Molding machine

In a molding machine of the type wherein a movable die plate carrying a movable mold is moved toward a stationary mold, the movable die plate is locked by a locking member to the tie bars, and then the mold tightening cylinder is operated to strongly urge the movable mold against the stationary mold, the locking member is operated by an electric actuator before the movable mold engages the stationary mold, or while the movable die plate is still being moved toward the stationary mold.

BACKGROUND OF THE INVENTION 
This invention relates to a molding machine such as an injection molding 
machine or a die cast machine and more particularly to the improvement of 
the mold tightening apparatus utilized in such molding machine. 
With the recent trend of increasing the capacity of the molding machine of 
the type described above, and for the purpose of decreasing the weight and 
floor space occupied by the machine as well as the price and operating 
cost thereof, decreasing the size of the liquid pressure actuator and 
increasing the operating speed of the machine, it has been proposed to use 
two operating cylinders, namely a boost cylinder for moving the movable 
die plate for opening and closing the mold, and a mold tightening cylinder 
for strongly urging the movable mold against the stationary mold instead 
of using a single cylinder for moving the die plate and tightening the 
molds. 
FIG. 1 of the accompanying drawing diagrammatically illustrates one example 
of such a two cylinder type molding machine comprising a stationary metal 
mold 1 secured to a stationary die plate 2 securely mounted on a bed, not 
shown, a stationary plate 3 also secured to the bed, and tie bars 4 
extending between plates 2 and 3. The lefthand ends of the tie bars 4 
slidably extend through the openings of the stationary plates 3, whereas 
the righthand ends slidably extends through openings of the stationary die 
plate 2 and are terminated with pistons 5 contained in cylinders 6 
fastened to the stationary die plate 2. The lefthand halves of tie bars 4 
are formed with screw threads or a plurality of axially spaced 
circumferential grooves. There is also provided a movable metal mold 7 
supported by a movable die plate 8 for cooperation with stationary mold 1. 
The movement of the movable die plate 8 is guided by tie bars 4. Locking 
members in the form of split lock nuts 9 formed on their inner surfaces 
with threads or axially spaced circumferential ribs adapted to engage the 
threads or grooves of the tie bars 4 are mounted on one side of the 
movable die plates 8 to be slidable in the radial direction with respect 
to the longitudinal axes of the tie bars 4. Thus, when the locking members 
are caused to engage or clamp the tie bars, the movable die plates 8 and 
tie bars 4 are locked together so that they are moved in unison. Above one 
of the cylinders 6 is mounted a boost cylinder 10 whose piston rod 11 is 
connected to the movable die plate 8. With this construction, when 
pressurized liquid is admitted into the lefthand chamber in the boost 
cylinder 10 while the stationary and movable molds 1 and 7 are separated 
the movable die plate 8 will be moved to the right along the tie bars. At 
the end of the stroke of the piston in boost cylinder 10, the locking 
members 9 are moved toward tie bars 4, in a manner to be described later, 
thus locking the movable die plate 8 to the tie bars 4. Then, the 
pressurized liquid is admitted into the lefthand chamber of mold 
tightening cylinder 6 for urging the movable mold 7 against the stationary 
mold 1 under a high pressure. 
With this arrangement, however, as the movable die plate 8 is locked to the 
tie bars by advancing radially inwardly the locking members 9 when the 
stroke of the piston in the boost cylinder 10 has completed, the time 
required for advancing the locking members causes in the decrease in the 
production speed. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved molding machine 
capable of eliminating the defect described above, thereby increasing the 
production speed. 
Another object of this invention is to provide an improved molding machine 
including means for coupling the movable die plate to the mold tightening 
cylinder before the movable mold engages the stationary mold, or while the 
movable die plate is still being moved toward the stationary mold. 
According to this invention there is provided a molding machine of the type 
comprising a stationary mold mounted on a stationary die plate, a movable 
mold carried by a movable die plate movable along tie bars, a boost 
cylinder coupled to the movable die plate for moving the movable die plate 
toward and away from the stationary die plate, at least one mold 
tightening cylinder coupled to the tie bars for strongly urging the 
movable mold against the stationary mold, and a locking member for locking 
the movable die plate to said tie bars, characterized in that electric 
contacts are arranged to be closed by the movement of the movable die 
plate before the movable mold engages the stationary mold and that an 
electric signal generated by the closure of the electric contacts 
energizes electric actuating means for actuating the locking member while 
the movable member is still moving toward the stationary mold. 
