Technical Information

G-2 Transformation of Molding Technology to be able to Cast Ultra Thin/Light Weight Parts due to Ultra High-Speed and Pressure

G-2 Transformation of Molding Technology to be able to Cast Ultra Thin/Light Weight Parts due to Ultra High-Speed and Pressure

Thin-walled and light-weight injection molded parts are now required in today's plastic molding industry and Toshiba Machine is meeting these requirements. Components like flat panel displays (FPD) for cellular phone, and IT-related visual devices are becoming thinning and lighter, an example is a light-guide plate making up the back light has gone from 0.40mm to 0.35mm in part thickness. To meet these requirements, we have introduced our EC100SX-2ZZ Ultra High-Speed and Pressure injection molding machine especially designed for extremely thin and light weight molding.

[Platform]
G. Manufacturing technology based on features of molds
[Applications]
Injection molding machine

[Technical points]

  • Ultra high-speed and high-pressure injection molding machine EC100SX-2ZZ
    Injection speed: 1300mm/s
    Acceleration: 8.3G
    Maximum Injection pressure: 350MPa
  • For the optical plate, the imprinting rate is as high as 97.0% at the micro-patterning depth.

1. Introduction

IT-related products that incorporate liquid crystal displays such as LCD televisions, cellular phones, digital cameras and car navigation systems are constantly in pursuit of higher performance, and their respective markets are insisting larger displays, higher luminance, thinning and lighter weight components. An example, is the fore mentioned light-guiding plate used in the cellular phone backlight unit, molding of this ultra thin-walled component whose L/T (Length of component by its Thickness) exceeds 200 which is leading injection molding technology. Generally, light-guide plates machined micro-patterns on its surface to make all plates can have the same light reflection and diffusion patterns. Also, Nano-imprinting technology that reproduces micro-pattern printing. In the injection molding of ultra thin components the molten resin must reach the filling finish position, before the skin layer cools over the die surface during the filling process. To achieve this requirement, an Ultra High-Speed and Pressure injection molding machine with the fastest acceleration is required.

2. Features of ultra high-speed and pressure molding

Fig. 1 Ultra high-speed and pressure injection  molding machine EC100SX-2ZZ

Fig. 1 Ultra high-speed and pressure injection molding machine EC100SX-2ZZ

Responding to the market needs for the Ultra High-Speed and Pressure molding, Toshiba Machine has developed the EX100SX-2ZZ, which was born by adding the specifications for Ultra high-speed and pressure molding to the base EC-SX series machine. Its development is based on the concepts of high productivity, precision and steady molding. EC100SX-2ZZ is pictured in Fig. 1 and the main specifications are in Table 1.

  Item Unit EC100SX–2ZZ EC100SX–2A (standard)
Injection unit Screw diameter mm 22 32
Injection volume calculated cm3 38 102
Maximum injection pressure MPa 350 220
Maximum holding pressure MPa 280 220
Injection speed mm/s 1300 200
Injection ratio cm3/s 494 161
Plasticization capacity (PS) kg/h 22 61
Maximum screw speed min–1 420 390
clamping unit Clamping force kN 980
Distance between tie rods mm 460´410
Platen dimensions mm 660´610
Clamp stroke mm 350
Maximum open daylight mm 900
Fig. 2 Fluctuation of minimum cushion with our previous control

Fig. 2 Fluctuation of minimum cushion with our previous control

In the molding of ultra thin components, the molten resin injected into the mold will solidify in an extremely short time period of 0.1s or less, it is extremely important to fill with a consistent amount of resin each time at an ultra high rate before the resin solidifies.
All EC-SX series machines are equipped with a "friction-free drive" utilizing linear guides supporting the sliding of the injection mechanism which drives the screw. The use of linear guides reduces the sliding resistance during the movement of the injection mechanism allowing faster acceleration and improves consistencies of injection pressure during injection, and improvement of back pressure control during metering is achieved.
The ultra high-speed and pressure injection unit uses a direct drive servo system, which directly connects the high power and low inertia motor with the injection unit's ball screw to achieve an amazing acceleration rate of 8.3G's with a maximum injection speed of 1300mm/s and a maximum injection pressure of 350MPa.
To achieve the precision and steady molding required even under ultra high-speed and pressure injection we developed the EC-SX series to have high-speed motor control and steady metering for plasticization with a highly rigid die clamping unit.
In figure 2, we show the fluctuation of the minimum cushion and visual appearance of the molded product with an injection speed of 1300mm/s using our previous motor control. The difference between good shot and short shot (the product is not yet filled) was caused due to the variation of controlling the holding pressure transfer position.

Fig.3 Fluctuation of minimum cushion and injection pressure at high-speed control

Fig.3 Fluctuation of minimum cushion and injection pressure at high-speed control

The EC100SX-2ZZ has successfully controlled the fluctuation of minimum cushion to 0.05mm (Fig. 3) during steady and continuous molding without any short shots. This is due to the high-speed capability of new INJECTVISOR-V50 controller, provided on the EC-SX series machine.

3. Example molding of ultra-thin walled components

Fig. 4 Ultra thin-walled optical plate (Left side: Machining of V-grooves, Right side: Dot patterning)

Fig. 4 Ultra thin-walled optical plate (Left side: Machining of V-grooves, Right side: Dot patterning)

An example, of an ultra high-speed and pressure molding of an optical plate with a minimum thickness of 0.3mm is shown.
The dimensions of this optical plate are 41mm wide and 75mm in length, which is equivalent to a 3.5 inch-wide screen. The molding of this plate is classified as ultra-thin component molding with an L/T value of 250. A two-cavity die is used and each cavity is provided with different micro-patterns.
To be successful molding ultra-thin components, creation of a total engineering team is required, from the molding material, die design and the injection molding machine. In the optical plate molding, we used the high flow grade of PC (Lupilon® HL7001 made by Mitsubish Engineering-Plastics) as the molding material. The die needs to be designed for high-speed filling and be rigid enough to withstand the high pressures while preventing creation of burrs. Gas venting and smooth filling is also necessary, but if too many gas vents are used burrs can easily occur. The EC-SX series machine is equipped with a high-rigidity die clamping unit called the "Double Rigid Plate" to help in controlling the generation of burrs.
Fig. 4 shows the sample of the fore mentioned optical plate which was molded an injection speed of 1100mm/s and a filling time of 0.036s. When the micro-patterning depth of the dies and sample mold product heights were measured, they were 2.770μm and 2.688μm respectively, which shows that a high imprinting rate of 97.0% has been achieved.

4. Conclusion

Ultra thin-wall & light-weight plastic component production is just one of the important market requirement which are demanded in the plastic molding industry, and further development is expected. We are determined to exceed in this diversified market in the plastic molding industry and to expand and improve ourselves in the machine and control technology and exceed in the expectations of the customers worldwide for years to come.