4 Keys to Successful Tooling Design
Here are four tooling design tips for injection molding with Eastman TritanTM copolyester:
Proper gating selection
- Most conventional cold gating styles work well with TritanTM copolyesters, including sub, pin, fan, edge, sprue, and diaphragm gates. Self-degating gate styles, such as sub gates or pin gates, typically require smaller gate sizes balancing the ability to limit pressure drop with degating.
- For hot runner systems, valve gates should be used. Critical design features of TritanTM valve gate systems include thermal control and independent water supply.
- Tritan™ copolyesters require good thermal control throughout the cavity for optimal processing.
This Old Mold 2 - Polishing
Eastman Tritan™ copolyester provides excellent gloss and picks up mold finish very well. When using it in a mold designed for other plastics, however, there are factors you need to consider in order to achieve success.
Here are some guidelines for polishing Eastman Tritan™ copolyester:
- Specify SPI mold finish standards.
- Specify surfaces smooth enough to minimize ejection force.
- Specify final polish in the direction of draw to minimize scuffing.
- Add a light 320 dry grit blasting (SPI B3 finish) to drafted walls to reduce the possibility of a vacuum forming during ejection.
It's important to keep in mind that surfaces polished smoother than required for ejection add to mold cost. 在大多数情况下，如果存在下拉的真空吸力或没有脱模区，高度抛光的表面反而会对顶出造成阻碍。如果不存在下拉真空吸力，抛光表面一般更易于脱模。
Clear or opaque? Applying different grades of Eastman Tritan™ copolyester
Each medical grade of Eastman Tritan™ copolyester offers a different combination of superior strengths that help optimize performance for specific medical applications. Depending on the needs of your device, you may need a clear or opaque material.
If your device is clear, such as fluid management and IV components, renal devices, or dialyzer housings, you’ll need a material with the following properties:
This Old Mold 1 - Cooling
The success of Eastman Tritan™ copolyester—especially in medical devices—makes more brand owners want to try it. One challenge to even
greater success has been how to use molds designed for other plastics. Sometimes it works fine - sometimes not so much.
Successful molding of any polymer depends on the ability to fill the part, cool the mold, and "freeze" the melted resin. Failure to do
Thank You for Asking:
In general, small thick-walled parts made with Eastman Tritan™ copolyester can be ultrasonically welded by
following the welder’s recommendations for other amorphous thermoplastics.
Mold design—critical factor #5
The coefficient of friction of copolyesters such as Eastman Tritan™ copolyester is at its highest near the heat deflection temperature (HDT) of the material-and competitive materials generally freeze at a higher temperature than Tritan. Keep this in mind if you're repurposing a mold that was originally designed for the cooling temperature of another plastic. Parts molded with Tritan must be adequately cooled to withstand ejection forces during demolding.
Three mold design and maintenance factors can also help ensure a clean and efficient release:
Draft—Part design features with minimal draft, such as long cores and deep ribs, often result in high ejection forces. The Eastman Design Services team recommends that all wall surfaces have a minimum draft angle of 1° in the direction of draw.
Mold design — critical factor #4
The gate is where it all comes together in injection molding. Mold design and part design. The molten resin and the solid molded product. Aesthetics and mechanical performance.
Skillful decisions about gate style, location, and size early in the mold and part design process can pay big dividends when it is time to start molding parts. And the benefits pay off in greater part performance and reliability.
Overriding considerations—aesthetics and mechanical properties
Regardless of gating type, location, or size, these two factors will drive most decisions made regarding gating:
The gate on an injection molded part leaves a "witness," or a vestige, where the part is separated from the runner system. This is considered an appearance defect and is typically hidden in an area of the part where it will not be obvious.
Overmolding for soft-touch designs
The medical industry has a great and growing demand for innovative soft-hard designs in devices, housings, and other equipment. A recent advance in liquid silicone rubber (LSR) technology makes it easier to satisfy this demand with medical grades of Eastman Tritan™ copolyester.
The advantages of Tritan are well-known to readers of this blog. Medical grades of Tritan offer a unique combination of properties including:
• Outstanding resistance to medical disinfectants and solvents
• Excellent impact strength and durability
• Made without BPA and halogens
• Excellent clarity and color retention after sterilization by ethylene oxide (EtO),
e-beam, and gamma irradiation
Mold design — critical factor #3
Fill pressure and fill pattern
To design greater manufacturability into molds-and parts-it's critical to achieve the most effective fill pressure, to anticipate the fill pattern, and to predict volumetric shrinkage. Eastman Design Services uses mold-filling simulation to evaluate the "moldability" of the part design and engineering resin combination.
Fill pressure and fill pattern go hand in hand.
Just as mold design is inextricably linked to part design, reasonable fill pressure and reasonable fill pattern should be evaluated together.
Reasonable fill pressure—excessive fill pressure can create several problems:
Mold design—critical factor #2
Thermal control is critical for injection molding Eastman Tritan™ copolyester. Keeping temperatures cooled below the heat deflection temperature (HDT) of Tritan helps ensure successful demolding with no dragging or sticking of parts. Preparing a cooling strategy early in the tool design process can pay big dividends in cycle time and processability.
One key to keeping it cool—just add water.
It's not that simple. But providing ample and well-positioned cooling water channels is critical to controlling the temperature of the cavity surface and the resin in the mold. Here's why controlling resin temperature is important: as the resin approaches HDT, it becomes sticky (the coefficient of friction increases) and parts cannot be ejected efficiently.