Mitsubishi Heavy Industries Technical Review Vol. 46 No. 3 (Sep. 2009)36"em Ⅱ" Series Two-platen Large Electric Injection
Molding Machine with High Throughput andReduced Environmental Burden
M I T S U B I S H I H E AV Y I N D U S T R I E SP L AS T I C T E C H N O L O G Y C O . , LT D .

Use of resin instead of steel and glass materials in automobiles is an environmental
technology that has been used to reduce weight and lower fuel consumption, resulting in lower
CO2 emissions. To produce the resin parts, electric injection molding machines, which use lessenergy, compared with traditional machines, and no hydraulic oil have been promoted since the1990s. Improvements in the productivity of moldings, including thin-wall moldings that
contribute to a reduced number of molding cycles and lighter products (due to the reduced
amount of resin), have sometimes been inconsistent with energy conservation principles, because
sudden accelerations, decelerations, and quick operations are required to produce them, so thathigh-power, high-speed injection molding machines are required. Mitsubishi Heavy Industries,
Ltd. (MHI) has developed the “em Ⅱ” series, which consists of two-platen large electric
injection molding machines featuring high throughput and high-speed injection. These machines
permit downsizing, and small footprint, energy, and resources (hydraulic oil), thereby reducing
their environmental burden. Features of these machines are discussed below.

|1. Features(1) Small footprint, compact, high-speed, high-precision two-platen mold clamping mechanism
The two-platen mold clamping mechanism, which, unlike a toggle mechanism, does nothave a toggle support board, is composed of two platens, a fixed platen and a movable platen.
Consequently, the machine is shorter and lighter (Figures 1 and 2). For these reasons,compared with toggle machines, two-platen machines use less resources to produce moldings,
require less energy (produce less CO2) for transportation and installation, require less materials(at a lower cost) to build a foundation to install the machine, and realize more effective use of
space in a factory.

Figure 1 Comparison of clamping mechanisms of two-platen and toggle machinesMitsubishi Heavy Industries Technical Review Vol. 46 No. 3 (Sep. 2009)37
A fully automatic toggle
machine with equivalent moldclamping force, manufactured
by a competitor.

The 1600emⅡ-240(screw diameter 120 mm),a two-platen electric machine
manufactured by MHI

Figure 2 Comparison of machine length

The two-platen machine consists of a fixed platen, a movable platen, an electric platen
open-close mechanism that drives the biaxial ball screws on the operation andcounter-operation sides, using our servomotor synchronization control system, and aservomotor drive mechanism, consisting of an injector and a split nut, reducing the moldopen-close time by 20%, compared with hydraulic machines. After the mold is closed, four
universal tie rods are locked by split nuts, and then a short-stroke clamping cylinder is boosted
to generate a mold clamping force. Thus, unlike toggle machines, the clamping force of which
varies, depending on mold temperature, two-platen machines feature a high-precision clamping
force, achieving stability in terms of the precision of the moldings and reducing gas problems.
(2) Eco servo pump system, using electric power regeneration that shortens the molding cycle andsaves energy
The eco servo system (patented/patent pending), which starts, adjusts, and stops a
low-noise vane pump, the rotation of which can be stopped, by an AC servomotor only at thetime of mold clamping, mold release and hydraulic core pull, providing high-precision andenergy-saving control. Additionally, the built-in hydraulic oil tank has a lower capacity (340 L)
because the heat generated from the hydraulic oil is reduced. The oil cooler coolant volume isas small as the volume of the coolant for the hydraulic unit for a hydraulic core pull (40 L/min)attached to a toggle electric injection molding machine.
The large capacity eco servo pump system reduces the molding cycle by decreasing thecore pull operating time, and it does not require separate hydraulic units for the shutoff valve,valve gate, or clamper. Additionally, while servomotors in conventional electric injection
molding machines, which work as electric power generators during deceleration, release theirregenerative energy to the atmosphere via regenerative resistance, the machine developed byMHI is equipped with an electric power regeneration system that recycles the regenerative
energy from all of the servomotors to the primary source, and uses that energy to run heaters
and control devices, reducing power consumption by 60%, compared with machines equippedwith separate hydraulic units (Figure 3).
(3) Highly responsive high-speed injection unit that uses a large-capacity direct-drive servomotor
to produce thin-wall molding
Fast responses and high speed are required when switching from the injection speed usedat start-up to pressure control used once the mold is filled to realize thin-wall molding. Toachieve fast response and high speed, the inertia at the injection ball screw driving body must
be reduced. However, improvements to responsiveness are limited in conventional servomotors,
which use a deceleration mechanism and a large-diameter pulley connected by a timing belt andgenerate a large inertial force.
The inertia was reduced by two axes large-capacity direct-drive (DD) servomotor (fouraxes for screw diameter larger than 120 mm) characterized by low revolutions and high torque,which was developed using our electromagnetic analysis and a synchronous control speed
enhancement technologies exclusive for our motors. As a result, the highest injection speed wasattained under the maximum injection force, and the rise time of the molding speed wasreduced by 1/3, compared with conventional machines that employ a pulley and belt system,
allowing us to realize thin-wall molding (Figure 4).

