How desktop digital manufacturing impacts abrasive waterjet cutting

FIGURE 1. The desktop digital manufacturing landscape comprises four main technologies: CNC machining, 3D printing, laser cutting, and waterjet cutting.

Today's custom sheet metal fabricators are all too familiar with the "one-off." A customer might want one or a handful of pieces for a very low-volume order, or perhaps just a quantity of one. That order might be for a prototype, and when it comes to prototyping, time is of the essence.

Prototyping requires rapid iteration. Designers spend ever-limited time on the crucial problem-solving process of trying, failing, and improving. In the past, this has meant leveraging a dedicated team of in-house professional modelers and machinists with a correspondingly large and specialized complement of complex equipment requiring skilled operators who were generally removed from the actual engineering and design objective. In a custom fab shop, these operators likely worked in a separate prototyping area.

Alternatively, a fabricator might send a rush prototype order to the production floor. Sheet metal fabrication machines are more flexible than they used to be. Even so, squeezing in a prototype or low-quantity order still disrupts the flow of production.

Some operations now are exploring a third option. They’re bringing machine tools into the engineering department itself. Some have experimented with 3D printers, both in plastic and metal, that prevent prototyping engineers from utilizing the machine shop. Others are utilizing an emerging profile-cutting technology that allows engineers to cut a profile themselves—no need to hand off the request to the prototyping shop or the production floor.

Desktop abrasive waterjet cutting is one process among a growing number of technologies in what's become known as desktop digital manufacturing. The concept has created new possibilities for product designers. The time spent going from an initial design concept to a final product is no longer the hurdle it once was. This is a direct result of the democratization of manufacturing. Today, fabrication can occur in production, in a prototyping cell, or in an area of the shop mere steps away from the engineer's workstation.

The practice of desktop digital manufacturing began more than a decade ago with desktop 3D printers. These are great at creating complex parts in various plastic materials. Then desktop laser cutters emerged, which can create precise 2D parts in soft, thin materials such as wood and plastic, feats that 3D printers could not achieve. Affordable CNC mills also became popular, offering the ability to create complex 3D parts in metal.

These technologies have given engineers flexibility to prototype parts in-house. However, one fabrication process remained elusive: Digital tools with the ability to make precise parts in plate or hard sheet material were still not available to most engineers. However, small-format waterjet cutters have recently entered the market, allowing engineers to produce precision parts in sheet metal, carbon fiber, glass, and rubber.

Waterjets cut an array of material by focusing ultrahigh-pressure water and abrasive particles into a nozzle, blasting the slurry at the workpiece. Since all materials erode, and since it is a cold-cutting process, waterjets can produce precise prototype parts with a great surface finish in many materials that 3D printers, low-powered lasers, or CNC machines couldn't handle (see Figure 1).

For instance, one design for a new piece of industrial equipment called for a large electric motor with a belt and pulley transmission. In this application, the gear ratio between the pulleys was a critical design variable that impacted the device's performance. To combat this, the design team recognized the issue and devised a simple solution to test and measure improvements to increase the efficiency of the design.

First, engineers created CAD drawings for a series of alternate-sized drive pulleys, some with more teeth and some with fewer, so the different drive ratios could then be tested to determine the one with the greatest efficiency. Instead of sending out the various pulleys to a machine shop and adding the associated time delays and production costs, the project engineers cut the pieces for the test pulleys in-house on their small waterjet cutter (see Figure 2).

FIGURE 2. A desktop waterjet cutter creates a functional prototype of an aluminum pulley.

CNC-machined pulleys and gears are notoriously expensive and time-consuming and require a highly skilled operator to reliably produce them. Here, there were no delays and no additional costs beyond those of the physical materials required to produce the parts. Using the abrasive waterjet also allowed them to create the pulleys in an end-use material—in this case, aluminum.

Engineers ultimately determined the optimum pulley design that met their specifications while maintaining the desired lifespan for the motor and drivetrain (see Figure 3). In the past, resources spent on such an iterative process would have required more financial and timeline considerations for the project than the manufacturer could likely afford to spend, leading to unwanted design compromises.

Virtually every manufacturer has faced the challenge of rework. It could be a surprise or expected because of a late design change. Whatever the scenario, a manufacturer's options have been limited, especially for purchased components. Sending the parts back to the supplier for rework could take weeks or even months. It's sometimes outright impractical, especially if the parts are big and have been shipped a long distance.

Enter desktop digital manufacturing, and the story changes. Tools like desktop waterjets give engineers the flexibility to address these challenges on the fly. For instance, one manufacturer needed to rework a set of large aluminum-extruded framing. Specifically, they needed to machine new features into the extrusions so that the existing inventory could be used in the updated assembly design. After they’re bent to shape, the aluminum extrusions were normally machined at a machine shop with large vertical machining centers that could accommodate the oversized parts—equipment that the manufacturer certainly did not have in-house.

With the help of a small-format waterjet, engineers fabricated a set of sheet metal jigs to guide the cutting of the new features using a hand-held router (see Figure 4). After a few iterations of the jig designs, engineers essentially transformed a hand-held power tool into a large-format CNC milling machine, albeit dedicated to the exact operations that they needed. The time savings ultimately saved the company money. Again, instead of waiting weeks for rework, engineers could fully vet their design and proceed quickly into full-scale production.

Rapid iteration in prototyping allows engineers, normally somewhat conservative, to be less conservative. Previously, a design that might have required significant development would have been shelved in favor of a less ambitious design that required less experimentation to develop, or worse, replaced by an ill-suited but readily available off-the-shelf part. Now, under the new prototyping model, the emphasis is on micro-iterations. These help push the boundaries of design to produce the greatest efficiency and usability, removing that need for conservative thinking.

For example, a design team was tasked with creating an injection-molded connector with a copper busbar insert. Normally, this would have been created as an overmolded part, something that is done every day by the tens of thousands. However, the final shape of the connector was still a work in progress. Machining the injection molding dies at this stage would have been exceptionally cost- and time-prohibitive, and there was no suitable off-the-shelf alternative.

This seemingly deal-breaking roadblock was cleared using both 3D printing and desktop waterjet cutting. The ability of the 3D-printed parts to emulate a material such as ABS plastic allowed the prototyped part to quickly evolve during the ever-changing design phase. Test iterations were also significantly less expensive than traditional CNC machining.

The copper busbar to be overmolded in the final product also needed to change to suit the design updates. Again, using a small in-house waterjet cutter, engineers altered the copper material to suit the latest design iteration. The combination of 3D printing and a small waterjet helped get this project to the finish line without spending weeks going back and forth between unrelated suppliers.

Desktop digital manufacturing has transformed how engineers create new products. It replaces the old-world, dedicated prototype shop with an environment where design iterations are quickly implemented, risks are minimized, and the time spent bringing new designs to market is dramatically reduced. When the quickest quote for a prototyping shop offers a two- to four-week lead time, there is no substitute for an engaged engineer in command of a well-stocked operation full of CNC technologies working in unison.

Digital desktop manufacturing systems can give a custom fab shops options. When designers prototype, the more iterations they can make in less time, the better. In this world, quick response is the key differentiator.