Although plastic components can be conceptualized, designed, and developed most efficiently, there are a number of phases (some of which overlap with one another) that must be completed to accomplish this.
 
We’ll explain the design of the part in simple terms.
 
  1.  Determine the needs of the end-users.
  2. Sketch the concept 
  3. Choose the materials
  4. Draw the part with materials
  5. Choose the right material
  6. Make manufacture simpler 
  7. Prototype
  8. Tools
  9. Manufacturing
 
Several design activities take place simultaneously at different stages of the process, but each of the stages is discussed separately.

During the entire product development process, specifications and end-use criteria are comprehensively and thoroughly described.

Based on these criteria, a product will be created by engineers and designers, and thus represents the first stage in the construction process.

In the case of non-conforming products, they cannot be used.

Instead of focusing on the quality of the product, it is important to design it based on its intended end-use.

A solid product should be defined with terms like “strong” or “clear”. It is more difficult to determine what a product should look like or withstand since it is not as straightforward.

The use of a product with all its end uses can, however, be hard to quantify when considering the possible misuse of that product. It is applicable if you replace existing products with new ones (e.g. conversion to metal), but not if you produce entirely new products.

Specifications such as these can be difficult to anticipate.

This stage of the design process is typically used to create prototypes (or models) to ensure we understand end-use specifications completely.

The most common considerations are structural loading, environment, size specification, standard requirements, and industry-specific problems.

It is important to consider and define loading types, speeds, loading time, and loading frequency. You should anticipate the loads while mounting, transporting, storing, and using the product. Typically, the plastic component is designed as part of the packaging process to ensure the product is properly packaged when shipping and storing.

The part’s manufacturer needs to consider both typical and worst-case loading situations. In this case, it is most important to decide which side will be affected most if the load fails.

A poorly designed product is more likely to fail, whereas a product designed without consideration of misuse will fail. Especially when the product failure is likely to cause serious injury, product designers must ensure their designs are reliable.

It is essential to specify the anticipated environmental conditions for use of the product because the properties of plastic materials are extremely sensitive to weather conditions. Radiation exposure, relative humidity, chemical environment, and temperature are among these conditions.
Also important is to carefully examine the environmental conditions to be met during assembly and storage (ovens for curing paint, chemicals, adhesives, etc.). Temperatures high enough for creep or oxidative degradation are not recommended, while temperatures low enough are not recommended.

Once again, the problem lies in anticipating misuse, formulating worst-case scenarios, and detailing requirements. If the product is to be used outdoors, the list of chemicals and any UV exposure risks must be clearly displayed.

Dimensions: Plastic parts measurements are often critical for practical reasons, as well as surface finishes and the like. Dimensional tolerance differences significantly affect costs associated with tooling and development.

Plastics are covered by some regulatory agencies in certain applications. Understanding which regulatory agency is responsible for a product is crucial.

If you get this step right, then it will be easy to conform to these standards. Materials can be sanctioned (food grades, flammability, etc.) or can be measured to achieve performance standards (EMI shielding, etc.).

A prototype or pre-production is often needed for the evaluation of products.

It is also specified during the first phase of the development process what a product’s maximum cost and replacement interval will be.

Developing a product that’s both attractive and affordable is the product development team’s priority.(i. e., the most efficient design). It is also important to quantify other limitations related to the market, such as color, size, and shape. The use of models (prototypes without functional components) is a great means of communicating aesthetic values since these are challenging to quantify.

In addition to what type of material will be used and how long it will last, the business must consider a lot of things regarding marketing.

Among the most important aspects of product design is the lowest possible cost (i.e., the most efficient projects). The consumer must be informed of market-related constraints like color and size at all times.

 

The product development team and industrial designers will work together to develop early concept sketches of the product once the end-use requirements have been specified.

These sketches are usually 3D renderings as opposed to CAD drawings.

Fig. 3.5

Areas of the part that require special attention are highlighted and detailed. As a result, it is best to identify whether a specific dimension or function is fixed or variable.

