Tie-bar-less machines for multi-cavity molds

A newly developed inhaler generation with exchangeable active ingredient cartridges required a new design of the drive tubes. These consist of various assembly and functional elements; polybutylene terephthalate (PBT) is used as the material. To increase productivity per unit area, Gerresheimer uses high-cavity molds in production. The specifications for the production of these demanding plastic precision parts in the cleanroom were defined as follows:

• Optimum use of the production area in the cleanroom

• Consistently high melt quality of the difficult-to-process material PBT

• Consistently high and uniform part quality in all mold cavities

• Gentle handling of the cost-intensive tools

Due to the mold design and the specifications, Gerresheimer became interested in the tie-bar-less, hybrid injection molding machine e-victory. Since there are no tie bars restricting the mold space, this series allows comparatively large molds to be mounted on smaller machines with lower clamping force. The area of the mold fixing platens can be fully utilized right up to the edges. This is directly reflected in the productivity per unit area and is a significant advantage, especially in high-cost cleanroom environments.

"When using a tie-bar machine, we would need a higher clamping force class for our multi-cavity molds. Tie-bar-less technology helps us select smaller machines with lower energy consumption."(Helmut Neuper, Expert Injection Molding Technology at Gerresheimer)

However, as Gerresheimer had not previously used tie-bar-less injection molding machines, there were some reservations about this technology: "What about platen parallelism when opening and closing the mold? Can you produce precision plastic parts without tie bars? Does tie-bar-less technology lead to faster wear of the mold? - These were the questions that occupied our technical experts," says Neuper.

Gerresheimer put an e-victory machine through its paces for a whole year. For this purpose, an XD laser measuring device was attached to the top of the mold and the distance to the moving platen was recorded in each case. And this was done several times over the entire injection molding cycle with different mold opening states and different mold temperatures.

Subsequently, a tie-bar-less injection molding machine was tested in production operation with a multi-cavity mold over a period of two and a half years. After another, final dynamic platen parallelism test, Gerresheimer was completely convinced by the results:

"We have been able to prove with the sound tests that the guiding accuracy on tie-bar-less machines is at least as good as on tie-bar machines." (Peter Felber, Global Senior Director Operational Excellence at Gerresheimer)

Based on the promising results of the test series, Gerresheimer opted for the tie-bar-less e-victory. ENGEL covered the requirements defined at the beginning as follows:

• Optimum use of the production area in the cleanroom

  The large, tie-bar-less mold area of the e-victory enables the use of compact machines with the exact clamping force required instead of oversized tie-bar machines.
  
  

• Consistently high melt quality of the difficult-to-process material polybutylene terephthalate

  The precise, electric injection unit of the e-victory was equipped with plasticizing components specially adapted to the requirements of PBT. High melt quality and repeatability are thus ensured.
  
  

• Consistently high and uniform part quality in all cavities

  The patented Force Divider of the tie-bar-less clamping unit ensures homogeneous clamping force distribution over the entire platen surface. Combined with the high platen parallelism, optimum part quality is achieved, especially with multi-cavity molds.
  
  

• Gentle handling of the cost-intensive molds

  Extensive tests of the e-victory injection molding machine by Gerresheimer show that the high guidance accuracy and platen parallelism of the tie-bar-less clamping unit prevent mold wear. These properties remain constant even with very heavy molds and over several years.

Today, Gerresheimer operates more than 30 tie-bar-less injection molding machines from ENGEL. These are used for the production of precision plastic medical parts on multi-cavity molds.