Plastic injection molding is one of the frequently chosen manufacturing methods for new products. With thousands of resins available today, and more being created every year, it’s no mistake that injection molding should be a consideration for your next new or updated product idea. The plastic resin typically gets all the credit, but there is a workhorse in the background making sure your products come to life. The tooling does the hard work day in and day out. If you want perfect plastic parts, your tooling must be up to the task. If you’re uncertain of what characteristics your tools need to have, these tooling tips will help you on the road to perfect parts:
Choosing the Right Materials is Key
Your resin choice and mold material work together as a team. Choosing the best resin for your product can lead to failure if the wrong mold material is partnered with it. Conversely the best mold material can also struggle with the wrong resin selected. As you whittle down your perfect resin selection, you must also decide what class of mold you need based on production volume and what material the mold will be made from. A steel mold will be harder than an aluminum mold and offer more choices for surface finish. Steel can be polished for a smoother surface finish, which can also be advantageous for painting or another secondary turnkey operation to enhance your product. Your tool must also account for shrinkage and flow rate of the resin chosen. The best option is a resin that offers minimum shrinkage with excellent flow capability. Plastic resin manufacturers can provide technical information on the shrinkage and melt flow rates of their resins, plus offer suggestions for melting / operating temperatures.
Match Shrinkage with Tolerance
Once you have an optimum resin selected, it will have a shrinkage rate that must be accounted for in the injection mold. Your tool designer will make the tool cavities larger than the finished part in order to accommodate the projected resin shrinkage. Your design must also account for any tolerance that the final part must hold to meet specifications. Allowing for incorrect tolerances to occur may prevent parts from assembling properly under the extreme fluctuation of the tolerance band.
Vents and Gates – A Partnership of Precision
There are two items in the design that can help with precision tolerances or hamper production quickly: the gate for resin to enter the mold, and how trapped air is vented. Gates need to be placed at the proper location to allow for molten resin to enter the mold and fill the cavities quickly without excessive pressure required. The gate must also be the correct size. Too large and excessive pressure may be required to move the molten resin, but too small may hamper the mold from being completely filled in the cycle time of the machine. Gates also should be placed in a spot that doesn’t require extra work to hide the location on the finished part. The backside of the part is a better recommendation that directly where a potential customer can see the location.
The single vent or multiple vents also play a key role in allowing the mold to fill completely in the allotted cycle time. Any trapped air inside the molding during the filling portion of the machine cycle can block resin from flowing through the mold. Vents can channel the air out of the mold and relieve any pressure inside of the mold. Sizing is also critical for proper venting. A small vent may not allow enough air out of the mold, while a large vent may allow flashing to occur with later work to remove it.
Be Cool
Your injection mold needs to stay at a consistent temperature while in use. That requires a cooling system up to the task, especially on long runs where thousands of parts are made at a time. The cooling system should be robust to avoid parts warping or shrinking. A proper cooling design will allow for a minimum cycle time to be achieved without excessive cooling time required.
Hit the Ejection Button
After the molding cycle is complete, the formed parts must be removed from the mold. Your ejection system will most likely include one main or multiple small ejection details to remove the part from the mold. The normal shape is a pin with a flat end that can easily push the part without causing damage. Each ejection pin needs to be sized appropriately based on the shape of the part, its size, and its wall thickness.
Run Trials to Prove the Mold Works as Intended
The last tip is just to simply run the mold to fine-tune the details. Sampling allows the actual cycle time to be verified against the theoretical time, allows for the machine settings to be documented, and the mold cycle can be verified to work. The physical molded samples can be checked for proper shrinkage, the surface can be visually inspected, and any secondary processes can completed for additional training opportunities.
Conclusion
One of the best ways to determine if your tooling is perfectly matched to your resin is to work with an experienced injection molding company. They will be able to identify future defects and know how to prevent them from occurring. At SEA-LECT Plastics we pride ourselves in tool and die manufacturing that allows us to deliver high quality products free from defects. You should be including discussion points on the function, environment, quantity, and recycling of your product to ensure the best resin is chosen for your product. SEA-LECT Plastics has an elite team that produces world-class prototypes and products, and we have decades of experience with plastic injection molding operations and creating tooling for perfect parts. We can offer support to determine what type of mold you need, what resin to choose, and how to best invest in your future. Give us a call at (425) 339-0288 or email us at mattp@sealectplastics.com. We’ll help to determine the best manufacturing for your next project.
Matthias Poischbeg was born and raised in Hamburg, Germany. Matt moved to Everett, Wash., after finishing his bachelor’s degree in business in 1995 to work for Sea-Dog Corporation, a manufacturer, and distributor of marine and rigging hardware established in 1923.
In 1999, Matt took over the reins at Sea-Lect Plastics Corporation, a sister company of Sea-Dog and a manufacturer of plastic injection molded products with an in-house tool & die shop. Matthias Poischbeg is also a contributor to Grit Daily.