Guide to plastic product design and manufacturing
Updated: Jun 7, 2022
Criador Labs | Plastic Design and Manufacturing Firm | USA & India
Designing plastic products is a heterogeneous job. It combines understanding your customers' needs, enhancing their experiences regarding those needs, and turning those ideas into something tangible made of plastic.
Its versatility can meet almost any design requirement, and its lightweight, durability, and versatility in color, touch, and shape give it significant marketing advantages. Aside from being easy to work and mold, plastic also has low production costs, a low density is waterproof, is an excellent electrical insulator provides good thermal insulation, and resists corrosion and many chemical factors.
As a result, plastic products are still used in the modern industrial sector the most. If all this weren't enough, plastic products are considerably less energy-intensive than metals, glass, and paper.
Different DFM aspects of plastics and manufacturing techniques
To achieve an effective plastic design, it is necessary to know both geometry and materials. These two factors interrelate, so it is important to have knowledge of each area. It is essential to adhere to specific rules regarding part geometry in plastic design to achieve the desired outcome.
To manufacture a new plastic product design, one shall have knowledge of industrial design, material selection, manufacturing, and product management, once its life cycle is over.
It is important to scrutinize surfaces such as wall surfaces, ribs, and holes in detail. To accomplish this, general design guidelines provide basic principles.
Specifications for plastic materials should include the following aspects:
Required strength
Specific service temperature range
Exposure to chemicals and harsh environments
Appearance requirements
Dimensional tolerances
Required agency approvals
Processing method
Assembly method
Recyclability considerations
(NOTE: As well, one must be aware of the limitations imposed by the legislative framework, similar products in the market, and certifications. Other issues to consider include assembly and storage.)
After the above checklist is checked, we move into CAD modeling. Depending on the above data observed and the type of manufacturing selected, the CAD modeling is moved forward. Depending on the manufacturing method, many variables change and need to be kept in mind. For eg, for injection molding, it is advised to keep a Uniform Wall thickness within a range of 1.5mm - 3 mm.
Manufacturing of Plastics:
The most common methods are:
Plastic extrusion
Injection moulding
Rotational moulding
Plastic extrusion & injection blow moulding
Vacuum casting
Thermoforming & Vacuum forming
Compression moulding
Nowadays 3D printing is also rapidly catching up to traditional manufacturing, but mainly are used in prototyping with smaller numbers to make a functional prototype.
The following are different 3D-printing methods:
Stereolithography (SLA)
Selective Laser Sintering (SLS)
Fused Deposition Modeling (FDM)
Digital Light Process (DLP)
Multi Jet Fusion (MJF)
PolyJet
Direct Metal Laser Sintering (DMLS)
Electron Beam Melting (EBM)
The cheapest among them is FDM, which gives almost near functional prototypes for testing and verification.
Selecting the Right Plastic Manufacturing Process
When selecting a manufacturing process, keep these factors in mind:
Form:
Do your parts have complex internal features or tight tolerances? The geometry of a design may limit manufacturing options, or it may require significant design for manufacturing (DFM) optimization to make it cost-effective to produce.
Volume/cost:
What is your planned annual production volume of parts? Despite high upfront costs for tooling and setup, some manufacturing processes produce parts that are inexpensive per unit.
Lead time:
What is the turnaround time for parts or finished goods? While certain high-volume production processes create first parts within 24 hours, tooling and setup can take months.
Material:
What stresses and strains will your product have to withstand? A variety of factors determine the best material for a given application. Affordability must be weighed against aesthetics and functionality.
Consider the features that are suitable for your application and compare them to the options accessible in a given production process.
For mass production, we can choose any method of manufacturing, depending on the above factors. But to make them reproducible and increase repeatability, we need to optimize the design according to the manufacturing process chosen for Design for Manufacturing and Assembly (DFMA).
What does DFMA - Design for Manufacturing and Assembly - mean?
DFMA is an engineering methodology that promotes the ease of manufacturing the product's parts and its simplified assembly into the final product during the early phases of the product lifecycle. It reduces both time-to-market and total production costs.
DFMA used to be two distinct methodologies: Design for Manufacturing (DFM) and Design for Assembly (DFA). In DFM, we focus on selecting cost-effective raw materials and taking steps to reduce the complexity of manufacturing processes during the product design phase (the least disruptive and expensive time to handle these issues) in order to minimize product component manufacturing time and cost. Likewise, DFA is concerned with minimizing the number of individual components, assembly steps, and quality variability of a build by minimizing assembly time, costs, and complexities.
DfMA allows waste or inefficiency in product manufacturing and assembly to be identified, quantified, and eliminated.
