Guide to plastic product design and manufacturing

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.

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.

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.

This will decrease assembly costs, reduce work-in-process, and simplify automation.

Design for ease of part-fabrication

Tolerances of parts

Clarity

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.

Speed

Higher quality and sustainability

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.

Safety

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.

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.

• 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.

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.

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.

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.

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.

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.

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.

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) 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 stresses designing parts with print accuracy intent in mind – sustaining tolerances with proper measurement on an ongoing basis.

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

• 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.