Three Key Decisions for an Optimal Ejection System
February 19, 2021
Injection molders want plastic parts to eject easily, consistently, quickly. Parts getting stuck causes damage and can break mold components, resulting in longer cycle times, manufacturing delays and increased costs. An experienced moldmaker knows how to manage the complexities of your mold design with the necessary ejection strategy, improving your part quality and saving you time and money over the life of your mold. For the optimal ejection system, your primary considerations should include ejection surface area, location and type. Let’s delve into these separately.
Ejection Type—Pros and Cons
In an ideal world, your moldmaker would use only KO pins in your plastic injection mold. However, most injection molded parts are just not that simple. Common ejector options include pins, blades, sleeves, bars, stripper plates and lifters—and each option brings its own tradeoffs. Different ejection options will leave different sizes and shapes of marks on the part and require different levels of maintenance.
Ejector pins offer the simplest and most cost-effective ejection system. As the default ejection system, they leave solid circular ejection marks on the part. The injection molding process subjects ejector pins to a great deal of pressure during ejection, so larger pin diameters present a safer option.
When ejector pins cannot fit within the allowable ejection area, blade ejectors offer a good alternative. These flat, rectangular pins can eject on thin part regions. Blades have more surface area than pins, so they can wear down more quickly. Because of their high wear, blade ejectors can be integrated into the mold as inserts for easier replacement.
Ejector blades have more surface area than pins and can therefore wear down more quickly.
Best Practice: An injection mold designer should know the pros and cons of each ejector type, and choose accordingly.
A robust ejection strategy will improve the quality of the parts, optimize the immediate and long-term costs related to the mold, and increase the time the mold spends making parts, while the wrong ejection system can decrease uptime and curtail the life of your mold.