The Engineering & Manufacturing Complexities of Injection Molding Automotive Barbed Hose Connectors

That said, glass fibers also make the injection molding process a little more complex. When glass-filled nylon is injected into the cavity, the glass fiber is lined up with each strand. As it nears obstructions, like core pins, it separates resulting in random angles, weakening the end product. Minimizing the number of turns will be vital towards minimizing and glass fiber filler risks.

There are three main design elements that need to be taken into consideration here:

• Barb's Outside Diameter (OD) - The OD of the barb(s) needs to be correlated to ID of the tube it will be attached too.  When designing a connector, the accuracy of the tube's ID, material, tube flexibility, and application will be critical. For tighter seals where no clamp will be used, you'll need to increase the OD of the barb(s), but be careful as to not go overboard. If you do, installation could become your biggest bottle-neck.
• Sharp vs. Rounded Edges - Depending on the tube/hose material used, you'll need to develop a barb that is just sharp enough to grip/seal the tube, yet round enough as to not cut into the tube.
• Parting Line - We'll go into more detail later in this post, but the parting line is often overlooked when it comes to the design of connectors even though it plays a crucial role. Essentially, injection molding tools must be designed to avoid a parting line being on the end barb itself. This is critical towards creating an effective seal.

Because barbs are designed to grip the inside of a tube, it's easy for someone to assume that more barbs will provide a stronger hold and seal, but that's not usually the case.

If you're able to space out the barbs to allow the tubing being used to relax between the barbs,  then the added barbs can actually be beneficial by providing additional grip.  For the most part, though, you'll see more single barbed connectors, as the right design will achieve the necessary sealing requirements. 

Another reason why you'll see more single barbed connectors has been due to the usage of clamps as a way of ensuring the hoses/tubes stay firmly on.

When determining where the gate location should be, injection molders will typically look to place it at the deepest cross-section in order to give it the best flow that will help minimize voids and sinking.  A poorly placed gate will result in the plastic resin 'freezing' off before hitting critical areas. 

The design/size of the gate is also going to play a major role in the injection molding process, and it's commonly overlooked when it comes to these components. In order to meet tight barbed connector specs, injection molders make the gate slightly larger in order to ensure molten plastic is injected fast enough to avoid part warpage and flaws.

Creating an effective seal is crucial towards the success of an automotive barbed connector. In order to achieve this in regards to the mold design related to the barbs, you need to factor in ejector pins locations.

One of your goals when selecting ejector pin locations is to minimize the effect they'll have on the part. When it comes to connectors, ejector pins can not be located on vital areas, such as the connector's barbs.

Mold engineers also need to under the difference between a complex design vs. simple designs, as the complex structures typically require more ejection force. Because of this, you'll need to find to balance it via increasing the number of ejector pins accordingly.

Injection molding is a dance between quality, cycle time, and cost.  All three are tightly wound together.  Experienced tool designers and molding partners will tell you that it’s really tricky to produce round parts.  It looks easy but plays hard.  This is because residual stresses in the part can make it challenging to hit the specs, leading to longer cycle times to let the part cool, increasing the cost. 

Residual stresses can warp round parts (like barbed connectors) after they are released from the mold.  This can be offset by exotic materials and longer cooling cycles, but that also drives up cost.

Quality tool engineers can balance melt flow and reduce cycle times with hot runner systems, increase cooling capacity with copper cores and forced air flows, and produce precise round parts with out-of-round tools (what??).  Yes, you read that correctly. 

Depending on the part design, material flow, and residual stresses, sometimes it takes an out-of-round tool to produce precision round parts like fluid connectors.  Molding partners that don’t know this can set themselves and their customers up for a very long and hard journey.