The deadliest cast: Creating a batch of rubber crabs
Tuesday, February 28, 2017
On the Discovery Channel's hit show, "Deadliest Catch," Derrick Ray is a captain for one of Alaska's most successful and beloved crab fishing ships, the Aleutian Ballad.
During the offseason for crabbing each summer, Ray and his crew take customers on the high seas to simulate the experience — at least without the rough weather, long hours and extreme danger. A staple of the Bering Sea Crab Fisherman's Tour is that the customers get to see the massive 10-pound crabs up close.
Every year, the team keeps between 500 and 800 of these crabs in tanks for the tourists during the summer.
A tank filled with Alaska's tastiest and deadliest catch, the Alaskan king crab.
Seeing crabs up close may be the highlight of the tour, but the costs and casualty of such a display were high. The crabs that are stored for use on the tours are put into nets and placed into the ocean. During the tour, they are pulled up to simulate a catch.
During every tour season, many of the crabs do not survive. And when they die, they start to rot and smell, then must be thrown away. Not only does the high value of the crabs cut into the company's bottom line, but the whole process is also wasteful.
Ray and his company wanted a more sustainable approach.
A close-up of one of the rubber crab dummies, cast with custom-colored resin.
If only there was a way to make an army of exact replicas of these crabs. Then, Ray and his crew would only have to buy the rubber dummies once and reuse them tour after tour, season after season. This would nearly eliminate the wasted crab produced by their business every year.
So Ray contacted us to see if we could solve his problem. We told Ray that despite the uniqueness of his request, we would have no problem creating a product that would exceed his and his customers' expectations.
A frozen crab shipped directly from Alaska. Looks tasty.
To kick off the job, Ray put two of his finest frozen crabs on a plane from Alaska to Portland, Oregon.
The first step was to figure out how to digitize the crabs through 3-D scanning. This was a difficult process because the frozen crabs were crumpled up (see above) in an unnatural position for a live crab, and therefore a direct scan of a whole crab would make for an unconvincing dummy.
Additionally, good casting requires obvious parting lines for demolding and easy flow from the gate into the cavities to make a workable mold. A 2-foot-long, eight-legged object is not conducive to making an easy casting, so we had to get creative.
Individualized scanned components, including claws, legs and the body.
The solution for making a realistic crab — both collecting hard-to-reach scan data (the scanner requires line of sight) and making manufacturable dummies — is to rip the crab apart into segments consisting of the six legs, two claws and bodies, and scan each segment individually.
Actually, we only scanned two legs, two claws and the body. A neat trick to reducing the workload and getting better consistency from leg to leg was to scan the front and back legs of the left side of the crab.
The largest leg was then scaled down in our CAD software to become a medium-sized leg. With three legs digitized, the team could simply mirror the set of left legs to create a set of right ones.
Reducing scanning time was a priority for before our office started to smell too much like Pike's Place Market.
Design for manufacture
A close-up of the Roman joints designed to make a fully assembled crab that is extremely tough.
Creating separate rubber legs and gluing everything together with a saltwater and low-temperature-safe epoxy was the best way to proceed with this project.
By designing Roman joints (above) and tapered "peg-and-hole" mating features, we created a strong bond that actually is more tear-resistant than the rubber material itself.
With segmented legs, we were able to digitally manipulate the legs into straight and bent positions. This way, half the crabs could look different than the others and add to the variation and realism without increasing the project's cost.
Additionally, we now had to design molds for the 12 legs, two claws and bodies as well as source rubber that could survive the harsh undersea conditions of the crab pot, including near-freezing temperatures, extremely high pressure and saltwater corrosion.
In all, we had to purchase hundreds of pounds of silicone and urethane resin weeks in advance of production to fill the order.
3-D printed master pattern
A 3-D printer (colorjet technology) in action. It lays down 0.004-inch layer after layer in a bed of powder until the entire pattern is finished. An 8-inch tall part consists of 2,000 unique layers.
Once all the data was captured, the project planned and the models redesigned, the team was ready to create the first physical representation of the crab, the master pattern.
The pattern is an exact replica of the final crab, but made of a hard and brittle 3-D printed composite. The patterns are much more expensive and time consuming to make than the castings and would not survive the harsh underwater environment.
For this reason, we only created one 3-D printed master pattern for the tooling. For large objects, due to machine time and high material cost, casting is a superior method for manufacturing units at quantity. Casting also gives customers a wider range of material options.
The pattern is 3-D printed in thin (0.004-inch) layers over the course of days. When finished, the pattern is dried and cured, so it becomes rock hard.
Silicone mold making
Silicone tooling for the crab. Top: small claw mold. Bottom: Two- part crab mold with master pattern pictured.
Once the pattern is finished, the mold making can begin.
We make soft-mold tooling by pouring silicone around the patterns to form a mold. The pattern itself is called a positive. The mold creates a negative around the pattern as it hardens. When the pattern is removed, it creates a large open cavity into which urethane resin can be poured to form the final part.
Molds are made by making large boxes and "claying up" the pattern to form a parting line. The top of the mold is poured first.
After it hardens, the pattern is removed from the clay. The mold is flipped over and the clay removed, exposing the parting line. From there, the bottom half of the mold is poured over the top half and cured. Mold release prevents the two silicone halves from bonding together.
Once everything has cured, we have a complete set of tooling that can be used repeatedly for many castings.
Urethane rubber casting
De-molding one of the large, bent crab legs after it has fully cured to a solid rubber. When poured, the resin is liquid.
The casting step is fairly simple: Mix, pour, wait then demold and repeat. Urethane rubbers are generally two-part thermoset polymer blended with a custom color (in this case red-orange) chosen and approved by the customer. Rubbery resins generally take longer than rigid ones to cure — from 8 to 16 hours — so for faster production, often multiple molds are necessary.
We generally cast parts in pressure pots to shrink air bubbles and create the most aesthetically pleasing part possible. Once cast, legs and bodies are inspected for quality and then paired up into sets of straight and bent.
From there, the team completes final assembly by gluing the crabs together with specialized epoxy. After one final inspection and quick cleaning, the crabs are ready to be boxed up for shipment.
A completed lot of crabs after final inspection and cleaning. These are ready to be boxed up for pickup by the customer. Job well done.
A satisfied customer.
For a fraction of the cost of one year's crab inventory, Bering Sea Crab Fisherman's Tour now owns a large supply of crab dummies that can be used year after year.
Before, the majority of their massive crab stock would die during the season. Now, they reduced their stock to under 10 percent of its previous size. The dummies now go in the net, and live crabs are shown to tourists safely in the tanks.
Last summer, they made it through the offseason without a single casualty.
Additionally, the tooling is available in the future for spot orders as the army of crabs experience wear and tear, keeping the process affordable.
The customer saves tens of thousands of dollars in wasted crab every year and gets to market itself as a more sustainable business.
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