From auto parts to running shoes, manufacturers constantly battle one chronic quality issue with adhesive and sealant dispensing on a production line – bubbles. Even the tiniest air bubbles can ruin the integrity of a seal or adhesive. On automotive powertrain lines, for example, components such as electronic subsystems, valve covers, oil pan covers, and various transmission assemblies require a precise and uniform bead of sealant to ensure an oil-tight integrity bond.
Where dispensing can go wrong
With today’s technology, adhesives, sealants, lubricants, coatings, and thermal interface materials can all be dispensed at high speed in milliliter, microliter, and nanoliter volumes. These materials are typically dispensed by precision displacement pumps that deliver material at a constant rate as the pump’s nozzle moves relative to the part.
Still, problems can occur:
- Mechanical – Nozzles partially blocked, bent, otherwise damaged
- Operator – Wrong nozzle used for application
- Variations – Temperature, speed, pressure affect viscosity, depth of the bead
- Supply line – Swapping out an empty dispensing barrel can lead to air in the line, creating a bubble
Tiny air bubbles present an unusually difficult challenge because the bubble defect is often less than 25% of the normal and acceptable pump ripple. This is compounded by the small modulations of the nominal discharge pressure. The result is a potential leakage path not easily detected during the assembly process.
See what a vision system can’t
Data is the key to tackling this challenge. The question is how do you collect, manage, and analyze all the data you need to detect and correct errors as they arise; prevent those errors from happening again; and prove compliance to customers and regulators?
The common choice for managing quality on a dispensing station is a vision system. But a vision system can only record bead quality, provided the lighting is just right so it has a clear image of the bead. It cannot collect the data to detect trapped air.
An American Tier 1 supplier in the automotive electronics industry wanted to look deeper than machine vision to tackle bubbles, drive quality, and carry out predictive maintenance on a new fuel control module production line. These electronic modules are critical to engine performance and must be protected from exposure to moisture and hot engine fluids. To ensure a perfect seal, the dispense operation for the sealant must be highly accurate, precise, and repeatable. Any bubbles can cause seal failure.
Joining forces battles the bubble
The manufacturer turned to fluid handling products and systems company Graco. Graco’s search for a more reliable dispense monitoring technology to couple with its dispense equipment led it to Sciemetric.
This collaboration resulted in the Graco Dispense Analyzer powered by Sciemetric, a more economical and effective process monitoring system for dispensing versus the typical vision system. Graco now offers Sciemetric technology exclusively on its dispense gasketing systems.
This system can detect miniscule air bubbles and bead errors in real-time and advise whether these issues will compromise the final product. It can also monitor and record data about each dispense such as pressure achieved and decay failures, average, maximum and minimum pressure, time of dispense, and other information.
This is accomplished by levering Sciemetric’s expertise in signature analysis. Sciemetric uses sensors to capture the full waveform of a process – hundreds of thousands of data points per cycle. Everything that happened during an operation can be visualized for easy interpretation.
Catching bubbles to ensure first-time quality
When it comes to detecting bubbles, a waveform picks up the blow-out that will occur after the dispense. When a material that is typically not compressible is applied using high pressure, trapped air will rapidly expand when exposed to the plant’s ambient air pressure. This change in pressure within the dispensed material isn’t visible to the human or machine eye. Micro-bubbles that can compromise integrity typically remain hidden to visual inspection, but they can’t hide in a waveform.
“The greatest challenge we seek to address for our customers is reducing the cost of rework – first-time quality is paramount,” says Graco Global Sales Manager Todd White.
Engine gaskets, typically vulcanized material applied at room temperature, demand reliable quality assurance systems. Without the ability to catch a flaw at the time of the dispense, or during the fitting of engine parts, the only chance to detect a compromised seal is during an end-of-line engine hot test. A flaw detected at that point means a full engine tear down. And more engines could have passed down the line with the same flaw.
“In the worst-case scenario, a failure from the flaw doesn’t occur until the consumer has that vehicle sitting in the driveway, puddling oil on the ground,” White says. “It becomes a warranty issue and the dealer has to pull the engine. But we consider the cost of that warranty repair less impactful than the word-of-mouth negative perception it creates for that brand. How do you put a price on that?”
Waveform makes a difference
The manufacturer that first used the Graco-Sciemetric system on its engine fuel control module production line:
- Collected reliable process information, tracked dispensing with a level of precision previously not possible
- Gathered useful diagnostic data for its entire dispense operation
During manufacturing line setup, engineers determined that a problem – the system dispensing too slowly – was the fault of a programmable logic controller that communicates using an Ethernet protocol. It took 30 minutes to trouble-shoot the problem, versus several weeks.
There is an easy way to conquer bubbles – a sensor-based system that collects and visualizes the full waveform of the dispensing operation and can tie into sophisticated big data management and analytics tools. To win the war on bubbles, you must look beyond the surface and harness the power of your data.
Sciemetric Instruments Inc.
About the author: Aaron Alberts, an account manager at Sciemetric Instruments, has 12 years of experience working with automotive, industrial diesel, and aerospace customers. He can be reached at firstname.lastname@example.org.