At the part level, the need for mold maintenance can be evaluated by checking for flash on parts at the parting line of the stripper plate or bar.

Maintenance involves ensuring that the stripper plate or block sits flush with the rest of the mold. Stripper systems eject a part on its perimeter. Because of their bigger size and high customization, ejection bars are typically high cost and high maintenance as the mold gets more wear. Unlike the preceding ejection systems, these systems tend to be larger and can utilize multiple pins beneath the bar. Ejection bars utilize multiple pins topped by a flat bar that evenly distributes their force. BarsĮjection bars offer a good option for ejection on lengths of flat surface. Checking this reduces the risk of plastic flashing into the ejection system. Maintenance for sleeves involves checking the fit of the outside of the core pin to the inside of the sleeve. The mark left on the part at the end of ejection mirrors the shape of the sleeve. The part forms onto the pin, and the sleeve moves when the ejection system actuates, pushing the part out of the mold.

The pin typically forms a part feature and extends past the sleeve in the mold’s unactuated state. Two components make ejection sleeves: a hollow sleeve and a smaller solid core pin that fits inside. As the blades wear, flash will appear on the part in those areas.Įjection sleeves distribute force evenly across small, circular features. Because of their high wear, blade ejectors can integrate into the mold as inserts for easy replacement. Blades have more surface area than pins so they can wear down more quickly. Plastics engineers use blades to eject on ribs because of the narrow but deep ejection requirements. These flat, rectangular pins can eject on thin part regions. When ejector pins cannot fit within the allowable ejection area, blade ejectors offer a good alternative. The injection molding process subjects ejector pins to a great deal of pressure during ejection, so larger pin diameters present a safer option. As the default ejection system, they leave solid circular ejection marks on the part. Different ejection options will leave different sizes and shapes of marks on the part and require different levels of maintenance.Įjection pins offer the simplest and most cost-effective ejection system. The part needs to eject without deforming, so thin part sections are bad candidates for ejection site locations.Ĭommon ejector options include pins, blades, sleeves, bars, stripper plates, and lifters. The functional and aesthetic requirements of the part inform which ejection system to use and where to place it. When you select your ejection system, you make two decisions: how and where to eject. The injection features on the cavity side do not allow the same flexibility. Proper drafting and part orientation reduce the risk of sticking to the cavity side. Core side ejection allows for the space necessary for the ejection features and actions. While cavity-side ejection is an option, it introduces cost and design complications. If the parts stick to the cavity side, they cannot be removed from the mold, potentially stopping production and causing damage to the mold.

The engineer wants the parts to stick to the core side so they can be ejected from the mold. The plastics engineer must think through which side of the part falls on the cavity side versus the core side of the mold. We have seen many of our clients select the wrong ejection system only to realize their mistake during molding.ĭuring part design for injection molding, the plastics engineer wants to make design decisions that support proper ejection over the life of the product. The plastics engineer can often trace this issue to the design phase. The last thing an operations manager wants to hear is that their manufacturing line went down and their mold has been damaged because of ejection issues. Why Your Ejection System is Critical to Part Success

Ejector pin marks