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1 2011 Ticona Gears Webinar Gears-007r1 EN 12/11
Design andDevelopment of
Precision Plastic Gear
Transmissions
David Sheridan
Sr. Design Engineer
December 2011
2011 Ticona Gears Webinar Gears-007r1 EN 12/11
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2 2011 Ticona Gears Webinar Gears-007r1 EN 12/11
Section Outline
1. Why Ticona for plastic gears
2. Why plastic for gears
3. Design and engineering
4. Specifications
5. Prototypes and inspection
6. Testing and validation
7. Production
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We Offer You a Broad Product Portfolio
Backed up by
A responsive service network
Skilled application
development and technicalsupport
Across the US, Europe andthe Asia-Pacific region
ImpetThermoplasticPolyester (PET)
VandarThermoplasticPolyester Alloy (PBT)
CelstranLong FiberReinforced
Thermoplastics (LFRT)
FortronPolyphenylene Sulfide(PPS)
VectraLiquid Crystal Polymer
(LCP)
Celcon /Hostaform
Acetal Copolymers(POM)
Global Service And Support
RiteflexThermoplastic PolyesterElastomer (TPC-ET)
CelanexThermoplasticPolyester (PBT)
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Ticona and the Gear Industry
Ticonas been a leader in plastic gear
technology for over 40 years 1961: Celcon POM commercialized
Gears were among early applications
1969: First Plastic Gear Design manual
Among founding members of AGMAPlastic Gearing Committee
With UTS (TK Solver) co-developedPlastic Gear Design software basedon Ticona gear design manual
Developed PGEAR test machine
First plastic material supplier toexhibit at AGMA Gear Expo
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Ticonas Gear Development Support
Our global technical centers supportcustomers through all stages ofapplication development
Gear analysis
Material selection
Gear material testing
Prototype tool design
Injection molding trials
Failure analysis Staff training from gear experts
Comprehensive gear material anddesign information
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Section Outline
1. Why Ticona for plastic gears
2. Why plastic for gears
3. Design and engineering
4. Specifications
5. Prototypes and inspection
6. Testing and validation
7. Production
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Plastic vs. Metal Gears
Lower cost Injection molding vs. machining
Especially for large quantities
As-molded, no finishing
Greater design flexibility
Parts consolidation Molded-in features
Allow other gear geometries
Easy to mold, difficult tomachine, e.g., internal and
cluster gears
Less noiseLower modulus
Do not transmit sound
Greater tooth deflectionincreases load sharing andreduces transmission erroreffects
Light weight, low inertia
Reduce dynamic loadingand noise
Plastic Advantages
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Plastic vs. Metal Gears
Inherent lubricity Do not need lubrication in
many low-load applications
Internal lubricants
For applications that
cannot use externallubricants
Computer printers
Motorized toys
Chemical and corrosionresistance External lubricants
Grease
Oil
Water Lawn sprinklers
Water meters
Shower heads
Plastic Advantages
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Section Outline
1. Why Ticona for plastic gears
2. Why plastic for gears
3. Design and engineering
4. Specifications
5. Prototypes and inspection
6. Testing and validation
7. Production
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The Plastic Gear Development Team
Molder
MaterialSupplier
Plastics Engineer
Quality ControlEngineer
ManufacturingEngineer
Gear Engineer
Project Engineer
Purchasing
ToolBuilder
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Plastic Gear Development
Prime mover
Torque and speed
Inertia, natural freq.
Load(s)
Torque and speed
Special conditions
Inertia, natural freq.
Duty cycle
Life
Physical limits
Ratio
Precision
Efficiency
Lubrication
Environment
Temperature
Chemical exposure
Moisture exposure
Test requirements
Other
Identify ApplicationVoice of the Customer (VOC)
Define Operating Requirements
Anticipate Future Applications
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Select Overall Transmission Geometry
From requirements
Minimum weight? Minimum size?
