Automated cell for bearing machining, parts sorting
Texas shop’s automation team deploys programmable gages for measuring and sorting mud-motor bearings. Process-controlled hard turning cell paid for itself in 18 days.
Conroe Machine is doing what most machine shops only dream of: hard turning a family of parts around the clock in a fully automated cell that operates a "self-controlled" process. The company is proof that the dream is achievable for any shop ready to use the talents of today’s young automation experts to exploit new technologies, including programmable gages. The turning cell, with software and programming developed by CNC programmer James Wardell and robotics technician Jeff Buck, integrates a robot with the gaging system, using software to provide communication for 100% part inspection and auto-compensation of a twin-spindle lathe. The cell also boxes and palletizes finished parts. According to the company, the cell paid for itself in 18 days.
The same automation team created a fully automated part measurement and sorting cell for a customer, this time combining two gages, robot, vision system, and multiple lanes of low-profile conveyor. In both applications, the gage demonstrated the value of programmable comparative inspection by quickly measuring a family of bearing races and 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. The company grew rapidly to about 150 employees operating in a climate-controlled 65,000-sq-ft (6000-sq-m) 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 manufacture of thrust bearing races for downhole mud motors. These parts are produced by the thousands each week, around the clock.
The bearings are roughed out on four lathes that originally did roughing and finishing, and were served by four operators. These machines are now split into two cells, loaded/unloaded by robots, doing only the roughing operation—these cells were among the shop’s earlier automation projects (see Conroe’s Johnny 5 robot on YouTube). The semi-finished parts are sent out to be case hardened to HRC 65 at a depth of 0.070 in. (1.7 mm) before the finish turning.
“Our production plateaued at 800 to 1000 total parts per day with these two cells,” explained 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.
“For our next step up, we conceived a fully automated process for the finish machining, with automatic part loading, post-process measurement, automatic tool compensation, part engraving, and boxing/palletizing the parts,” he added. “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 must 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 gave no speed advantage.” While working on other projects, the company found out about the automated gages.
Process-control tools, software
The low-cost, flexible alternative to dedicated gaging uses the comparison method of measuring. A master part with known measurements taken on a CMM is used to "master" the gage, with all subsequent measurements compared to the master. Repeatability is 0.00007 in. (0.002 mm) immediately after mastering. To compensate for shop temperature changes, the gage can be re-mastered at any time. The gage uses a 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 gaging software. The gage can be used manually with push-button ease, but its software for automation also makes it ideal for integration into cells like Conroe’s.
Conroe engineers saw the gage at an open house at Hartwig in early 2012, along with a twin-spindle dual-gantry lathe, said Wardell. “Apart from being automation ready for parts of our type, the lathe’s [Microsoft] Windows-based dual-path control has an open-architecture, PC-based operating platform, which was important in our plan for developing our own auto-compensation software.”
Gaging as part of the automated cell
Wardell and Buck went on to install a cell consisting of the twin-spindle lathe, gage, an engraving machine, and a 6-axis robot. In practice, the lathe’s two part carousels are loaded with raw workpieces, approximately 300 parts. 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 and palletizes the finished parts.
“We developed our own tool compensation software” to run on the lathe control software, Wardell added. The software uses measuring results from the gage, transmitted in a CSV file, to offset the tools when the part deviates from tolerance. Machining removes about 0.015 in. (0.38 mm) from each side of the part, with the tightest tolerance at ±0.001 in. (0.025 mm) and an 8 microinch (0.5 micron) surface finish. Parts range in size from about 3 to six 6 in. O.D. The gage 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-process parts by size, so changeovers of chuck jaws and other tooling are minimized.” Gage 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 degrees F” [22.2 C].
Inspection, automated flexibility
The measuring methodology for the parts is simple. “We made an aluminum block with a hole in the center,” which is placed in the center of the gage fixture plate, Wardell explained. “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 gage 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.”
Measuring, sorting used parts
The hard turning cell currently produces about 600-700 finished parts per day, and it led to a follow-up project involving a parts sorting cell for a customer. Based on a concept sketched out by Touchette, Wardell and Buck are developing a measurement and sorting cell for used mud-motor thrust bearing races.
In oil field service shops, used motors are disassembled, refurbished, and put back into service. “The customer was visually inspecting used races to determine if the parts were reusable, and they knew they were throwing away some good parts—and money,” said Wardell. “We wanted to give them a plug-and-play measurement and sorting system that takes human judgment out of the process, so more good races can be salvaged.”
Still in development when this article was written, the cell Buck and Wardell are assembling consists of two gages, a 6-axis robot, multiple lanes of low-profile conveyor, a vision system, and a quick toolchanger for the robot’s end-effectors. The vision system tells the gage what part number is being presented and what measurement program to run. Good parts are subsequently placed on the appropriate conveyor, and bad parts are placed on a scrap conveyor.
“We designed this system to be trucked in for delivery as a unit, and user friendly for the motor shop people—just turn on the power and load parts onto the conveyor,” Buck says.
“For our machining cell, there was no other cost-effective, shop-floor measuring tool comparable to the Equator,” Wardell added. “And we hope that our venture into cell integration for a customer opens a new business avenue in this area for our entire company.”
– Dave Emmett is Renishaw Inc. business manager/CMM and Equator products. Edited by Mark T. Hoske, content manager CFE Media, Control Engineering, email@example.com.
- Conroe Machine hard-turning work cell uses robotic part handling and part inspection.
- Programmable gages measure and sort mud-motor bearings.
- Process-controlled hard turning cell paid for itself in 18 days.
- Vision system helps sort and separate good parts from bad.
How much more productive could you be with a fully automated CNC workcell?