Problem Description: PA66+GF30 injection molding cores keep breaking; the mold manufacturer replaced 8 sets of cores for free but still couldn’t fix the problem.
A user asked: What type of mold steel should be used for mold cores to prevent breakage? His operating conditions are:
— Injection molding of PA66 reinforced with 30% glass fiber;
— Each mold set has 2 cores, with a core height of 70 mm; the 7-piece core assembly features a central boss and central gate;
— The cores repeatedly break, forcing the mold to be converted from a two-cavity to a single-cavity setup; to meet deadlines, production must continue despite the issues, resulting in a 50% drop in efficiency;
— The mold manufacturer has already replaced eight sets of cores free of charge. They have tried beryllium copper, Fake LG, and Fake 8503, but even the best beryllium copper only lasted a few tens of thousands of cycles—the mold manufacturer has explicitly stated that “they can’t fix it.” The injection molding factory had no choice but to search online for information and reached out after seeing a video claiming that “high-toughness LG doesn’t break even when bent.”
Conclusion First: This is a classic case where the material fails to meet both wear resistance and toughness requirements. The slender core of high-glass-fiber-reinforced plastic requires a combination of “high hardness and high toughness”; we recommend genuine LG mold steel.
Trial-and-Error Analysis: Why did beryllium copper, Fake LG, and Fake 8503 all fail?
| Material | The problem |
| Beryllium copper | Its hardness is only approximately 40 HRC, and its wear resistance is poor; it cannot withstand the erosion caused by PA66+GF30, leading to rapid wear and loss of its profile. Furthermore, due to its low strength, it will fracture when used in thin-walled, slender cores—failure occurs after tens of thousands of cycles—demonstrating that it is unsuitable for such cores. |
| Fake LG | Acquiring counterfeit products. LG’s high-toughness mold steel is a proprietary product of Yuhui Mold Steel; however, due to its high market visibility and the fact that customers specifically request this material, it has been widely imitated by competitors across all online platforms. As a result, counterfeit products are ubiquitous, making failure to meet quality standards inevitable. |
| Fake 8503 | Similarly, the counterfeit materials lack the toughness required to meet the standards of genuine products. |
Solution: High Toughness LG Die Steel (Genuine)
Key Parameters of LG Die Steel:
| Project | Parameter |
| Hardness | 54-58 HRC |
| Tenacity, | 8–9 times that of DC53 |
| Actual Performance | Bendable without cracking |
Toughness Test: Mr. Yu from Zhejiang bent a 60mm-high LG wire-cut scrap piece 180° without breaking it; after releasing the force, it even sprang back—demonstrating both rigidity and toughness. Friends in the plastic mold industry are scrambling to take these scraps to use as cores for wire cutting.
Verification Case: Mr. Jin was having trouble inserting cores; spring steel, H13, and Fake LG all failed, but LG solved the problem
Mr. Jin’s working conditions closely resemble those in this case study:
—- The height of the mating core is 40 mm, with a wall thickness of 3.5 mm;
—- He had previously tried spring steel, H13, and Fake LG wire: the harder materials
snapped immediately, while the softer ones deformed, resulting in scrapped products;
—- After switching to genuine, high-toughness LG wire: the problem was solved.
Cost Analysis: Broken Cores Result in a “Losing-Losing” Situation
For Mold Manufacturers: While core materials are inexpensive, machining costs are high. Providing eight cores free with a single mold means there’s virtually no profit on that order, and the customer experience suffers.
For Injection Molding Factories: Efficiency drops from two shots per cycle to one—effectively cutting it in half—so even free cores aren’t cost-effective. As long as the cores don’t break and efficiency is restored, even the most expensive mold steel becomes cost-effective.
Core Logic: Slender cores for injection-molding PA66+GF30 require both wear resistance and toughness; LG’s combination of high hardness and high toughness is a perfect match.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.