《Choosing the right adhesives for automotive assembly》：
Considering the many types of structural materials used in cars and planes, joining them securely and reliably has become more complicated, which is why tons of work is being done to bring about new structural adhesive technologies that bond disparate materials, reduce the need for fasteners and improve welded bonds, and can be easily integrated into high-volume production lines. It is difficult to meet the requirements for the automotive assembly of production cars.
The laser-like focus of automotive OEMs on meeting regulators’ gasoline emission targets for 2025 CAFE standards means that lightweighting is a major emphasis. That’s because many easier-to-implement technologies for taking weight out, like in the powertrain, have already been done. In turn, adhesives can be a great enabler for using lightweighting materials technologies to reach those targets, Tonja Sutton, global strategic market manager for Dow Automotive Systems, told Design News.
This image of a Corvette shows all the areas where structural adhesives are, or might be, supplementing and possibly replacing rivets and welds in automotive assemblies. These adhesives are playing a greater role to enable the use of lightweight substrate materials, add strength to rivets or welds, and make possible bonds between different materials. (Source: Bayer MaterialScience)
Materials substrate technologies for automotive lightweighting include a growing list: aluminium, some composites, some magnesium, and also some advanced high-strength steels with a difference balance of properties from previous steels. Others are polymers such as glass-filled sheet moulding compounds and reinforced nylon. Adhesives are especially effective at bonding dissimilar materials that often can’t be joined using rivets or welds. Structural adhesives also help reduce noise, vibration, and harshness, and can improve crash performance.
There are many cases of different types of polymer components that must be bonded to other structures, Mansour Mirdami, chief engineer for Dow Automotive Systems, told us. For example, in the front-end module, a structural component made of a glass-filled composite may be bonded to a metal frame. Adhesives may be used for such structural purposes or for other areas, where a component has some structural contribution but it’s not a significant one, like the rear lift gate.
“When we look at joining with adhesives, we need to know three things,” said Sutton. “First, what are the substrate materials we’re bonding? They may have different requirements. Second, we look at where in the manufacturing process we’re going to do the assembly: in the body shop portion where the body is assembled and welded, or in the later, trim shop portion?” Assemblies done in the body shop or paint shop stages require adhesives that can withstand high temperatures, and their application must be adapted to those assembly requirements. If an assembly occurs in the trim shop, that means room-temperature joining, and the possibility of accelerating cure times with localised heating or induction curing. The third question is, what is the application: a structural or a hang-on part
The two different types of structural adhesives used for joining parts are one-part and two-part epoxies and two-part polyurethanes (PUs). The one-part epoxies generally withstand higher temperatures, so they are used for body shop bonding of closures and body structures, and are cured during an e-coat or paint shop stage. Two-part epoxies are more common for repairs. Epoxy structural adhesives reduce the number of welds needed and have excellent adhesion to automotive steels, coated steels, and pre-treated aluminium, so they’re often used for bonding dissimilar metals, said Sutton. Because they provide a corrosion barrier between dissimilar materials they’re especially useful in joining aluminium to steel, for example, which can be problematic because of galvanic corrosion.
Epoxies also tend to be more rigid and less flexible than PUs. Dow Automotive’s BETAMATE family of epoxy structural adhesives, for example, can be used to bond multiple materials such as composites with lightweight metals, said Sutton. In an earlier model year of the BMW 5 series, the car’s aluminium front-end was bonded to its steel body using a formulation of this adhesive, with clinching as a secondary attachment. In another example, the 2014 Corvette Stingray uses a formulation of this adhesive for multi-materials bonding. Substrate material combinations that have been bonded with this adhesive family include steel to steel, aluminium to steel, aluminium to aluminium, carbon fibre to uncoated steel, carbon fibre to steel, and carbon fibre to aluminium.
A robot applies Dow Automotive Systems’ BETAMATE epoxy structural adhesive to the door section of a typical passenger car’s side frame, which will be bonded to the body structure. The substrate material is zinc-coated steel. (Source: Dow Automotive Systems)
PU structural adhesives are room-temperature curing materials for post-paint trim shop assemblies. Some can be cured faster with localised heating or induction curing. These adhesives generally have high modulus, high strength, and high elongation, being more flexible than epoxies. When bonding dissimilar materials there are several issues to consider, especially different thermal and mechanical properties such as expansion rates. Although some PUs require primer, Dow Automotive’s BETAFORCE PU-based adhesive doesn’t. It’s also used for bonding multiple materials such as composites, metals, and sheet moulding compounds (SMCs). For example, the aluminium roof of an earlier model year of the BMW 7 series was bonded to its steel body with a formulation of this PU structural adhesive, using no secondary attachment. This enabled an average reduction of more than 15lbs in the vehicle’s weight.
