Assembly Magazine: How to Error-Proof the Dispensing Process

Automated defect detection ensures the quality of bonded joints.

By Austin Weber

Article excerpt from Assembly Magazine

Avoiding part-to-part variation ensures the proper location of adhesive beads. Photo courtesy Coherix Inc.

June 6, 2025

No matter what type of product is being assembled, mistakes happen. Rather than pointing a finger at who caused the mistake, it’s important to understand how the mistake can be avoided in the future.

To ensure the quality of joints assembled with threaded fasteners, engineers can measure torque and angle. To ensure the quality of press-fits, engineers can measure force and distance. To ensure the quality of welded parts, engineers can use vision systems to monitor surface characteristics and detect defects.

Adhesive bonding differs from other assembly processes because it distributes loads evenly over a broad area, reducing stress on joints. Adhesives are applied inside the joint and are nearly invisible within the assembly. However, they are prone to a variety of errors, especially when incorrect cure times or temperatures are used.

Many mistakes can be avoided simply by choosing and using the correct type of adhesive or dispensing tip. However, engineers have a variety of technologies at their disposal to ensure consistency and quality.

Inline 3D inspection during the dispensing cycle prevents rework and scrap. Photo courtesy Coherix Inc.

 

Preventing Mistakes

Error-proofing refers to mechanisms or techniques implemented to prevent mistakes from occurring during a process or to make mistakes immediately apparent. It can involve using devices, sensors, software or process modifications to ensure that errors are minimized or easily detectable, ultimately improving product quality and reducing the likelihood of defects.

“The principle of error-proofing can primarily be characterized by two critical dimensions: process integrity and system reproducibility,” says Alexander Vogt, senior process engineer for technology development at DELO Industrial Adhesives. “Process integrity focuses on ensuring that the procedures followed during adhesive assembly avoid errors that could compromise the final product.

“A common issue within this dimension is the incorrect dispensing of adhesive,” explains Vogt. “This could involve either the application of an incorrect amount or poor application, such as dispensing drops with many bubbles inside. Such errors can significantly impact the effectiveness and reliability of a bond, potentially leading to product failures.

“Reproducibility involves the consistent and accurate replication of the assembly process by different operators over many operating hours and days,” notes Vogt. “User errors are a notable concern here. These can range from the use of wrong materials or mishandling the adhesive, which could weaken its effectiveness.

“Additionally, operational mistakes can occur due to incorrect setups, when the assembly process is not correctly configured, leading to suboptimal results or failures,” Vogt points out. “Failures may also arise from mechanical issues, such as malfunctions in dispensing systems, which can disrupt the consistency and efficiency of the assembly process.”

“Error-proofing in adhesive inspection refers to the automated detection of defects in adhesive beads during or after dispensing, ensuring they meet defined quality standards,” adds Juergen Dennig, president of Coherix Inc., a company that has developed 3D laser-based adaptive process control technology. Its customers include numerous automakers and suppliers, such as BMW, Bosch, Ford, General Motors, Honda, Hyundai, Magna, Mercedes-Benz, Nissan, Toyota and Volkswagen.

According to Dennig, several parameters can be used to compare actual vs. specification in dispensing applications:

• Bead width. Is the bead the required width throughout?
• Bead height. Is the height of the adhesive bead correct?
• Positioning. Is the bead correctly applied to the component geometry in the correct location?
• Volume. Has the bead been applied with the correct amount of adhesive?

“Error-proofing is essential today, because production quality is no longer negotiable,” says Alexander Herbstritt, senior application and sales engineer at Marco System Analysis & Development LLC. “OEMs expect zero-defect parts, full traceability and process transparency.

“[New technology] enables this by monitoring every dispense in real time,” explains Herbstritt. “Integrated bubble sensors detect trapped air in media lines, and high-resolution volume checks identify deviations before they cause damage or failure. This leads to fewer process escapes, stable quality even in high-mix environments, and readiness for audits without additional rework loops.”

“Error proofing with adhesives is different than with mechanical fastening applications,” adds Matt Quast, adhesive dispensing product specialist at Atlas Copco IAS, which makes tools and equipment for bonding and screwdriving. “Both have intrinsic controls that provide feedback on performance and quality.

“However, error-proofing is less complex with mechanical fastening, because with a bolt, we can measure parameters like torque, angle of rotation and insertion depth,” notes Quast. “Adhesive dispensing errors can be harder to verify and visualize, due to variables such as bead size, position and cure rate.”

 

This low-volume failure was detected by 3D visual inspection. Illustration courtesy Coherix Inc.

 

Error-Proofing Tips

No matter what type of adhesive is being used, there are several simple ways that engineers can make the dispensing process more reliable and error-free.

“The selection of suitable dosing devices plays a central role, such as the endless piston principle, which enables extremely precise dosing regardless of the viscosity of the material,” says Sebastian Gerauer, components and devices business unit manager at ViscoTec GmbH. “The integration of sensors in the dispensing process…also helps to prevent errors by enabling real-time monitoring and automatic corrections.

