In the past decade for medical devices, the machine shop has relied on a flexible, honing tool for a wide range of automated CNC machining applications such as cross hole deburring, cylindrical honing, surface finishing, edge blending, and cleaning.
By integrating flexible hones into the machining process, complex parts with cross-drilled holes and other difficult-to-access features can be deburred, honed, surface finished, etc. in house, at less cost. In automated machining, removal of burrs and sharp edges in cross-drilled holes and other difficult-to-access areas such as undercuts, grooves, slots, or internal holes can be tedious and time consuming.
Despite the challenges, the removal of burrs from the production process for medical devices is an absolute must for high-quality, precision parts. In many applications, cross-drilled holes act as conduits for fluids, lubricants, and gases. Failing to remove burrs can cause blockage of these critical passages or create turbulence in the flow. Burrs can also lead to part misalignments, affect dimensional tolerances, and limit the overall efficiency of machined components.
“Eliminating burrs is critical because if any loose material gets dislodged during use, there can be serious consequences,” says Janos Garaczi, president of Delta Machine Company.
For such applications, Garaczi selected the Flex-Hone from Los Angeles-based Brush Research Manufacturing (BRM). Characterized by the small, abrasive globules that are permanently mounted to flexible filaments, the product is a flexible, low-cost tool utilized for sophisticated cross-hole deburring, honing, surfacing, and edge blending. The hones are available in a variety of abrasive types, sizes, and grit selections. Flexible hones are ideal because the tools are a cost-effective solution to smooth edges and produce a blended radius for cross-hole deburring.
“In terms of accessibility, I haven’t found any other tools that can do what a Flex-Hone can, whether for multiple cross holes or internal grooves, says Garaczi. “There is really no way to effectively reach those areas with any sort of other tool. Right now, we are making more and more complex parts, especially when it comes to housings with ports all over the part.”
For best results for medical devices, the deburring tool is typically rotated into the main bore into which the cross holes break. After a few clockwise strokes, the tool is removed, and the spindle reversed to rotate and stroke the flexible hone in a counterclockwise direction for a few more strokes. The forward and reverse rotation creates a symmetrical deburring pattern. Coolant should be used to keep metal cuttings and deburred metal in suspension.
According to Garaczi, removing burrs can be particularly problematic when dealing with machined superalloys, such as titanium, Monel, Inconel, Incoloy, Invar, Rene, and Hasteloy, which are some of the most difficult materials to machine.
“The burrs are one of the biggest problems, particularly when machining super-alloys,” says Garaczi. “Even during ‘grooving,’ if you cut the material from one side, it just pushes the burr to the edge; and if you approach it from the other side, it just pushes it back. It doesn’t want to break off the material cleanly. As soon as the tool gets a bit dull it gets a lot worse. So, sharp tools with the right geometry are key.”
Garaczi notes that the Flex-Hone is available with a premium nickel-coated diamond abrasive for use on materials like carbide, ceramic, and steel alloys; as well as a CBN (cubic boron nitride) option that is even harder and is specifically designed for superalloys, which can exhibit of high ductility and work hardening that produce a gummy machining behavior if the correct abrasive tool is not utilized.
He notes that when deburring superalloys such as titanium or 13-8 stainless alloy, utilizing the Flex-Hone has been very helpful. “Most of the 13-8 we machine is heat-treated, so it is subject to significant burrs. The hone is ideal for removing even the most stubborn burrs,” says Garaczi.
Garaczi is installing the flexible hones into CNC equipment to automate the process and reduce the time required to finish superalloys and stainless steels.
Despite the fact that these are abrasive tools, Garaczi says that even though “abrasives” are often all lumped into the same category, a distinction must be made between abrasives used for aggressive material removal and abrasive finishing tools. Finishing tools release little to no abrasive grit during use, and the amount generated is comparable to the metal chips, grinding dust and tool abrasion created during the machining process itself.
Even if minimal fine solids are produced, the filtration requirements for abrasive tools are not much different than for machining. Any particulate can be easily removed using inexpensive bag or cartridge filtration systems.
He says that when making decisions about what tools to purchase it is often on a project-by-project basis. However, if the tool can reduce cycle times versus its cost, it is an easy decision.
The use of the hone is even helping Delta cope with the demands placed on it by COVID-19, by accommodating more work being done in an automated manner. This not only requires less labor, but also facilitates social distancing for any workers on the production floor. “I want to do everything on the CNC machines whenever I can, especially now,” he says.
To achieve this, the machine shop incorporates Flex-Hones in a variety of sizes in its tool carousels.
“For a part, we might use two to three different size hones, depending on the number of cross port intersections and different hole sizes,” says Garaczi. “However, it is really easy to put a Flex-Hone into a toolholder, give it a simple tool path cycle and let it run.”
Garaczi says that automating cross-hole deburring eliminates a lot of off-line work, since Delta Machine’s parts are usually complex with many intersecting holes.
“It is difficult for a person to reliably repeat such work to the level of required quality. Automating this with the CNC machine usually will produce more consistent results, while enabling greater social distancing among our staff on the production floor,” says Garaczi.
For more information, visit here .