Guide to Designing and Cost Reduction Tips in Injection Molding

 

At Creatingway, we follow a few practical guidelines in designing the common features of injection molding. These features are key to improving the functionality of our designs. There are also a few cost reductions tips that our team of experts has come up with to aid in minimizing the cost of production. Here is further insight into these tips.

What’s The Common Design Features For Injection Molding?

• Threaded fasteners (Inserts and Bosses)

There are three ways that we use when adding fasteners to an injection molded part. These are namely adding a boss to where the screw attaches, directly adding a thread on the part. We also include a threaded insert. Though modeling a thread directly on to part is possible, we do not usually recommend it like the teeth of the thread are undercut. The process drastically increases the complexity and cost of the mold. One common example of a part with a thread is a bottle cap.

• Bosses

It is a component of injection molded parts that provides a point of attachment or assembly. It comprises basically of cylindrical projections with holes that are receptive to threaded inserts, screws, and other types of assembly or fastening hardware. You can picture it as a rib that closes itself in a circle. When utilizing bosses as points of fastening, we recommend that the outer diameter be at least 2x the diameter of the insert or screw while its inner diameter is equal to the core of the screw. Even if the full depth is not key for assembly, the hole of the boss should extend to the base-wall level, to maintain a uniform wall in the entire feature. We occasionally add a chamfer to ease the insertion of the insert or screw.

• Threads

We add threaded inserts to plastic injection molded parts to provide a durable threaded hole for fasteners like machine screws. The benefit of using inserts is that they allow us to perform many cycles of assembly and disassembly. We install inserts by using thermal, ultrasonic, or in-molding insertion. The diameter of the insert is a key determinant that guides us in designing bosses that will receive a threaded insert.

• Ribs

We use ribs to improve the stiffness of a wall, even when the maximum ideal wall thickness is not enough to meet the functional requirement of an injection molded part. The ribs should be equal to 0.5 x main wall thickness, use a base fillet with a radius greater than o.25 if the rib thickness and you should add a distance between ribs and walls that is 4x the rib thickness.

• Snap-Fit Joints

It is a simple, rapid, and economical way that we use to join two parts without the use of tools or fasteners. There is an array of design possibilities that exist for snap-fit joints. The rule of thumb states that the deflection of a snap-fit joint depends mainly on the permissible force that applies to its width and its length. We consider snap-fit joints as an example of an undercut, with the most common one being the cantilever snap-fit joint.

• Cost Reduction Tips

The following guideline provides insight into the main cost determinants in injection molding and actionable design tips that aid us in minimizing reduction costs.

• Cost Drivers

The most important cost in injection molding are:

• Tooling costs; that arise from the total cost of machining and designing the mold.
• Production costs; that is the sum of the time the injection molding machine uses up.
• Material costs; come from the volume of the material and its cost per kilogram.

Tooling costs are generally constant as it is independent of the total number of parts under production, while the production and material costs are heavily dependent on the volume of production. For smaller production volumes, the tooling cost is the major determinant of the overall cost. We, therefore, make necessary adjustments when dealing with simplifying the manufacturing process. Some of the measures we choose to incorporate from time to time are namely,

• Sticking to the Straight-Pull Mold

In-mold mechanisms such as side-action cores significantly increase tooling cost by 15% to 30 %. We thus choose to avoid using them unless it is necessary.

• Redesigning the injection molded parts to avoid undercuts

Undercuts often increase the complexity of a part which translates to more costs. Redesigning may eliminate undercuts.

• Fitting Multiple Parts in a Single Mold

Normally, six to eight identical parts that fit into the same mold reduce total production time be 80%

• Minimizing Part Volume Through Reduction of Wall Thickness

It usually translates to the use of less material and also accelerated the injection molding cycle.

By looking at the steps we take to cut our cost of production and the design of common injection molding features, you will see that Creatingway is ideal for your injection molding needs. Contact us today if you have any further inquiries.

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