New generation of aircraft fuselage processing requires new tool materials
2018-10-30 15:03:18
With the increasing use of composite materials, titanium alloys and laminates made of two materials in aircraft structural parts, the aircraft fuselage manufacturing industry is undergoing tremendous changes, as well as the need to use high hardness, high toughness tool materials. The cutting process presents challenging requirements.
Changes in airframe manufacturing technology In order to improve aircraft flight efficiency and reduce its life cycle costs, aircraft manufacturers are increasingly using composite materials and titanium alloys. For example, most of the fuselage of the Boeing 787 and Airbus A350 will be made of composite material (by weight). In the business jet market, the fuselage of Hawker Beechcraft's Premier IA and Hawker 4000 aircraft will be made entirely of composite materials; the wing and fuselage of the Aviation EV-20 Vantage aircraft are also Full composite materials will be used.
The use of composites facilitates the merging and joining of parts, reducing the number of fasteners required. However, most of the fasteners that have been eliminated are "area fasteners" - a large number of small diameter fasteners that can be machined in an automated process. Therefore, most of the fasteners retained have larger mounting holes and thicknesses, and are laminated with a variety of materials, making processing more difficult. Since the contact between the graphite composite and the aluminum may cause chemical current corrosion, the structural members mounted on the graphite composite are usually aluminum. Both materials are difficult to drill, and it is more difficult to combine them into a laminate for drilling. Therefore, in addition to the different drilling parameters than the traditional workpiece materials, different tool materials are required.
Difficulties in the processing of carbon fiber The processing difficulties of carbon fiber composite materials include:
(1) The material has high abrasiveness, which makes the tool wear rate high;
(2) The material has anisotropy (produced by a combination of a softer substrate and hard fibers arranged in different directions), meaning that the tool must withstand different cutting resistance;
(3) The plastic substrate limits the cutting temperature;
(4) When processing reinforcing fibers, in order to obtain clean and tidy apertures, sharp cutting edges, high shear blade geometry and high speeds are required;
(5) If the cutting force is too large (such as during strong drilling), the laminated structure of the workpiece may have separation of layers;
(6) Dust (not chips) is generated during processing and needs to be controlled by vacuuming or filling with coolant.
Difficulties in processing titanium alloys The unique processing difficulties of titanium alloy materials include:
(1) Titanium has a low modulus of elasticity. Because the material is pushed away by the tool during the cutting process and then rebounded, the tool needs to adopt a larger relief angle;
(2) The poor thermal conductivity of titanium results in high cutting temperatures (80% of the cutting heat is transferred to the tool and only 50% when cutting steel);
(3) Titanium has strong chemical reactivity at high temperature, which is easy to melt with the tool, causing tool chipping and failure;
(4) It is easy to produce work hardening phenomenon (especially when processing at low feed rate);
(5) Maintain high strength even when the temperature rises;
(6) Producing segmented chips to force the tool to circulate and prone to metal fatigue;
(7) During processing, the surface of the material is more likely to be damaged, which will slightly reduce the fatigue life of the workpiece.
In addition to the challenges of drilling these new materials that are assembled from different materials, current aircraft fuselage assembly presents new challenges to the performance and quality of drilling operations:
(1) It is necessary to drill a larger diameter hole on a thicker laminated composite material;
(2) In order to shorten the assembly time of the fuselage, the demand for “one-off†drilling, dry or near dry drilling and efficient assembly is increasing;
(3) Despite the increasing use of large-scale and small-scale automated processing, pneumatic rigs are still mainly used in the final assembly process;
(4) The application of lean processing principles is increasing.
All of these factors can significantly shorten the life of the tool. Therefore, in order to reduce the processing cost per hole and increase the productivity, new tool materials are needed. In addition, in order to shorten the process time of the final assembly process, it is also necessary to increase the service life of the tool. For example, the Boeing 787 final assembly process has a target process time of only three days; Lockheed Martin's F-35 Lightning II final assembly process target time is to assemble an aircraft every day. In contrast, Boeing 737 currently has a process time of 10 days (22 days in 2000 and 8 days in the future); Boeing 777 has a 25-day process time. The Boeing 787's process time can be reduced to three days, in part because some of the machining operations are transferred to the upstream process, and the various components that arrive at the assembly process are pre-installed with the various systems of the aircraft. However, as noted earlier, drilling is the most challenging process in the final assembly process.
