As known, tooling life is an important standard to judge the quality of a mold being good or not. And among all factors that affect mold life, steel plays a decisive role as well. Thus it is very important to choose the right steel for your injection mold, otherwise it may ruin the whole project. We paid high fees for the lesson 4 years ago.
We built a plastic injection stack mold of toilet Seat for Walmart. It is a 1+1 tooling that to be produced on Vertical Injection Machine. Plastic material is PVC and the required mold steel is Stainless harden to 42/44 RC. Cavity needs to be polished to A1 level. In fact, before this, we had built over 20 seat molds of such kind and accumulate rich experience on the whole manufacturing process.
We could build the mold with closed eyes, this was our thinking at that time. An army puffed up with pride is bound to lose. When ordering steel, we decided to give a try to the new supplier, whose sales haunted to our boss office door for almost half a year everyday. We were told that they have large stock of 420SS in the warehouse and showed us picture. What is the most attractive is that their pricing is 10% cheaper. In front of direct temptation, human nature of greedy wins.
The steel was delivered. Manufacturing process started as normal, deep drilling,rough machining, heat treatment, wire cutting, CNC precise machining,ect. All went smoothly. No one expected that tragedy happened at last step-mirror polishing. Worker told us that large area of pitting was found on the steel surface. They tried different polishing skill and the pitting is still there. And it seems to be deep into the steel, not just on the surface.
We called the supplier instantly. He came and saw the terrible fitting. Here came the professional explanation, for this large block of stainless steel(size is xxxx), no one could guarantee that no pitting was contained through the whole block and where it might appear. Even the most advanced equipment could not detect it.
Boss stopped him rudely, I’m not here to listen to your explanation, tell me directly, how to solve it?The supplier proposed that they could replace a steel but could not guarantee about the pitting. And they would not answer to the incurring manufacturing cost. It is impossible that we would continue using his mold steel as we could not afford any further loss.
In this case, argument would never solve issue. We then traversed the streets around our city in hope to get a professional polishing company to handle the issues. We finally got a branded one and they promised that the fitting could be removed with special solution formula plus polishing skill. However the pricing is double. This seems to be the best solution to reduce loss. After thorough consideration, we decided to give it up. No one got to know that how long the production could last. Since the pitting is deep into the block, what if the polished surface gets worn after a short production？ The cost moving the mold back is highly huge. What is worst, client may lose trust on us.
We decided to confess the truth to client. Client was quite upset at start. However, when we proposed that we would build a new mold and the mold would be shipped by air to Toronto instead of sea shipment at our own cost, client calmed down and told us, everybody makes mistake, the most important is to take correct actions and solve problems. This accident made us lose around 50000$ including air cost. My boss said, MBA lesson of 4 years cost less. Then i told him, you could never learn the lesson from MBA book. Society is the most valuable institute!
Since this happening, we keep tight control on supplier. We only work with local trusted steel supplier such as LKM, YIBAI and etc. Contract needs to be sighed and all steel should be delivered with certificate report.
Of course, there are also other factors might be considered thoroughly.
Steel type Different types of steel should be used for various applications in the manufacturing of all types of products, such as high gloss,texture or corrosion resisting.
Mold Cost Steel property strikes enough.The best might not suit your needs.The most expensive might not be the best.Select the mold steel that is properaite to part quantity. Avoid needless waste.
Heat treatment. It is also important to have heat treated on mold surface. Nitride helps to increase steel surface hardness and makes mold life longer while plating could improve steel property, especially for the parts that require high gloss and corrosion resistance