Last Updated March 2023
Predicting production outcomes in manufacturing relies on accurate data that calculates the variables that actually affect things like reliability, performance, and longevity of the product, like the soundness of bonds. There are countless tests to examine every conceivably measurable aspect of production.
Metrology is inextricable from quality assessment. But are manufacturers measuring everything they need to guarantee a zero-defect production process?
If all the aspects that determine the quality of a process, like adhesion, aren’t measured and controlled, then how can you be certain that every product is flawless?
It’s no secret that adhesion, in all its many forms (e.g., bonding, coating, printing, painting, gluing, laminating, over molding, sealing, etc.), is a concern for nearly all manufacturers in every major industry. And adhesion is difficult to understand and even harder to control. Adhesion is reliant upon the adhesive or coating, the curing process, and the quality of the surface being adhered to. Unless you have the proper way to manage those three elements adhesion is reliant upon, you face possible critical bond failures, which could shut down your factories. This increases your overall production costs and bottlenecks, all factors of your supply chain.
Manufacturers have a firm grasp on the proper composition of the adhesive or coating they need for a given application. What’s typically left to chance is the quality of the bond surface. The chemical characteristics of the top 1-5 molecular layers of a material can be all that stands between perfect, strong adhesion that meets all performance requirements and weak, unpredictable bonds that fail intermittently. Those failures will ultimately lead to a high scrap rate, large amounts of R&D backtracking and rework, not to mention a loss of raw materials.
Chemical cleanliness is a specific state of cleanliness where the molecules present on a surface are adhesion-promoting or at least not detrimental to adhesion. This is a difficult characteristic to measure without the right method, and there are very few techniques that are sensitive enough to detect weak bonds. There are even fewer devices that make these measurements accessible during automation or “near to action” on real parts.
Using Contact Angle Measurements to Predict Adhesion
Contact angle measurements are sensitive to extremely minute surface energy changes and, therefore, can detect, with ruthless accuracy, how prepared a surface is for adhesion. Every place in a production process where the surface has an opportunity to change in a way that affects adhesion outcomes is called a Critical Control Point (CCP).
When contact angle measurements are taken at each critical control point, manufacturers can be certain they know whether the surfaces of their raw materials are within the tolerances for excellent adhesion, thus guaranteeing the maximum output at a much higher quality level.
The sensitivity of these measurements makes them perfect for root cause analysis as they can easily forecast where in the process, something is going awry. One of the examples we’ll discuss in this article includes the story of when one of the world’s leading manufacturers of high-performance wires and cables was experiencing inexplicable and intermittent failures of adhesion that needed to be dealt with. Once they employed contact angle measurements to measure surface energy and get an accurate picture of what their surface quality looked like, the solution became clear and decisive action was able to be taken.
The result? A high-efficiency production process that limited the amount of scrap and kept product quality sky-high.
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The Cost of Adhesion Failure: High Scrap Rates and Increased Downtime
Another pertinent example of the cost of adhesion failure brings us back to the early 2010s when a manufacturer of medical cable and connectors made a critical change to their production process.
The cables they produce have silicone over-molded connectors on each end. The connectors are typically chrome-plated, but to increase manufacturing efficiency, they decided to remove a chrome-plating step and instead started molding silicone over the chrome plating, but it wasn’t adhering consistently.
For one year, the manufacturer experienced intermittent bonding failures, some days resulting in nearly 60% of the day’s production being scrapped, but then the next day, only 3% would fail - an untenable gap in reliability that was creating a large amount of scrap.
Rework for those hundreds of failed parts was taking resources away from producing high-quality parts the first time around. Every cable that is reworked equals one cable that is not being produced. The cycle that is run for the reworked cable is the same cycle run for a new cable. So, each rework represents a double loss in raw materials and doubles the amount of scrap.
The manufacturer conducted rigorous root cause analysis by examining their cleaning and handling process. They enlisted the help of a laboratory, but the data they received was vague and consisted mostly of a verbal report that nothing unusual was found. This dead end left the manufacturer on its own again.
Subsequent Failure Modes and Effects Analysis (FMEA) efforts led them to begin an initiative to reduce the amount of manual handling each part would go through in order to reduce the risk of contamination. They even went through an exercise to closely monitor temperature and humidity in their facility to see if there was a meaningful impact, but nothing was successful.
The over molded connector then become the number one reject in the plant - a nightmare for engineers and management, not to mention donors.
