General Design Principles for DuPont Engineering Polymers - Module

Figure 11.64A shows a variation which can be used
where appearance is important or where an uninterrupted
surface is required. The stud is welded into a
boss. The outside diameter of the boss should be no
less than 2 times the stud diameter. When welding into
a blind hole, it may be necessary to provide an outlet
for air. Two methods are possible, a center hole
through the stud, or a small, narrow slot in the interior
wall of the boss.
When the amount of relative movement during
welding between two parts being assembled is limited
such as when locating gears or other internal components
between the parts, a double stepped stud weld as
in Figure 11.64B should be considered. This reduces
the movement by 50% while the area and strength of
the weld remain the same.
Figure 11.63 Stud welding—variations
A B
Before After Before After
Figure 11.64 Stud welding—variations
Before
After
B
Before
After
A–Blind hole B–Double stepped
This variation is also useful when welding plugs into
thin walls (1.5 mm) as seen in Figure 11.65. With the
standard stud joint, the requirement lead-in reduces
the available area and strength.
Standard horns with no special tip configuration (as
needed for ultrasonic heading) are used. High amplitude
horns or horn and booster combinations are
2B
109
generally required. Best results are obtained when the
horn contacts the part directly over the stud and on the
side closest to the joint. When welding a number of
pins in a single part, one horn can often be used. If the
studs are widely spaced (more than 75 mm between
the largest distance of the studs) small individual
horns energized simultaneously must generally be
used. Several welding systems which can accomplish
this are described earlier in the report.
Figure 11.65 Stud welding—plugs in thin-wall parts
T
0.4 mm
T =
Before After
0.2 mm
Before After
0.25 mm 0.4 mm
c) Ultrasonic Inserting
Metal parts can be ultrasonically inserted into parts of
DuPont engineering plastics as an alternative to
molded-in or pressed-in inserts. Several advantages
over molded-in inserts are:
• Elimination of wear and change to molds,
• Elimination of preheating and hand-loading of
inserts,
• Reduced molding cycle,
• Less critical insert dimensional tolerances, and
• Greatly reduced boss stress.
The inserts can be ultrasonically inserted into a
molded part or the molded part can be assembled over
the insert as seen in Figure 11.66. There are several
varieties of ultrasonic inserts commercially available,
all very similar in design principle. Pressure and
ultrasonic vibration of the inserts melts the plastic at
the metal-plastic interface and drives the insert into a
molded or drilled hole.
The plastic, melted and displaced by the large diameters
of the inserts flows into one or more recesses,
solidifies, and locks the insert in place. Flats, notches,
or axial serrations are included in the inserts to
prevent rotation due to applied torsional loads. The
volume of the displaced material should be equal to or
slightly more than the volume of free space corresponding
to the groove and the serrations of the insert.
0.5 T