“Before series production, comprehensive dosing tests should be carried out under real conditions to determine the optimum process parameters,” suggests Gerauer. “These parameters can then be monitored. In addition, adapted, highly dynamic dosing drives are essential for the dosing heads to ensure a precise and stable material supply.

“Another important measure is the exact coordination between material, dosing system and curing unit to ensure a functioning system,” notes Gerauer. “In addition, a visual inspection of the components can monitor the correct placement and distribution of adhesive. For comprehensive error prevention, the entire dispensing process should be continuously monitored to detect potential errors at an early stage.”

“Engineers can set up an error-proof process by selecting the appropriate adhesive viscosity and compatible dispensing technology,” adds Marc Lauter, application engineer at Panacol-Elosol GmbH. “Adhesive viscosity directly affects flow characteristics, with low-viscosity materials better suited for applications requiring capillary action or fast spreading. High-viscosity adhesives are preferred for applications where the adhesive should not sag or drip.

“To ensure consistent results, the dispensing method must be matched to the rheological properties of the adhesive, the required dispensing dimensions and accuracy,” says Lauter. “For example, time-pressure systems are commonly used for dispensing adhesives, but can be affected by viscosity fluctuations.

“Positive displacement pumps provide precise volume control regardless of viscosity changes,” explains Lauter. “In high-speed or noncontact applications, jet dispensing technology may be necessary, especially for low- to medium-viscosity formulations.”

“Error-proofing the dispensing process should focus heavily on prevention [and requires paying attention] to design, process, work instructions and continuous improvement,” adds Dave Filbert, business development and applications manager at Precision Valve & Automation (PVA).

According to Filbert, design is often overlooked and leads to challenges down the road. “Part design, along with where and how the material is to be applied, plays a key role in the ability to develop a robust and repeatable process,” he points out. “Proper material selection is also vital.

“Selection of the wrong material for the application can add unnecessary complexity to production, and increase overall cost and scrape rate,” warns Filbert. “Involve your material and equipment suppliers early on in the process to avoid pit falls.”

“Incorporation of in-process controls, error detection and in-process testing is critical to keep your final product in specification with minimal scrap,” claims Filbert. “A good design and process is meaningless unless thorough and clear work instructions are provided and followed by operators.

“Too many times while troubleshooting a dispensing issue I have seen different operators perform tasks or steps differently, or skipping in-process testing,” explains Filbert. “This not only leads to errors, but makes the troubleshooting process more difficult, due to unknown variables.”

 

Quality Control

Error-proofing is becoming more important in dispensing applications today, especially with automation increasingly used to address labor shortages and quality concerns.

“Production lines are becoming faster and more automated, leaving less room for manual inspection,” says Coherix’s Dennig. “Inline systems must therefore deliver extremely high reliability.”

Dennig believes several factors are driving this trend, including:

• Rising quality standards. “Especially in safety-critical industries, such as automotive, battery assembly and medical technology, adhesive joints are essential for product integrity,” notes Dennig. “Defective beads can result in product failures or recalls.”
• More complex dispensing tasks. “Geometries and materials are becoming more complex, while adhesive beads must be precise, consistent and repeatable,” warns Dennig.
• Cost reduction through scrap or failed parts avoidance. “Inspection errors cause higher material consumption, downtime or rework,” claims Dennig. “Accurate inspection helps minimize these costs.
• Traceability and documentation. “Modern production demands full quality traceability, including adhesive applications,” says Dennig. “Error detection is a key part of that documentation.”

“Error-proofing is gaining importance due to evolving industry trends like miniaturization,” adds DELO’s Vogt. “As components become smaller and more complex, the likelihood of errors during the adhesive application process increases.

“Additionally, the area on which the adhesive performs becomes smaller too, making it even more important for it to work perfectly,” say Vogt. “This presents substantial challenges, particularly in sectors such as automotive and consumer electronics, where products are expected to consistently perform to high standards of reliability and safety.

“Errors in adhesive assembly can have severe impacts,” warns Vogt. “For consumer products, faults may lead to safety hazards, posing potential risks of injury. Errors occurring during the production process can also result in downtime, directly impacting manufacturers through delays and financial losses. Therefore, there is a significant push [today] to minimize these risks.”

 

Industry 4.0 Technology

Artificial intelligence, data analytics and other Industry 4.0 technology is being harnessed to improve the adhesive dispensing process. It shifts error-proofing from reactive to predictive by enabling real-time image processing and intelligent defect detection. Benefits include deeper process insight, adaptive control and scalable error-proofing that evolves with increasing production complexity.

“At DELO, we are focusing on enhancing data management and integration to ensure process data security,” says Vogt. “One of the key advantages of this technology is the ability to trace each component and its associated parameters back to its source. Data can be accessed by customers at any time.

“A key aspect of employing Industry 4.0 technologies for error-proofing is predictive maintenance,” explains Vogt. “By leveraging artificial intelligence, changes in dispensing results and certain cycle counts can be accurately detected. This allows for immediate identification of potential errors and their sources, facilitating fast correction.

“Additionally, the use of sensors and vision systems allows for real-time monitoring of adhesive dispensing,” notes Vogt. “When systems are connected, they contribute to a comprehensive platform that significantly boosts fault diagnosis and correction capabilities, drastically reducing downtime and increasing productivity. These systems provide instant feedback and facilitate the precise control of processes, further minimizing the risk of errors.”

