. The only inconvenience of using this tool is that it is necessary to adjust the blade diameter of the self-rotating tool in the original tool changing station. In addition, the structural design of many existing processing equipment is not entirely compatible with the use of self-rotating tools. For this reason, it is necessary to modify and adjust the existing production line, although this requires a certain amount of time and money, plus the cost of the self-rotating tool itself. It's not low ($40 blade, $225 tool holder), but it's worth it compared to the benefits of using a spin tool. Now the processing life of each tool has been increased from about 500 to 5,000 to 7,000.
The DaimlerChrysler engine plant began using spin tools in early 2000. Prior to this, the plant had conducted several years of testing and evaluation of the tool. For many years, the problem of heating and lubrication of the tool holder bearing of the rotary tool has been plaguing technicians. With the appearance of new tool holder bearing materials and grease, the problem of knife holder heating when processing grey cast iron has been better solved, but there is still a small amount of knife holder heating phenomenon in the processing of CGI cast iron, and the use of the reverse milling method can be compared Good solution to this problem. For up-cut milling, the tool enters the cut with a small cut-in angle (eg, 15°). During the cutting process, the chip thickness gradually increases from zero to maximum, which is the exact opposite of the straight-milling method commonly used for machining engine casing. The cut-in angle is larger (eg, 90°). The depth of cut is greatest when cutting in, and the chip thickness is gradually reduced to zero during cutting. For conventional tools, the reverse milling method is unfavorable to the life of the tool. Because the tool moves forward and rotates, the bottom of the insert always rubs against the workpiece, causing heat and wear. However, the up-cut milling is more advantageous for self-rotating tools because it can extend the life of the toolholder bearing. In addition, the up-cut milling is also beneficial to the complex surface of the engine housing (including the thin-walled cross-section). Reduce the impact vibration of the workpiece, so as to obtain a better surface roughness. Smaller cut-in angles are also important because Si3N4 ceramic inserts, which are the most commonly used spin tools, are more susceptible to damage than carbide inserts due to the impact of cutting.
Currently, Lamb's technicians are working to reduce the size of the tool holder for rotary tools. A new type of tool holder has been preliminarily designed to reduce the diameter to approximately 15.24 mm. This small-size tool holder can be allowed to More blades are placed on the body. According to the original rotary boring tool and its tool holder design, the smallest hole diameter that can be machined is 76.3mm, which is difficult to use for boring other machining operations outside the cylinder hole. After the tool holder is reduced in size, the smaller aperture can be realized. Cutting. For the self-rotating milling cutter, the newly designed tool holder is only about half the size of the original tool holder, so the number of inserts can be increased on the same diameter of the tool body, thereby increasing the feed rate of the cutting workpiece. The development of this new tool holder can greatly expand the application of self-rotating tools. In the aerospace industry, a large number of titanium alloy parts need to be machined, and more end mills are used. By developing small-diameter tool holders, small-diameter, self-rotating end mills as small as 38 mm can be designed. By further developing a self-rotating tool with a positive rake angle or a positive/negative rake angle, it is also possible to extend the application range of the self-rotating tool to high-speed machining of steel and aluminum alloy workpieces.
Many people think that the use, maintenance and repair of spin tools are time-consuming and laborious, but it is not. In addition to cleaning the tool holder, it does not require a lot of maintenance work. After replacing the blade and cleaning the tool holder, grease can only be added through the small hole behind the tool. It took less than half an hour to install a 254mm diameter 13- tooth self-aligning milling cutter.
Lamb said that it will further improve the structural design of the spin tool system. For example, the new structure will eliminate the need to add grease to toolholder bearings. In addition, the company will conduct in-depth studies on the microcracks generated by the thermal shock of the blades when high-speed milling of CGI cast iron. When the milling insert cuts into the workpiece material at room temperature, its temperature rises rapidly to about 480°C, and then it rapidly cools under the action of air and cutting fluid. At this time, the blades are prone to hot cracks. Although blade manufacturers have developed high-temperature-resistant carbide and Si3N4 ceramic inserts, hot cracking may still occur when using high-speed cutting tough CGI cast irons with high-speed cutting.
Rotary Technologies currently owns technology patents for machining non-CGI materials (including engine shells) using spin tools; Lamb, with the assistance of Rotary Technologies, is working on the application of self-rotating tool holder systems and has only one application in the world. Rotary Tools Milling and boring technology patents for CGI cast iron materials, therefore, this processing technology is currently only applied to Lamb's machine tools.
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