DESIGN FOR MOULDABILITY (PART 2)
Here we shall look in more detail at adding strength by the addition of ribs. In particular how ribs and bosses should be designed for both performance and appearance.
Here we shall look in more detail at adding strength by the addition of ribs. In particular how ribs and bosses should be designed for both performance and appearance.
Component Section = S; Draft per Rib Side = A = 0.5 – 1.5 Deg; Rib Height = H = <5 x S (usually 2.5-3 x S);Radius = R = >0.25 x S – 0.4 x S; Rib Thickness = X = 0.4 x S – 0.8 x S; Rib Spacing = 2 x S – 3 x S
Ribs can be used to increase the stiffness or strength of a component without increasing the overall wall thickness and so increasing the weight of the component. However, ribs can increase the risk of warping and appearance problems. For successful rib design the following guidelines should be followed:
Support ribs may be used as reinforcement for corners, side walls or bosses. The following guidelines should be adhered to wherever possible:
Bosses are usually incorporated to facilitate mechanical assembly. They can be designed to accommodate self-tapping screws, push-in or moulded-in inserts or used for ultrasonic welding. Therefore, the boss may have to withstand a variety of forces – tension, torsion, compression, shear and flexing.
Design suggestions:
Undercuts should be avoided if at all possible. Ideally mould tools should be straight open and close. In certain circumstances mouldings with slight undercuts can be ‘bumped’ off the core. The same results as an undercut can be achieved using certain design techniques. For some complex components, it may still be necessary to have side movements in the mould tool but it has to be accepted that this will increase tooling costs.
There are various alternative solutions that Rutland Plastics would be happy to discuss and advise on.
Click below to request a free Design Guide that covers all aspects of designing for injection moulding.
Cold Overton Road
Oakham
Rutland
LE15 6NU
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01572 723 476
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