Design with plastic

Plastics offer a number of advantages when they are used.

Plastic is the material group with the most members. This means that the material can be selected much more precisely in order to find the material that is optimally suited to the requirements.

Material properties

Today, material properties can be largely customised to requirements by adding additives. When designing plastic components, however, properties must be taken into account that do not apply to metals in this form.

With plastics, many more functions can be integrated into a component, as there are more options for integrating functional elements. The properties of the material also allow for flexible elements.

Another possibility is to be able to combine hard and soft materials, for example to realise sealing lips on a housing.

But there are also some disadvantages:

While material properties such as modulus of elasticity can be assumed to be constant for metals, they are highly dependent on temperature for plastics and are also influenced by the load speed.

Another - negative - point is the large tolerances that occur in plastic constructions when they are produced by injection moulding or as extrusion profiles. However, other properties can also cause problems. Here, solutions can and must be found in the design to avoid problems.

There is a lot to consider when selecting the plastic. In addition to the mechanical properties, the behaviour of the material within the temperature range for which the components are intended must be taken into account. The type and duration of the load must also be taken into account. The surface of the product also plays a role. Not every plastic can be electroplated and some plastics are more difficult to bond than others or cannot be bonded at all.

Manufacturing process

In addition to the familiar manufacturing processes such as sawing, drilling and milling, plastics are primarily extruded, injection moulded or blow moulded.

In extrusion - roughly speaking - soft plastic is heated up and pressed through a mould. When it becomes cold, the mould is retained. Not only profiles with a constant cross-section are possible, but now also profiles where the cross-section changes.

We usually encounter blow-moulded components in the form of plastic bottles. In this process - or to be more precise, there are several variants - a soft plastic raw part is inflated. In addition to the bottles I have already mentioned, many hollow parts are produced in this way. In addition to toys, air ducts should also be mentioned.

Injection moulding offers us the most possibilities in terms of design. In this process, liquid plastic is injected into a mould where it cools down sufficiently for the component to be removed.

Many injection moulded parts are visible. Surface defects such as sink marks, areas with white spots or visible weld lines are undesirable (visual appearance). These defects can often be avoided by design measures such as wall thickness ratios or flow-optimised design of the component geometry. The designer is required to ensure that his design does not exhibit these faults.

When designing the component, it must be taken into account that the concept for the injection moulding tool is at least partially reflected in the component. For the designer, this means that he must not only be familiar with the design of plastic components, but must also familiarise himself with the mould technology.

Many injection moulded parts are in the visible area. Surface defects such as sink marks, areas with white spots or visible weld lines are not desirable there (optics). These defects can often be avoided by design measures such as wall thickness ratios or flow-optimised design of the component geometry. With the help of a filling study, problems with the filling of the mould can be better identified and remedied from the outset. It therefore makes sense to carry out such studies at the design stage - not just when designing the moulds.