Balanced multi-cavity injection molding of cable ties

Balanced injection molding in a multi-cavity mold of a plurality of ties having a uniform maximum thickness between opposite broad sides of the tongue of the tie is accomplished by providing mold pieces in which the relative dimensions of projections for forming ratchet teeth on the tongue of the ties in different mold cavities are non-uniform such that when plastic material is injected into the mold cavities, the injected plastic material flows through the different mold cavities at respective flow rates that cause the mold cavities to be completely filled approximately simultaneously with the injected plastic material. In making the mold pieces, the dimensions of the projections initially are larger than required for forming ratchet teeth of a preferred dimension. After measuring the extent to which the different cavities are filled, the relative dimensions of the projections are adjusted such that the projections for at least one of the mold cavities are of a dimension required for forming ratchet teeth of the preferred dimension and/or such that the projections for at least one the mold cavities are of a dimension larger than required for forming ratchet teeth of the preferred dimension and the projections for at least another of the mold cavities are of a dimension smaller than required for forming ratchet teeth of the preferred dimension.

BACKGROUND OF THE INVENTION 
The present invention generally pertains to injection molding of ties that 
are useful for forming a loop for retaining a bundle of elongated 
articles, such as cables and is particularly directed to an improvement in 
multi-cavity injection molding of such ties. Such a tie is commonly known 
as a cable tie 
One type of tie includes an elongated tongue with two ends and two broad 
sides, a locking head at one end of the tongue, a tip at the other end of 
the tongue, a first set of ratchet teeth extending along one broad side of 
the tongue and a second set of ratchet teeth extending along the other 
broad side of the tongue, wherein the locking head has sides defining an 
opening for receiving the tip of the tongue. Referring to FIG. 1, the 
sides include a movable pawl 10 that is hinged at one side of the opening 
and an abutment surface 12 that is across the opening from the pawl. The 
pawl 10 has pawl teeth 14 disposed for engaging the first set of ratchet 
teeth 16 when the tip of the tongue 18 has been inserted through the 
opening with the first set of ratchet teeth facing 16 facing the pawl 10. 
When at least one pawl tooth 14 is so engaged, the pawl 10 is movable 
toward the abutment surface 12 in response to a pulling force applied to 
the tongue 18 in a direction opposite to the direction of insertion 20 in 
order to force the second set of ratchet teeth 22 against the abutment 
surface 12. Teeth 24 are disposed on the abutment surface 12 for engaging 
the second set of ratchet teeth 22 when the tip of the tongue 18 has been 
inserted through the opening with the second set of ratchet teeth 22 
facing the abutment surface 12 and the side of the tongue including the 
second set of ratchet teeth 22 is forced against the abutment surface 12 
by movement of the pawl 10. Such a tie is described in U.S. Pat. No. 
4,473,524 to Paradis. Another type of tie differs from the tie described 
above in that it includes a set of ratchet teeth on only the broad side of 
the tongue that faces the pawl when the tongue is inserted through the 
locking head opening. 
For efficient manufacture, it is preferred to injection mold ties 
simultaneously with a multi-cavity mold. A problem incident to 
multi-cavity injection molding of ties is that all of the cavities of the 
mold in which the ties are formed are not always completely filled 
simultaneously with the injected plastic material. Referring to FIG. 2, 
which illustrates a plurality of injection molded ties 26 formed in the 
cavities 28 of one mold piece 30 after the mold pieces defining the 
cavities have been separated, it is seen that failure to completely fill 
all of the mold cavities simultaneously results in some of the cavities 
28a being incompletely filled, such that the ties 26a therein are not 
completely formed, and other cavities 28b being overfilled, such that a 
flashing of excess plastic 32 is attached to some of the ties 26b formed 
therein. The gates through which the plastic material is injected into the 
mold cavities 28 are located at the ends of the cavities 28 at which the 
locking heads 34 of the ties 26 are formed. 
