A Brief Introduction to Ejector Pin Design


Eject the molded part from the injection mold.

Considerations for the ejection system:

1. Ejector pin holes should be at least 3/32” away from other holes;

2. At least a clearance of 1/32” for pin holes on the ejector plate;

3. At least a clearance of 1/64” for pin holes on the mold plate;

4. All ejector pins should adopt the standard dimensions; the ejector base cannot be ground lower;

5. During the injection molding process of nylon, LDPE or PP, the diamter of each ejector pin must be measured, because flash might occur when the clearanc between the pin and the hole is greater than

6. All ejector pin holes must be vertical and glossy (Ra ~ 0.25μm);

7. For plastic materials like PP, PE and Nylon, hole diameter = pin diameter + 0.01mm; for plastic materials like HIPS, PC and ABS, hole diameter = pin diameter + 0.02mm;

8. Ejector pin should pass through the base plate, ejector plate and mold components in a straight downward way;

9. After all ejector pins are installed, the ejector plate should be able to slide downwards freely;

10. Labels in the same direction should be provided near the location of all ejector pins and screw heads, so as to prevent wrong installation;

11. All pins need to come with dowels, to prevent wrong installation (the application of square-shaped pinhead should be avoided, unless the distance between ejector pins are very small; it cannot adopt the symmetric layout, but only the one-sided way. Usually, the 1st one should be applied; apply the 3rd when there is not sufficient space);

12. Upon installation of ejector pins, everything needs to be checked before covering the back panel;

13. After installation of the supporter, use a flashlight to examine each rib and hole from the direction of the mold core, to see if there is any problem with pins or sleeve ejectors. Cover the back panel when everything’s OK;

14. When designing the location of ejector pins, in addition to guaranteeing sufficient ejection force, it has to be ensured that the product can be ejected in a straightforward way;

15. There are two types of ejector pins, i.e. though-hardened and nitrided;

15.1 Though-hardened – surface hardness is 65 – 74HRC, and steel core hardness is 50 – 55HRC;

15.2 Nitrided – the nitrided surface hardness is 65 – 74HRC.


Design of Runner Ejector Pins

  1. Purpose:

Eject the gate/runner from cavity.

  1. Forms of Pins

2.1 Option 1 (for general purpose)

ejector pin design

2.2 Option 2 (for general purpose)

ejector pin design

2.3 Applied to transparent materials like PMMA

ejector pin design for runner

Design of Ejector Pin Location

  1. Pin Locations

1.1 The ejector pin should be 0.040″ – 0.100″ away from the top edge of the upper mold;

ejector pin location

1.2 Try to place the ejector pin at the bottom of the product, such as the Pin A shown below. Try to keep a distance of at least 0.010” from mold core. Don’t place on the top (Pin B)

ejector pin position

1.3 If an ejector pin has to be placed on a slope, Location “A” is the first option,followed by “B” and “C”, because a product tends to dislocate on a slope, and the ejector force may decline due to the existenc of the slope. If “C” is the only choice, small blocks should be added to increase ejection force.

ejector pin

1.4 To avoid the upper mold from being damaged by the ejector pin, the ejector pin has to be placed in location “A”.

ejector pin location

1.4.1 The pin has to be ground lower for 0.0005”, for venting purposes;

1.4.2 A spring is needed under the return pin.

ejector pin with spring

1.5 When product is too high or draft angle is too large, draw the ejection path on a layout plan, to help avoid mistake when placing the ejector pin. When the product has a large R, draw the tangent of the R on a layout plan, as a boundary for ejector pin placement.

1.6 Place ejector pins under ribs

ejector pins under ribs

Among the above-mentioned 5 methods, 1 is the best, and 5 is the worst.

Ejector pin location design

Ejector pin location design




Leave a Comment