Product Design

Plastic material selection is a pivotal factor for plastic product design, influencing the plastic part design, performance, and manufacturing cost. Therefore, materials should be primarily selected based on the functional requirements of the part. Functional requirements include physical properties like the ability to operate over a wide range of temperatures, withstand chemical and other environmental conditions, electrical, optical, and any other conditions that can be elucidated by testable parameters.

There isan abundance of plastic material grades available in the market, yet few commercial-grade plastic materials are extensively used to manufacture plastic parts.While selecting the plastic materials, thermal properties like product maximum and minimum working temperature, heat dissipation during the product operation, heat deflection temperature, and melting temperature have to be considered. Likewise, physical properties such as impact resistance, tensile strength, wear resistance, material strength and stiffness, and creep resistance are equally important in the selection process of plastic materials. Further, the capability of injection molding which encompasses material melting temperature, melt flow rate, shrinkage, and dimensional ability are influencing factors in plastic material selection. Apart, design considerations which include raw material cost, processing and tooling cost, recyclability, familiarity, and accessibility in the market have an impact on the plastic material selection.

For instance,

There are different types of plastics with different properties. To acquire the desired properties to use it for intended applications, you need to understand the relationship between the required plastic material and plastic manufacturing processes like injection molding, blow molding, extrusion, rotational molding, and thermoforming. 

Injection Molding requires melting the plastic material which is injected it into a mold under high pressure where the mold is cooled, and the plastic part is ejected from it. Injection molding is used for thermoplastics and thermosetting plastics. 

Blow Molding entails the melting of plastic material which is blown it into a mold, and it takes the shape of the mold. After that, the mold is allowed to cool and the part is removed from the mold. It is sued for PVC, high-density polyethylene, or resins.

Extrusion requires themelting of plastic material like ABS, polyethylene, polypropylene, acrylic, etc., which is forced through a die and is shaped. 

In Rotational Molding, mold is heatedand rotated around two perpendicular axes and the material is poured in the mold where it melts and adheres to the mold's surface. After the mold cools, the part is removed. Polyethylene terephthalate is widely used in this process. 

Thermoforming involves heating a sheet of plastic and shaping the plastic vacuum pressure or mechanical force. Thermoforming has it range on acrylic, ABS, polycarbonate, PVC etc.

The details about the four main types of plastic used in manufacturing, along with their suitable manufacturing processes is described in the table below. 

source:shibaura-machine.co.jp

Some key design considerations for plastic manufacturing to reduce the negative impact of plastic waste on the environment are explained below.

1. Avoid using more than one type of plastics
2. Check compatibility – plastics, labels, foils, caps, adhesives
3. Use colorants cautiously
4. Always use plastics identification codes
5. Disassembly – ease of emptying, use snap fittings or break points to replace component or separate for recycling.
6. Avoid secondary finishes and coatings
7. Avoid composite materials
8. Avoid metal foils, components and fasteners
9. Avoid toxic additives
10. Don’t over specify or over order
11. Establish possible reuses
12. Provide clear information on recyclability to end user

Due to the advent of growing interest in sustainability, reduce and recycle principle, many manufacturers are exploring ways to lessen waste and initiate the use of more environmentally friendly materials, such as bio-plastics. Bio-plastics are made of renewable resources and can biodegrade, supporting the "reduce, recycle and reuse" slogan.

Source: https://www.mdpi.com 

The design process has to be closely considered in order to enhance its recyclability. By designing and manufacturing plastic products with main factor: recyclability in mind, you can help ensure the concept of circular economy. Factors like material selection, packaging types and product color also makes a difference in product's recyclability.

• Material selection

Some of the parts are recyclable while some are not. Permanent combination of two separate materials in which only one material is recyclable makes the whole package unrecyclable. By excluding the harmful chemical substances that only contributes in ruining the recycling process, a wider circularity of materials (recycle, reuse) will be enabled. Plastics including Polyethylene Terephthalate, polypropylene and High-Density Polyethylene are commonly recycled but the recycling process of PVC, ABS etc. are comparatively more difficult.

• Type of packaging

Rigid packaging has a mono polymer and mono layer structure that makes it easier to recycle than the flexible packaging that has multi-polymer multi-layer structures. Most household recycling schemes don’t cover the flexible packaging systems.

• Product color

Clear/transparent or white plastics are often easier to recycle as they have wide range of recycling options than colored plastics that can make the sorting process using automatic NIR spectroscopy difficult, and colored plastics have a lower resell value as well.

• Labels and adhesives

Labeling or inking the parts and denoting the types of materials and its status of recyclability are crucial at the design stage. When it comes to labeling, use same material as the packaging in order to make the recycling process less complicated. Water soluble adhesives are preferred as they can be easily removed while reprocessing.

Designing plastic products for durability is important to ensure that the product can withstand the rigors of everyday usage and also to maintain products’ functionality and aesthetics over an extended period.

