Plastic products are ubiquitous in our daily lives. From our mobile phones and computers, to our tableware and toys, to automotive interiors and components for industrial equipment, plastic, thanks to its lightweight, low-cost, highly malleable properties, has become an indispensable material in modern manufacturing. However, a superior plastic product relies not only on high-quality plastic materials but also on carefully designed structural components. Design of plastic product structural components is like skeleton of a product, supporting its overall structure and determining its performance, reliability, durability, manufacturing ease. Today, we will delve into key points and reference methods for plastic product structural component design.

 

Plastic product structural component design is a critical step in transforming a product from concept to reality, profoundly impacting its performance, quality, cost, and user experience.
From a product performance perspective, a sound structural design ensures sufficient strength and stability. Take plastic components in automotive interiors, for example. They must not only withstand vibration and impact of driving but also maintain stable performance under varying temperatures and humidity conditions. If structural design is inadequate, these components may deform or break over time, affecting aesthetics and safety of interior. Another example is casing of an electronic product, a crucial structural component that protects delicate electronic components from external impact, dust, and moisture. A well-designed mobile phone casing provides reliable protection without adding excessive weight or bulk, while also ensuring good heat dissipation, ensuring stable operation during extended use.
From a user experience perspective, structural component design directly impacts a product's appearance, feel, and ease of use. Take mouse we use every day, for example. Shape of its plastic casing, button layout, and tactile feel are all achieved through meticulous structural design. Ergonomic design ensures hand comfort and reduces fatigue during extended use, while precise button structure enhances user experience by making operations more responsive and smooth. For example, structural design of household items, such as plastic chairs, requires consideration not only of load-bearing capacity but also of whether chair's shape aligns with human sitting habits and whether surface texture is comfortable. An inappropriate structural design can lead to discomfort and even adverse health effects.
Structural design also plays a key role in cost control. A sound structural design can simplify production process, reduce scrap, and thus lower production costs. For example, optimizing structural design, reducing mold complexity can reduce mold manufacturing and maintenance costs. Furthermore, properly selecting materials and determining wall thicknesses to avoid overdesign can reduce material costs while ensuring product performance.

Plastic materials come in a wide variety, each with unique properties that determine their suitability for different products.
ABS (Acrylonitrile-Butadiene-Styrene): It offers excellent overall performance, including high strength and rigidity, good dimensional stability, and a high surface gloss. It is also easy to process and shape, can be processed through various processes, including injection molding, extrusion, and thermoforming. It also easily undergoes surface treatments, such as painting and electroplating, to meet diverse aesthetic requirements. Therefore, it is widely used in housings for electronic products such as televisions, computer monitors, and printers, as well as automotive interior components such as instrument panels and armrests. However, ABS's weather resistance is relatively poor, it is susceptible to aging and discoloration with long-term exposure to sunlight, limiting its use in some outdoor applications.
PP (Polypropylene): It is a lightweight, non-toxic, odorless thermoplastic with excellent chemical stability and good resistance to many acids, bases, and organic solvents. Its relatively low price makes it cost-effective for mass-produced daily necessities. It also has good heat resistance and can withstand long-term use at temperatures around 100℃. Common applications include household items such as plastic tableware, buckets, and basins, as well as automotive components such as bumpers and ventilation ducts. However, PP is highly brittle at low temperatures and prone to cracking in low-temperature environments, so its low-temperature performance needs to be considered when used in cold regions.
PC (polycarbonate): Its outstanding features are its excellent transparency, approaching that of glass, and its excellent mechanical properties, particularly its high impact strength, making it resistant to cracking when impacted. It also exhibits excellent heat resistance, allowing for long-term use within a temperature range of 120℃ to 130℃. It is commonly used in manufacture of optical lenses, such as eyeglass lenses and camera lenses, as well as transparent housings for electronic devices, such as mobile phone screen protectors and tablet cases. However, PC has poor hydrolysis resistance, and long-term use in humid environments may lead to performance degradation.
When selecting a plastic material, it is important to comprehensively consider multiple factors, including product's operating environment, performance requirements, and cost budget, to ensure that selected material meets all product requirements.

