Muoviteknologia Teppo Vienamo Joints / attachments Principles of joining plastics parts Mechanical...

MuoviteknologiaTeppo Vienamo

Joints / attachments

•Principles of joining plastics parts•Mechanical joints / attachments•Adhesives •Welding


Combining functions?• Minimizing amount of parts and

joints• Taking advantage of material

properties• Suitable material for combined

functions

• DFMA Design for Manufacturing and Assembly


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


Mechanical joining

• Integrated joining parts

• Screws

• Rivets

• Inserts


Press Fittings

• Various materials– thermal expansion of

material

• Plastic in tension• Pin in a hole


Snap-fit

• Placing and attachment of a part

• Permanent or repeating• Demanding shapes• Avoid tension peaks

• Bayer snap fit joints manual


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


Separate joining parts

• Threaded joining parts– Screws– Bolts– Nuts

• Inserts / out-serts

• Not threaded joining parts


Threads in plastic

• Rounding in bottom of the thread

• Male thread is easy

• Female thread requires often rotating or collapsing core


Screws

• Self threading screw– Thread shaping, requires

plastic forming => soft plastics

– Thread cutting, not for joints to repeating closure

– Wide variety for different use


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


Screws

• Flat base screws recommended

• Conical base causes tension

• Washer spreads load


Sewing

• Typically textile and thin materials• Fast• No tooling cost

Velcro

• Fast joints• Attachment by

– Sticker – sewing– Ultrasonic welding



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


Hardening adhesives

• Chemical reaction– Epoxy-, polyester- or urethane-based glues– Cyanoacrylate based glues – Anaerobic glues


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


Other adhesives

• Hot-melts

• Adhesive tapes – Double sided tapes– With or without carrying film

• UV-hardening adhesives– Fast and expensive


Welding plastics

• Thermoplastics

• Heat and pressure

• Be aware– Not to burn plastics– contaminant: release agents, dirt, water


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


Fusion welding (Hot plate)

• Hot plate between parts melts surface

• Remove heater

• Press parts together

• cooling

• E.G. Tube connections, car lamps


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


Friction welding

• Typically for rounded bars • Rotating part melts by friction

and heat• Stop and press• Strong attachment

• Vibration


Stacking

• Press molded stud

• Heat, friction, ultrasonic, cold

• Materials that don't melt together


Laser welding

• Both lap and butt joints l • No heat stress• Fast method

Muoviteknologia Teppo Vienamo Joints / attachments Principles of joining plastics parts Mechanical...

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