The Designer's Edge: Venting

Burn at end of fill knit line from inadequate venting.

If you have been reading my Plastics Technology column or MMT blogs, you know that I spent the first half of my career building and designing injection molds. During this time I was focused on building the highest quality mold to produce a clean part. However, at that time I had no idea how the tool could affect the process window on the molding side, which later exposed some big gaps in my tool standards. All of this experience has lead me to speak with tool shops and moldmakers about their opinions on venting and how some of the tool standards they use can cause issues on the molding side.

Venting is a daily challenge when it comes to part quality and processing. Inadequate venting can cause weak knit lines, gloss issues, bubbles, splay, burns, erosion, increased cycle times, excessive cleaning of the parting lines and very small process windows when lack of venting is processed around.

So, what is adequate venting? There are various thoughts on venting and many are based on opinion without true knowledge or experience. Despite the varied opinions, one thing is for sure: tool shops impact tool standards. For example, a tool can be sent out to have vents added or deepened. Then it comes back and the part now has flash, so the mold is sent back out again. This time it returns with burns on the part from welding up the vent. Varied opinions on venting and indiviual moldmaker work quality can complicate matters when it comes to mold standards.

My next blog on Friday, May 29th, will review a few old standards and how they do not provide adequate venting. It will also examine how parting line bearing surface plays a critical role with keeping vents open.

For more on this and other Designer's Edge topics, catch up with Randy the Amerimold Expo on June 17 for his talk on "Overcoming Repair and Part Quality Challenges with Design." Click here to register to attend.