“Reliable fluid control is of central importance in dosing technology,” adds ViscoTec’s Gerauer. “We have integrated various Industry 4.0 functions [into our dispensing systems] to detect errors at an early stage and ensure process reliability.

“For example, we monitor the prepressure upstream of the dispenser to ensure that sufficient material is always provided in the required quantity and time,” says Gerauer. “This allows errors, such as empty containers or blocked lines, to be detected at an early stage.”

By using intelligent sensors, wear parts can be detected and replaced at an early stage before sudden system downtimes occur. This ensures a smooth production process and minimizes unplanned downtimes.

Sensors also record transient processes and provide data that enables detailed analysis. This allows deviations or faults to be detected at an early stage, which improves quality assurance.

“Sensor data is used for feedback in our preeflow eco-DUOMIX two-component dispenser control system to meet the highest accuracy requirements,” Gerauer points out. “This ensures precise dosing and optimizes process quality.

“Another important component is the use of pressure sensors, such as the flowplus-SPT M6J, which measure the dispensing pressure downstream of the dispenser,” says Gerauer. “These sensors allow the pressure to be monitored during the process and protect the dispenser from damage caused by hardening in the line.”

Dispensing pressure also serves as an indicator for quality assurance. Fluctuations in pressure can indicate air bubbles, blockages or an incorrect position of the dispensing needle in relation to the substrate.

“We measure other parameters, such as temperature and flow rate, to continuously monitor the process and detect potential sources of error at an early stage,” explains Gerauer. “Other integrated safety functions include the detection of air bubbles, blockages, curing and process interruptions. These diverse measures enable us to guarantee a high level of process reliability and consistent product quality.”

This bead was plowed through by a dispensing nozzle. Error-proofing technology can prevent this type of problem from occurring. Illustration courtesy Coherix Inc.

 

Error-Proofing Tools

Engineers have a variety of products available to error-proof adhesive dispensing applications.

For example, Coherix has developed advanced technology to monitor and adjust the application of adhesives and sealants. Its 3D laser-based, computer-vision systems can track the application of adhesive beads as small in width as two human hairs. It works at speeds up to 1,000 times per second faster than 2D systems currently in use.

The 3D Mini sensor provides 100 percent inline inspection of adhesive beads as they are being dispensed. Its small footprint enables the device to be mounted around the dispensing nozzle. Four high-speed sensors provide a 360-degree view of the bead in any dispensing direction with no added complexity to robot programming.

“3D Mini’s adaptive process control (APC) eliminates the need for additional inspection stations,” claims Dennig. “[It features] real-time software that learns, compares, adjusts on-the-fly and does not require human intervention. Our newest APC feature, lateral tracking, dynamically adapts to each part’s individual variations to maintain acceptable bead-to-edge distance, preventing scrapped parts and unwanted squeeze-out.”

Other error-proofing features built into Coherix products include:

• AutoRepair, which automatically repairs gaps, bubbles, neck downs and low volume with no human intervention.
• Z-Tracking dynamically adapts to each component’s individual variations to maintain acceptable tip to part distance, preventing broken nozzles and scrapped parts.
• Volume Adaptive Control detects instantaneous volume variation and automatically adapts the bead volume, ensuring a high-quality bead of the specified volume is dispensed.
• LocationMaster locates a part in 3D space and sends offset data to the robot to alter the dispensing path accordingly.
• Data Analytics is leveraged to analyze trends and variation inline, so the right conclusions can be drawn and the necessary measures initiated, enabling continuous improvements in efficiency and quality.

The latest error-proofing tool from Marco is the StepDot Dispensing Head, a system that combines ultra-fast dispensing with synchronized camera feedback. While the piezo valve dispenses, a camera tracks movement and verifies results live, with image analysis handled on Nvidia Jetson.
“With our new Gantry System, camera-based correction takes over fine positioning, adjusting alignment dynamically to hit sub-100 micrometer targets,” explains Herbstritt. “As a result, we deliver a fast, adaptive dispensing application with closed-loop verification.

“We use high-precision piezo valves that deliver consistent dosing, even at high speed,” says Herbstritt. “Every dispense is monitored in real time by integrated cameras with controlled lighting to ensure contrast and visibility across different surfaces. Image analysis is processed directly on the system using Jetson, allowing us to detect issues without latency.

“To capture 3D characteristics such as height variations, we use a pulsed red laser,” Herbstritt points out. “Our bubble sensors check for trapped air in media lines, which is a common but critical failure source in adhesive processes. All components are synchronized by a dispensing control unit that manages triggers, controls the cameras and dosing channels, interfaces with robots and HMIs, and logs process data for traceability.”

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Austin has been senior editor for ASSEMBLY Magazine since September 1999. He has more than 21 years of b-to-b publishing experience and has written about a wide variety of manufacturing and engineering topics. Austin is a graduate of the University of Michigan.

 

KEYWORDS: dispensing equipment, error-proofing, quality control, dispensing vision, 3D inspection