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What is Scientific Molding?

Scientific molding is a disciplined, systematic approach to establishing key processing parameters of plastic injection molding. This controlled process is data driven and highly repeatable, yielding products of Six-Sigma quality. By applying strict scientific molding principles and methodologies, we’re able to establish all molding variables in the manufacturing process to achieve consistent and repeatable results. This is often accomplished by using the inline monitoring system where, through a video feed, customers can view and assess their products in real time as they are being manufactured. PTI is largely staffed with certified master molders.

Decoupled I (DI) is the traditional method of injection molding desecribed as the trial-and-error method that relies heavily on processor experience. Each stage of the process flows together as one stage, meaning that the filling is done with one shot under constant pressure to pack and hold the mold cavity. So a loss in pressure or a fluctuation in temperature is not accounted for or corrected. An error here results in another trial.

Just as operator experience may vary, the parts they produce can too. However, with advances in machine technology, using machine controls to accomplish the transfer from first stage speed control to second stage pressure made more sense and, as a result, operator experience becomes less of a factor while part quality and consistency got better.

For process engineers, the most important variable to control is the viscosity of the material (which, in practicality, equates to the resistance to flow) which will naturally fluctuate throughtout the injection molding process. And fluctuations can cause short shorts and/or flash (material seapage along the parting line).

The ultimate goal of decoupled molding is to stop the flow of plastic precisely at the end of the cavity consistently. By separating these three vital stages, it allows for better control of viscosity which results in higher quality, consistent parts.

DII and DIII are true scientific injection molding processing that pick up where traditional injection molding (DI) leaves off.

Unlike the trial-and-error method of traditional molding (DI), Scientific Injection Molding (DII and DIII) is data-driven, using a methodical approach that relies on the principles of polymer science and engineering to optimize the injection molding process.

The First stage is filling the part based off a defined shot transfer position where the cavity is filled to 95% under a constant velocity, the machine switches to a pressure mode and further molten material is added to pack the cavity under constant pressure.

The separate application of constant velocity and pressure ensures the nullification of inconsistencies such as machine stroke speed or response time in the equipment used. The optimized consistency leads to the manufacturing of higher quality parts compared to traditional injection molding.

The Second stage is the pack/hold phase. It is used to finish mold filling, compensate for part shrinkage, and hold the part with pressure until gate seal is achieved (at which time, the polymer at the gate is frozen and no more plastic is packed into the cavities or flows back out).

Decoupled III, while similar to DII molding as it separates the Fill stage from pack and hold, it further divides the pack and hold phase into two separate phases.

The First stage is filling the part to a shot position of roughly an 80% full part.

The Second stage pack pressure is then utilized to pack the part to a set cavity pressure, utilizing an external transfer trigger (for instance, an RJG cavity pressure sensor in the mold), at a slower injection speed.

Finally, the Third stage of a DIII process is the hold phase, where hold pressure is utilized to achieve gate seal and prevent material from flowing back out of the mold. This is the most consistent and repeatable of the decoupled molding techniques as the part is consistently packed to a set cavity pressure, regardless of natural viscosity shifts in the material.

The scientific injection molding process enables manufacturers to achieve consistent quality when manufacturing medical devices in medium or large volumes.

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Mold Design

Mold Design is a crucial step in the injection molding process. Once you’ve finalized your part in CAD software for fit and function, it must then be transformed into a design for molding to ensure the capture of all the specified details. In some cases, certain features of the part design may not be manufacturable via the injection molding process.

At PTI, we collaborate with you to achieve the best possible design for manufacturability. In fact, we have a FREE guide to help you with this.