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General comments on design function
Definition: mold. 1) A hallow form or matrix into which a plastic material is placed and which imparts to the material its final shape as a finished article. 2) To impart shape to a plastic mass by means of confining cavity or matrix. B side 1) Moveable / cold side of mold that opposite of stationary side or injection half. 2) Ejector side, the half which in most cases ejects the parts
The B side, movable side of the mold base is that mold half which bolts to the moveable platen. It is hopefully where the parts are retained when the mold opens so that they may be ejected off when fully opened. Please note that some mold designs may be backwards and parts are ejected off this half but it is bolted to the A platen, as always within the molding area there are exceptions to the standard.
What is critical about the B side is the stack up of the mold plates and their thickness. If one reviews the basics as shown above it can be seen that the B side of the mold is composed of:
B Plate:
This plate may have the cavities, cores, runner and vents cut into it. This plate is what mates up to the A Plate to form the seal around the cavities, runners and also vents. Since this plate see's force it should be tough and hard, though in different classes of tool build it may be soft since inserts may take the load.
In some cases there is only a B plate in the mold and no support plate and in those cases it is critical to have a thick enough plate to take all the forces.
Support Plate:
This plate is to support the B plate in the mold. If cavity inserts are used in a tool than this plate can capture the shoulder of the inserts against the B plate retaining it in the mold and allowing assembly of the tool. Since as the name implies it is a support plate, thickness of this plate is what gives it its strength. This is especially true if within the ejector housing there is no room for support columns to aid in the non-bending of the plate when a load is applied. As can be seen above the support plate bridges the span over the ejector housing.
Note** 2 plates in stack up do not equal the strength of one plate of equal thickness to the two plates. Thus if a support plate is bending and support columns are not possible the support plate should be replaced with a thicker plate and not just adding an additional plate of equal or lesser thickness.
Ejector housing:
The ejector housing is area which houses the ejector mechanism in the mold. While the view above shows it as one piece cut out, in many cases it can be made up of 2 rails for the side pieces and Top Clamp plate. The opening or span in the support plate is the working area where it is possible to install the ejector pins, though some areas around the corners are for guide pins and possible push backs for the ejector plate.
The height or stroke of the ejectors is limited by the thickness of the ejector plate assembly subtracted from the height of the rails of the housing.
Ejector retainer plate:
This plate is where the location the ejector pins is, with counter sinks below to capture the heads of the ejector pins.
Ejector plate
This plate bolts to the ejector retainer plate capturing the ejector pins and taking the load of the ejector pins on the part back to the plate. Thus is must be strong enough so as to not warp or bend when being pushed upon and also when the pins push onto the part and back to the plate.
When the mold is assembled there is one off-set pin per each plate so as to assemble correctly at all times. This is most often marked by a 0 in the corner of the plate. Further as one can observe that the stack up of all the plates must be done with precision, as when clamped in the press at high tonnage any misalignment, non-conformance within the system can be magnified and cause issues with the production of the parts.
SLSILVEY
01052014
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