How do you design mold vents to prevent gas traps and burn marks?

Vents for an injection mold should always be designed at the opposite end of the gate. Another way is to mold a short shot as close as possible to a full shot. This can show the area where the vent can be made.

In my experience I have seen less and less understanding of proper venting of injection molds. I have had conversations where the “head of tooling” for a multi-national contract molding supplier state that they never vent molds before first trial. I smiled and responded with a question of “where do you think the gases will go if you don’t provide venting”. In many cases I’ve been told the mold will naturally vent because of the inserts. It has been my experience that optimizing the vents both primary and vent dumps to atmospheric pressure will improve stability of the process overall and improve first pass yields on every part I have made. No exceptions. #iworkgforgm

First off, check the mould flow and relate back to the tooling GA to ensure the last places to fill are covered with easily accessible and cleanable vents. If its not easy to install then think of a plan B. Have a mould peripheral vent channel, so that any further areas of gas traps and potential shorts can be easily covered with a local vent. One thing overlooked is the clamp pressure, start with the calculated/recommended clamp pressure and then start to drop off shot by shot, ensuring no flashing or change in the moulded part. I find most people crank the clamp pressure to max, stops the tool from breathing and cause's the tool to bed in more which can lead to more gas burns.

Why on part issues are noted the burning may also etch the tool and surface finish if left un checked. As per Kevin reply, too many times I too have seen no vents in tools, and or no exhaust channel capable of taking gas to atmosphere.

Uma vez em uma consultoria percebi uma pe?a queimada, com efeito diesel. Na hora imaginei que poderia ser saída de gases ineficiente. Conversando com o ferramenteiro ele disse que n?o havia nenhum sistema de escape de gases no molde. Por isso sempre fique atento: muitos ferramenteiros costumam posicionar saída de gases depois do try-out, sendo que é possível prever na etapa de projetos e evitar retrabalho.

I agree that Juicing out of FR systems in the past was an issue with vents in tools - The FR system in the first of the halogen free FR systems were not very stable and the result would be that you would have a juicing / leaching out of a corrosive substance from the material onto the tool ( down the vent channels or ejector pins) - the solution suggested by at least on material manufacture was to have no gas vents so the juice would not be allowed to form and would remain in the polymer. Over the years as FR packages have improved this is now not a consideration.

Mold venting allows the even flow of material without resistance, though in some cases minimum vents help in surface finish with FR materials of the past.

Acredito que n?o somente uma saída de gases bem dimensionada, é necessário também posicionar os pontos de inje??o para que esses escapes n?o estejam localizados em regi?es estéticas ou de controle dimensional.

The vents on each mold must be designed into the mold from the outset. This allows purposeful inserts,ejection types and artifacts as well as implementations of gas counter pressure( an example is #moldvac) into mold design. Often in the preliminary mold design a full venting methodology is not well defined or allowances to implement into the mold. It seems like many times the idea of venting only comes up after the mold is tested and trapped gases become a process problem. At the stage of mold trials it’s far too late in mold design/build and development to properly implement venting. Critical aspect of venting is primary vent depth, primary vent land length and secondary (vent dump) to atmosphere. #iworkforgm

Utilizing simulation tools such as Moldflow can identify gas/air traps. This will give an early indication of where to place vents. Also watching the flow of the material through the mold in simulations can also give good guidance. Venting is more than just for gas/air traps, it is about maximising melt flow, allowing air to escape as the material advances. Placing vents at known weld line locations can improve the strength and apperance of those weld lines. Often overlooked is good venting in runner systems, especially where the runner changes direction.

In areas of trapping gas that is not at the parting line a use of a vent insert and vacuum is an asset. Also consider Porcerax material in tough areas of the part design.

Adding perimeter venting is best practice. Vent depth in primary vent channel is paramount. If vents are too deep flash is high risk. Vents not deep enough have flash as high risk. This may seem counter intuitive however if the vents aren’t deep enough the compression of outgases the resin will superheat at the last point of fill, changing viscosity of which will change resin viscosity and flash into the vent. This anomaly will appear the “vents are too deep “ when in actuality vents aren’t deep enough. Use of peripheral vents insure that entire flow front is being vented and as last point to fill is converged the gases have been diminished and have ability to evacuate from tool effectively . #iworkforgm

In my opinion, during the mold design phase, it is essential to examine the type and flow path of the molten material both through software simulation and experimentally. Sampling from available materials in the market must be done before mass production injection, and the physical conditions and properties of the materials should be controlled. One crucial factor might be the Melt Flow Index (MFI), which, if smooth, swiftly reaches the intended areas and prevents air entrapment.

Lors de la conception d'évents de moule, il est important de prendre en compte plusieurs facteurs pour assurer un fonctionnement efficace du moule et obtenir des pièces de qualité. Voici quelques-uns des facteurs clés à considérer comme :taille des évents,position,nombres,formes, et dimensionnement des evants

é importantíssimo que o engenheiro responsável pelo projeto do molde entenda também do processo de inje??o, para que possa estimar ou calcular com a maior precis?o possível o tempo de enchimento (ou inje??o). Uma vez que esse é um dado fundamental para determina??o da vaz?o necessária de gás no escape.

Most mold flow simulation software can predict last point(s) if fill and weld line locations. Venting must be properly implemented to help achieve good weld line strength. Mold filling simulation used with venting added in setup of simulation and incorporated into the mold design offers the results to show effectiveness and influence with venting included in the simulation results. #iworkforgm

Identifiez les problèmes courants liés aux évents de moule tels que les pièces incomplètes, les marques de br?lure, les déformations, etc. Cela vous aidera à définir les objectifs de test et d'optimisation.

Things I have used over the last 40 years to insure that my parts were properly vented. First I do not use peripheral vents I’ve found out that you get some venting a vent after but after .500 wide collapses in the middle and only vents on either end of the vent so edge vents around the parts .500 or less around the part has always worked best for me. It’s always important to try to have self cleaning vents when using pin or blade vents, but if you can’t designing them with easy access for cleaning is important and time consuming because a not self cleaning vent will plug!

There are few devices on market that create vaccum to suck the trapped gases. That would be the way to go when venting is hard to achieve or if you already maxed out the vent depth per the standard depth for a given resin. Runner imbalances also cause differential viscosity and temperature gradient throught and each cavity may end up having different venting needs.

One way to think about venting is what is speed of air flow out of vent, an interesting exercise to explain the bang, some may hear, and or to show that there is not enough vent.

Mold Maintenence should be considered. Vents can, over time accumulate residues and this can vastly reduce the effectiveness of the venting. Careful monitoring during early production will help establish maintenance intervals that address vent cleaning. Split line vents are often easy to access and clean during production, but venting in hard to reach places such as sliders, lifters or insert venting will require the mold to be stripped down and cleaned.

Great info sharing, thanks. In my experience, already when working with digital tooling / 3D-printed low volume molding tools, you can start exploring both gate and vent options from the first try / first day. I have enabled clients to be able to make 4-6 mold designs same week, and explore everything from venting, material or design iterations. #whatwouldyoumake if everything you could design, you could also mold - using Digital tooling?