1.New Tooling
New tooling considerations involve only a few items that are not part of a conventional tooling design. Quality input is imperative to determine location and shape of gas channels and for design advice regarding ribs, bosses and heavy sections of the molded product.

Most often, tool design is simpler than with conventional injection molding, as the constraints of part design are fewer. What we see most often is the need for quality input to what new options are available in part design, and to assist the molder or tool builder in understanding the concepts of flow and gas channels in the process and part design.

When injecting through the nozzle, gate size and location is critical, and simplicity is the key. A single gate is preferred in the majority of parts that are conducive to that configuration. Flow channel/gas channel feed to ribs, bosses and heavy sections require input from experienced Gas Assist engineers or molders. Please note that a hot runner must be avoided when injecting nitrogen through the sprue. This does, however, allow for reduced tooling costs.

As a part of our service function, GAIN Technologies offers consultation on any developmental or current molded part. GAIN provides design input and recommendations on molded parts, part prints, and tool prints for existing products. Once the concept of the displacement of resin in the flow/gas channels is realized, the concept becomes simple. A molder new to the Gas Assist process should consult with GAIN Technologies to acquire the input necessary for successful startup of the Gas Assist process.

GAIN regularly performs tryouts and demonstrations at prospective customers plants to demonstrate the system and prove-out the process to the application. It should be noted that there are no mechanical additions to an injection mold in order to facilitate gas injection, unless injecting through pins in the tool.

2.Converting Existing Tooling
Existing tooling can easily be converted to Gas Assist injection, provided the basic part design is conducive to the process. As mentioned previously, nitrogen cannot be injected through a hot runner.

A tool with a hot runner has two options: 1) Inject gas through pins in the tool, or 2) modify the tool to eliminate the hot runner and revise the gating method. Gas channels may need to be cut to facilitate the flow/gas channels, and to follow to the areas where gas is desired. The channels would lead to areas of intersecting ribs, under heavy bosses, and to any additional areas that would benefit from a gas channel.

3.Spill-overs
Spillovers are pockets cut into an injection mold, outside the area of the cavity itself, which are used to receive “spilled over” resin from the cavity during gas injection. The spillover is used for one of the following basic functions:

1)The spillover receives resin displaced from flow channels and sections of the molded product when the part design prevents resin in those areas from being displaced to areas further down-stream during gas injection. In certain product design, this condition is unavoidable due to part design considerations.

This condition results in from an areaof the cavity, which would usually be last to fill, filling early in the plastic injection phase. When gas injection takes place, there is no area for the resin in those areas to be displaced to, therefore the spillover is cut into the area adjacent to the cavity, and during gas injection, the resin is displaced from that area into the spillover

2) A spillover can be used to create a complete, continuous gas channel, with the channels actually meeting, joining, and extending into the spillover. This is the method used to join (2) separate channels in a molded part.

3) A spillover may be used to eliminate weld lines or hesitation lines, and undesirable surface appearances in a product by displacing the resin, which includes those characteristics into the spillover, rather than remaining in the molded product.