Mold Parts and Parting Lines
The injection molding process involves injecting hot liquid plastic into a mold. Once cooled the liquid adopts the shape of the mold. This method is very material efficient, as little of the injected liquid goes to waste.
The locating ring is a crucial part of the mold that resides inside the injection mold. It is often made of hard tool steels that can withstand high temperatures and pressures during the injection molding process.
Parting Lines
The parting line on a plastic injection molded product is the place where two halves of the mold come together during production. It is also where the ejector pins push the molded products out of the mold after the injection molding process has finished. The location of the parting line can have a large impact on the aesthetics of the finished product. A stepped or contoured parting line may be more appealing than a straight one, depending on the type of product and its properties.
There are many different types of parting lines, but they all have the same basic function: to separate the two halves of the mold for ejection. The shape, structure and material of the injection molded product usually determine the type of parting line needed. The machinists who are responsible for the design of the mold need to ensure that the parting line is properly positioned to allow for easy ejection of the finished product.
For instance, a poorly positioned parting line could result in the formation of flash on the molded product after it is removed from the mold. This can increase the costs of the injection molding process, because secondary operations are required to remove the excess molded resin. This can be done by hand trimming, vibratory tumbling in rough media, media blasting or cryogenic deflashing.
Ejector Pins
Ejector pins are tiny co-workers that make sure your newly molded plastic product gets out of the mold without a hitch. They are typically positioned in the B-side mold half (mounted on the moving side of the injection molding machine) and push the cooled and hardened part out after the injection process. Pins come in a variety of shapes and sizes, each with a unique knack for dealing with specific part surfaces or shapes.
The placement, type and size of ejector pins is an important consideration when designing a mold. The right combination of features will ensure your finished product is ejected in one piece that’s free of blemishes like ejector pin marks. Pin marks are caused by a forceful push from the pins as the B-side mold half is separated from the A-side mold half after the injection molding process. Pin mark defects can occur if the pins are too small or too few, if they are positioned on slopes or if the pins strike soft areas such as metal inserts or ribs.
To reduce the likelihood of ejector pin marks, choose large-diameter pins that distribute the force across a wider area. Locating the pins on hard parts like pillars, metal inserts and mould parts ribs will also help. In addition, make sure the flat ‘pad’ they push against is designed to be perpendicular to the direction of the pin movement. This prevents a ‘flash’ from taking place between the pin and its hole.
Gating
The gate is the point of entry for molten plastic into the mold cavity, impacting both the functionality and appearance of the final product. Proper gate placement and type is critical for ensuring uniform mold fill, minimizing defects, and maximizing production efficiency.
The type of gate you choose depends on part geometry, design, and specifications. For example, complex parts may benefit from a pin gate to facilitate precise control over the injection process, while larger flat parts might require a fan gate to ensure uniform flow and avoid weld lines.
Another consideration is the ejection and trimming requirements of your part. A submarine gate, for example, can be located below the mold parting line for easy ejection car parts mold and automatic trimming. This gate type can also help prevent shearing during ejection, which is necessary for maintaining a high-quality finish.
There are many different types of gates available for injection molding, and each has its own advantages and disadvantages. For instance, the pin gate has a narrow opening that limits the amount of molten plastic that flows into the cavity, which can be useful for reducing waste and cycle time. However, this gate type can leave a small mark on the finished part, making it less suitable for aesthetic applications. Other popular gate designs include the fan gate and valve gate, both of which utilize a mechanical valve to precisely control the flow of molten plastic into the mold.
Cams
In injection molding, cams are mechanical devices that pull undercut mold surfaces out of the way to allow ejection of the finished part. They are used to produce a variety of shapes that cannot be made using a two-part, straight pull mold.
For example, consider a thimble with curved sides that are perpendicular to the direction of mold opening. In a simple straight-pull mold, this would require a very large amount of draft to prevent a core from getting stuck on the outside of the thimble and not being pulled away cleanly during ejection. Injection molding with side action cams allows a thimble with this shape to be produced without the need for extra draft.
There are several different types of cams, but the most common is a traditional horn pin and lock style slide. The horn pin engages and disengages from an angled hole in the cam body, which retracts when the mold opens and closes. An angled lock then seats the slide, holding it in place against the pressure of injected resin.
Other types of cams include a collapsible core action that is useful for releasing circular undercuts and threaded features. Both types must be carefully designed to ensure that the locking mechanism can be molded in and then unscrewed. The sliding shutoff also needs to be designed to be able to withstand the same amount of pressure that the cam does during injection and ejection, or it could suffer from premature wear and damage to the mold.
