All Things you Need to know about Knockout Pins

What is Pin?

Cold heading is a forging method that uses a mold to shape metal at room temperature. It is usually used to manufacture the heads of screws, bolts, rivets, etc., which can reduce or replace cutting processing.

After the workpiece is forged, it needs to be taken out of the mold cavity. Generally speaking, the workpiece with a relatively regular shape. The workpiece can automatically fall off the mold cavity under the action of gravity.

However, when processing special workpieces and the workpiece is cold-headed. Some part of the cross-sectional area becomes larger, and some material will keep in the cavity.

In addition, the weight of the workpiece is small, and the workpiece cannot be released from the cavity under the action of its own gravity.

When encountering this kind of workpiece, after cold heading, it is necessary to withdraw the pin from the spring die, and insert another longer pin into the mold cavity to eject the workpiece.

How many types of Pins?

According to the material distinguished, the pin is divided into two materials: tungsten carbide and high-speed steel.

Commonly used cold heading accessories mainly include high-speed steel SKD11 material, SKH51 material, and tungsten carbide with better performance.

As a superhard metal, cemented tungsten carbide has good physical properties, suitable for continuous and durable precision stamping operations.

Tungsten carbide pins have a longer service life and maintain a better surface finish than high-speed steel pins, moreover, tungsten carbide pins have a life span of 20 to 50 times that of high-speed steel.

According to the size of the drawing and technology, the common types can be divided into:

  • Ejector Pins: Also known as knockout pins, use these pins to push parts out of molds. Pins are precision-ground to tight tolerances and hardened for strength and wear resistance.
  • Shoulder-Style Ejector Pins: A thick shoulder underneath the head makes these pins more rigid than standard ejector pins. They’re precision-ground to tight tolerances and hardened for strength and wear resistance. Machining is not recommended.
  • Core Pins: Mold plastic around these pins to form small holes, or use them to perforate parts. They have a flat head to fit into a counterbored hole. Made of M2 tool steel, these pins are wear-resistant and stay sharp at high temperatures
  • Punch Pins: Use these pin blanks with a die to punch 1/8″ and larger holes.  Made of M2 tool steel, these pins are wear-resistant and stay sharp at high temperatures. Heads are drawn to a Rockwell hardness of C45 to prevent breakage from shock.

Installation and adjustment of pins in a cold heading machine

The whole process of cold heading is composed of multiple cold heading dies, there are three common combinations, and there are six cold heading dies as a group for more precise product requirements. The following will briefly introduce the installation and adjustment of the pins in a cold-heading machine with three cold heading dies.

  • In the first mold
    • Put a pin into a punching cavity, then put it into a punching cavity of the die seat, and then use an arc-shaped bolt to securely lock a pin to prevent serial movement.
  • In the second mold
    • After the first punch is installed and adjusted to the correct position, first clean the dirt, grease, etc. in the cavity of the second punch, and then install it into the second punch after confirming that it is clean.
    • After loading the second punch, use the inching switch to test the blank, and check whether the workpiece is on the same center line and whether there is any deviation from the left and right positions of the first punch. If there is a deviation, the concentricity of the punch can be adjusted with the adjusting bolts on both sides of the punch.
    • If the second touch and the third punch have been installed, the test blank has been sent from the first punch to the first mold, and the diameter reduction process has been carried out. At this time, the first punch is lifted to the moldless position on the upper part of the first die, the second punch is raised to the impact position of the first die, and the workpiece is taken out after upsetting the workpiece, which plays its second function, that is, the role of the clamp. According to the length of the workpiece, adjust the coordination between the running time of the machine slider and the ejection time of the blank in the die, and the modified part is the feeding mechanism.
    • The billet taken out of the first die by the second is sent into the second die, and it is upset and forged at the same time, and it is initially formed, and then the length of the product rod is adjusted according to the size requirements of the product.
    • Adjust the length of the blank and the rod with steps, and then proceed to the next step of adjustment.
  • In the third mold
    • after checking that there is no foreign matter in the cavity of the three-punch, install the three-punch. After the three punches are installed, the blank is tested for heading.
  • Correct maintenance of pins

    If you want to extend the service life of the punching pins, you need the staff to pay more attention during the processing and use. If some lubricant can be applied, it will reduce the external friction, so to a certain extent, it can reduce wear. Therefore, for some high-end punches, lubricants are used for maintenance before use. It can maintain a good lubrication effect to a certain extent, and at the same time can reduce the risk of damage to the punch, which can reduce the cost. , The effect of increasing the profit rate.

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