Authored by:
Toby Ringdahl
Manager of the global CAD and technical development group
The Timberland Co.
Stratham N.H.
timberland.com

Edited by:
Leslie Gordon

Our company manufactures shoes, boots, and sandals, and, as such, works with what are called “lasts,” the foot-forms on which shoes are built. Previously, we dealt with an outside last maker. We would describe design changes and the firm would then turn lasts on a lathe out of plastic. The entire process typically took about two weeks. Our company also used model makers to handbuild physical models of sole units. This process also took about two weeks. Outsourcing this function cost about $1,000 a model.

A few years ago, we experimented with a 3D printer from Z Corp., making lasts in-house to cut costs and accelerate the design cycle. Lasts often must change, either for a function or end use, or perhaps to follow a fashion trend. The 3D printer cut the time to get a last to only a few hours. Our company currently uses the ZPrinter 650, having beta-tested it since last August. The machine has a 10 × 15 × 8-in. build envelope — larger than other 3D printing machines.

During a shoe design, we typically begin with the last. If a physical last is available, we might 3D scan it to capture the shape. From there, the data file goes into software for conversion to file formats such as STL for 3D printing, or IGES or STEP for 3D CAD manipulation.

There are two components to the printer software: ZPrint, which lets users position parts, and ZEdit Pro which lets users color parts and apply labels and decals. The printer software requires watertight models, so it warns users about problems such as surfaces facing the wrong way. It also automates the correction of such problems.

Our design team loads the build area with as many components as possible, making for an efficient way to use the printer, especially because we usually run it overnight. Because models are used for representation, the team doesn’t directly fit a model onto someone’s foot. However, we do check measurements from a printed last to ensure it meets design specifications.

The software takes a 3D file, slices the object into thin layers, and directs the machine to “print” a layer on the powder bed, one layer at a time. Think of the process as similar to pages in a book: After one layer completes, the machine lowers the build plate, sweeps on another layer of powder, and prints another cross-section using a colored binder that reacts with the powder and hardens it.

The ZPrinter 650 operates similarly to a 2D paper printer or plotter, dispensing cyan, yellow, magenta, or clear with off-the-shelf HP inkjet cartridges. The ZPrinter 650 model adds black, especially useful in the printing of footwear because outsoles are black. The machine provides true-to-life colors and it builds lifelike models.

The ZPrinter 650 has an integrated depowdering station with compressed air for removing remaining powder while a vacuum captures it for reuse. This is an improvement over older models, which forced users to dig-out parts from the powder. The ZPrinter 650 comes from Z Corp., 32 Second Ave., Burlington, MA 01803, zcorp.com.