The ideal tool material In general, the tool material properties we want include:
(1) The grain size is small, so that a sharper cutting edge can be produced;
(2) It has high hardness (including high heat hardness), so as to provide excellent wear resistance;
(3) It has good toughness (high tensile strength and fracture toughness), so that the sharp cutting edge can be prevented from chipping or deforming under the dynamic cutting force;
(4) It has good thermal conductivity, so that the cutting zone can be quickly dissipated;
(5) It has good thermal stability, so that the tool can maintain its integrity under cutting high temperature;
(6) It has a low chemical affinity or reactivity with the workpiece material.
The pros and cons of each of the characteristics required for the tool material depend on the workpiece material. It is very difficult to require all the above properties of the same tool material, so it is usually necessary to make trade-offs between hardness and toughness. However, these two characteristics are essential for the processing of carbon fiber reinforced polymers and aluminum matrix composites.
Drilling of carbon fiber reinforced composites such as CFRP is similar to drilling wood. The key to machining is the clean and neat cutting of carbon fibres (especially at the exit of the orifice), which requires high shear geometry and high cutting speeds. CFRP is also highly abrasive and therefore requires a very high hardness of the tool material (preferably like diamond).
Cutting titanium alloys also requires high shear forces, but at high cutting speeds required to machine composites, a large amount of cutting heat is generated, and work hardening of titanium in the laminate material can reduce the fatigue life of aircraft components. In addition, titanium has chemical affinity with most tool materials. Therefore, for the processing of most titanium alloy workpieces, cobalt high speed steel and cemented carbide are the main tool materials used. However, these tool materials do not have the wear resistance required to extend tool life when processing composite materials. When the cutting edge of the tool which is blunt by the composite material is cut to remove titanium, work hardening occurs and the tool will fail. Although titanium alloys can be processed with PCD tools, good results are obtained, but in order to prevent chipping, the knife needs to have better toughness. In the laminate material for the manufacture of aircraft fuselage, in addition to composite materials and titanium alloys, it is also possible to use aluminum alloy or stainless steel, which have different cutting requirements.
Improvements in tool materials With the advancement of the times, processing technology continues to improve, and the material removal rate of roughing and finishing titanium alloys is also increasing. It can be seen that the improvement curve of titanium alloy processing has become flat, indicating that the space for improvement has been limited. In order to further improve the processing efficiency, new processing techniques are needed. Considering the increasing proportion of titanium alloys and composites in aircraft structural materials, it is important to improve the processing efficiency of these materials.
The following areas of improvement are possible with tool materials for drilling composite/metal laminates:
(1) Material grades with higher hardness and better toughness;
(2) Gradient functional materials (customized different cutting performance in different parts of the tool);
(3) Nanotechnology (nanostructure);
(4) different combinations of components (such as non-cobalt binders);
(5) Self-lubricating ability (can be used for dry or near dry cutting);
(6) lower tool material costs;
(7) Lower tool manufacturing and regrind costs;
(8) Improved coating bonding method.
Development steps for tool materials Once a material with suitable properties has been identified, the following basic steps can be followed in order to develop it into a tool material that can be used in actual production:
(1) Concept development 1 theoretical synthesis of expected materials; 2 verification of material properties.
(2) Trial: Select the tool made of this material and carry out the cutting test 1 blade; 2 round cutter.
(3) Determine the practicability of the material 1 tool type; 2 workpiece material; 3 cutting speed and feed range.
(4) Commercialization 1 Mass production in a cost-effective manner; 2 is to promote product training sales team.
The time period for this development process can be quite long (especially when some technical issues are difficult to resolve). As can be seen from the development chronology of superhard tool coatings, many obstacles may be encountered during the development process. Therefore, linking suppliers to the correct application of tool materials is key to the successful commercialization of tool materials. The next question is: Are these tool materials large enough for market size to be developed?
