To assemble today's highly demanding medical devices, device makers need adhesives and application equipment to perform superbly. Keeping a close eye on the whole assembly process is a must because of the exacting nature of the entire package, including the substrate and surface treatment. But scrutinizing the manufacturing process is only one necessary measure; device makers must also take certain steps before assembly.

For one, they should partner with both the adhesive manufacturer and the dispensing equipment supplier to ensure that the adhesive will perform without a glitch. Second, they may need to get help from automation or integration experts to verify that all components of the assembly system work well together. Here are other important precautions to take in assembling medical devices:

Analyze the process.

You must carefully analyze the application before establishing the parameters to which the entire process will adhere. Engineers often do this by inspecting other products believed to have comparable assembly requirements. Sometimes, they decide to use the same adhesive that joined, potted or otherwise put together a current device even though its assembly needs are completely different. Remember that this approach can yield satisfactory results or lead to the failure of the adhesive because of misapplication.

To avoid the latter situation, you need to form a partnership with the adhesive manufacturer or supplier. Make sure that the supplier provides you with test data and samples to demonstrate that its adhesive is right for the job. You must consider factors such as thermal stresses, strain and durability.

Cost should certainly factor into your decision process, but don't let it outrank the adhesive's performance characteristics. And in figuring out which adhesive will perform best, consider the speed of your production. Will your desired rate of production entail uncomplicated manual techniques or more intricate automated work cells? By defining the production speed, you can determine the type of adhesive and dispenser you will need and how you will have to handle the process after curing.

Control environmental factors.

You will need to keep assembly areas clean, in accordance with Federal Standard 209E. For example, the standard assigns cleanrooms a classification number such as 10,000, meaning that the maximum particulate level, measured in parts per million, should not exceed that number within these rooms.

To make sure you're in compliance, install and regularly monitor an air-filtration system that can maintain the required particulate-level limits. Also, check for proper worker clothing, eye protection and facial coverings, all of which are usually required to prevent the contamination of the assembly area. You must also keep temperature and humidity within specified levels to avert product flaws. And if you use dispensing equipment running on pneumatic cylinders, you must exhaust air from the cylinders to keep the assembly area air clear from lubricating oils and other contaminants.

Choose dispensing equipment carefully.

In selecting the most ideal dispensing device for your medical application, you have to consider many factors. For starters, you have to make sure you adhere to rules concerning the construction and cleanliness of such devices. Also, you have to gain knowledge of every aspect of the material to be dispensed. Furthermore, in choosing the pump or valve, you have to consider the dispense pattern, such as beads or dots, to be followed and rate at which the adhesive must be applied.

The material's filler content can make it too viscous to be delivered by certain sizes of hoses, tubing, needles or check valves. Filler particle size will also raise similar issues. Remember that particles can be nonabrasive or extremely abrasive, based on whether they are crystalline or amorphous. The filler's hardness will affect the choice of the pump or valve's construction materials. Additionally, you have to factor in the adhesive's corrosive properties in metal and seal selection.

Certain material viscosities call for specific dispenser styles. For example, various low-viscosity fluids or adhesives could be properly dispensed by a simple time-and-pressure valve with disposable pinch tubing. Meanwhile, high-viscosity materials may be delivered by rod-displacement-type pumps or valves, but keep in mind that this style is harder to clean.

Pay attention to the pump style.

You can choose from 7 basic pump types—piston, metering, rod metering, ball-check, peristaltic, gear and progressive cavity. Remember that each is suited for certain materials.

For example, piston pumps are very accurate and work well with shot or short-duration bead applications. They can handle filled resins or materials much better than gear pumps can, but they cannot sustain long-duration continuous flows. They are sensitive to viscosity, able to cycle nearly 30 times per minute if the material is almost water-thin and only about half that rate if the material resembles molasses.

The other kinds of pumps also offer specific advantages. For example, the metering pump can keep metering accuracy steady through changes in viscosity while the ball-check style can pump in both directions. Meanwhile, the fifth pump design—peristaltic—appeals to many applications because its wetted portion can be readily disposed.

The last two pump designs excel in continuous flow applications. Gear-style pumps are ideal for both steady flow and bead applications, but you must take care not to use them with filled materials. This is because fillers shorten gear life, which can negatively impact pump accuracy. In comparison, the last pump style—progressive cavity—presents a fitting choice if you want to accurately and continuously convey high-viscosity, abrasive-filled materials to device parts.

You can take advantage of the different pump styles' strengths by combining them in a single machine frame and utilizing cutting-edge electronic drives and controls. In this manner, you can create a sophisticated metering, mixing and dispensing system for your assembly process. Additionally, wherever applicable, consider using robots or work cell hardware because they can reduce rejects and boost throughput, leading to substantial savings in production costs.

Embrace new technology.

Indeed, pump technologies are rapidly improving and driving the advancement of adhesive dispensing systems for medical device applications. Manufacturers should not shy away from new technologies but rather, consider applying them to optimize the assembly of medical devices.

Source: Critical Care in Dispensing
Jerry Drake
Medical Device & Diagnostic Industry, May 2003
http://www.devicelink.com