SUMMARY OF THE INVENTION 
The present invention provides a method of balanced injection molding of a 
plurality of ties in a multi-cavity mold such that a plurality of mold 
cavities are completely filled approximately simultaneously with the 
injected plastic material. For injection molding a plurality of ties in a 
multi-cavity mold, wherein each of at least two mold cavities defines a 
tie comprising an elongated tongue with two ends and two broad sides, a 
locking head at one end of the tongue, a tip at the other end of the 
tongue, a first set of ratchet teeth extending along one broad side of the 
tongue and a second set of ratchet teeth extending along the other broad 
side of the tongue, wherein the locking head has sides defining an opening 
for receiving the tip of the tongue, the sides including a movable pawl 
that is hinged at one side of said opening and an abutment surface that is 
across the opening from the pawl, wherein the pawl has at least one pawl 
tooth disposed for locking engagement with the first set of ratchet teeth 
when the tip of the tongue has been inserted through said opening with the 
first set of ratchet teeth facing the pawl and wherein the abutment 
surface includes at least one tooth for locking engagement with the second 
set of ratchet teeth when the tongue has been inserted through the opening 
in such a direction that the second set of ratchet teeth face the abutment 
surface and the side of the tongue including the second set of ratchet 
teeth is forced against the abutment surface by movement of the pawl, the 
method comprise the steps of: 
(a) providing mold pieces defining therebetween said at least two cavities 
for forming said ties having a uniform maximum thickness between the two 
broad sides of the ties, wherein at least one of the mold pieces includes 
projections for forming the ratchet teeth; and 
(b) injecting plastic material approximately simultaneously into at least 
both of said at least two mold cavities to form the ties; 
wherein step (a) comprises providing mold pieces in which the relative 
dimensions of the projections for forming the first set of ratchet teeth 
and/or the second set of ratchet teeth in said at least two mold cavities 
are non-uniform such that when plastic material is injected in accordance 
with step (b) injected plastic material flows through said at least two 
mold cavities at respective flow rates that cause at least both of said at 
least two mold cavities to be completely filled approximately 
simultaneously with the injected plastic material. 
The present invention also provides a multi-cavity mold for injection 
molding a plurality of ties, wherein each of at least two mold cavities 
defines a tie comprising an elongated tongue with two ends and two broad 
sides, a locking head at one end of the tongue, a tip at the other end of 
the tongue, a first set of ratchet teeth extending along one broad side of 
the tongue and a second set of ratchet teeth extending along the other 
broad side of the tongue, wherein the locking head has sides defining an 
opening for receiving the tip of the tongue, the sides including a movable 
pawl that is hinged at one side of said opening and an abutment surface 
that is across the opening from the pawl, wherein the pawl has at least 
one pawl tooth disposed for locking engagement with the first set of 
ratchet teeth when the tip of the tongue has been inserted through said 
opening with the first set of ratchet teeth facing the pawl and wherein 
the abutment surface includes at least one tooth for locking engagement 
with the second set of ratchet teeth when the tongue has been inserted 
through the opening in such a direction that the second set of ratchet 
teeth face the abutment surface and the side of the tongue including the 
second set of ratchet teeth is forced against the abutment surface by 
movement of the pawl, the mold comprising mold pieces defining 
therebetween said at least two cavities for forming said ties having a 
uniform maximum thickness between the two broad sides of the ties, wherein 
at least one of the mold pieces includes projections for forming the 
ratchet teeth; wherein the relative dimensions of the projections for 
forming the first set of ratchet teeth and/or the second set of ratchet 
teeth in said at least two mold cavities are non-uniform such that when 
plastic material is injected approximately simultaneously into at least 
both of said at least two mold cavities the injected plastic material 
flows through said at least two cavities at respective flow rates that 
cause at least both of said at least two mold cavities to be completely 
filled approximately simultaneously with the injected plastic material. 