Market size The market forecast for the next 10 years is that there will be a general increase in the production of aircraft. Listed below are the number of aircraft that need to be manufactured in the coming years based on recent orders:
Commercial aircraft:
(1) Delivered in 2007: Boeing aircraft: 441 (worth $29.5 billion); Airbus aircraft: 453 (worth $23.9 billion);
(2) Orders accepted in 2007: Boeing aircraft: 1413 aircraft; Airbus aircraft: 1341 aircraft;
(3) Backlog of orders (as of December 2007): Boeing aircraft: 3,427 aircraft; Airbus aircraft: 3,421 aircraft; the specific number of each type of aircraft is as follows:
1 Boeing 787 Dreamliner: As of February 2008, the order volume was 857, with a maximum productivity of at least 10 per month; 2 Airbus A350: As of February 2008, the order volume was 370, with a maximum productivity of 13 per month. .
(4) Recent market outlook (2007-2026): 22,700 to 28,600 commercial aircraft, valued at 2.6 to 2.8 trillion US dollars. The specific quantities of each model of these two types of aircraft are as follows:
1 Freighter: The recent demand is 1980. The total demand during 2007-2026 is estimated to be 4,000, of which about 870 are new cargo aircraft, and the rest are modified by passenger aircraft. 2 regional passenger aircraft: recent demand is 2886, 2007-2026 The total demand during the period is expected to be 3,700.
Military aircraft:
(1) F/A-18E/F "Super Hornet" combat attack aircraft: By 2012, the US Air Force's planned demand is 581, each worth $57 million, with a maximum productivity of 48 aircraft per year.
(2) F-22 Raptor: By 2010, the United States alone had orders of 183, each worth $150 million, with a maximum productivity of 32 per year.
(3) Eurofighter Typhoon Typhoon fighters: The planned demand for more than 700 aircraft in 2016 is approximately $51 million to $58 million, with a maximum productivity of 52 aircraft per year.
(4) F-35 Joint Strike Fighter: The global planned demand for 2,035 is 3,173, each worth about $50 million, with a maximum productivity of 48 per year.
Tool Performance Improvements Here are a few recent examples of tooling improvements for aerospace manufacturing tooling:
(1) Processing Example 1: A commercial aircraft component supplier drills a material with a thickness of 0.200′′ (about 5 mm) using a solid carbide taper drill when machining a fiber reinforced composite workpiece. The drill can only drill 150 to 200 holes, and the tool has to be replaced due to unacceptable fiber tear. The supplier changed to a new type of CVD diamond coated carbide drill with a large number of drill holes. Increased to 2,200 holes. Although the cost of the new drill is 15 times that of the old drill, the cost per hole is reduced by 80% due to the extended life of the drill, the reduced number of tool changes, and increased machining time.
(2) Processing Example 2: Lockheed's life of the cutting tool and the quality of the cutting edge are unsatisfactory when the composite wing of the F-35 Joint Strike Fighter is being trimmed. To this end, a new type of CVD diamond coated tool has been developed with tool life (measured in linear length) from 9 feet (only 1/3 of the thickness of the cutting material) to 57 feet (full thickness of the cutting material), thus A wing with a 24mm blade can be used to machine a wing skin. As a result, each aircraft can achieve a cost-effectiveness of $80,000, and for the 2,783 F-35s planned for the US market, it is expected to save money (cost reduction) by $222.6 million.
(3) Processing Example 3: The upper deck floor girders of the Airbus A380 are made of CFRP composite material and need to be mounted on the aluminum alloy frame of the fuselage. The original uncoated solid carbide drill used to process this CFRP and aluminum alloy laminate can only process 90 holes. After switching to a diamond-coated carbide drill, the machining life of each drill is increased to more than 500 holes.
As a hypothetical example, it is assumed that 90 specific sized holes need to be machined on a composite/aluminum alloy laminate. If the cost per drill is $150, but only 20 to 30 holes can be machined, then It takes 3 to 5 times extra time to replace the drill bit. In addition, in order to minimize production interruptions, an additional rig with a drill bit installed on it may be required. If the life of each drill can reach 100 holes, even if the cost of the drill is doubled or more than before, the processing cost per hole can be reduced and the processing time can be shortened.
