Manufacturing time is a direct cost in any assembly process — hours of labor, machine utilization, and throughput rate determine the economics of a production program. When structural epoxy is evaluated against riveting or spot welding as a joining method, the comparison is rarely as simple as adhesive cost vs. fastener cost. The adhesive assembly process eliminates entire process steps that exist in fastened assembly — drilling, deburring, sealant application, fastener insertion, driving, inspection of each fastener — and replaces them with bead application and a cure dwell time that in many cases requires no active labor. Understanding where the time savings accumulate, and where adhesive bonding requires extra process discipline, allows production engineers to accurately model the assembly time and cost impact of transitioning from mechanical fastening to structural bonding.

Process Steps Eliminated by Structural Epoxy

Drilling and deburring. Each rivet requires a drilled hole sized to the rivet diameter. For aluminium sheet assembly with hundreds of rivets, the drilling cycle alone — drill, withdraw, brush, inspect — consumes significant cycle time. Deburring the hole removes the burr raised by drilling, required both for structural reasons (burrs concentrate stress) and for corrosion reasons (burrs are sharp and damage protective coatings). Neither step exists in a bonded assembly.

Sealant application at fasteners. In aerospace and marine structures, every fastener hole receives wet sealant applied to the fastener shank before insertion to prevent water ingress at the hole. This is a per-fastener manual operation that scales linearly with fastener count. Structural epoxy bonding seals the joint continuously as part of the primary bonding process — no separate sealant application step is required.

Fastener insertion and driving. Rivet driving, whether manual, pneumatic, or automated, is a per-fastener operation. For blind rivets in production automotive assembly, a typical cycle time is 3 to 8 seconds per fastener. For aerospace solid rivets driven with a bucking bar, the cycle time is 30 to 90 seconds per rivet, requiring two-person access to both sides. A bonded assembly replaces all of these operations with a single continuous bead application pass.

Per-fastener inspection. Quality control for riveted assemblies requires inspection of each rivet: head seating, driven head geometry, absence of cracks in the surrounding sheet, and torque verification for bolts. This inspection is eliminated for bonded assemblies, replaced by bond line inspection methods — ultrasonic, visual at the bead edge, or mechanical testing of representative samples.

If you need assembly time modeling data, process step comparisons, and cure scheduling guidance for transitioning from riveted or spot-welded assemblies to structural epoxy bonding, Email Us — Incure provides process engineering support for production adhesive bonding programs.

The Adhesive Process: Where Time Is Spent

Structural epoxy bonding eliminates fastener-by-fastener operations but introduces different time requirements:

Surface preparation. Adhesive bonding requires surface preparation that mechanical fastening does not: solvent degrease, abrasion, and primer application. For production aluminium assembly, this is typically 2 to 5 minutes per part. This is the main added process step — it is required for bond reliability and cannot be skipped. However, preparation time is usually less than the total drilled-and-riveted time it replaces for assemblies with high fastener counts.

Adhesive application. Automated robotic adhesive dispensing applies structural adhesive at 100 to 300 mm/s along programmed bead paths. A 1-meter bead takes 4 to 10 seconds at this rate. A riveted joint requiring 50 rivets at 50 mm spacing over 2.5 meters of joint length takes far longer than a single robot pass depositing a continuous adhesive bead over the same path.

Cure dwell time. Adhesive cure requires time that riveting does not. Room-temperature-cure epoxy achieves handling strength in 30 to 60 minutes for one-component or two-component fast-cure systems. The curing assembly occupies fixturing for this period. Two strategies address this: accelerated cure (moderate oven temperature, 60°C to 80°C, reducing handling time to 10 to 15 minutes) or staged production with multiple fixtures so assembly labor continues on other units while previous units cure.

Spot Welding Comparison

For steel panel assembly, the comparison between structural epoxy and spot welding has a different profile. Spot welding is fast — each weld takes 0.5 to 2 seconds — but requires both-sided access, copper electrode tooling, and frequent electrode dressing to maintain weld quality. Spot welds in visible locations require subsequent surface finishing to remove the weld mark. The heat input from spot welding creates residual stress and can distort thin-gauge panels.

Structural epoxy bonding of steel panels is slower than spot welding at the joint level but eliminates electrode maintenance, both-sided access requirements, post-weld surface finishing, and distortion management. In automotive BIW (body-in-white) manufacturing, spot welding and structural adhesive are used together — the adhesive provides stiffness and fatigue performance while spot welds provide assembly fixturing during cure. This hybrid approach captures the speed of spot welding for fixturing and the structural performance of adhesive bonding in the finished joint.

Where Bonding Is Not Faster

Bonding does not reduce assembly time in all cases:

• Low fastener count assemblies — if fewer than 20 to 30 fasteners are being replaced, the surface preparation time for bonding may exceed the fastener installation time
• Field repair — in-service repair requiring bonding at location is slower than bolt replacement because preparation and cure dwell time are required at a location not optimized for adhesive work
• High-turnover production with no fixtures — if a production line cannot accommodate cure dwell time within the takt time, bonding requires restructuring the line or adding fixtures

For high-volume panel assembly, body-in-white production, and large-area structural joints with dozens or hundreds of fasteners, structural epoxy consistently reduces total assembly time and part count while improving the structural performance of the finished joint.

Contact Our Team to discuss process engineering, cure scheduling, surface preparation integration, and automation options for structural epoxy bonding in your production assembly program.

Visit www.incurelab.com for more information.