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.
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.
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.
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.
Precision molding is the latest technology in plastic injection molding. This type of plastic molding is the most sophisticated process of mold design on the market. It may be used for components that require an exceptionally precise form of plastic injection molding.[1]
Precision injection molding is a highly technical process requiring precision machines and molds. The process of precision molding is different from conventional injection molding techniques and is often used for developing precise plastic parts with complex geometries. These parts are often used as lightweight replacements for high-precision metal parts in industrial applications.
The precision of a part is dependent on the precision injection mold and its suitability for the engineering requirements. Many factors impact the precision injection mold, including:
Injection molding is a cost-effective way to replicate aspheric, spherical, and freeform surfaces and combine them with mounting features. There are three components to successful injection molding:
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The mold used to manufacture polymer optics includes the cavity details, optical inserts, and housing to hold the cavities and inserts. Optical and mechanical features may be combined into one platform with polymer optics, which may lead to a mold with high complexity.
Molds are built to the negative of the final part, and the mechanical features of the part are drafted for easy removal once the molding process is complete. Most optical inserts are created from nonferrous alloys that are diamond turned for high accuracy.
Thermoplastics shrink as they cool. The shrinkage is roughly 0.5 to 0.6%, which must be considered when creating the mold.
The optical injection molding machine, called a press, includes a fixed and a moving platen, a clamping unit, and an injection unit. The mold is placed on the press with one half mounted to the fixed platen, and the other half is mounted to the moving platen. Plastic pellets are melted, fed into the injection unit, and injected into the mold.
A clamp mechanism holds the two mold halves together during the injection process. As the polymer cools, it takes the shape of the cavity details and solidifies to create the final optic. Once cooled, the mold is opened and ejects the finished optic.
Injection molding uses complex variables and controls. Without a robust process, even the best mold will experience drift from tool wear, changes in ambient conditions, fluctuations in resin content, and more. This is why it’s essential to find an optics manufacturer with a high degree of skill in scientific molding techniques.
With the proper process, optical injection molding techniques can produce optical components with a high degree of repeatability and accuracy.
Any application that calls for an optical component, such as components for machine vision, scanning, imaging, medical, or general illumination, may use a polymer optic.
You’ll often find polymer optics in supermarket barcode scanners, LIDAR, automobile sensors, and medical applications. They are also used in sophisticated laboratory equipment like spectrometers, cleanroom particle counters, document scanners, and more.
As applications grow, polymer optics finds its place in telecommunication products and microstructured surfaces such as diffractive optical elements and microlens arrays. Other examples include imaging systems for near-to-eye displays, PC peripherals, and consumer devices like DVD players and smartphones.
Many of these applications are the result of the advantages that polymer optics have over glass components. These advantages are a direct result of the materials and the injection molding process.
Several factors impact the quality of the finished optical component and the repeatability of the process. The design engineering process must include precise guidelines to reduce defects and ensure top quality. Apollo Optical Systems’ molding technology creates consistent, high-quality parts that meet or exceed industry standards for successful finished optical components. Contact us to discuss your custom optics project!
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[1] https://www.sciencedirect.com/science/article/abs/pii/S