Wall thickness is a key parameter in design of plastic product components, significantly impacting product strength, molding quality, and cost. From a strength perspective, excessively thin walls can lead to deformation and cracking during use due to inability to withstand external forces. For example, small plastic toys with excessively thin walls can easily break due to collisions and crushing during children's play. Conversely, while excessive wall thickness can enhance product strength, it can also lead to a series of other problems. Firstly, it increases material usage, thereby increasing product costs; secondly, it prolongs product cooling time, reduces production efficiency, can also cause internal defects such as shrinkage holes and bubbles.
Recommended wall thickness range varies for different product types. Generally speaking, small products such as mobile phone cases and internal components of small electronic devices can maintain a wall thickness between 0.8 and 1.5 mm; whereas, larger products such as plastic storage boxes and industrial equipment casings typically have a wall thickness between 1.5 and 3 mm. Of course, this is only a rough guideline; actual design adjustments should be made based on product's specific function, load conditions, and material properties.
Maintaining consistent wall thickness is a key principle in wall thickness design. Uneven wall thickness can cause internal stress during injection molding process due to inconsistent cooling rates in different areas, leading to product warping and deformation. For example, if walls of a plastic box are thicker in some areas and thinner in others, box may warp after cooling, or lid may not close properly. To avoid uneven wall thickness, a gradual transition can be used, or reinforcing ribs can be added to areas with significant thickness variations to enhance structural strength.

 

Reinforcement ribs play a key role in plastic product structures, enhancing product strength and rigidity and preventing deformation. They are like steel beams in a building: while they occupy a small space, they significantly enhance stability of the overall structure.
In terms of shape design, reinforcement ribs are typically triangular or trapezoidal. Triangular ribs are simple and effectively distribute stress, while trapezoidal ribs provide greater support while reducing material usage. Height and thickness of ribs also require specific design considerations. Generally speaking, height should not be too high, otherwise problems such as underfill and air entrapment can easily occur during injection molding. Height is generally 1-3 times wall thickness. Thickness should also be moderate, otherwise it will cause dents on product surface corresponding to ribs, affecting appearance quality. Thickness is typically 0.5-0.7 times wall thickness.
Layout of ribs is equally important, should be arranged appropriately based on direction of force and shape of product. For example, for a plastic sheet subject to bending forces, ribs should be arranged along bending direction to enhance its bending resistance. For a round plastic container, ribs can be distributed radially or in a circular pattern to increase container's compressive strength. Furthermore, spacing between ribs must be properly controlled. Too small a spacing increases material cost and molding difficulty, while too large a spacing prevents ribs from fully functioning. Generally, a spacing of 2-3 times wall thickness is appropriate.

Draft refers to angle of inclination set on sidewalls of a product during mold design to facilitate smooth ejection from mold. This seemingly small angle has a significant impact on product production and quality.
After a product is formed in a mold, it needs to be ejected from mold. Without a draft angle or with an insufficient draft angle, friction between product and mold will be high, potentially causing damage to product, scratches, or even damage to mold during ejection process. An appropriate draft angle can effectively reduce friction, allowing product to be ejected smoothly from mold, ensuring surface quality and integrity.
Different materials and surface treatments require different draft angles. Generally, recommended draft angle for ordinary plastic materials is 1-3°. For textured surfaces, increased surface roughness increases friction, so draft angle should be increased, typically 3-5°. Furthermore, shape and size of product also influence choice of draft angle. For example, products with greater depth and complex shapes require a larger draft angle to ensure smooth ejection.
Size of draft angle also affects mold manufacturing and product dimensional accuracy. The larger draft angle, the easier it is to manufacture mold, but product's dimensional accuracy will be affected to a certain extent. This is especially true for products requiring high dimensional accuracy, where a trade-off between draft angle and dimensional accuracy is necessary.

In design of plastic product components, corner fillet design is an often overlooked yet crucial aspect. While seemingly simple, this can improve product performance and quality in many ways.
From a mechanical perspective, plastic parts with sharp corners experience localized stress concentrations at these corners during molding. When subjected to external forces or shock or vibration, these stress-concentrated areas are prone to cracking or breaking, reducing product's strength and service life. Using a rounded corner transition effectively disperses stress, increasing product strength and reliability. For example, sharp corners on some plastic casings are prone to cracking when impacted, but a rounded corner design can significantly reduce this risk.
In terms of appearance quality, rounded corners can create smoother, more natural lines, enhancing product's aesthetic appeal. Whether it's household items, electronics, or toys, rounded corners often create a refined and comfortable feel, enhancing product's overall quality and attracting consumers' attention.
When determining corner radius, a range of 0.5-2mm is generally recommended. Specific value depends on factors such as product size, wall thickness, and desired appearance. For small products, corner radius can be relatively small; for large products, radius can be increased to ensure sufficient strength and aesthetics.
Corner design also has a positive impact on mold processing and injection molding. During mold processing, rounded corners can prevent stress concentration in mold cavity, reduce risk of cracking caused by stress concentration during heat treatment, and extend mold's service life. During injection molding, rounded corners can improve flow characteristics of plastic melt, making it easier for plastic to fill mold cavity and reducing injection defects such as bubbles and short shots.

