Gear Inspection: How do we do it? Why is it important?
Gear Inspection occurs throughout the manufacture process for higher precision gears. Gear Inspection can be done in different methods depending on how the gear is called out on an engineering blueprint. The inspection process is vital to insure the quality of the gears we produce and methods will vary depending on the type of manufacture, what is being inspected and the level of precision of the components. Depending on the final quality of the geared component, workpieces can go through multiple inspections during the manufacturing process. On an average job at Marples Gears, a random sample of the job will be inspected no less than once a day by our inspection staff, while our machinists are also inspecting the parts that they are working on. As a rule of thumb, the higher the quality of gear and the higher likelihood of the gear or blank deforming, will determine a larger amount of time spent inspecting the part throughout manufacturing. Because some special processes can affect gear quality, some gears would be inspected before and after to determine if the gears are still able to be used.
The quality of the blank component, a workpiece without the gear teeth generated yet, directly affects the end quality of the gear being produced. The higher the end quality of the gear, the higher precision the blank component needs to be. With that being said, any time that Marples Gears only generates the gear teeth on a workpiece the blank component is inspected and some parts are inspected before the gear teeth are generated. The runout of a bore on the gear blank component is a major factor in the quality and production of a gear, because it can determine the slop in the gear once it has been cut. Hobbing and Shaping gears are both equally sensitive to this type of error in machining. In some cases though a bore feature on a blank can be in print and considered a good part, it would need to have additional operations to true the bore so the gear can be cut with the quality demanded by the client. This can lead to an increase in scrapped parts and production time. Another solution maybe that the gear machinist would indicate every part before cutting, and while this does not create a large increase in lead time on small, prototyping runs, this would cause a larger production run to turn from a job that only takes a few hours to a job that would require days to complete.
Measurement over Pins and Balls:
The most common method for gear sizing is measurement over wires or balls. Which is when specific sized wires are placed in between gear teeth across from one another and the distance between the outside of the wires is then measured with micrometers. This measurement can also tell you if the gear has the proper gear tooth profile. For larger gear a span measurement can be used in place of a diameter reading to insure the gear is the correct size. Many times on blueprints specific wires are called out for the measurement over wires feature, but in many cases alternative wires can be used if say the wires needed are lost or some other special circumstance.
Double Flank Roll Checking:
Roll checking, also known as double flank testing, where two parts are roll in tight mesh and measuring the center distance deviation between the two gears. One of the gears in mesh are the workpiece while the other is a precision master gear. Rolling checking is a form of functional gears, which simulates a controlled version of the conditions under which the produced set of gears will be operating under. The total composite error can also be measured by double flank roll checking, because the deviation of center distances reflects the total composite gear action can be caused by improper gear profile, tooth thickness variations, gear runout or pitch errors. Surface finish errors, nicks, or scratches in the gear teeth can also contribute to the center distance variations. Runout is the variation of the distance between a surface of revolution and a datum surface, measured perpendicular to the datum surface. Runout of a gear can be measured with a dial indicator over a pin placed in successive tooth spaces. Runout measurement is used to assure correct backlash and minimum variation of rotary motion.
Analytical Gear Inspection:
A CNC analytical gear measurement system is a machine that uses a probe similarly to a CMM inspection system to determine various gear callouts that would be difficult to measure otherwise. Analytical Gear Inspections systems traditionally measure the index, helix and involute profiles of the gear teeth, but through breakthroughs in computers, controls, and probing these machines can now also account for error compensation in related geometric features of a workpiece with respect to gear features. This increase in knowledge gain has helped to decrease the time troubleshooting in gear manufacturing development process for both traditional and nontraditional methods of manufacture.