1. Material Selection: Selection of the right plastic material is paramount to the durability of the product. Different plastics have varying properties, which are strength, flexibility and resistance to wear & tear. Thorough analysis of the product’s requirements and environmental conditions is important to finalize the most suitable material.
2. Mechanical Design: For plastic product durability mechanical design also plays very crucial role. The product design must incorporate different features like gussets, ribs and reinforcements to improve structural integrity.
3. Stress Analysis: Use of different computer simulations to conduct a stress analysis can help to identify and diagnose the weak points in the design. This analysis helps us to optimize and enhance the design to withstand the expected load and pressure
4. Wall Thickness: Wall thickness variations may result in weak places leading to affect the durability of product so maintaining the consistent wall thickness throughout the product is important for even distribution of stress
5. UV Stabilization: UV stabilizers can be included into the material to prevent degradation and maintain the strength and look of plastic products that will be exposed to sunshine.
6. Impact Resistance: Product may subject to impact or shock during its lifespan so we must consider its likelihood. Incorporation of different impact-resisting features, such as shock-absorbing elements or flexible zones, can enhance its durability.
7. Corrosion: Plastic products can experience a certain form of degradation that is similar to corrosion which is referred as environmental stress cracking or chemical attack. To be safe from that materials with high resistance to corrosion must be selected and extra layers of protective coatings can also be implemented.
8. Quality Control: Implementation ofvarious quality control measures throughout the manufacturing process to identify any defects or issues that may affect the product's durability.
9. Proper Assembly: Products that consists multiple parts should be undergo with proper assembly techniques to maintain its functionality and prevent permanent failures.
10. User-Friendly Design: A meticulously developed ergonomic design minimizes the possibility of improper handling, thus increasing the product's durability.

Optimization of the plastic product design for manufacturing efficiency can be achieved with several methods which are listed below:

Design for manufacturability (DFM):It is the process of designing a part which results the easy and efficient way to manufacture. It takes into account factors such as manufacturing process, thermal process and the assembly process.

Use of standard components: Using standard components can significantly increase the manufacturing efficiency with reducing manufacturing costs and lead times. Those components are easily accessible, so workforce can divert to another complex task which results the decrease in total time consumption and increase in manufacturing efficiency.

Wall Thickness

The thickness of the wall, in a part can impact how efficiently it is manufactured. When the walls are thicker it requires material, it can result in longer cycle times. It is important to maintain a consistent wall thickness across the product to ensure cooling is during molding. If there are thicknesses in the walls it can cause differences, in cooling rates, which may lead to warping or other defects. Making sure that the material is evenly distributed helps achieve uniform filling during injection molding reducing the chances of voids or sink marks.

Youtube video link : Designing of Plastic Products for Injection Moulding - Lecture Wall Thickness - YouTube

Draft Angle

The draft angle is the angle, at which the walls of the object slope from the line where the mold separates. It is important to have an angle of inclination in order to enable the removal of the object from the mold. Appropriate angles of inclination help to reduce friction between the mold and the object making it easier for it to be smoothly ejected and reducing any harm or damage, to the product.

Source: https://www.upminc.com

Part consolidation:

Part consolidation refers to the practice of merging parts into a single component as part of product design. This method aims to make the assembly process easier and minimize the requirement, for fasteners or adhesives thus making production more streamlined and reducing points of weakness. Manufacturers can achieve efficiency and cost effectiveness in production while simultaneously enhancing the reliability of the product by consolidating parts.

Ribs and gussets: 

Adding ribs and gussets to a part can enhance its strength. Its crucial to bear in mind that it may also increase the complexity of the molding process. When designing parts, with these features it becomes essential to weigh the trade offs between strength and ease of manufacturability.

Photo link: Injection Molding: Rib Design - 3 Space

Minimize the number of parts: Fewer the parts, easier and time-efficient manufacturing. Having very few numbers of parts can meaningfully reduce the assembly time lowering the tooling cost

Simplify the design: Avoiding the complex structures, features and curves can make design simple resulting reduction of cost and time for manufacturing.

Here are some additional tips for optimizing plastic product design for manufacturing efficiency which includes use of appropriate materials, use of automation, use of CAD etc., Some of them are explained below:

• Use of computer-aided design (CAD) software:With the use of simulation for manufacturing process, potential problems that may occur can be identified.
• Consulting with a plastics engineer: A plastics engineer can help designers in the process of selection of right material and process for manufacturing ensuring the product to be manufactured meet the required specification.
• Testing:Testing the plastic product to understand whether it meet all the required specifications or not is important. It will help to identify any potential problems that can be face during the manufacturing process.

