Molding Better Miniature Medical Parts with CAM

This atomizer dome directs and accelerates medications to the device’s orifice.

Wolfe Tory Medical Inc., Salt Lake City, UT, is a supplier of miniature, syringe-driven atomizers for drug delivery. The company was eager to develop a relationship with a U.S.-based medical components molding specialist that could consistently hold tight tolerances for critical components of its products. This need reached high priority status in 2004 when the firm’s current supplier announced that it would be moving all of its tool building and molding operations to Asia.

Perry Croll, vice president, engineering and RAQA, Wolfe Tory, says, “We had no desire to have our tools maintained and our parts molded in Asia. We had also concluded that it was very important for us to work with a molder that was 100% medical. After two unsuccessful attempts with other sources, we contracted to work with Image Molding Inc., Denver, CO, an ISO 13485-certified firm that only produces medical components. That decision was based on my previous experience working with Ewan Grantham, co-owner of the company (along with Tony Lonardo) and someone I consider to be an exceptional toolmaker, molder, and designer.”

In short order, SolidWorks CAD files were flying back and forth between Croll and Grantham over the Internet as the two collaborated on the next generation of Wolfe Tory Medical’s patented Mucosal Atomization Devices (MAD) designed to provide precise micro-particle distribution of topical solutions across the nasal and oropharyngeal mucous membranes. Even in the preliminary phases of this work, Grantham had already imported the design into his Mastercam Mill Software (from CNC Software Inc., Tolland, CT) to begin resolving manufacturability issues surrounding the tooling.

Crux of the Problem
The Wolf Tory MAD is a tiny device that attaches to a syringe directly, or to tubing with a standard Luer connector. The clinician draws medication into the syringe then navigates the delivery end of the atomizer via the nose or trachea to within close proximity of the mucosal area requiring treatment. The clinician plunges the syringe, and the medication transforms from a liquid state to a fine mist that has a very specific spray pattern, plume geometry, and particles that are no smaller than 10µ and no larger than 30µ in diameter.

Top: Attention to detail and a keen eye are required when working with components requiring consistently tight tolerances. Bottom: The Wolfe Tory Atomizer creates a plume of medication with particle sizes held between 10µ to 30µ. Atomization of fluid is by ejecting it through a 0.0090" diameter orifice. Critical dimensions of the molded components for this device must be held to within ±0.0010". Image Molding of Denver, CO, used Mastercam X5 Mill, from CNC  Software, Tolland, CT, to create CNC programs for cutting the fragile EDM electrodes used in making the mold’s core’s and cavities. In some cases, tolerances for the electrodes had to be held to within ±0.0005" in order to meet final product specifications.

Croll explains that particle size is particularly important because it has a direct bearing on the bioavailability of the medication. Particles that are too large would be absorbed too slowly and ones that are too fine could be absorbed so rapidly (by the alveoli in the lungs for example) that they would pass through with only a minimal dwell time in the target area. As such, precision manufacturing of particular atomizer components, the turbine section in the mixing chamber, the cone, and the orifice, are of critical importance.

The delivery section of the atomizer is a small component that is only 0.0900" long and 0.0600" in diameter. It has a conical section that has a 0.0150" diameter that leads up to an orifice that is just 0.0090" in diameter. Direction of fluid is to the cone from a turbine section in the devices mixing chamber. Centrifugal force accelerates the fluid up the cone in a spiral pattern until it projects from the orifice as fine mist.

“For these components to work effectively,” Croll says, “they must be manufactured to a level of repeatability comparable to automotive fuel injectors.”

However, machining of these disposable device components is not from exotic alloys. Rather production is through molding from relatively inexpensive plastic. The trick is to minimize any blemishes in the tooling that might cause even the smallest amount of flash that would almost certainly compromise product performance.

What You See is What You Get
“My challenge to Ewan was to have him figure out how to make these super critical parts with very tight process variability resulting in a CPC of 1.33 or higher. We were asking him to hold tolerances of ±0.0010" and in some cases 0.0005". He has done that on a regular basis.”

In the early stages of the project, Grantham took Croll’s SolidWorks file and evaluated all of the critical aspects of the design for manufacturability. He also imported the SolidWorks into his Mastercam Mill software, generating preliminary toolpaths for manufacturing the EDM electrodes needed for burning the mold cores and cavities. He used Mastercam’s Backplot simulation feature to check the cutting action of the tool and also estimate machining time for these highly finished electrodes – four or five would be required for each core and each cavity – so that he could obtain an accurate estimate of machining costs.

Using this information, in combination with his experience in medical part tool design and molding, Grantham made a number of design change recommendations for improving manufacturing consistency without compromising the functionality of the device. Once the final tool design received approval, it was time to create the toolpaths for cutting the critical EDM electrodes using Mastercam.

This is where it required great care in order to eliminate inappropriate presentation of the tool to corners and other close geometries or flexing of the tool. Either of these could create tiny blemishes in the electrodes, which, in turn, would result in surface imperfections to the core and cavity that would result in flash during molding. Of particular importance was the 0.0090" orifice where the slightest amount of flash or out-of-roundness could compromise the plume pattern and particle size.

Finished Atomizer Core

To this end, Image Molding’s CNC programmer, Wayne Gruver, used Mastercam’s Verify simulation feature to examine the resulting condition of the electrode, virtually, from every possible angle after creation of the toolpath. He also used Verify to examine the entire CAM model of the machined part after the written manufacturing program was complete. When changes are required, Mastercam provides tools that allow him to zoom into the area of concern and make small incremental changes to the toolpath to correct the problem.

Grantham states, “It is enormously helpful to be able to blow up our electrode which is smaller than a pea and see it the size of basketball. Viewing the part in this way always allows us to see imperfections in the electrode that could cause problems in the tool during molding. Frequent use of Verify helps us accelerate the pace of tool development because we do not have to be continually recutting electrodes to get them right. We only cut once and we are done. We have complete confidence in this process.”

Smaller and Better Things
Since undertaking the initial project for tool development and molding, Image Molding has become the primary source for prototype tool development, tool maintenance, and production molding for Wolfe Tory Medical. Recently Grantham took on a project that involved reconditioning a 16-cavity tool (sourced offshore) to bring it up to the company’s exacting repeatability standards.

He has also worked with Croll to scale down one of Wolfe Tory’s most popular products to manufacture what Croll calls, The World’s Smallest Atomizer.

CNC Software Inc. (Mastercam)
Tolland, CT
www.mastercam.com

Wolfe Tory Medical Inc.
Salt Lake City, UT
800.788.7999

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