Design for manufacture in injection moulding

The concept of Design for Manufacture (DFM) is the process of designing parts, components or products in such a way that they are easier to manufacture. The DFM concept exists in almost all engineering disciplines, althoughimplementation differs widely depending on the manufacturing technology. The goal of DFM is to produce an effective, efficient product at lower cost by simplifying, optimising and refining the product design.

Ideally, DFM needs to occur early in the design process, well before any tooling has started. In addition, DFM should include all the stakeholders: engineers, designers, contract manufacturer, mould builder and material supplier. This cross-collaboration is aimed at challenging the product design at all levels: component, sub-system, system and holistic levels, to ensure the design is optimised and does not have unnecessary hidden costs associated.

Five key principles of DFM

Process – the manufacturing process chosen must be the correct one for the part or product. In determining the manufacturing process, DFM takes into consideration the quantity of parts being manufactured, the material being used, the complexity of the surfaces, the tolerances required and whether there are any secondary processes required. In injection moulding, a complex design typically requires a complex mould tool, and a complex mould tool is more expensive to design and manufacture.

Design – design is an essential element of DFM. The actual drawing of the part or product has to conform to good manufacturing principles for the chosen manufacturing process. With plastic injection moulding the following design principles apply:

• constant wall thickness, to allow for consistent and quick cooling
• simple transitions from thick to thin features
• wall thickness not too small – this increases injection pressure
• no undercuts or features that require side action
• specify tolerances that enable a good product to be manufactured
• ideally as few sharp corners or edges as possible, as these provide stress points (weaknesses) on the product.

Material – material properties to consider during DFM include:

• mechanical properties – how strong does the material need to be
• thermal properties – is resistance to heat required
• colour – is a specific colour is required
• optical properties – does the material to be reflective or transparent
• electrical properties – is the material an insulator or a conductor
• flammability – what level of flame resistance is required

Waste is also an important consideration, especially in environmentally conscious times. Ideally product sections and walls should be as thin as possible without effecting product performance and strength. This also reduce costs in two ways, firstly by reducing material content, and secondly by allowing the product to cool quicker in the mould, reducing moulding cycle times.

Environment – what is the normal application environment of the product? The product design will be influenced by the environment and external properties that the product is subjected to. The product must be able to function reliably and consistently under its normal operating conditions: temperature, humidity, vibration and shock characteristics should be considered.

Compliance – All products will need to comply with safety and quality standards. These may include international standards such as TÜV, BSI, IEC and ISO, industry specific compliance standards, and other third-party standards. Internal, company-specific standards may also apply.

Expert knowledge

Skar has considerable knowledge and experience designing and manufacturing complex plastic moulded products and components that are used across a broad range of high-reliability and safety critical industries. Design for manufacture is actively employed and applied during Skar’s design and manufacturing processes.