Make the Right Choice 3D Printing and Injection Molding in Plastic Processing Compared

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RKT Rodinger Kunststoff- Technik GmbH

Wuxi InfiMotion Technology Co., Ltd.

Additive manufacturing with plastic creates remarkable components in small series. Injection molding is ideal for mass production. What should be considered when making the choice?

Plastic parts are indispensable in many areas of daily life. For medical technology components, certain plastics are particularly suitable due to their properties such as biocompatibility, chemical resistance, sterility, and strength. Injection molding has proven to be effective for manufacturing these components. However, there are now also 3D printing processes suitable for producing plastic parts. For example, the injection molding specialist Rodinger Kunststoff-Technik (RKT) has experience with both processes. A comparison of the specific features of these plastic processing methods will show which criteria favor the application of one process over the other. Ultimately, the user's benefit always counts. It is important to note that in many industries, an injection-molded part cannot be replaced by a 3D-printed part without prior validation. RKT has over 50 years of experience as a manufacturer of injection-molded parts for high-tech industries such as medical technology, diagnostics, and life sciences. RKT has its own tool and mold making and uses 3D printing for internal tasks such as the production of operating materials and prototypes, as well as for development projects and for demonstration purposes with a focus on customers and suppliers.

The Differences in Component Creation

The injection molding process is a highly precise manufacturing process in which typically thermoplastic—therefore, repeatedly meltable—plastics are melted as granules through heat and friction in the so-called plasticizing screw of the injection molding machine. The melt is then injected under high pressure into a mold (injection mold). The so-called cavity in the steel injection mold defines the exact geometry of the desired end product. In this, the plastic cools in a controlled manner after the injection process and solidifies into a component. Once the cooling phase is complete, the mold opens, and the finished component is removed or ejected. This process allows for the series production of complex plastic parts with high repeatability and efficiency. In 3D printing, often referred to as additive manufacturing, workpieces are not manufactured all at once but built up layer by layer. This involves the use of a laser or a so-called extruder (a kind of "meat grinder" for plastics). Depending on the process, the plastics are processed as powders, liquids (resins), or filaments (thermoplastics).

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Injection Molding is not Always Possible, but Fast

As mentioned above, injection molding is ideal for mass production of plastic parts. Injection molding processes are characterized by very high repeatability in terms of injection parameters and part dimensions. However, for every type of plastic part, there must also be its own injection mold. If something changes on the part, this must also be reflected in the mold, which can become expensive. The process flow and parameters as well as product quality remain the same and can be easily monitored. Injection molding processes are known for short production times—so-called cycles. Unlike injection molding, 3D printing does not require expensive molds and injection molding machines. It is possible to produce parts with very complex geometries, structures, undercuts, and cavities that are difficult or usually impossible to manufacture by injection molding. However, compared to injection molding, building a part takes much more time. Depending on the method, this time can be reduced accordingly by using multiple laser heads or extruders working in parallel.

These Aspects are Crucial in the Selection:

Criteria for choosing the manufacturing process include the geometry, surface texture, mechanical strength, and size of the parts to be manufactured. As mentioned, parts with complex shapes and internal cavities are difficult or impossible to produce by injection molding. If both processes are possible for a manufacturing task, additional criteria must be compared. These include the quantity of parts to be produced, the tolerances to be maintained, the production time for a part, and the associated machine hourly rate, material costs, and in the case of injection molding, the costs for manufacturing the injection mold. Another question is whether the parts are ready for installation or need further post-processing. From these criteria, the expected unit costs can be calculated. At a certain batch size, a so-called "break-even point" is reached, where the cost-effectiveness of both processes is equal. Generally, for a higher quantity, injection molding will be more economical, while for a lower quantity, 3D printing will be more economical.

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