Living hinges are popular in low-cost containers, like the ones you see on Tic Tac or floss containers. But the use of living hinges can vary widely, and so the molding technique is also often used for producing medical instruments such as hemostats.
As you could expect, molding living hinges would be much more difficult without modern plastic injection molding technology. Especially seeing as the hinge itself relies on the plasticity of the material to last longer.
What Are Living Hinges?
Don’t know what a living hinge is? Well, actually it’s quite simple.
Like a normal hinge you’d expect to see somewhere like on a door, living hinges can be used to make things like swinging container lids. The only difference is that, unlike normal hinges, living hinges don’t have loops and pins to make up the hinge mechanism. A normal hinge typically merges two different parts together in this way. However, living hinges are more like a line where the plastic bends to allow movement. Basically, it’s a “seamless” hinge, because there aren’t two parts merged together by a hinge. Instead, the hinge in molded into a single-part product.
What this means is that living hinges have to be able to flex constantly without tearing. This is what makes plastic a good option for molding living hinges, seeing as metal would break as a result of metal fatigue if one were to make a living hinge from it. Materials such as wood, on the other hand, aren’t even bendable. By the time wood is thin enough to bend, it would simply splinter if it were to be flexed so much.
But just because plastic is a good material for molding living hinges, doesn’t mean that all living hinges molded out of plastic are perfect. On the contrary, products that have living hinges typically have a lifespan that lasts as long as the living hinge is functional. After a certain amount of time, even a plastic living hinge can grow weak and tear along the hinge line.
For the most part, living hinge failure isn’t such a big problem, seeing as living hinges aren’t usually molded into products that need to have a long lifespan. However, living hinge failure can become a problem if the hinge doesn’t last long enough to fulfill its purpose. This can be especially true in the case of something like a container that breaks before its contents is all used. So even though living hinges don’t have to last forever, they at least need to last long enough to fulfill their purpose.
To mold durable living hinges will take some careful consideration on your behalf.
How to Mold Durable Living Hinges
To mold a living hinge that lives up to your expectations, every step of part creation is important, from the actual design of the part to the material used to make it. Different plastics have different uses, and not all plastics are a good choice for molding plastic hinges into a part.
So, although molding a hinge into a part might seem like a challenging task, it’s much like molding anything else, as long as you plan everything properly and pay attention to detail during every step of part creation, you’ll get the results you were hoping for.
For the most part, experts tend to recommend homopolymer PP for molding living hinges. However, your molding will also have a big influence on the quality of your final part, so don’t neglect checking the ideal molding temperatures and processes, seeing as you’re likely to get better results molding hinges at lower temperatures.
Mold Design and Construction
When it comes to molding any plastic part, the design and construction of your mold is just as important as what polymers you use and the process itself. Unfortunately, plastic molding isn’t a simple process. There are many things that can go wrong along the way, and a bad mold could very well be one of them.
Things to consider in mold design and construction include where to place gates and understanding how your material will flow through the mold once it’s entered. This might seem like a small things, but the flow pattern of the molten plastic in your mold can have a potentially huge impact on the quality of the parts a mold can produce, and unfortunately some molds with faulty designs are simply incapable of producing parts that live up to their intended purpose.
Of all the steps in molding a part with living hinges, having your mold designed and made will usually be the most costly, and so it’s important that the mold delivers as you hoped it would from the start.
The first step in getting your mold made would be proper part design, of course, so don’t neglect proper part design and prototyping. There’s simply no sense in having a high quality mold made for a part that was poorly designed to start with.
However, once you have a good part, your mold’s ability to accurately produce the part becomes the next most vital step in molding a proper part. Because unlike with selecting your polymer, changing your mold and experimenting with it won’t be as simple.
To get a mold that you can rely on, be sure to contact us at Quality Mold Shop. We’ve produced a large number of molds for almost every industry, and our precision equipment allows us to manufacture high quality molds for creating even the most detailed parts.