B-1-Design Preparation

There are many ways to produce products, why choose “plastic injection molding” ?? I see 3 reasons below after comparing several manufacturing processes:

  • Less Cycle time
  • Lower cost in long term
  • Simpler manufacturing process

Here are some principles (not limited) I will consider during design stage if we decide to produce a part with plastic injection molding process, many factors affect plastic-part design. Among these factors are: functional requirements, such as mechanical loading and ultraviolet stability; aesthetic needs, such as color, level of transparency, and tactile response; and economic concerns, such as cost of materials, labor, and capital equipment. These factors are discussed in this post.

Design Process

A successful plastic product design and production requires team effort and a well-developed strategy. When designing plastic part, your team should consist of diverse players, including conceptual designers, stylists, design engineers, materials suppliers, mold makers, manufacturing personnel, processors, finishers, and decorators.

As the designer, you shall consider these factors early in strategy development and make adjustments based upon input from the various people of design team.

Solicit simultaneous input from the various “players” earlier in product development, before many aspects of the design have been determined and cannot be changed. Accommodate suggestions for enhancing product performance, or for simplifying and improving the various manufacturing steps such as mold construction, processing, assembly, and finishing. Too often designs pass sequentially from concept development to manufacturing steps with features that needlessly complicate production and add cost.

Early input from various design and manufacturing groups also helps to focus attention on total product cost rather than just the costs of individual items or processes. Often adding a processing step and related cost in one area produces a greater reduction in total product cost. For example, adding snap latches and nesting features may increase part and mold costs, and at the same time, produce greater savings in assembly operations and related costs.

When designing and developing parts, focus on defining and maximizing part function and appearance, specifying actual part requirements, evaluating process options, selecting an appropriate material, reducing manufacturing costs, and conducting prototype testing. For the reasons stated above, these efforts should proceed simultaneously.

Defining Plastic Part Requirements

Thoroughly ascertain and evaluate your part and material requirements, which will influence both part design and material selection. When evaluating these requirements, consider more than just the intended, end-use conditions and loads: Plastic parts are often subjected to harsher conditions during manufacturing and shipping than in actual use. At least aspects of part and material performance in below shall be considered.

  • Mechanical Loading: Evaluate all types of mechanical loading including short-term static loads, impacts, and vibrational or cyclic loads that could lead to fatigue. Ascertain long-term loads that could cause creep or stress relaxation. Clearly identify impact requirements.
  • Temperature: material properties in plastics — impact strength, modulus, tensile strength, and creep resistance to name a few — vary with temperature. Consider the full range of end-use temperatures, as well as temperatures to which the part will be exposed during manufacturing, finishing, and shipping.
  • Chemical Exposure: Plastic parts encounter a wide variety of chemicals both during manufacturing and in the end-use environment, including tool releases, cutting oils, de-greasers, lubricants, cleaning solvents, printing dyes, paints, adhesives, cooking greases, and automotive fluids. Make sure that these chemicals are compatible with your selected material and final part.
  • Weather Resistance: Temperature, moisture, and UV sun exposure affect plastic parts’ properties and appearance. The end-use of a product determines the type of weather resistance required.
  • Appearance: Aesthetic requirements can entail many materials and part-design issues. Color play an important role. Plastics must often match the color of other materials used in parts of an assembly. Some applications require the plastic part to weather at the same rate as other materials in an assembly. In polymers, custom colors generally cost more than standard colors, particularly for small-order quantities. Photoetching the mold steel can impart special surface textures for part. Styling concerns may dictate the product shape, look, and feel, especially if the product is part of a component system or existing product family. Note all cosmetic and non-cosmetic surfaces. Among other things, these areas may influence gate, runner, and ejector-pin positioning.
  • Life Expectancy: Many functional parts need to meet certain life-cycle expectations. Life expectancy may involve a time duration, as in years of outdoor exposure, time at a specific set of conditions, such as hours in boiling water, or repetitions of an applied load or condition, Determine a reasonable life expectancy for your part.
  • Dimensional Tolerances: Many applications have features requiring tight tolerances for proper fit and function. Some mating parts require only that mating features have the same dimensions. Others must have absolute size and tolerance. Consider the effect of load, temperature, and creep on dimensions. Over-specification of tolerance can increase product cost significantly.
  • Process: Determine if your part design places special demands on processing. For example, will the part need a mold geometry that is particularly difficult to fill, or would be tend to warp or deform. Point out all potential issues may happen in the future process.
  • Production Quantities: The number of parts needed may influence decisions, including processing methods, mold design, material choice, assembly techniques, and finishing methods. Generally for greater production quantities, you should spend money to streamline the process and optimize productivity early in the design process.
  • Cost: Plastic-part cost can be particularly important, if your molded part comprises all or most of the cost of the final product. Be careful to consider total system cost, not just part and material cost.
  • Assembly: Address assembly requirements, such as the number of times the product will be disassembled or if assembly will be automated. List likely or proposed assembly methods: screws, welds, adhesives, snap-latches, etc. Note mating materials and potential problem areas. Be sure not to overlook any requirements relevant to your specific application. Also do not over-specify your requirements. Because components perform as intended, the costs of over specification normally go uncorrected, needlessly increasing component cost and reducing component competitiveness.

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