Amid the general euphoria about the opportunities presented by additive manufacturing, there are those who take a more level-headed view of the disruptiveness of the technology. According to Nigel Flowers, United Kingdom managing director of Sumitomo (SHI) Demag, for example, injection molding and additive manufacturing are more complementary to one another than competitors.

"While we cannot knock the level of innovation happening in the 3D printing space, in reality, additive manufacturing is not the universal panacea it's made out to be. Right now, it continues to perform strongest for prototyping rather than mass manufacturing," Flowers said.

The idea that 3D printers are about to overthrow traditional manufacturing techniques — including molding, forging, casting and even subtractive CNC manufacturing — is simply scaremongering, he said.

"There is space for all of these technologies. The key for any manufacturer is to make a well-informed decision based on a number of criteria," Flower said.

For manufacturing components in high volumes, 3D printing today is currently not fast or cost-effective enough to produce precision parts in large quantities. Where 3D printing is beneficial is for prototyping and for generating customized parts in low volumes.

The medical sector has successfully used 3D printing to produce prosthetics, implants, hip replacements, hearing aids and even dentures. For these individual parts, injection molding would not be a financially viable option due to tooling cost.

The tipping point for injection molding will come relatively quickly once mass production ramps up. Calculating the payback involves comparing the unit costs and production time for 3D printing and offsetting this against the cost for tooling development, making, testing and shipping the tool, plus the new unit costs and any assembly. Typically, a contract mass molder producing electronic casings estimates a return on investment of 10,000 parts.

The sustainability credentials of 3D printing are often inconclusive. While some advocates say printing locally saves on transportation costs, the true environmental impact is inherently more complex.

As an example, take energy consumption. While injection molding machines, particularly all-electric systems, continue to cut energy use — the latest Sumitomo IntElect range, for example, uses the same amount of energy as switching on a household kettle — some 3D printing processes used 50-100 times more electricity than injection presses.

Many people equate 3D printing with less material waste. Yet in rapid prototyping, where the development cycle could involve printing multiple versions, waste is still high. Additionally, because of the mix of different materials, grinding up parts that have been 3D printed can be challenging.

Printing on demand is one thing. Take, for example, a medical situation where surgeons pop next door to print a heart valve. Although data is involved in the process, given the time it takes to print one item, can this really be defined as real-time manufacturing?

Instead, smart factories with fleets of injection molding machines, connected and capturing data to achieve speed and scale, is probably the most revolutionary example of real-time manufacturing, especially when production schedules can be automatically adjusted based on stock levels.

For mass volume production runs, repeatability is nonnegotiable. Today's injection molding machines are designed to deliver quality parts, consistently, with tight tolerances and a high cosmetic finish, often in just a few seconds.

If decorative features are required, in-mold labeling can produce a good, repeatable finish. In many instances, this technology is used in combination with stack molds to increase output while maintaining repeatability and quality.

Similarly, the use of digital files means that 3D printing can deliver repeatability, albeit in smaller quantities.

For short-run commodity parts that don't have critical dimensions or demanding mechanical performance requirements, additive manufacturing can deliver functional parts. However, because the parts are printed in layers, the surface finish can be a bit rough and ready.

In injection molding, the finish and surface texture can be created by the tool itself. However, once molded, the part may need to undergo additional post-production finishing, although these processes can be automated within the molding cell.

Traceability of 3D printed parts has been a key concern. Counterfeiting has also been raised as a major issue, and protecting intellectual property is another challenge.

These concerns can be addressed by ensuring software and hardware are fully connected and the 3D print supply chain completely transparent. Other options include printing QR codes and embedding digital files into the component.

Traceability in injection molding is more advanced, with most machinery suppliers providing secure data capture and documentation.

Variations in strength and durability will depend on the materials used. However, taking PET as an example, a 3D printer will create a part in layers. Therefore, the 2D contour might be strong, but the bonding between the layers will not be comparable to a solid mass that has been molded.

Do you have an opinion about this story? Do you have some thoughts you'd like to share with our readers? Plastics News would love to hear from you. Email your letter to Editor at [email protected]

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