Design Mistakes to Avoid in Plastic Injection Moulding Projects

When it comes to plastic injection moulding, even small design oversights can lead to costly production delays, part failures, or quality issues. For many businesses, the process seems straightforward-create a design, build the mould, and start moulding. But the truth is far more complex. Effective plastic manufacturing in the UK requires thoughtful planning, precise engineering, and a deep understanding of how materials behave inside the mould. That’s why avoiding common design mistakes is essential for ensuring efficient production, optimal performance, and long-term reliability. Below are the most frequent design missteps-and how you can prevent them to achieve consistent success in your injection moulding projects.

Ignoring Material Behaviour in Design

One of the biggest mistakes designers make is selecting a plastic material too late in the process. Each polymer behaves differently in terms of flow, shrinkage, chemical resistance, and temperature tolerance. If you choose a material after the design stage, you risk creating a part that cannot be moulded effectively or fails prematurely during use. To avoid this, always select the material early and design around its properties. Consider melt flow, expected loads, UV exposure, operating temperatures, and regulatory requirements. Early material alignment eliminates the need for extensive redesigns later.



Overly Thick or Inconsistent Wall Sections

Uniform wall thickness is a fundamental principle of successful plastic injection moulding. Thick walls cool slowly, creating sink marks, warping, internal stresses, and potential structural weaknesses. On the other hand, thin areas may not fill properly, resulting in incomplete moulding or weak points. Aim for even walls throughout the part, or if variation is unavoidable, transition gradually between thick and thin areas. This promotes smooth material flow, reduces defects, and shortens cycle times, improving both quality and efficiency.


Poorly Designed Draft Angles

Insufficient draft angles are a common but avoidable problem. Without proper draft, parts can stick inside the mould, leading to damage during ejection, extended cycle times, or premature tool wear. For most plastics, a minimum of 1–2 degrees of draft is recommended, though textured surfaces may require more. Adding draft early on ensures easy part release and decreases stress on both the mould and the part.


Relying on Sharp Corners Instead of Radii

Sharp corners might look clean on a CAD model, but they cause stress concentrations in moulded parts and lead to weak points or cracking over time. Sharp internal corners also hinder resin flow, trapping air and causing voids. Incorporate radii wherever possible. Smooth transitions encourage better flow, reduce stress, and extend the life of the mould tool. Even a small radius can make a major difference in both structural integrity and manufacturability.


Incorrect Rib and Boss Design

Ribs and bosses are essential for adding strength without adding excessive wall thickness. However, incorrect rib proportions-especially ribs that are too thick-often result in sink marks or flow disturbances.

A good rule of thumb is designing ribs at 50–60% of the adjoining wall thickness. Bosses should be supported with ribs and designed with appropriate draft angles. When properly engineered, these features increase stiffness, reduce weight, and enhance part longevity.


Overlooking Gate Placement

Gate location significantly impacts fill pattern, surface finish, part strength, and potential warping. Poor gate placement can lead to weld lines, excessive stress, or cosmetic imperfections. Gate selection should be based on part geometry, material viscosity, and expected load-bearing areas. Ideally, gates should allow uniform filling of the cavity while minimising flow disruptions. Early collaboration with tooling and moulding experts is essential to get gate positioning right.



Failing to Consider Tolerances Realistically

Plastic components typically cannot achieve the same tight tolerances as machined metal parts. Designing tolerances that are too strict can make moulding expensive or impossible. Understand the achievable tolerances of your chosen material and process. If certain areas demand precision, consider adding features such as inserts, secondary machining, or strategic reinforcements.


Neglecting Early Collaboration With Manufacturing Experts

One of the most avoidable mistakes is waiting too long to involve your moulding partner. Complex features, undercuts, or assembly requirements may seem feasible in CAD, but prove challenging or uneconomical during moulding. By collaborating early with a specialist such as Rutland Plastics, you gain access to design-for-manufacture insight that prevents costly redesigns. Manufacturing experts can guide material selection, mould tool engineering, flow analysis, assembly planning, and cost optimisation.


Final Thoughts

Successful plastic injection moulding isn’t just about producing a part-it’s about producing the right part in the most efficient, durable, and cost-effective way. Avoiding these common design mistakes will help ensure that your project runs smoothly from concept to production. Whether you’re designing a simple component or a complex functional assembly, careful planning and early expert involvement will always deliver better results in plastic manufacturing in the UK.


Read More: How to Design Plastic Parts for Easier Moulding and Lower Costs

Comments

Post a Comment

Popular posts from this blog

How Plastic Injection Moulding Works: From Concept to Product

Image
This technology can be adopted in almost all countries around the world without compromising the local environment or even the world's environment. Its application encompasses industries or sectors having truly diverse applications from light industries to heavy manufacturing. Plastic injection moulding is, therefore, the backbone of most industries that seek an efficient, scalable, cost-effective method for producing plastic parts—for example, from bottle caps and phone cases to automotive components and medical devices. In the UK, where precision, quality, and sustainability are priorities, such molding of plastic assumes a critical importance in modern plastic manufacture. But how does plastic injection moulding work exactly? Let's take a journey from the initial idea into this concept until finished product stage. Concept and Design Everything begins with an idea. It could be a new part or simply a change for an existing item. The first step is to convert that idea int...
Read more

Designing for Durability: Key Considerations for Injection Molded Parts

Image
In today's evolving manufacturing landscape, durability is no longer a bonus — it is an expectation. Consumers and industries alike want products that will last, reliably perform, and withstand stress, impact, and environmental exposure. In the realm of plastic components, durability for injection molded parts starts at the design stage.    Whenever you are producing anything from automotive parts , and medical devices , to consumer electronics, ensuring wise design choices will ensure the longest life span and durability of molded plastic parts. Below is an overview of the most important design considerations that help ensure durability in injection molded components. Material Selection is Critical The base of every durable injection molded part is the material and grade selected to use. Each polymer has differing strengths, weaknesses, and performance properties depending on the environment in which it will be used. For instance: Nylon has incredibly high mechanic...
Read more

Design for Manufacturing in the Automotive Industry

Image
In today's dynamic , competitive automotive market, the drive for cost reduction, improved quality, and shorter production cycles is enormous . One of the best solutions to achieve these is by using Design for Manufacturing . This remarkable product development strategy deals with the optimization of the design of parts and assemblies to make the manufacturing process simpler and more efficient—yielding fewer defects, reduced costs of production, and quicker time to market. Design for Manufacturing is not a new ideology, but its significance has increased only in the time when precision, consistency, and efficiency are more sought after. In the case of injection molded parts, DFM holds a crucial position where both product functionality and manufacturability are perfectly harmonized. What is Design for Manufacturing? Design for Manufacturing is the design of a product keeping in mind the manufacturing process right from the initial stages of development. Rather than desi...
Read more