The choice is not which adhesive is 'best', but which possesses the right trade-offs for your production line. A UV-cure adhesive provides a bond in under three seconds which is ideal for high throughput, but is ineffective without a clear light path for the curing lamp. A two-part epoxy, conversely, creates a structural bond that withstands harsh chemicals, but can require hours to fully cure and introduces work-in-progress delays.
Selecting the wrong adhesive turns a repeatable robotic process into a source of inconsistent quality and rework. Our engineering teams at Olympus Technologies see this frequently: a fast-curing cyanoacrylate that becomes too brittle, or a strong epoxy that is too viscous for the chosen dispensing valve. The key is to balance cure speed, bond strength, substrate compatibility, and the cost of the associated dispensing equipment.
Adhesive Comparison for Automated Dispensing
We use this framework to guide initial selection with our clients. It maps the core attributes of the four most common adhesive families used in robotic dispensing, highlighting the critical trade-offs between speed, strength, and application constraints.
| Attribute | Hot Melt Adhesives | Two-Part Epoxies | UV-Cure Adhesives | Cyanoacrylates (CAs) |
| Cure Mechanism | Cooling | Chemical Reaction | UV Light | Moisture (Ambient) |
| Typical Cure Time | 10 - 60 seconds | 5 minutes - 24 hours | 1 - 5 seconds | 5 - 30 seconds |
| Bond Strength | Low to Medium | High to Very High | Medium to High | Medium |
| Gap Filling | Excellent | Excellent | Poor | Poor to Fair |
| Substrate Fit | Porous (cardboard, wood) | Metals, Composites, Plastics | Clear Plastics, Glass, Coated Metals | Plastics, Rubber, Metal |
| Equipment | Heated Tank & Hose | Static/Dynamic Mixer, Dual Cartridge | UV LED Lamp, Shielding | Simple Valve, Needle |
| Relative Cost/kg | Low | High | Very High | High |
Note: Values are typical and vary significantly based on specific formulation and application conditions.
When to Use Hot Melt Adhesives
Hot melt is the go-to for high-volume packaging applications like case sealing and carton forming. Its primary advantages are its low cost and rapid setting time, which is governed purely by cooling. Because it is applied molten, it has excellent gap-filling properties on porous or irregular surfaces like corrugated cardboard.
The trade-off is its limited structural strength and poor performance at elevated temperatures, where it can re-soften. We would never specify hot melt for an assembly that must withstand mechanical stress or operate in an environment above 60°C. Its use is almost exclusively for packaging, product assembly with non-structural bonds, and woodworking.
When to Use Two-Part Epoxies
For structural bonding of metals, composites, and engineered plastics, two-part epoxies are often the only viable choice. When correctly mixed and cured, they create bonds that are frequently stronger than the substrates themselves, offering exceptional chemical and heat resistance. This makes them essential in automotive, aerospace, and heavy engineering.
Their primary drawback is the cure cycle. While 5-minute formulations exist, they often don't achieve full strength for 24 hours, creating a bottleneck that requires batch processing or large buffer zones. The dispensing process is also more complex, requiring a static or dynamic mix nozzle to combine the resin and hardener, which becomes a consumable part.
When to Use UV-Cure Adhesives
UV-curing adhesives offer the best of both worlds: the speed of a hot melt with strength approaching that of an epoxy. Cure times of 1-5 seconds are achievable, enabling extremely high throughput in medical device assembly, electronics (conformal coating), and glass bonding. The process is clean, with no mixing and minimal waste.
The defining limitation is the absolute requirement for a direct line of sight between the UV lamp and the entire bond line. Opaque substrates or shadowed areas within a joint will leave the adhesive uncured. This restricts their use to applications involving transparent or translucent materials or where the adhesive bead is fully exposed.
When to Use Cyanoacrylates (Super Glues)
Cyanoacrylates (CAs) are surface-tack champions, curing in seconds through a reaction with ambient moisture. They excel at bonding smooth, non-porous materials like plastics and rubber, making them popular for small component assembly in electronics and consumer goods. The dispensing equipment is simple, often just a time-pressure valve and a fine-tip needle.