Some cars have been redesigned to take advantage of both multiple lightweight materials and adhesive bonding, said Mirdami. One was redesigned so a large portion of the front structure was aluminium and the rear structure was steel, which were then bonded together with Dow Automotive’s PU adhesive. Since aluminium weighs so much less, being able to join aluminium structures with steel structures has enabled much of the influx of aluminium into car bodies and the resulting weight savings.
Adhesives are complementing and reinforcing, as well as sometimes replacing, rivets and welds. Components that are joined using weld bonding—adhesive bonding with welding as a secondary attachment—instead of standard spot welding alone can sustain higher loads, enable the use of lighter-weight materials such as down-gauged steel, and reduce stress in bonded joints, thereby improving a vehicle’s durability. Not only can structural adhesives help join lighter-weight materials to each other, they can also help reduce weight: between 0.6kg and 1.1kg of mass can be eliminated for every metre of structural adhesives applied, said Sutton.
A survey conducted recently by Bayer MaterialScience consisted of exploratory discussions within the automotive industry aimed at uncovering unmet needs for structural adhesives used in light vehicles. The company produces raw materials for adhesive makers that join multiple materials, including two-component PU adhesives. During the survey, researchers talked to adhesive makers and OEMs, as well as substrate material suppliers, said Danielle Hunter, market manager of adhesives.
Much of the findings about joining techniques are dependent on the substrate materials, she said. For example, most automotive OEMs are presently shifting from steel to advanced high-strength steels and aluminium. By 2025 when CAFE standards take effect, steel will decline about 8 per cent to 10 per cent, while non-metals including composites, plastics, carbon fibre composites, and magnesium will increase about 3 per cent to 4 per cent. During the same period, aluminium usage is expected to increase by about 7 per cent.
Some examples of 3M’s family of structural adhesives for joining a variety of substrate materials, including metals and mixed material structures. The two-part epoxy SA5026 is formulated for steel hem flange body-in-white bonding applications and SA5027, for hem flange bonding applications on aluminium, steel or sheet moulded compounds. SA9820 is a two-part adhesive for bonding composite and aluminium body-in-white component joint substrates. (Source: 3M)
Aluminium, however, requires three times the force to weld that steel does, and costs almost twice as much per weld, Hunter told us. Using structural adhesives can eliminate some of those welds, since they provide a more continuous bonded surface area than spot welds or rivets. More and more, adhesives will be used in the body-in-white, and as structural reinforcements where rivets and welds are typically used today. “There are OEMs on both ends of the spectrum of whether to replace rivets and welds with adhesive bonding,” said Hunter. “Rivets and welds, which are fast and efficient, will remain as a secondary bond, especially when joining aluminium and steel substrates.”
In 2013, about two-thirds of automotive adhesives sold were epoxies used in pre-e-coat assemblies, Hunter said. The balance was used in interior, windshield, and exterior structural applications. Some car models, though, are made without an e-coat oven, which means that in the future, more PUs could be used for room-temperature assemblies.
Bayer’s survey resulted in a list of prioritised needs for automotive structural adhesives. The top two are improving the bond between dissimilar materials and combining high elongation and high strength in a single product. “There are good products available now,” said Hunter. “But as the industry moves towards higher volume production and combining new substrate materials, we need to understand better what’s happening and develop better raw materials in the lab.” Another major need is establishing a consistent, available global supply with the same feedstocks for a given adhesive in one location as in another location a continent away. In addition, non-destructive testing and modelling are needed for adhesive bonds, which can’t be viewed, to avoid the destruction of expensive assemblies in order to test whether bonds are working.
More adhesives that can handle higher temperatures in the body shop could also help cut assembly costs. If a car’s design could be changed to move the assembly of multi-material structures into the body shop for assembly instead of the trim shop, that would take advantage of the existing manufacturing infrastructure in place, said Dow Automotive’s Sutton. That’s because the body shop is less labour intensive than the trim shop, where multi-material structures are usually assembled. This could be done with the right adhesives that manage higher temperatures and have different property balances among thermal performance, modulus, and elongation. Such an adhesive could also potentially eliminate any secondary attachments like rivets and welds, which are sometimes needed in assembly to hold the two pieces together while curing.
