Plastic injection molding is the primary processing technique used to manufacture consumer and industrial plastic products. The injection molding process involves using materials like polyamide, polycarbonate, ABS, and polyoxymethylene to achieve a range of finished product designs. POM injection molding typically uses polyoxymethylene as a material for plastic product design and manufacture.
POM has various physical, chemical, and mechanical properties making it suitable for various applications. This article is an in-depth guide on POM injection molding, the properties of POM, and processes involved in POM molding to help you grasp a better understanding of its suitability for your projects.
What is POM and What are POM Properties
POM is commonly adopted as an alternative to metals, and they are used for making precision parts for automobiles, electrical appliances, and other household appliances. Before getting to the processes involved in POM injection molding, let’s look at what POM is and its properties that make it suitable for diverse applications.
The Definition of POM
POM is also known as acetal, polyacetal and polyformaldehyde, and polyoxymethylene. It is an engineering thermoplastic obtained from the polymerization of purified formaldehyde. POM is of two types;
- Homopolymer (POM-H)
- Copolymer (POM-C)
POM is 100% recyclable and has a host of desirable properties. Other technical names associated with POM are polymethylene glycol and polyoxymethylene glycol. Various brand names indicate the slightly varied products developed by different parent companies, such as Celcon®, Delrin®, Tepcon®, etc.
Various Properties of POM
POM has a range of properties that make it desirable for many applications.
- Mechanical Properties: Polyoxymethylene is a rigid and elastic material with a very low coefficient of friction. It has high tensile and flexural strength and excellent resistance to wear, creep, friction, abrasion, and fatigue. The acetal polymer has outstanding sliding properties and excellent machinability, making it suitable as an engineering material for high-precision machining. It is resistant to fuels and organic solvents, which makes it dimensionally stable. POM has impressive impact strength and good electrical insulation even at very low temperatures. In addition, POM has low water absorption and is resistant to hydrolysis up to ~60 °C.
- Physical Properties: POM is white and semi-crystalline. Generally, products made with extruded POM have a glossy finish on the surface. POM also has a shrink rate of 2-2.5%.
- Flammable Properties: With moderate heat stability, POM is not sufficiently resistant to flame. Homopolymers are more resistant to high temperatures than copolymers which can only be continuously used under 100°C (212°F).
Advantages of POM in Injection Molding
POM plastic is a significant plastic material in injection molding because it has many beneficial characteristics that make it suitable. The features of POM make it relevant in diverse industries ranging from automotive, health, packaging, and so on. POM injection molding is, therefore, an excellent choice for plastic product designs as a result of the following advantages;
- Little Tendency to Creep: Creep testing and analysis are important. Creep testing measures how a polymeric material deforms when subjected to constant stress–tensile, compressive, shear, or flexural–at a constant temperature. Polyoxymethylene possesses high tensile strength, rigidity, and toughness, making it resistant to creep and impact.
POM has minimal tendency to get deformed when it comes to creeping. Its stiffness and highly stable dimensions provide a sufficient basis for maintaining its shape for a long time, even at low temperatures. This stellar advantage makes it useful for mechanical finishing operations like threading.
- Favorable Machinable Performance: POM has a very low coefficient of friction (static and dynamic), so it is ideal for use in high-precision machine parts. In addition, polyoxymethylene is resistant to impact and abrasion. POM also demonstrates excellent hydrolytic stability as well as fatigue endurance. All these properties point to its usability for gears and moving parts.
- High Chemical Resistance: Polyoxymethylene is resistant to fuels and organic solvents that might otherwise affect its performance. Compared to the other plastic materials used in injection molding, POM is an excellent choice.
- High Dimensional Stability: POM has high dimensional stability as it does not absorb moisture. Even after continuous exposure to high humidity over a prolonged period, dimensional changes, if any, is minimal.
- Good Wear Resistance: POM is resistive to wear following its low friction coefficient. It also has great self-lubrication properties and is excellent for moving parts.
- Excellent Appearance: Polyacetal has a glossy surface finish when molded. This makes it attractive.
