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Using the runner as a fixture for parts
Definition: Runner Design: a design/configuration of a feed system for the flowing of plastic into individual cavities, which is ejected with the parts after it, solidifies. Secondary operations: a process which occurs in additional to the molding of the parts to impart/or apply something to the part prior to it becoming finished. Examples would be sonic welding, hot stamping etc.
In many cases with the advent of smaller parts and assembly requirements it is sometimes necessary to lay out a tool and the runner not only to feed material to the cavity/cavities but also to allow for the design of the runner as a holding device so as to preform secondary and or assembly operations to the part.
These operations can be anything from painting, flocking, or other decoration to that of holding the part so as to be able to assembly it in an operation.
An example is one for the cosmetics industry in which the applicators were molded using what might be called a fishbone type arrangement. What this means is the flow of material was not uniform, since the requirement was only to have full parts. But what this did do is allow all the parts to be in a row so as to present themselves to the next step which was the application of the brush/applicator to be attached to the parts.
Example:
As viewed on the flat one can see that all the parts are still on the runner, and held there by the gate. In the next step the round portion is treated, coated and dried. In the final step they are then shipped in this array so as to be assembled into kits at end use customer and or separated from the runner and bulk packed. As viewed one can envision that the parts are feed into some sort of automation which due to spacing can now index and handle the parts.
In another case a small lens like part must be assembled into a part. With the prototype tool the parts were sub gated which proved to be an issues with parts going everywhere and the handling of the parts became a real issue. Since this was to be a high volume manufacturing operations one possible solution was to mold the small parts onto a runner arrangement which than could be held and upon assembly into the finish product the parts would be assembled and the gate area removed in one step. This allowed for the parts to be manufactured, handled and actually pre-loaded for the next step.
Examples:
The above shows a uniform fill for a small part which must be inserted into a mating part but one which is high volume thus necessitating some sort of automation. The red section indicates the keyway as shown in the next photo. This key way aligns the unit to a set position so as to indicate how it is to be used in the automation equipment.
In the design stage for any of the operations some key points are to know the following:
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What has to be performed?
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Well the assembly be handled by robotics or people?
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Well it eventually go to robotics
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If robotics will be used is there a need for an index, locator for orientation.
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Is there any additional operation that must be performed such as plasma treat coating, etc.?
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Well the operations eventually become a cell structure with all being done at the machine?
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Is bowing allowed in total part? Meaning runner assembly unit.
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How firm should the parts be held? Meaning gate design adhesion should be good so as not to lose parts in transport.
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Since the runner is now part of the product so to speak, minimizing size is critical from a material usage, cooling time, and other factors.
While the above list is only partial it is a good start. Further while the cost of manufacture for material may be higher, due to use of runner as a fixture/ holder, does it lower cost to rejects, and or handling of parts.
As manufacturing cost become more competitive, it is sometimes the thinking outside the box which can lead to becoming less expensive for total part cost.
SLSILVEY
22092014.01
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