friction related explicit calculations on vending machine sector
DESCRIPTION
Our day life is characterized by the use of vending machines. We are used to get cans, bottles, snacks, coffee from a big variety of vending machines spread out everywhere. From an engineering point of view what is inside a vending machine is an incredible mess of mechanical and electrical components working together, cooperating, heating, cooling in a lot of different external and internal conditions. This means that the design of a vending machine and of its components has to be robust, reliable and affordable. N&W, as market leader in vending sector (EU and a strong presence WW) and with a 70 people R&D Dep., has faced many problems related to sliding plastic/rubber components in presence of friction issues due to moisture, sugar powder (micro and macro), heat transients and pressure. To do that a testing campaign has been performed in order to achieve all the data needed to characterize friction coefficients relevant for the numerical activities.TRANSCRIPT
Friction Related Explicit Calculations in the Vending Machine Sector
June 24-26, 2014 - Munich
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Matteo Adobati [email protected]
Fabio Rota [email protected]
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Contents
1. N&W Group
2. R&D Department
3. Scope
4. Tea infusion sliding piston
5. Sugar dispenser sliding system
6. Conclusion
1. N&W Group
10.000 customers
200.000 150.000
OCS and Horeca machines / year
Vending machines / year
500 suppliers Worldwide presence
To be the leading producer of coffee-based drink and snack & food dispensers world-wide, by delivering an unrivalled and consistent consumer experience.
Caring for our customers, our people and the environment are the keys to our success.
1.500 3 6 15 manufacturing sites world-wide branch offices european R&D centres employees
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4
Brands & product ranges
Vending O.C.S. Ho.Re.Ca.
1. N&W Group
550
Innovation, design, excellence
100 5%
• A consolidated project management approach • Structured working flows and procedures on both Product and
Innovation development processes • Product development supported by advanced virtual validation methods
in both Design and Lab test stages
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2. N&W R&D Department
Percentage of the turnover invested
in R&D Engineers in R&D
Registered patents
Friction issues
Project targets
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3. Scope
• Sliding [plastic/rubber] - [plastic/plastic] - [steel/plastic] • Changing geometries during movements • Dry/wet surface interaction • Presence of sweetening powder or moisture • Contact pressure • Heat transient condition
• Investigate the contact finding the right LAW • Friction coefficient charaterisation - static/dynamic • Testing campaign vs FEM results comparison • Mechanical solution optimization:
contact force/pressure decrease robust and reliable assembly
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4. Tea infusion sliding system
4.1 – Finite element model Tea-Brewer
Tea-leaves infusion mechatronic dispenser
N&
W p
ate
nt
regis
tere
d
Solvers: •Optistruct NLSTAT/NLGEOM (preliminary analysis)
•Radioss
3D & FEM model
Boundary conditions: • Infusion chamber:
1 DOF (z axis) • Piston: grounded fixed • Chamber movement:
IMPVEL (z axis)
Piston Rubber gasket
Infusione chamber
Elements: •Hexa8 (# 120000)
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4. Tea infusion sliding system
4.2 – Contact surfaces
Infusion chamber - Rubber Gasket
Rubber Gasket - Sliding piston
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4. Tea infusion sliding system
4.3 – Material & contact
• Material: Infusion Chamber - PEI (Polyetherimide) Rubber gasket - Sylicon rubber 60 Shore Piston - PEI (Polyetherimide)
• Material numerical formulation: PEI (Polyertheremide) - Elastic - LAW1 Sylicon rubber - Ogden - LAW42
• Type7 contact interfaces • Contact parameters environment:
Assembling rubber preload Wet (low friction) / Dry (worst case) Changing piston motion direction [down - up]
Sliding piston
Supplier rubber graph used to define the Ogden law parameters: E = 4.5 Mpa
1 = 0.948 Mpa
2 =-0.236 Mpa
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4. Tea infusion sliding system
4.4 – Friction behaviour
Contact pressure (dry condition)
Piston positions:
UP: t_step: 0,5 s Phase: Plug + sliding down: Piston Force: Fmax = 2.5 N
DOWN: t_step: 4,5s Phase: Reverse direction: Piston Force: Fmax = 12 N
Transient cycles:
t = 0,0 0,5 s Piston plug
t = 0,5 4,4 s Sliding down
t = 4,4 4,6 s Reverse direction
t = 4,6 6,5 s Sliding up
Normal Tangential
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4. Tea infusion sliding system
4.5 – Results & test compaign
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4. Tea infusion sliding system
4.6 – Conclusion
• Explicit analysis able to predict the rubber behavior
• Good support to calibrate material blend
• Samples reduction vs final solution design
• Good contact response despite of relevant mechanical clearances presence
• Good understanding on dynamic mechanism performances friction’s influence
• Good driver to improved solutions
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5. Sugar dispenser sliding system
5.1 – Finite element model Solvers: •Optistruct NLSTAT/NLGEOM (preliminary analysis)
•Radioss •Motionsolve
Boundary conditions: • Fork: 1 DOF (axis rotation) • Plate: grounded fixed • Fork rotation: IMPVEL • Cap spring: CLOAD
Elements: •Tetra10 (# 126000) •RBE2 (# 6)
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5. Sugar dispenser sliding system
5.2 – Contact surfaces
Cap - slider
Slider - frame
Cap - frame
Slider - fork
Fork - plate
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5. Sugar dispenser sliding system
5.3 – Material & Contact
- Material: POM (Polyoxymethylene)
- Material numerical formulation – Law1
- Type 7 contact interfaces
- Contact parameters environment:
> humidity / temperature
> sugar powder accumulation during lifecycle
> mechanical clearances
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5. Sugar dispenser sliding system
5.3 – Friction behaviour
- Numerical – experimental data correlation
Fu
Cam rotation [°]
Sliding force [N]
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5. Sugar dispenser sliding system
5.4 – Results
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5. Sugar dispenser sliding system
5.5 – Conclusion
• Explicit simulation very close to real dynamic mechanism
• Predictive solutions to optimized configuration design
• Good contact response despite of relevant mechanical clearances presence
• Good understanding on dynamic mechanism performances friction’s influence
• New leverages’ design
• Friction environment new mechanism robustness
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Thank you for your attention!
Any questions?
www.nwglobalvending.com