Some Disadvantages of POM
Although POM has several beneficial features, specific characteristics make them undesirable for injection molding. Some of these disadvantages have effects on the overall performance of POM. The disadvantages of POM are;
- Longer Molding Cycle Times: POM takes longer to mold. Before a product is molded and a replica made with an injection mold, a prototype must first be designed, which involves different stages. This takes a long time from the mold design to the final.
- High Mold Shrinkage: POM typically has high mold shrinkage of approximately 2%. This high shrinkage can easily cause warpage and inaccuracy of dimensions in the material. POM also has a long post-shrinkage meaning that the design for a uniformly thick-walled product must be achieved as soon as possible to avoid inaccuracies.
The Process of POM Injection Molding
POM injection molding involves a series of steps that are explained below to achieve the finished plastic product. These processes are:
- POM Injection mold design: The POM injection mold design phase involves creating a detailed design of the products that need to be manufactured and designed the mold that will be used to generate this design. This includes determining the size, shape, and functionality of the part, as well as any specific requirements such as surface finish. The mold designer needs to consider factors such as part geometry, gating system, and cooling channels in the mold design.
- Melt and injection: In the melt stage, POM pellets or granules are fed into the injection molding machine’s hopper. The pellets are then transported to the heating cylinder, where they are heated and melted into a viscous liquid. Once the POM material is melted, it is injected into the mold under high pressure using a reciprocating screw or a plunger. The injection speed, pressure, and time are precisely controlled to ensure that the material fills the mold cavity completely and uniformly.
- Inject the POM into the mold: The injection stage begins once the mold and material are preheated. The injection molding machine uses a reciprocating screw or a plunger to move the melted POM material into the mold cavity through a flow channel. The material is injected at high pressure to ensure that it fills the cavity completely and uniformly.
- Hold and cool time in POM injection molding: Hold and cool time are critical stages in the POM injection molding process that help ensure that the final product is produced with the desired properties and dimensions. During the hold time stage, the mold is held closed under high pressure for a set period, while during the cool time, the POM is allowed to cool to a temperature where the POM material solidifies.
- Demold the POM part: Demolding is the process of removing the POM part from the mold after it has been cooled and solidified. After the cooling time has elapsed, the mold is opened, and the part is ejected from the mold, usually with the help of an injector pin. After ejecting the mold, an inspection will be conducted on the ejected product. Defects are noted, and the mold may be adjusted or repaired to prevent similar defects from occurring in future production runs.
- Post-processing: the post-processing stage aims to improve the quality of the molded product and present the molded pom product in its final form. It involves heat treatments and welding to join two or more POM parts or repair defects such as cracks and voids. It also involves assembling multiple parts together and coating the POM product to improve its appearance and property.
A Trustworthy POM Injection Molding Services Provider
Since 1978, FOW Mould has been a reliable provider of quality and cost-effective manufacturing mold solutions worldwide, with representatives in USA, Russia, and Egypt. FOW Mould offers a wide range of services to different industries, which include automobiles, furniture, baby products, storage, home appliances, and many more.
FOW Mould has over 40 years of experience using the plastic injection molding technique. This technique has produced several products, such as plastic baby toy sets, buckets, home appliances, plastic molded chairs, POS displays, auto plastic parts, solar panel parts, and many more.
In addition to these services, FOW Mould offers dynamic POM injection molding services starting from the product’s design to POM mold designing and POM mold manufacturing and the production of the finished POM products. Our company has a QMS that is internationally certified with quality control processes that monitor our daily POM injection molding products. Since we typically have a close relationship with our clients, we can troubleshoot issues at the early stage and save costs.
Our Chinese-based facility has dedicated project managers committed to helping you make your project a reality. And we will also get you going from the ideation phase with product sketches and drawings through the mold construction phase and the final production of your designs. Our team is more than equipped to provide our clients with quality and expert service.
Contact FOW Mould today to discover all we can do for you. You can even upload your design files and get a quote!
The POM injection molding process is very easy to understand. Investing in the right machines with quality time spent learning how to operate them will find that the processes are not complicated. Understand all there is to know about POM molding and how it impacts business, especially if you are in the plastic manufacturing industry. If you need help, our customer service team is always ready to help you.
For more information on how FOW Mould can serve you for your POM injection moulding projects, get in touch with us or request a quote today. Also, visit our website for more resources on POM injection moulding problems and solutions.