 

Shrinkage is a common defect in plastic product components, manifesting as localized depressions on the surface or internal voids. Main causes of this problem are as follows:
Uneven wall thickness: When product wall thickness varies significantly, thicker parts cool more slowly and shrink more, while thinner parts cool faster and shrink less. This leads to differential shrinkage in wall thickness transition area, causing shrinkage. For example, if wall thickness of a plastic box with ribs is too thick at ribs while the rest of box is thinner, ribs are more likely to shrink during cooling process.
Insufficient injection pressure: During injection molding process, insufficient injection pressure prevents sufficient plastic melt from filling all areas of mold cavity, especially in areas with thicker walls. This can easily lead to shrinkage due to insufficient material filling.
Insufficient holding time: Holding stage is designed to compensate for volumetric shrinkage of plastic melt during cooling. If holding time is too short, plastic melt cannot be fully replenished, resulting in shrinkage depression in product.

 

Following solutions can be used to address shrinkage:
Optimize wall thickness design: Ensure consistent wall thickness as much as possible to avoid sudden changes in wall thickness. If functional requirements necessitate a difference in wall thickness, a gradual wall thickness transition should be adopted, or wall thickness should be appropriately reduced in thick-walled areas, such as by removing glue, to reduce material accumulation and minimize shrinkage differences.
Adjust injection molding process parameters: Appropriately increase injection pressure to ensure plastic melt fully fills mold cavity; extend hold time to ensure continuous replenishment of plastic melt during cooling process, minimizing shrinkage; properly adjust injection speed to avoid uneven filling and air entrapment caused by excessively fast or slow speeds.
Add ribs: Strategically placing ribs in areas prone to shrinkage not only enhances product strength but also distributes shrinkage stress, reducing likelihood of shrinkage. However, pay attention to rib design parameters, such as height, thickness, and spacing, to avoid other problems caused by improper rib design.

Deformation is also a key concern in design and production of plastic product components, as it can seriously affect product's appearance and assembly accuracy. Main causes of deformation are:
Uneven cooling: After injection molding, during cooling process, if mold's cooling system is poorly designed, resulting in inconsistent cooling rates across product, differential shrinkage can occur, leading to deformation. For example, if mold's cooling channels are unevenly distributed, some areas cool faster than others, which can cause product to warp after cooling.
Excessive internal stress: During injection molding process, plastic melt rapidly fills mold cavity under high pressure, causing molecules to align. After cooling and solidifying, these aligned molecules attempt to return to their disordered state, generating internal stress. Furthermore, uneven wall thickness and uneven external forces during demolding can also contribute to internal stress. When internal stress exceeds product's tolerance, it can cause deformation.
To address deformation, following measures can be taken:
Improve mold cooling system: Optimize layout of mold's cooling channels to ensure uniform cooling across mold cavity. Cooling efficiency and uniformity can be improved by increasing number of cooling channels, adjusting their diameter and location, properly setting cooling medium flow rate and temperature.
Optimizing product structural design: When designing product structure, appropriately add reinforcing ribs and support structures to increase product rigidity, reduce possibility of deformation. At the same time, avoid overly complex designs or structures that are prone to stress concentration, such as sharp corners and sharp transitions between thin and thick walls.
Post-processing to eliminate internal stress: For molded products, annealing can be used to eliminate internal stress. Heating product to a certain temperature, holding it for a period of time, then slowly cooling it allows sufficient time for molecules to relax, thereby reducing internal stress and minimizing deformation.

