Draft refers to the angle of incline placed between the vertical surfaces of the plastic moldings and the mold opening direction. Draft is normally applied to facilitate ejection of the moldings from the mold. Product designers frequently avoid the application of significant draft, since it alters the aesthetic form of the design and reduces the molding’s internal volume. Even so, draft is commonly applied to plastic moldings to avoid ejection issues and extremely complex mold designs.
Draft angles on ribs must be carefully specified. In the previous rib design shown in Figure 2.3, for instance, a 2° draft angle was applied to facilitate the ejection of the molded part from the mold. In terms of product functionality, a lesser draft angle may be desired since this allows taller and thicker ribs with greater stiffness. Unfortunately, lower draft angles (such as ½ or 1°) may cause the part to excessively stick in the mold. This issue of sticking upon part
Table 2.13: Texture examples
Texture Image Texture depth SPI finish required
Sand 50 µm B
Leather 125 µm C
Netting 150 µm C
Wood grain 250 µm D
2.3 Design for Injection Molding
50 µm B
Leather
33
2.3.6 Draft
Draft refers to the angle of incline placed between the vertical surfaces of the plastic moldings and the mold opening direction. Draft is normally applied to facilitate ejection of the moldings from the mold. Product designers frequently avoid the application of significant draft, since it alters the aesthetic form of the design and reduces the molding’s internal volume. Even so, draft is commonly applied to plastic moldings to avoid ejection issues and extremely complex mold designs.
Draft angles on ribs must be carefully specified. In the previous rib design shown in Figure 2.3, for instance, a 2° draft angle was applied to facilitate the ejection of the molded part from the mold. In terms of product functionality, a lesser draft angle may be desired since this allows taller and thicker ribs with greater stiffness. Unfortunately, lower draft angles (such as ½ or 1°) may cause the part to excessively stick in the mold. This issue of sticking upon part
Table 2.13: Texture examples
Texture Image Texture depth SPI finish required
Sand
50 µm B
Leather 125 µm C
Netting 150 µm C
Wood grain 250 µm D
2.3 Design for Injection Molding
125 µm C
Netting
33
2.3.6 Draft
Draft refers to the angle of incline placed between the vertical surfaces of the plastic moldings and the mold opening direction. Draft is normally applied to facilitate ejection of the moldings from the mold. Product designers frequently avoid the application of significant draft, since it alters the aesthetic form of the design and reduces the molding’s internal volume. Even so, draft is commonly applied to plastic moldings to avoid ejection issues and extremely complex mold designs.
Draft angles on ribs must be carefully specified. In the previous rib design shown in Figure 2.3, for instance, a 2° draft angle was applied to facilitate the ejection of the molded part from the mold. In terms of product functionality, a lesser draft angle may be desired since this allows taller and thicker ribs with greater stiffness. Unfortunately, lower draft angles (such as ½ or 1°) may cause the part to excessively stick in the mold. This issue of sticking upon part
Table 2.13: Texture examples
Texture Image Texture depth SPI finish required
Sand 50 µm B
Leather 125 µm C
Netting 150 µm C
Wood grain 250 µm D
2.3 Design for Injection Molding
150 µm C
Wood grain
33
2.3.6 Draft
Draft refers to the angle of incline placed between the vertical surfaces of the plastic moldings and the mold opening direction. Draft is normally applied to facilitate ejection of the moldings from the mold. Product designers frequently avoid the application of significant draft, since it alters the aesthetic form of the design and reduces the molding’s internal volume. Even so, draft is commonly applied to plastic moldings to avoid ejection issues and extremely complex mold designs.
Draft angles on ribs must be carefully specified. In the previous rib design shown in Figure 2.3, for instance, a 2° draft angle was applied to facilitate the ejection of the molded part from the mold. In terms of product functionality, a lesser draft angle may be desired since this allows taller and thicker ribs with greater stiffness. Unfortunately, lower draft angles (such as ½ or 1°) may cause the part to excessively stick in the mold. This issue of sticking upon part
Table 2.13: Texture examples
Texture Image Texture depth SPI finish required
Sand
50 µm B
Leather 125 µm C
Netting 150 µm C
Wood grain 250 µm D
2.3 Design for Injection Molding
2.3.6Draft
Draft refers to the angle of incline placed between the vertical surfaces of the plas- tic moldings and the mold opening direction. Draft is normally applied to facilitate ejection of the moldings from the mold. Product designers frequently avoid the application of significant draft, since it alters the aesthetic form of the design and reduces the molding’s internal volume. Even so, draft is commonly applied to plas- tic moldings to avoid ejection issues and extremely complex mold designs.
Draft angles on ribs must be carefully specified. In the previous rib design shown in Fig. 2.5, for instance, a 2° draft angle was applied to facilitate the ejection of the molded part from the mold. In terms of product functionality, a lesser draft angle may be desired since this allows for taller and thicker ribs with greater stiffness. Unfortunately, lower draft angles (such as ½ or 1°) may cause the part to excessively stick in the mold. This issue of sticking upon part ejection can be compounded when molding with mica- and/or glass-filled materials that have low shrinkage and high surface roughness. As such, the allowable draft angle is a complex func- tion of the material behavior, processing conditions, and surface finish.
Table 2.3 Draft Examples
Surface finish Resin Roughness (µm) Draft
Class A1 Acrylic 0.01 0.5°
Class B3 ABS 12 1.5°
Sand texture 20 % GF PC 12 2°
Leather texture Soft PVC 125 4°
Leather texture ABS 125 7.5°
A minimum draft angle of 0.5° is normally used, with 1 to 2° commonly applied according to material supplier recommendations. Rough and textured surfaces typically require additional draft, with an additional 1° of draft commonly applied per 20 μm of surface roughness or texture depth. Table 2.3 provides some recom- mended draft angles for a few different surface finishes and materials; the recom- mended draft angle increases with the surface roughness. With respect to the material properties, the draft angle should increase for glass-filled and/or low shrinkage materials but may be decreased for highly flexible materials such as soft PVC.
39
2.3 Design for Injection Molding