Designing The Best Living Hinge

Digital manufacturing has revolutionized the way products are designed and produced, enabling enhanced functionalities, cost savings, and faster delivery. One area where innovation can be observed is in the incorporation of living hinges into plastic parts.

A living hinge is a thin piece of plastic integrated into a molded plastic part, allowing rotational movement and the ability to fold. Consider a plastic pill box as an example. Without a living hinge, manufacturing this product would involve two separate molds for the box and the lid, two molding operations for each mold, and final assembly. However, by incorporating a living hinge, both the box and the lid can be created as a single molded part in a single molding operation.

Living hinges have become ubiquitous in consumer products. A notable example is the bottle caps on personal hygiene bottles, where the living hinge enables the opening and closing of the bottle. Hinges can be added to a part post-molding, and at Quickparts & Engineering, injection molding is one of the key services offered. Customers rely on the expertise of Quickparts in determining the optimal timing and method for integrating hinges and other features such as text or logos, snaps, threads, inserts, overmolds, and surface finishes.

Living hinges are commonly made of plastic with a high melt flow, making them ideal for injection molding. These plastic hinges have replaced metal hinges in many applications due to several advantages. While they may not support heavy loads, plastic hinges reduce the number of components in an assembly, eliminate the need for traditional fasteners, lower material and assembly costs, and simplify the overall design. Moreover, plastic hinges offer benefits to end-users, such as resistance to corrosion and rust, minimal friction, the ability to fold or bend up to 180 degrees, and long-lasting durability.

To fully realize the benefits of a living hinge, proper design is crucial. Well-designed living hinges should be able to fold and flex repeatedly without losing strength or flexibility throughout the part’s lifespan. Material selection is a critical factor, with polypropylene being the preferred choice, followed by polyethylene if polypropylene is unavailable. The hinge’s thickness should be carefully considered, as a hinge that is too thin may lack strength and tear, while a hinge that is too thick may fracture due to excessive stress. The radius of the bend should be appropriate to minimize stress concentration and maximize durability. Additionally, gate placement and moldability of the part are essential considerations for optimal hinge performance.

In addition to injection molding, 3D printing technologies can also be employed to create custom living hinge designs. Selective laser sintering (SLS), PolyJet, multi jet fusion (MJF), and stereolithography (SLA) are suitable additive manufacturing methods for producing functional and smooth-surfaced 3D printed living hinges.

Designing for moldability is crucial when incorporating living hinges, as they can present challenges during the molding process. Careful design and gate placement are necessary to ensure successful molding. Mold flow analyses can be utilized to identify potential issues and optimize the living hinge design. Engaging an expert molding partner early in the part design process can provide valuable feedback and ensure the design is mold-ready, avoiding common pitfalls like knit lines, sink and warps, and shrinks.

Quickparts & Engineering, founded in 1996, is a leading provider of on-demand digital manufacturing services. With a focus on injection molding and rapid prototyping, Quickparts employs a team of experts who leverage their engineering-centric approach to deliver high-quality products on time and within budget. Their expertise and commitment to customer satisfaction have earned the trust of tens of thousands of product developers and engineers across North America.

In summary, digital manufacturing has opened doors for innovation in product design, including the integration of living hinges. These hinges offer numerous benefits, and their proper design, material selection, and moldability are critical factors in achieving optimal performance. Quickparts & Engineering stands as a trusted partner in providing expert guidance and services in injection molding and rapid prototyping, enabling companies to bring their products to life.

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