What are Mold core and cavity inserts

Mold core and cavity inserts are components of a mold used in the manufacturing of plastic and metal parts.

A mold core (sometimes small inserts we call core inserts) is the internal part of the mold, which is normally located at the core side (moveable side). This creates the internal features of the part being molded. The core is typically made out of steel, such as 1.2344, S136, etc., and is typically removable from the mold plate (B plate or pocket plate).

A mold cavity insert has the same function as core insert, but is located on the fix side. It is the external part of the mold that creates the external shape of the part being molded. The cavity insert is typically made out of steel, such as NAK 80, S136, 1.2344, and H13, and is typically removable from the mold.

 

Both the mold core and cavity insert are typically made using the processes of EDM (Elektroerosive Bearbeitung) and CNC (computer numerical control) machining. The core and cavity inserts are then assembled into a mold base to get the complete Plastikform. The mold is then used in the injection molding or casting process to produce the desired parts.

Of course there are many manufacturing processes to make plastic mold, such as lathe machining, grinder machining, polishing, wire cutting, milling etc. but CNC and EDM machinings are the most improtant manufacuring process to make an injection molding, belew are briefly explain for EDM and CNC machining:

EDM:

• First, a mold design is created in 3D modeling software.
• The working piece (cavity and core steel) is then loaded into the EDM machine, which uses electrical discharges to erode the surface of a conductive material (such as steel or aluminum) to create the desired shape of the core or cavity insert.
• The finished working piece is then polished or textured according to requirement.

CNC:

• The process is similar, but instead of using electrical discharge machining, a CNC machine uses cutting tools (such as end mills or drills) to remove material from a block of steel or aluminum to create the desired shape of the core or cavity insert.
• The finished working piece is then heat-treated to increase its strength and durability, if sue pre-harden steel then no need addtional heat treatment, can move to the EDM machining process directly.

Both EDM and CNC can produce very precise and accurate parts and are widely used in the manufacturing of mold cores and cavity inserts, one important procedure that needs to explain, the working sequence between EDM and CNC, normally CNC machining will start first, then use EDM machining to remove some of area which CNC machining can not do, for example some corners, ribs, bosses, etc.

Some guideline to manufacture mold core and cavity inserts

When we manufacture the mold core and cavity inserts during mold manufacturing, there are some dimensions that we need to manufacture with some tolerances so that they fit well in the pocket of the insert plate or mold cavity or core.

And this will save some work when we fit the mold cavity and core. High tolerance and good manufacturing technology will save lots of time for the mold master. Below are some manufacturing mold core and cavity insert guidelines that we need to pay attention to to make high-quality plastic mold.

1. When we make the corner radius In the manual milling machine, make a 0.2-mm  step there; after hardening, we don’t have to grind on the corner when we fit the insert.
2. For the outside dimension of the Schimmel cavity or core inserts, the tolerance should be +/-0.015mm; this will be easy fitting into the pocket, smooth, and of good quality.
3. The tolerance for the hole in the sprue bushing should be H7 (0/+0.015 mm).
4. The depth of the treading should be 1.5–2 multiplied by the diameter of the tread. In this case, for the M8 screw, the depth of the treading should be 1.5 to 2 multiplied by 8, equal to 12–16 mm.
5. The guidance of the ejector pin should be about 15-20 mm long; this will make sure that the ejector pins are ejecting smoothly with a long lifetime.
6. The clearance area for the ejector pins should be 1 mm bigger than the diameter of the ejector pins. For any question about mold, please contact us.

Making injection mold cavtiy and core inserts are not easy, it must be made by a professional mold manufacturer, if you are running a injection molding shop, and need to make some mold cavity and core inserts to replace the old inserts, or if you have a new mold that want to make all of cavity and cores and assembly this in your molding shop, you are welomce to contact us, we can make injection mold cavity and core inserts or completely mold cavtiy and core, moldbase, or completely plastic injection mold for you.

Guidelines to manufacture mold core and cavity plates (pocket plates)

As you already knew mold manufacturing is not an easy job, if you do not have any good team or experience in this field, I suggest you find a profession plastic mold company to support you, you could do the molding process at your side but make the mold outsource, because make plastic mold need very high technical skill for every worker, compared to injection molding process, mold manufacturing needs more manual jobs than injection molding service, and need high technical requirement as well, below is one of manufacturing guideline for A plate of mold.

When we manufacture the core and cavity plates for a plastic mold, there are some dimensions that we need to manufacture with some tolerances so that our cavity and core insert components or our standard mold components can smoothly assembly in to the plate pocket, and the straight guidance blocks can fit well in the mold base, below are some key points that we need to take care during A plate manufacturing.

When we have straight interlocks at each side of mold base (A and B plates), the tolerance for this dimension should be H7 (0/+0.015mm), that the interlocks can easy to the assembly in the mold base but keep high precision guiding function.

The pocket dimensions for the cavity and core inserts, we should follow the tolerance requirement H7 (0/+0.015mm), so that our cavity/core insert can be smoothly guided into the pocket but have precision dimension.

The location of the hole for the locating pin is important, this is assembly with clamping plate, and the dimension must match to the related hole on the clamping plate, so the tolerance for the locating pins must keep in ±0.01mm, the locating pinholes must have related tolerance H7 (0/+0.015mm), so that the locating pin can easily go in.

If the mold has the hot runner system to work properly, the fitting area needs to have a tolerance of ± 0.01mm, please see below explain.

For the o ring track depth, the tolerance is ± 0.05mm, for the o ring track diameter

The tolerance is ± 0.25mm, this is the same requirement for all of o-ring in the mold.

 

Guideline for the clamping plate manufacturing

When we manufacture the cavity side of the clamping plate, there are some dimensions that we need to control with some tolerances so that our standard mold components and other parts can fit well in the clamping plate.

For the locating pinholes, the tolerance should be H7 (0/+0.015mm)

The hole diameter for the locating ring, the tolerance should be ±0.02mm

The hole diameter for the Hot runner manifold support insert, the tolerance should be ±0.05mm

The height dimension for the air venting groove on the Hot runner manifold support insert, the tolerance should be ±0.01mm

The slot for the locating pin to the sprue bushing, the tolerance should be 0/+0.10mm

The location of the hole for the locating pin is important, this is connecting to another plate, like hot runner manifold plate, or A plate, tight tolerance we make sure that the mold base assembly very well, the tolerance for it should be ±0.01mm.

Sincere Tech is one of best top 10 mold manufacturers in China, if you have a project that needs to make molds or molded parts from China, you are welcome to send us your requirement for quotation, we can send you a mold price or both mold and molding unit price, we can make first samples fast  in 15 days to support your business.

90% of our molds are export to America, and Europe, we are not only making plastic molds for our customer but also have injection molding shop to offer injection molding service.

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