Importantly, low-volume steel molds can support the creation of complex parts with a high degree of injection molding quality. Compared to low-volume rapid injection molding<\/a> with 3D-printed molds, steel molds last longer and can achieve part designs with tighter tolerances and finer features.<\/p>\n\n\n\n This article examines steel tools for low-volume injection molding, how low-volume injection molding works, and when to use it for prototyping or production. In addition, you\u2019ll learn how to design parts for low-volume injection molding, how injection molds are made, and how to ensure your project\u2019s success with expert design for manufacturing (DFM) assistance.<\/p>\n\n\n\n The low-volume injection molding process begins when plastic pellets or granules are poured into a hopper that\u2019s connected to an injection molding machine. Typically, this equipment is smaller than the machinery used with high-volume injection molding. In addition to a smaller footprint, low-volume injection molding machines are designed for faster changeovers because the production runs are smaller. <\/p>\n\n\n\n After the plastic pellets or granules leave the hopper, the feedstock is dispensed into a barrel where the plastic is heated and melted into a liquid. A large reciprocating screw pushes the molten material toward the lip of the barrel while raising the injection molding pressure and temperature. As with high-volume injection molding, achieving and maintaining the proper temperature and pressure is essential for avoiding injection molding defects<\/a>.<\/p>\n\n\n\n When enough material and pressure build up inside the barrel, a ram pushes the screw toward the injection mold. This forces a \u201cshot\u201d of plastic out of the barrel into a system of channels in the mold called \u201crunners.\u201d From the runners, the molten plastic passes through openings called \u201cgates\u201d and into the mold cavity. This hollow section of the mold fills with plastic, which then cools.<\/p>\n\n\n\n There are two types of runner systems in low-volume injection molding: hot and cold. Hot runner systems cost more but help reduce defects associated with fluctuating pressure levels and underfilled molds. Cold runner systems cost less but tend to generate more material waste. Still, the cost-effectiveness of cold runner systems can make them attractive for low-volume injection molding projects. <\/p>\n\n\n\n When an injection molded part is ready, the mold is opened and the part is released with ejector pins that are attached to the mold core. Sometimes, part ejection also requires hand loads or sliders and lifters<\/a>. Sliders release external undercuts\u2014recesses or projections on a part\u2019s outer surface that prevent direct removal from the mold cavity. Lifters release internal undercuts instead.<\/p>\n\n\n\n Hand loads cost less than sliders or lifters, but still add injection molding costs since each hand load must be removed from a molded part and then returned to the tool during the next molding cycle. Nevertheless, hand loads are a cost-effective choice for low-volume injection molding for prototyping or production. These release mechanisms can also support complex part geometries such as threads.<\/p>\n\n\n\n After injection molding is complete, post-processing may be required. For example, excess plastic material called \u201cflash\u201d may escape between the parting line where the mold\u2019s core and cavity meet. Some amount of flash is expected, but excessive flash requires removal because it mars part surfaces. A skilled injection molder can reduce the incidence of flash. <\/p>\n\n\n\n Clamping pressure is the force needed to hold the injection mold closed. If pressure isn\u2019t set high enough, the mold may open prematurely and produce flashing. Yet the injection mold also needs to be able to withstand the clamping pressure from the injection molding machine. Typically, the smaller equipment for low-volume injection molding has a lower clamping pressure than a high-volume injection molding machine. <\/p>\n\n\n\n Low-volume injection molding has specific applications for prototyping and production. Whether you\u2019re just starting out or have an existing design, it\u2019s worth considering the relationship between 3D printing<\/a> and plastic injection molding<\/a> so that you understand when to use these complementary processes. Fictiv provides both types of services, along with CNC machining and urethane casting.