Considering the growing market demand for aircraft, the use of composite materials and aluminum alloys on new aircraft is increasing, and the assembly process time is required to be shorter, and the opportunities for improving cutting tools are enormous. Tool manufacturers develop and provide for the aviation industry. Tool products with better processing performance are just the right time.
Changes in airframe manufacturing technology In order to improve aircraft flight efficiency and reduce its life cycle costs, aircraft manufacturers are increasingly using composite materials and titanium alloys. For example, most of the fuselage of the Boeing 787 and Airbus A350 will be made of composite material (by weight). In the business jet market, the fuselage of Hawker Beechcraft's Premier IA and Hawker 4000 aircraft will be made entirely of composite materials; the wing and fuselage of the Aviation EV-20 Vantage aircraft are also Full composite materials will be used.
The use of composites facilitates the merging and joining of parts, reducing the number of fasteners required. However, most of the fasteners that have been eliminated are "area fasteners" - a large number of small diameter fasteners that can be machined in an automated process. Therefore, most of the fasteners retained have larger mounting holes and thicknesses, and are laminated with a variety of materials, making processing more difficult. Since the contact between the graphite composite and the aluminum may cause chemical current corrosion, the structural members mounted on the graphite composite are usually aluminum. Both materials are difficult to drill, and it is more difficult to combine them into a laminate for drilling. Therefore, in addition to the different drilling parameters than the traditional workpiece materials, different tool materials are required.
Difficulties in the processing of carbon fiber The processing difficulties of carbon fiber composite materials include:
(1) The material has high abrasiveness, which makes the tool wear rate high;
(2) The material has anisotropy (produced by a combination of a softer substrate and hard fibers arranged in different directions), meaning that the tool must withstand different cutting resistance;
(3) The plastic substrate limits the cutting temperature;
(4) When processing reinforcing fibers, in order to obtain clean and tidy apertures, sharp cutting edges, high shear blade geometry and high speeds are required;
(5) If the cutting force is too large (such as during strong drilling), the laminated structure of the workpiece may have separation of layers;
(6) Dust (not chips) is generated during processing and needs to be controlled by vacuuming or filling with coolant.
Difficulties in processing titanium alloys The unique processing difficulties of titanium alloy materials include:
(1) Titanium has a low modulus of elasticity. Because the material is pushed away by the tool during the cutting process and then rebounded, the tool needs to adopt a larger relief angle;
(2) The poor thermal conductivity of titanium results in high cutting temperatures (80% of the cutting heat is transferred to the tool and only 50% when cutting steel);
(3) Titanium has strong chemical reactivity at high temperature, which is easy to melt with the tool, causing tool chipping and failure;
(4) It is easy to produce work hardening phenomenon (especially when processing at low feed rate);
(5) Maintain high strength even when the temperature rises;
(6) Producing segmented chips to force the tool to circulate and prone to metal fatigue;
(7) During processing, the surface of the material is more likely to be damaged, which will slightly reduce the fatigue life of the workpiece.
In addition to the challenges of drilling these new materials that are assembled from different materials, current aircraft fuselage assembly presents new challenges to the performance and quality of drilling operations:
(1) It is necessary to drill a larger diameter hole on a thicker laminated composite material;
(2) In order to shorten the assembly time of the fuselage, the demand for “one-off†drilling, dry or near dry drilling and efficient assembly is increasing;
(3) Despite the increasing use of large-scale and small-scale automated processing, pneumatic rigs are still mainly used in the final assembly process;
(4) The application of lean processing principles is increasing.
All of these factors can significantly shorten the life of the tool. Therefore, in order to reduce the processing cost per hole and increase the productivity, new tool materials are needed. In addition, in order to shorten the process time of the final assembly process, it is also necessary to increase the service life of the tool. For example, the Boeing 787 final assembly process has a target process time of only three days; Lockheed Martin's F-35 Lightning II final assembly process target time is to assemble an aircraft every day. In contrast, Boeing 737 currently has a process time of 10 days (22 days in 2000 and 8 days in the future); Boeing 777 has a 25-day process time. The Boeing 787's process time can be reduced to three days, in part because some of the machining operations are transferred to the upstream process, and the various components that arrive at the assembly process are pre-installed with the various systems of the aircraft. However, as noted earlier, drilling is the most challenging process in the final assembly process.