As a benchmarking tool, it may also be used to analyze the products of competitors.
DFMA core principles are:
Minimize the number of components
This will decrease assembly costs, reduce work-in-process, and simplify automation.
Design for ease of part-fabrication
Part geometry is simplified and pointless capabilities are avoided.
Tolerances of parts
Parts should be designed so that they are within the capability of the process.
Clarity
It is best for components to be designed so that only one assembly method can be used.
Limit the use of flexible components
Parts made of rubber, gaskets, cables, etc., are generally more difficult to handle and assemble. As an example, design for ease of assembly, using snap-fits or adhesive bonding rather than threaded fasteners. An effective product is one that has a base component for locating other components quickly and accurately.
Design for ease of assembly
Eg: the usage of snap-fits and adhesive bonding instead of threaded fasteners together with nuts and bolts. A product should be developed with a basic component that can be used to quickly and precisely locate other components.
Remove or reduce required adjustments
Designing adjustments into a product leads to more out-of-adjustment situations.
Advantages of DfMA:
DFMA has a number of advantages, including:
Speed
The use of prefabricated elements in DfMA construction reduces the program on-site significantly.
Lower assembly cost
DFMA lowers the cost of assembly by reducing labor requirements, using fewer parts, and reducing the number of unique parts.
Higher quality and sustainability
Each step can be made more efficient and quality by using an automated process. There may be less waste generated during construction, greater efficiency in site logistics, and fewer vehicles moving materials to the construction site.
Shorter assembly time
The DFMA uses standard assembly techniques such as vertical assembly and self-aligning parts to reduce assembly time. By ensuring a smooth transition from the design phase to the production phase, DFMA also ensures that the production process is as efficient and rapid as possible.
Increased reliability
DfMA increases reliability by reducing the number of parts, thereby reducing failures.
Safety
Safety can be improved substantially by removing construction activities from the site and placing them in a factory environment.
DFM Guidelines for Reducing Costs and Challenges in Manufacturing Plastic Components:
Before tooling begins, start DFM early in the design process
Engineers, designers, the contract manufacturer, the mold maker, and the material supplier should meet to discuss the design
Create the product in such a way that the number of parts is kept to a minimum.
Build it with a modular design
Limit the number of machine operations needed
Use standard components
Design parts to be multi-functional
Design parts for multi-use
Design for ease of fabrication
Avoid separate fasteners
Minimize assembly directions
Maximize compliance
Reduce handling and consider how a design affects part packaging and shipping.
Why DFM is necessary for the Injection Molding Process
Beyond estimating manufacturing costs, your injection moulding vendor should use DFM principles to reduce component costs, assembly costs, support production costs, and identify the impact of DFM decisions on other factors throughout the entire design and production process.
The increasing complexity of plastic injection moulded parts is another reason to choose a moulder who follows DFM principles. To meet the quality/cost requirements of customers, tolerance, draft angles, undercuts, and other factors must be considered during the design stage.
Critical Elements of Design Optimization
Best DFM practices for plastic injection moulded parts include the following critical elements prior to the creation of a mould:
Considering Material Shrink Rate:
Shrinkage is the contraction of a moulded part as it cools after injection. Depending on the resin (amorphous vs. crystalline materials) family, each material shrinks at a different rate. , mold design, and processing conditions. Depending on the direction of flow, the resin may also shrink differently. As a rule of thumb, a 10% change in mould temperature can result in a 5% change in original shrinkage. Furthermore, injection pressure has a direct impact on shrinkage rates. The lower the shrinkage rate, the higher the injection pressure.
Draft:
The type of draft required is determined by how the features of a part are formed in a mould. Most bosses, ribs, and posts formed by blind holes or pockets should taper thinner as they extend into the mould. If the mould separates from the surface before ejection, surfaces formed by slides may not require a draft. Consider incorporating draft angles on product features such as walls, ribs, posts, and bosses that run along the direction of release from the mould, thereby facilitating part ejection.
For most materials, a draft angle of at least one-half degree is acceptable. One to two degrees of draft may be required for the high-heat and exotic resin. For every 0.0254 mm of texture depth, add one degree of draught.
Draft all surfaces parallel to the mould separation direction.
Angle walls and other part features are formed in both mould halves to aid ejection and keep wall thickness uniform.
Uniform Wall Thickness:
To avoid thick sections, uniform wall thickness throughout a part (if possible) is essential. Non-uniform walls can cause warping of the part as the melted material cools.
