Page 97 - Engineering Plastics Handbook

Processing 71

4. Vibration
5. Hot plate
6. Laser
7. Electromagnetic
8. Hot bar and impulse (for films)
9. Radio frequency
10. Infrared
11. Induction

plus variations of these welding methods and joint designs [17].
Press-fitting a metal shaft into the hollow core of a rigid tube or hub
has a variety of assembly applications. Key cautions include
1. Very close tolerance between shaft outer diameter and hub inner
diameter, with sufficient but not excessive holding force
2. Long-term stress or loading value, such as 14 MPa for polycarbonate
3. Dimensional strength
4. Maximum allowable hoop stress
5. Diametric interference
There are three types of snap-fits:

1. Cantilever, which is the most common
2. Torsional
3. Annular

Snap-fits are injection-molded into the two components of the assembly.
Two general heat staking methods are low profile and high profile.
Methods of the two types include spherical, flush, hollow, and knurled.
In addition, there are cements and adhesives, and a mechanical fas-
tening assembly. Whatever assembly method is used, the choice is usu-
ally made at the design stage.

Trends

Processing is dedicated to two objectives, quality and productivity; and
trends improving these objectives are as follows:

1. Flexibility and versatility by using modular retrofitting, hybrid process
technologies, voice-activated controls, and artificial intelligence for