《Choosing the right adhesives for automotive assembly》：
Considering the many types of structural materials used in cars and planes, joining them securely and reliably has become more complicated, which is why tons of work is being done to bring about new structural adhesive technologies that bond disparate materials, reduce the need for fasteners and improve welded bonds, and can be easily integrated into high-volume production lines. It is difficult to meet the requirements for the automotive assembly of production cars.
The laser-like focus of automotive OEMs on meeting regulators’ gasoline emission targets for 2025 CAFE standards means that lightweighting is a major emphasis. That’s because many easier-to-implement technologies for taking weight out, like in the powertrain, have already been done. In turn, adhesives can be a great enabler for using lightweighting materials technologies to reach those targets, Tonja Sutton, global strategic market manager for Dow Automotive Systems, told Design News.
This image of a Corvette shows all the areas where structural adhesives are, or might be, supplementing and possibly replacing rivets and welds in automotive assemblies. These adhesives are playing a greater role to enable the use of lightweight substrate materials, add strength to rivets or welds, and make possible bonds between different materials. (Source: Bayer MaterialScience)
Materials substrate technologies for automotive lightweighting include a growing list: aluminium, some composites, some magnesium, and also some advanced high-strength steels with a difference balance of properties from previous steels. Others are polymers such as glass-filled sheet moulding compounds and reinforced nylon. Adhesives are especially effective at bonding dissimilar materials that often can’t be joined using rivets or welds. Structural adhesives also help reduce noise, vibration, and harshness, and can improve crash performance.
There are many cases of different types of polymer components that must be bonded to other structures, Mansour Mirdami, chief engineer for Dow Automotive Systems, told us. For example, in the front-end module, a structural component made of a glass-filled composite may be bonded to a metal frame. Adhesives may be used for such structural purposes or for other areas, where a component has some structural contribution but it’s not a significant one, like the rear lift gate.
“When we look at joining with adhesives, we need to know three things,” said Sutton. “First, what are the substrate materials we’re bonding? They may have different requirements. Second, we look at where in the manufacturing process we’re going to do the assembly: in the body shop portion where the body is assembled and welded, or in the later, trim shop portion?” Assemblies done in the body shop or paint shop stages require adhesives that can withstand high temperatures, and their application must be adapted to those assembly requirements. If an assembly occurs in the trim shop, that means room-temperature joining, and the possibility of accelerating cure times with localised heating or induction curing. The third question is, what is the application: a structural or a hang-on part
The two different types of structural adhesives used for joining parts are one-part and two-part epoxies and two-part polyurethanes (PUs). The one-part epoxies generally withstand higher temperatures, so they are used for body shop bonding of closures and body structures, and are cured during an e-coat or paint shop stage. Two-part epoxies are more common for repairs. Epoxy structural adhesives reduce the number of welds needed and have excellent adhesion to automotive steels, coated steels, and pre-treated aluminium, so they’re often used for bonding dissimilar metals, said Sutton. Because they provide a corrosion barrier between dissimilar materials they’re especially useful in joining aluminium to steel, for example, which can be problematic because of galvanic corrosion.
Epoxies also tend to be more rigid and less flexible than PUs. Dow Automotive’s BETAMATE family of epoxy structural adhesives, for example, can be used to bond multiple materials such as composites with lightweight metals, said Sutton. In an earlier model year of the BMW 5 series, the car’s aluminium front-end was bonded to its steel body using a formulation of this adhesive, with clinching as a secondary attachment. In another example, the 2014 Corvette Stingray uses a formulation of this adhesive for multi-materials bonding. Substrate material combinations that have been bonded with this adhesive family include steel to steel, aluminium to steel, aluminium to aluminium, carbon fibre to uncoated steel, carbon fibre to steel, and carbon fibre to aluminium.
A robot applies Dow Automotive Systems’ BETAMATE epoxy structural adhesive to the door section of a typical passenger car’s side frame, which will be bonded to the body structure. The substrate material is zinc-coated steel. (Source: Dow Automotive Systems)
PU structural adhesives are room-temperature curing materials for post-paint trim shop assemblies. Some can be cured faster with localised heating or induction curing. These adhesives generally have high modulus, high strength, and high elongation, being more flexible than epoxies. When bonding dissimilar materials there are several issues to consider, especially different thermal and mechanical properties such as expansion rates. Although some PUs require primer, Dow Automotive’s BETAFORCE PU-based adhesive doesn’t. It’s also used for bonding multiple materials such as composites, metals, and sheet moulding compounds (SMCs). For example, the aluminium roof of an earlier model year of the BMW 7 series was bonded to its steel body with a formulation of this PU structural adhesive, using no secondary attachment. This enabled an average reduction of more than 15lbs in the vehicle’s weight.
