Injection molding design: what common mistakes to prevent

[Marian Wang]

Injection molding design: what common mistakes to prevent

[Kanye Z]

Is widely used in a wide range of industries, from large-scale consumer product manufacturing to smaller-scale manufactures of big components like vehicle body panels.

Tool or mold, often made of hardened steel or aluminum, is used in the procedure. An exact replica of your final product is created in a precision-machined mold. The thermoplastic material is then fed into the barrel, mixed, and pressed into the metal mold cavity. injection molding is an excellent method for producing large quantities of consistent and high-quality components at low costs.

When designing for injection molding, industrial designers, engineers, and product designers may encounter difficulties. In order to create injection molded components that perform well, designers should avoid the following three blunders.

Walls That Aren’t Even
Injection molded parts typically have a wall thickness of 2mm to 4mm as a minimum (.080 inch to .160 inch). Because the molten plastic does not have to be pushed through varied constraints as it fills the mold cavity when parts with uniform wall thickness are used, the cavity may fill more accurately.

The thinner areas of uneven walls cool first. Stresses develop at the junctions of the thin and thick walls when the thicker parts cool and shrink. Because the thin piece has already hardened, it resists the tension. Warping and twisting of the component can occur as the thick parts yield, which can lead to fractures.

If it is difficult to have consistent wall thicknesses due to design constraints, the shift in thickness should be as gradual as feasible. In order to keep the wall portions consistent, a procedure known as coring might be used. As an alternative to using gussets, support structures can be included into the component itself.

It is easier to take out parts when you do not use mold drafting. The draft angle must be offset from the mold opening and closure. If the part is deep enough in the mold or has a certain end-use function, it affects the optimal draft angle.

It is best to allow the mold to have as much draft as possible, so that components may be readily removed from it. Most of the time, one to two degrees of drafts with an extra 1.5 degrees for every 0.25 mm of texture depth are sufficient. In order to keep the draft to a minimum, the mold portion line must be placed in such a way that it divides.

Pointy Ends
Sharp corners enhance stress concentration, which can lead to part failure if the stress concentration is high enough. Sharp edges can often be found in locations that aren’t evident, such as a boss linked to a surface or a rib that provides additional support.
As the radius of the sharp corner changes for a given thickness, care must be taken to monitor stress concentration. When R/T is less than 0.5, the stress concentration factor is large; however, when R/T is greater than 0.5, the stress concentration factor decreases. At a minimum, an inner radius of 1 times the thickness should be required.

When molten plastic is poured into a mold, the radius of the fillet reduces stress and makes the process more efficient. The proposed inside radius is 0.5 times the thickness of the material, while the outer radius is 1.5 times the thickness of the material. If possible, employ a larger radius in the design.

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