Plastic fabrication offers a world of possibilities for design and manufacturing, but successfully navigating this domain requires a deep understanding of material characteristics, tolerances, and finishing techniques. Whether you’re an experienced engineer or a newcomer to the field, this article aims to shed light on crucial design considerations to help you make informed decisions. If you’re in the market for high-quality plastic fabrication, we strongly recommend considering Johndec Engineering Plastics WA for your next project.
Material selection: more than just a first step
Before you even begin drafting a design, it’s crucial to select the right material. Plastic materials vary widely in their mechanical properties, thermal characteristics, and chemical resistance. Here are some factors to consider:
- Mechanical strength: What level of mechanical stress, including tension, compression, and torsion, is the part expected to endure during its operational lifespan?
- Thermal properties: Will the part be subjected to extreme temperature conditions, either high or low, during its usage? How well does it need to conduct or insulate heat?
- Chemical resistance: Is the part likely to be exposed to chemicals, solvents, or other corrosive or reactive substances? What is its required level of resistance to these elements?
Material families
When it comes to selecting materials for a project, understanding the distinct families of materials and their characteristics is vital for making an informed decision. Below, we delve into some common categories of materials frequently used in engineering and manufacturing:
Thermoplastics
Thermoplastics comprise materials like polyethylene, polypropylene, and polystyrene. One of the primary advantages of thermoplastics is their ease of moldability; they can be readily shaped and reshaped using heat, making them versatile for various applications. Additionally, they tend to be relatively inexpensive, providing a cost-effective solution for low-stress applications. However, it’s important to note that thermoplastics may not possess the best mechanical strength. This limits their use in applications requiring high resistance to mechanical stress or thermal conditions.
Engineering plastics
In contrast to thermoplastics, engineering plastics include materials such as polycarbonate, PEEK (polyether ether ketone), and nylon. These materials are designed for applications requiring higher mechanical strength and thermal resistance. They can withstand more demanding conditions and are often used in engineering applications like automotive parts, medical devices, and industrial machinery. The trade-off is that these materials are generally harder to mould and are more expensive. Due to the increased cost and the specialised equipment often required for moulding, they are generally reserved for applications where their enhanced properties are necessary.
Tip: Prototype with different materials:
Creating prototypes with a few different material types can offer invaluable insights into how the material’s characteristics affect the design and fabrication process. This can save both time and money in the long run.
Tolerances: the fine line of precision and cost
Tolerance is the permissible limit or limits of variation in a physical dimension. In the context of plastic fabrication, tolerances can make or break your design, both literally and financially. Here are some tips for specifying tolerances:
Use standard tolerance ranges
In the realm of manufacturing, tolerances define the acceptable limits within which a physical dimension may vary. Whenever possible, sticking to standard tolerance ranges can greatly simplify the manufacturing process. Using standard tolerances usually means that specialised tooling or processes aren’t required, which can significantly cut down on both time and costs. This approach also increases the likelihood of achieving consistent quality across multiple production batches.
Prioritise
When it comes to designing parts, it’s crucial to remember that not all dimensions and features have the same level of importance. Some are critical for the part’s function, fit, or assembly, while others may have less stringent requirements. Being selective in specifying tight tolerances only where they are essential can save money and make the manufacturing process more straightforward. This prioritisation minimises the need for complex machining or quality control procedures and makes it more feasible to meet project deadlines and budgets.
Simulate first
Before committing to any physical manufacturing, it’s highly advisable to conduct simulations using advanced CAD (computer-aided design) software. Many modern CAD tools offer features that simulate how plastic will flow during the moulding process, accounting for factors like temperature, pressure, and material properties. This simulation helps identify any potential issues or bottlenecks in the design, such as air pockets or uneven material distribution. By adjusting the design’s tolerances in the simulation stage, you can preemptively solve problems, thereby reducing the risk of expensive redesigns or retooling once production has started.
Draft angles: easing the moulding process
The concept of a ‘draft angle’ is a critical consideration when it comes to moulding or casting parts. In essence, a draft angle is the amount of taper given to the walls of the part so that it can be easily removed from a mould without damaging either the part or the mould.