According to one embodiment of this invention, the locking member is 
mounted on the movable die plate to be movable toward the tie bar which is 
operated by the mold tightening cylinder, a supporting plate is connected 
to the tie bar, a rod is mounted on the movable die plate to extend 
through the supporting plate, a stop member is mounted on one end of the 
rod protruding from the supporting plate and switch means is provided to 
be operated when the stop member engages the supporting plate for 
generating an electric signal which is used to actuate the locking member 
thus locking the movable die plate to the tie bar. In this manner, before 
the movable mold engages the stationary mold the movable die plate is 
locked to the tie bar so that it is possible to tighten the molds as soon 
as they are caused to engage with each other. Thus, the time required for 
locking the movable die plate to the mold tightening cylinder does not 
increase the overall operating time of the molding machine. 
In a modified embodiment, the stop member is fixed to the tie bar so that 
when the movable die plate engages the stop member an electrical signal 
for operating the locking member is generated. 
In another modification, the piston of the mold tightening cylinder is made 
hollow and a compression rod is connected to the movable die plate to 
extend through the hollow cylinder. A stop member is mounted on one end of 
the compression rod protruding beyond the hollow cylinder for generating 
an electrical signal when the stop member engages one end of the hollow 
cylinder. The locking member responsive to the electrical signal is 
mounted on the opposite end of the hollow cylinder so as to couple the 
movable die plate to the hollow cylinder of the mold tightening cylinder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 2 of the accompanying drawings illustrating one 
embodiment of the invention, elements designated by reference numerals 1 
to 11 inclusive are identical to those shown in FIG. 1. However, in this 
embodiment the stroke of the pistons 5 contained in the mold tightening 
cylinders 6 is made larger than that of the pistons 5 shown in FIG. 1. A 
supporting plate 22 is secured to the outer ends of tie bars 4. A bar 23 
is connected to the lefthand side of the movable die plate 8 and extends 
through a central opening of the supporting plate 22. A plurality of 
circumferential grooves 24 are formed near the outer end of the bar 23, 
the number of the grooves 24 being determined in accordance with the 
thicknesses of the molds 1 and 7. A stop ring 25 is removably fitted in 
one of the grooves 24. 
In operation, upon admission of pressurized liquid into the lefthand 
chamber of the boost cylinder 10, the movable die plate 8 is moved to the 
right. A little before engagement of stop ring 25 and supporting plate 22, 
the quantity of the pressurized liquid admitted into boost cylinder 10 is 
decreased thereby decelerating the righthand movement of the movable die 
plate 8. Then, upon engagement of stop ring 25 against supporting plate 
22, tie bars 4 are also moved to the right. When a command signal for 
advancing the locking members 9 is generated by electric contacts 26 or a 
switch, not shown, which are disposed to be closed at an instant when the 
stop ring 25 engages the supporting plate 22, the locking members 9 
constructed as above described are caused to engage the tie bars by 
suitable actuating means 20, for example electromagnetically operated 
plungers or electrohydraulic actuaters connected to be energized by the 
command signal while these bars are still being moved to the right so that 
it is possible to cause the locking members 9 to engage the tie bars 4 
before completion of the stroke of the piston of the boost cylinder 10. 
Although illustrated diagrammatically, actually the actuating means 20 are 
mounted on the movable die plate 8 so as to move the locking members 9 in 
the axial direction along one side of the movable die plate 8. When 
movable mold 7 engages stationary mold 1, mold tightening piston 5 is 
operated in a manner well known in the art. For example, when movable mold 
7 engages stationary mold 1, a microswitch, not shown, is operated to 
energize a valve for admitting operating fluid to the left of the piston 5 
to urge the movable mold 7 against the stationary die 1. 
