Can you eliminate ejector pins marks?

I am working on an air pressure expulsion mechanism for plastic injection molds, to avoid the use of ejector pins and eliminate or reduce the ejector pins marks. I would like to know other possible solutions to reduce the marks when you eject the parts from the cavity. I will appreciate your comments or ideas!

1) Ensure you have adequate cooling circuits for the cavity or if possible the ejector pins
2) Confirm correct holding time/pressure to eliminate over packing of cavities
3) Consider ejector pin diameter to better disperse pressure
4)Adjust injection molding machine ejector pressure/speed, or use a soft start of multi speed ejector stroke to slow down/reduce initial ejector impact on the molded component
5) Confirm that molded component is not hanging up on the cavity prior to ejection (i.e. burrs, correct draft angle, any ribs or tool features are well polished)

- - - -> by: Rank

Consider if possible a stripper ring construction, or ejector blocks, as this increases surface area which is a plus point, and can be hidden using clever design, if this is not possible and pins must be used, then the way is to use high quality ejector pins, measure the diameter of the pins, then wire erode the ejector pin hole 3 micron maximum per side clear, build the tool up and jack the ejector plates back to its maximum home position as if it was in the molding press, then Polish the pin and the cavity together until the desired surface finish is reached, after polishing the pins should be almost invisible to the naked eye, upon molding the component you will find almost invisible ejection marks, believe me this is the way.

- - - -> by: Eley

I would like to share with you my experience in the injection molding with epoxy resin. I worked on the same subject for a some products in semi-conductor, the objective; was completely eliminated the mark of ejectors, to have a completely insulating product using Epoxy resins.

Some major problems:
-The surface condition or quality of the mold coating to avoid the sticking of the material during ejection after molding transfer,
-To use the melamine for cleaning the mold surface after a some shots of production
-Setup the parameters; clamp decompress position, speed, timing...

- - - -> by: Nabil

This problem of pin marks could be the result of many factors. The most prominent contributing factor is not enough take time. Such conditions prevent enough time for part formation to take place and so ejecting the part too early will create a pin or ejector mark. Another contributory factor is no or a not enough cooling. Is part produced without liquid cooling?

And the mold temperature has to be cooler than room temperature so that a faster part formation in whole will take place. Also, if the holding time is not enough, not only will you get pin marks but you will get a part with progressive heat transitioning into a destructive phase induction at post production leading to down the road creep deformation.

Another factor to consider is the length of pin push that can be adjusted by pressure.

If you cool a part good enough and don't try to make thousands of parts in a day by reducing a production take time from a favorable production take time, you will not have the problems.

Using air could solve the problem but creates a safety problem. Could you consider using a robotic arm that grabs the part by suction?

Hope this is helpful.

- - - -> by: Freid