General Design Principles for DuPont Engineering Polymers - Module

Another joint design, with flash trap, is shown in
Figure 11.76D. This joint has been used successfully
in vibration welding of covers for air-intake manifolds
at frequencies of up to 250 Hz, with amplitudes of
1.2 mm.
Figure 11.76 Joint design—non circular parts
1.0
B = 2–3 T
D
R R
R = 0.1 T
b
D
3–3.5 T
A B
2.5
=
Cover
7.0
2.5
1.5
Air intake
D
DETAIL
=
2.0
2.0
2.0
1.2 T
2.0
2.0
2.0 3.0
c
3 T
5.0
a
2.5–3.0
C
Jig
Amplitude: 0.9 – 1.2 mm
Depth of weld to be determined
Frequency: 240 – 280 Hz
a
115
Test Results on Angular Welded Butt
Joints
The rectangular box shown in Figure 11.77 was used
for extensive pressure tests in various DuPont materials.
The burst pressure of any vessel is influenced by
three main factors:
• overall design
• material weldability
• joint design
The results obtained and described below should
therefore be applied carefully to parts having different
shapes and functions. The same part molded in
different plastics will show quite different behavior.
Whereas in some cases the weld may be the weakest
spot, in other engineering plastic resins it may prove
to be stronger than the part itself.
Joint Strength versus Welded
Surface
Figure 11.78 shows the tensile strength as a function
of joint width, obtained on the vessel shown in Figure
11.77. A linear strength increase can be observed up
to a ratio W//T of approximately 2.5. Above this value
the curve tends to flatten out and increasing the width
does not further improve strength.
Figure 11.77 Burst pressure test piece
36
45
Figure 11.78 Joint strength vs. joint size
Burst pressure
W
T
1 1.5 2
Ratio
2.5 3
W
T
7 cm 2