The Next Generation of Epoxy Adhesives
Technology for Transportation Assembly:
Low Bake One-Component Epoxies
Daniel R. Daley
Senior Consultant
The ChemQuest Group, Inc.
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Introduction
• With over 30 years of experience at Navistar International, a
truck and engine OEM, Dan Daley has held various senior
polymeric materials engineering and lab management
positions.
• Daley’s technical leadership included solving problems in
material compatibility and chemical interactions, and
improving material performance/cost ratios and strategic
sourcing.
• The range of materials managed included soft trim such as
textiles, foams, composites, seating, upholstery and acoustic
materials and energy management solutions; fluid connectors;
lubricants and fluid systems; elastomers; automotive paint
and coatings; adhesives, sealants and joining systems.
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What is the Unmet Need in Assembly?
• Automotive and truck body manufacturing plants have predominantly used 1K epoxy structural adhesives due to their superior bonding performance and manufacturing-friendly properties.
• Adhesives are co-cured in an electro-coat (e-coat) epoxy prime system at high temperatures (175ºC).
• Commercial vehicle body manufacturers that are unable to justify the capital equipment expense of a full immersion e-coat system cannot take advantage of the processing and performance benefits of a 1K Epoxy System.
• A school bus body assembled with mechanical fasteners and 2K epoxy or methyl methacrylate (MMA) adhesives is one such example.
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A Significant Development is Currently Underway
• The emerging low bake 1K epoxy technology is a significant development.
• It promises to deliver all the advantages of 1K epoxy adhesives: Efficient assembly operations
High strength with toughness
Weld-thru property
• It provides assembly operations lacking the capital and infrastructure to invest in high bake systems with an ability to leverage the key advantages of technology commonly used in automotive and aircraft assembly.
• Finally, it will allow automotive manufacturers and others to use lighter weight materials that would not survive high bake conditions.
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Vehicle Body Construction
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Vehicle Body Construction
• The body is constructed predominantly of metal in spite of a
wider range of available materials that offer key advantages
• Low Capitalized Body Systems mix arc welding (MIG, TIG)
and fasteners
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Vehicle Body Construction
• High Capitalized Body
Systems utilize resistance
spot welding
• Aluminum systems mix
welding (resistance and arc)
with fastening for reliability
• Prime systems are based on
capital and final market
requirements
• High-end Adhesives users
use analytical tools to
optimized performance
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Construction Materials and Joining Methods
Body Construction
• Stamped Steel
Assembly Method
• Spot Weld
Commercial Auto Body
Prime
• E-coat
Bonding Technologies
• 1K epoxy structural
adhesive
Body Construction
• Steel and Aluminum
Assembly Method
• Spot Weld and SPR
Light Truck
Prime
• E-coat
Bonding Technologies
• 1K epoxy structural
adhesive
Body Construction
• Aluminum and Steel
Assembly Method
• SPR, Rivets,
Fasteners & Welding
Heavy Truck
Prime
• E-coat, Precoat
Bonding Technologies
• 1K & 2K Epoxies,
PUR, methyl
methacrylate (MMA)
Body Construction
• Fabricated Steel
Assembly Method
• Rivets, SPR,
Welding
School Bus
Prime
• Precoat
Bonding Technologies
• 2K Epoxy, 2K methyl
methacrylate (MMA)
SPR = self piercing rivets
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Future Construction Materials and Unmet Needs
Future Construction
• Steel, Aluminum & Composite
Unmet Needs
• Low bake 1K epoxy structural
adhesive and primer
• Composite Fastening
Commercial Auto Body
Future Construction
• Aluminum & Composite
Unmet Needs
• Low bake 1K epoxy structural adhesive
and primer
Light Truck / Heavy Truck
Future Construction
• Improved joining methods, paint
systems
Unmet Needs
• Low-bake cure 1K epoxy
structural adhesive
School Bus
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School Bus Manufacturing
• School bus joints must be in compliance with federal
regulation, “49 CFR 571.221 - Standard No. 221; School bus
body joint strength”
Requirement “shall hold the body panel to the member to
which it is joined when subjected to a force of 60 percent of
the tensile strength of the weakest joined body panel”
• Test sections are cut into “dog bones” necked down to 8”
through the joint.