The ideal tool material In general, the tool material properties we want include:
(1) The grain size is small, so that a sharper cutting edge can be produced;
(2) It has high hardness (including high heat hardness), so as to provide excellent wear resistance;
(3) It has good toughness (high tensile strength and fracture toughness), so that the sharp cutting edge can be prevented from chipping or deforming under the dynamic cutting force;
(4) It has good thermal conductivity, so that the cutting zone can be quickly dissipated;
(5) It has good thermal stability, so that the tool can maintain its integrity under cutting high temperature;
(6) It has a low chemical affinity or reactivity with the workpiece material.
The pros and cons of each of the characteristics required for the tool material depend on the workpiece material. It is very difficult to require all the above properties of the same tool material, so it is usually necessary to make trade-offs between hardness and toughness. However, these two characteristics are essential for the processing of carbon fiber reinforced polymers and aluminum matrix composites.
Drilling of carbon fiber reinforced composites such as CFRP is similar to drilling wood. The key to machining is the clean and neat cutting of carbon fibres (especially at the exit of the orifice), which requires high shear geometry and high cutting speeds. CFRP is also highly abrasive and therefore requires a very high hardness of the tool material (preferably like diamond).
Cutting titanium alloys also requires high shear forces, but at high cutting speeds required to machine composites, a large amount of cutting heat is generated, and work hardening of titanium in the laminate material can reduce the fatigue life of aircraft components. In addition, titanium has chemical affinity with most tool materials. Therefore, for the processing of most titanium alloy workpieces, cobalt high speed steel and cemented carbide are the main tool materials used. However, these tool materials do not have the wear resistance required to extend tool life when processing composite materials. When the cutting edge of the tool which is blunt by the composite material is cut to remove titanium, work hardening occurs and the tool will fail. Although titanium alloys can be processed with PCD tools, good results are obtained, but in order to prevent chipping, the knife needs to have better toughness. In the laminate material for the manufacture of aircraft fuselage, in addition to composite materials and titanium alloys, it is also possible to use aluminum alloy or stainless steel, which have different cutting requirements.
Improvements in tool materials With the advancement of the times, processing technology continues to improve, and the material removal rate of roughing and finishing titanium alloys is also increasing. It can be seen that the improvement curve of titanium alloy processing has become flat, indicating that the space for improvement has been limited. In order to further improve the processing efficiency, new processing techniques are needed. Considering the increasing proportion of titanium alloys and composites in aircraft structural materials, it is important to improve the processing efficiency of these materials.
The following areas of improvement are possible with tool materials for drilling composite/metal laminates:
(1) Material grades with higher hardness and better toughness;
(2) Gradient functional materials (customized different cutting performance in different parts of the tool);
(3) Nanotechnology (nanostructure);
(4) different combinations of components (such as non-cobalt binders);
(5) Self-lubricating ability (can be used for dry or near dry cutting);
(6) lower tool material costs;
(7) Lower tool manufacturing and regrind costs;
(8) Improved coating bonding method.
Development steps for tool materials Once a material with suitable properties has been identified, the following basic steps can be followed in order to develop it into a tool material that can be used in actual production:
(1) Concept development 1 theoretical synthesis of expected materials; 2 verification of material properties.
(2) Trial: Select the tool made of this material and carry out the cutting test 1 blade; 2 round cutter.
(3) Determine the practicability of the material 1 tool type; 2 workpiece material; 3 cutting speed and feed range.
(4) Commercialization 1 Mass production in a cost-effective manner; 2 is to promote product training sales team.
The time period for this development process can be quite long (especially when some technical issues are difficult to resolve). As can be seen from the development chronology of superhard tool coatings, many obstacles may be encountered during the development process. Therefore, linking suppliers to the correct application of tool materials is key to the successful commercialization of tool materials. The next question is: Are these tool materials large enough for market size to be developed?