Good plastic designs may use moregears with split power path
Carefully consider added features Runout
Distortion
Shafting and bearings
Precision Efficiency
Housing considerations
Stiffness
Tolerances
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Relative Gear Train Size
15:1 Reduction
Single Reduction100%
Double ReductionSingle Branch
40%
Double Reduction
Double Branch25%
2 Stage Planetary
9.5%
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Preliminary Gear Sizing
Select materials
Select preliminary gear geometry
Number of teeth
Size (pitch or module)
Profile (tooth proportions) Nominal ambient conditions
Simple load analysis
K-factor
Unit load
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Select Materials
Suit operating environment
Temperature range Dimensional behavior
Property behavior
Chemical environment
Dimensional behavior
Property behavior
Appropriate property mix Fatigue
Stiffness
Impact
Creep
Interaction with other components Friction
Wear
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Precision Engineering Components
Dimensional Requirements(i.e., Tolerances)
MUSTEqual Manufacturing
Capabilities
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Concentricity Tolerances
for Unfilled Acetal
AGMA
12 DP
24 DP
12 DP24DP
Q7
Q10
1 2 3 4Gear Diameter (in.)
AGMA vs. SPI*
SPI Commercial Tolerances
SPI Fine Tolerances
12
10
8
6
4
2
0
Concentricity(10-3i
n.)
*The Society of the Plastics Industry
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Gear Engineers Job
To develop gear tooth geometry and assembly
specifications that will produce gears that functionsatisfactorily under all operating conditions andacross the entire range of manufacturing tolerancesand environmental influences on dimensions.
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One Approach
Use analytical models for gear
tooth geometry and load analysis
Include all possible tolerances andenvironmental influences ondimensions in effective operating
center distance Design Perfect gear geometries
Develop gear geometry at tightmesh, maximum materialcondition
Re-analyze at open mesh,minimum material condition
Analyze worst load condition
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Determine Production Tolerances
For All Components
Gears
Outer diameter and tolerance
Root diameter and tolerance
Tooth thickness and tolerance
Tooth tip radius and tolerance
Accuracy grade
Total compositetolerance (TCT)
Total Composite Error, TCE
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Determine Production Tolerances
Housing
Mounting center distance and tolerance
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Determine Production Tolerances
Shafts, bushings, bearings
Diameters and tolerance
Maximum and minimum radial play
Concentricity (TIR)
Maximum radial play Minimum radial play
Maximum bushing diameter Minimum shaft diameter
Minimum bushing diameter Maximum shaft diameter
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Develop at Tight Mesh,
Maximum Material Condition
Maximum material condition Maximum tooth thickness Maximum outside diameter
Maximum root diameter
Minimum tooth tip radius
Select minimum effectiveoperating center distance
Optimize geometry Maximize contact ratio Minimize root clearance
Tip interference?
Minimize backlash
Minimize specific sliding
Load analysis at temperature Minimize or balance stresses
Excessive tooth deflection?
Tip relief?
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Determine Effective Operating
Center Distance Range
Assembled center distance range Mounting center distance and
tolerance
Bushings, bearings, and shafts Maximum and minimum radial play
Runout (TIR) Gears
Total composite tolerances (Accuracygrades)
Environmental effects Environmental conditions
Temperature range
Humidity range
Chemical exposure?
Dimensional responsebetween housing and gears Thermal response (CLTE)
Moisture or chemical response
Examine when humid-hot
humid-cold
dry-hot
dry-cold
Determine extreme CD rangeand conditions
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Analyze at Open Mesh,
Minimum Material Condition
Minimum material condition Minimum tooth thickness Minimum outside diameter
Minimum root diameter
Maximum tooth tip radius
Maximum effectiveoperating center distance
Check geometry Contact ratio > 1? If not, go back to beginning,
Select new diametral pitch ormodule
Change tooth proportions
Renegotiate tolerances
Load analysis attemperature Load capacity
Excessive tooth deflection?
Tip relief?
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Analyze Other Load Conditions
Tight mesh condition is often
hot and humid Open mesh condition is often
cold and dry
But worst load condition
Open mesh - minimum loadsharing
Hot and humid - minimummaterial properties
Transient conditions
Cold housing and hot gears
Hot housing and cold gears
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Finally
Iterate until all of the above works
Design time cheap
Changes during/after development costly ($ and )
Computer programs are necessary Analytical programs preferred
Graphical programs oftencause problems
Write specifications
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Section Outline
1. Why Ticona for plastic gears
2. Why plastic for gears
3. Design and engineering
4. Specifications
5. Prototypes and inspection
6. Testing and validation
7. Production
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Specifications
Plastic gear transmissions require significant engineering effort.
Components
Gears
Housings
Shafts
Bearings Variations
Manufacturing tolerances
Operating conditions(i.e., temperature, moisture)
Dimensions
Material properties
Making certain the resulting design intent is specified clearly,accurately, and precisely to the gear manufacturer is essential toensuring performance, cost, and delivery requirements are met.
