A netizen called to ask me: For PPS+GF20 reinforced plastic, is SKD61 or 8503 a better choice for mold steel?
This netizen is developing a new mold with an annual production volume of 200,000 units, but the mold is intended for long-term use—perhaps even for ten or twenty years. The design engineer said SKD61 would suffice, but I felt it wouldn’t last that long, so I did some research online. I discovered that 8503 mold steel, which is non-stick, can achieve a cycle life of 1 million cycles when used with a 30% glass-fiber-reinforced nylon compound. Now I’m unsure, so I’m calling to ask you: What mold steel should I use for PPS+GF20?
For PPS reinforced with 20% glass fiber, the glass fiber content is somewhat high, which causes severe erosion of the mold. You need to select a mold steel with high hardness and non-stick properties to withstand the erosion caused by the reinforced plastic.
There is no one-size-fits-all answer when selecting mold materials. The key is to ensure the performance of the mold steel matches your mold’s performance requirements, while the cost aligns with the mold’s price point and meets your expectations.
A few days ago, a user asked me about a nylon compound reinforced with 30% glass fiber that requires a mold life of 50,000 cycles. They wondered if using 45 steel that has been quenched and tempered would meet the requirements.
Since the product only requires 50,000 cycles and the production volume is low, there’s no need to use quenched and tempered 45 steel just to reduce costs. Quenched and hardened molds require secondary machining, which is quite costly. Non-alloy mold steel has high penetrability during quenching, leading to severe mold deformation. Rather than going this route, it’s better to combine the costs of heat treatment, secondary machining, and the purchase of 45 steel, and simply buy pre-hardened P20 material instead. This approach actually results in lower material costs while still meeting production needs.
SKD61 is a medium-carbon steel with a carbon content of 0.38% and a hardness of HRC 50. It has good toughness but poor wear resistance. When used for injection molding PPS compound with 20% glass fiber, it’s impossible to produce 200,000 parts in a single run. Perhaps after 50,000 or 80,000 parts, the parting line area will be worn away, causing flash on the products, and you’ll need to repair the mold. If you can accept these frequent mold repairs, then SKD61 is a cost-effective option.
If you’re looking for a mold for long-term use, you can choose 8503 mold steel, which resists material sticking.
8503 is a proprietary non-stick mold steel from Yuhui Mold Steel. It has a hardness of 55–61 HRC and twice the toughness of DC53. Compared to DC53, its performance is doubled without a corresponding increase in price, and it offers the added benefit of non-stick properties. In particular, this non-stick property, combined with its high hardness, provides a fundamental and effective solution to the problem of molds for materials with high glass fiber content being easily eroded, which leads to flash on the product.
Mr. Yu from Ningbo mentioned that using 8503 mold steel for glass-fiber-reinforced molds works exceptionally well—even with continuous molding, there’s no flash. Mr. Wan also noted that for nylon compounds reinforced with 30% glass fiber, 8503 mold steel can easily withstand 1 million cycles.
Regarding the PPS+20% GF reinforced plastic mentioned by the netizen, which is better: SKD61 or 8503? If you want the mold to last a long time, then 8503—with its non-stick properties—is definitely the better choice; if you’re looking for a cheaper option, SKD61 is more affordable.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.