Technical Information

B-1 Five New Technologies of the Injection Molding Machine Series EC-SX

Toshiba Machine has proposed the five new technologies to respond to the processing needs of today's plastic molding market; "Solid Clamp" clamping device, "S-Cube" injection unit, "INJECTVISOR-V50" HMI controller, "DST" automatic molding condition correction function and improved processing screws lineup, The EC-SX has been developed to incorporate these technologies.

[Platform]
B. Processing and molding machines Engineering abilities
[Applications]
Injection molding machine

[Technical points]

  • High-rigidity die clamping: Rigidity of platen has increased by 30%, compared with our previous system.
  • Linear guide system: Clean molding environment and high-precision stable molding.
  • Dynamic acceleration/deceleration control: Cycle time has reduced by up to 20%, compared with our previous system.
  • DST-Press: Compensation of clamping force.
  • DST-Fill: Detection of change in monitor values to compensate molding conditions.
  • BF screw: Prevention of dark spots in molding of engineering plastics.

1. Introduction

The need for thin-wall and light weight mold products are on the increase in the plastic molding market, and at the same time further improvement of productivity and stability are needed to minimizing defects, reducing environmental impacts and production cost. In response to these requirements, Toshiba Machine, as the injection molding machine manufacture has developed the five new injection molding technologies and incorporated them in the most sophisticated electric injection molding machine the EC-SX series. In this report, we introduce the new five injection molding technologies included on the EC-SX series.

2. Five injection molding technologies

2.1 New Mold clamping unit "Solid Clamp"

Fig. 1 Link line toggle and double rigid platen

Fig. 1 Link line toggle and double rigid platen

To manufacture high quality thin-wall and light-weight molded products, the use of a high rigid clamping unit is required to minimize deflection at the time of molding. We have developed a new die clamping device ("Solid Clamp") which significantly improved the rigidity of the platens by 30%, compared with our previous clamping unit. Thanks to the use of the link line toggle (inclined toggle) which transfers the link force to the center of the movable platen, and double structure of the stationary platen (Note 1) and the movable platen (i.e., double rigid platens), uniform distribution of die clamping force can be realized. Molding with reduced die clamping force also becomes possible. (Fig. 1 and Fig. 2)

Fig. 2 Distribution of movable platen deflection

Fig. 2 Distribution of movable platen deflection

The supporting method of the moving die platen has been improved from the previous tie-bar guide method to a linear guide method (without tie-bar bushing). This new method reduces the sliding resist and linearization at the time of opening and closing. This structure is been used in applications where extremely high dimensional accuracies are required for parallelism linearization of the die platens, as in lens molding. With the use of this standard structure, the sensing function for die protection is improved due to the low sliding resistance of the movable die platen. The linearization of the mold opening and closing extend the service life of the dies. With the absence of tie-bar bushing, grease-lubrication of the tie-bars is unnecessary, as a result grease will not stick to the die set surface of the moving die nor will it drop into product drop area. The mold and working clothes of personnel are not contaminated with grease left on the tie-bars during die replacement. A clean molding environment is realized and our machines are having the highest reputation among customers all over the world. Furthermore, the dry cycle time of the Solid Clamp is reduced due to evaluation of the toggle characteristics and innovative control method of new controller "INJECTVISOR-V50" (as described later); shorter cycle time is now possible.

Note 1: The double structure of the clamping mechanism as been incorporated on all EC350SX and under.

2.2 New injection unit "S-Cube

Fig. 3 Friction-free drive system

Fig. 3 Friction-free drive system

The "S-Cube", which signifies "Simple, Steady and Smooth", is the injection unit which can achieve steady molding operations with a simple structure and configuration, and smooth motions. To achieve smooth motions, a friction-free drive system (Fig. 3) is used, which utilizes a linear guide for the sliding part of the injection ram that drives the screw.

Fig. 4 Schematic diagram of linearization correction

Fig. 4 Schematic diagram of linearization correction

The friction-free drive system contributes to the precise steady and smooth molding during injection due to minimized sliding resistance and the enhanced accuracy of the screw back pressure control during recovery (or metering). The smooth and steady motions are very effective during high-speed, high pressure molding in high-precision applications such as thin-walled micro-pattern forming. A significant advantage that is important with steady molding in precision molding operations is the reduction of, "dimensional error", which signifies an error of mold product accuracies when molding the same product in two or more machines. The "S-Cube" uses a digital load cell for pressure detector and correction. The individual difference characteristics of the load cell are minimized reducing the dimensional error that can be seen between multiple machines. (Fig. 4)

2.3 New controller "INJECTVISOR-V50"

Fig.5 INJECTVISOR-V50

Fig. 5 INJECTVISOR-V50

To accomplish steady molding in high-speed injection molding and micro-pattern forming applications where molding quality is influenced by the filling performance and holding pressure (transfer) changeover (a key point of the molding process), we developed the new controller "INJECTVISOR-V50" (Fig. 5) with shortened control speed (62.5μs) of each servo motor axis. This enhance the holding pressure changeover accuracy.