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Current Process
Assembly Steps
Coil coated (primed) steel is fabricated into sheets and forms
Assemblies – adhesive applied, fixture, drilled (unless SPR) then riveted
Major structures are Arc welded
Final structures – fixture, bonded, drilled and fastened
Prime and seal with cure bake
Top-coat paint – usually yellow with black rails and white roofs
Pitfalls
Mostly arc welding, little
spot welding
Metal debris from drilling
may contaminate the
joint
Riveting may cause
excessive equipment
wear (and worker
fatigue/repetitive use
injuries)
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Current School Bus Joining Methods
Semi Tubular Rivet
Mono Bolt Rivet
Self Piercing Rivet
Source: American Society of Mechanical Engineers (ASME)
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Comparison of Adhesive Technologies that Meet Required
Joint Strength
• 2K Epoxies
Long open time systems
Often pre mixed and used at application
Ultimate strength may require bake
Full cure shear strength at 14 – 17 MPa (2,000 – 2,500 psi)
Issues – Open assembly time, waste, clean up, post bake bonding
• 2K Methyl Methacrylate (MMA)
Short open times
Mix at application
Ultimate strength independent of bake
Ultimate shear strength 17 – 21 Mpa (2500 –3000 psi)
Issues – sociability - odor, open assembly time, cannot weld thru, flammable, repair
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Contrasted to a Low Bake (120ºC) 1K Epoxy Adhesive
• Compatible with any current fastener type
• Can be resistance spot welded
• Can co-cure with sealant and prime bakes
• Does not cure until bake (pre-bake clean up is easy)
• Bulk dispense, bulk purchase
• No mix
• High strength – shear 24 – 27.5 Mpa (3,500 – 4,000 psi)
• Higher strength is greater tolerance on regulation or opportunity to reduce fastening
• No open time limits - No line stripping for partially assembled joints.
• Low bake is practical with large bodies
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Required Testing Methods
FMVSS 221 Joint Test
Joint A B C D E F G H I
2k Epoxy 220F Heat Cure 6597 10131 14040 8683 8679 6314 11475 7264 9283
1k Heat Cure Estimate 12976 13048 30721 13884 13866 5232 13633 23819 31239
Min. req. 5962 5995 14115 6379 6371 2404 6264 10944 14353
FMVSS Factor 3.51 3.53 8.30 3.75 3.75 1.41 3.68 6.44 8.44
Substrate 1"x4" Plate Steel (1.6mm)
Cure Schedule 30' @ 250°F
Closed Joint Open Joint
Lap Shear (psi) Lap Shear (psi)
Initial 3,877 3,877
CF CF
1 week 4,021 3,978
CF CF
CF = Cohesive Failure
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Benefits for School Bus Manufacturers
• Lower Manufacturing Costs
Replace fasteners for spot welds
Reduce fastener usage
Reduce drilling
Less waste
Better Assembly Line Management
Better energy management opportunity
Co cure in existing process
• Improved Joint Performance (e.g., side intrusion, roll over, roof strength)
• Improved Quality
Better corrosion control
Reduced repetitive injuries to workers
Less paint damage
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Additional Savings and Opportunities
• Paves the way for a greater freedom in body design and improved efficiency in vehicle body assembly operations
Opportunity to incorporate lower temperature resistant materials into assemblies.
Compatible primer technologies
Low bake E-coat is under development
Lower energy usage (bake ovens estimated to be 60% of an assembly plant’s energy consumption)
Opportunity for non-automotive assembly operations to take advantage of the process improvements
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Conclusions
• While 1K Epoxies offer superior processing and performance advantages, the direct (and indirect) costs of conventional high temperature curing created barriers to use.
• Those barriers are removed with a low bake 1K Epoxy System – a significant advantage to non-automotive industries.
• When an OEM switches from a 2K to 1K system:
Waste is greatly reduced
Quality is improved
Superior joining methods become available
Greater freedom in body design is realized.
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Conclusions
• Moreover, a low bake system coupled with low bake immersion primer systems (120ºC or lower cure) will reduce energy costs and broaden the range of materials that can be used to meeting lightweighting requirements and further reduce costs.
• The 1K Epoxy technology will facilitate new methods and materials in the process, assembly and paint operations for other vehicle assembly operations (including School Bus assembly) for improved efficiency, performance and safety.
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Headquarters
The ChemQuest Group, Inc.
8150 Corporate Park Drive
Suite 250
Cincinnati, Ohio 45242
Phone: (513) 469-7555
Fax: (513) 469-7779
www.chemquest.com
Contacts
Dan Murad
President and CEO
Dan Daley
Senior Consultant
A Special Thanks to Frank Billotto at Dow Automotive
(248) 391-6578 [email protected].
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