What is injection molding? The process, benefits, and important tips!

 

Material products are widely used in many industries, from household appliances to medical equipment, auto parts and so on. Therefore, plastic injection molding is a manufacturing process widely used in various industries.

Injection molding is a manufacturing process in which a plastic polymer is melted and then cured under pressure in a preprocessed mold to form a specific shape. It enables the efficient production of Plastic Molded Parts with a wide range of shapes, including complex designs, at an affordable speed.

 

The importance of injection molding in manufacturing

Today's popularity of plastic injection molding in manufacturing is not surprising. Plastics are popular in many industries due to their affordability, durability, and wide range of functions. High-end plastics have excellent strength, excellent durability and flexibility, and pleasing aesthetics.

 

In addition, the availability of many recyclable plastic materials ensures environmental sustainability. Plastic molding technology takes place in closed industrial cycles, helping to minimize waste generation. In addition to being environmentally friendly, the process is cost-effective, highly flexible and precise. It ensures that products are manufactured in short cycle times.

Plastic injection molding process steps

Design of injection mold

Now that you've seen how injection molding has evolved and why it's so valuable in manufacturing, it's important to understand the step-by-step process to help you get the most out of your project.

 

1. Design the mold

Making a mold is a key step in the process. The machinist uses CAD design and CNC machining to determine the specifications of the die, including size, geometry, and surface texture.

 

The mould has been carefully designed to have the functions of cavity, core, gate, gate, runner, ejection system and moving parts. The cavity is the fixed part where the molten plastic is injected, while the core is the moving part used to shape the final part.

 

Manufacturers often use high-quality steel or aluminum to produce durable molds that can withstand multiple production runs. For short-term projects, 3D printing can help reduce production costs. This stage requires a high level of skill and precision, and rigorous testing and simulation is performed to ensure that the mold meets the specific requirements.

 

Mold design, manufacture, and approval are usually the most time-consuming stages of the injection molding process, and the initial cost can be quite high. Common types of die tools include:

 

Single cavity mould

This is the most basic mold type and involves the molding of only one part per injection cycle. It is suitable for small and medium-sized production. It also ensures better control of the process, allowing continuous operation of injection molding. In addition, the tool cost of the single-cavity mold is relatively low. Therefore, they are an excellent choice for applications with lower budgets.

 

Multiple cavity mold

Multi-cavity molds can produce multiple identical parts at the same time, which is very suitable for mass production. They can produce multiple parts in a single injection cycle, thereby shortening production time and reducing costs. However, these types of injection moulds are more difficult to manufacture and require larger tonnage machines. Therefore, the initial mold cost is higher compared to the single-cavity mold.

 

Although the initial cost of multi-cavity molds is higher, they contribute to cost savings in the long run. Therefore, they are an excellent choice for projects that require thousands to hundreds of thousands of units.

 

Overlapping pattern

Stacked die with multiple die plates arranged in parallel. They typically have up to four levels to ensure increased efficiency. Building stacked molds takes longer than conventional molds, resulting in higher initial costs.

 

However, manufacturers can reduce the clamping tonnage required per cycle to ensure lower operating costs. In addition, manufacturers can design laminated molds to accommodate multiple materials, resulting in increased efficiency.

 

2K injection mold

2K injection molds help manufacturers combine two or more different materials or colors to make a single plastic part. This technique allows the creation of customized components that meet specific functional and aesthetic requirements. The chemical bonding process of the connecting material contributes to the superior aesthetics and performance of the finished product. Overall, 2K injection molding is an advanced and versatile manufacturing process that enables unique designs and material combinations.

 

2. Choose plastic

Before starting the molding process, it is essential to select the plastic resin that best fits the desired part. Material and mold interactions must be considered when choosing, as some options may not be compatible with a particular mold design.

 

Testing the selected material using this tool is essential to ensure that the final product meets the desired properties. Different plastics have unique molecular structures that lead to different mechanical and thermal properties. These characteristics will determine whether the material is suitable for certain molds and products.

 

3. Install the machine

A key step in the molding process is the setting of the injection molding machine. Die installation requires meticulous attention to detail to ensure that the die is properly aligned and secured to the machine platen. It is essential to check the specifications of the machine to ensure that it can accommodate its size and weight before installing the die.

 

The machine platen shall be clean and free of debris or contaminants that may interfere with the molding process or damage the mold. When the machine is ready, the die is carefully placed on the platen and aligned with the nozzle of the machine. Correct alignment is required to ensure that the molten plastic resin flows evenly into the mold cavity, resulting in the production of high-quality parts with consistent dimensions.

