Published 10/17/2012

More Demanding Than Production

The challenges of prototyping have dramatically increased. This company reinvented itself to specialize in the tight-leadtime process development that prototyping now entails.

Peter Zelinski

Editor-in-Chief, Additive Manufacturing

Tony Cremers has seen prototyping change dramatically. A prototype (such as the one he’s holding) is now essentially a production part. His company has changed to meet the new demands.

The most basic resource for responding to tight lead times is capacity—enough so that jobs don’t have to wait. Craft has more than doubled its number of machining centers in the last five years.

Prototyping for castings has been the most active area of Craft’s business lately.

The triangle-shaped part at right offers a particularly good illustration of why fourth-axis machining is valuable. Pivoting this part within the cycle allowed features facing out from all three points of the triangle to be machined in one setup.

As part size increases, competition decreases. Craft finds its best opportunities in prototyping larger parts using equipment such as this bridge-type machine.

Several of Craft’s machining centers now have fourth-axis capability. This part runs in the fixture in the next photo, which enables the spindle to reach machined features all around the part during a single cycle.

This fixture illustrates the shop’s approach to workholding. Because any given part is unlikely to be seen again, the shop cuts temporary fixtures out of machinable plastic.

Portable CMM arms provide dimensional validation, as Craft project manager Steve Shade explains. A second arm in addition to this one provides in-process measurement. It can be taken to the shop floor and clamped to a machining center for inspecting a part before it leaves the machine.

Mr. Cremers is president of Craft Pattern & Mold of Montrose, Minnesota. The company used to make foundry patterns primarily, but that’s no longer the main focus. Instead, during the last five years, Mr. Cremers and the rest of the company’s small staff have transformed Craft into a prototyping service provider—with “prototyping” defined according to the more rigorous meaning that has as much to do with process development as making a prototype part. Today, Craft performs this advanced prototyping not only for parts that will be cast, but for other types of parts that also use 3D tooling, such as molded plastic components and fiberglass sections. For new component designs using any of these manufacturing possibilities, Craft can now refine the part design, prove out the process and deliver an early run of representative parts that are suitable for validating both the form and performance of the real production component.

There is just one catch. While customers have expanded their expectations of prototyping, they have not similarly expanded their time window. Prototyping today is high-value work within a quick-response timeframe. Craft’s transformation therefore illustrates the types of investments necessary to adapt to a challenge many manufacturers face—namely, the challenge of shrinking margins of lead time.

In-House Advantage

The industries and types of parts that are the most active for Craft seem to go through phases. Lately, equipment for agriculture and earth-moving has commanded the company’s attention. Many components for this equipment begin as castings, so this work brings Craft back to its foundry-related roots.

In the past, says Mr. Cremers, companies in these sectors were more willing to risk going into production with an unproven and sub-optimal process. They were also more willing to risk designing a part that might have been more expensive than it needed to be, owing to a few problematic details that might otherwise have been discovered and changed. The relatively lax attention to the effect of design decisions on production added cost that went unseen, because the cost wasn’t easy to quantify.

Craft and companies like it are now seen as an important part of the solution to this problem. Craft’s role is to understand all of a part’s manufacturing steps well enough to suggest design changes that would make production easier. The company manufactures parts to tight tolerances and performance standards not only so that the customer can have nearly nominal first parts for testing, but also so that the customer has room for variation when it later translates the part’s process into full-scale production.

This effectively means that Craft needs to own a range of operations that most manufacturing suppliers would not have under one roof. For a prototype machined casting, for example, the shop performs pattern making, casting, heat treating, machining and painting. All are in-house because owning these operations is the best way to understand them. All are in-house also because the time constraints Craft faces leave little margin for coordinating with outside suppliers.

Two of the steps in that list—pattern making and machining—involve CNC machine tools. Thus, meeting tight lead times has involved investments in machining capacity in particular. Formerly, prototyping so often meant 3D printing that Craft called its stereolithography devices prototyping machines. Not today. Now, the company’s most vital prototyping resources are CNC machining centers—which is why Craft has so many of them.

Machining Centers

The manufacturing area today includes 17 vertical and horizontal machining centers (in addition to various other machine tools) for a company with a total staff of only 24. This is more than double the company’s number of machining centers five years ago. Meeting short lead times means having enough capacity available that no job has to wait long.

The majority of the machining centers come from Milltronics, another Minneapolis-area company. The Milltronics machines at Craft range from VM-model verticals with 25 and 30 inches of X-axis travel to BR-model bridge mills with X-axis spans of 120 inches. The upper end of the machine sizes reveals another reason why prototyping is now synonymous with machining centers, Mr. Cremers says. Lately, much of the company’s work is beyond the build size typical of 3D printing. Because competition decreases as part sizes increase, Craft finds its best opportunities in prototyping larger parts.

Keeping these machines responsive and productive has also involved investing to increase the machines’ capabilities along with their quantity. In particular, Mr. Cremers points to fourth-axis machining and on-machine measurement.

Capability Improvements

He says fourth-axis machining—adding one rotary axis to complement the three linear axes—is valuable for cast prototypes because of the way machined features on castings often locate with reference to features on other faces. Making multiple, precision setups to hold these tolerances would take more time than prototyping tends to permit. Therefore, Craft pivots the part in the cycle instead. Both horizontal and vertical machines in Craft’s shop now feature a fourth axis, with some existing machines retrofitted to obtain this capability.

Some machines have also been retrofitted with Renishaw probes, measuring both tool and workpiece dimensions. While measuring cutting tool dimensions in-cycle saves considerable time by eliminating offline manual tool setting, letting the machine measure its own finished parts allows checking certain critical features before the part leaves the machine tool.

Craft even uses its offline inspection capability for measuring parts that are still on the machine. The shop validates machined parts using two Faro arms, one of which frequently leaves the quality room so it can magnetically affix to the machining center for measurement there. Inspecting workpieces before they are unclamped from the setup prevents losing time on additional setup effort if the part needs further machining.

The next technology investment will likely be five-axis machining, Mr. Cremers says. It has become clear that the continued advance of the shop will produce the need for this type of machining—it’s just a matter of time.

Even so, the company’s capabilities are already advanced enough to replicate the steps likely to be used in manufacturing even a highly engineered component. The company’s ability to deploy these capabilities is similarly advanced. As a result, whenever Craft struggles with a particular prototyping job, that struggle is a sign, says Mr. Cremers, and repeat customers have learned to welcome this news as early notice of a potential problem. If Craft is challenged to make a part effectively, this suggests the same difficulties are bound to occur later, in full production, unless something changes before the part reaches this stage.