Here are some additional resources that you may find helpful:

• The Society of Plastics Engineers (SPE): https://www.spe.org/
• The Plastics Industry Association (PLASTICS): https://www.plasticsindustry.org/
• The American Society of Mechanical Engineers (ASME): https://www.asme.org/

• Not considering the manufacturing process:When creating an item, it is crucial to take into account the manufacturing method that will be employed. This encompasses aspects like the kind of plastic to be utilized the injection molding procedure and the necessary tools. If the design isn't compatible, with the manufacturing process it can result in issues, like flaws, expensive production and extended production timelines.
• Using the wrong materials: Choosing the materials is an aspect of designing plastic products. It's essential to select a material that aligns well with the intended use and manufacturing process. If the wrong material is chosen it can result in issues, like changes, in dimensions, subpar performance and early breakdown.
• Not considering the shrinkage of the plastic: When plastic undergoes the cooling process it naturally contracts in size. This reduction, in size needs to be considered during the product design phase. If the design does not allow for shrinkage, different problems such as voids, warping, and dimensional inaccuracies can occur.
• Not using draft angles:Draft angles are slopes that are incorporated into the design of a plastic product to allow it to be ejected from the mold. If draft angles are not used, it can be difficult to remove the product from the mold, which can lead to damage.
• Using sharp corners and edges:Stress concentration can be occurred due to the presence of sharp corners. Due to this, early failures can be occurred. Filleting the edges can significantly reduce the problem.
• Not testing the product: It is important to test plastic products before they are released into production.Testing plastic product is important before it going to production cycle. This process plays important role to identify the problems before going to any manufacturing process.

By avoiding these common mistakes, plastic product designers can help to ensure that their products are manufactured successfully and meet the required specifications. Here are some additional tips for avoiding common mistakes in plastic product design:

• Consult with a plastics engineer
• Use computer-aided design (CAD) software
• Get feedback from potential users
• Test the product thoroughly

Prototyping plays a crucial role in plastic product design. It allows product designer or product design engineers to test and improve their model before going to full scale production. This can reduce production cost as there is very low probability to be manufacturing defect in mass production.

Product Visualization:

It allows designers to visualize the real product and get feedback from stakeholders. It also helps to validate the ideas comparing the prototype model. Prototype can be very efficient to understand the product as compare to 2D drawing and 3D model.

Functionality test:

Prototyping aids in functionality test, which helps to evaluate the product’s performance, durability, safety and identity any functional shortcomings. This can help to ensure that the product meets the all-desired needs of the products before going to the full-fledged production cycle.

Material and compatibility test:

It allows designers to examine different plastic material and determine which one suits the product’s need considering different properties such as strength, flexibility, etc. It also allows to understand the relationship between production material, its properties and cost, so that designers can choose the best combination of it.

Risk Mitigation

As mentioned above, prototyping minimizes the risk of potential failures resulting cost reduction as it reduces costly reworks in the later stages of development process.

Stakeholder engagements

Presenting tangible/physical prototype to the stakeholders can helps to get quick feedback and support for the final design for the product.

Though there are many more advantages of prototyping in plastic product design, some of them are explained above, and some more are listed below:

• Iterative design improvement
• Manufacturability assessment
• User feedback and usability evaluation
• Cost optimization
• Ergonomics and human factors evaluation
• Continuous improvement

There are different prototyping methods that can be used for plastic products:

• 3D printing
• CNC Machining
• Injection Molding

CAD has revolutionized product design scenarios with help of realistic 3D visualization. CAD serves as virtual testing ground, validating product functionality and performance. Here are some of the specific benefits of using CAD in plastic product design:

Validating Designs through Simulation and Analysis:

Different CAD software integrates simulation features, it allows designers to analyze the product with various simulations such as structural, thermal and fluid-flow. This helps to find the structural problems of the product before developing the real model or physical prototype of the product. It also allows the design validation for feasibility and functionality.

Comprehensive Design Documentation with CAD

Design documents developed from CAD software helps manufacturer to understand the product development and assembly procedure based on the precise drawing, specification and assembly instructions.

Optimization and Waste Reduction with CAD

CAD design enables designers to efficiently and precisely design the product controlling the dimensions, tolerances, and shape of the product components. It facilitates development of intricate design effectively using the material without compromising on product functionality. As CAD drives efficient resource usage it leads to development of sustainable and comparatively environmentally responsible product.

Integration with Manufacturing Processes

CAD designs interfaces with Computer-Aided Manufacturing (CAM) system, which develops link between design phase of the product and the physical realization of the product. The automated translation of CAD-CAM eliminates the potential errors and discrepancies that may occur during manual data transfer, this ensures accuracy and reliability of the manufacturing process.

Here is some more role of CAD in plastic product design.

• Reverse Engineering and Surface Modeling
• Virtual Reality (VR) and Augmented Reality (AR) Visualization
• Kinematic and Motion Simulation
• Surface Texturing and Aesthetic Design Visualization
• Interference Checking and Tolerance Analysis