Class Notes (806,973)
Canada (492,546)
IAT 336 (11)
Ken Zupan (11)

IAT336_Week 10.docx

4 Pages
Unlock Document

Simon Fraser University
Interactive Arts & Tech
IAT 336
Ken Zupan

Joining Plastics There are 3 ways to join plastic materials Chemical Bonds-using chemical adhesives and solvents to join plastic parts E.g. methyl-chlorate to bond styrene Thermo Bonding-use heat to fuse together plastic parts The two main types are friction and applied heat Mechanical Bonds-using physical attachments to bond plastics together E.g. rivets, screws, molded snap fit fasteners Chemical Bonds Adhesive Bonding-plastic parts and shapes may be bonded to one another as well as to dissimilar materials using a widely available range or commercial adhesives -because adhesive bonding involves the application of chemically different substances between two parts, the end use environment of the assembled unit is of major importance -operating temperatures, environments, unit shape, and production volumes must be considered Epoxy and acrylic adhesives are recommended because of their versatile properties and fast cure rates Solvent Bonding (welding)-involves a chemical agent dissolving the outer skin of a resin sufficiently to allow it to be joined with other compatible parts -after the solvent has been evaporated, a true bond is created with no intermediate material -the cleanliness of the area to be bonded, the type of joint design, and the influence of speed are factors that may be influenced by evaporation rate of the solvent used Factors to Consider when using Adhesives The cure of the adhesive must not exceed the heat-deflection temperature (melting of plastic) Adhesives not tested for compatibility should be avoided or tested on an off-cut Adhesive testing for compatibility should consider operational conditions of temperature and stress Thermo Bonding Ultrasonic Welding In ultrasonic welding a tool or horn vibrating at an ultrasonic frequency is brought into contact with one-half of the part being assembled Pressure is applied and frictional heat is generated as the high-frequency vibratory energy melts a molded ridge of plastic on one of the mating surfaces Benefits -uniform results are gained because energy transferred to the joint and released as heat is consistent, occurs rapidly, and is confined to the immediate joint area -tensile shear strengths of up to 3000 PSI may be attained in the joint area Ultrasonic Staking or Swaging Most staking applications involve the assembly of plastic to metal or other dissimilar materials A hole in the part to be joined is located to receive a molding mating stud in the plastic part The vibrating horn has a contoured tip that when brought into contact with the stud melts and reforms it to a locking head Benefits -consistent frequency, pressure, and time -tight assembles are assured because the reformed stud is allowed to cool under pressure, eliminating material memory Mechanical Bonds Snap-fit Assembly-a method of assembly that works well with many resins -since no additional materials are needed, the mating parts can be assembled quickly and economically on the assembly line or at the final use location A snap-fit assembly is generally used less than 10 times so many cycles could accelerate fatigue. A tapered beam will provide more efficient and stronger finger Hinges and Snap/Locks Products with lids or covers are normally designed with molded hinges and snaps These lids and housing can be easily designed to incorporate hinge and locking mechanism Self-Tapping Screws When using thermoplastic resins in injection-molded parts, the use of thread-cutting self- tapping screws is recommended This type of screw cuts its own threads during installation and has a slot cut out of the bottom where the chips may accumulate Thread-cutting screws offer the advantage of low residual stresses in the area around the boss Self-Tapping Screws Design Considerations The receiving hole should not exceed the pitch diameter of the screw Boss height should not exceed two times the boss outer diameter Boss hole depth should not exceed two times the boss outer diameter Hole depth should be slightly longer than the screw length to allow for chip accumulation Use minimum torque to keep screw assembly stress within the design limits of the material Excessive torque can cause cracks in the boss/part Threaded Metal Fasteners Metal screws and bolts are commonly used to assemble parts or attach various components In this case, metal assembly puts the part into compression under the bolt and nut Threaded metal fasteners require bosses molded in the plastic parts The bosses may require thread via metal inserts However, uncontrolled assembly torques with this type of assembly can cause excessive compressive forces in the mold
More Less

Related notes for IAT 336

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.