Plastic Parts Manufacturing Processes

Plastic parts can be seen everywhere in our daily lives, different plastic parts are made from different manufacturing processes and they replace glass in a lot of applications. But do you know how plastic parts are made? Today, In this article, KUSLA will help you understand all the plastic parts manufacturing processes and guidelines to help you select the right option for your application.

Types of Plastics

Plastic is a synthetic or semi-synthetic material that’s made of polymers. it is solid or elastomer at room temperature, and it can be heated during manufacturing to make it a fluid and molten liquid, then be shaped and molded into any parts. Plastics can be divided into “thermoplastics” and “thermosetting plastics” according to their characteristics.

Thermoplastics

Thermoplastics are plastics that can be deformed under external force after heating within a certain temperature range to form various shapes. These plastics are recycled and can be repeatedly processed by heating and cooling to get various molded and machined parts.

Common thermoplastic materials: acrylic (PMMA), acrylonitrile butadiene styrene (ABS), polyamide (PA), polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyether ether ketone (PEEK).

Thermosetting Plastics

Thermosetting plastics are cured after heat treatment or chemical reaction, and their cured form is irreversible at high temperatures. These plastics have high chemical and heat resistance after curing, as well as high strength and structural stability, and are not easy to deform.

Common thermosetting materials: Cyanate Ester, Epoxy Resin, Polyester, Polyurethane, Vulcanized Rubber.

What is plastic manufacturing?

Plastic manufacturing is the process of making various forms of raw plastic materials (powders, polymer pellets, liquid resins) into products of the desired shape. This process generally includes engineering, raw material preparation, ‌forming, ‌ machining, finishing, and assembly. ‌

Plastic Parts Manufacturing Steps

From nothing to a plastic part, there are several steps in the plastic manufacturing process. The main steps we summarize below:

Step 1: Material Preparation

The first step is Material preparation according to the properties of the parts. this step involves Polymerization, adding additives to adjust the color, strength, flexibility, resistance to heat and UV rays, and other properties of the plastic.

Step 2: Forming and molding

After the Raw materials are ready, Choose the right plastic manufacturing process according to the geometry of the part, either forming plastic sheets to have a secondary machining or molding the plastic parts directly.

Step 3: Secondary machining

Some parts are made based on plastic sheets such as plastic trays which means a second machining process such as thermoforming plastic sheets, bending plastic sheets, or CNC machining on plastic sheets is needed to manufacture the final plastic parts.

Step 4: Post Finishing

Once you finish making the geometry of the part, a post-finishing process is required to give the part the desired look and functionality. it includes mechanical assembly such as bonding, welding, and polishing and also surface finishing such as painting, coating, printing, and more. The type of finishing technique used will depend on the needs of the finished parts.

16 Types of Plastic Parts Manufacturing Processes

There are many types of Plastic Parts Manufacturing Processes today in the world, Here, we list the main 16 types of them below:

Injection molding

Injection molding is one of the most common plastic manufacturing processes, it involves injecting the molten plastic pellets through the injection machine into the mold, and then the plastic material is cooled and cured, finally forming the desired shape of the plastic product. The molding cycle of injection molding is short (a few seconds to a few minutes), and it can manufacture parts with complex shapes and inserts with high accuracy. Therefore, this method has strong adaptability and high production efficiency, it is perfect for mass-producing intricate, high-precision plastic parts.

Extrusion

Extrusion is a process in which plastic pellets are melted through an extruder and then extruded into the desired shape in a profile mold. Extrusion is mainly used to produce pipes, sheets, and profiles. Its advantages include good production stability, low cost, and the ability to achieve long and complex shapes.

Thermoforming

Thermoforming is a process that turns flat thermoplastic sheets into various products. The flat sheet is clamped on the frame and heated to a softened state, Under the external force created by mechanical pressure or a vacuum chamber, the plastic sheet is pressed close to the mold surface and forms a shape the same as the mold surface after cooling.

Vacuum casting

Vacuum casting, also called urethane casting, is a process that involves using the master part to create a silicone mold in a vacuum state, then Casting urethane and other materials through the silicone mold to clone the same replica as the master part. this process is great for manufacturing plastic prototypes and small batches of plastic parts.

CNC machining

CNC machining belongs to the second machining process that works on a plastic block cut from a plastic sheet. it uses computer-controlled high-speed rotated tools to remove materials from the plastic block to create a high-precision part. This process is widely used for creating plastic prototypes before launching the injection molding process. it is used in different industries such as Automotive lighting prototypes because CNC prototyping can offer great precision to achieve optical functions.

3D printing

3D printing uses plastic powders and liquid resin to make plastic parts through a 3D printer creating layers by layers of plastic materials. it is an additive manufacturing method with a digital model as a guide. It’s perfect for 3D printing prototyping and low-volume manufacturing because of its rapid lead time and cost-effectiveness.

