Design considerations for successful injection plastic mouldings

Designing a plastic part for injection moulding involves more than just creating a 3D model of the desired shape. To ensure a successful injection plastic moulding process, designers need to consider various factors that impact the quality, cost, and manufacturability of the final product.

In this article, we’ll explore key design considerations for injection plastic moulding.

  1. Wall Thickness: One of the critical design considerations is maintaining uniform wall thickness throughout the part. Uneven wall thickness can result in defects such as warping, sink marks, and excessive cooling times. Designers should aim for consistent wall thickness to ensure an even distribution of material and minimise defects.
  2. Draft Angles: Draft angles are essential for easy part ejection from the mould. Without proper draft angles, the part may get stuck in the mould, leading to production delays and potential damage to the mould. Typically, a draft angle of 1-2 degrees per side is recommended.
  3. Ribs and Bosses: Reinforcing ribs and bosses can add strength and stability to a plastic part. However, it’s crucial to design them carefully to avoid excessive thickness variations and sink marks. Proper placement and design of ribs and bosses are essential for maintaining part integrity.
  4. Undercuts: Parts with undercuts, such as threads or snaps, can be challenging to mould. Designers should consider mechanisms like slides or collapsible cores to create these features without causing moldability issues.
  5. Gate Placement: The gate is the point at which molten plastic enters the mould cavity. The gate location can affect the part’s appearance, strength, and warping. Strategic gate placement can help minimise visible gate marks and optimize part performance.
  6. Material Selection: The choice of plastic material has a significant impact on part design. Different materials have varying shrinkage rates and mechanical properties, so designers must select a material that suits the intended application.
  7. Tolerance and Inspection: Clearly define critical dimensions and tolerances on the design drawings. This ensures that the final part meets the required specifications. Additionally, plan for post-moulding inspection and quality control measures.
  8. Mould Design Collaboration: Collaboration between the product designer and the mould designer is crucial. Mould designers need to consider factors like mould steel selection, cooling system design, and part ejection mechanisms to optimize the moulding process.
  9. Prototype Testing: Before finalising the design, it’s beneficial to create prototypes for testing. Prototyping can help identify potential issues and refine the design for better mouldability and performance.
  10. Sustainability: Consider sustainable design practices, such as minimising material usage and designing for recyclability, to reduce the environmental impact of the injection plastic moulding process.
  11. Successful injection plastic moulding begins with thoughtful part design. 


By considering these key factors during the design phase, designers can optimise the manufacturing process, reduce production costs, and ensure the quality of the final product. 

Collaboration between design and manufacturing teams is essential to achieve the best results.

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