Short cycle time, precise and steady molding are capable and when combined with the "S-Cube" (described above) every molding quality has been improved, from molding of thick-wall products requiring better holding pressure accuracy, steady molding of exterior parts requiring multi-stage control of injection speed and pressure, high-speed molding of thin-wall products and molding of fine mold parts with small shot volume. In addition, with the use of a toggle type clamping unit acceleration/deceleration characteristic of the movable platen stating position because speed ratio of the cross head (i.e., ball screw unit for the mold opening and closing) and movable platen changes with the movable platen starting position.

Fig. 6 Comparison of mold open/close dry cycles

Fig. 6 Comparison of mold open/close dry cycles

To rectify this situation, we have developed the "dynamic acceleration/deceleration control" for controlling the acceleration/deceleration characteristic of the movable platen, regardless of the movable platen position. As a result, we have accomplished high-response mold opening and closing motions without any impact, at any movable platen position and reduced the dry cycle time by up to 20%, compared with our previous system (Fig. 6)

Fig. 7 Effect of RA ejection control

Fig. 7 Effect of RA ejection control

The "RA" (Rapid Action) ejection control is incorporated as standard to accelerate the ejection response, which significantly reduces the ejection cycle time when multiple ejection strokes are required. The reduction of ejection cycle time is illustrated in (Fig. 7) when 5 ejection strokes were executed. A "Signal Customizing function" has been added, which allows random selection of an output signal to the sent to peripheral equipment. The INJECTVISOR-V50 allows for easy settings of the output conditions and output format, thus saving time and labor cost when output configurations are required between peripheral equipment and the injection molding machine.

2.4 Automatic Molding Condition Compensating Functions

Fig. 8 Example of quality compensation with DST-FILL (compensation of molding conditions)

Fig. 8 Example of quality compensation with DST-FILL (compensation of molding conditions)

Two automatic molding condition compensating programs have been put to practical use to maintain steady molding against variables such as a change in mold temperature and changes in lot to lot quantity of the plastic material. The first program is "DST-Press" (DST-Dynamic Self Tuning) for compensating die clamping force. During continuous molding operations, variations in die temperatures can cause changes in clamping force; "DST-Press" maintains a constant clamping force allowing for a consistent and steady molding cycle. In the case where die clamping force is required to adjust, it does not affected cycle time. The adjustment occurs during the mold full open position of the movable platen and does not affect the overall cycle time and maintaining a steady, smooth cycle.
The second program is "DST-FILL" is for compensating the molding conditions by detecting a change in the monitoring values including the holding transfer pressure and minimum cushion position. (i.e., most forward position of the screw during the injection process) Fig. 8 shows example where a short shot (i.e., defective molding condition where filling of the product is not complete) was generated in the molded product after the lot change of molding material (liquid Crystal Polymer: LCP) changed from A to B. DST-FILL compensated the process to a good product. In this case, a minor drop in viscosity characteristic of the material was seen. This was caused by a change in material from A to B material, increasing the monitor value) (i.e., holding transfer pressure). DST-FILL compensating by adjusting the barrel temperatures (i.e., the barrel temperature was increased), the viscosity characteristic of material then became equivalent to that of lot A and the monitor value (i.e., holding transfer pressure) was returned to the previous value to eliminate the short shot problem. DST-FILL is very effective for change in the mixing ratio of regrind to the molding material.

2.5 Strengthened screw lineup

We have developed the BF screw (*BF: Burn Free Full Flight) to prevent generation of dark spots in the molding of engineering plastics such as PA and PBT, and added it to our screw variation (Table 1). The BF screw has a special coating applied to the surface to improve separation of the molding material. The reduction of adhesion and residence of the molding material to the screw surface prevents burn of resin caused by thermal deterioration. The BF screw design has increased the molding material feeding ability, even while molding regrind material. Residence of the resin at the screw flight area is prevented due to steady plasticization.

Fig. 9 BF screw (effects on grind)

Fig. 9 BF screw (effects on grind)

Table 1 Screw variation
DBG screw (standard) General-purposed
SRB screw Engineering plastics
DBC screw Hard polyvinyl chloride
GN4 screw PMMA, transparent resin
BF screw Engineering plastics (prevention of dark spots)
Fig. 10 Screw condition after continuous three-month molding of POM resin

Fig. 10 Screw condition after continuous three-month molding of POM resin

Testing shows even when molding PA66 containing regrind metering time and (shot) cushion volume were stabilized (Fig. 9). Fig. 10 shows the screw surface after the screw was drawn out after three-month of continuous molding of POM material. You can see adhesion of the molding material to the screw surface is extremely small.

3. Conclusion

Each injection molding machine manufacturer is competing hard to differentiate its own machines from those of their competitors with a focus to improve the capabilities of the machines. We have incorporated our new five injection molding technologies in our EC-SX series machine, aiming to be a forerunner on this global market. We will also make utmost efforts to satisfy the market requirements by supplying highly valued-added technologies for our customers.