BGA Technical Awareness Seminar 2010 - Dontyne Systems · -A mapping technique has been developed...

© Dontyne Systems Limited 2008Dontyne Systems Limited is a company registered in England and Wales with company number 05973058Registered office: 1 Simonside, Prudhoe, Northumberland, ENGLAND, NE42 6LJVAT Registration Number: 902 9027 45

© Dontyne Systems Limited 2010

24 November 2010

BGA Technical

Awareness Seminar

2010

Modelling Production Techniques for Accurate Gears

Dr. Mike Fish Dr. David Palmer

© Dontyne Systems Limited 2010BGA Gears 2010 Technical Awareness Seminar

Introduction� Short Explanation (Dontyne Systems Limited)

� Problems in Manufacture- Metallic Gear Production (Hobbing, Dressing, Grinding)

- Study in Injection Moulding

- Creating a Mould

- Inspection

- Optimisation

- Interface To Machines

� Examples

� What Does That Mean?


AimsProducts And Services For The

Transmission Industry

� Software Products for Gear Design, Analysis, and Manufacturing

� Bespoke Development

� Gear Design Consultancy

� Product Training and Gear Theory Courses


Design Tools

There are many geardesign tools on the market which often

do not take into account the effects

of production method on rating or

performance


Contact Analysis Model

Transmission Error Bearing PatternTE including

Pitch/Run-Out Simulation or Error

Profile/Lead Modification or Measured Data Simulated or Measured Surface

Contact model would benefit from manufacturing simulation


Gear GenerationCommon 2D Tool Profile Definition & Component Generation

Tool Definition Hob/Grind Component Generation


Gear Generation

20° Pressure Angle Gears � Same flanks, different fillet

Tool & Machine Settings Influences Component Generation

11° Hob 20° Hob 25° Hob


Gear GenerationChoice of tool can result in a severe change in root strength

11° Hob 20° Hob

25° Hob

The root strength can

be changed by 30% by

choice of tool


Gear Generation3D thread generation simulations

Profile Dressing Profile/Base-Line Grinding


Gear GenerationThread generation simulation

Grinding Disk ZK worm generation relative to ZN (red) and ZI

(black) profile for increasing curvature worm

Threads 1, Ø 300mm Threads 3, Ø 150mm Threads 3, Ø 100mm


Gear Generation3D hobbing/grinding simulation

Target Surface

Defined in 2DHobbing/Grinding Model


Gear GenerationGrinding simulation highlights Bias (Twist) effect

Target Surface Calculated Surface


Gear GenerationCutting Simulation under load unbalanced forces in cutting


Plastic/Formed Gears

Final part depends upon :

� Mould form

� Material type

� Batch quality

� Feed rates

� Feed position (Gates)

� Cooling time

VERY difficult to predict!


Plastic/Formed GearsErrors in injection mould gears are large and unpredictable

so require corrective action

� Define theoretical surface

� Create tool based on linear expansion and symmetry

� Inspect gear produced by mould

� If outside tolerance grade, invert errors and add to tool

for next iteration

Repeat if necessary !


Plastic/Formed GearsFurther corrective action to mould...

� often 3-10 iterations for high accuracy applications

with modifications done manually on a CAD system

� often 4 moulds (or cavities/inserts) in one tool with

individual shrink characteristics

� will require complete restart for a change in material

specification

� costs @£7-8k per iteration


Create MouldLinear expansion 0-2% of theoretical gear form

Common factors used to

determine initial mould form :

� Material type

� Material below rim diameter

� Tooth aspect ratio (small variation

over tooth height)

� Flank and rotational symmetry

Mould

Gear (Ideal)


InspectionForm Deviation (2D Scan in Transverse plane from CMM)

Process surface scan data :

� Centred in X-Y Plane

� Axis Alignment

� Best Fit

� Measured Data (red) is

compared to a Theoretical Tooth

Form (black)

� Scaled Errors (green) illustrate

deviation

Error Map on one tooth


Inspection

Parameter Evaluation :

� Tip/Root diameter

� Profile

�Tooth Thickness

�Runout

�Root form

Gear Quality

Error Map of transverse section


Inspection

�Mathematics in all devices

using normal surface vectors

is wrong for relatively large

errors such as those in plastic

gearing

Large pitch error results in inaccurate

form error at tips by CMMs


Inspection

�Mathematics in all devices

using normal surface vectors

is wrong for relatively large

errors such as those in plastic

gearing

Unrealistic reporting at tips was often observed. Feed

rate and sample number were eliminated as causes.