Although not shown in the drawing, molten metal or plasticized resinous 
material is injected into the cavity defined by the molds 1 and 7 under a 
high pressure usually through the stationary mold. According to this 
invention, it is possible to operate the mold tightening cylinders 6 at 
the same time when the movable mold 7 engages the stationary mold 1. When 
compared with the prior art arrangement wherein the tie bars and the 
movable die plate are locked together only after the piston of the boost 
cylinder 10 has completed its stroke, according to this invention as the 
locking of the movable die plate to the tie bars is performed during the 
stroke of the piston of the boost cylinder 10 it is possible to decrease 
the operating time of the molding machine by the time required for 
advancing the locking members thereby decreasing the overall operating 
time of the molding machine. 
In a modified embodiment of this invention shown in FIG. 3, elements 
designated by reference numerals 1 to 11 inclusive, 20 and 26 are 
identical to those shown in FIGS. 1 or 2. In this embodiment, at about the 
central portions of tie bars, there are provided a plurality of 
circumferential grooves 30 of the number determined by the thicknesses of 
the metal molds 1 and 7 for receiving stop rings 31 each divided into two 
halves for mounting and dismounting. 
The operation of this embodiment is similar to that of the embodiment shown 
in FIG. 2. Thus, a short time before engagement of the righthand side of 
the movable die plate 8 and the stop rings 31 the quantity of the 
pressurized liquid admitted into boost cylinder 10 is decreased thereby 
decelerating the movable die plate 8. At the time when the movable die 
plate 8 engages the stop ring 31 contacts 26 are closed so that a command 
signal for radially advancing the locking members 9 is applied to 
actuating means 20 thereby locking the movable die plate 8 to the tie bars 
4 while the former is moving at a low speed. When the piston of the boost 
cylinder 10 completes its stroke, pressurized liquid is admitted into the 
lefthand chamber of mold tightening cylinder 6 thus urging movable mold 
against stationary mold under a high pressure. 
In another embodiment shown in FIG. 4, elements designated by reference 
numerals 1 to 11, 20 and 26 are identical to those shown in FIGS. 2 and 3. 
In this embodiment, a mold tightening cylinder 43 having a stroke longer 
than the boost cylinder 10 is secured to the outer ends of tie bars 4. A 
hollow piston 42 is secured to or made integral with a sleeve 44 contained 
in the cylinder 43. A compression rod 47 is slidably contained in sleeve 
44 and one end of compression rod 47 is secured to the lefthand side of 
movable die plate 8 which is reciprocated along the tie bars 4 by the 
piston rod 11 of boost cylinder 10 which is secured to the bottom of the 
mold tightening cylinder 43. The other end of the compression rod which 
protrudes beyond sleeve 44 is provided with a plurality of axially spaced 
circumferential grooves 46 to receive a stop ring 45 also divided into two 
halves. In this example, the locking member 9 is mounted on the righthand 
side of the sleeve 44 to be slidable in the radial direction. When 
advanced radially inwardly the locking member 9 engages one of a plurality 
of axially spaced circumferential grooves 41 provided for compression rod 
47 for locking piston 42 thereto immediately before the operation of 
cylinder 43. 
In operation, pressurized liquid is admitted into the lefthand chamber of 
the boost cylinder 10 to advance the movable die plate 8 and the movable 
mold 7 to the right. At an intermediate point of this movement stop ring 
45 engages the lefthand end of sleeve 44 so that the sleeve 44 is also 
moved to the right together with piston 42. During this movement the 
locking member 9 is advanced inwardly by the electric actuating means 20 
described above thus locking piston 42 to compression rod 47. In this case 
the electric actuating means is mounted on the piston 42. In this manner, 
by the time when the piston in the boost cylinder 10 completes its stroke 
so that the movable mold 7 has been brought to abut the stationary mold 1, 
the piston 42 has already been locked to compression rod 47. Accordingly, 
it is possible to urge movable mold 7 against stationary mold 1 under a 
high pressure at the same time or immediately after engagement of the 
molds. In other words, no additional time is required for locking the 
movable die plate to the piston of the mold tightening cylinder, thus 
decreasing the overall time required for the operation of the injection 
molding machine or the die cast machine.