Blow molding

Blow molding, also known as hollow blow molding, is extruding the molten thermoplastic raw material into the mold, and then blowing air into the raw material to make it expand and stick to the surface of the mold cavity, finally cool and solidify into the desired product shape. This process is mainly used in the manufacture of packaging containers and bottles.

Compression Molding

Compression molding is the main process for molding thermoset plastics. This process involves pressurizing the raw materials in a mold that has been heated to a specified temperature, so that the raw materials melt, flow, and evenly fill the mold cavity. After a certain time under the conditions of heating and pressurization, the raw materials form the parts.

Rolling forming

Rolling forming is a process in which the molten thermoplastic plastic passes through the gap between two or more parallel counter-rotating rollers so that the molten plastic is extruded, and stretched by the rollers to become a continuous sheet product. The rolling forming process is commonly used in the production of plastic films or sheets.

Rotational molding

Rotational molding process involves rotating the mold after plastic particles are pre-injected to form a product. Rotational molding is mainly used to produce plastic chairs, flower pots, and other products. It is a simple manufacturing process with low cost and can be used for large-scale production.

Foam molding

Foam molding is a process in which appropriate foaming agents are added to foam plastic materials (PVC, PE PS, etc.) and then inject these materials into a mold to create a microporous structure in the molded plastic parts. Almost all thermosetting and thermoplastic plastics can be made into foam plastics.

Drip molding

Drip Molding is a process in which molten plastic is dropped into a mold for molding. Drip molding is usually carried out manually, semi-automatically, or fully automatically, and the operation is simple and flexible. The molten plastic is dropped on the surface of the mold evenly, After the plastic is cured, the finished part can be taken out.

Slush molding

Slush molding process is to pour the paste plastic into a mold that is preheated to a certain temperature, and the paste plastic close to the inner wall of the mold cavity will gel due to heat and then pour out the paste plastic which has not gelled and a hollow product will be formed and can be taken from the mold.

Dip molding

Dip molding refers to immersing the product model to be formed as a mold in a container filled with paste plastic, and then slowly lifting the mold out so that its surface is dipped in a layer of paste plastic, which can then be heat treated, cured and then be Peel off from the product model.

Laminating

Laminating is a process of combining multiple layers of the same or different materials under heating and pressure. it is commonly used in plastic parts manufacturing, and also in rubber parts manufacturing.

Transfer molding

Transfer molding is a molding process for thermosetting plastics. During transfer molding, the material is first heated and melted in a heating chamber and then pressed into the heated mold cavity to cure. These plastics have great fluidity before reaching the curing temperature, and have a fast curing time after reaching the curing temperature.

Guide to Choose the Right Plastic Manufacturing Process

There are many factors to be considered to choosing the right plastic manufacturing process for your part manufacturing project. below is the main factor for detailed consideration.

Part Geometry

Part Geometry is the first factor to be considered when you choose the plastic manufacturing process, this is because some processes are used for solid geometry and some processes only work for hollow parts. Even if it is a solid geometry part design, complexity, and undercut will also affect the choice. for example, some undercuts such as interior geometry can not be molded with a molding process, then you can choose 3D printing. if you are going to make sheets or tubes, then extrusion will be your first consideration.

Precision

Precision is another factor that affects the choice of plastic manufacturing process due to different processes creating different levels of precision products. for example, injection molding and CNC machining are the best processes to create high-precision parts that can achieve 0.01mm tolerance. if you need high-precision parts, then injection molding and CNC machining will be your first choice.

Production Volume

Production Volume can largely determine the process you are going to choose. for example, 3D printing and CNC machining are ideal for low-volume manufacturing of plastic, and vacuum casting is ideal for mid-volume productions. For high-volume parts manufacturing, injection molding, thermoforming, and extrusion will be the best choices in terms of the cost of each piece.

Materials

thermoplastics and thermosetting plastics are used for different plastic manufacturing processes. you need to consider the final function to determine the materials, and after that choose the right manufacturing process for the material you choose. For example, compression or transfer molding is ideal for creating parts with thermosetting polymers, which harden permanently following an initial heat form.

if you need exactly engineering plastic parts, then 3D printing and vacuum casting will not be a good option due to they are using plastic resins. you may consider low-volume injection molding or high-volume injection molding.

Cost

Cost is one of the major factors to be considered in all projects. it can influence the choice of the manufacturing process heavily. for prototype projects, 3D printing, CNC machining, and vacuum casting will be cost-effective choices. For mass production, if possible, thermoforming will be a more cost-effective choice than injection molding.

Conclusion

With all these plastic part manufacturing processes, there are pros and cons. It is very critical to check all the factors before you choose a manufacturing process to make a good quality part. However, Partnering with a professional plastic manufacturing supplier will be your best option to finish the plastic part manufacturing projects. KUSLA, with over 10 years of experience in plastic part manufacturing service can help you get the right process and save your project cost but with high-quality products.

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