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A Pitch for Plastic

When a major truck manufacturer starts using ABS plastic to make jigs and fixtures, it’s time for an attitude adjustment about using plastics in additive manufacturing for fabricating tasks.

FAB Shop recognizes the many applications for additive manufacturing (“AM,” or “3D printing”) in industry, but we’ve taken a cautious approach when it comes to fabricating. We’ve paid little attention to plastics, but AM with plastics is vastly cheaper and faster than AM with metals, and it is sweeping the table in making prototypes, test models, casting patterns, and many other industrial functions. So we sat up and took notice when we learned that Volvo Trucks, and others, are using AM and ABS plastics for production tooling. Now they’re hitting close to home. Volvo Trucks has reduced turnaround times of assembly-line manufacturing tools by more than 94% since incorporating AM technology at its engine production plant in Lyon, France. Pierre Jenny, manufacturing director at Volvo Trucks, says that the company has reduced the time taken to design and manufacture certain tools, traditionally produced in metal, from 36 days to just two days in thermoplastic ABS plus using its Stratasys Fortus 3D Production System.

Strength and stiffness aren’t just about materials

But how do plastics stand up to the rigors of production metalworking? A lot better than you might think. It’s a matter of applying some basic engineering principles to get the stiffness and strength one needs for the task.

We dragged out our dusty Engineering Statics textbook to run some numbers. You can do this with stiffness or strength, but the results are similar either way.
Steel’s bending stiffness is around 30 million pounds – we won’t bother with units here, because we’re just doing a comparison. ABS plastic is on the order of 300,000 pounds. At first glance, steel appears to be 100 times stiffer.

But the stiffness of a beam – or a metalworking finger clamp – varies with the cube of its depth. So, to get the stiffness of a 1-in. square steel clamp, an ABS clamp only has to be around 4.6 in. deep, for the same 1-in. width. The ratio is a lot better for ABS versus aluminum.
That sounds like a bulky clamp, and it is. As you can see from the photos, for unspecified tools, they have a massive appearance. But so what? And the AM plastic can be made into much better structural shapes than a plain rectangle. In terms of material usage, the ABS clamp can be much more efficient, because you don’t have to machine or weld the structural shapes. You just draw the shape you want in CAD and push a button. Often, you can make a tool in one piece that used to require several.

Volvo’s Jenny has worked out the cost on a per­cubic-inch basis. That may sound like an odd way to compare tool costs, but not so much when you think about how easy it is to make that plastic into any shape you want with AM. The all-in cost ratio is roughly 100:1. Metal tools at Volvo Truck cost 100 times more per cubic inch than plastic ones.

No doubt, more readers are now sitting up and taking notice. So you have a process that saves 94% of the time to make tools, and their finished cost, on a cubic-inch basis, is 1/100th as much.

Jenny says “Stratasys 3D printing has made an incredible impact to the way we work. The capability to produce a virtually unlimited range of functional tools in such a short timeframe is unprecedented and enables us to be more experimental and inventive to improve production workflow.”

Improvements in Three Months

Within three months of buying their AM machine, Volvo Trucks had already 3D printed more than 30 different production tools. These include durable but lightweight clamps, jigs, supports, and even ergonomically designed tool holders that produce a more organized working environment.

“We’re working in the heavy-industry sector, so reliability is naturally critical. So far, every piece that we have 3D printed has proved to be 100% fit­for-purpose,” adds Jean-Marc Robin, technical manager, Volvo Trucks. “This is crucial from a practical aspect, but also instils trust among operators and quashes any traditional notion that everything has to be made from metal in order to function properly.”

According to Robin, developing production tools using AM also enables the equipment design team to be far more responsive, including coping with last-minute design changes.
“The fast and cost-effective nature of additive manufacturing means that we are far less restricted than we were even six months ago, allowing us to constantly improve our processes,” he says. “We now have operators approaching our 3D print team with individual requests to develop a custom clamp or support tool to assist with a specific production-line issue they might be having. From a time and cost perspective, this is unimaginable with traditional techniques.”

We used a finger clamp as an example for our stiffness comparison because it’s close to a worst-case. The majority of tools for gauging, aligning, and other fabricating and assembly jobs don’t have to bear such heavy stress loads. Having the ability to make a jig or fixture in hours, rather than weeks, suggests that a lot more time-saving tooling can be made in plastics – tools that might not even be considered if they were made with traditional methods.
Stratasys is a multinational company, one among many builders of AM machines, but they have put some real thought and development into

The Volvo Trucks example is just one of many. It’s worth a visit to their website to see what other possibilities are emerging. It just might spark an idea for a tool you’ve wanted to have, but just couldn’t justify the cost or the time to make it.