CMMs offer a capable, affordable and flexible gear inspection option.
Gear inspection has long been considered a highly specialized, expensive and difficult part of the gear manufacturing process, requiring a wide variety of complicated gages, testers, dedicated CNC equipment and highly trained experts.
But if you want to make good gears, you need to have all that stuff, right?
Well, maybe not, says John Fox, senior CMM software application engineer for 番茄社社区. According to Fox, the time may be right to consider a coordinate measuring machine (CMM) for your gear inspection needs.
鈥淲e have many customers who are using a CMM for gear measurement, production and setup,鈥� Fox says. 鈥淐ustomers including Honda, Kawasaki, Hitachi, Molon Motors, etc. use the CMM to measure purchased gears. And there are high-precision gear companies, such as Gear Manufacturers Inc., that incorporate our higher-accuracy CMM for setup and some production.鈥�
A lower price tag is one of the main reasons to consider CMMs over conventional dedicated gear inspection equipment, Fox says. A single piece of today鈥檚 sophisticated, fully programmable, fully automated dedicated gear-checking equipment, limited to a single gear size range (gears up to 15 inch diameter, for example) plus software, might cost twice as much as a CMM machine equipped with a rotary table, high-speed scanning probe head and gear-checking software, Fox says. Of course, exact prices for either type of system depend on options and machine size.
The type of CMM used to measure gears depends mostly on the part鈥檚 size and weight. When measuring large gears鈥攖hose with diameters of more than a meter or which are extremely heavy鈥攁 high-precision, horizontal-arm CMM with a rotary table would be required. This style of CMM is generally used for inspecting large-scale gears such as those used in ship and heavy equipment powertrains, turbine gearing and gears used in nuclear and thermal power plants and wind turbines. Inspection of large-scale gears is easier to perform with this style of CMM聽due to its open-access structure.
On the other hand, bridge CMMs are usually the right machine for measuring small or medium-size gears. Two styles of bridge-type CMM are available. One has a fixed table with moving bridge, and the other has a moving table with a fixed bridge. This second style of CMM offers greater accuracy. Some models of bridge CMMs have quite large capacities, overcoming the need for a horizontal arm machine.
In addition to replacing dedicated gear inspection equipment, CMMs can also replace many of the smaller, handheld and functional gages often used in gear inspection. 鈥淗andheld gages are subject to operator interpretation,鈥� Fox says. 鈥淩epeatability between operators using manual inspection methods is lower. Speed of measurement is certainly slower. Written reporting is open to incorrect values being recorded. An automated CMM can be measuring parts, while the operator continues to produce parts. Once the CMM program is proven out, you know you will get good accuracy, repeatability and reporting.鈥�
In some cases, the CMM can even be placed right on the shop floor, alongside production machines.
鈥淭he two major enemies for a CMM are rapid and dramatic temperature changes and vibration,鈥� Fox says. 鈥淓ven when on a shop floor, if the temperature is somewhat stable, there is no major noticeable error. 番茄社社区 equipment has temperature sensors on each scale. Therefore, proper compensation is made for temperature fluctuations. 番茄社社区 has many customers that place the CMMs on the shop floor and are very pleased with the repeatability and accuracy obtained. 番茄社社区 manufactures a specific CMM, the Strato, which is made for use on a shop floor. The Strato scales incorporate non-expanding glass scales; the ways are completely protected with covers and bellows and active vibration dampening using auto leveling air spring units.鈥�
Take another look
Those who might have considered CMMs in the past should definitely take another look, Fox says.
鈥淚n the past 5-10 years, 番茄社社区 CMMs have become much more precise with the incorporation of high-performance controllers, greater scanning technology, minimizing internal heat generation, faster servo drive mechanisms with accelerations of up to 2.598 mm/sec2,鈥� Fox says.
With regard to precision, 番茄社社区 makes both high-accuracy CMMs as well as commodity-level equipment. The commodity-level machines allow a maximum permissible error (MPEE) of 1.7+3L/1,000 microns, while 番茄社社区鈥檚 mid-range and high-accuracy machines allow 0.9+2.5L/1,000 microns and 0.6+1.5L/1,000 microns, respectively.
