Conventional Mold Design Changes Were Not an Option
How Mold-Vac helped eliminate flow lines, clogged vents and significant outgassing
A consumer packaging molder faced a major problem. While developing a new cosmetic tub assembly they discovered the PET they had chosen was causing molding issues. The parts design required multiple gate locations to fill with flow lengths over 4 inches and cross-sections less than .100 inch, but resulted in unacceptable knit lines from the multiple flow fronts. Running high temperatures and aggressive fill speeds to minimize the knit lines resulted in significant outgassing of the material, which clogged vents quickly, preventing a sustainable production cycle.
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The rapidly clogging vents, which did not allow the mold to run even a full day, meant frequent shut-downs for cleaning vents, mold disassembly and maintenance. Due to the design of the part and mold, many of the vents were static and not self-cleaning, which required mold teardowns for manual cleaning. This would increase exponentially once production ramped up, shrinking productivity, impacting quality, increasing waste and squeezing delivery times.
Redesigning the tool, however, wasn’t an option. They’d already designed and engineered full assemblies and gating, created prototypes for three similar parts, and run samples that had been approved.
“Based on the prototype results, we saw this would be a hard-to-fill mold,” said Accede Mold & Tool Operations VP Brett Lindenmuth, whose company was chosen to scale up to a 4-cavity tool for the customer. “We had to address the knit lines and venting issues and we quickly knew conventional changes in tool design to improve flow were just not feasible. Conventional vents were already maximized to the point where they were flashing and not making an acceptable part. That’s when we recommended they use Mold-Vac. As soon as we integrated the unit into the molding assembly, sealing conventional vents to atmosphere and adding a vacuum channel for the Mold-Vac system, there was an immediate improvement in part cosmetics, as well as injection and release properties.” The part was easier to fill, knit lines were minimized and virtually unnoticeable, vents remained open so fill properties did not change during extended runs and the blow-back feature of the Mold-Vac system also aided in ejection and part release from the mold.
Mold-Vac from CAE Services is a standalone system designed to eliminate molding problems resulting from gas and air entrapment. Its vacuum/blowback functions were designed specifically for injection molding. The two-phases of the blowback function are: Phase 1 – Mold-Vac provides a burst of air just prior to the mold opening to assist in part ejection; Phase 2 – Compressed air to purges vented pins, primarily stationary pins that are not self-cleaning. This helps eliminate residue build-up and helps reduce mold maintenance. Mold-Vac’s custom precision microprocessor allows for precise control of vacuum and blowback functions. Vacuum control can be adjusted to 1/10th of a second, eliminating flash and improving part quality. Its rapid vacuum capability removes air and gas to improve resin flow and minimizes the outgassing that clogs vents.
When the Mold-Vac is recommended, Accede customers see first-hand how the
Mold-Vac improves part quality and injection and release.
“Over the years, I have seen customers try to use other vacuum systems to fix molding issues, but with limited success,” stated Brett. “However, those systems were not built to displace the volume of air and gas. Mold-Vac, on the other hand, has a surge tank that rapidly evacuates large volumes. It was designed for injection molding.” The Mold-Vac surge tank serves as a vacuum reservoir, removing air and gas instantly. A venturi-style system would have to have up to 150 cfm right at the machine to achieve a similar instantaneous vacuum.
Accede was first introduced to Mold-Vac about eight years ago when a customer asked them to look at the unit and recommend whether or not it would solve their molding issues. In addition to recommending Mold-Vac for that customer, Accede has continued to do so whenever they believe it’s the best solution for a challenging mold design, such as where additional venting, re-design of the part, or re-engineering of the mold are not acceptable options or won’t solve the problems experienced during molding.
...there was an immediate improvement
in part cosmetics, as well as injection
and release properties.
Brett Lindenmuth, Accede
“As part of our service, we have injection molding units from 80 to 400 ton, multi-shot presses, and a variety of auxiliary equipment,” added Brett. “When a customer comes to our company for on-site trials, we want them to see the entire molding process. If we are recommending the Mold-Vac, we want to show how it works, so Accede purchased a unit for ourselves.”
If the customer agrees with Accede’s recommendation to use a Mold-Vac for their assembly, they can purchase it directly from CAE Services, or Accede will purchase it for them. “We only recommend,” explains Brett. “Our goal is to provide the customer with the best solution.”
In addition to owning several molding machines, Accede has invested in several
auxiliaries, including Mold-Vac. If Accede recommends using Mold-Vac they want
customers to see how it performs on the customers mold.
Selecting a Mold-Vac unit is based on first-stage fill times, cavitation and part volume. For example, if a mold had a fill time of 1.5 seconds, the recommended Mold-Vac model would be able to create a vacuum in 1-second or less. “CAE has supplied us with the data and volume information to determine the right size unit,” said Brett. “Their design and engineering experience has been very helpful in ensuring that we recommend the right unit.” Selecting the right Mold-Vac unit is based upon a number of variables, such as 1st stage fill time, total cycle time, part volume (in3), cavitation and material.
Another design challenge for Accede and Mold-Vac was a recent project on a medical labware mold. The mold had 96 products, called Wells, and mold flow showed significant gas entrapment as a major concern in each of the 96 Wells on the part, “so we considered the Mold-Vac as part of the whole molding process solution from the start,” said Brett. “When the customer saw the extent of gas trapping, they were immediately open to adding the Mold-Vac unit to ensure higher part quality.”
While the goal is to design and engineer a tool that provides optimum flow, high quality, fast cycle times, and minimal tool maintenance, some mold assemblies still have fill challenges, such as Accede’s customer molding cosmetic tubs. That’s when the Mold-Vac provides an efficient and economical solution. “They are using the Mold-Vac and running longer before the mold requires cleaning or clearing vents, explained Brett. “Its blowback helps with injection and release.”
The real proof came after the customer did their own test, molding with and without Mold-Vac. “They’ve been running the Mold-Vac all the time ever since,” added Brett.