As an [injection molder](/process), you are always looking for ways to eject your plastic parts consistently, quickly and easily. Parts that get stuck cause damage and can even break mold components. Flaws like that have a real impact on your process: higher costs, longer cycle times and delays in [product manufacturing](/process). Every experienced mold maker knows how much depends on pairing the mold design with the right ejection strategy. The decisions you make here save you time and money for the entire life of the tool. In this article we zoom in on three key decisions for your ejection strategy.
1. Ejector surface: flatter is better
In the ideal scenario your ejection surface looks like the finest turf you can find: every blade of grass cut to exactly the same height, no bumps anywhere. That is proverbial, of course, but it makes the point that a perfectly flat ejection surface gives the best results.
Recessed flats also help, because they provide a surface parallel to the parting line. That makes parts far easier to knock out.
Tip of the day: locate your ejection point at the deepest part of the plastic part.
2. Ejection area: small parts are tougher
Good ejection depends on geometry and part size. When a part lacks ejection surface, you pay for it in rejected parts and deformation. That means slower cycles and longer running times, exactly what you want to avoid. Aim for larger ejection surfaces so parts release easily: it is one of the most effective steps in optimising your ejection strategy.
Tip of the day: do not be greedy with ejection surface, within reason. Avoid knockout pins under 3/64 inch (roughly 1.2 mm) in diameter.
3. Ejection type: pros and cons
Choosing the right type of ejection means working through a number of options. As an experienced molder you need to know when to use pins, bars, sleeves or blades. Each option has its own trade-offs: different types leave different shapes or marks on the part, and each needs its own kind of care.
Knockout pins are among the most reliable and least expensive options. They are also easy to install, modify and maintain. They do not suit every situation, but they are a solid option that is worth considering when you put your ejection strategy together.
Get your product injection molded by Production Heroes
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And we do more than manufacture: we have two dozen professionals on our floor with over twenty years of experience in design, engineering and manufacturing, who can help take your innovation to the next level. Feel free to get in touch.
Frequently asked questions
- Why do my parts stick in the mold?
- Usually too little ejection surface, or an ejection face that is not flat. A perfectly flat surface releases best, and recessed flats parallel to the parting line make parts far easier to knock out.
- How small can ejector pins be?
- Avoid knockout pins under roughly 1.2 mm (3/64 inch) in diameter. Below that you pay for it in deformation and rejected parts, which costs more than the pin ever saved.
- Which ejection type is the most economical?
- Knockout pins are among the most reliable and least expensive, and they are easy to install, modify and maintain. They do not suit every geometry, but they are the first option worth considering.
- What does a poor ejection strategy actually cost?
- Rejected parts, deformation, longer cycle times, and damage to mold components. Because the decision is built into the tool, those costs run for the entire life of the mold.