A fixed-function is one in which the designer is not able to express his creativity regarding the design of the product (e.g., dimensions defined by a standard, etc. ); while a variable function is being developed in the stage that it must be designed in.

Fig. 3.5 shows a typical nozzle of a garden hose.

The task is designing an all-plastic hose nozzle. If 10 designers are given the same set of specs and independently design the hose nozzle, it’s likely to come up with ten completely different designs.

Additionally, certain aspects of every design will be the same because certain dimensions are governed by standards and no room for variation or creativity. For instance, the inside dimensions of the inlet thread will be the same because these dimensions are governed by standards.

However, other features vary from design to design, such as the shape of the product or the way it shuts off the water flow.

The die-cast metal nozzle shown in Fig. 3.5 looks a lot like the plastic nozzle. Likely, the plastic part designers were greatly influenced by existing metal designs.

On the other hand, the other plastic hose nozzle is a completely different design from the other hose nozzle in Fig.3.5. This product has a different image.

The fact is that in a replacement metal part application such as this it is best to stick with the specifications rather than the existing metal part alone.

As soon as a designer sees the functioning of a metal component, it will be extremely difficult to avoid copying the current design.

If the designer does not think outside the box, then innovation and creativity are less likely to result in significant quality improvements and component or cost reductions.

In addition, the possibility of infringing upon patented designs is greater if the design process begins without a detailed analysis of existing competitive products.

plastic material

After a specific end-use requirement for a part has been defined, designers can begin searching for plastic materials to meet those requirements in the material selection or screening process. These decisions are based on whether a particular plastic material’s physical properties meet the end-use requirements.

More plastic materials are available in the marketplace than ever before, so a designer can likely find a material that is suitable for the application.

During the initial material selection process it is generally preferable to identify several potentially suitable material candidates (e.g., 3-6 specific formulations/grades).

The sheer number of material grades available can sometimes make the screening process extremely challenging. To determine the most appropriate material for the application, it is best to consider the material properties that cannot be enhanced by design.

The coefficient of thermal expansion, transparency, chemical resistance, softening temperature, and agency approval are characteristics that can’t be altered.

For example, polycarbonate injection molding is not suitable for gasoline containers because it does not provide adequate resistance to hydrocarbons. High-density polyethene is not suitable for window applications because it is translucent or opaque.

In both cases, altering the design of the part will fail to solve the problem.

By utilizing these kinds of features the process can be fairly easily extended by eliminating entire families of materials that share the same characteristics, thereby eliminating the number of potential plastic material candidates.

Coatings, additives and co-injection technologies complicate the materials selection process. Coatings can change chemical resistance, hardness, and abrasion resistance, and make parts look nice.

For coatings, a material that would not otherwise be suitable for the application can be utilized. In addition, adding additives to the material choice process can complicate material selection.

Melt blending or compounding is a technique that can be used to selectively modify the properties of plastic materials.

Unlike the mechanical properties listed above, most of the mechanical properties of a polymer can be enhanced by design, provided the specific application temperature is met.

Generally, designers evaluate a material’s modulus when selecting a candidate for metal replacement applications.

One of the problems with metals in this regard is that they are both rigid and tough, whereas most rigid plastics are relatively brittle (e.g., many glass-reinforced grades are both rigid but fragile).

In many instances, engineering polymers with a lower degree of reinforcement or without reinforcement are superior to others.

Although the modulus values may be low (and they may creep more rapidly), the part geometry can be altered (by making the ribs deeper, for example) to compensate for this reduced modulus.

At this point in the design process, the application would benefit from knowing about and comparing several candidate materials. Various properties make each material grade unique, as well as different geometries that pertain to each material.

For example, a designer is considering applications involving static loads and organic solvent exposure in high-density polyethene, polypropylene, and nylon 6/6.

The designer feels that each material has its advantages. A final decision on the use of a particular material will have to be made once each part has been designed because the material consumption and manufacturing cycle times will differ in each case.

