3D Printing

Using injection molding to reduce part count

3D printing is often viewed as the best technology to use to reduce part count. But there are times when injection molding serves this function better.

For Smalley, an Illinois-based wave-spring manufacturer that serves aerospace, automotive, oil and gas, medical, and other industries, injection molding helped reduce component count, and save time and money.

The challenging part was a wave-spring that serves as a salesperson’s handheld “comparator” that shows the relative size and performance of a wave spring compared with a larger but functionally equivalent coil spring. In a variety of industrial applications, flat-wire wave springs can replace traditional coil springs because a wave spring is half the height of a coil spring, and can still deflect the same amount of weight under the same load.

Illinois-based Smalley Steel Ring Company turned to Proto Labs for prototyping and low-volume production of this “comparator,” a sales demo device. The company offers more than 10,000 standard rings and springs as well as custom designs in diameters ranging from 4 mm to 3,000 mm (0.165 in. to 120 in.).
Illinois-based Smalley Steel Ring Company turned to Proto Labs for prototyping and low-volume production of this “comparator,” a sales demo device. The company offers more than 10,000 standard rings and springs as well as custom designs in diameters ranging from 4 mm to 3,000 mm (0.165 in. to 120 in.).

Smalley turned to Proto Labs for help when it redesigned the comparator to reduce costs. The original versions cost about $100 to produce so the marketing team typically had only 20 made. They wanted an initial run of 1,000 redesigned comparators at a target cost of about $15 each.

The original comparator design consisted of 23 parts, many of them individually machined or purchased. The most costly single part was a linear bearing that allowed smooth compression of the springs. The hope was that injection molding would allow multiple parts to be combined and a number of individual fasteners eliminated. The new comparator design now has just seven parts.

Smalley engineers created initial prototypes on an in-house 3D printer, which approximated the shape of the designed components. But the printing process was slow, the resin was not like the material that would be used for molded parts, and it tended to absorb moisture affecting its performance. The rough surface texture from the layering process caused moving parts to bind instead of slide smoothly, hampering functional testing of the new device.

Proto Labs’ online quoting system, ProtoQuote, analyzed the CAD file for design for manufacturability (DFM). It flagged potential moldability problems including a couple of features in which walls were too thick for effective molding.

Proto Labs sent resin sample “tiles” to help with material choices of feel, finish, and color. Smalley engineers chose Lustran ABS 433, a general-purpose grade of ABS with high impact resistance and a glossy appearance. This material eliminated the separate linear bearing in the original comparator and reduced friction between moving parts.

Proto Labs’ injection molding service worked well for reducing the number of components needed for Smalley’s new comparator. The new design required just seven pieces. The original comparators each consisted of 23 parts.
Proto Labs’ injection molding service worked well for reducing the number of components needed for Smalley’s new comparator. The new design required just seven pieces. The original comparators each consisted of 23 parts.

The completed comparator consisted of three molded parts made by Proto Labs, a wave spring, two retaining rings made by Smalley, and a purchased coil spring that matches the performance specs of the comparison wave spring. Smalley ordered 1,000 injection-molded pieces from Proto Labs that the company assembled into the new comparators.

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Proto Labs
www.protolabs.com