Enter the Matrix: Turning Performance

Courtesy of 2L

A scanner reads an engraved 2-D data matrix bar code.

Tools and techniques for engraving 2-D data matrix bar codes on machined metal parts.

Whether you’re reading a magazine, shopping or simply strolling around town, 2-D data matrix bar codes are becoming ubiquitous. That’s because those bar codes can contain a large amount of information in a small space, be read with smart phones and other portable devices and require only about a 20 percent contrast ratio for commercial scanners to read them (about a 30 percent ratio for a smart phone app). Redundant data in the bar code allows it to be read even if part of the code is missing.

Those characteristics make 2-D data matrix bar codes attractive for tracking machined parts as well, including parts for the aerospace, off-road equipment, electronics, automotive and firearms industries. Some of the newer specifications require 2-D data matrix bar codes on firearms in addition to standard serial numbers, noted Lance Nelson, president of 2L inc., Hudson, Mass. When consuming a minimal amount of a part’s real estate is an issue, he pointed out that 2L has produced bar codes as small as 0.1 “×0.1 “.

Another industry using the codes is medical. “We’re seeing a lot of medical applications, where the liability and traceability chain is important,” said Jason Marsh, director of R&D for Kyocera Micro Tools, Costa Mesa, Calif. The information a 2-D data matrix bar code can contain includes device manufacturer, expiry dates, device make and model, serial or lot number and any special attributes the device may possess, he added.

Various methods exist for engraving 2-D data matrix bar codes, and this article covers applying engraving tools in a CNC machine, micropercussion engraving and scribing.

CNC Machine Engraving

When producing 2-D data matrix bar codes, more part manufacturers are gravitating toward engraving them in the CNC machine tool that produced the part, especially with the proliferation of multitask machines, which enable a part to be completed in one chucking. “More customers want to set it up one time,” said Jeff Davis, vice president of engineering for Harvey Tool Co. LLC, Rowley, Mass. “It only makes sense. The more shop departments that part has to go through, the slower the output and the more inefficiency. This includes engraving applications.”

Marsh concurred. “A shop wants to do everything in one operation—no additional fixturing.”

When shops engrave in a CNC machine, they simply place the engraving tool in the machine’s automatic toolchanger. “You just have to have the software capable of converting the data into a 2-D data matrix bar code,” Nelson said, noting that 2L developed software to generate G code for engraving. The software also enables engraving incremental serial numbers in a part run without having to create a separate program for each number.

Tools for a non-CNC dedicated engraving machine typically measure 6 ” or longer, according to Dale Newberry, president of Micro 100 Tool Corp., Meridian, Idaho. He noted that Micro 100’s engraving tools are designed for CNC operations and are from 1½ ” to 4 ” long, depending on the diameter. The carbide, single-flute tools come to a point with a 0.005 ” flat on the end. “So you have a cutting edge but not an absolutely sharp point that would break off,” he said.

Because the tool point is tiny, Newberry emphasized that, similar to applying a microscale tool, it should be run at a high spindle speed to efficiently engrave. The biggest hurdle is usually the spindle speed of the machine. Many machines only provide a maximum spindle speed of 8,000 to 12,000 rpm, but 20,000 to 40,000 rpm is more effective, he noted. “That would be ideal,” Newberry said. “However, due to the proprietary process our carbide is run through, Micro 100 tools are strong enough to allow them to run at a slower rpm.”

Courtesy of Kyocera Micro Tools

Kyocera Micro Tools offers a variety of engraving tools for creating 2-D data matrix bar codes.

When the CNC machine that performs the bulk of the machining does not have a spindle that’s fast enough for effective engraving, a shop might engrave in a separate, high-speed machining center sized for micromachining, Kyocera’s Marsh pointed out. “On the big machines, spindle runout becomes a question when small-size engraving,” he said. Marsh added that Kyocera provides engraving tools with shank lengths from ¾ ” to about 4 “, but primarily supplies tools with overall lengths from 1½ ” to 2½ ” to minimize deflection.