The present invention further provides a method of making a multi-cavity 
mold for injection molding a plurality of ties, wherein each of at least 
two mold cavities defines a tie comprising an elongated tongue with two 
ends and two broad sides, a locking head at one end of the tongue, a tip 
at the other end of the tongue, a first set of ratchet teeth extending 
along one broad side of the tongue and a second set of ratchet teeth 
extending along the other broad side of the tongue, wherein the locking 
head has sides defining an opening for receiving the tip of the tongue, 
the sides including a movable pawl that is hinged at one side of said 
opening and an abutment surface that is across the opening from the pawl, 
wherein the pawl has at least one pawl tooth disposed for locking 
engagement with the first set of ratchet teeth when the tip of the tongue 
has been inserted through said opening with the first set of ratchet teeth 
facing the pawl and wherein the abutment surface includes at least one 
tooth for locking engagement with the second set of ratchet teeth when the 
tongue has been inserted through the opening in such a direction that the 
second set of ratchet teeth face the abutment surface and the side of the 
tongue including the second set of ratchet teeth is forced against the 
abutment surface by movement of the pawl, the method comprising the steps 
of: 
(a) providing mold pieces defining therebetween said at least two cavities 
for forming said ties having a uniform maximum thickness between the two 
broad sides of the ties, wherein at least one of the mold pieces includes 
projections for forming the ratchet teeth, with said projections being 
uniform for at least both of said at least two mold cavities; 
(b) injecting plastic material at a minimal injection pressure 
approximately simultaneously into at least both of said at least two mold 
cavities in order to form the ties and completely fill one of the cavities 
with the injected plastic material; 
(c) measuring the relative extent to which said at least two mold cavities 
are filled with the injected plastic material; and 
(d) when at least both of said at least two mold cavities are not 
completely filled approximately simultaneously, adjusting the relative 
dimensions of the projections for forming the first set of ratchet teeth 
and/or the second set of ratchet teeth in at least both of said at least 
two mold cavities to be such that when plastic material is injected in 
accordance with step (b) injected plastic material flows through said at 
least two cavities at respective flow rates that cause at least both of 
said at least two mold cavities to be completely filled approximately 
simultaneously with the injected plastic material. 
The forgoing aspects of the present invention also are applicable to 
multi-cavity injection molding of a plurality of cable ties in which 
ratchet teeth are provided on only one side of the tongue for engagement 
with the pawl. 
Additional features of the present invention are described with reference 
to the detailed description of the preferred embodiments.

DETAILED DESCRIPTION 
Referring to FIGS. 3, 3A, 4 and 4A, a preferred embodiment of the mold of 
the present invention includes at least two mold pieces 40, 42 defining 
therebetween at least two cavities 44, 46 for respectively forming ties 
48, 50 having a uniform maximum thickness T between the two broad sides of 
the ties 48, 50. One of the mold pieces 40 includes projections 52 for 
forming the first set of ratchet teeth 16 that engage the pawl teeth 14. 
Another of the mold pieces 42 includes projections 54 for forming the 
second set of ratchet teeth 22 that engage the abutment surface teeth 24. 
The relative dimensions of the projections 52 for forming the first set of 
ratchet teeth 16 in the two mold cavities 44, 46 are non-uniform and/or 
the relative dimensions of the projections 54 for forming the second set 
of ratchet teeth 22 in the two mold cavities 44, 46 are non-uniform such 
that when plastic material is injected approximately simultaneously into 
both of the two mold cavities 44, 46 the injected plastic material flows 
through the two cavities 44, 46 at respective flow rates that cause both 
of the two mold cavities 44, 46 to be completely filled approximately 
simultaneously with the injected plastic material. 
