Types of injection moulds
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Types of injection moulds and possibilities
Injection moulds come in many different shapes, types and dimensions. We describe a number of main groups and their characteristics here. This gives you more insight into the various options.
Example of an injection mould.
These are also referred to as ‘Rapid Tools’. They are casts of the final product into which liquid plastic can be poured under relatively low pressure. These injection moulds are used for small series of at most a few pieces. AKF Plastics does not supply silicone moulds. If required, we can purchase these for you.
Although aluminum is a relatively expensive metal, it is fast and relatively easy to machine and add changes into. This allows aluminum injection moulds to be constructed and manufactured relatively fast, and therefore cheaper in comparison to other metals. Aluminum is used as a material for injection moulds in the following cases:
- for the production of Rapid Tooling
- for smaller series
- as “test mold ‘in which major changes are expected
- as the mold cavities are bulky (shorter process time)
- if there is better cooling required (aluminum has better thermal conductivity than steel)
- or just for the production of relatively cheaper molds.
Due to the lower surface hardness of aluminum and the relatively high pressures which are being applied in injection moulding, aluminum molds are more vulnerable. As such their life span is limited. AKF / AGF Industrie BV guarantees the life span of aluminum moulds for several thousands of shots. We consider aluminum moulds as pilot moulds.
Such molds are constructed for smaller series in which there is little or no risk of surface damage. Untreated tool steel can be easily machined by milling, turning and drilling. In this way it is possible to manufacture injection moulds which are more expensive than test moulds but have a longer lifespan of up to several hundreds of thousands pieces.
Such molds are, in whole or in part, manufactured out of hardened tool steel (52-54 HRc). By surface treatment and through and through hardening such moulds are very rigid and suitable for very large production runs up to millions of shots. By hardening machining is much more complex. Therefore such molds are relatively costly and are used for very large productions, or for products which create risks for the mould surface during injection moulding.
It goes without saying that the higher the quality of a mould is the higher the cost structure is.
A second classification of injection moulds may take place based upon the number of cavities. Each product requires a cavity inside the mould. It is possible to project more than one, identical or different, cavities inside an injection mould. The advantage here is particularly economical. By injection moulding multiple products in one production cycle (shot) simultaneously, the machining costs per individual product will drop. This classification is divided into two main groups:
These are injection moulds with only one cavity per mould. These are used if the expected demand is relatively of low volume. In such cases the additional costs for extra cavity areas are not being justified (payback calculation method). We also design single-cavity if there are technical limitations on multiple-cavity.
Such moulds have several (identical or geometrically different) mould cavities. This can vary from 2 up to high numbers of cavities ; there are 200-cavity injection moulds on the market. The dimensions of the injection moulding machine often form the limiting factor to multiple cavity moulds.
The choice between single or multiple cavity injection moulds is often based upon economic considerations. Plurality implies a higher investment in the mould, but lower costs per product. Boundaries are set by technical issues and limitations.
Method of spraying
A third classification can be made based upon the technological injection method. There are two different types of methods to guide the liquid plastic into the mould cavity:
Pistons inject the liquid plastic into the injection mould.
In such a system, the liquid plastic is guided through a central hole and additionally channel(-s) in the mould surface towards the mould cavity. This cone and sprue are reduced to waste after demoulding. This waste is in some cases re-usable after grinding as regrind (internal recycling).
In such a system a heated channel is built into the mold. This heated channel keeps the plastic liquid continuously and trasnports it directly into the mould cavity. Such a system has the greatest advantage that it eliminates intentional waste. This saves material, energy, cooling time and possibly afterworks. The disadvantage is that such a system is quite costly.
The choice for the application of a hot-runner system yes or no is often based upon economic grounds with technical limitations.
Direction of movement Injection moulds
Injection moulds can also be classified by movement(-s). Since the injection moulding process takes place between two, in a straight line, moving plates, this is actually a 2-dimensional process. The shape can be designed perhaps three-dimensional, but if there are so-called “undercuts” in the product, it requires mechanical demoulding. To this end, it may be necessary to equip a mould with angled or straight mechanical sliders. These are divided into roughly the following three groups:
An injection mould in action.
These are moulds that can do their job in one line and do not require additional sliders.
These moulds are equipped with sliders which are being commanded by angled commander pins. The sliders begin to move as the mould opens or closes due to the angle of the commander pins. These are reliable systems and enable certain undercuts to be demoulded.
These are moulds aimed at demoulding products of such geometrical complexity that mechanical sliders are not sufficient. In those cases sliders can be operated by means of electronically controlled hydraulics and make slider movemenets independent from the mould movements.
Such moulds are designed to carry out extremely complex demoulding movements. It goes without saying that the costs of an injection mould increase with the complexity regarding sliders. All of this is predetermined primarily by the geometrical complexity of the product.
Free eGuide with Tips & Advice Cost Mould
To answer the most frequently asked questions, we have compiled a handy eGuide series with Tips & Advice. Part 1 provides insight into the costs, financing options, lifetime expectancy and tax aspects of a mould.
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