5 Must-Have Features in a Global Mould Manufacturing Partner
Designing Complex Injection Molding Features - Protolabs
Living Hinges
While we’re on the topic of lids and flexible materials, living hinges are a great way to keep the two halves of a molded container together. Take a look at a vitamin dispenser or mint box—chances are good there’s a clip of some sort on one side and a living hinge on the other. The biggest consideration here is material. Where polycarbonate might make a good clip, it definitely won’t survive the thousands or millions of cycles expected of a living hinge. Shoot for polypropylene instead.
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Breakaway tabs are similar to a living hinge. If you’ve ever peeled away the plastic cap on a refilled propane bottle or ice cream container, you know how they work. Whether tab or hinge though, some design accommodations must be made. The section should be thin enough to flex but thick enough to survive repeated bending. Depending on the expected range of motion, you might need a radius or groove at the midpoint of the hinge to allow it to fold over on itself. And because you’re attempting to mold two mating halves simultaneously and the material flow will likely be thick-to-thin-to-thick, flash and fill problems might occur. Be sure to pay close attention to the design for manufacturability (DFM) analysis you receive with your quote.
Tall Features Like Bosses and Stand Offs
Not everyone likes the boss. But if you need somewhere to stick a threaded insert, a boss will certainly be necessary. Yet bosses, like tall ribs and thick standoffs, are potential problem areas. Additional draft up to 3 degrees or more might be needed to avoid ejection problems. Make any of these part features too thick and sink becomes an issue. The taller the feature, the deeper the mold must be, which means longer end mills and slower feedrates are needed to cut it. This also raises concerns for venting that may result in shorts, burning, or simply incomplete parts.
Some ways to avoid this include using vertical ribs or gussets around the periphery of the boss to support it, thus allowing thinner walls to be used. Be aware that Protolabs may need to place vent holes in deep (tall) ribs, standoffs, and bosses. And when angled, features such as this are a real pain in the neck because their axes diverge from both the direction of mold pull and the parting line, pretty much guaranteeing a hand-loaded insert will be needed.
Text on Parts
Designing a product name or company logo on a part is a regular occurrence. But beware, this small detail can create big problems if approached incorrectly. For starters, tiny fonts are fine, but they should be a non-serif font (Arial or Century Gothic, for example) and the smallest stroke length—the cross bar on a T or A, or the legs on a K—must be at least 0.020 inch across.
Raised rather than sunken text is both easier to create and more legible, and unless the text is very large—like the big print book your grandpa reads—should be no more than 0.015 inches high (which means deep, as far as the mold is concerned). Text located down inside a pocket might be tough to reach with an end mill—any chance you can place it somewhere closer to the parting line or away from tall standing features in the mold? And unless you’re molding a squishy material like liquid silicone rubber (LSR) or thermoplastic elastomer (TPE), the text should always face the direction of mold pull, else part ejection can be problematic and we would need to incorporate hand-loaded inserts or side actions.
Overmolding
Rapid overmolding is a great way to add an ergonomic grip to a screwdriver handle, a no-slip, sanitary grip to a surgical device, and an impact resistant shell to an instrument housing. There’s no longer a need to glue or screw these coverings to your injection-molded part, because overmolding accomplished it in a two-step process that provides far better adhesion than traditional bonding methods.
It works by placing a previously molded part into a secondary mold and then shooting it with overmold material. There are some things to be aware of, however. The two materials should be compatible—thermoplastic polyurethane (TPU) over ABS or polycarbonate make good partners, as do TPE and some polypropylenes. LSR is also a desirable overmold material, but its molding temperature is high enough to bake a casserole (around 350 degrees F), so the substrate must be able to handle the heat. Glass-filled nylon is one good option.
The type of bond should also be considered. Each of the examples listed provide a secure chemical bond, but some materials are not so compatible and must be mechanically bonded. By now you might be leery of undercuts on your injection-molded parts but this is actually an effective way to assure a no-fail mechanical interlock on overmolded parts. Regardless of the materials under consideration, most polymer manufacturers recommend a double whammy of chemical and mechanical bonding. It’s also a good idea to speak with the overmolding material supplier before embarking on any large scale project. That’s something a Protolabs applications engineer can also help you with.
Along those lines, as always, feel free to contact Protolabs with any questions, at 877-479- or [ protected]. To get your next design project started today, simply upload a 3D CAD model at protolabs.com for an interactive quote within hours.