Although nylon 6/6 is a more expensive material per unit weight or volume, the results of lessening the material’s wall thickness and decreasing the cycle time may partially offset the higher price per unit of material.

Fig. 3.6

Figure 3.6 shows two-part geometries with equivalent stiffness values, namely, they have sections with the same section modulus or moment of inertia value (where the section is any dimension), and these values have been corrected for the material differences.

While the example given here has a relatively simple geometry, in practice many other geometrical features associated with the performance or assembly of a device would vary based on the materials specifications.

At this stage in product design development, the designer is not required to commit to a particular primary material at this stage as long as they retain the option of remaining flexible materials in case an unanticipated problem occurs later in the development process (e.g., during prototyping or production).

It’s unlikely any of these candidates’ stuff fits the job perfectly.

The materials that are proposed for consideration have their advantages and limitations. The designer may have a favourite material based on experience. While it may be useful to work with familiar material, the other candidate materials may be better suited for the application.

Nevertheless, decisions formulated solely based on the cost of materials and manufacturing do not take into account performance or processing advantages.

It is recommended that candidates be evaluated in terms of their processing costs, end-use performance, and overall characteristics of manufacturing.

By weighing properties or characteristics, designers can select the best candidate materials based on an essentially unbiased grading system.

Figure 3.7 presents the three materials for the chemical and static-load application polypropylene, HDPE, and nylon 6/6.

Figure 3.7

Although the individual numerical ratings associated with a given house tend to be somewhat arbitrary, I believe that most of the time, these ratings are based on actual numerical data about the house.

All of the important factors will be considered, and then a semi-quantitative method will be used to choose the best material candidates on balance.

Once the material and initial design have been established, the design must be altered for manufacturing. Input from tooling and process engineers is extremely valuable.

Fig. 3.8

The part geometry that has been developed must be moldable. Designers must consider the impact that the various phases of the injection molding process can have on the part design.

Each stage of the injection molding process, namely mold filling, packing, holding, cooling, and ejection, has its special requirements.

Consider the part shown in Fig. 3.8. The part has been designed with ribs to support the service loads.

In practice, the part must be modified with radii to assist in flow (and reduce stress concentrations), draft angles to assist with part ejection, and surface texturing to improve the visual appearance of the sink marks (due to material shrinkage) on the wall opposite the ribs.

These are but a few of the possible design modifications that are required from a manufacturing point of view.

The effect of these modifications on the end-use performance of the part should be evaluated after they are made, because design changes, such as the addition of draft angles to ribs, can have a significant influence on the maximum deflections and stresses that occur due to service loading.

Part design checklists, such as the one shown in Fig. 3.9, can be useful during planning stages or as final checks to ensure that all aspects of manufacturing and assembly have been considered.

The final part design, modified for manufacturing is generally prototyped at this point to evaluate both the manufacturability and performance capabilities of the part.

Prototyping is required because all process (e.g., molding simulations) and performance design work (e.g., structural analysis) done up to this point in time have been “theoretical” and must be verified.

This is particularly important for molded plastic parts because many manufacturing-related problems are difficult to predict in advance (weld line appearance and strength, warpage, sink marks, etc.).

In order to obtain realistic results, it is necessary to mold prototype parts using the intended production material. This typically involves building a single (unit) cavity tool for smaller parts or soft (often simplified) tools for larger parts.

The prototyping process can take a great deal of time and money; however, it is best to detect manufacturing or end-use performance problems with a unit cavity or soft tool, rather than a multi-cavity, hard production tool.

Steel safe practices should be followed to minimize the cost of tool rework.

While molded prototypes provide the type of information that is required to verify engineering functions and manufacturing, other more easily fabricated prototypes (rapid prototypes, etc.) can be produced very quickly (within hours or days) and provide invaluable hands-on models for communication and limited functionality long before the prototype tool is built.

Once the prototype tools and parts have been evaluated and modified as necessary, pre-production or production tools are built.

To save time, it is common to begin the more basic work on the production tools long before this point in time. Once the tools are built and debugged, the part goes into the initial stage of manufacturing.

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