Tie-bar-less machines for multi-cavity moulds

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. In order to increase productivity per unit area, Gerresheimer uses high-cavity moulds in production. The specifications for the production of these demanding plastic precision parts in the clean room were defined as follows:

• Optimum use of the production area in the clean room

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

• Consistently high and uniform part quality in all mould cavities

• Gentle handling of the cost-intensive tools

Based on the mould design and the specifications, Gerresheimer became aware of the tie-bar-less, hybrid injection moulding machine e-victory. Since the machine has no tie bars to limit the mould space, comparatively large moulds can be mounted on smaller machines with low clamping force in this series. The area of the mould fixing platens can be fully utilised right to the edge. This is directly reflected in the productivity per unit area and is a tangible advantage, especially in the expensive cleanroom.

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

However, as Gerresheimer had not previously used tie-bar-less injection moulding machines, there were some reservations about this technology: "What about platen parallelism when opening and closing the mould? Can you produce precision plastic parts without tie bars? Does tie-bar-less technology lead to faster wear of the mould? - 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 mould and the distance to the moving platen was recorded in each case. And this was done several times over the entire injection moulding cycle with different mould opening states and different mould temperatures.

Subsequently, a tie-bar-less injection moulding machine was tested in production operation with a multi-cavity mould over a period of two and a half years. After a further, 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 clean room

  The large, tie-bar-less mould 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 plasticising components specially adapted to the requirements of PBT. High melt quality and reproducibility are thus ensured.
  
  

• Consistently high and uniform part quality in all cavities

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

• Gentle handling of the cost-intensive moulds

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

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