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MuoviteknologiaTeppo Vienamo
Joints / attachments
•Principles of joining plastics parts•Mechanical joints / attachments•Adhesives •Welding
MuoviteknologiaTeppo Vienamo
Combining functions?• Minimizing amount of parts and
joints• Taking advantage of material
properties• Suitable material for combined
functions
• DFMA Design for Manufacturing and Assembly
MuoviteknologiaTeppo Vienamo
Size of series / joint type
Large series– Few parts– Integrated functions – Expensive tools– Lot of design work
Small series– Simple parts– Minimize design work– Laborious production– No moulds / cheap tooling
MuoviteknologiaTeppo Vienamo
Mechanical joining
• Integrated joining parts
• Screws
• Rivets
• Inserts
MuoviteknologiaTeppo Vienamo
Press Fittings
• Various materials– thermal expansion of
material
• Plastic in tension• Pin in a hole
MuoviteknologiaTeppo Vienamo
Snap-fit
• Placing and attachment of a part
• Permanent or repeating• Demanding shapes• Avoid tension peaks
• Bayer snap fit joints manual
MuoviteknologiaTeppo Vienamo
Living hinge
• Thin film between thick plastics parts• Minimising part amount avoiding
hinge parts– Injection moulding– Machining
• Crystalline plastics• polypropylene and polyethylene
– 106 bending
1,5
R 0,25
0,1-0,4
0,15-0,4
R 0,7
MuoviteknologiaTeppo Vienamo
Separate joining parts
• Threaded joining parts– Screws– Bolts– Nuts
• Inserts / out-serts
• Not threaded joining parts
MuoviteknologiaTeppo Vienamo
Threads in plastic
• Rounding in bottom of the thread
• Male thread is easy
• Female thread requires often rotating or collapsing core
MuoviteknologiaTeppo Vienamo
Screws
• Self threading screw– Thread shaping, requires
plastic forming => soft plastics
– Thread cutting, not for joints to repeating closure
– Wide variety for different use
MuoviteknologiaTeppo Vienamo
Thread-inserts
• Repeated attachment• Big disengage strength• Amounting
– ultrasound, fast, good attachment – heat, cheap, slow, good attachment– in-molding, tensions caused by shrinkage, risk of
harming the mould– hit-serts, fast and easy, poor attachment, – Expanding inserts, fast and easy tension to plastic– Thread cutting screw insert
MuoviteknologiaTeppo Vienamo
Screws
• Flat base screws recommended
• Conical base causes tension
• Washer spreads load
MuoviteknologiaTeppo Vienamo
Sewing
• Typically textile and thin materials• Fast• No tooling cost
Velcro
• Fast joints• Attachment by
– Sticker – sewing– Ultrasonic welding
MuoviteknologiaTeppo Vienamo
MuoviteknologiaTeppo Vienamo
Adhesives
• Easy • Differing materials • Equal tension• Seal • Elasticity • Cheap • No tools• Insulation • Easy to repair• Aesthetic
• Chemical fitting• Holding • Thermal stability• Handling the adhesive• Poisonous • Preparing the surfaces
MuoviteknologiaTeppo Vienamo
Hardening adhesives
• Chemical reaction– Epoxy-, polyester- or urethane-based glues– Cyanoacrylate based glues – Anaerobic glues
MuoviteknologiaTeppo Vienamo
Solvent clueing
• Dipping the surface in solvent• Compression in a jig• Solvent evaporates • Well fitting surfaces • Only for amorphous plastics• result ”one part”
• E.G. trichloroethylene, xylene and acetone
• Possible to make filling paste of solvent and pieces of plastic
MuoviteknologiaTeppo Vienamo
Other adhesives
• Hot-melts
• Adhesive tapes – Double sided tapes– With or without carrying film
• UV-hardening adhesives– Fast and expensive
MuoviteknologiaTeppo Vienamo
Welding plastics
• Thermoplastics
• Heat and pressure
• Be aware– Not to burn plastics– contaminant: release agents, dirt, water
MuoviteknologiaTeppo Vienamo
Methods
• Hot gas welding– Melting base- and added
material with hot air blower
• Extruder welding– Like hot gas welding but
added material is heated in extruder
– Thick materials
MuoviteknologiaTeppo Vienamo
Fusion welding (Hot plate)
• Hot plate between parts melts surface
• Remove heater
• Press parts together
• cooling
• E.G. Tube connections, car lamps
MuoviteknologiaTeppo Vienamo
Ultrasonic welding
• 20000 Hz vibration• Special tool or horn to transfer
vibration• Moulded ridge of plastic melts by
the friction heat • pressure• Fast method 1-5 seconds• Strong attachment
MuoviteknologiaTeppo Vienamo
Friction welding
• Typically for rounded bars • Rotating part melts by friction
and heat• Stop and press• Strong attachment
• Vibration
MuoviteknologiaTeppo Vienamo
Stacking
• Press molded stud
• Heat, friction, ultrasonic, cold
• Materials that don't melt together
MuoviteknologiaTeppo Vienamo
Laser welding
• Both lap and butt joints l • No heat stress• Fast method
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