Waterjet Technology Solves Quality Engineers’ Material Cutting Woes

The method delivers clean, readily inspectable specimens while preserving the original properties of the material being tested

Published: Thursday, December 22, 2022 - 13:03

Quality assurance and quality control (QA/QC) are a continual part of any manufacturing process. No matter how many times your factory has executed the same procedure, you must regularly perform quality checks to maintain the same quality level of your process. Quality control on a manufacturing line often involves regularly testing samples of whatever is being produced. Most important, the samples must come from the production line.

By definition, no substitute sample is valid; otherwise, it’s not a “sample.” A quality control process might involve testing raw materials to verify material properties, testing manufacturing steps to ensure they are done correctly, and inspecting the finished product to ensure conformity.

In quality control applications where a specimen must be physically cut out to prepare the sample for testing, there are several challenges that quality engineers face when designing these sample-cutting procedures. First is speed: Since in-line quality checks can hold up a production batch, the samples must be produced quickly. Second, when a visual inspection is needed, the feature might not be easily visible. Finally, cutting material or production-line samples in preparation for a quality control test may alter the material’s integrity.

An abundance of cutting methods, each with limitations

While there are numerous ways to cut samples, each brings unique challenges for quality control.

Many methods exist for cutting metal. Each is generally limited to certain types of metal. Conventional machining is mainly used for metal billets; shearing for sheet metal; laser cutting for nonreflective sheet metal; and plasma cutting for thick, conductive sheet metal.

Even fewer cutting processes are practical for nonmetal materials. Fibrous composites produce noxious dust when cut with saws or spinning blades. Ceramics can crack or chip, even when cut with special wet saws. Plastic and rubber materials may melt, gum up, or emit fumes when cut with blades or a laser.

To make matters worse, the cutting process often distorts the material. Laser cutting produces a heat-affected zone that hardens the edge being cut. Sawing or shearing may bend or deform the edge of sheet material, and plasma cutting introduces heat that can warp thin materials. Therefore, each of these specimen-cutting technologies threatens the integrity of the quality control results.

Fortunately, there’s a cutting process that works for nearly all materials while minimally distorting the material being cut: abrasive waterjet cutting. Waterjet cutting combines a narrow stream of high-pressure water with abrasive particles and ejects the slurry through a nozzle to penetrate a workpiece. It’s a micro-erosion material-removal process that cuts without introducing heat or mechanical stresses to the material. Because all materials erode, they usually cut well with a waterjet and are left with a smooth surface finish akin to a sand-blasted finish.

Waterjet-cutting technology is uniquely suited to quality control applications where there’s a need to ensure material integrity or the integrity of the part being inspected. However, quality assurance departments typically can’t justify the capital investment for a large-format waterjet cutter, the only type of waterjet machine that existed until recently. Newly available and affordable desktop waterjet cutters now make this unique cutting method accessible to quality engineers in need of quickly cutting the exact material samples that they work with in-house.

Affordable waterjet cutters make the technology accessible for in-house quality control applications.

Introducing waterjet cutting to quality control processes

Consider an automotive supplier performing laser-welding operations to join thin steel parts. A sample weld from every production line shift must be inspected to verify the integrity of the welds in the entire batch. How do you visually inspect a weld joint? You must cut through a cross section of the weld without distorting the weld integrity during the cutting process. You can’t introduce excessive heat during the cutting process, so you can’t laser cut, plasma cut, or use an angle grinder. As a result, specimens are often cut by hand with a bandsaw. Even tier-one automotive suppliers hand-cut weld samples with a bandsaw on the production line for quality control.

Waterjet cutting technology is an appropriate solution to this problem because waterjets cut without heat and without shearing or otherwise distorting the weld as it cuts. It preserves the weld joint in its original form so the weld cross section may be easily inspected, is valid, and can be trusted.

Cross section of laser weld joint made visible by waterjet cutting

When evaluating thin, stamped-metal parts, quality engineers also face the challenge of preparing samples without damaging them. For example, a manufacturer of aluminum cans must inspect the top and bottom of the cans (the “can ends”) after they’re stamped into shape to ensure the ridges are properly formed. A representative sampling is regularly inspected as a quality control step. To inspect the cross section, the can ends must be cut in half vertically. How do you cut a stamped, thin aluminum sheet without undermining the stamped shape and ridges on the can ends? Answer: Embed the can end in epoxy, let it cure, then bandsaw the puck and remove the epoxy.

Unfortunately, this time-consuming process delays the collection of QA data, and potentially further delays the identification and remediation of related production deficiencies. A faster, simpler, and more consistent solution is to use a waterjet cutter. There’s no chance of shearing the thin metal when cutting, or warping it by introducing excessive heat.

For quality engineers at aerospace companies that must verify the material properties of their raw materials, using a waterjet cutter to cut tensile coupons is the obvious choice. Hardened steel, a material created by quenching and then tempering the metal, is tedious to cut by conventional methods due to rapid tool wear. Companies often outsource this job to a waterjet cutting service because they can’t afford a traditional large-format machine in-house. This causes delays and introduces risk by relying on an outside supplier for a critical quality-control procedure. Doing this with an affordable small-format waterjet cutter greatly reduces this risk and puts the quality assurance team in control of the entire process.

Hardened-steel tensile coupon cut in-house with a desktop waterjet cutter

Accelerating the development of new materials

Material testing and quality evaluation doesn’t occur just on the production line. It’s also part of the product development process for materials companies. For example, a urethane materials manufacturer needs to test a sample of each new formulation it develops to evaluate the quality of the material. It had already been using a waterjet to cut the tensile coupons but had to outsource the actual cutting to a waterjet-cutting service since, until recently, waterjets were large, expensive machines that were used only in high-volume production environments. The R&D department of a typical small materials company simply couldn’t afford one. Another problem was that the lead time could easily be two or three weeks before samples were returned, which severely slowed not only the testing process but also any follow-up iterations that were needed. With the emergence of desktop waterjet-cutting machines, materials manufacturers of any size can now insource material specimen cutting, which shortens iteration cycles and accelerates product development schedules, all while retaining full control of QA/QC process.

Revolutionizing quality control with waterjet technology

Although waterjet cutting has been associated with production manufacturing processes, its benefits are clearly apparent for quality control. Unlike preparing test samples using laser, plasma, or traditional machining operations, waterjet cutting delivers clean, readily inspectable specimens—and does so while preserving the original properties of the material being tested in assemblies, such as welds, and shapes such as can ends. Equally important, waterjet cutters are now smaller, more affordable, and easier to use, so quality engineers can readily locate and operate them in-house at production, testing, or development labs. This helps to dramatically accelerate the testing cycle while also improving the integrity of quality control data.

About The Author

Nisan Lerea

Nisan Lerea is co-founder and CEO of WAZER, and an inventor of the world’s first desktop waterjet cutter. His years of experience as an engineer lead to the eventual design and launch of WAZER with another University of Pennsylvania engineering student, Matt Nowicki, in 2016.