<\/p>\n\n\n\n 3D printing is ideal for early-stage projects with less than 100 parts and lead times of 1 to 15 days. There\u2019s a point at which it makes sense to switch from 3D printing to prototype injection molding<\/a>, however, and it\u2019s largely a function of design maturity, part volumes, and testing requirements. There are different ways to categorize design maturity, but proof-of-concept, looks-like, and works-like prototypes are all early-stage.<\/p>\n\n\n\n Sometimes, early-stage prototypes aren\u2019t ready for injection molding. The quantities are too low, or the part design is immature and could change significantly during rapid prototyping. If you spread the cost of an injection mold across a handful of parts, it\u2019s hard to justify the expense of tooling. In addition, major design changes can require extensive tooling changes, which add injection molding costs and longer project timelines.<\/p>\n\n\n\n Prototypes with mature designs are less likely to require significant tooling modifications. Plus, designers may need these pre-production prototypes in quantities that justify the cost of an injection mold. Depending on the nature of your project and its testing requirements, you may also need <\/a>injected molded prototypes for a first article inspection (FAI). <\/p>\n\n\n\n For example, let\u2019s say you\u2019re designing a medical device<\/a> that you plan to injection mold. You could use 3D printing for your early-stage prototypes and iterate your design without paying for or waiting for tooling. However, 3D-printed plastics don\u2019t have the same end-use properties as their injection-molded counterparts. For an FAI, you\u2019ll need to use the same material and the same process as production.<\/p>\n\n\n\n Low-volume injection molding is used for short-run production with volumes ranging from 1,000 to 10,000 parts. Because low-volume molds cost less than high-volume tools, it\u2019s possible to justify the cost of a low-volume injection mold by spreading it out across several thousand parts. Still, the economics of low-volume injection molding aren\u2019t the only reason to invest in bridge tooling.<\/p>\n\n\n\n During low-volume production, an injection molder can identify and resolve any tooling-related issues that require part design changes. A molder can also optimize machine and process parameters before making more expensive high-volume injection molds. Modeling and simulation software can also highlight potential problems, but low-volume injection molding actually puts parts in your hands. <\/p>\n\n\n\n If you\u2019re scaling up from 3D printing to injection molding, you\u2019ll benefit from the DFM feedback that Fictiv provides. 3D printing and injection molding use different file types, but you\u2019ll need to do more than just convert your STL files to CAD files. 3D printing has different design rules than injection molding, and you may decide that it\u2019s better to injection mold a complex 3D printed part as multiple pieces. <\/p>\n\n\n\n Designing a part for low-volume injection molding begins with material selection for the end-use properties your application requires. You can choose either commodity plastics<\/a> or specialty plastics and polymer blends<\/a>. Commodity plastics cost less and have lower minimum order quantities (MOQs). Specialty plastics cost more and have higher MOQs.<\/p>\n\n\n\n The table below describes some of the thermoplastics you can choose for low-volume injection molding.<\/p>\n\n\n\n![\"low-volume](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/11\/low-volume-injection-molding.gif\")
How Low-Volume Plastic Injection Molding Works<\/h2>\n\n\n\n
Filling the Mold<\/h3>\n\n\n\n
![\"Low-volume](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/11\/Low-volume-injection-mold-jpg.webp\")
Ejecting the Part<\/h3>\n\n\n\n
Post-Processing<\/h3>\n\n\n\n
![\"injection](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/11\/injection-molding-machines-jpg.webp\")
When to Use Low-Volume Injection Molding <\/h2>\n\n\n\n
Injection Molding for Prototyping<\/h3>\n\n\n\n
![\"3D](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/11\/3D-printing-jpg.webp\")
Short-Run Production<\/h3>\n\n\n\n
![\"Injection](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/11\/Injection-molding-design-1-jpg.webp\")
<\/a>Part Design for Low-Volume Injection Molding<\/h2>\n\n\n\n
Low-Volume Injection Molding Materials and Resin Selection <\/h3>\n\n\n\n
![\"low-volume](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/11\/low-volume-injection-molds-jpg.webp\")
![\"low-volume](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/11\/low-volume-steel-molds-jpg.webp\")