Conroe Machine is doing what most machine shops only dream of – hard turning a family of parts around the clock in an unmanned cell that operates a 'self-controlled' process. It uses Renishaw EZ-IO software to integrate a FANUC robot with the Equator gauging system for 100 per cent part inspection and auto-compensation of a twin-spindle Okuma 2SP-250 lathe. The cell also boxes and palletises finished parts. The company states that the turning cell paid for itself in an amazing 18 days.
Conroe is proof that it is possible for any shop willing to use the talents of today's young automation experts to exploit new technologies like Renishaw's programmable Equator, with software and programming developed by CNC Programmer James Wardell and Robotics Technician Jeff Buck.
The same automation team has gone on to create an unmanned part measurement/sorting cell for a customer, 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, and with no problems from a shop floor environment.
Conroe Machine is a relatively young company, founded by Murray 'Tippy' Touchette in 2000, with the expressed objective of producing parts with the best manufacturing technology available. The company grew rapidly to about 150 employees operating in a climate-controlled plant of 65,000-square-foot (6000m2). 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. These machines are now split into two cells, loaded/unloaded by FANUC robots, performing only the roughing operation – these cells were among the shop's earlier automation projects. The semi-finished parts are sent out to be case hardened to HRC 65 at a depth of 0.070" (1.7mm) before the finish turning.
James Wardell explains: "Our production plateaued at 800-1000 parts per day with these two cells, so 400–500 per cell. 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/palletising the parts. 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 gauging and shop-floor CMMs. Hard gauging was very expensive and required setup attention, and the CMM gave no speed advantage. While working with Renishaw on other projects, the regional manager, Sheila Schermerhorn, introduced us to the Equator as a possible solution."
Equator is a low-cost, versatile alternative to dedicated gauging; 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" (0.002mm) 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 pushbutton ease, but in this case it is designed for integration into Conroe's automated systems, with the EZ-IO software for automation.
Wardell says: "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. 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.”
Equator in an automated cell
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 dual 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/palletises the finished parts.
Wardell adds: "We developed our own tool compensation software to run on the OSP control. 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" (0.38mm) from each side of the part, with the tightest tolerance at +/-0.001" (0.025mm) and an 8 microinch (0.5 micron) surface finish. Parts range in size from about three to six inches outside diameter. Wardell states: "The Equator is easily able to measure within our tolerances with a high margin. 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 minimised. 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 72degF [22.2degC]."
The measuring methodology for the parts is surprisingly simple, as Wardell explains: "We made an aluminium block with a hole in the centre which is placed in the centre of the Equator fixture plate. We use this to determine our centre and set our co-ordinate system. Each part is placed in the centre of that block. We touch to get a centre 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 EZ-IO automation software on the Equator, 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, so only one cell is now needed compared with two before. It has also 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. Wardell says: "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. We wanted to give them a plug-and-play measurement and sorting system that takes human judgement out of the process, so more good races can be salvaged."
Still being developed when this article was written, Buck and Wardell are assembling a cell that consists of two Equators, a FANUC LRMate 200iC six-axis robot, multiple lanes of low-profile conveyor, a FANUC iR Vision system and an ATI quick toolchanger for the robot's end-effectors. The vision system tells the Equator 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.
Buck says: "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." Wardell adds: "For our machining cell, there was no other cost-effective, shop-floor measuring tool comparable to the Equator. And we hope that our venture into cell integration for a customer opens a new business avenue in this area for our entire company."
Follow the link for more information about Renishaw's Equator and other gauging products.