Injection molding is a well-known manufacturing procedure perfect for easily creating proper tools and equipment using complex shapes without having much waste of material. Typical applications include packaging, mechanical parts like gears, automotive dashboards, and also popular kids’ toys.
Several different processes fall under the types of injection molding, including two shot injection molding as well as over-molding. However, these two procedures have a few primary distinctions — here’s what designers and designers must know.
What is injection mold used for?
Before we talk about two-shot molding and overmolding, let us learn what is the purpose of this procedure.
Injection molding is the process of manufacturing which allows for the parts/components to be manufactured in more significant volumes. It functions by injecting molten substances into the mold. It is generally used as a process of the mass production process for manufacturing thousands of like items.
Let’s talk about Two-shot molding.
The process of Two-shot molding, also referred to as multi-shot, dual-shot, or double-shot molding, is a subset of injection molding, allowing engineers to make multi-material or multi-coloured parts by leaving out the addition of extra assembly steps.
This molding process is perfectly understood in terms of the various layers of colours or materials which the injection molding machine has created.
The initial material is first injected into a mold for creating the substrate. Around this, the other substances or substances are going to be molded. Before it is transferred, it is allowed to substrate solidified and cooled — using the robot arm, one’s hand, or rotary plane — to the various cavities of the mold.
Now, the mold is opened, and the side having the substrate is rotated 180° for meeting the different chambers of the mold and the injection molding nozzle. The substrate, once placed, the second substance is injected into the mold, and it binds with the substrate forming a firm hold.
Once the next layer cools, the last part is ejected. Engineers must know that this process of molding can either be sped up or slowed down depending upon how the substance is transferred to the different chambers of the mold.
Robot arm as well as hand transfers is going to take a longer time than the rotary plane, however rotary platen molding is more costly, and typically only an effective alternative for large volume product runs. Along with that, molds need to be made out of elements that will immediately bond mutually and that the mold will align precisely, preventing damages in part.
Benefits and limitations of two-shot molding
Two-shot injection molding is an effective and pocket-friendly manufacturing process. This procedure also provides extremely durable terminal components and assemblies.
From the point of view of designing, two-shot molding offers designers a huge amount of flexibility as this process can generate complex geometric frames and change to multiple colours for producing more lovely parts.
Additionally, since one machine produces the complete part, no post-processing is needed, and engineers can adequately reduce the manufacturing time, therefore reducing the manufacturing costs.
But it must be noted that the first two-shot molding apparatus may be expensive, and a two-shot molding machine is more costly than any conventional injection molding machine. Luckily, these costs are generally offset by savings of labour costs and assembly costs toward large-scale product runs.
Let’s talk about Over-molding.
Over-molding, similar to two-shot molding, is a process of multi-shot injection molding that provides a single end product arising from two or several various thermoplastics. This procedure is perfect for engineers to build functional, robust, aesthetically pleasing tools that will not separate over time.
To start the process of over-molding, an engineer or designer injection molds a substance out of the extra rigid over molding material. Insert mold into the molding device. Now, the substrate is set in an over-mold device or over-molding cavity within that equipment.
The molten over-molding substance is then ejected onto, into or in surrounding areas of the substrate. Once the molten material has cooled, the substrate, as well as the over-mold, are mechanically or chemically bonded. The whole overmolding process could take as less as 30 seconds.
Compatibility usually is not a problem with mineral substrates as they could be used along with any synthetic over-mold. However, product teams could encounter issues of compatibility when they are over-molding plastic materials with plastic. The final product could be deformed or poorly bound in case the substrate and over mold isn’t compatible.
However, in case, two plastics having less-than-ideal compatibility should be used. In that scenario, teams could design features of mechanical bonding into the various parts after the fact. Still, this is going to result in more significant costs.
Benefits and limitations of over-molding
Over-molding and two-shot molding share several similar advantages. Both the processes are ideal for quickly creating reliable, durable, and vibration-resistant components having complex geometries. However, over-molding is wholly suited for low-volume product runs.
In comparison to two-shot molding processes, over-mold designs are quicker to make as engineers are able to use any of the conventional injection molding machines for working out this process.
Regarding limitations, the tolerances of components made through over-molding are usually secondary to those obtained with the two-shot injection molding process. It’s also vital to consider that plastic compatibility conditions can compel designers.
Choosing between the two processes
Two-shot injection molding and overmolding are both efficient and straightforward procedures for making durable components made of two or several materials or two or more extra colours.
To choose between them, engineers must reflect on the size of their production run.
Two-shot injection molding ordinarily only makes sense for greater production runs. However, over-molding is ideal for low volume production run.
However, teams must still do their due evaluation and diligence to check all critical conditions of all potential manufacturing procedures against the particular project needs for ensuring the choice that they are making.
With the help of injection molding the process of equipment making has been made easier. One can choose from the two methods stated above, according to the needs of the company.
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