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
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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
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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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Brands & product ranges
Vending O.C.S. Ho.Re.Ca.
1. N&W Group
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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
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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