Tips on Successfully Performing the Undercut Process of Injection Molding

Plastic injection molding utilizes thermoplastics and thermoset materials to produce plastic components for various products. At Creatingway, we widely use it in the manufacture of parts for commercial purposes. The Undercut process is a feature in injection molding that we utilize to prevent the abrupt dislodging of parts of the mold. An undercut is essentially a cavity, protrusion, or hole that is essential in the insert molding and over-molding processes.

 

What is an Undercut process of injection mold?

As aforementioned, it is a protrusion or cavity in a molded part that prevents the dislodging of the mold fill. We perform this by adding interlocking features or a latch to the part. There are various techniques that we utilize in the making of undercuts. Namely:

• Slide
• Slide Core
• Hand Load
• Cam

In order to form the appropriate shape, undercuts require an extra mold material or an internal core lifter. This is, however, only applicable when the undercut is on the inner side. Single-sided cores handle undercuts that are on the same side of the part. There are a variety of tips that we use to perform part modifications, which significantly improves the undercut process. These include:

• Parting lines
• Side actions
• Bump-offs

Parting Lines

It is one of the simplest ways we use when dealing with undercuts. We perform it by moving the mold’s parting line to intersect with it. In instances where we design the manufacture of the locking feature of the motor housing, we may need a round or square standoff. It is because of the draft on the outside part, which we normally adjust its draft angles achieves intersection with the standoffs. In some cases, we deal with multiple features similarly, by zigzagging the parting line to enable intersection with each feature. Factors that determine the parting line replacement and orientation include:

• Geometry
• Material flow

We thus must be careful by having Plan B, which is perpendicular side actions.

Side actions

Take, for instance, a tubular-shaped part, such as a hose barb. It is an awesome example where we use perpendicular side action in forming a hole that runs lengthwise like in control knobs or screwdriver handles. We often split the mold halves horizontally along the long axis of the part. When the molding cycle commences, the mold closes, and side action slides on an angled pin at a similar rate. This ensures they are seated shut at the same moment. As the mold opens, the side action again slides on the angled pin at a similar rate, which retracts it far enough for the undercut to free from the part on ejection.

We limit side-actions to 8.419 inches wide by 2.377 inches high and a travel distance that does not exceed 2.9 inches. Hence, at Creatingway, we produce a lot of molds using a multiple side-actions so that we do not encounter the limitation of one per mold. Similarly, factors like part size, complexity, and multi-cavity molds limit the size and number of side actions. Extensive research proves that side-action works best on rigid raw materials like nylon, polycarbonate, and acetal. Flexible materials are likely to stick to the cylinder upon retraction, which leads to its yanking out of the cavity.

Bumpoffs

We use it to manufacture mold lens covers, container caps, and other parts that require them to snap into place. Instead of using a side-action, we machine an insert that the applied undercut bolts into the mold where a pocket matches the dimensions of the insert. During ejection, we depend on the plastic material to compress and release the material from the undercut.

Bumpoffs are often smooth, well-radiused, not too radical, and the material is flexible. Excellent material choices include Low-density polyethylene (LDPE), Thermoplastic elastomer (TPE) and thermoplastic polyurethane (TPU).

Another important consideration is the ejection part, which must be adequate so that the parts do not damage the ejector system by poking through or into the surface of the part.

 

What’s the purpose of undercuts?

• Example of Medical Undercuts.

We often utilize undercuts in the manufacture of medical parts. Some key feature includes parts that use side action to unscrew from a part after the injection molding process to produce threads. We ensure the continuation of threads throughout the entire interior so that the interior hand load does not die lock.

• Undercuts in electronics for Consumers

Electronic device housings such as cell phone casings contain many undercuts. You should know that he holes on the side of housings are undercuts. The functional features include hinges, buttons, and portholes. Each undercut, however, adds complexity to the mold. If the space is inadequate, the hand load die locks permanently.

In summary, we at the Creatingway model our clients’ parts to suit their needs and intentions. We also help in the adjusting of designs to enable proper tool building and injection molding processes, especially in the case of undercuts. Feel free to contact us with any inquiries or quotes.

 

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