Product cost can be reduced by replacing metal parts with plastic. Other than cost, plastics offer various other advantages. In this article we will discuss advantages and disadvantages of plastic over metal parts.
Advantages of Plastic over Metal
Plastic materials are low in cost, weight and also have the advantage of low processing cost. Therefore industries are converting their metal parts in plastics. Plastic parts have the following advantages compared to metal parts.
High Strength and Toughness
Plastic has the advantage of higher strength to weight ratio. And they are very tough in nature. Therefore, plastic parts are lighter in weight compared to metal parts.
Superior Design Flexibility
Plastic parts are manufactured by flowing molten plastic in injection mold. This process has an advantage of manufacturing complex features, geometries and integrating multiple metal parts in one plastic part. Therefore it helps in reducing product cost.
Lower Weight and Material Cost
Thermoplastics parts are lighter in weight. Therefore plastic part weight and cost are less compared to metal parts.
Low Manufacturing Process Cost
Plastic parts are manufactured with injection molding process. Which has relatively lower cycle time. Lower cycle time helps in reducing plastic part manufacturing cost compared to metal parts.
No need for Secondary finish Operation
Metal parts require secondary finishing operations to achieve required aesthetics and corrosion resistance. Whereas plastics have inherent corrosion resistance properties and required aesthetic finish can be achieved during injection molding. Therefore plastics offer advantages of eliminating secondary finish operation.
Fasteners can be Eliminated
Plastics manufacturing process has advantages of Integrating assembly features in plastic parts itself. Assembly features such as snap are used to join plastic parts. As a result product assembly time and cost is reduced. Read this article for more details on snap joints.
Plastics are corrosion resistant and non-conductive in nature.
Reduced Waste / Scrap
Plastic parts are manufactured by flowing molten plastic in the mold. Whereas metal parts are machined from relatively larger blocks. Therefore plastic has the advantage of manufacturing parts with negligible wastage compared to metal parts. If production volumes are high. Plastic wastage during injection molding can be reduced by using hot runner injection mold.
Disadvantages of Plastics over Metal
Along with so many advantages, plastic parts have the following disadvantages as well.
Higher Initial Tooling Cost
Plastics have an disadvantage of higher injection molding tool development cost. Different parts require different injection molds. Whereas machined metal parts do not require special tooling.
Higher Lead Time for Tool Development
Injection molding tool development has longer lead time. But For smaller volumes Plastic Prototyping techniques are used to get samples quicker. Therefore plastic part has disadvantage of higher lead time compared to metal parts
Electrical and Thermal Conductivity
Plastics are not good conductors of heat. Therefore plastic parts can not be used where high heat and thermal conductivity is required. To solve this problem plastic parts are used in conjunction with metal parts.
Lower working Temperature Range
Plastics can not be used for very high and low temperature ranges.
Injection molding process is very difficult to control. If plastic parts design is not as per guidelines or process is not controlled, various Plastic injection molding defects are observed.
To sum up, Designers across various industries are reducing product cost by incorporating plastics parts. You can expect 25 to 30% cost saving with metal-to-plastic conversion.
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