During the 297th live stream, a viewer asked what mold steel to use for injection molding 40% fiber-reinforced PPS. They noted that H13, even after heat treatment to increase hardness, is not durable, and the same applies to 2344.
H13 and 2344 are 4Cr5MoSiV1 medium-carbon steels with a carbon content of 0.38%. Their hardness is only 50 HRC. While they have good toughness, their wear resistance is too poor. They cannot withstand the erosion caused by 40% fiber-reinforced plastic on the mold, which will quickly wear the mold down, resulting in flash on the product.
Based on past feedback from users, when using H13 or 2344 with 40% glass-fiber-reinforced compounds, the injection molding cycle life does not exceed 100,000 cycles before flash begins to appear on the products. For 40% glass-fiber-reinforced PPS, depending on the performance requirements of the mold and based on past successful cases, I recommend using 8503 as the core material for its non-stick properties.
8503 has a hardness of 55–61 HRC and twice the toughness of DC53. Compared to DC53, its performance doubles without doubling the price, while also offering the added benefit of non-stick properties. In particular, these non-stick properties, combined with its high hardness, provide a fundamental and effective solution to the problem of molds being worn down by high-glass-fiber-content materials, which leads to flash on the products.
As Mr. Yu from Zhejiang puts it, using 8503 with 30% glass-fiber-reinforced nylon compound works exceptionally well—even with continuous molding, there’s no flash. Additionally, Mr. Wan reported that using 8503 with a 30% glass-fiber-reinforced nylon compound resulted in a mold life of 1 million cycles.
Regarding the 40% glass-filled PPS mentioned by the user, neither H13 nor 2344 mold steels are durable enough for this application. For the mold cavity, you should use the non-stick 8503 steel; for the core, tilting pins, and inserts—which require exceptionally high toughness—you can use high-toughness LG mold steel.
We have a client who injection molds 30% glass-filled PC. He originally used Japanese-imported DHA1 mold steel, but could only produce 50,000 parts before the mold cavity surfaces became rough, resulting in poor surface finish on the molded products. He now uses 8503 (non-stick grade) for the mold cavity material and high-toughness LG for the cores and tilt pins. He has been using this combination for the past 2–3 years.
The mold supervisor told me that using 8503 for the cavity inserts ensures the mold cavities won’t become rough, the parting lines won’t be eroded, and the mold’s service life is guaranteed. For mold inserts, wear resistance is the primary consideration, so non-stick 8503 mold steel is sufficient. However, for cores, inclined ejectors, and small bosses, I use LG steel for insert machining. LG has 8 to 9 times the toughness of DC53, with a hardness of 54–58HRC, It’s so tough that it won’t break even if you bend it with a hammer; it won’t fracture when used as a core, ensuring high toughness without being worn away. By using this combination, I’ve reduced my mold costs. The molds last longer and require fewer repairs, so it’s cost-effective for me.
In response to the user’s question about injection molding 40% glass-filled PPS: using H13 or 2344, even after heat treatment and hardening, results in poor durability. I recommend using 8503 non-stick material for the mold inserts. For molds with fine slanted ejectors and cores, use high-toughness LG mold steel.
If you’re currently using H13, 2344, SKD61, or even S136 for molds that process glass-filled materials, the molds are prone to wear, and the products will quickly develop flash. You might want to try the non-stick 8503 mold steel.
*************
Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.