If different thicknesses of sections are required, make sure the transition is as smooth as possible to make the material flow evenly inside the cavity. This ensures the entire mold will be completely filled, lowering the possibility of defects.. Thickness transitions that are rounded or tapered reduce molded-in stresses and stress concentrations caused by sudden changes in thickness. Incorporating the right wall thickness for your part can have a significant impact on the cost and speed of production. The least wall thickness that can be used is determined by the part's size and geometry, structural requirements, and resin flow behavior. Injection moulded parts typically have wall thicknesses ranging from 2mm to 4mm (0.080" to 0.160"). Injection moulding with thin walls can produce walls as thin as 0.5mm (0.020"). Work with an experienced injection moulder and design engineer to ensure that the proper wall thicknesses are used for the design and material selection of your part.
Radii to Edges:
Aside from the main areas of a part, uniform wall thickness is an important design element for edges and corners. Adding generous radii to rounded corners will improve the design of a plastic part by reducing stress concentration and increasing the material's ability to flow. Parts with large radii are also more cost-effective and easier to manufacture, as well as having more strength.
Ribs:
Many people think that by making the walls of an element thicker, the strength of the part will increase. When essentially, making walls too thick may lead to warpage, sinking, and other defects. The purpose of using ribs is that they increase the strength of an element without increasing the thickness of its walls. With less material required, ribs will be an economical solution for added strength. For increased stiffness, increase the amount of ribs instead of increasing height and space a minimum of double the nominal wall thickness except each other.
Draft Angle:
How features of a part are formed during a mold determines the type of draft needed. Most bosses, ribs, and posts formed by blind holes or pockets should taper thinner as they extend into the mould. Surfaces formed by slides won't need a draft angle if the mould separates from the surface before ejection. Incorporating angles or tapers on product features like walls, ribs, posts, and managers that lie parallel to the direction of the discharge from the mold can ease the ejection of part.
Finishing:
Surface finish options for injection molded parts vary reckoning on part design and therefore the chemical make-up of the fabric used. Finishing options should be discussed early within the design process because the material chosen may have a big impact on the kind of finish implemented. within the case where a gloss finish is employed, material selection is also especially important. When considering additive compounds to attain the required surface finish and enhance the standard of a component, working with an injection molder that's aligned with knowledgeable material science professionals is crucial. Consideration of those elements is prime for integrating engineering and manufacturing expertise to catch mistakes, see opportunities for efficiencies and price reduction, and even assess the viability of contract requirements. Typically, your injection molder will conduct an in-depth analysis of those elements together with your team well before the tooling process is initiated. DFM isn't a “stand-alone” guideline or principle when it involves manufacturing plastic injection molded products. It works with other approaches for optimization of design like designing for functionality, assembly, and sustainability, each of which is discussed further, below.
A Four-step procedure to Plastic Part Design and Optimization-
Design for Manufacturing (DFM)
Design for Manufacturing (DFM) elaborates the process of designing a product to reduce its manufacturing cost, allowing problems to be sorted during the design phase itself which is the least expensive phase to address.
Depending on the different types of manufacturing processes, there are set guidelines for DFM practices that define various tolerances, rules, and manufacturing checks related to DFM.
Design for Functionality (DFF)
In the plastic product design process, it is imperative to keep the focus on the functional requirements of the product. Experienced engineers should make recommendations about modifications that will help ensure the product meets its functional requirements including what elements the product will be exposed to, chemical or corrosive materials the product will need to withstand, functional cosmetic attributes, etc.
Design for Assembly (DFA)
Design for assembly (DFA) is a process that ensures ease of assembly in mind with the final goal of reducing assembly time and cost. The reduction of the number of parts of an assembly is usually where the major cost benefits of DFA occur.
Design for Sustainability (DFS)
Design for sustainability stresses designing parts with print accuracy intent in mind - sustaining tolerances with proper measurement on an ongoing basis.
Plastics materials Selection for Injection Molding
Below are the points to keep in mind before selection of material:
Chemical resistance
Child safety
Color
Compliance with FDA standards
Compliance with NSF standards
Compliance with REACH standards
Compliance with RoHS standards
Dielectric properties
Economic or cost constraints
Embossing requirements
Environmental conditions
Finish requirements
Flexibility
Food safety
Heat, flame, or burn resistance
Material strength
Mechanical conditions
Need for reflectivity or transparency
Pressure resistance
Rigidity
Shelf life
Weight resistance
Plastic Material Finishes
Super high glossy finish
High glossy finish
Normal glossy finish
Fine semi-glossy finish
Medium semi-glossy finish
Normal semi-glossy finish
Fine matte finish
Medium matte finish
Normal matte finish
Satin textured finish
Dull textured finish
Rough textured finish
Criador Labs has vast experience in plastic product design and manufacturing. You can learn more about our consulting services here.