Assembly issues are also common in production and use of plastic products, affecting their overall performance and user experience. Main causes of assembly issues include:
Insufficient dimensional accuracy: Insufficient mold manufacturing precision, or during injection molding process, fluctuations in process parameters and unstable material shrinkage can lead to deviations between actual product dimensions and designed dimensions, thus affecting assembly accuracy. For example, if two plastic parts that need to fit tightly together have large dimensional deviations, assembly may be too loose or too tight.
Improper fit tolerances: During design, improper fit tolerances, without fully considering impact of manufacturing errors and product's operating environment, can also lead to assembly problems. For example, too small a fit tolerance can make parts difficult to install; too large a fit tolerance can affect product's assembly accuracy and stability.
To address assembly issues, following suggestions can be taken:
Improve mold accuracy: Utilize advanced mold manufacturing processes and equipment to ensure mold processing accuracy meets product design requirements. Furthermore, during mold manufacturing, strictly control processing errors, regularly inspect and maintain mold to ensure mold accuracy and stability.
Rationally design fit tolerances: Determine appropriate fit tolerances based on product's functional requirements, material properties, and manufacturing process. During design, fully consider impact of various factors on dimensional accuracy, allow for a certain tolerance margin to ensure smooth assembly and meet performance requirements after assembly.
Incorporate positioning features: Incorporating positioning features, such as locating pins, locating holes, and locating slots, into product structural design can improve part positioning accuracy during assembly, ensuring accurate and consistent assembly. These positioning structures can be considered during mold design and manufacturing to ensure dimensional and positional accuracy.
For plastic parts with smooth surfaces, high dimensional accuracy requirements, and minimal shrinkage, a smaller draft angle, such as 0.5°, should be used.
For taller or larger parts, a smaller draft angle should be calculated based on actual conditions. For example, ribs on a double-cylinder washing machine tub should be calculated to be 0.15° to 0.2°.
For parts with significant shrinkage, a larger draft angle should be used.
Thicker plastic parts increase molding shrinkage, so a larger draft angle should be used.
For transparent parts, draft angle should be increased to avoid scratches. Generally, draft angle for PS materials should be no less than 2.5° to 3°, for ABS and PC materials, no less than 1.5° to 2°.
For sidewalls of plastic parts with surface treatments such as leather grain or sandblasting, a draft angle of 2° to 5° should be used, depending on the specific grain depth. The deeper grain, the larger draft angle should be. When structure is designed for interlocking, insertion surface slope is generally 1°-3°.

 

Most plastic products have ribs. Ribs can significantly increase the overall strength without increasing the overall thickness of product. They are particularly useful for large and stressed products and also prevent deformation.
Rib thickness is generally 0.5-0.7 times the overall plastic thickness. Ribs thicker than 0.7 times are susceptible to shrinkage. Ribs with a height of 0.5-1.5° should be used (due to increased resistance to demolding). Ribs with a shorter height may not require any slope.

Using a common tablet housing as an example, we will delve into intricacies of its structural design. In today's digital age, tablets have become an indispensable tool in people's lives and work, structural design of their housing directly impacts the overall performance and user experience of product.
Design goal for this tablet was to create a lightweight, portable, durable, and easy-to-manufacture product. To achieve this, a thin-wall design concept was adopted for structural components. Through in-depth research and simulation analysis of material properties, housing wall thickness was controlled to approximately 1.2mm, successfully reducing weight by approximately 20% compared to traditional designs, making product lighter and more portable.
To compensate for potential strength deficit associated with thin-wall design, reinforcing ribs were strategically arranged within housing. These ribs are arranged in a grid pattern, closely aligning with positions of key components such as motherboard and battery. In motherboard area, layout of reinforcing ribs effectively disperses external impact forces, protecting delicate electronic components on motherboard. In battery area, ribs not only enhance structural strength but also assist in heat dissipation, ensuring optimal heat dissipation during operation. This meticulously designed rib significantly enhances the overall strength and rigidity of housing without significantly increasing weight, making product more resilient to impacts and crushing during daily use.

 

In assembly design, a clever snap-on mechanism is employed. These snaps are located around perimeter of housing and at key joints. Precise dimensional design and mechanical calculations ensure that each snap provides sufficient locking force. Furthermore, to facilitate user disassembly and repair, snap-on design also takes into account ease of disassembly. By strategically designing snaps' opening angles and operating methods, users can easily open housing with simple tools. This snap-on design not only simplifies assembly process and improves production efficiency, but also reduces risk of assembly errors and loosening that can occur with screw connections.
This case study offers valuable design lessons: When designing electronic product housings, it's crucial to fully consider product's intended use case and user needs. Through innovative design concepts and a rational structural layout, a win-win situation for both product performance and user experience can be achieved. Clever use of design techniques such as thin-wall design, rib placement, snap-fit connections can effectively reduce costs and improve production efficiency while ensuring product quality.