Referring to FIG. 1, it is seen that the first set of ratchet teeth 16 have 
a preferred depth A.sub.P and the second set of ratchet teeth 22 have a 
preferred depth B.sub.P. In the portion of the mold shown in FIG. 3, the 
projections 52 of the one mold piece 40 have a depth dimension A.sub.L 
that is larger than required for forming a first set of ratchet teeth 16 
having the preferred depth A.sub.P, and the projections 54 of the other 
mold piece 42 have a depth dimension B.sub.L that is larger than required 
for forming a second set of ratchet teeth 22 having the preferred depth 
B.sub.P ; whereby the first set of ratchet teeth 16 have a depth A.sub.L 
that is larger than the preferred depth A.sub.P and the second set of 
ratchet teeth 22 have a depth B.sub.L that is larger than the preferred 
depth B.sub.P, as shown in FIG. 3A . 
In the portion of the mold shown in FIG. 4, the projections 52 of the one 
mold piece 40 have a depth dimension A.sub.S that is smaller than required 
for forming a first set of ratchet teeth 16 having the preferred depth 
A.sub.P, and the projections 54 of the other mold piece 42 have a depth 
dimension B.sub.S that is smaller than required for forming a second set 
of ratchet teeth 22 having the preferred depth B.sub.P ; whereby the first 
set of ratchet teeth 16 have a depth A.sub.S that is smaller than the 
preferred depth A.sub.P and the second set of ratchet teeth 22 have a 
depth B.sub.S that is smaller than the preferred depth B.sub.P, as shown 
in FIG. 4A. 
The relative differences between the depth dimensions A.sub.P, A.sub.L and 
A.sub.S and the relative differences between the depth dimensions B.sub.P, 
B.sub.L and B.sub.S are greatly exaggerated in the drawing. The actual 
differences in these depth dimensions is such that the strength of locking 
engagement between the ratchet teeth 16, 22 and the, respective pawl teeth 
14 and abutment surface teeth 24 is not significantly affected even though 
the pawl teeth 14 do not extend to the full depth A.sub.L of the first set 
of ratchet teeth 16 when the depth A.sub.L of the first set of ratchet 
teeth 16 is larger than the preferred depth A.sub.P and the abutment 
surface teeth 24 do not extend to the full depth B.sub.L of the second set 
of ratchet teeth 22 when the depth B.sub.L of the second set of ratchet 
teeth 22 is larger than the preferred depth B.sub.P, as shown in FIG. 3A 
and/or the first set of ratchet teeth 16 do not extend to the full depth 
of pawl teeth 14 when the depth A.sub.S of the first set of ratchet teeth 
16 is smaller than the preferred depth A.sub.P and the second set of 
ratchet teeth 22 do not extend to the full depth of the abutment surface 
teeth 24 when the depth B.sub.S of the second set of ratchet teeth 22 is 
smaller than the preferred depth B.sub.P, as shown in FIG. 4A. 
In the preferred method of making the molds, the mold pieces that are 
provided initially define therebetween at least two cavities 44, 46 for 
forming ties 48, 50 having a uniform maximum thickness T between the two 
broad sides of the ties 48, 50, wherein each of the mold pieces 40, 42 
includes projections 52, 54 for forming the ratchet teeth 16, 22, with the 
projections 52 for forming the first set of ratchet teeth 16 being uniform 
for at least both of the at least two mold cavities 44, 46 and with the 
projections 54 for forming the second set of ratchet teeth 22 being 
uniform for at least both of the at least two mold cavities 44, 46. 
Preferably, the projections 52, 54 have depth dimensions A.sub.L, B.sub.L, 
as shown in FIG. 3, that are larger than required for forming ratchet 
teeth 16, 22 of the preferred dimensions A.sub.P, B.sub.P shown in FIG. 1. 
Plastic material is then injected at a minimal injection pressure 
approximately simultaneously into at least both of the at least two mold 
cavities 44, 46 in order to form the ties 48, 50 and completely fill one 
of the cavities 44, 46 with the injected plastic material. 
