1. 2.3 Ribs Ribs are often used to enhance the plastic part strength and stiffness without a thicker wall. Ribs could also improve material flow conditions during molding Air bubbles Fig 1-3 adding ribs to reduce wall thickness Fig 1-3(a)shows a thick and uneven wall design. Fig 1-3(b) shows a wall design of even thickness It saves material and enhances its strength and stiffness while avoiding air bubbles shrinkage cavities dents and warpages. Rib dimensions are shown in Fig. 1-4. Their thickness is usually smaller than the wall thickness When considering adding ribs to a plastic part design, the focus is to minimize the concentration of the material in an area, to avoid air bubbles and shrinkage cavities. Fig. 1 -5 shows a rib arrangement Fig 1-5(a) shows an undesired arrangement where material concentrates in one area. Fig 1-5(b)shows a better arrangement. Rib should not be too big; they should be short and more in quantity. The distance between ribs should be equal or greater than twice the wall thickness. As shown in Fig. 1-6, a good lesign can avoid shrinkage cavities and increase part strength and stiffness. The orientation of rib arrangement should be in line with the material flow direction, to ease filling out the cavity and to avoid disturbing the flow. There should be a gap between rib's end and the part support surface <(0.50. R=t/81.2.3 Ribs Ribs are often used to enhance the plastic part strength and stiffness without a thicker wall. Ribs could also improve material flow conditions during molding. Fig.1-3: adding ribs to reduce wall thickness Fig.1-3(a) shows a thick and uneven wall design. Fig.1-3(b) shows a wall design of even thickness. It saves material and enhances its strength and stiffness, while avoiding air bubbles, shrinkage cavities, dents and warpages. Rib dimensions are shown in Fig.1-4. Their thickness is usually smaller than the wall thickness. When considering adding ribs to a plastic part design, the focus is to minimize the concentration of the material in an area, to avoid air bubbles and shrinkage cavities. Fig.1-5 shows a rib arrangement. Fig.1-5(a) shows an undesired arrangement where material concentrates in one area. Fig.1-5(b) shows a better arrangement. Rib should not be too big; they should be short and more in quantity. The distance between ribs should be equal or greater than twice the wall thickness. As shown in Fig.1-6, a good design can avoid shrinkage cavities and increase part strength and stiffness. The orientation of rib arrangement should be in line with the material flow direction, to ease filling out the cavity and to avoid disturbing the flow. There should be a gap between rib’s end and the part support surface. Fig.1-4 Rib dimensions Air bubbles < (0.5~0.7) t < 3 t t R = t / 8