Building a Better Tool
Diamond Tool and Engineering is a precision plastic injection mold builder headquartered in Bertha, Minnesota, that specializes in tight-tolerance, multi-cavity tooling for the medical industry. Diamond recently built an injection mold that was designed to push the limits of traditional moldmaking, and collaboration was essential to the project’s success.
Four years ago Diamond built a 600-pound six-rotation, hydraulic unscrewing mold for a medical cap made from a medical-grade polycarbonate resin using a hydraulic cylinder. The resin required the part to cool completely and for unscrewing to take place very slowly. The mold design caused inefficient cooling of the runner and part, and a cold runner tunnel gate added 0.046 ounce of material, an 87-percent increase in material. A 35- to 40-second cycle time was required on this traditionally designed tool—with a round cooling channel around the outside of the cavity block, a hydraulic unscrewing mechanism and a cold runner. This left Diamond engineers wondering how they could battle the complexities of unthreading a polycarbonate part without smearing the threads, and do it quickly.
To beat this time and to build a better tool, Diamond partnered with several technology suppliers to incorporate a dovetail collapsing core and a 3D printed stainless steel cavity block with conformal cooling. Partners include Toshiba for the press and processing; 3D Systems for the machine to print the cavity block; 3DPrintedParts.com to print the cavity block; Progressive for the wireless CVE monitor, slide locks and other mold components; Roehr Tool for the Dovetail core and machining; DME for the mold base, and Mold-Masters for the valve-gate hot drop.
Roehr Tool provided a DT collapsing core for the threaded undercuts (14 mm), which created the inside thread detail, eliminating the need for a slow unscrewing mechanism, hydraulics or other complex actuation.
3DPrintedParts.com direct metal laser melted the 3D-printed cavity block with conformal cooling, focusing around the hot tip, as this is the hottest part after it completes injection of the plastic.
The increase in cooling and simplicity via the smaller frame with the collapsing core and no hydraulics to run the mold, brought on by the combination of these technologies resulted in more than a 50-percent reduction in cycle time on this class cleanroom mold.
“We changed a few things on the part in terms of how the top functioned, but the resin, size and threaded undercuts remained,” says Kevin Finley, sales manager for Diamond Tool. “The result was 47-percent runner and gate waste savings due to the valve gate hot tip, much quicker cooling from 35 seconds to under 10 seconds and very fast cycle time. Also, mold setup and run was simplified due to the quicker purge allowed by the hot tip, no hydraulics to hook up and ejection handled with shoulder bolts pulling the B plate forward to strip the parts.”
The mold ran consistently at 6.7 seconds and hit a record time of 3.8 seconds, at local trade event, while still producing visually consistent parts. It ran again last month at MD&M West/Plastec West in Anaheim, but needed to be slowed down for the automation cell developed by Toshiba. It hit 7.5 seconds for three days straight.
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