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This article discusses design rules and the best materials to use when producing 3D printed hinges.
Living hinges are a basic, low-cost method of connecting two rigid plastic parts with a flexible joint. This article will discuss the advantages of using living hinges and present design rules and material recommendations when using 3D Printing to produce living hinges.
A living hinge is a thin flexible web of plastic that connects two or more rigid sections. Typically the larger rigid sections and the living hinge will be produced of one continuous little bit of plastic. The reduced simplicity and cost of living hinges make sure they are a popular option for most applications. They can be entirely on almost every commercial item: from beverage and shampoo bottles to workshop storage space containers and food product packaging. Living hinges and the linked rigid sections are produced almost as you part through injection molding exclusively.
Living hinges are found in a large selection of items from shampoo bottles to storage space containers
Living hinges are a highly effective solution when two rigid sections have to be became a member of together. A few of the advantages of a full time income hinge include:
Low Cost - Because of the simplicity, living hinges generally are a much cheaper alternative in comparison to other hinge types.
Durability - Living hinges are specifically designed to be opened repeatedly. They encounter very little friction when opened and closed and this typically results in a long lifespan.
Reduced inventory - Living hinges are integrated into a part eliminating the need for extra components.
Appearance - Compared to other connection options (assembled hinges, snap match connections etc), living hinges are an pleasing and non-obtrusive connection solution aesthetically.
The primary limitation of living hinges focuses on their inability to bear any load.
While injection molded living hinges are created to withstand a large number of cycles without breaking, the type of 3D printed parts anisotropic (usually, brittle, layer-by-layer constructions) implies that 3D printed living hinges are usually used for prototyping or proof-of-concept models in which a few cycles are needed. This makes 3D published living hinges suitable for the verification of a style before needing to spend money on costly injection molding tooling.
The main great things about 3D printing a full time income hinge are:
No dependence on expensive tooling.
The design doesn't need to integrate features necessary to injection molded parts such as for example gates, sprues or runners.
Designs can easily end up being modified and iterated to achieve the optimal design.
3D printing will be able to produce parts quickly further accelerating the design process.
A container imprinted from PLA on an FDM machine with a functional living hinge
Because of the additive, layer-by-layer character of 3D printing the proper parts that are produced are usually anisotropic (particularly when printing with FDM). To guarantee the performance of a full time income hinge, parts ought to be orientated so the width of the hinge as opposed to the length is made up one level at the same time (the central axis of the hinge ought to be orientated in the z-direction). This means printing the component in the vertical build path often, as demonstrated in the picture below.
2 containers with living hinge connections; the remaining one is demonstrated in the right print orientation producing a stronger hinge as the best container can be in the wrong orientation in accordance with the print bed
For some prototyping applications, simply printing a thin strip of materials is adequate if the hinge is necessary to be functional for few cycles. If a lot more cycles is necessary the hinge geometry ought to be optimized.
A smartly designed living hinge includes a longer outer surface area to take into account tensile stresses when starting and closing the hinge
As a hinge is closed, it really is put through bending: the outer surface is placed under tension (and stretches), as the inner surface area is compressed. To take into account this, an excellent living hinge design must have a long, curved size on the outer surface area and a brief inner surface. The picture below illustrates a typical injection molded living hinge with sizes in mm.
Recommended sizes for a full time income hinge created for injection molding
For 3D printing, even more materials and a stiffer hinge is normally required to enhance the quantity of cycles before failing. Note though that increasing the thickness of the hinge will also increase the tensile stresses that the outer surface is subjected to. The figure below shows the dimensions of an FDM printed living hinge that achieved 25-30 cycles before failure (all dimensions are in mm).
Dimensions for successfully printed FDM living hinge. Dimensions will vary by technology (see below for recommended dimensions by technology)
The materials and processes that each 3D printing technology produce parts with can vary significantly. Because of this, different design rules often apply to each technology. The 3D printing processes listed will be the the most suitable for creating living hinges below.
A step-by-stage CAD tutorial on developing living hinges with Fusion 360 are available here.
Technology | |
Fused Deposition Modeling (FDM) | The perfect design for a full time income hinge produced through FDM is to printing the hinge with an individual strand of thermoplastic built-into the rigid parts of the build (because shown in the picture below).
The living hinge ought to be printed in one strand of thermoplastic to boost strength This may imply that the component will be printed vertically, resulting in a large amount of required support structure. This will add to the cost and build time of the part. Some dual extrusion FDM printers offer the option to print the hinge section in a secondary flexible material (like TPU) which will further improve hinge performance and the number of cycles before failure. Build orientation is still important for these materials. Recommended hinge specifications: Minimum of 2 coating thicknesses with 0.4 - 0.8mm recommended |
Selective Laser Sintering (SLS) | While SLS parts are much less vunerable to delamination of layers in comparison with FDM, the build path is an important factor when making living hinges still. SLS parts are often imprinted in nylon (PA 12) and the created hinges typically last around 30 - 50 cycles before failure. Recommended hinge specs: 0.3 - 0.8mm solid and at the least 5 mm long |
Material Jetting | Parts produced via Materials Jetting are typically even more isotropic than either FDM or SLS parts. The material jetted parts have become smooth and so are often aesthetically comparable to injection molded parts. The general rigid photopolymers used in Material Jetting are brittle and unsuitable for prototypes, where more than 10 cycles are required. One of the major advantages of Material Jetting though is the ability to produce multi-material prints. By printing the hinge section in a flexible material (like TangoBlack) a living hinge design can be produced that will last a large number of cycles. Recommended hinge specifications: 0.4 - 0.8mm heavy |
Living hinges could be annealed after printing to improve the true amount of cycles before failing. This is may be accomplished by warming up the hinge (for instance by gently owning a flame over the hinge untill it reaches a flexible state without melting), working it back and forth for several cycles at that elevated heat and then leaving it in the closed position to cool down.
Injection molded living hinges are made almost exclusively from polyethylene (PE) and polypropylene (PP) plastics. Both materials are versatile and soft with a minimal melting point relatively.
For 3D printed living hinges, materials which have a higher elongation at break and great tear resistance are the most suitable. The suggested components for each process referred to above are summarised in the desk below.
Technology | Recommended material |
FDM | Single materials: Nylon 12 Multi-materials: PLA or Ab muscles for your body and flexible TPU for the hinge |
SLS | Nylon (PA 12 or PA 11) |
Material Jetting | Single materials: Durable resin (PP-like) Multi-materials: Durable resin (PP-like) or Digital ABS for your body and versatile Rubber-like resin for the hinge |
Living hinges produced via 3D printing are suitable for proof concept designs before buying costly injection mold tooling.
Living hinge geometry should have a long outer surface path and a short internal path.
Dimensions and materials for the best suited 3D printing technologies for generating living hinges are summarised in the table below:
Technology | Dimensions | Material |
FDM | 0.4 - 0.6 mm | Nylon 12 |
SLS | 0.3 - 0.8 mm thick and a minimum of 5 mm in length | PA 12 or PA 11 |
Material Jetting | 0.4 - 0.8 mm thick | Durable resin (PP-like) and/or flexible Rubber-like resin |
