Weld Amplitude; Weld Force; Hold Force; Weld Time - Dukane VWA-4300 User Manual

Linear Vibration Welder 4000 Series, Model VWA User's Manual

Weld Amplitude

Amplitude has less effect upon the weld strength than weld
time. Figure 9 -2 shows the relationship of weld strength
for generic POM as a function of weld force for a fixed
weld depth and two different amplitudes. Higher weld
strength occurs at lower clamping pressures because the
weld time is longer and the penetration distance greater.
However as clamping pressure increases to shorten the
weld time, the weld strength decreases more rapidly for
the low amplitude weld joint. Figure 9 -3 shows the rela-
tionship of weld strength of different thermoplastics as a
function of weld depth (collapse distance) for a fixed weld
amplitude and weld pressure.

Weld Force

Increasing the weld force increases the collapse but not
the weld penetration. The welding force required for
different materials is determined by a combination of
the polymer's melt flow index, the glass transition or
crystallization temperature and molecular weight. The
approximate melt index range for some common ther-
moplastics and their welding pressure range are given in
Table 9-I. Since there is such a wide range of melt flow
rates for even common polymers, depending upon their
molecular structure, the welding pressure required can
initially only be estimated. The optimal values must be
determined experimentally.
Pressure is force per unit area, so the weld force setting
is the desired welding pressure multiplied by the total
effective joint area. Remember to keep the units of mea-
surement consistent (pounds and inch
2
newtons and meter ) when calculating the desired weld
pressure.

Hold Force

Clamping under pressure while the bond hardens, corrects
warping problems by forcing the parts into the proper ge-
ometry. Decreasing the welding pressure at the beginning
of the hold cycle can reduce the flow of molten material
and thus reduce the size of the weld bead or flash. In ad-
dition, this can reduce shear thinning to create stronger
welds. The hold time must be long enough however, so
that the temperature of the weld seam is below the glass
transition or crystallization temperature. A holding time
of between one and five seconds is usually enough.
Page 114
2
, Megapascals or
Material – POM (Acetal, Delrin)
Weld Distance = 1.0mm
15
10
5
0
1 2 3
Pressure (MPa)
Relationship of Weld Strength as a
Figure 9 - 2
Function of Weld Pressure
Weld Pressure – 2MPa
Amplitude 1.0mm
20
15
10
5
0
1.0
Weld Depth (mm)
Relationship of Weld Strength as a
Figure 9 - 3
Function of Weld Depth
Thermoplastic
Abbv
Chemical Name Trade Name
Acrylonitrile Lustran
ABS
Butadiene Styrene
Nylon 6
Polycaprolactam
PA6
Nylon–6/6
Polyhexamethylene–
PA66
adipamide
Polycarbonate Lexan
PC
High Density Chevron
HDPE
Polyethylene
Polymethyl Lucite
PMMA
Methacrylate
Polyoxymethylene Delrin, Acetal
POM
Polypropylene Herkulon
PP
Polyphenylene Ether
PPE+SB
+ Styrene/Butadiene
Polystyrene Styron
PS
Styrene–Acrylonitrile Lustran
SAN
1 psi = 6.895x10 -3 MPa; 1 MPa = 1.450x10
Approximate Welding Pressure for
Table 9- I
Common Thermoplastics
Dukane Manual Part No. 403-592-00
Amplitude 1.4mm
Amplitude 1.0mm
4 5
POM—Acetal,
Delrin
PPS—Fortron, Techtron
PBT—Celanex
LCP—Vectra
1.1 1.2 1.3
Melt Flow Rate Welding Pressure
3
(cm /10 min) (psi) (MPa)
2–50 145–290 1.0–2.0
18–110 145–290 0.5–3.0
10–180 72–435 0.5–3.0
3–12 145–290 1.0–2.0
0.1–80 72–1160 0.5–8.0
1–25 145–290 1.0–2.0
1–40 145–580 1.0–4.0
1–100 72–580 0.5–4.0
8–270 145–870 2.0–6.0
3–25 145–580 1.0–4.0
8–25 145–290 1.0–2.0
2 psi; 1 MPa = 1x10 6 Nt m -2