Machine Tool Case Studies

Transcription

1 Machine Tool Case Studies Copyright ANCA Pty. Ltd

2 Case 1: My Lost Mercedes S500 Problem: Evidence of early failure of the TGX Z axis ballscrew. Methodology: Grind standard ball nose endmill and log Z axis motor torque. Convert this figure to RMS torque and use standard formula to estimate life of ballscrew. L (hrs) = 1/(60n) * (Ca/Fa.fw)^3. 10^6 Ca Basic dynamic load rating (kgf) Fa Axial Load (kgf rms) n Rotating speed rpm fw Load factor ( factor depending on operation conditions)

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4 Design Solution > Life of ballscrew estimated to be 1.8 years :Too short!! > Solution: Design and fit hydraulic counter balance with dual cylinders and compact power pack. > Approximate cost ~$11,000 > No of machines fitted ~65 Therefore total cost $715,000 > New Problem: Premature failure of counterbalances.

5 Simpler Solution > From manufacturers handbook > Ca (5 mm pitch ballscrew) = 2060 kgf > Ca (6mm pitch ballscrew ) = 2810 kgf > Substitute into standard formulae - For same load ballscrew life = 5.5 years Acceptable. - Cost Zero > Moral: Doing careful experiments and accurate calculations does not stop expensive mistakes.

6 CASE 2 Machine that would not hold size > In 1991 ANCA introduced the TG7 seven axis tool grinder at EMO in Paris. > Huge success; became industry leader. Still very valued on resale market. > In 1994 ANCA introduced MG7. Small Highly accurate tool grinder. > Initial success but - Machine would not hold size!

7 Remedial Actions Reports from customers were initially disbelieved Researched fitting of linear scales to eliminate ballscrew expansion. No benefit Researched recipe for polymer concrete. Significant improvement in performance of polymer concrete but no improvement in thermal stability Researched fitting of thermocouples and deriving a compensation scheme. Prototype successful Developed software compensation using post process measurement using probe. Successfully implemented in the field. Largely solved production problem at expense of cycle time.

8 MG7

9 TG7

10 TG7 Base

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12 Real Problem - Thermal symmetry.

13 > Look for the bleeding obvious Moral

14 Tool Runout > Problem: > Major move in metal cutting is towards high speed machining particularly in tool and die industry. - E.g 4 flute endmill at 40,000 rpm and 2000mm/min feedrate. - This implies a chip thickness of 12.5 micron. - Tool runout of 6 micron means chip thickness varies from 6.5 micron to 18.5 micron cyclically. This will cause destructive vibration. - Customers demand tools with tir less than 3 micron.

15 Design Problem Runout has two components Radial Axial Design Task An adjustable collet that has less than 3 micron 50mm from the face of the collet

16 Ancient Greek Solution Ancient Greeks developed concept of mechanical advantage of inclined plane Use inclined plane to provide adjustment of angular error Use simple push screws to provide adjustment of radial error

17 Micro Adjusting Collet System: Maccs

18 Exploded view

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20 Solid view

21 Transparent View

22 Case 4 Tool Measurement Problem Customers are looking to produce cutters with profile accuracy less that 2.5 micron.

23 Mechanical Design Tools Solid Modelling Kinematic Simulation FEM analysis Photo realistic imaging

24 Mechanical design & Machine build > All machines and their components as well as accessories are designed, manufactured and tested by ANCA. 3D Modeling of the machine concept and components Manufacture, build & assembly Appliance of design testing techniques.

25 L Thank you for your attention. L If you would like to visit ANCA and tour our facility you would be most welcome.