Plastic Injection Molding Questions: 17 Top FAQs
Aluminum seldom makes sense if a mold is fabricated in China (which we cover later). Steel is the most common injection mold material, but choosing the right injection mold steel material is similar to selecting the foundation for a building: it dictates the mold&#;s durability, performance, and ultimately, the quality of your parts. As engineers, we understand the critical nature of this decision.
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Let&#;s delve into the three most common types of hard steel and pre-hardened steel utilized in injection molding:
Hard Steels:
1. / / H13: This trio offers a workhorse option. After hardening, they achieve a Rockwell C hardness of 49-53 HRC, making them suitable for ordinary hardening molds. Their versatility allows for applications across various projects.
ESR: This steel takes the performance of the previous group a notch higher. It boasts the same hardness range (49-53 HRC) after hardening but excels in applications demanding both durability and a highly polished finish.
S136 / S136SUP / : Don&#;t be fooled by the &#;steel steel&#; reference &#; these are actually high-performance stainless steels. Their strength lies in corrosion resistance, making them ideal for molds processing materials like POM and PVC, which can be corrosive to standard steels. Additionally, they hold their own when it comes to achieving a polished finish.
Lifespan: Mold tooling made from hard steels like 1.#, #, and # will usually last for around 300k-500K shots, but can reach 1 Million if the mold structure is simple.
Pre-Hardened Steels:
S50C / S55C: These steels offer a cost-effective option for mold bases, providing adequate strength and machinability. However, their lower hardness limits their suitability for high-wear applications.
718 / 718H: Renowned for their toughness and ability to achieve a good surface finish with standard polishing techniques, 718 and 718H are popular choices for mold cavities and inserts. Their well-rounded properties make them a versatile option for various applications.
738 / 738H: Offering superior rigidity compared to 718 grades, 738 and 738H excel in core and insert applications. While their polishing capabilities are considered &#;ordinary,&#; their rigidity often outweighs this limitation for specific applications.
A Note on P20: It&#;s important to clarify the perception of P20 steel in China. While technically encompassing a series that might include materials like 718 or 738, the term &#;P20&#; in China often refers to a lower-grade steel with potentially less desirable properties compared to the 718/738 series.
NAK80 / XPM: The champion of pre-hardened steels, NAK80 boasts a hardness of 37-43 HRC. This, coupled with its excellent polishing capabilities, makes it the go-to choice for molds requiring high-precision parts from materials like PC, PA+GF, and PC+GF.
Remember, this is just a starting point. Selecting the optimal steel grade requires careful consideration of factors like part complexity, plastic-type, production volume, and budget. Consulting with experienced mold makers and material suppliers is crucial to ensure you make the best choice for your specific project.
Lifespan: For pre-hardened materials the mold life is usually 100K-300K shots.
In particular:
- 278#; 718#; p20#: 100k-200K;
- NAK80; XPM: 200-300K
Watch these videos on how to test steel&#;s properties which may help you to select the types you require.
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8 Questions to think about when choosing your Injection ...
Injection Molding is one of the most common ways to manufacture your product in production. The first step is choosing a tooling option that works for your project. Here are 8 questions from actual customers that will help make it a little easier to choose your Injection Mold Tooling.
What is the scope of the project?
This is the probably the most important factor in determining which tooling method to use.
If the part is for pre-production then the answer is simple, aluminum tooling. This is common when the project requires the part to be made with the end production injection mold material. Aluminum tooling offers lower costs and faster lead times. If the material requirement is not needed see alternative options on RTV Molding and 3D Printing.
If the part is for production then there are a couple things to consider. What are the EAUs on the part? How long will the project run?
How does part size effect tooling?
Part size plays a big factor in determining tooling. Larger parts will need to be built in a standalone tool however smaller parts that fit within the size parameters may be subject to a (more efficient) cheaper alternative. Insert tools are extremely popular for smaller components. Instead of paying the full price of a standalone tool we can look to build an insert tool that fits into the (standard MUD) base unit on our press.
For example, you have a small housing that is 3&#;x 2&#;x 1/2&#; and needs to be produced via Injection Molding. Instead of building a full standalone tool for such a small part we will build an insert tool out of aluminum or steel that fits into our pre-existing bases on our press. This is an extremely economical and waste minimization method to produce smaller components. We offer insert sizes ranging from a 5&#;x 5&#; all the way up to a 11&#;x 14&#;.
How does part volumes effect tooling?
Part volumes can effect tooling especially when the volumes reach a higher level. The standard is a single cavity tool for low volumes of a couple hundred or a couple thousand parts per year, but as the part volumes grow you can look to add multiple cavities on the tool to produce parts more economically. When quantities and life of project are unknown or there is no solid forecast, single cavity tools are a good place to start. You can always look at building multi-cavity tools later on. Multiple cavity tools come with a little more upfront cost on the tool but it can significantly lower the piece price on your part.
Does part material effect tooling?
Yes, it does. The part material has direct effect on tooling for a couple of reasons. Mild injection mold resins like a Polypropylene are a lot easier on a mold therefore contributing to a longer tool life. Harsher injection mold resins like a Glass Filled Nylon wear down a tool much easier. This can be a crucial deciding factor when your part has a life of 8,000-12,000 pieces and you are deciding between aluminum or steel tooling.
Does part geometry effect tooling?
Yes, it does. We thoroughly evaluate each part before quoting. We look at part features that will effect the tool. Does it have undercuts? Cores? We also look at surface finish requirements. Will it be grained? Polished? Textured? These all effect the decision on the type of tooling used.
What is the life expectancy of a tool?
Aluminum tools are good for a lifespan of anywhere from 2,000- 10,000 parts depending on the type of aluminum used, part material and geometry.
Steel tools are good for a lifespan of 100,000 + parts depending on the material and geometry of the part. The tool may need re-worked after it has been in production for awhile.
What is the timeline to build a tool?
This changes on a part by part basis but a good rule of thumb would be:
Aluminum tools can be built in anywhere from 4-6 weeks for small parts and 6-10 weeks for larger parts while steel tools can be built in anywhere from 6-8 weeks for small parts and 8-12 weeks for larger parts.
What is the cost difference for Injection Mold Tooling?
This also changes on a part by part basis but typically a steel tool costs anywhere from 20-30% more then an aluminum tool.
For more information, please visit injection molding case studies.
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