Moulding Side Cores And Side Cavities

12.0  SIDE CORES AND SIDE CAVITIES

1    Introduction:-

A side core is a local core which is normally mounted at right angled to the mould axis for forming a hole or recess in the side face of a moulding. This side core prevents the in-line removal of the moulding and some means must be provided for withdrawing the side core prior to ejection. Figure 12-1 shows the side core in action.

The side cavity performs a similar function to the side core, in that it permits the moulding of components which are not in line of draw. This element allows for components with a projection or projections on one or more of their side faces. Figure 12-2 shows the side cavity in action. Typical examples of components which necessitate the use of either a side core or a side cavity are shown in Figure 12-3.

12.2    Mouldings embodying side holes, recess or slots:-

In general, any component which has a local recess, holes or slot which is not in line of draw will necessitate the incorporation of a side core in the mould design. However there are a few exceptions. For example, a hole in the side face of a component could be moulded in the line of draw by astute component design. The hole can be formed by a part of the core abutting on to the slopping face of the cavity. To achieve this condition the component must be designed with a definite step as shown in Figure 12-4. When a step is not permissible an alternative design may be adopted as in Figure 12-4b. In this the side wall of the component is caused to slope at an obtuse angle with respect to the base. This permits the hole to be formed by a projection from the core which abutts on to the cavity as shown. Please note that the top face of the projection must be such that it does not create an undercut. Moulded holes of this type are very simple and if designer agrees this can de adopted.

A hole can also be incorporated in to the side face of the moulding by a subsequent machining operation. This method should always be considered by the mould designer before proceeding with a side core design as it has the following advantages.

1. The mould in simple and therefore relatively cheap.
2. Ease of operation of the mould creates less likely hood of production problems.
3. Whereas a side core breaks up the normal flow of material entering the impression and there is a probability of flow lines developing, with this method it is impossible for this to happen.

The general form of the component may make use of the split design more appropriate than the side core design. However, note that if the component necessitates a slender core, the side core design can be used with advantage.

if the component has a hole that is not parallel to the parting surface as shown in figure   12-5 , the side core must be withdrawn at a suitable angle to the parting surface of the mould (figure 12-5A). Curved holes can be moulded, providing the component design allows the curved core to be withdrawn on a rediused path (figure 12-5B).

Now consider the case where it is preferable to use the side core technique for what would normally be considered a split mould component. A component which is shown in figure 9-6 is a circular section which is having a slender hole at the middle. It incorporate a peripheral undercut on the exterior as shown. By adopting the side core design, the outside shape of the moulding is formed in the two mould plate, the component being moulded at right angles to the mould’s axis.

The advantages are

1. The long slender core is guided at a time in one of the mould plate. This protects the core against accidental damage.
2. As the component is adjacent to the parting line surface, a great saving in mould height can be achieved as compared with split design. Reduction in mould thickness often allows the component to be moulded in a smaller injection moulding machine.

12.3    The design requirements for side core and side cavity:-

1. Arrangements must be made for guiding the assembly
2. Means must be incorporated for actuating the assembly
3. The assembly must be securely locked when in the moulding position.

Mould designs incorporating side cores and side cavities for components having holes or projections vary considerably according to the position number of form of the restriction. The design can be classified as follows:

1. Design for mouldings with peripheral undercuts with slender center holes.
2. Design for moulding with holes or slots in one or more sides.
3. Design for mouldings with recess or projections in on or more sides.
4. Designs for mouldings with curved holes.

12.4    Internal side core or side cavity assembly: -   The side core assembly is similar to splits and similar methods are adopted for guiding, locking and operating it. The carriage     (Fig.12-7) is mounted in guides which are securely attached to the moving mould plate. The side core element is secured by the retaining plate to the carriage. The actuation of the carriage is by means of a finger cam, and is locked in forward position by a locking heel.

a) Internal side core or side cavity assembly details: -The assembly consists of a carriage and either a side core element or a side cavity element. These elements are secured to the carnage either directly or by means of a retaining plate. The carriage is provided by a pocket machined in both mould plates. the major part of the carriage is accommodated below the parting surface in a pocket. The width of this pocket is sufficient to accommodate the gib. The portion of the carriage which projects above the parting surface must be accommodated in a pocket in the fixed mould plate. One face of this pocket is angled to form the locking heel.

b) Guiding arrangements:- The guiding arrangements for the internal side core or side cavity is similar to that of guiding splits. The assembly is relatively small unit.

c) Method of actuation:-

The internal side core assembly can be actuated by means of a finger cam. Other method like dog leg cam actuation and spring actuation are also commonly used.

