Plastic Injection moulding is one of the most omnipresent and accessible processes that can be used in the manufacturing of your plastic products. Injection moulding is very versatile and that makes it such a good choice for so many products. It does not, however, mean that some design aspects and considerations can be ignored.
Fully understanding the injection moulding process and the qualities of product design most suited improves the efficiency of production runs and the quality of the products.
Don’t forget the essentials of the process: Two halves of a mould are hollowed with a negative image of your part. Hot, liquefied plastic is injected into the mould and allowed to cool. The two halves of the mould are separated, and the part is released.
It is essential that there is a location in the mould and on the part for the base material to be injected into. This is known as the gate and It will need to be removed from the finished part. The position of the gate is very important in injection moulding design. It will normally be located at a thicker, intersectional area of the part where it can be removed without concern for its structural integrity. Gate removal will likely also leave a mark, something to consider at the outset.
During the cooling process the liquefied plastic will shrink as it cools and hardens. When the two halves of the mould are separated, there will be a “parting line,” inevitable as the mould consists of two halves.
Different wall thicknesses can make for a more difficult process. Some moulders will say that they can only produce injection moulded parts with a consistent wall thickness. While this can make it easier to manufacture, it is not essential to the process. As one might expect thicker wall areas will cool and solidify slower than thinner areas. If you combine the shrinkage and cooling factors, in the case of improperly designed moulds, it can lead to uncooled, still-liquefied plastic running to areas of the part where it should not be.
Your part needs to be designed with manufacturability in mind, our design team can help with that. Thicker areas can be located at lower parts of the mould, enabling gravity to keep still cooling material where it should be.
Draft in your injection moulded product design serves the purpose of making it easier and smoother to separate the mould from the manufactured part. This is achieved by adding a few degrees of taper to the design. This should ensure that the surface of your part remains undamaged when separated from the mould and the whole process progresses more efficiently.
By etching or milling the mould to create a finish you can build in texture, rather than adding a second finishing process. This gives a much greater degree of control and uniformity over the look and feel and saves money and time by incorporating both processes into one. We can provide secondary process services such as creating threads or ultrasonic moulding should they be required.
Material selection is one of the most critical decisions in the design of your part. It can affect many aspects of the process including shrinkage factor, cooling time and flexibility. Materials have different minimum and maximum wall thicknesses and can require different degrees of draft.
We are experts in a range of materials and their properties at Paul Norman Plastics, including ABS, acrylic, HDPE, LDPE, polypropylene and more. We can assist and advise on your selection of the right material for your part and ensure we incorporate those material properties into your design. If you would like to know more or discuss this further, then please do not hesitate to call 01453 833338 to talk to one of our experts.