BGA Technical Awareness Seminar 2010

Transcription

1 BGA Technical Awareness Seminar 2010 Modelling Production Techniques for Accurate Gears Dr. Mike Fish Dr. David Palmer Dontyne Systems Limited Dontyne Systems Limited is a company registered in England and Wales with company number Registered office: 1 Simonside, Prudhoe, Northumberland, ENGLAND, NE42 6LJ VAT Registration Number: November 2010

2 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?

3 Aims Products 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

4 Design Tools There are many gear design tools on the market which often do not take into account the effects of production method on rating or performance

5 Contact Analysis Model Contact model would benefit from manufacturing simulation Profile/Lead Modification or Measured Data Simulated or Measured Surface Transmission Error TE including Pitch/Run-Out Simulation or Error Bearing Pattern

6 Gear Generation Common 2D Tool Profile Definition & Component Generation Tool Definition Hob/Grind Component Generation

7 Gear Generation Tool & Machine Settings Influences Component Generation 11 Hob 20 Hob 25 Hob 20 Pressure Angle Gears Same flanks, different fillet

8 Gear Generation Choice 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

9 Gear Generation 3D thread generation simulations Profile Dressing Profile/Base-Line Grinding

10 Gear Generation Thread generation simulation Grinding Disk Threads 1, Ø 300mm Threads 3, Ø 150mm Threads 3, Ø 100mm ZK worm generation relative to ZN (red) and ZI (black) profile for increasing curvature worm

11 Gear Generation 3D hobbing/grinding simulation Target Surface Defined in 2D Hobbing/Grinding Model

12 Gear Generation Grinding simulation highlights Bias (Twist) effect Target Surface Calculated Surface

13 Gear Generation Cutting Simulation under load unbalanced forces in cutting

14 Plastic/Formed Gears Final part depends upon : Mould form Material type Batch quality Feed rates Feed position (Gates) Cooling time VERY difficult to predict!

15 Plastic/Formed Gears Errors 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!

16 Plastic/Formed Gears Further 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 7-8k per iteration

17 Create Mould Linear expansion 0-2% of theoretical gear form Mould Gear (Ideal) 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

18 Inspection Form Deviation (2D Scan in Transverse plane from CMM) Error Map on one tooth 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

19 Inspection Parameter Evaluation : Tip/Root diameter Profile Tooth Thickness Runout Root form Gear Quality Error Map of transverse section

20 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

21 Inspection Mathematics in all devices using normal surface vectors is wrong for relatively large errors such as those in plastic gearing Large radial error results in inaccurate form error on tips Unrealistic reporting at tips was often observed. Feed rate and sample number were eliminated as causes.

22 Inspection Jumps in root measurement 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

23 Inspection Edit function developed and automated to compensate for problems in measurement data Arc Insertion Element edit types : Cut point/region Insert line Insert arc Tip/root rounding Edited contour (blue) of section to be replaced to correct for irregular measurement

24 Mould Optimisation Large 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

25 Mould Optimisation New technique uses mapped error vectors independent of surface normals to calculate more accurate modified mould New Tool Surface Old Tool Surface Bad Correction Error Map Surface Normals Error Map Vectors

26 Mould Optimisation Full transverse section correction using mapped error Error Calculation Tool Iteration

27 Mould Optimisation Comparison of Segment Example 1 of 4 Before 1st Attempt After 1st Iteration

28 Mould Optimisation Comparison of Segment Example 2 of 4 Before 1st Attempt After 1st Iteration

29 Mould Optimisation Comparison of Segment Example 3 of 4 Before 1st Attempt After 1st Iteration

30 Mould Optimisation Comparison of Segment Example 4 of 4 Before 1st Attempt After 1st Iteration

31 Mould Optimisation Arbitrary form correction using mapped error technique Non-circular gear segments (designed by KISSsoft AG, produced Gaudlitz GmbH) to which corrective action was successfully applied

32 Mould Optimisation Many optimise parts now in production Non-circular gear segments (designed by KISSsoft AG, produced Gaudlitz GmbH) to which corrective action was successfully applied

33 Interface To Machines Format 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

34 Interface To Machines Format data in 2 planes for Export to Wire Erosion Machine Input Side (Warmer) Output Side (Cooler) 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

35 Interface To Machines 3D - Full correction possible using modified surface model such as STEP or IGES definition linked to 5-axis machine

36 Further Development Model 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

37 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

38 What Does That Mean? When designing gears... -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

39 What Does That Mean?...and benefits for the business: More control Faster production Improved efficiency Product development

40 Thank You!