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 3 (Sep. 2009)38

The adoption of the DD servomotor also eliminated problems such as elongation of thetiming belt and displacement of the synchronizing belt, resulting in reduced noise.
Additionally, the injection accuracy remained stable for a long time with no maintenance,including belt tension adjustments or replacement.

Figure 3 Eco servo pump system using electric power regeneration

Figure 4 Comparison of injection units and injection speed start-up performanceMitsubishi Heavy Industries Technical Review Vol. 46 No. 3 (Sep. 2009)39(4) New control unit, the MACVIII+
Our control unit, the MACVIII, is highly rated because it is equipped with a 12-inch
LCD screen and a direct touch panel for selecting molding conditions, and it uses
easy-to-operate select switches, instead of small seat switches. The new MACVIII+ has aJapanese language input function and a cumulative power consumption display screen,
supporting USB external memories and printer terminals, and is more convenient to use(Figure 5).

Clamp open-close operation setting screen

Eco screen display(cumulative power consumption display)

Figure 5 New control unit, the MACVIII+

Existing functions
Large 12-inch LCD screen
Easy-to-use direct touch panel(Standard)(Option)New functions- Japanese language input function- Cumulative power consumption display screen- Screen shot (screen image storage)- External memory (supports USB memory)- Packet MAC (supports USB memory)- Supports USB printer(5) Security and safety
Noise reduction was realized by the DD servomotor and the eco servo pump, which led
to a clean and quiet working environment. The product was developed with security and safetyin mind, and meets the risk management requirements specified by the revised Industrial Safety
and Health Act and complies with the JIMS K-1001 safety rules stipulated by the Japan Societyof Industrial Machinery Manufacturers.

|2. Specifications
Performance specifications of the emⅡ series are shown in Table 1.
Table 1 Performance specifications of the emⅡ series
Item
Clamping force
Tie bar spacing (H  V)
Clamping stroke/day light
Screw diameter
Theoretical injection Volume
Injection rate
Injection pressure
Overall dimensions (L  W  H)

UnitkN (tf)mmmmmm
cm3cm3/s
MPam1050emⅡ-160
10 290 (1 050)
1 300 x 1 300
1 750/2 250
1054 540
1 385
177
10.3 x 3.2 x 2.9

1300emⅡ-160
12 749 (1 300)
1 450 x 1 400
1 850/2 500
105
4 540
1 385
177
11.3 x 3.5 x 3.2

1600emⅡ-240
15 691 (1 600)
1 850 x 1 520
2 400/3 200
120
6 780
1 415
177
12.5 x 3.9 x 3.3