Designing Plastic Parts Through Injection Molding

While designing the parts, plenty of considerations should be taken into consideration to ease the manufacturing and assembly process. One of the manufacturing processes of plastic parts is injection molding and this could be considered while designing the plastic parts too. Through this article, we are going to be learning the planning guidelines we must always consider while designing plastic parts which undergo injection molding. 

Part Requirements in Plastic Design:

The first stage of the plastic part design is to know the necessities. Whether the part is exposed to any heat or radiation and what the loading conditions are on the part to the looks. It also includes the processing techniques/methods, and production quantity.

Wall Thickness Considerations in Plastic Design:

Thickness determines the strength of the part. It depends on both the material and geometry. normally increasing, the wall thickness increases the stiffness and reduces the deflection during impact. Also, the wall thickness shouldn't exceed the critical thickness, making it brittle. Higher wall thickness also increases the material cost and production time.

The flow of fluid depends on the wall thickness, and hence uniform wall thickness is provided. Fillets and chamfers should be accustomed make a smooth transition of the wall thickness when varying thickness is required.

Draft Angles:

The minimum draft angle should be added to any or all the parts including the ribs within the parts which eases the ejection process within the Injection Molding Process. The worth of the draft depends on the sort of fabric used and, therefore the form of surface finish required.

Part with a smooth surface requires less draft whereas the identical dispense with the external textures requires more draft. Providing less draft angle makes the ejection process harder because of friction between the molded part and also the mold ends up in wear enter the mold. This affects the scale of the part.

Adding a draft angle to the part reduces the wall thickness and therefore the rib thickness should be provided accordingly.

 

 

Undercuts in Plastic Design:

Undercut can be either internal or external. External undercuts won’t cause a problem as a further sliding component is utilized in the molding process to provide that feature. Whereas some design modifications must be in dire straits the interior undercuts for the simple manufacturing and ejection of parts.

One such example is the design of snap-fit features in any part.

 

 

Design of Ribs:

Ribs increase the structural stability of the part. Thickness, height, and placement are the few parameters that govern the right rib design. Because the draft is provided to the ribs too, the adequate thickness should be added to the ribs. To supply better strength to the parts, the placement of the ribs is most significant.

The first rib design won’t undergo warpage but whereas the second rib design will easily undergo warpage.

In the above part, a rib(red in color) of equal thickness to the geometry has been created. The identical one is supplied with the 0.5 deg draft inwards, which made the peak of the rib decrease. To counter this, extra thickness should be provided to support the draft angle.

 

 

In the above part, a rib(red in color) of equal thickness to the geometry has been created. The same is provided with the 0.5 deg draft inwards, which made the height of the rib to be decreased. To counter this, the additional thickness should be provided based on the draft angle.

 

Design of bosses:

Bosses that are created to have the screw should not be placed at the corner. Having the bosses at the corner creates the sink marks and thus it should be offset away from the corner and needs to be supported with the ribs. 

 

 

Molding Defects:

Common molding defects like warping, sink marks, and short shorts should be taken care of. Poor rib design and improper wall thickness cause these defects.

 

 

Lettering:

Molded parts also possess the manufacturer's name and logo as letters, numbers, and symbols. The depth and height of the letters should be a minimum of 0.5 mm which eases the mold machining process and also letters are readable. Having less size will make the machining tougher and better sizing increases the mold defects.

 

Tolerances:

Plastic parts are being employed in all told industries which demand high tolerances. Tolerance will get full of warping and shrinkage. To nullify it low-shrinkage materials should be used. The component should be analyzed to spot the distortion location and therefore additional relief should be provided. Always confine mind that high tolerances increase the assembly cost of the component and will be used only if required.