However, CAs form rigid, often brittle bonds with poor impact resistance and minimal gap-filling capability. They also exhibit poor performance against moisture over the long term, a phenomenon known as hydrolysis. We only recommend them for small, well-mated parts under compressive, not peel, load.
Beyond the Datasheet: Factors That Redefine Adhesive Choice
A technical datasheet provides a baseline, but real-world manufacturing conditions introduce variables that can invalidate your initial selection. The performance of an adhesive doesn't just depend on its chemistry; it is equally affected by the substrates being joined, the operational environment, and any industry-specific regulations that apply.
For example, bonding two materials with vastly different coefficients of thermal expansion (like aluminium to glass) requires a flexible adhesive, not a brittle one, regardless of its raw strength. The repeated stress of thermal cycling will fracture a rigid bond line. Similarly, an assembly destined for a medical device requires an adhesive with ISO 10993 biocompatibility certification, which immediately disqualifies thousands of industrial-grade options.
What If Your Assembly Requires Optical Clarity?
When bonding lenses, displays, or transparent covers, the adhesive must do more than just hold parts together; it must be optically invisible. This requires an optically clear adhesive (OCA) with a refractive index matched to the substrates to prevent distortion. Both UV-cure acrylates and specific two-part epoxies are available in these formulations.
The primary challenges are preventing yellowing over time due to UV exposure and avoiding microscopic air bubbles during dispensing. An automated dispensing process from Olympus Technologies uses degassed cartridges and precisely controlled robot motion to lay a perfect bead, which is essential for these cosmetically critical applications. Failure here results not in a weak bond, but in a rejected product.
How Do You Bond Low-Surface-Energy Plastics?
Standard adhesives struggle to wet out and bond to low-surface-energy (LSE) plastics like polypropylene (PP), polyethylene (PE), and PTFE. The liquid adhesive beads up on the surface instead of spreading, resulting in a weak, unreliable bond. Attempting to use a standard epoxy or CA on these materials without preparation is a guaranteed failure point.
To solve this, surface preparation is mandatory. This can involve chemical primers that modify the surface or, for a more robust and automated solution, in-line plasma treatment. A plasma jet directed by the cobot just ahead of the dispensing needle activates the plastic's surface, dramatically increasing its energy and allowing the adhesive to form a strong, covalent bond.
Frequently Asked Questions
What's the difference between volumetric and time-pressure dispensing?
Volumetric dispensing systems, like those using a piston or progressive cavity pump, deliver a precise volume of adhesive with every shot, regardless of changes in material viscosity. Time-pressure systems are simpler, applying air pressure for a set duration, but the amount dispensed can vary if the adhesive gets warmer or colder. For applications requiring bead consistency better than ±0.5 mm, we specify volumetric systems.
How important is surface preparation for automated dispensing?
It is the single most critical factor for bond consistency. At a minimum, all substrates must be clean, dry, and free of oils or mould-release agents. For LSE plastics or critical structural bonds, we integrate automated surface prep like plasma or corona treatment directly into the robot cell to eliminate operator variance and ensure a perfect bond every time.
Can a cobot be used for Form-in-Place Gaskets (FIPG)?
Yes, this is a perfect application for robotic dispensing. A cobot, such as a Universal Robots UR10e, moves a dispensing nozzle along a programmed 3D path to lay a precise bead of liquid gasket material, typically silicone or polyurethane. This bead cures in place, creating a custom-fit seal that is more reliable and often cheaper than a pre-cut solid gasket.
Next Steps and Related Resources
Now that you understand the key trade-offs, the next step is to evaluate your specific part, process, and performance requirements.
- Explore Our Solutions: See how we apply these principles in our turnkey cobot dispensing solutions.
- Book a Consultation: An incorrect adhesive choice can cost thousands in rework. Speak with one of our automation engineers to validate your selection for your specific application.
- Dispensing End Effectors: The dispenser is only one part of the system. Learn more about the bespoke EOAT we design and build for complex dispensing tasks.
