In some plastic products, there are undercuts. If it is a small undercut, and the requirements of shape and size accuracy are low, or the plastic material has sufficient plastic deformation and toughness, the parts can be ejected/ demoulded by force. 

According to the different structures and requirements of plastic parts, the slider and lifter mechanisms is adopted to solve the problems in mold design.

With the vertical movement of the mold opening, the diagonal support pin and the slider move relatively. The slider moves horizontally because of the action of the pressing block, so that it can be released from the undercut, and then the product can be ejected smoothly.

When there is undercut on external side, it will use lifter to remould. 
The principle of lifter is through the ejection of the ejector plate, the lifter is limited by the guide block and Core, so it only eject along the oblique direction and get a certain horizontal translation. In this way, so that the undercut parts on the side wall can be demoulded.