Market size The market forecast for the next 10 years is that there will be a general increase in the production of aircraft. Listed below are the number of aircraft that need to be manufactured in the coming years based on recent orders:
Commercial aircraft:
(1) Delivered in 2007: Boeing aircraft: 441 (worth $29.5 billion); Airbus aircraft: 453 (worth $23.9 billion);
(2) Orders accepted in 2007: Boeing aircraft: 1413 aircraft; Airbus aircraft: 1341 aircraft;
(3) Backlog of orders (as of December 2007): Boeing aircraft: 3,427 aircraft; Airbus aircraft: 3,421 aircraft; the specific number of each type of aircraft is as follows:
1 Boeing 787 Dreamliner: As of February 2008, the order volume was 857, with a maximum productivity of at least 10 per month; 2 Airbus A350: As of February 2008, the order volume was 370, with a maximum productivity of 13 per month. .
(4) Recent market outlook (2007-2026): 22,700 to 28,600 commercial aircraft, valued at 2.6 to 2.8 trillion US dollars. The specific quantities of each model of these two types of aircraft are as follows:
1 Freighter: The recent demand is 1980. The total demand during 2007-2026 is estimated to be 4,000, of which about 870 are new cargo aircraft, and the rest are modified by passenger aircraft. 2 regional passenger aircraft: recent demand is 2886, 2007-2026 The total demand during the period is expected to be 3,700.
Military aircraft:
(1) F/A-18E/F "Super Hornet" combat attack aircraft: By 2012, the US Air Force's planned demand is 581, each worth $57 million, with a maximum productivity of 48 aircraft per year.
(2) F-22 Raptor: By 2010, the United States alone had orders of 183, each worth $150 million, with a maximum productivity of 32 per year.
(3) Eurofighter Typhoon Typhoon fighters: The planned demand for more than 700 aircraft in 2016 is approximately $51 million to $58 million, with a maximum productivity of 52 aircraft per year.
(4) F-35 Joint Strike Fighter: The global planned demand for 2,035 is 3,173, each worth about $50 million, with a maximum productivity of 48 per year.
Tool Performance Improvements Here are a few recent examples of tooling improvements for aerospace manufacturing tooling:
(1) Processing Example 1: A commercial aircraft component supplier drills a material with a thickness of 0.200′′ (about 5 mm) using a solid carbide taper drill when machining a fiber reinforced composite workpiece. The drill can only drill 150 to 200 holes, and the tool has to be replaced due to unacceptable fiber tear. The supplier changed to a new type of CVD diamond coated carbide drill with a large number of drill holes. Increased to 2,200 holes. Although the cost of the new drill is 15 times that of the old drill, the cost per hole is reduced by 80% due to the extended life of the drill, the reduced number of tool changes, and increased machining time.
(2) Processing Example 2: Lockheed's life of the cutting tool and the quality of the cutting edge are unsatisfactory when the composite wing of the F-35 Joint Strike Fighter is being trimmed. To this end, a new type of CVD diamond coated tool has been developed with tool life (measured in linear length) from 9 feet (only 1/3 of the thickness of the cutting material) to 57 feet (full thickness of the cutting material), thus A wing with a 24mm blade can be used to machine a wing skin. As a result, each aircraft can achieve a cost-effectiveness of $80,000, and for the 2,783 F-35s planned for the US market, it is expected to save money (cost reduction) by $222.6 million.
(3) Processing Example 3: The upper deck floor girders of the Airbus A380 are made of CFRP composite material and need to be mounted on the aluminum alloy frame of the fuselage. The original uncoated solid carbide drill used to process this CFRP and aluminum alloy laminate can only process 90 holes. After switching to a diamond-coated carbide drill, the machining life of each drill is increased to more than 500 holes.
As a hypothetical example, it is assumed that 90 specific sized holes need to be machined on a composite/aluminum alloy laminate. If the cost per drill is $150, but only 20 to 30 holes can be machined, then It takes 3 to 5 times extra time to replace the drill bit. In addition, in order to minimize production interruptions, an additional rig with a drill bit installed on it may be required. If the life of each drill can reach 100 holes, even if the cost of the drill is doubled or more than before, the processing cost per hole can be reduced and the processing time can be shortened.
Considering the growing market demand for aircraft, the use of composite materials and aluminum alloys on new aircraft is increasing, and the assembly process time is required to be shorter, and the opportunities for improving cutting tools are enormous. Tool manufacturers develop and provide for the aviation industry. Tool products with better processing performance are just the right time.
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