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Mold Bases: What Every Molder Should Know

Mold Bases and Plates

Standard Mold Base Styles

For most applications, a standard mold base will fit the bill.

The most common of these is the “A-style,” which has the

flexibility to fit into the widest variety of molding applications.

A-style models have a four-plate design: (from top to bottom)

top clamp plate, A-plate, B-plate, support plate, ejector

retainer, ejector bar, and ejector housing. Mold makers using

an A-style mold base typically machine through pockets in

the “A” and “B” plates to accept just about any kind of core

and cavity insert.

The B-style mold base represents an economy version of

the A-style. The B-style’s two-plate design combines the top

clamp plate and the “A” plate into one component called the

“A-Clamping Plate” or ACP. Likewise, a beefed-up “B” plate

eliminates the need for a support plate on the core side of

the mold.

Molders can use the less-costly “B” Series when the part

design allows the cavity and core to be machined directly into

the cavity plates. If the mold will be used with cavity inserts,

they must be machined into blind pockets. The compactness

of the “B” series mold base also makes it applicable

whenever overall mold height must be limited in order

to fit the tool in a given molding machine.

A-Series Mold Base Assembly

The most frequently used standard assembly, the “A” Series Mold

Base, is available in 43 sizes from 7.875 x 7.875 to 23.75 x 35.5.







Today’s mold-building process is a complex one for the molder, who must grapple with a long list of

design details before placing a tooling order. It’s understandable that much of the buyer’s attention

goes to the “heart” of the injection mold, the core and cavity inserts, since they have the most visible

influence on the molded part. Yet all sorts of ancillary tooling components, to which the molder might

not be inclined to give much thought, can also make or break a mold.

One item that sometimes gets lost in the shuffle is the mold base, even though the wrong one can severely limit

a mold’s productivity. Rather than an afterthought, mold base selection should be considered critical to the profit-

ability of the entire molding project.

When selecting a mold base for a particular job, first ask a few key questions about the part’s design and processing

demands: What kind of ejection does it need? Does it have a cam action or some other mold-action device? What

are the volume requirements? What type of machine will it run on?

Answer these design and processing questions, and you’ll be well on your way to picking the standardized or

special-purpose mold base best suited to your application.

“Core and cavity inserts … have the

most visible influence on the molded

part yet … mold base selection should

be considered critical to the profitability

of the entire molding project.”

Mold Bases and Plates


Mold Bases: What Every Molder Should Know