鈥淚t is because of the accuracy at the mid-range and high end that 番茄社社区 CMMs are very well suited for the extremely tight tolerances required for gear measurement,鈥� Fox says.
鈥淥ne thing to be aware of is 番茄社社区 manufactures every component that is used in all 番茄社社区 equipment, including all of our CMMs,鈥� Fox says. 鈥淲e have excellent control over the quality of the components that go into our CMMs. This enables 番茄社社区 CMMs to have the longest meantime between failures, which is from 25,000 to 30,000 hours.鈥�
Some of the key ingredients to 番茄社社区 machines鈥� accuracy include machine construction and precision components. 鈥淭he Y axis is cut and ground from the same piece of granite as the plate,鈥� Fox says. 鈥淭he Y axis will never change because of this, unlike CMM manufacturers that use a separate piece of granite that is glued and attached by lag bolts. In addition, 番茄社社区 has always produced the best scales, which have minimal to no expansion. 番茄社社区 incorporates temperature compensation on each scale.鈥�
Beyond the precision and accuracy of the machines, one of the keys to accurate gear measurement鈥攚hether on a CMM or a dedicated machine鈥攊s the software, Fox says. For example, calculation of whether an involute curve is correct based on data points extracted during measurement requires the use of high-level mathematical formulas and sophisticated algorithms.聽GEARPAK聽is very exact in these calculations, Fox says, and 番茄社社区 has received certification of the algorithms from Physikalisch-Technische Bundesanstalt (PTB), Germany鈥檚 highest national technical certification authority.
In order to achieve certification of the software, 番茄社社区 had to provide PTB with聽GEARPAK calculations based on data points supplied by PTB. The range of calculations included complex gear flank evaluation for gear tooth profile and flank line; tooth profile deviations, such as slope and form; profile crowning; tip and root relief data; helix slope and form deviations; crowning of the flank line; a variety of end relief data, including modifications of curvatures and reliefs; gear pitch; tooth thickness; tooth spacing; dimension over wires, or balls; displacement dimensions; and tip and root diameters including concentricity, or runout. The results were sent back to PTB where they were compared with the correct results. In order to receive PTB Certification the results of test data must be less than 0.1 碌m (0.0001 mm or 0.000004 inch) from the PTB鈥檚 reference values.
惭颈迟耻迟辞测辞鈥檚听GEARPAK聽software for bevel gears supports Gleason geometry straight bevel, spiral bevel and hypoid gears. 罢丑别听GEARPAK聽for worm gears module supports ZA, ZN, ZI and ZK tooth forms, as well as single- or multi-start worms.
罢丑别听GEARPAK聽software is incorporated with 惭颈迟耻迟辞测辞鈥檚听MCOSMOS聽software package (番茄社社区 Controlled Open System for Modular Operation Support). By combining intuitive icon-based programming with the ability to import native CAD models,聽MCOSMOS聽enables even novice users to easily import part and fixture models and 鈥渧irtually鈥� place them in the volume of their specific CMM.聽MCOSMOS聽graphically defines the CMM, racks, probes, and even styli. Selected graphically, all measurement points are clearly displayed on a 3-D graphic view which can be rotated, zoomed or panned to any convenient viewpoint. Animation enables offline running of a workpiece before ever placing it on the CMM, thus providing machine volume verification and collision avoidance. Then,聽MCOSMOS聽enables users to choose various software modules to analyze measurement results, to document and present results, and to archive the data in practical structures. Furthermore,聽惭颁翱厂惭翱厂听integrates with networked systems for in-line process control applications as well as to enable true enterprise-wide functionality.
The other attractive feature of CMMs for gear inspection is that they can easily be used to inspect other features, Fox says. By incorporating high-level software, CMMs can measure virtually any type of geometry. For example, airfoils, compressor scrolls or turbine blade geometry can be inspected with the appropriate software. In addition, 鈥渢he ability to incorporate components such as vision probes using edge detection technology and laser line scanning probes have made CMMs much more flexible and powerful,鈥� Fox says.