Insert molding is a special form of injection molding used to embed plastic or metal parts (inserts) into the final plastic product. Some inserts, such as wood and metal reinforcement inserts, may only be used for structural support, but others will add functionality to the product, such as threaded inserts.
The exact technique used to embed components varies with the size and shape of the component, so it is important to choose the right technique to ensure stable, durable results. When done right, insert molding can produce stronger, more durable parts than injection-molded parts. It is also an extremely cost-effective and efficient process, making it a viable option for clients with a variety of budgets.
Whatever your motivation for choosing insert molding, our team at elimold will guide you through the selection of the best choice for insert type, material and manufacturing method to achieve the best results.
What is insert molding
Insert formed metal and plastic together into a formed part, or form multiple metals or materials together into a single formed part. We sometimes call it metal insert molding or metal screw/brass insert molding, and sometimes we also call insert molding overmolding.
Insert molding can be used in industries such as automobiles, cookware, household appliances, instruments, fixtures, knobs, electrical components, etc.
Not only does insert molding reduce assembly and labor costs, it is better than assembly parts, reduces part size and weight, increases part reliability, and provides improved part strength and structure, while enhancing design flexibility .
insert molding step
The first step in insert molding is to customize a tool to accept a solid component or part as an insert. The blade is placed in the tool and thermoplastic elastomer (TPE) is injected into the tool cavity, coating the blade in a smooth layer of plastic. After cooling, open the tool, remove the part and inspect it.
An insert can be a single part or assembly, or a combination of individual components that are carefully configured inside the tool and then sealed together with the plastic during the insert molding process.
This method of insert injection molding can actually yield greater strength, flexibility or functionality than joining individual parts individually in a post-production assembly operation. Secondary steps can often be reduced or eliminated entirely by insert molding, saving time and reducing production costs.
Insert molding process
The process is the same as the injection molding process, the same injection molding machine is used to inject the molten raw material into the plastic mold, then the plastic is solidified through a cooling system – then the press is turned on and the molded part is ejected, the difference is that before the mold is closed, we need Put the metal in the mold and start all the injection molding process like injection molding,
Insert molding uses the same materials as the injection molding process, except that metal or screws are added to the mold before closing the mold. For strong, use the same thermoplastic. The same mold steel, the same mold structure, the same molding machine, sometimes a vertical injection molding machine may be required for some special cases, but they are all injection molding machines for thermoplastics
Some injection molding manufacturers use vertical/vertical injection molding machines that utilize gravity to aid the insert molding process by holding the insert in place during mold clamping. Insert into place when closing the mold.
Most vertical insert molding machines have the ability to utilize multiple bottom mold halves for use with a single cavity half. When one bottom half is formed with the cavity half, the other bottom can be loaded with metal and other inert formed parts.
Cycle time is shortened as multiple lower halves allow inserts to be placed in one lower half while the other is in the forming step.
We excel at making inert formed parts. There are screw insert molding, metal insert molding, brass insert molding, etc. If you have any project that requires brass insert molding or any metal insert molding, please send us your requirements for a quote.
5 Advantages of Insert Molding
Inserts can be male or female. Inserts are used to make round fittings within the surrounding plastic. When these types of inserts have internal threads, they are called nutserts. There are many advantages to using male and female inserts to enhance the appearance and practicality of a product.
5 Advantages of Insert Molding:
Reduce molded part size
Since the metal insert of the molded part is molded with the plastic, the part size can be designed smaller compared to the assembled part, and the part weight will be less than the assembled part, which will reduce the material cost, which means saving with better results cost.
Reduce assembly and labor costs
Because insert molding is a single shot, but has two or more parts joined together in one end-molded part, this reduces assembly and labor costs, and only requires workers to put the insert into the mold during molding production , an insert or multiple inserts can be molded in one shot, more complex insert molded parts offer more benefits than insert molding.
Insert molding is formed together by a plastic molding process. As a result, each part is tightly molded with thermoplastic, and insert molded parts prevent loose parts, mismatches, misalignments, and other issues. Plastic resin provides better shock and vibration resistance.
Increase design flexibility
As a designer, you should be aware that it is a molding process using insert molding. Because we have this insert molding process, designers will save time thinking about how the parts will fit together. Heat fix metal parts and plastic parts together. How to save space for other components to make their design work process more efficient.
