KIA ES05224-00 Commercial Tolerance - Plastic Molds

The standard “KIA ES05224-00 Commercial tolerance - Plastic molds” developed by Hyundai-Kia Motors Company, the oldest motor vehicle manufacturing company in Korea, stipulates the tolerance of dimension not specified by number or symbol between plastic parts molded by injection molding and finished by coating, plating, hot stamping, vacuum coating and other finishing processes. This standard is also applicable to compression molding (stamping molding) and foam products.

Tolerances for general dimensions must be in accordance with the table titled “Length tolerance” given in the standard. Tolerances for basic angle (division) and squareness must be in accordance with the table titled “Angle tolerance” given in the standard. At the same time, the tables titled “Material classification” and “Dimension classification” are applied to the material division and size classification specified in the first table, respectively.

In the table titled “Material classification” the classification is made as follows:

• Type 1: Urea resin, phenol resin, ABS resin, acetyl cellulose resin, poly carbonate, acrylic resin, ace resin, melamine resin, polyacetal, soft vinyl chloride resin, polysulfone (a high precision product can be obtained).
• Type 2: Polyamide, polypropylene, polyethylene, PBT resin (a normal level of product can be obtained).

In the table titled “Size classification” the classification is made as follows:

• A: Size determined directly by the mold:
  • Overall size
  • Distance between centers
• B: Size not directly determined by the mold:
  • Distance between centers determined by combination of molds
  • Distance between added patterns
  • Dimension crossing the dividing line
  • Size determined by combination of split patterns
  • Side wall thickness or corresponding dimension

Drawing specification method: Commercial tolerance is basically specified in a certain part of the title of a drawing as shown in the figure given in the standard or it is specified in writing in a part of the space for importance in a drawing.

The characteristics of plastic molding products and the mold shrinkage allowance that must be taken into account for the operation of this standard are explained in the standard as follows:

• Characteristics of plastic molding products: The dimension level of plastic molding products is different from the dimension level of molding parts, and may be different by various elements, as shown in the following explanation. Accordingly, if precision is required, it is mandatory to consult with the material and technology sector and specify the dimension in the drawing using the dimension specified in the “Analysis table” fish table.
  • Since the linear expansion coefficient of plastic material is 5-10 times larger than that of metal material, the level of dimensional change depending on temperature is high.
  • Although the hygroscopicity of plastic materials is generally small, there are materials with high hygroscopicity, such as polyamide (nylon) and cellulose acetate plastic. These materials have a high degree of dimensional change due to moisture.
  • In the cooling process after molding, plastic molding products have post-shrinkage phenomenon, with the molecular orientation being relaxed. Especially the effect on highly oriented materials such as polypropylene and polyethylene is significant, which will lead to a large change in size.
  • Since crystalline resins such as polyethylene, polyamide and polypropylene have directional properties related to crystallinity and molecular orientation, it is easy to have any warping in the molding products.

Since the size specified in this table is close to the allowable molding limit, it makes sense to specify a slightly larger size instead of using the actual size. The tolerance of a part where the size is not directly determined by the mold is determined by adding plus/minus 0,10 to the value in the table.

• Mold shrinkage allowance: Plastic molding products are provided with mold shrinkage allowance to facilitate the removal of products from the mold. However, its setting and operation should be determined by considering the following factors:
  • Technically, the mold shrinkage allowance varies according to each size, shape and material of the molding products, but generally the size in the analysis table is applied.
  • The value of mold shrinkage allowance can be added to the tolerance of the dimensions of molding products.

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