Polaris Industries teamed up with Craft Pattern & Mold to solve a steel fabrication conversion design challenge on a line of custom motorcycles.

Denise Kapel, Senior Editor

(Click here to see the story as it appears in May/June's Metal Casting Design & Purchasing.)

Once an experimental field, with some players excelling while others succumbed to economic pressures, rapid manufacturing is hitting its stride. Additive 3-D sand printing technology enables the production of quick-turn metal castings for applications ranging from proof-of-concept prototypes to high quality preliminary runs and onward into full production. For casting buyers, the benefits of using this flexible design method are impressive.

When Polaris Industries, Medina, Minn., was evaluating ways to improve its Indian “Big Chief Custom” line of motorcycles, metalcaster Craft Pattern & Mold, Montrose, Minn., proved itself a key player.

One structural component in the redesigned girder style suspension system achieved a 30% weight savings through conversion to metalcasting. Typically a steel fabrication, the part is a prototype of the upper triple clamp for the front steering assembly on the motorcycle.

“The use of high strength aluminum alloy allowed for critical weight savings, a key driver of performance in the motorcycle industry,” said Tony Cremers, president, Craft Pattern & Mold. “The cast aluminum design is much lighter. Also, the shock mounts and the pivot arms tie in with it, so it’s incorporating three things into one component.”

Other noteworthy benefits to casting the part was Polaris’ ability to incorporate its logo directly into the part, as well as the part’s better appearance overall. 

“We didn’t want to give the appearance of a true finished part,” said Steve Shade, project manager, Craft Pattern. “We’re bringing it out as that raw look the customer wants, but with new functionality.”

The Proof Is in the Printing

Decisions made during the casting design process have far-reaching consequences.

“Many manufacturing and performance issues created at this stage have long-term impact on product cost,” said Tom Prucha, vice president, technical services, American Foundry Society, Schaumburg, Ill. With no additional cost for complexity, additive sand technology opens up new possibilities in metal casting engineering, and it allows part designers to make changes on the fly.

Polaris was updating its motorcycle suspension, which was built on a technology introduced many years ago.

“We wanted to use an air over spring shock in the front, which this component does mount, and we wanted to integrate the handlebar mounts and the pivot arms,” said Tom Hanegraaf, senior computer-aided industrial design (CAID) designer, Polaris Industries. “The industrial designer was the one to conceive how this was going to be packaged together, and I needed to come up with a design for Craft Pattern, so they could produce the molds.”

All together, the group had no more than three weeks to accomplish this part design.  Craft Pattern & Mold used 3-D sand printing technology to produce the prototype sand mold for the steering clamp, now a single 6.5 x 5 x 3-in. 356-T6 aluminum casting weighing 2.6 lbs.

“We had a total of six casted parts to complete for this one-off concept bike,” Hanegraaf said. “[3-D printing] allowed me to hand off these models, making changes as needed during the prototyping process.”

“Near-net-shape castings eliminate costly machining and fabrication processes,” Cremers added. “Timeframe was a factor, and also the customer’s need for one or two pieces. Usually that is a good candidate for [rapid prototyping], where you don’t have to invest the time in producing a pattern tool, then make your sand mold and pour your parts.”

The rapid 3-D sand printing process significantly reduced cost and lead time obstacles to producing this casting conversion. Craft Pattern drew up gating and machining plans, and the parts were on their way to completion. Prototype delivery was accomplished in days rather than weeks.

Determining the Right Rapid Method

The right rapid manufacturing process to use is specific to each job. While it usually bears a price premium versus traditional tooling methods, it offers benefits that offset the cost.

“The typical use of additive manufacturing creates a one-off object that can only be used one time, while other rapid prototyping techniques can create either one-off objects, like an expandable pattern for lost foam or investment casting, or tooling that can be used multiple times for low volume runs,” Prucha said.

Rapid methods for lost foam casting can be additive or subtractive, by printing a foam block or CNC machining pieces to be assembled into a pattern. Prucha offered an example of an assembly consisting of eight fabricated parts, which is now produced as one lost foam casting produced by CNC machining the foam patterns.

Subtractively CNC machining sand molds-another rapid method to produce ready-made molds for casting without tooling-offers advantages when producing a very large part. Sand binder-jetting equipment is limited in size and takes time to build up large layers, incurring additional cost. In addition, sand mold and core material composition is more flexible with subtractive methods, which can be a key benefit when using certain alloys.

Additive manufacturing options involving 3D metal printing are lacking in scope for metalcasting patterns, coreboxes and tooling, according to Prucha. “Efforts are underway to create smaller pieces, but print size, part density and the types of metal that can be deposited currently limit its use,” he said.

A single company probably won’t have all of the available technology, choosing instead to specialize in one or two areas.  But, there is a tendency toward collaboration among casting suppliers providing rapid solutions, as well as jobbing out to one another.

The Benefit for Buyers

For original equipment manufacturers (OEMs) buying castings, rapid manufacturing offers a variety of benefits. Design and engineering ideas that were not always possible can be realized. The precision of additive methods in particular enables feats of draft and wall thickness that have not been possible in the past.

For metalcasters running automated lines that are cost-prohibitive for prototyping, rapid methods can be used to make molds that fit into that equipment for a trial run.

Rapid methods also are being used to make production pattern equipment for longer runs. While prototyping doesn’t always have stringent demands in early design stages, often the parts are made as close as possible to the versions that will be cast in full production.

Prucha recommends an integrated approach to rapid manufacturing using computer-based technology. “[It] not only reduces lead time but improves the design,” he said. “This should be managed via a disciplined program management system. Technologies that assist in creating samples quickly will help maximize the evaluation time and decisions made during this critical phase.”

Rapid manufacturing enables metalcasters to produce components for physical testing that match the castings to be created in full production using other methods. It’s a game changer in the market’s ever increasing competition to produce lightweight, high performance components.

“I was at one of the bike shows and a lot of people were intrigued with us using the latest suspension,” said Hanegraaf. “We were mounting up the fork itself to the triple clamps. That bodes well from a marketing standpoint to have those highlighted areas, to show people the days of old versus what we’re capable of doing now.” He credits his relationship with Craft Pattern and the shop’s introduction of 3-D sand printing as key enablers to the proof of concept and straightforward production of this Polaris prototype.