Save injection cost and improve work efficiency
Using inserts at the molding stage can sometimes make it more difficult for the operator to place the insert in the correct position in the mold than on a standard injection molding machine. Like some small metal parts or multiple metal parts or some inserts are easy to fall to the floor when putting the inserts into the mold, so the vertical injection molding machine is the most efficient, which will save a lot of time and injection cost.
Disadvantages of insert molding
While insert molding has many advantages, designers should be aware of some potential disadvantages.
The labor cost is higher when inserting manually.
Cycle times vary with manual loading. Why is this important? For plastic injection molding, the most important variable that must be carefully controlled to maximize cost savings is machine cycle time, or the time it takes to manufacture each part. If this time is variable, it is impossible to control costs or accurately predict product shipping dates. For relatively small volumes, say less than 20K per year, it still makes economic sense to use manual loading instead of investing in expensive automation. But as volumes increase, it will eventually become more cost-effective to use automation, which will pay for itself by effectively reducing labor costs.
The resin will shrink around the insert, causing it to crack. This is especially a problem for polycarbonate plastics. Later, we will discuss ways to solve this problem.
Due to molding pressure, resin is forced into the insert. When this happens, the excess flash must be removed in a separate step.
The tool design must be compatible with the blade. If the molds do not fit together properly when they are closed and under injection pressure, the molds can be damaged or destroyed.
When to use insert molding
You should consider insert molding for several main reasons. The first is that your product application requires robust mechanical fittings to hold two or more parts together, usually in an enclosure or enclosure. Threaded nuts are great for this, but there are also many types of snap-on connectors.
Insert molding is used to put rubber or plastic handles on metal parts, such as you might find on hand tools or kitchen knives. Insert molding is ideal for sealing wires and electrical connectors into permanent plastic enclosures that keep out dust and moisture.
Inserts should be used whenever the plastic case needs to be occasionally opened for repairs and then locked again, such as when performing routine maintenance or changing batteries. They cost a little more, but offset the cost by making a more durable end product.
Insert Molding Design Guidelines
Designers can face some unique engineering challenges when using insert molding. The advantages of increased strength and versatility must be weighed against the need for more careful design for manufacturing review. Here are some helpful guidelines to consider:
The biggest problem is shrinkage of the resin. This creates hoop stress around the joint, which can lead to cracking over time, especially if the part is under mechanical tension. Here’s how you can counteract this:
1.Use resin materials with relatively low shrinkage;
2.Use filler-reinforced resin material;
3.Surround the plug-in with a larger area of plastic;
4.Support inserts with bosses and stiffeners;
5. Preheat inserts before molding. This allows the resin and insert to cool and shrink together, relieving some of the stress between the materials.
6.Use a prefab insert with a knurled surface to help lock it in place.
7.Avoid sharp corners and use rounded contours to reduce stress.
8. Design the inserts so that they are slightly recessed. This helps avoid damaging the tool.
Suitable for insert molding applications
Many believe that insert injection molding is limited to standard compression limiters – metal cylinders are insert molded to create plastic covered parts and bolted to other components such as brackets or mounts (compression limiters hold the bolted load, preventing plastic creep or hoop stress).
However, other components that can be insert molded include bearings, custom stampings, flex circuits, and parts made from powdered metal or rubber.
Plastic Insert Molding Materials
Part of the flexibility of insert molding comes from its compatibility with a variety of materials. Reinforcing inserts are usually made of metal, but wood is a low-cost alternative that still offers some benefits. The molding material is usually a thermoplastic or elastomer selected for its physical properties.
Materials compatible with injection molding include:
4.Copolymer and homopolymer polypropylene
6.High Density Polyethylene/Low Density Polyethylene
11.Polyarylene ether ether ketone
Elimold has all of these materials and most other compatible plastics except rigid PVC.
Elimold professional insert molding manufacturer
At elimold we have our insert molding and injection molding services to ensure our approach is as affordable and efficient as possible. We use almost any plastic suitable for injection molding, and we make components of any size and in almost any volume. With our state-of-the-art presses, we can achieve tolerances as low as 0.005 inches, and our focus on precision makes us an excellent choice for industries such as aerospace, military, optics, medical, electronics, and more.
To discuss with our team the best insert molding process for your component, contact us today or request a quote.