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Specifications
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Specifications
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Section Outline
1. Why Ticona for plastic gears
2. Why plastic for gears
3. Design and engineering
4. Specifications
5. Prototypes and inspection
6. Testing and validation
7. Production
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High-Precision Gear Molding
Accurately predicting andconsistently controlling
(precision) shrinkage.
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The Controlling Principle
Shrinkage is only affected by materials:
Orientation (polymer and reinforcement)
Temperature
Pressure
Almost everything can have an effect on at leastone of these three things and will effectshrinkage.
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Prototypes
Verification of part and material performance
Verification of manufacturing capabilities with dimensionalcontrol
Represent production as mush as possible
Mold Mold material
# cavities, runners, gates, etc.
Cooling channels
Molder
Molding machine
Barrel size residence time
Injection rate
Clamp tonnage
Molding conditions Temperatures
Mold
Melt
Cycle profile Injection speed
Hold time & pressure
Cooling time
Screw RPM & backpressure
Identical to Production
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Accuracy vs. PrecisionThe Target Analogy
High Accuracy
Low Precision
High Precision
Low Accuracy
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Prototype Mold DevelopmentPrecision
Follow material suppliers molding recommendations
Establish appropriate processing window Maximize material properties
Resist correcting dimensions with extremeprocessing conditions
Wide, stable processing window Minimal variational effects on properties and dimensions
Maximize dimensional stability Consistent as-molded dimensions
Precision vs. cycle time
Minimize post-molding shrinkage Mold temperature must exceed operating temperature
Pay now, or pay later!
Design of experiments (DOE)
Stability Equals Precision
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Prototype Mold DevelopmentAccuracy
Then correct tooling for shrinkage
Cut molds steel safe Undersized cavities
Oversized cores
Use inserts
Iterate
Measure thoroughly
Make what you designed
ThenCorrect for Accuracy
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Plastic Gear Development Cycle
Design & Engineering
Prints & Specifications
Prototype Tool & Parts
Measurement & Inspection
Testing
Production
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Inspection and Geometry Verification
During development
Elemental inspection (CNC) Profile error (involute error)
Lead error (helix angle error)
Pitch error (spacing error)
Runout (radial position error)
General inspection Outside radius
Root radius
Tooth thickness Measurement over pins or balls
Elemental Inspection for Development
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Inspection and Geometry Verification
During production
Composite inspection (Double-flank roll checker) Total composite error (TCE)
Tooth-to-tooth error (TTE)
Runout
Stability Equals Precision
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Section Outline
1. Why Ticona for plastic gears
2. Why plastic for gears
3. Design and engineering
4. Specifications
5. Prototypes and inspection
6. Testing and validation
7. Production
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Testing and Validation
Geometry verification!
Realistic Properly represents end-use conditions Continuous testing when end-use is
intermittent Overheating No thermal or dimensional recovery
time
Temperature control Effective
Static loads Creep and creep rupture
Impact loads Motor stall load
Motor rotor inertia load Appropriate
Test procedures often developed formetal gears
Keep It Real
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Plastic Gear Development Cycle
Design & Engineering
Prints & Specifications
Prototype Tool & Parts
Measurement & Inspection
Testing
Production
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Section Outline
1. Why Ticona for plastic gears
2. Why plastic for gears
3. Design and engineering
4. Specifications
5. Prototypes and inspection
6. Testing and validation
7. Production
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Production
Utilize prototype knowledge
Minimize deviations Mold
Mold machine
Molding conditions
Wide, stable process
Maximum material properties
Consistent dimensions
Correct tooling for accuracy
Measure thoroughly
Run capability study
Establish production QC methodology
Produce!
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David Sheridan
Sr. Design [email protected]
Product Information800-833-4882
www.ticona.com
mailto:[email protected]:[email protected]://www.ticona.com/mailto:[email protected]:[email protected]://www.ticona.com/8/9/2019 Gear TiconaGearDesignPPT AM 1211 Gear-007R1
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Information is current as of December 2011 and is subject to change
without notice.
The information contained in this publication should not be construedas a promise or guarantee of specific properties of our products.
Any determination of the suitability of a particular material and part
design for any use contemplated by the user is the sole responsibility ofthe user. We strongly recommend that users seek and adhere to themanufacturers current instructions for handling each material they use.
Any existing intellectual property rights must be observed.
2011 Ticona. Except as otherwise noted, trademarks are owned by Ticona or its affiliates.
NOTICE TO USERS: