The key to a successful die casting is an excellent tool design. One of the hardest components to design and maintain for good tool life is a core pin. A “core” is the separate and replaceable part of the die that forms an internal feature of the casting. Core pins come in all shapes and sizes, but the most commonly used shape design is circular. Core pins may be fixed to the die cavity or to a slide, actuated through the mechanical opening/closing of the die, or by hydraulic cylinder or other means. While core pins are the backbone of good tool design, when not properly designed, it can result in severe downtime and inefficient productivity.
On a high-volume die casting project for heat sinks, there were 24 core pins. After the PPAP process, there was an unexpected increase in downtime (every 1000-2000 shots) along with core pins breaking. The team in charge of the project, began their analysis.
Root Cause Analysis
An MES quality engineer, along with the tooling engineer and supplier team, evaluated various reasons using a fishbone diagram. There were three critical reasons identified:
1.) Guide show wear out in the machine
2.) Guide pillar/guide bush wear out in the die
3.) Weaker core pin in the die
After two days of examinations, the team evaluated and ruled out #1 (guide show wear out in the machine) and #2 (guide pillar/guide bush wear out in the die). They discovered that the core pin design to be the biggest reason for the breakage and downtime. The current core pin was determined to be too long for the diameter required (Figure A) for the heat sink castings.
After a thorough investigation, the team came up with a modified two-piece pin design as the most durable and reliable option. The original one-piece core pin design proved to be ineffective. There was no way to have one-piece design due to the length to diameter ratio and part features that limited options. The two-pin designed was fabricated with exceptional precision, which prevented flashing around the area.
The decision was made to change to the new two-piece pin design, and run another production lot. Instead of pins breaking at the 1000-2000 unit run, the two-piece pin design lasted for over 10,000 shots. All 26 pins were changed to the two-piece design.
MES Engineers around the world work closely with suppliers to develop robust tooling to make sure suppliers can make production parts of acceptable quality and capacity. Good tooling design is at the heart of any quality die casting. MES has specialized tooling engineers to help and ensure proper tools are built to meet our customer’s quality.