1、AGMA905-A17AGMA 905-A17 AGMA Information Sheet Inspection of Molded Plastic Gears AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 905-A17 AGMA 2017 All rights reserved i Inspection of Molded Plastic Gears AGMA 905-A17 CAUTION NOTICE: AGMA technical publications are subject to constant improvement, revi
2、sion or withdrawal as dictated by experience. Any person who refers to any AGMA Technical Publication should be sure that the publication is the latest available from the Association on the subject matter. Tables or other self-supporting sections may be referenced. Citations should read: See AGMA 90
3、5-A17, Inspection of Molded Plastic Gears, published by the American Gear Manufacturers Association, 1001 N. Fairfax Street, Suite 500, Alexandria, Virginia 22314, http:/www.agma.org. Approved May 24, 2017 ABSTRACT Due to their specification, design, and manufacture, plastic gears have unique issues
4、 that can affect the measurement methods and results obtained. This information sheet describes industry accepted practices to inspect molded plastic gears. It identifies the unique characteristics of molded plastic gears that influence the accuracy and/or repeatability of gear measurements. Publish
5、ed by American Gear Manufacturers Association 1001 N. Fairfax Street, Suite 500, Alexandria, Virginia 22314 Copyright 2017 by American Gear Manufacturers Association All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, withou
6、t prior written permission of the publisher. Printed in the United States of America ISBN: 978-1-55589-735-2 American Gear Manufacturers Association AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 905-A17 AGMA 2017 All rights reserved ii Contents Foreword vii 1 Scope 1 1.1 Inspection methods included i
7、n this document . 1 1.2 Types of gears 1 2 Normative references . 1 3 Definitions and symbols 2 4 Tooth flank labeling 3 4.1 Applications . 3 4.2 Labeling systems 3 5 Conditioning 4 5.1 Time 4 5.2 Temperature . 4 5.3 Humidity 4 5.4 Other considerations . 4 6 Distortions . 5 6.1 Out-of-round 5 6.2 Ta
8、per, “hour-glass”, and barrel shape 6 6.3 Wobble 7 6.4 Banana 8 6.5 Internal gear distortions 8 6.6 Sector gear distortions 8 6.7 Rack distortions 9 7 Datum surfaces. 9 7.1 Identification of datum surfaces 9 7.1.1 Datums for external gears, sectors and worms . 9 7.1.2 Datums for internal gears . 11
9、7.1.3 Datums for racks 13 7.2 Adaptation for inspection 13 7.2.1 Substitute datum surfaces 13 7.2.2 Special arbors or fixtures . 14 8 Inspection instruments 14 8.1 Pins . 14 8.1.1 Bores and datum 14 8.1.2 Measurement over/between pins . 15 8.2 Ring gages 15 8.3 Calipers . 15 8.3.1 Standard calipers
10、. 15 8.3.2 Gear tooth calipers . 16 8.4 Micrometers 16 8.4.1 Standard micrometers 16 8.4.2 Ball anvil micrometers 17 8.4.3 Disc micrometer . 17 8.5 Visual inspection . 18 8.6 Optical methods 18 8.6.1 Optical comparator . 18 8.6.2 Video measuring systems 18 8.7 Indicators 18 AMERICAN GEAR MANUFACTURE
11、RS ASSOCIATION AGMA 905-A17 AGMA 2017 All rights reserved iii 8.8 Double flank inspection . 18 8.8.1 Principle of measurement 18 8.8.2 Advantages and disadvantages . 20 8.8.3 Limitations to use of double flank composite measurements 20 8.8.4 Master gear design considerations 21 8.9 Single flank insp
12、ection 22 8.10 Coordinate measuring machine, CMM . 24 8.10.1 Conventional CMM . 24 8.10.2 Gear checking CMM 24 9 Features to be measured . 26 9.1 Datum features . 26 9.2 Number of teeth 27 9.3 Normal module 27 9.4 Normal pressure angle . 27 9.5 Helix angle/lead angle 27 9.6 Hand . 28 9.7 Reference d
13、iameter 28 9.8 Axial pitch 28 9.9 Lead 28 9.10 Tooth thickness . 28 9.10.1 Gear tooth thickness measurement methods 30 9.10.2 Influences on the tooth thickness measurement for plastic gears . 40 9.11 Measurement of gear tip diameters or tip height on a rack 41 9.11.1 Outside tip diameter for externa
14、l gears with even numbers of teeth . 41 9.11.2 Outside diameter for external gears with odd numbers of teeth 42 9.11.3 External sector gears . 43 9.11.4 Minor tip diameter for internal gears 43 9.11.5 Rack tip height . 44 9.12 Measurement of gear root diameters 44 9.13 Tip radius 44 9.14 Root fillet
15、 radius 45 9.15 Runout over a ball or pin . 45 9.16 Double flank composite inspection . 45 9.16.1 Tight mesh center distance 46 9.16.2 Test radius 46 9.16.3 Functional tooth thickness 47 9.16.4 Total composite deviation 47 9.16.5 Tooth-to-tooth composite deviation 47 9.16.6 Total composite deviation
16、 over k teeth 47 9.16.7 Eccentricity . 48 9.17 Single flank inspection 48 9.17.1 Single flank total composite deviation 48 9.17.2 Single flank tooth-to-tooth composite deviation . 48 9.18 Analytical, or elemental, inspection 48 9.18.1 Single pitch deviation . 49 9.18.2 Cumulative pitch deviation . 4
17、9 9.18.3 Functional tooth thickness 51 9.18.4 Measurement over pins or balls by analytical inspection . 51 9.18.5 Runout by analytical inspection . 51 9.18.6 Total profile deviation . 51 9.18.7 Profile form deviation . 53 9.18.8 Profile slope deviation 53 9.18.9 Total helix deviation . 53 AMERICAN G