Some cars have been redesigned to take advantage of both multiple lightweight materials and adhesive bonding, said Mirdami. One was redesigned so a large portion of the front structure was aluminium and the rear structure was steel, which were then bonded together with Dow Automotive’s PU adhesive. Since aluminium weighs so much less, being able to join aluminium structures with steel structures has enabled much of the influx of aluminium into car bodies and the resulting weight savings.
Adhesives are complementing and reinforcing, as well as sometimes replacing, rivets and welds. Components that are joined using weld bonding—adhesive bonding with welding as a secondary attachment—instead of standard spot welding alone can sustain higher loads, enable the use of lighter-weight materials such as down-gauged steel, and reduce stress in bonded joints, thereby improving a vehicle’s durability. Not only can structural adhesives help join lighter-weight materials to each other, they can also help reduce weight: between 0.6kg and 1.1kg of mass can be eliminated for every metre of structural adhesives applied, said Sutton.
A survey conducted recently by Bayer MaterialScience consisted of exploratory discussions within the automotive industry aimed at uncovering unmet needs for structural adhesives used in light vehicles. The company produces raw materials for adhesive makers that join multiple materials, including two-component PU adhesives. During the survey, researchers talked to adhesive makers and OEMs, as well as substrate material suppliers, said Danielle Hunter, market manager of adhesives.
Much of the findings about joining techniques are dependent on the substrate materials, she said. For example, most automotive OEMs are presently shifting from steel to advanced high-strength steels and aluminium. By 2025 when CAFE standards take effect, steel will decline about 8 per cent to 10 per cent, while non-metals including composites, plastics, carbon fibre composites, and magnesium will increase about 3 per cent to 4 per cent. During the same period, aluminium usage is expected to increase by about 7 per cent.
Some examples of 3M’s family of structural adhesives for joining a variety of substrate materials, including metals and mixed material structures. The two-part epoxy SA5026 is formulated for steel hem flange body-in-white bonding applications and SA5027, for hem flange bonding applications on aluminium, steel or sheet moulded compounds. SA9820 is a two-part adhesive for bonding composite and aluminium body-in-white component joint substrates. (Source: 3M)
Aluminium, however, requires three times the force to weld that steel does, and costs almost twice as much per weld, Hunter told us. Using structural adhesives can eliminate some of those welds, since they provide a more continuous bonded surface area than spot welds or rivets. More and more, adhesives will be used in the body-in-white, and as structural reinforcements where rivets and welds are typically used today. “There are OEMs on both ends of the spectrum of whether to replace rivets and welds with adhesive bonding,” said Hunter. “Rivets and welds, which are fast and efficient, will remain as a secondary bond, especially when joining aluminium and steel substrates.”
In 2013, about two-thirds of automotive adhesives sold were epoxies used in pre-e-coat assemblies, Hunter said. The balance was used in interior, windshield, and exterior structural applications. Some car models, though, are made without an e-coat oven, which means that in the future, more PUs could be used for room-temperature assemblies.
Bayer’s survey resulted in a list of prioritised needs for automotive structural adhesives. The top two are improving the bond between dissimilar materials and combining high elongation and high strength in a single product. “There are good products available now,” said Hunter. “But as the industry moves towards higher volume production and combining new substrate materials, we need to understand better what’s happening and develop better raw materials in the lab.” Another major need is establishing a consistent, available global supply with the same feedstocks for a given adhesive in one location as in another location a continent away. In addition, non-destructive testing and modelling are needed for adhesive bonds, which can’t be viewed, to avoid the destruction of expensive assemblies in order to test whether bonds are working.
More adhesives that can handle higher temperatures in the body shop could also help cut assembly costs. If a car’s design could be changed to move the assembly of multi-material structures into the body shop for assembly instead of the trim shop, that would take advantage of the existing manufacturing infrastructure in place, said Dow Automotive’s Sutton. That’s because the body shop is less labour intensive than the trim shop, where multi-material structures are usually assembled. This could be done with the right adhesives that manage higher temperatures and have different property balances among thermal performance, modulus, and elongation. Such an adhesive could also potentially eliminate any secondary attachments like rivets and welds, which are sometimes needed in assembly to hold the two pieces together while curing.
– Ann R. Thryft
Materials & Assembly