Design of automotive interior parts must meet numerous stringent requirements. This article examines key points and challenges of structural design for a vehicle center console.
As a crucial component of vehicle interior, center console must not only possess an aesthetically pleasing appearance but also meet specific performance requirements, including high and low temperature resistance, wear resistance, and environmental friendliness. A high-performance modified PP material was selected. This material, through a special formulation and modification process, exhibits excellent high and low temperature resistance, maintaining stable physical properties within a temperature range of -40℃ to 80℃, effectively preventing deformation and cracking caused by temperature fluctuations. It also offers excellent wear resistance, withstanding friction and scratches of daily use, ensuring long-term aesthetics and service life of interior components. Furthermore, this material meets strict environmental standards and does not release harmful gases, safeguarding health of vehicle passengers.
In terms of structural design, an integrated injection molding process was employed to meet complex shape and functional requirements of center console. By optimizing mold design and injection molding process parameters, high-precision molding was achieved, ensuring dimensional accuracy and surface quality of interior components. To enhance strength and stability of interior components, reinforcing ribs and support structures were installed in key locations. Ribs of appropriate thickness were placed along edges of center console and in areas subject to high stress. Shape and orientation of these ribs were carefully designed based on stress analysis, effectively enhancing structure's resistance to deformation. Specialized support structures were designed at connections to other components to ensure a secure and stable connection, preventing loosening and unusual noises caused by vehicle vibration during driving.
Design process also presented challenges. Complex shapes of automotive interior components posed significant challenges in mold design and manufacturing. To address this issue, advanced computer-aided design (CAD) and computer-aided engineering (CAE) technologies were utilized. CAD software enabled 3D modeling and structural analysis, enabling pre-emptive design optimization and mitigation of design flaws. CAE software also enabled injection molding simulation analysis to predict potential molding issues, such as sink marks and bubbles, and to tailor mold structure and process parameters accordingly. Furthermore, surface treatment of interior components was a critical step. To meet aesthetic and tactile requirements, specialized surface texturing and painting techniques were employed. Carefully designed surface texture not only enhances interior components' texture and aesthetics but also provides a certain degree of anti-slip properties. Environmentally friendly, wear-resistant paint was selected for painting process, ensuring a glossy and durable finish.
This case study demonstrates that design of automotive interior components requires comprehensive consideration of multiple factors, from material selection and structural design to manufacturing processes and surface treatment. Each step is crucial. Only through continuous innovation and optimization can interior components that meet high standards of automotive industry be designed.

Plastic product structural component design is a comprehensive process, encompassing numerous key aspects, from material selection, wall thickness design, rib design, draft angle design, and corner fillet design. Each of these key aspects is interconnected and collectively impacts product performance, quality, manufacturing, and cost control. During design process, we must fully consider multiple factors, including product's operating environment, functional requirements, user experience, and production process. Applying scientific design methods and advanced technologies, we meticulously design every structural detail to ensure product meets market demand and user expectations.
With continuous advancement of technology and development of society, design of plastic product structural components will face new opportunities and challenges. In the future, design of plastic product structural components will develop towards lightweighting, intelligentization, and environmental protection. In terms of lightweighting, adoption of new materials and optimized structural design can further reduce product weight, improve energy efficiency and performance. This is particularly important in automotive, aerospace, and other fields. Intelligence involves integrating intelligent components such as sensors and chips into plastic product structures, enabling them to possess more intelligent functions and meet demands of Internet of Things era. Environmental protection requires greater attention to material selection and production process optimization during design process, employing recyclable and biodegradable materials to reduce environmental pollution, achieve sustainable development.
As designers, we must keep pace with times, continuously learning and mastering new knowledge and technologies, actively exploring innovative design concepts and methods, and contributing to advancement of plastic product structural component design. I also hope that this article will help more people understand, master key points and methods of plastic product structural component design, avoid mistakes in practical work, and design more excellent plastic products.

 

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These are my insights and experiences in plastic product structural component design, which I hope will be helpful. I understand that in practical design work, everyone encounters a variety of unique problems and challenges, and accumulates valuable experience. We sincerely encourage everyone to share their experiences, insights, and challenges in designing plastic product components in the comments section. Whether it's a success story or a lesson from failure, every exchange is an opportunity to learn and grow. Let's learn from each other and make progress together in this community. If you have any other questions about plastic product component design that you'd like to learn more about, please feel free to ask.