Insert molding is a type of injection molding with properties similar to overmolding. This method is widely used in various industries to create highly functional components. Engineers and product designers use the insert molding design guide to ensure the efficient combination of plastic parts and threaded metal inserts.
This article examines the insert molding technique and its processes. We will then provide detailed insert molding design guidelines to assist you in getting the best results from the process. Let's get right into it!
Insert molding uses threaded inserts to strengthen plastic components' mechanical properties and functionality. Instead of repeated assembly, it provides an effective method of fastening these materials together. Here's an overview of the insert molding process.
Insert molding requires high-end molding machines for product production. These machines are usually vertical and are specifically designed for insert injection molding. The machines also come with injection molding design guidelines that the engineering team must follow.
Based on the part design, the machine must be set to the desired specifications. The insert molding machinery has tight tolerances, ensuring the accuracy of the manufactured parts. A minor error in the injection molding tolerances can fail such a product.
Several inserts are available for use in the engineering design of molded parts. Plastic molding inserts are commonly made of stainless steel, brass, or regular steel. Threaded surfaces are widely used on these molds to improve adhesion to the product. The molds are positioned vertically in the machine by CNC machining or hand. The components are inserted into the mold using robot arms during the automated insertion process. As a result, efficiency, consistency, and precision are guaranteed. Furthermore, computerized machines are faster and can withstand higher temperatures during molding.
On the other hand, hand insertion is an excellent choice for low-volume production. This procedure ensures the presence of a full-time operator to perform detailed part inspections. However, hand insertions may have an impact on precision and repeatability. It may also be an issue for operators because of the high temperature of the molding process. After inserting the mold, gravity will help it maintain its position during the insert molding process. The molten plastic can now be injected into the mold and closed. The injection is performed under high pressure to force the molten plastic resin into all mold parts. As a result, it ensures that the plastic adheres entirely to the inserts.
The next step is molding. The molten plastic enters the cavity and covers the precisely placed insert. Maintaining a constant temperature during the molding process is essential to ensure uniform solidification. Maintaining holding pressure will also help to reduce shrinkage and prevent backflow into the barrels. The molding cycle time is determined by the materials used and the size of the intended component.
You need to understand the insert molding design guide. These are some of the essential factors to consider in your design:
The volume of production determines whether the manufacturer uses automated or manual loading. The automatic loading is more efficient and precise. However, it requires the use of highly advanced CNC machines, raising injection molding costs. As a result, selecting the proper loading includes performing a cost-benefit analysis and understanding the requirement for the production.
It is essential to consider the project budget for cost-sensitive parts. The budget includes the cost of the inserts and the cost of contracting a manufacturing partner. When inserts are added, the price of molded parts increases, which is another cost element to consider.
Another factor to consider when designing an insert mold is the depth and size of the parts. They are essential in determining how long a molding process will last. Some parts will require a new design and mold, increasing cost and manufacturing time. You can use rounded knurling inserts since it has no sharp corners.
This is one of the essential factors to consider when designing an insert mold. Although insert molding is compatible with several materials, knowing the best material for different applications is still essential.
Product teams should follow standard DFAM best practices when making custom-molded inserts, like using rounded knurling, avoiding sharp corners, and making the most of draught angles. Undercuts, also called mechanical locks, add to the complexity and cost of any part. However, adding an undercut to the design of the insert mold gives the part more pull-out strength. A good rule of thumb when making inserts is to ensure they are small compared to the plastic part. The insert should generally go at least 0.016" (0.4 mm) into the mold cavity. To keep sink marks from appearing in the plastic, the molding under the insert should be at least one-sixth the diameter of the insert.
One common problem with this method is that the plastic around the metal inserts cracks after making it. If the molded-in hoop stress of the insert is not considered, the part's two parts can easily come apart as the injected resin shrinks and cools, ruining the part. It is best to use toughened, more durable resins because these materials have better elongation and breaking resistance properties.
Material bonding is another issue that often comes up with insert molding. Overmolded parts can use the chemical bonds between layers of different thermoplastic resins, but metal inserts don’t form chemical bonds with overmolded plastics. So, the metal and plastic parts must be made so that they can be joined together mechanically. One of the main benefits of molding threaded inserts into plastic parts is that it can improve the part's mechanical properties. The metal makes the whole part stronger and more durable, which is useful for device shells and electronic housings. Metal bushings or sleeves can be put on mating parts to increase their resistance to wear and make them last longer.
Here are some of the most common insert molding materials available for use depending on the application of the final product:
Thermosets and thermoplastics are almost identical. However, these plastic polymers cannot be recycled or reused. Because thermosets are not economical or environmentally friendly, manufacturers hardly use them. These are some of the most common thermosets used for insert molding:
● Phenolic
This is a thermoset substance with high resistance to chemicals and electricity. It has exceptional hardness and dimensional stability and can withstand heat. Phenolic resins can create circuit boards, electrical equipment, etc.
● Epoxy
This type of thermoset undergoes processing without melting and then permanently hardens or solidifies. As a result, they are excellent candidates for complex uses. They adhere well and are highly heat- and chemical-resistant.
These materials repeatedly, they are environmentally friendly since they can be reused. They are perfect for ensuring variation and sheen in the insert molding process because of their excellent chemical resistance. These are some of the most common thermoplastics for insert molding:
● Polystyrene
Low melting point, clear, and lightweight plastic is polystyrene. Due to its resistance to base and acid can be used in commonly used products like consumer goods and medical equipment.
● Nylon
This thermoplastic polymer has a robust and sturdy construction by nature. Additionally, it is resistant to abrasions and chemicals. Due to its relatively high melting point, it can be used in various applications instead of metal. As a result, it is frequently required for heavy products used in extraction and manufacturing.
● Polyethylene
Along with being resistant to chemicals, this type of thermoplastic polymer is typically lightweight and extremely tough. Dielectric and impermeability characteristics are present. LDPE, HDPE, and MDPE are common polyethylene thermoplastic materials.
The elastomers are natural and artificial polymers that resemble rubber in some ways. Due to their excellent elasticity and recyclability, engineers use elastomers in various applications. They are best suited for making various plastic automotive and home appliances due to their eco-friendliness. Polyurethane and natural rubber are two examples of the more frequently used elastomer types:
● Organic Rubber
This resin is solid and adaptable. It can be used to make various household appliances and tires.
● Polyurethane
It has increased wear and tear resistance in addition to outstanding abrasion resistance. High impact resistance and elasticity characterize the plastic. In addition, it can endure higher temperatures than most materials because of this.
Insert molding eradicates the complicated process of putting together parts to make large parts without using different processes that could raise production costs. This method can be used with various materials and end-use applications. From this guide, you can see that the process can be hard to understand. So, you need a professional and dependable injection moulding partner like Ares Prototyping. We offer various insert molding services to ensure your parts meet all requirements.
Ares Prototyping can look at your design and give you an analysis and report on how it can be made. Just upload your design files to our online quoting platform, and we'll reply quickly. We make sure you get the best results with our dedicated engineering team, strong insert molding capabilities, and strict quality inspection standards. Contact us immediately, and we'll take care of your next project.
