What are Ejector Pins and Why They are Used in Aluminum Die Cast Mold Making

Ejector pins are an important aspect of designing and molding phase of die cast mold making with aluminum. Also known as knockout pins, they are attached to the movable half of the casting known as the ‘ejector half’ in order to push out the casting from the mold cavity. Once the solidified mold ejects from the machine, the casting stays on the mold cavity as the component and the drafts are tailored for the same task.

Pushing the ejector pins forward is a plate placed inside the movable half of the casting. With force, the pins also advance causing the casting to eject from the mold cavity. Once ejected from the machine, the casting would be removed from the sides of the knockout pins with the use of robots. However, the cyclical process of manufacturing another casting would resume.

Apart from knocking out the solidified casting from the die, ejector pins would leave pin marks on the component. They also help in keeping the die cast parts from bending.

Placement of Ejector Pins

Their placement inside the casting machine needs to be discussed early on to avoid die revisions. Determining where to place the ejector pins is at the discretion of the die casters but customers’ consensus is also considered in co-design. In situations where the surface finishing is important, the placement of knockout pins is discussed before designing the die.

Their size, volume alongside placement, and the number of bosses needed would differ according to the size and the geometry of the part and other aspects in die cast mold making. The pin marks on most of the castings may be depressed or raised by 0.015 inches – foundries prefer the latter for achieving optimal production. However, more tolerances may be required for ejecting large castings properly.

Ejector pin marks on the casting would also be surrounded by flashings. Usually, pin flashes won’t be removed except it hampers the function of the end product. However, they may be flattened or crushed as specified by the die casters – both may come off in thin pieces when the component is put to use.

Removing the ejector pin flash from the casting is another key aspect, which is considered in the design phase. Even with new molds, there would be flashings on the part to an extent on the ejector pins and hence they especially get addressed at the start of large-scale projects.