They continued internal FMEA tests for a year or two before reaching out to Brighton Science to help investigate the issue, diagnose the root cause, and implement a permanent solution. That’s when the manufacturer decided to start monitoring surface quality.
Through examining exactly how the parts were failing - at the interface between the silicone and metal - and how extra cleaning and priming steps greatly increased the success of the bond, it became clear that unidentified contaminants present on the connector were the likely root cause of the adhesion failure.
They began a closer examination of the cleaning process that the metal components were subjected to. During one of the first visits to the manufacturer’s facility, Brighton Science was able to show their technicians that if you scrubbed the side of the metal housing, you could have a positive impact on surface energy. This simple demonstration made it evident that whatever contaminant was on the surface, it was removable. However, sitting there and scrubbing down every component in production wasn’t a viable situation, nor a good use of company time.
After our experts were able to identify the contaminants on the metal housing, we took a look at strategies for optimizing the cleaning processes the manufacturer was currently using.
The Challenges of Process Changes in Medical Device Manufacturing
In medical device manufacturing, OEMs are limited in the changes they can implement. Once a certain cleaning chemical or piece of equipment is approved, any changes to that chemistry or equipment need to go through additional vetting and approval processes by a regulatory body. These product verification procedures can require significant effort and can be time intensive, so any modifications needed to be double-checked before being passed to the regulatory committee.
This particular cable manufacturer had been using a vapor degreaser for the primary cleaning step before conducting the over-molding process. Using the handheld Surface Analyst to take contact angle measurements, the investigative team was able to see major inconsistencies in parts that came out of the vapor degreaser - meaning it wasn’t getting clean enough or even at all in certain parts.
Root Cause Analysis using FTIR and Contact Angle Measurements
Samples of the manufacturer’s vapor degreaser cleaning fluids were sent to the Brighton Science Surface Laboratory to see if the contaminants found on the metal surfaces were being transferred during the cleaning process.
Through FTIR spectroscopy analysis of the degreaser bath solution, we were able to determine that there was silicone in the cleaning fluids, the probable source of contamination.
Using this knowledge to make informed manufacturing process decisions, the engineers at the cable manufacturer began overhauling their preventative maintenance (PM) program. More frequent changes in the cleaning chemistry, as well as more thorough cleaning of the interior of the tank once the fluid is removed, helped reduce the risk of cross-contamination among parts from washer fluid drag out.
The Surface Analyst was used in two ways to assist the process:
- As a routine quality control metric to ensure parts leaving the degreaser were sufficiently clean
- A predictive trending metric to let the quality engineering team anticipate when cleaning tank changeovers were necessary
Over time, using this new data-driven approach, it became clear that the vapor degreaser just wasn’t able to produce the cleanliness levels needed. So, instead of spending the money to change out their equipment and the pain of going through the expensive requalification process, the engineering team opted to convert the vapor degreaser into an ultrasonic washer.
Using the ultrasonic washer, not only were surfaces routinely and consistently ready for bonding, but adding 30 seconds of plasma pen treatments brought contamination to unquestionably low levels (See Figure 1).
Figure 1. With 30 seconds of treatment from a plasma pen, we found contamination levels were dramatically reduced.
The knowledge of our surface intelligence experts and the Surface Analyst technology helped put an end to a costly and frustrating 5+ years of trial-and-error and failed FMEA.
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Measuring Surface Cleanliness Leads to Measurably Better Adhesion Outcomes
Using the Surface Analyst to test 100% of the metal housings before they go into and after they come out of the washer and then correlating the surface quality data the Surface Analyst provides, equipped this renowned cable manufacturer with a cleaning process that is finally producing the level of successfully bonded connectors they need to satisfy their customers’ demands.
They began seeing low scrap rates, declining as much as 95%), a feat that seemed impossible just months earlier. They were able to accomplish their production and quality goals while, in turn, avoiding a significant capital expenditure in acquiring and commissioning new cleaning equipment and getting the process approved by a regulatory board.
Unlike the first laboratory they looked to for help, the comprehensive data supplied by Brighton Science allowed them to make knowledgeable decisions and see measurable gains from the new approach.
There's no programmable setting on a molding machine that's going to guarantee it will bond. That would make manufacturers’ lives much easier. Instead, if you can guarantee the housing is clean 100% of the time, then bonding will be successful 100% of the time. Once the cable manufacturer was able to measure the cleanliness of their metal surfaces and verify that each one was always as clean as necessary, then their bonding procedure was far more successful.
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