In injection molding the use of cam-action slides in injection molds is the most common and most efficient method to cast any type of undercut on a plastic part.
During the initial design stage, the first thing that is looked for on a part print or a solid model is to determine the parting line and if there are any undercuts present. For the ease of explaining the cam-action function, we will assume the part to be injection molded is a five sided square. This is a very easy part to injection mold, until a hole is added to one or more of the sides. The addition of a hole will now require the use of a core that will have to slide back and forth. The requirements of the core movement are as follows: Mold close (core in), Mold open (core out).
The first component of the cam-action function is a slide which houses the core. The slide usually has a flange on the sides at the bottom which is used as an area so gibs can be used to hold the slide from falling out of the injection mold but allows it to move back and forth easily. Gibs are made from various types of wear resistant steel. The slide also has an angle on the back that is used for locking the slide in position during the injection molding cycle. The angle on the slide is anywhere from 20° to 28°. On the stationary half of the mold, a lock is mounted that has the same angle as the slide. The lock is also made from various types of wear resistant steel. The last component is a horn pin which is mounted on the stationary half of the mold. The horn is on an angle which is 2° to 5° less than the slide and lock angle. The length is determined by the length of movement needed to cast the hole. The horn pin is only used for moving the slide in and out.
In some instances the lock can serve as a horn pin and also the lock. The use of this style is limited to a slide movement usually up to 3/8”. This style also requires a strong spring to move the slide back as the mold opens.
In injection molding there are other ways to move cores in or out such as with the use of hydraulic or air cylinders. The cylinders need to be tied in to the machine control and must be set right or damage could occur to the injection mold. Toth Mold/Die Inc. always uses the cam-action function first because it is all mechanical and reduces the risk of mold damage.