The finger cam: Method of actuation is used when a short delay is required. The amount of clearance between the cam and cam hole determine the actual delay period. The finger cam must be of sufficient length to withdraw the side core from the moulding completely (Fig.12-7.)

The dog - leg cam:-Method of actuation is specified if a longer delay period is required. It is desired to withdraw the moulding completely from the fixed half before retracting the side core. The ensures that the moulding remains in the moving half in readiness for ejection (Fig.12-8)

The spring loaded system: - This is used for mouldings with shallow undercuts or projections. The figure 12-9 shows a section through a side core assembly. The component has a small indentation in one side formed by a side core mounted in a standard carriage assembly. For spring actuation, a stud is attached to the bottom of the carriage as shown in figure, and this is accommodated in a slot machined in the mould plate. A spring or springs are fitted in the slot and cause the side core assembly to withdraw immediately the mould opens. Note that the locking heel is used to progressively return the assembly when the mould is being closed.

d)        Locking the carriage assembly   :-The final closing movement and locking of the carriage assembly are by means of a locking heel (Fig.12-1O). The angle specified for locking heel, and the corresponding angle of the carriage are normally 15⁰ and 40⁰. When the finger cams are used to actuate the carriage, the angle must always be greater than the operating angle. To provide wear resistance surface for the locking heel, and to provide an adjustment for wear, wear plates are fitted on the angle surface. The locking heel normally protrudes above the parting surface and two alternative designs are shown in figure.

12.5    External side core or side cavity assembly

In this design, the side core or cavity is coupled to an externally mounted carriage. This carriage often supported by an outrigger arrangement, is generally actuated by hydraulic or pneumatic means although cam and spring actuation are occasionally used. An example is shown in the figure 12-11

Side core or side cavity assembly details:-

A side core or side cavity assembly consists of a side core or side cavity element, retaining plate and a carriage(figure 12-12). Positive alignment of the side element is a must and in design shown the side cores are fitted in close tolerance holes, machined in the side wall of the cavity. It is important to allow these side cores to float in the retaining plate in a similar manner to the ejector pin float.

In most designs, the carriage is supported on the columns of the outrigger as shown. The columns pass through suitably bushed holes in the carriage. The carriage must be locked in it’s forward position to withstand the force applied to the side element by the pressurized melt.

The outrigger :-

The primary purpose of the outrigger is to provide a platform upon which to mount a hydraulic or pneumatic actuator. The secondary purpose is to provide means of guiding and supporting the carriage. This is of particular importance when cam and spring method of actuation are used. Several designs are shown in figure 12-12

Methods of actuation :-

The actuator   : -The most common method of operating the external carriage is by means of an actuator. The ram of the actuator may be either directly coupled to the carriage or indirectly coupled via a toggle linkage system. In the first case, the actuator is mounted on a outrigger platform and the ram coupled to the carriage either by a screw or by a flange connection. A typical example is shown in figure 12-14.

In the second case, a toggle unit is attached to the side core. The basic assembly is shown in figure 12-14. The ram is actuated by a hydraulic or pneumatic actuator via a toggle linkage system. When the cylinder ram is actuated, the pull link causes the toggle links to withdraw the ram, which slides in phosphor bronze bearings within the frame.

Camactuation: - Finger cam, dog leg and plate cams can be incorporated in certain designs to operate the external carriage. These methods are confined to those designs where the side core is mounted on the parting surface. Examples of these types are shown in figure 12-15

Spring actuation: - If it is required to move the side core only a short distance, then spring actuation may be considered. The figure 9-16 shows a part section through the relevant details of the system.

12.6    Types of side cores and side cavities

The component form determines the type of the side element which may be used. For example, a component which incorporates a hole on the parting line requires the side core to be mounted on the parting surface of the mould. If the hole is below parting surface or component incorporates a projection, the side coring becomes more difficult as there are various factors to take into consideration (figure 12-17)

When a component has a hole in it’s side at an angle (other than right angle), generally the design requires the side core assembly to be mounted at a corresponding angle in the mould. Refer figure 12-18.

When the designer has to deal with a curved hole in a component, an even more complex system is required as the curved core, to form the hole, must be withdrawn on a radius. Refer figure 12-19.

When flash is liable to develop, it is important that mould design is such that wherever possible the flash is in line of draw. Unless close attention is paid to this point, the ejection of the moulding may be impeded and build-up of flash may prevent the side element from operating efficiently.