18、EAR MANUFACTURERS ASSOCIATION AGMA 905-A17 AGMA 2017 All rights reserved iv 9.18.10 Helix form deviation 53 9.18.11 Helix slope deviation 55 9.18.12 Tip relief 55 10 Statistical techniques in measuring plastic gears . 55 10.1 Inside and outside diameters 55 10.2 Total composite deviation . 55 10.3 T
19、ooth-to-tooth deviation 56 10.4 Tight mesh center distance or test radius . 56 11 Measurement system analysis . 56 11.1 Issues with Gage R helical; cylindrical worm; external, internal, and rack forms; sector gears. 2 Normative references The following documents contain provisions which, through ref
20、erence in this text, constitute provisions of the information sheet. At the time of publication, the editions were valid. All publications are subject to revision, and the users of this information sheet are encouraged to investigate the possibility of applying the most recent editions of the public
21、ations listed. AGMA 909-A06, Specifications for Molded Plastic Gears ANSI/AGMA 1012-G05, Gear Nomenclature, Definitions of Terms with Symbols AGMA 915-2-A05, Inspection Practices Part 2: Cylindrical Gears Radial Measurements ANSI/AGMA 2002-C16, Tooth Thickness and Backlash Measurement of Cylindrical
22、 Involute Gearing ANSI/AGMA ISO 1328-1-B14, Cylindrical Gears ISO System of Flank Tolerance Classification Part 1: Definitions and Allowable Values of Deviations Relevant to Flanks of Gear Teeth ANSI/AGMA 2015-2-B15, Accuracy Classification System Radial Measurements for Cylindrical Gears AMERICAN G
23、EAR MANUFACTURERS ASSOCIATION AGMA 905-A17 AGMA 2017 All rights reserved 2 3 Definitions and symbols The symbols used in this information sheet are shown in Table 1. NOTE: The symbols and terms contained in this document can vary from those used in other AGMA documents. Users of this information she
24、et should assure themselves that they are using these symbols and terms in the manner indicated herein. The terms used, wherever applicable, conform to ANSI/AGMA 1012, Gear Nomenclature, Definitions of Terms with Symbols. Table 1 Symbols and terminology Symbol Definition Units Where first used D Sen
25、sitivity parameter - - Eq A.1 Fidv3 Total composite deviation of the master gear m Eq 4 Fr3 Runout of the master gear m Eq 5 K Statistical coverage factor for a specific confidence level - - Eq 3 mn Normal module of the product gear mm Eq 1 mn3 Normal module of the master gear mm Eq 1 N Number of me
26、asurements needed for an individual subgroup - - Eq A.1 /2N Number of standard deviations above zero in a normal distribution - - Eq A.1 N The probability value that the analysis will detect a shift in standard deviation between subgroups - - Eq A.1 pbn Normal base pitch mm Eq 1 UA Uncertainty assoc
27、iated with the gage blocks or setting discs used to setup tight mesh center distance or test radius according to its calibration accuracy m Eq 3 UGBCE Calibration error of the gage block or setting disc m Eq 8 UM Uncertainty associated with the accuracy of the master gear m Eq 3 UP Uncertainty assoc
28、iated with the probe or instrumentation readout m Eq 3 UPCE Calibration error of the probe or instrument readout m Eq 9 UR1 Uncertainty associated with the repeatability of multiple rolls usually determined by artifact or alternate process m Eq 3 UR2 Uncertainty associated with the system reproducib
29、ility element of the measuring system process m Eq 3 U95 Total uncertainty model with the measuring system and process using the statistical 95% confidence level m Eq 3 n Normal pressure angle of the product gear degrees Eq 1 n3 Normal pressure angle of the master gear degrees Eq 1 Helix angle of th
30、e product gear degrees Eq 2 3 Helix angle of the master gear degrees Eq 2 Historical standard deviation - - Eq A.1 A Standard deviation for 5 parts tested 10 times each on a double flank tester by Appraiser A, m; m Eq 6 B Standard deviation for 5 parts tested 10 times each on a double flank tester b
31、y Appraiser B, m; m Eq 6 C Standard deviation for 5 parts tested 10 times each on a double flank tester by Appraiser C, m; m Eq 6 30 Standard deviation over 30 rolls of the double flank parameter being evaluated m Eq 5 Meshing shaft angle on a double flank tester degrees Eq 2 AMERICAN GEAR MANUFACTU
32、RERS ASSOCIATION AGMA 905-A17 AGMA 2017 All rights reserved 3 4 Tooth flank labeling Modern CNC gear inspection equipment, which is used to report measurements for individual or the full succession of gear teeth, identifies teeth by their count from an initial tooth numbered one. It also identifies
33、the flank of each tooth on which the measurement was made by reference to a “left flank” and a “right flank”. Identification of each tooth and feature is also essential with other inspection methods, even if the labeling of the measurement data is to be made manually. Identification of the particula