Top 5 Injection Mold Design Tips for Durable Plastic Parts - EuroPlas
1. Overview of the Importance of Injection Mold Design
The Importance of Injection Mold Design
Injection mold design is the backbone of any successful plastic manufacturing process. It involves creating a precise mold that forms the shape and structure of a product when molten plastic is injected into it. Here’s why it’s so crucial:
Quality Control: A well-crafted injection mold design is essential for maintaining product consistency. Proper design ensures that each part produced meets the required specifications without defects, such as warping, flashing, or sink marks.
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Cost Efficiency: Effective injection mold design can significantly lower production costs. By optimizing the design for ease of manufacturing and minimizing material wastage, manufacturers can save money on materials, reduce cycle times, and extend the lifespan of the molds.
Production Efficiency: A good design minimizes the potential for production issues such as short shots, burn marks, or flow lines. This allows for faster cycle times and higher productivity, which is especially important when scaling up for large production runs.
Durability of Molds: A robust injection mold design also affects the durability of the mold itself. By considering factors like stress points, cooling channels, and proper gating systems, designers can create molds that withstand repeated use without premature wear or damage.
With the importance of injection mold design established, let's dive into the practical tips that can enhance your design process.
2. Top 5 Injection Mold Design Tips
1. Focus on Proper Material Selection
The choice of materials for both the mold and the product is a critical first step in injection mold design. Different plastics have varying melting points, flow characteristics, and shrinkage rates, which can affect the final product’s quality. Additionally, the material used for the mold itself (such as steel or aluminum) impacts the durability and cooling efficiency of the mold. Understanding the properties of materials ensures compatibility between the mold and the injected plastic, leading to optimal performance.
Pro Tip: For high-volume production, opt for hardened steel molds as they offer durability and can handle the heat and pressure of multiple cycles. For prototyping or low-volume runs, aluminum molds can be a cost-effective and faster option.
2. Optimize Part Geometry for Moldability
Injection Mold Design in manufacturing
The geometry of the part being produced directly affects how easy it is to mold. Complex shapes with undercuts, thin walls, or intricate features can complicate the design process, increasing the likelihood of defects. Designing parts with uniform wall thickness, avoiding sharp corners, and incorporating draft angles ensures smooth ejection from the mold and reduces internal stresses.
Pro Tip: A draft angle of 1-2 degrees is generally recommended for easy ejection, but this can vary depending on the plastic material used. Including radii in corners instead of sharp edges also helps to distribute stress evenly.
3. Design Efficient Cooling Channels
Cooling time is a significant part of the injection molding cycle, often constituting 50-70% of the total cycle time. Efficient cooling channel design in the mold can drastically reduce cooling time, leading to faster cycle times and improved productivity. Properly placed channels ensure uniform cooling, which minimizes warping and shrinkage, resulting in more accurate parts.
Pro Tip: Use conformal cooling, which follows the contour of the mold cavity, to achieve more even cooling across complex shapes. This method can reduce cycle times and improve part quality, especially in intricate designs.
4. Use Flow Simulation Software
Leveraging modern technology, such as flow simulation software, is a game-changer in injection mold design. These tools allow designers to predict how molten plastic will flow through the mold cavity, identifying potential issues like air traps, weld lines, or short shots before physical testing. This simulation helps to optimize gate placement, runner size, and cooling systems, leading to better first-time accuracy and reduced mold rework.
Pro Tip: Use softwares for detailed analysis. This will save time and resources by minimizing trial-and-error adjustments in the design phase.
5. Pay Attention to Gate Design
Multiple Injection Mold Design
Gates are the entry points through which molten plastic flows into the mold cavity. The location, type, and size of the gate have a direct impact on the final product’s appearance and strength. An improperly placed gate can lead to defects like sink marks or excessive residual stress in the part. It’s essential to select a gate type that suits the part’s geometry and the type of plastic being used.
Pro Tip: Consider using hot runner systems for large or complex molds to reduce material waste and improve cycle time. Cold runner systems, while simpler, can be suitable for smaller runs or less intricate parts.
3. Conclusion
Mastering injection mold design is a blend of art and science, requiring a deep understanding of materials, part geometry, cooling systems, and the latest simulation technologies. A well-designed mold not only ensures high-quality products but also optimizes production efficiency and cost-effectiveness. By following these top 5 tips—focusing on material selection, part geometry, cooling channels, simulation software, and gate design—designers can achieve better outcomes in their injection molding projects.
For injection mold design enthusiasts, continuously refining your skills and staying updated with the latest tools and techniques is key to staying competitive in this ever-evolving field. Implementing these strategies can elevate your design process and ensure consistent success in plastic manufacturing. Happy molding!
4. About EuroPlas
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