Dimensional Stability

What guidance do you have for achievable limits on DST injection urea machines regarding the number of cavities that can be reliably balanced to give dimensional stability. Part is about 15Grammes and approx 8mm x 14mm x 5mm with a wall thickness around 2mm generally.

These have been moulded up to 20 impressions before I believe, but some people that we approach for this type of work aren't confident to be able to balance the pressures down the cavities of the tool as the distance increases from the injection point.

Andy,

Your comments about the difficulties maintaining consistent cavity pressures as the distance increases from the injection point indicates an unbalanced runner.

An unbalanced runner will definitely give dimensional instability but having said that a properly sized runner system can significantly improve the situation. Calculating the right size in each branch of the runner is the difficult part and simulating software is normally required. The higher the number of cavities in the tool the higher the risk of instability.

The other alternative is to design the mould with a balanced runner system and then you can add as many cavities that the moulding machine will allow. This will eliminate any instability.

Admin.


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