34、r cavity and the tooth orientation in that cavity is recommended to correlate the tooth labeling used for inspection. 4.1 Applications A labeling system imposed on the reported measurement data, accompanied by appropriate marking on the inspected gear, can be applied in several ways. Any inspection
35、anomalies that stand out in the measurements can be accurately associated with the corresponding tooth surfaces. This permits further examination of those surfaces to help identify the nature and cause of the particular inspection result. 4.2 Labeling systems Labeling systems defining the direction
36、of the tooth number sequence, clockwise or counter-clockwise, and the flank designation have been established by standards or by inspection equipment design practices. Examples of tooth numbering systems that comply with both AGMA and ISO standards are shown in Figure 1 for external gears and Figure
37、 2 for internal gears. The labeling system needs to be clearly understood by the inspector, designer, molder and tool builder. Figure 1 Notation and numbering for external gears Figure 2 Notation and numbering for internal gears AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 905-A17 AGMA 2017 All righ
38、ts reserved 4 5 Conditioning Any newly manufactured gear should be conditioned before being inspected. For metal gears the conditioning can be as simple as allowing enough time for the newly formed gear to cool to laboratory temperature. However, for plastic gears a number of considerations are invo
39、lved in selecting the proper conditioning for inspection. The injection molded plastic gear emerges from the mold hot. As the material has low thermal conductivity it can take considerable time to cool to laboratory temperature. Semi-crystalline thermoplastics, which comprise most of the materials u
40、sed in plastic gears, will continue to crystallize and shrink for some time after reaching ambient temperature. The high pressures used in the molding process along with the relatively fast cooling rate in the mold will produce residual stresses in the molded gear. Relaxation of these residual stres
41、ses along with continued crystallization of the polymer chains will lead to dimensional changes. Semi-crystalline thermoplastics also exhibit varying degrees of dimensional changes as they absorb moisture from the environment. Other exposures, such as external lubricants, can affect the dimensions o
42、f the thermoplastic gear in operation. Therefore, conditioning prior to inspection by both the customer and the supplier should be carefully considered. Common practice is for plastic parts to be conditioned at 20C and 50% relative humidity. These conditions may need to be adjusted depending on the
43、material, design, tolerance requirements and application of the gear. ISO 1 1 and ANSI/ASME Y14.5 Clause 1.4 (l) 2 discuss conditioning at temperature only since these documents apply to a wider range of materials than just plastics. ISO 291 3 and ASTM D618 4 are standards that specifically apply to
44、 plastics and include temperature and humidity conditioning requirements. 5.1 Time Selecting the times at which inspections will be made is a critical decision. From a process control perspective, one would like to inspect as soon as practical. This would aid in detecting any changes that might have
45、 occurred with the process. Dimensions measured shortly after ejection from the mold will not produce the same results as measurements taken at a later time. Dimensional studies are recommended to determine the correlation between the initial measurements and required gear dimensions. For increased
46、measurement certainty, it is recommended to delay the time after molding before final inspection is performed to ensure effective and full dimensional stabilization of the parts. Tooling, processing conditions, and material can have a considerable influence on the time required for the parts to stab
47、ilize. It is common in the plastics industry to condition parts 2448 hours after molding before final dimensions can be verified. 5.2 Temperature Generally, gears are stabilized and inspected at standard laboratory conditions of 20C. Final dimensions can also be influenced by the end-use operating e
48、nvironment. Extreme temperature variations in the operating environment can lead to additional dimensional change. In this case, a post molding process such as annealing or thermal cycling may be necessary to determine the final dimensions. Typically, such exposure conditions would be specified foll
49、owed by stabilizing at standard laboratory conditions before measuring. 5.3 Humidity Conditioning at a standard laboratory condition of 50% relative humidity is recommended. This is satisfactory for most plastic materials. 5.4 Other considerations The environmental exposure history of the gear, including time, temperature, and humidity can influence the inspection result. Therefore, it is advisable to specify the history of the gear prior to measuring. Any given plastic can absorb one of the components
