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Shop Solutions: Grinding Optics On CNC Machining Centers

During the past decade, Optimax (Ontario, NY) has experienced exceptional growth due to the tremendous demand for specialized optics and lenses that it manufactures for a wide range of applications including: aerospace, defense and medical devices, lithography, and biomedical. As a result, the company’s staff has expanded from approximately 100 to 200 people, shifts have risen from two to three (five days a week), and manufacturing technology equipment has grown from ten to approximately fifty pieces of CNC machinery.

Three, four, and five-axis machining centers are used for grinding, polishing and shaping the lenses with diamond tooling. Even though there is five times more equipment operating over three shifts (a nearly 10x increase in spindle hours), the manpower required to write programs for and operate this advanced CNC equipment has barely doubled. Being able to output ten times the work with only double the manpower translates into roughly a five-fold increase in manufacturing productivity. Of course, the actual productivity increase is significantly greater than that because four- and five-axis equipment allows many of the more complex operations to be performed at high speeds with a single setup.

Al Gould, mechanical engineer for Optimax, said his company’s ever-improving manufacturing agility and productivity has occurred in tandem with the rapidly expanding feature set of its chosen CAM software, Mastercam from CNC Software (Tolland, CT). The company has three seats of Mastercam with a maintenance license that entitles it to free annual upgrades. Working closely with its reseller, Optipro Systems, the company routinely implements new toolpaths and features that will enhance programming productivity and reduce machine cycles. Eight staff members at Optimax use Mastercam day in and day out. Another eight are gaining proficiency and can step in as needed to support the primary programmers.

Optimax uses Mastercam CAM software to program machining centers to grind sophisticated custom lenses using diamond-cutting tools.

Many of the R&D initiatives that have taken place at Optimax play a pivotal role in the direction and magnitude of the company’s growth. “R&D activities at Optimax are primarily SBIR projects funded by the Navy, Air Force, and NASA. All of these agencies have a need for optics that can’t be made currently. So we submit proposals to develop a process for making these unusual optics,” said Gould. “The other job we have in R&D is to take what we learned in those projects and apply it to what we do on the shop floor. We try to take things that are related to our work here at Optimax—whether it involves extremely hard materials or extremely difficult geometries—and apply it to our own manufacturing. Things that we are doing now in the SBIR projects that are pie-in-the-sky, we will be making commercially in five years.”

Recent R&D programs have focused on asymmetric lenses, which are even more geometrically complex optics. These completely free form optics are in development for both commercial and defense applications. Asymmetric lenses can be used as windows that correct distortions present in other optical devices that are focused through them. The shape of an asymmetric lens for a particular application is defined by a unique equation that is translated into a Mastercam program governing the precise grinding of the shape into a glass substrate using a five-axis machining center.

A goal of recent asymmetric lens projects has been to meet form tolerances of approximately one micron over an area of approximately 250 mm2. Manufacturing them involves a meticulous process that begins by fine grinding lenses on the machining center. Intense polishing then imparts additional dimensional properties and surface finish. After measuring the lens, a final polishing step corrects any deviation from spec found during measurement. Gould explained that there is no room for error in this process, since a blank of the material that you can hold in the palms of two hands can cost up to $5000. Even more disconcerting, it may be the only one in existence and it could take up to six months to “grow” another one in a vacuum chamber.Optipro lenses are inspected after polishing. Mastercam advanced high precision toolpaths have helped reduce subsequent polishing requirements by about 50%.

When Optimax completes an R&D project it generally delivers a part along with documentation of a complete manufacturing process using its existing manufacturing and metrology equipment. R&D projects are completely integrated with all of the other manufacturing work that is taking place at Optimax. Fast turn-arounds of R&D projects is a function of on-going general improvements in the company’s manufacturing capabilities.

Gould said that Mastercam has provided a number of advancements that have significantly improved the throughput of both its conventional and R&D optics manufacturing. For example, integration with solid models is easily accomplished. Some projects come in as marked up drawings via PDF. Most typical geometries for objects can be defined with four terms: thickness, diameter, and radius. “We just drop them into Mastercam and away we go,” Gould said.

Machine configurations for all of CNC equipment, regardless of type, are available from within the Mastercam programming environment. So there are times where operations for milling, lathe and wire EDM are generated from within a single program.

“Creating a program to make a new lens is really quick. You pick the machine, you pick the toolpath, and you set a few parameters using menus. The longest part is waiting for the CAM program to generate the toolpath, if there’s a lot of complex geometry or for it to generate the posts. One of the nice features of Mastercam is that it is multi-threaded, so while those things are going on in the background, you can be working on another part,” said Gould.

Toolpath selection is critical in using diamond tools to grind super precise shapes that require minimal polishing. One of the most frequently used is Mastercam’s multi-axis Flowline toolpath for both roughing and finishing. This selection keeps the tool always moving in the same direction, which is critical to creating precise surfaces. Using this toolpath, it may take 4 to 16 hours to grind a precision lens. While this seems a long time, this process actually eliminates many more hours that would be required for subsequent polishing. These precision machining capabilities have reduced polishing requirements by about 50%.

Programmers continually use Mastercam’s Backplot and Simulation modes to assure that toolpaths have no interferences and that material removal is correct. This prevents damage to expensive materials that may be irreplaceable.

Aspheric optics have one or more surfaces that have a non-linear radius of curvature, but they have at least one axis along which they are symmetrical. One aspheric lens can take the place of three lenses in conventional applications in aerospace, defense, medical devices, lithography, and biomedical industries.

The five-axis machine is one of the most heavily scheduled pieces of equipment in the building because of it exceptional productivity. Optimax also has another CNC machining center that was designed especially for 3+2 machining. Multiple 3D machining operations for 3+2 machining can be programmed rapidly by quickly selecting tool orientations using Mastercam’s WCS (Work Coordinate System).

Optimax is eager for its CAM partner to pursue lines of development that are particularly advantageous for manufacturing lenses on standard production equipment. Gould is impressed by how closely Mastercam listens to requests for additional functionality. There have been a number of times when he and others at the company have met with reseller Optipro Systems to review desired features impacting optical manufacturing precision and productivity. In time, unique features much like those described appear in subsequent versions of the software. While Optimax is developing advanced optics that will be mainstream in five years, Mastercam is at work developing CAM software tools that will allow them to be manufactured more efficiently. ME

For more information from Mastercam/CNC Software Inc., go to www.mastercam.com, or phone 860-875-5006.

 

This article was first published in the June 2014 edition of Manufacturing Engineering magazine. Click here for PDF.  


Published Date : 6/1/2014

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