Large radial error results in inaccurate form error on tips


Inspection

�Problems at roots with

contact probes on small gears

�Proposed non-contact

solutions (laser, visual, and X-

ray) sometimes have their own

problems

�Difficult to confirm root form

has been reproduced

Jumps in root measurement


InspectionEdit function developed and automated to compensate for

problems in measurement dataArc Insertion

Edited contour (blue) of section to be replaced to correct for irregular measurementElement edit types :

� Cut point/region

� Insert line

� Insert arc

� Tip/root rounding


Mould OptimisationLarge errors not correctly represented, so the vector mapping technique was developed to illustrate true error in tooth form

No Error reported at

Corner

Vectors show shift in contour

Surface Normal Error Map Vector Error Map


Mould Optimisation

Error Map Error Map

Old Tool Surface

Bad CorrectionNew Tool Surface

New technique uses mapped error vectors independent of surface normals to calculate more accurate modified mould

Surface Normals Vectors


Mould OptimisationFull transverse section correction using mapped error

Error Calculation Tool Iteration


Mould OptimisationComparison of Segment Example 1 of 4

Before 1st Attempt After 1st Iteration


Mould OptimisationArbitrary form correction using mapped error technique

Non-circular gear segments (designed by KISSsoft AG, produced

Gaudlitz GmbH) to which corrective action was successfully applied


Mould OptimisationMany optimise parts now in production

Non-circular gear segments (designed by KISSsoft AG, produced

Gaudlitz GmbH) to which corrective action was successfully applied


Interface To MachinesFormat wire path for export to machine or accuracy is lost

through modifications applied by machine operator

Filter Types:�Minimum Radius

�Element type (arc/line/both)

�Maximum number of elements

�Minimum element length

�Tangent elements (<5°)

Precision calculated


Interface To MachinesFormat data in 2 planes for Export to Wire Erosion Machine

Consider:�Measurement at �Input� and

�Output� side of gear face differ

due to differing shrinkage

�Input and Output path can be

independently corrected to

remove conicity across

facewidth

�Point distribution in each layer

must be same number and

approximate position

Input Side

(Warmer)

Output Side

(Cooler)


Interface To Machines3D - Full correction possible using modified surface model such as STEP or IGES definition linked to 5-axis machine


Further DevelopmentModel shrinkage better by considering:

� Properties of material (viscosity)

� Quality of material batch

� Orientation in tool

� Time in mould

Non Symmetric mould

AIM: 20-30% of first casts within accuracy tolerance


Conclusion of Study- Metrology equipment does not accurately report larger

errors found in plastic gears

- A mapping technique has been developed to correct tool

form for large errors in plastic gears

- The mapping technique can be used on arbitrary forms

- There are limitations in the machines which affect

potential accuracy

- Corrective action can be quickly applied during

manufacture with large savings in time and costs


What Does That Mean?

-manufacturing processes contain inherent 3D effects

which affect component geometry

-if they are often not considered they could affect

performance causing lost production or failures

-the effects on geometry can be calculated and should be

assessed at the design stage

-corrective action can be quickly defined during production

or on analysis of existing product lines

-error may not be a significant influence

When designing gears...


What Does That Mean?...and benefits for the business:

� More control

� Faster production

� Improved efficiency

� Product development


Thank You!

BGA Technical Awareness Seminar 2010 - Dontyne Systems · -A mapping technique has been developed...

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