 

Once in place and secured to the machine platen with bolts, fixtures, or other fastening mechanisms, operational testing is essential to ensure proper operation. Testing involves passing some molten resin through a forming machine to check the particles for blockades, leaks, or other problems.

 

Setting up an injection molding machine requires skill and expertise. Correct machine setup ensures that finished parts are of high quality and consistent, thus reducing the risk of mold or machine damage.

 

4. Injection molding process

There are many types of injection molding, including:

 

Plastic injection molding process

This is a continuous cycle consisting of several steps. After the mold was closed, the plastic resin was heated and fed into the machine. After applying appropriate pressure to the tool and screw, the sprue opens and the screw moves forward. The molten plastic was then injected into the mold to fill the mold.

 

Forming small plastic parts

When the melted plastic reaches the end of the bucket, the mechanic closes the gate that controls the injection of the plastic. The screw is then moved backward and a predetermined amount of plastic is inhaled, creating pressure in the screw for injection.

 

At the same time, the clamping pressure helps to keep the two parts of the mold together. Balancing the injection pressure and clamping pressure is essential to ensure that the part is correctly shaped and that no plastic escapes from the tool during the injection process.

 

Cladding molding process?

Cladding is a specialized injection molding technique that combines two or more different materials to produce a single finished part. Molding a base or substrate component, placing it in a mold cavity, and then overmolding it with a second material can produce a finished product with improved functionality, durability, and aesthetics. The hard plastic is usually the base material, while the second material is softer.

 

This secondary molding process is usually divided into two stages:

 

Molding the substrate or base component: The mechanic molds the first material, usually hard plastic, to the desired shape and size at this stage. Then, the base component is inserted into the second cavity to begin the cladding molding process.

Cladding with a different material: a second material, usually a softer and more flexible plastic or elastomer, is moulded on the base component at this stage. The second material combines with the first to form a strong, long-lasting finished part.

Insert molding process?

Insert molding uses prefabricated inserts placed in a die cavity and molded on plastic resin to fabricate finished parts. The insert molding process usually involves the following steps:

 

Create inserts: Inserts made of metal, ceramic, or plastic are made prior to molding. Their design enables them to be loaded into the cavity, and their adhesive coating facilitates their adhesion to the plastic resin.

Placing the blade into the cavity: The design of the insert molding involves specialized tools, clamps, and fixtures. They help to fit the blade into the cavity. The machinist places them precisely to ensure that they are firmly in place during the molding process.

Plastic resin molding: This step involves the injection of plastic resin into the cavity and molding on the insert.

5. Cool and solidify

After filling the mold with plastic, including its runner, runner, sprue, and other components, it is kept at a specific temperature to allow the material to solidify uniformly into the desired part shape. Maintaining the holding pressure during this period helps prevent backflow into the barrel and reduces the shrinkage effect.

 

Plastic molding process for custom parts

The holding pressure is essential to ensure that the plastic is properly packaged and shaped, resulting in a high-quality final product. The size and complexity of the part, the type of plastic used, and a number of other factors determine the holding time.

 

The screw is retracted after the pressure holding stage, releasing pressure and allowing the newly formed part to cool in the mold. At this stage, the part remains in the die and the die temperature is kept constant to ensure uniform cooling throughout the part.

 

The cooling time is essential to ensure that the plastic part solidifies properly and maintains its shape when it is released from the mold. If the part is removed too early, it may warp or deform, which can lead to injection molding defects. Depending on the size and complexity of the part, the time can range from seconds to minutes.

 

6. Parts pop out

After the plastic part cools, the mold opens and the thimble or top plate pushes the finished part out of the tool. The injection molded parts are placed in compartments or conveyor belts to await finishing. Finishes can be polished, spray-painted, or sprue removal. Polishing can help smooth out rough surfaces or defects on parts, while spray painting can add color to parts.

 

7. Inspection and quality control

 

General rules of thumb for injection molding processes

It is crucial to consider the right parameters before starting the molding process. Then, you'll find the right balance between performance, speed, and cost.

Injection molding design

Ensure that parts are designed with uniform wall thickness

Ensuring uniform wall thickness is a fundamental principle in injection molding design. Inconsistent thickness can lead to many problems. These include mechanical failures, such as stress concentration and microcracks propagating over time.