Choosing the right draft angle is not a one-size-fits-all endeavour; rather, it depends on various factors such as the material used, the geometry of the part, and even the manufacturing process itself. Below are some key considerations for choosing an appropriate draft angle:
Material dependent
The type of material you’re working with can greatly impact the required draft angle. Softer materials, like certain types of rubber or low-density plastics, may only require a small draft angle. This is because softer materials are more flexible and can accommodate a more straightforward release from the mould.
On the other hand, rigid or brittle materials like some grades of engineering plastics may necessitate a larger draft angle. In these cases, a steeper angle ensures that the part can be removed without applying excessive force, which might otherwise lead to breakage or deformation. Knowing the material properties will guide you in selecting a suitable draft angle.
Part geometry
The complexity of the part’s geometry also plays a vital role in determining the appropriate draft angles. Simple geometries with straightforward, vertical walls may require less consideration, but as complexity increases—with features like undercuts, ribs, or bosses—the need for varied draft angles becomes crucial.
It’s advisable to consult with an experienced fabrication team such as Johndec Engineering to understand the intricacies of the part’s geometry. We can provide insights into what angles will work best for each feature, helping to avoid issues like tearing or sticking during the demolding process.
Part complexity
In the context of plastic fabrication, ‘part complexity’ refers to the intricacy of the part’s design, including its geometric features, dimensional tolerances, material properties, and the interactions between these factors. Complex parts may have a variety of intricate features that add to the difficulty of fabrication and may require specialised manufacturing techniques or equipment. Here are some elements that could contribute to part complexity:
Geometric features:
- Undercuts: Features that prevent straightforward ejection from a mould.
- Holes and slots: Especially if they are non-uniform or placed at complex angles.
- Ribs and bosses: These can make the moulding process more challenging by creating areas where material has to flow in complex patterns.
- Threads: Integrated threads for screws or other fasteners can add complexity.
- Varied wall thickness: Can lead to issues like sink marks or warping if not designed carefully.
Material properties
- Type of plastic: Engineering plastics like PEEK are harder to mould than standard thermoplastics like polyethylene.
- Fillers/additives: Some materials have fillers or additives like glass fibres or flame retardants that make the material harder to work with.
Dimensional tolerances
- High-precision requirements: Tight tolerances can make manufacturing more challenging.
Assembly complexity
- Number of components: A high number of components can mean more complex assembly processes, such as insert moulding or over-moulding.
- Interactions with other materials: If the part needs to be bonded, welded, or otherwise joined with other materials, this adds another layer of complexity.
Manufacturing process
- Multi-stage processes: Some parts may require multiple fabrication steps, like injection moulding followed by CNC machining.
- Special finishes: Textures, coatings, or other surface finishes can add complexity.
Surface finishes and textures: the final touch
The finishing touches on a plastic part can make a big difference in both looks and functionality. There are mainly two approaches for achieving this—in-mould and post-processing—and each comes with its own set of considerations.
Types of finishes
- In-mould: A cost-effective but less flexible option where textures are part of the initial mould design.
- Post-processing: Offers more flexibility but adds extra cost and time due to additional steps like sanding or painting.
Practical considerations
- Ease of cleaning: Textured finishes can make cleaning more challenging, an important factor for items requiring frequent sanitisation.
- Wear and tear: Think about how the finish will hold up over time, especially for frequently handled parts.
Conclusion: turn your design vision into reality with Johndec Engineering Plastics WA
Nailing the details in plastic fabrication is an art and a science. From choosing the right material and optimising tolerances to picking the appropriate draft angles and surface finishes, every decision counts. By paying attention to these critical areas, you’re not only ensuring the functional efficiency of the part but also potentially saving time and resources in the production process.
When quality, reliability, and expertise matter, make Johndec Engineering Plastics WA your go-to choice for all your plastic fabrication needs. We offer a range of services and materials to fit your specific requirements, ensuring you get the best out of your design. So why wait? Turn your design considerations into a tangible, high-quality product with Johndec Engineering Plastics WA today.