# A Uniformity Coefficient-Based Method for Improving the Wear Resistance of Mold Ejector Pin Guide Holes via Oblique Laser Shock Peening

## TL;DR

This paper introduces a new method combining nitriding and oblique laser shock peening to reduce wear in mold ejector pin guide holes.

## Contribution

The novel composite method N-OLSP improves wear resistance by optimizing laser shock peening uniformity.

## Key findings

- N-OLSP significantly increases surface hardness and residual compressive stress.
- The wear rate at the orifice was reduced to 0.60 μm/h with N-OLSP treatment.
- N-OLSP reduced wear rate by 66.85% compared to untreated samples.

## Abstract

To address the severe wear of the hole wall and orifice in ejector pin guide holes of injection molds caused by frequent hole-shaft sliding, this study proposes a composite strengthening method that combines nitriding with oblique laser shock peening (N-OLSP). The strengthening uniformity in both circumferential and axial directions was evaluated by defining a laser shock peening uniformity coefficient (k). By strictly controlling the uniformity coefficient ratio of two adjacent spots to be no less than 0.98, the optimal step angles for circumferential and axial directions were determined. Comparative experiments were conducted on three types of samples: Untreated, Nitrided, and N-OLSP treated. The results demonstrate that N-OLSP significantly enhances both surface hardness and residual compressive stress of the guide hole, and the degree of improvement increases with a higher value of k. Among the tested samples, N-OLSP exhibited the best wear resistance at the orifice, reducing the wear rate to 0.60 μm/h. Compared with the untreated and nitrided samples, the wear rate reduction achieved by N-OLSP was 66.85% and 16.67%, respectively.