DESIGN | CASE STUDY
Design challenges for large moulded products
Right: BPO introduced innovative design features in the bin lid
How should a design company approach a new product to ensure the needs of injection moulding and mould design are factored into the project? In this article, leading design group BPO shares its expertise in designing for manufacturing in the context of injection moulding, which is illustrated in a case study on wheely bins made by Craemer
Plastic products vary in weight and size from less than a gram to heavier than 40 kg and more than two metres in diameter. For large plastic products, even more than for products of normal size, the designer must take into account the possibilities and limitations of injection moulding and mould construction. Before a plastic product can be produced, a mould must be built. This mould is constructed based on a 3D model of the product. The design of such a new product follows a structured, systemic method. The program of requirements and wishes is an important tool for recording the functional requirements for a product, but also, for example, what the intended cost price, investments and available production options are.
Below: BPO has long experience of designing large products, such as the Craemer MGBneo4 wheelie bins
Cost and technology Especially with large products, it is essential to take these preconditions into account from the start of the design process, even with the first ideas. A good designer continuously considers the consequences for injection moulding and mould construction when making design choices. Ultimately, the design is an optimal compromise between function, cost, and injection moulding technology. Important parameters that determine the cost price of a product are, in addition to the design
itself, the material and the cycle time. In addition, the required machine size is an important factor that, in combination with the cycle time, deter- mines part of the cost price. A specific injection moulding machine has a maximum closing force, bar distance and opening path. These place restrictions on the construction of the new product and thus the mould used to produce it. Within these limitations, a designer makes
choices regarding, for example, the dimensions, the direction of draft, the wall thickness distribu- tion, the maximum projected surface and whether or not to use (long) cores, for example for under- cuts and for the formation of rigid structures, such as corner columns in pallet boxes. With a large injection moulded product, several injection points are usually required to fill the product. The exact number and locations must be considered in the design process in order to arrive at an optimal design that balances performance and costs.
Moulding simulation Injection moulding simulations are a powerful tool for comparing different options and making an optimal choice. These computer analyses can also be used to identify and prevent possible risks associated with the production of large products, such as warpage and the deformation of the mould itself (core bending). In addition, the weight of moulds for large plastic products is often more than 50 tonnes. This makes a trial-
24 INJECTION WORLD | March 2023
www.injectionworld.com
IMAGE: CRAEMER
IMAGE: BPO
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