Part volume can also dictate whether users produce and engrave parts in the same machine. “If it’s a job shop for an aerospace company, and, let’s say, they’re making 500 brake control valves, then it’s probably no big deal to engrave them in the same machine,” Marsh said. “If they’re making notebook computers in a building with 10,000 machining centers and trying to maximize machine utilization, then it’s a different equation.”

Spring into Action

Practically any engraving tool—as well as many small endmills—can generate a 2-D data matrix bar code, according to Nelson. “Most machine shops can get just about anything to work, but you will have the best results if you use the right tool for the job,” he said.

With that in mind, 2L developed the Data Matrix Tool to create such bar codes. The multifaceted, pyramid-shaped tool is made of ultrafine, submicron-grade carbide for achieving long life when engraving 2-D data matrix bar codes and other information in most materials, the company reports. Nelson explained that the tool has a 120° included angle, which is the optimal angle for a scanner to read a 2-D data matrix bar code’s dots, or cells. Essentially, that angle maximizes the contrast between the bar code and the workpiece surface, allowing even inexpensive scanners to read the data. But, “you could pretty much use any tool if you have one of the better scanners,” Nelson said.

Courtesy of Kyocera Micro Tools

Kyocera Micro Tools recommends a multiple-flute cone tool when engraving 2-D data matrix bar codes in hard and casehardened materials.

Although not required, 2L recommends using its spring-loaded engraving toolholder when applying a Data Matrix Tool. With that arrangement, a spring pushes the tool bit against the workpiece, enabling the engraving of consistent dot sizes and depths—even when the workpiece surface is uneven, such as on a casting, or curved, Nelson explained. “The benefit of that is you don’t have to know exactly where the surface is,” he said. “The dots need to be consistent in size; otherwise the bar code scanner will have a hard time reading them.”

In addition, the spring-loaded holder allows feeding the tool at as high a rate as the machine can go, thereby reducing cycle time. For example, a 2-D matrix bar code might take 30 seconds to engrave with a spring-loaded holder compared to 2 minutes when using a rigid holder, Nelson noted. “If you’re doing prototyping, I don’t think anybody really cares,” he said about the cycle-time reduction. “But if you’re making thousands of parts like in the automotive industry, then it’s a big deal.”

Workpiece Issues

Similar to other machining operations, the workpiece material has an impact on the engraving process. Engraving malleable metal, such as brass and bronze for watch components, tends to generate burrs, according to Kyocera’s Marsh.

At the other end of the machinability spectrum, nickel-base and titanium alloys, especially titanium with a high vanadium content, small grain size and high stacking fault energy, exhibit “horrible” workhardening.

“Whenever you’re machining nasty, workhardening titanium, you want to take off quite a bit of material with each pass, more than you normally would like to because of that workhardening zone,” Marsh said. “But engraving is not a big material-removal exercise. The depth when engraving is a few thousandths of an inch.”

Courtesy of 2L

2L designed the multifaceted, pyramid-shaped Data Matrix Tool for creating unique identification marks, such as 2-D data matrix bar codes.

Fortunately, steel, a commonly engraved material, poses little challenge. “That’s the [engraving] sweet spot, from our experience,” Marsh said.

Aluminum and stainless steel parts are also frequently engraved. In lab tests, Marsh noted that Kyocera was able to effectively engrave aluminum at a 10-ipm feed rate at a 15,000-rpm spindle speed, but 300 series stainless steel became too hot at those parameters and burrs formed. Therefore, the company recommends engraving that type of stainless at 5,000 rpm and 5 ipm.

When engraving 2-D data matrix bar codes and other “spotting” applications in hard materials, including green-state ceramics, and casehardened materials, Marsh recommends applying a multiple-flute cone engraving tool. For standard engraving of aluminum and softer steels, he suggests a half-round tool, which means the blank is split, or halved, on center to produce a single-lip tool that has one cutting edge. He added that for engraving high-nickel and tough stainless alloys, a spade tool is usually more suitable. Originally designed for scoring electronic parts, a spade tool has a shallow cone profile and can also be used for beveling.

Impressing the Surface