Shop Solutions: Precision Programmable Gage Cell
A Texas shop’s automation team has incorporated an Equator programmable gage from Renishaw Inc. (Hoffman Estates, IL) into a process-controlled hard-turning cell for measuring and sorting mud-motor bearings. Conroe Machine (Conroe, TX) is doing what most machine shops only dream of—hard turning a family of parts around the clock in an untended automated cell that operates a self-controlled process.
Conroe Machine is demonstrating what any shop that uses the ability of today’s young automation experts to exploit new technology, like Renishaw’s programmable Equator gage, can accomplish. The hard turning cell, with software and programming developed by CNC programmer James Wardell and robotics technician Jeff Buck, integrates a FANUC robot with the Equator gaging system, using Renishaw EZ-IO software to provide simple, comprehensive communication for 100% part inspection and auto-compensation of a twin-spindle Okuma 2SP-250 lathe. The cell also boxes and palletizes finished parts and, according to the company, has “paid for itself in an amazing 18 days.”
The same automation team has created an untended part measurement/sorting cell for one of its customers, this time combining two Equators, a FANUC robot, a vision system and multiple lanes of low-profile conveyor. In both applications, the Equator demonstrates the value of programmable comparative inspection by quickly measuring a family of bearing races, doing it cost effectively without fixturing or problems from a shop-floor environment.
Conroe Machine is a relatively young company, founded by Murray “Tippy” Touchette in 2000, with the objective of producing parts with the best manufacturing technology available. The company grew rapidly to about 150 employees operating in a climate-controlled 65,000 ft2 (6000-m2) plant. While it is a general-purpose shop, Conroe’s location near Houston results in a high percentage of business from the oil and gas industry, principally for drilling components. One of the company’s continuously running jobs for the industry is the manufacture of thrust bearing races for downhole mud motors. These parts are produced by the thousands each week, around the clock.
The bearings are currently roughed out on four Doosan Puma lathes that originally did both roughing and finishing, and were served by four operators. The machines are now split into two cells, loaded/unloaded by FANUC robots, doing only the roughing operation. The cells were among the shop’s earlier automation projects and can be seen on Conroe’s Johnny 5 robot in action on YouTube. The semifinished parts are sent out to be case-hardened to Rc 65 at a depth of 0.070" (1.7 mm) before the finish turning.
“Our production plateaued at 800–1000 parts per day with these two cells, so 400–500 per cell,” said James Wardell. “We had a single operator loading the machines and inspecting the parts. However, you can rely on an operator to correctly inspect only so many parts with this kind of volume, and we needed even more output," said Wardell.
“For our next step up, we conceived a fully automated process for the finish machining, with automatic part loading, postprocess measurement, automatic tool compensation, part engraving, and boxing/palletizing the parts,” Wardell said. “We had pretty good ideas for the components of such a system, except for the part-measurement technology, CNC type and software for tool compensation. Inspection needed to be fast to keep up with the cycle times on the parts, which can be as short as 98 seconds. Originally, we looked at white light laser inspection because of its speed, but the parts are too reflective. We also looked at hard gaging and shop-floor CMMs. Hard gaging was very expensive and required setup attention, and the CMM provided no speed advantage. While working with Renishaw on other projects, regional manager Sheila Schermerhorn, introduced us to the Equator as a possible solution.”
The Equator is a low-cost, flexible alternative to dedicated gaging. It uses the comparison method of measuring. A master part with known measurements taken on a CMM is used to “master” the Equator, with all subsequent measurements compared to the master. Repeatability is 0.00007" (0.002 mm) immediately after mastering. To compensate for shop temperature changes, the Equator can be re-mastered at any time. The Equator uses an SP25 probe for touch and scanning data collection, at speeds of up to 1000 points per second. Styli are stored in an integral six-port changing rack, and the system is programmed through MODUS Equator software. The Equator can be used manually with push-button ease, but EZ-IO software makes it well-suited for integration into automated cells like Conroe’s.
“We attended an open house at Hartwig in early 2012 and saw the Equator in action, along with Okuma’s twin-spindle dual-gantry lathe,” said Wardell. “Apart from being automation-ready for parts of our type, the lathe’s Windows-based OSP dual-path control has an open-architecture, PC-based operating platform, which was important in our plan for developing our own auto-compensation software.”
Wardell and Buck went on to install a cell consisting of the Okuma 2SP-250H, a single Equator, an engraving machine, and a FANUC M20iA six-axis robot. In practice, the lathe’s two part carousels are loaded with about 300 raw workpieces. The lathe’s dual-gantry loaders feed the spindles and place finished parts on a chute leading to a conveyor for pickup by the robot. The robot places the part on the Equator for measurement and, if acceptable, transfers it to the engraving machine, and finally boxes/palletizes the finished parts.
“We developed our own tool compensation software to run on the OSP control,” Wardell said. “This software uses measuring results from the Equator, transmitted in the form of a CSV file, to offset the tools when the part deviates from tolerance.” Machining removes about 0.015" (0.38 mm) from each side of the part, with the tightest tolerance at ±0.001" (0.025 mm) and an 8 μin. (0.5-μm) surface finish. Parts range in size from 3 to 6" (76–152-mm) OD.
“The Equator is easily able to measure within our tolerances with a high margin,” said Wardell. “Our OD/ID stays spot on, with perhaps a couple of tenths variation on radius. We batch parts by size, so changeovers of chuck jaws and other tooling are minimized. The Equator’s speed allows it to easily keep pace with the process. We re-master only once a day, because our shop is climate controlled to 72° F (22.2° C).
The measuring methodology for the parts is surprisingly simple. “We made an aluminum block with a hole in the center which is placed in the center of the Equator fixture plate,” Wardell said. “We use this to determine our center and set our coordinate system. Each part is placed in the center of that block. We touch to get a center on the part, then surface scan for everything else. We planned the measurement process to work without a part fixture or stylus changing. The robot chooses, through the Equator’s EZ-IO software, which measuring program to run for each type of part. We know the critical features we must measure to ensure the part is within tolerance.” ME
For more information from Renishaw Inc., go to www.renishaw.com, or phone 847-286-9953.
This article was first published in the September 2013 edition of Manufacturing Engineering magazine. Click here for PDF.