Case Study

N95 MASK PRESS

Background:

The COVID-19 crisis of 2020 has led to a global shortage of N95 masks, resulting in a critical need. In response, Diabase has created an open source solution: a heat-staking mask press, manufactured with the H-Series along with the support of other machining tools.  The design files for this prototype has been made available to the public through GitHub, under a GPLv3 license.

After just a few short weeks of development Diabase was invited to present the system to the Department of Defense, who issued a call for American manufacturers to propose solutions to address the coronavirus pandemic. 

 

The H-Series has proved invaluable to the construction of the mask press, given its versatility and utility.  The open, accessible construction combined with diverse workholdings and motion control options makes the H-Series a cornerstone in any shop.  With projects that require small feature machining, as with the mask press (detailed below), the H-Series can be the tool of choice, complementing larger and more expensive equipment.  

Process:

 

A simple prototype press was initially created to define the time, temperature, and pressure requirements of the various non-woven materials.  The 12k rpm spindle on the H-Series was used to accurately machine a recessed grid pattern and small diameter bored holes for the aluminum die plates. 

With the results from the time-temp-pressure tests, a three-cavity mask press was designed and built using materials on-hand.  While the bulk machining of the press components was done on a vertical machining center, the finish machining and many of the secondary system components was completed using the H-Series.

 

The goal here was to use a single press operation to both form and bond the multiple layers of melt-blown non-woven material. The concept is shown in the whiteboard drawing below. The fabric would be loaded in spool form on one side of the press, fed through idler rollers to the dies, pulled through by feed rollers, and slit into individual mask forms ready for secondary assembly steps.

The first main assembly in the build was the die set. This consisted of two heated 3-cavity die plates and three mask forms.  After machining the primary features of the die plates on a VMC, the H-Series was used to cut the finely spaced features necessary for heat staking. Because of the tiny cutter required to mill these features, this is an extremely slow process. Using the H-Series for these features in a secondary operation freed up the VMC for cutting the other die components.

The frame for the material feed system utilized T-slot aluminum extrusion. The recessed fasteners for attaching extrusion members at a right angle required a hole to be bored in one of the T-slots. This was also an ideal job for the H-Series. The parts were quickly fixtured with the standard flat vise in the dovetail plate. The touch probe was used to quickly locate a corner of the workpiece to set the work offset. 

In order to attach the fabric spools to their mounting shafts, spacers were required to ensure concentric motion for consistent feed tension. These spacers were printed on the H-Series using a 98A TPU. The urethane material was chosen to allow a secure press fit in order to transfer torque between the shaft and spool.

Finally, in order to make the idler rollers for the feed system, a 3” ABS pipe was used. The H-Series allowed quick modification of off-the-shelf end caps for mounting the tubing. Rather than machining soft jaws to mount the end caps in a vise, the old machinist’s trick of double-sided tape was deployed. The tool loads of a ⅛” end mill in ABS plastic are low enough that the bond of 3M tape was more than sufficient. By running the “find center of cavity” probing function on the H-Series, the press-fit bore was machined extremely concentric with the ID of the end cap. This guaranteed that the OD of the tube would run very true to the OD of the shaft.

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