Our Engineers Specialize in Plastic Product Design

Designing plastic components is fundamentally different from designing other products, and surprisingly few engineers are truly experienced in this field.
Plastic component design requires the accumulation of unique know-how such as the following:

■ Know-how on Dimensional Accuracy of Plastics
Unlike metal parts, plastic parts cannot be defined with strict dimensions. With injection molding, molten plastic is poured into a mold. As plastics shrink by roughly 0.2% to 1.5% when solidifying, even highly accurate molds cannot guarantee precise dimensions. Plastics are also greatly affected by temperature changes. On the other hand, plastics are flexible with unique spring elasticity, meaning that parts may still fit even with slight interference. Designers must know how to prioritize which dimensions truly matter.

■ Know-how in Selecting Plastic Materials
Plastic materials vary widely, with differing properties and shrinkage rates. Selecting the right material is far more complex than with metals. Beyond theoretical knowledge, extensive practical experience is critical for material selection.

■ Know-how in Shapes Specific to Injection Molding
Since most plastic parts are produced by injection molding, designers must follow certain molding rules, such as: avoiding uneven wall thickness, providing draft angles, and specifying gate positions. Designers must not only know these rules but apply them effectively.

■ Know-how on Plastic Molds
Even if a design seems feasible in theory, the mold structure required may render it impossible. For example, some slide-core designs cannot be manufactured due to clearance issues. Understanding mold construction and the molding process is essential.

■ Know-how on Mass Production Issues (warpage, distortion, etc.)
Even if the mold is correct, plastic parts often warp or distort during production. Designers must predict these issues and incorporate countermeasures into the design, such as ribs to reduce warpage or assembly structures that counter deformation.

Only with such know-how can plastic parts be designed and manufactured smoothly.

In practice, plastic part design and production often face problems such as the following. Without anticipating them, countermeasures cannot be planned. Below is a summary of potential defects and solutions.

Problem	Example	Solution
Mold dimensions were fundamentally incorrect.	・Wrong shrinkage rate set in mold machining. ・Machining tolerance exceeded JIS standards. ・Dimensions misinterpreted during machining.	Rather than blaming individuals, the root cause must be identified and corrected using the least costly method.
Part is deformed.	・Long flat parts twist or warp. ・Box walls collapse or spread. ・Rod-shaped parts bend.	Deformation can be corrected at design, mold, molding, or post-processing stages, but earlier intervention is more effective.
Function cannot be met for unknown reasons.	・Waterproofing or acoustic performance fails. ・Design not fully reflecting product requirements. ・Design intent not translated into mold-making.	If discovered after mold completion, fixing is difficult and costly. Sometimes mold modification suffices, but severe mismatches may require remaking the mold.
Tactile/fit function not met.	・Parts don’t assemble despite no major individual defects. ・Movable parts are too tight. ・Locks or gears don’t engage.	Tactile adjustments require iterative trial molding and fine-tuning of part designs. If mold structure doesn’t allow adjustment, it becomes very difficult.
Assembly issues occurred.	・Button feel ・Lid closure ・Lock engagement	Often caused by cumulative tolerances. Reviewing assembly sequence usually resolves the issue.
Final product appearance unsatisfactory.	・Cheap appearance overall. ・Minor finishing flaws noticeable. ・Movements feel flimsy.	Improved by adjusting material color, sharper product definition, and reducing hollow sounds through thickness adjustments.

Manufacturing inevitably involves challenges. Unlike trading, where defects can simply be rejected, when producing products oneself, pushing responsibility onto others doesn’t solve issues. Strong collaboration and willingness to resolve problems are essential. Ultimately, costs from additional work must be shared fairly through discussion. Understanding this process gives insight into the true difficulty of manufacturing.