Most companies would be pleased with a return on investment (ROI) of six months for capital machinery. One machining shop in Conroe, Texas, claims an ROI of only 18 days for an automated cell it developed with a twin-spindle lathe, robot, programmable gaging system, and boxing and palletizing equipment.
The company, Conroe Machine, is a general-purpose shop that focuses on high-technology processes. Located 40 miles from Houston, much of its business involves the machining of drill components for the region’s oil and gas industry.
Among products the company fabricates are thrust-bearing races for down-hole mud motors. These are progressive cavity positive displacement pumps that add power to drilling bits. (“Mud” refers to drilling fluid used in the pump.)
Weekly demand for the races runs into the thousands of pieces at Conroe. The previous production process involved four Doosan Puma lathes, each run by one operator, which did roughing and finishing operations.
The company decided that an automated work cell would better meet production and inspection needs. Conroe invested in an Okuma 2SP-250H lathe and a Fanuc M20iA 6-axis robot that is integrated with an Equator gaging system from Renishaw.
Selecting a measuring device was initially a sticking point. Owing to rapid fabrication of the races — cycle time for each is as little as 98 sec — measurement had to be fast and repeatable for every part. The company looked at white light laser measuring, which is fast but expensive; hard gaging, also expensive and in need of monitoring; and a shopfloor coordinate measuring machine (CMM) that didn’t meet speed requirements.
The Renishaw Equator turned out to be a cost-effective and adaptable option. The device, Renishaw’s first gaging product, uses a comparison technique in which a master set of measurements, taken by a CMM and recorded on the instrument’s MODUS software, are the basis for part inspections. The Equator has an SP25 probe that records 1,000 points/sec. The probe’s styluses are stored in a six-port rack. The supplier’s EZ-IO automation program integrates Equator’s operations with the work cell and selects which measuring program to run for different parts.
Repeatability of the Equator is 0.00007 in. (0.002 mm), and the device can be re-mastered to compensate for changes in shop temperature. Since Conroe’s 65,000-sq-ft plant is climate controlled, re-mastering only occurs once a day.
The machining process is relatively simple. The Okuma lathe has two-part carousels loaded with 300 workpieces. The dual-gantry loaders feed the spindles and place finished parts in a chute that leads to a conveyor, where they are picked up by the robot and placed on the Equator measuring device. If parts meet dimensional specs, the robot transfers them to an engraving machine, then boxes and palletizes them.
The parts’ outer diameters range from 3-6 in. Machining removes 0.015 in (0.38 mm) from each side of a part, while maintaining tolerances of 0.001 in. (0.025 mm). It also removes 0.5 microns of surface finish.
The four Doosan Puma lathes have since been installed in two work cells (two each) where they only do roughing operations.
With the automated work cell, Conroe’s production of thrust-bearing races is 600-700 parts per day.