Injection Molding: New Servo-Driven LSR Systems For Standard & Micro Molding

Servo drive adds accuracy and repeatability to standard and micro molding.

Two suppliers recently came out with LSR metering systems driven by highly precise and repeatable electric servomotors. First, Dopag (US) Ltd., Erlanger, Ky., introduced within the past year the Silcomix PE200 meter/mix system with servo-driven piston pumps, pressure-controlled metering, and 7-in. color touchscreen. This compact system (960 × 1320 × 1920 mm) is designed for simultaneous drainage of both A and B drums, automatically compensating to even out any variation in emptying speed, and to ensure less than 1% material residue in the drums.

In addition, Kipe Molds Inc., Placentia, Calif., has made several enhancements to its MicroDeck (MD) system (photo) for micromolding LSR parts as small as 0.007 g with no waste. The developmental version unveiled at NPE2015 in Orlando, Fla., was pneumatically actuated and had a 1/8-in. plunger with 4-in. stroke. The commercial version was released last December in three versions with plungers of 1/8-in., 3/16-in., and ¼-in. diam., all with 6-in. stroke. It also offers more robust programming for a greater range of injection velocity-control functions. The operator screen can control two valve gates rather than one, and recipe storage and data collection have been added to suit the system to medical/pharmaceutical applications. Most significant, the software is now designed to integrate a material buffer for two-component feed from pails. The original 2015 version used a cartridge prefilled with premixed LSR. That option is still available, but now the MicroDeck also can feed two components with the buffer system, developed through collaboration between Kipe Molds and Sadaplast Americas, Inc., Campobello, S.C. The buffer is a material accumulator that is positioned in the feed system at the entry to the feedthroat of the MicroDeck or machine barrel. It is designed to overcome the problem of mixing efficiency in small shots. Depending on the application, the chamber holds a minimum of 10 g of silicone, said to be a good balance between fast recharge and good pot life for small shots. The buffer creates constant pressure at the feed throat, which is said to be essential for shot-to-shot repeatability in LSR micromolding. Kipe says it may also be useful for larger shots on standard injection machines where shot-size control is critical.

Further extending this concept to standard LSR molding, Kipe and Sadaplast will soon introduce a vacuum premix tank for short-to-medium production runs. When molders have short runs or multiple color changes, setup of a full pump system is not cost-effective, according to Kipe. The new solution allows the molder to weigh out equal parts of LSR A and B sides—up to 8 lb total—then mix them together in a vacuum and use the mix tank as a pressure pot to dispense the material. The tank can be direct mounted to a machine barrel for operation at around 100 psi, or it can be used to feed the Kipe/Sadaplast buffer system.

Kipe plans to offer both the buffer and Vac-mix tank for beta testing this fall, aiming
for commercial introduction at NPE2018 next May in Orlando.