What is Insert Molding?| Insert Molding vs Overmolding

 Insert Molding vs Overmolding: 

There are a couple of ways that plastic injection molding can be used to combine two (or more) materials into a single part. 

In today's Post, We are Going to Learn about  What is Insert Molding?| Insert Molding vs Overmolding. 

Read this post Till the End and you will get Useful pieces of Information to read after this post.

Do you know the difference between insert Molding and Two-shot Overmolding?

 How can this help a product developer?

Now here take a closer look at the advantages of insert molding and overmolding.

What is Insert Molding?

Insert molding is a process that allows the plastic to bond to an insert placed within a mold cavity. for example, 

We can add a threaded brass insert to a faceplate Add inserts to the cavity, injecting the cavity.

Incorporating parts into the molding process can eliminate assembly and reduce costs. use plastics metals ceramics or any material that can withstand the molding process.

 Place threads or secure wire connectors, knobs, controls, warnings labels, and electronics.

 Insert molding means placing one component the insert - onto a pin or other holding fixture inside of a plastic injection molding tool.

When the mold closes, thermoplastic resin is then molded around the insert, permanently sealing it into place. 

The insert is usually a small metal or plastic pieces like a threaded screw fitting or an electrical contact. 

By the way, threaded fittings are called 'nutserts' - and no, we're not going to make a pun about that.

 Using inserts in this way, especially for screw fittings, makes sense because.

 It avoids the need for extra drilling and tapping which takes time and money.

And inserts can also be used on thin-walled cases that otherwise wouldn't be thick enough to allow for a tapped hole. 

Most importantly, though, is the fact that insert molding works with conventional injection molding machines so there's no need to invest in equipment upgrades.

 Are there drawbacks to insert molding?

 There are a couple of concerns when using inserts. 

• First, if they're installed by hand it slows down production time which in turn increases labor costs.

•  Second, if holding strength is especially a concern then the plastic case might need to be designed so that it locks the insert in place.

•  And finally, it's possible that cracks can form around the insert due to stress.

This is because the resin shrinks while the metal does not. This is especially a problem with polycarbonate plastic. 

As a general rule of thumb, hand-loaded inserts only make sense if the annual production volume is low, maybe up to 20 to 50,000.

 Above those kinds of annual volumes, it probably makes more sense to invest in automation.

 It’s very common to have specialized End Of Arm Tooling for the robots on a plastic injection molding machine picking up and inserting Nutserts.

 Insert Molding vs Overmolding : Overmolding also known as two-shot, multiple material molding, two-shot, or 2K, which comes from the German “Zwei Komponenten”, is a type of plastic injection molding where a rubber or elastomer such as TPU or TPE is permanently.

Over-molded onto a more rigid plastic substrate.

Sometimes we can even mold one rigid material over another rigid material, just to get a two-tone effect.

Why do product developers use overmolding? 

Well, there are many potential advantages and applications. For example,

Overmolding can improve the appearance of many products.

 This is helped by the fact that the over-molded material doesn't need to be the same color as the substrate.

But instead can be a contrasting or complementary color.

 You'll often find this on toothbrush handles. Over-moldings provide texture that improves the grip and feel of the user. 

This is common on power tools or cooking utensils. Over-moldings can also reproduce a designer's logo or trademark image on the product.

 Functionally speaking, over-moldings offer electrical and thermal insulation, and they make air- and watertight seals for cases.

And the process can be used to encapsulate other components, holding them firmly in place to prevent mechanical vibration.

 How does overmolding work?

 Overmolding is done with a special injection molding machine that has two barrels.

One barrel typically holds a rigid thermoplastic, and the other has some form of elastomers such as TPE, TPU, or silicone. 

[8] But it's not just the machine that's unique - so is the design of the mold.

 In a conventional mold tool, there might be one cavity and one core, with the two halves together forming the final shape of the part. 

With over-molding, we typically have 3 halves to the mold tool. Three halves I hear you say?

 You heard that right, and as you may have guessed, I didn’t do well in mathematics at school. 

The two main types of automatic over-molding processes are known as Shuttle Molding and Carousel Molding. 

Both of these processes require 3 halves.

 The first two halves are the core and cavity that mold the substrate. This substrate remains on the Core Side of the mold, 

This “half” is shuttled or rotated around to meet up with a secondary Cavity Side. 

The mold is then closed, and the over-molding material is injected into the gap between the substrate and the second enlarged Cavity With a very low quantity of molding, 

We will often just make two completely separate molds, and hand transfers the substrate into the second mold for over-molding.

 What are the advantages of two-shot molding?

• The main advantage of two-shot molding is that the bond between the materials is very strong, often exceeding the shear strength of the TPE.

• This is helped by the fact that both materials are still hot and, in the case of a TPU, not fully cured when they're joined so they're effectively glued together.

•  Also, different Shore harnesses and colors can be mixed to achieve a variety of effects.

•  And the process is largely automated so it's ideal for large production runs.

 What are the drawbacks of two-shot molding?

 The design of over-molding mold tools is more complex, so it takes more time and costs more money.

Also, dedicated equipment is necessary, although it is possible to add an auxiliary "piggyback" barrel to convert a conventional machine to two-shot molding.

The most important consideration, however, is to make sure that your choice of elastomer is compatible with the thermoplastic substrate.

 For example, nylon, PEEK, ABS, and some other engineering grades can be difficult to form a good bond with. 

To deal with this it's possible to use plasma surface preparation and other treatments that help improve bonding.

 Remember, to get the best results, you need to work closely with your manufacturing partner in the early planning stages to optimize tool designs while also ensuring that you use the right materials and process parameters. 

We'll be back soon with another fascinating and fun-filled Post on Serious Engineering for serious engineers.

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