The relative extent to which the at least two mold cavities 44, 46 are 
filled with the injected plastic material is measured; and when at least 
both of the at least two mold cavities 44, 46 are not completely filled 
approximately simultaneously, the relative depth dimensions A, B of the 
projections 52, 54 for at least both of the at least two mold cavities 44, 
46 are adjusted to be such that when plastic material is injected at a 
minimal injection pressure approximately simultaneously into at least both 
of the at least two mold cavities 44, 46, the injected plastic material 
flows through the at least two cavities 44, 46 at respective flow rates 
that cause at least both of the at least two mold cavities 44, 46 to be 
completely filled approximately simultaneously with the injected plastic 
material. 
The depth dimensions A, B of the projections 52, 54 are adjusted by 
reducing the extensions of the tips 56, 58 of the respective projections 
52, 54, with the tips 56 of all of the projections 52 for forming a first 
set of ratchet teeth 16 being reduced by a first uniform depth, and with 
extensions of the tips 58 of all of the projections 54 for forming a 
second set of ratchet teeth 22 being reduced by a second uniform depth, 
which may or may not be the same as the first uniform depth by which the 
tips 56 of the projections 54 are reduced. Alternatively the depths of 
only some of tips 56 and/or 58 of the projections 52 and/or 54 for forming 
one or more ties 48, 50 are reduced and/or such reduction is not 
necessarily uniform for all of the tips 56, 58 as to which the depth is 
reduced. 
In alternative preferred embodiments, the depth of only either the tips 56 
of the projections 52 that form the first set of ratchet teeth 16 or the 
tips 58 of the projections 54 that form the second set of ratchet teeth 22 
are reduced. 
Preferably, the dimensions of the projections 52 for forming the first set 
of ratchet teeth 16 and/or the dimensions of the projections 54 for 
forming the second set of ratchet teeth 22 are adjusted so that the 
projections 52 and/or 54 for at least one of the at least two mold 
cavities 44, 46 are of the dimensions required for forming ratchet teeth 
16 and/or 22 of the preferred dimensions A.sub.P and/or B.sub.P. 
However, if such an adjustment doesn't result in the injected plastic 
material flowing through the at least two cavities 44, 46 at respective 
flow rates that cause the at least two mold cavities 44, 46 to be 
completely filled approximately simultaneously with the injected plastic 
material, the dimensions of the projections 52 for forming the first set 
of ratchet teeth 16 and/or the dimensions of the projections 54 for 
forming the second set of ratchet teeth 22 are adjusted so that the 
projections 52 and/or 54 for at least one of the at least two mold 
cavities 44, 46 are of a dimension A.sub.L and/or B.sub.L larger than 
required for forming ratchet teeth 16 and/or 22 of the preferred dimension 
A.sub.P and/or B.sub.P and so that the projections 52 and/or 54 for at 
least another of the at least two mold cavities 44, 46 are of a dimension 
A.sub.S and/or B.sub.S smaller than required for forming ratchet teeth 16 
and/or 22 of the preferred dimension A.sub.P and/or B.sub.P. 
When such adjustments result in the injected plastic material flowing 
through the at least two cavities 44, 46 at respective flow rates that 
cause the at least two mold cavities 44, 46 to be completely filled 
approximately simultaneously with the injected plastic material, the 
multi-cavity mold is provided for balanced injection molding of a 
plurality of ties and plastic material is injected approximately 
simultaneously into at least both of the at least two mold cavities 44, 46 
to form the ties 48, 50. 
The advantages specifically stated herein do not necessarily apply to every 
conceivable embodiment of the present invention. Further, such stated 
advantages of the present invention are only examples and should not be 
construed as the only advantages of the present invention. 
While the above description contains many specificities, these should not 
be construed as limitations on the scope of the present invention, but 
rather as exemplifications of the preferred embodiments described herein. 
Other variations are possible and the scope of the present invention 
should be determined not by the embodiments described herein but rather by 
the claims and their legal equivalents.