How to Make Plastic Molding
- October 15, 2020
- Controlled Thermal Processing
- Cryogenic Processing
Molds are the perfect way of ensuring that the product being casted retains the correct shape and dimensions. It’s difficult to guarantee that if you just try to wing it or try to guess just how much pliable material needs to be used to achieve the intended shape.
The simplest way to go about this and to reduce your own effort is to just use molds. It’s the same concept as using baking molds for cupcakes, for example. Molds can be used to create a wide variety of products, even those that are to be used for industrial applications.
There are a couple of ways that can be used to make plastic molds. Again, it depends on the use case. There are highly precise methods that are better suited for industrial uses and there are also very simple methods that can be used at home to create a simple mold. It all depends on what kind of job needs to be done.
How are plastic molds made?
Molds are used in the mass manufacturing of plastic products. The mold itself is a hollowed-out block that’s filled with a pliable raw material like plastic. When the liquid sets and hardens inside the mold, it takes on the shape of the mold.
Bi-valve molding is the most common method. It uses one mold for each half of the object. In some cases, articulated molds may also be used. These have multiple pieces that are joined to make up the complete mold.
Molds are precisely made from materials like steel and aluminium. They’re precision-machined to form the specific features of the product that needs to be reproduced at scale. One-piece molds are machined when the objective is to produce simple shapes like tubes. This eliminates mold join lines in the final product.
There are many factors that need to be considered when making a mold, and mold design is one of them. The shape of the molded part has a direct impact on the time that it would take to make the mold. It’s important to include angles on the side walls so that the plastic molding can be removed from the mold when it’s done.
With surface finishes like embossing or etching, the aesthetic qualities of the molding can be improved. It’s vital to make sure that there are no imperfections on the finish of the mold because they will then transfer to every single molding made.
All aspects and transformations of heat treatment are considered when making a mold. Regions that have abrupt variations in the cross-section can cause warpage during heating and quenching. The machining process also introduces stresses in the material that need to be relieved. Cryogenic processing is a great way of relieving these stresses from the metal.
Professional injection-molded plastic vs. at home
Injection molding is a widely used process for creating plastic parts with metal molds. Liquified plastic is injected with extreme pressure into the mold which is then cooled with internal cooling lines and die spray on the cavities. The mold is then opened to remove the molding once it sets properly and cools down.
There’s a lot of flexibility in the plastic injection molding process and this leads to faster production lines. It’s also possible to use different plastic and polymer materials along with filters to further increase the strength of the plastic molding.
The finish is almost always very accurate since the extreme pressure used to inject plastic into the mold ensures that it properly takes on the shape.
Injection molding is a great way to inexpensively produce a lot of parts. There’s low labor and material costs compared to other casting methods. That’s not to say there are no costs involved. Professional-quality plastic injection molding machines and other related equipment can cost a pretty penny.
While the process is fairly simple and entirely possible to do at home, it won’t be possible to reproduce plastic moldings at scale without investing in professional quality equipment. If you just want to create a couple of moldings for a passion project then there’s little reason to consider professional equipment.
However, if you’re selling products that require injection molded parts, then it’s always best to go with the professionals unless you have the resources available to invest in your own high-end injection molding equipment.
Plastic molding and cryogenic deflashing
Once the liquified plastic sets into the mold and creates the molding, there may be excess material around the edges that needs to be removed.
This is an important part of the process because the molding can’t be damaged. If it is, the reproduced part is basically of no use and it can’t be utilized.
Exceptional care needs to be taken at this stage. To reduce manual work and increase success rates, cryogenic deflashing is now the preferred method to help in the deflashing process. In this process, cryogenic temperatures are used to help remove the flash on molded pieces. At such low temperatures, the excess material becomes brittle and breaks away from the mold very cleanly.
Cryogenic deflashing is carried out by first loading the molded pieces into a basket. A cryogenic material like liquid nitrogen is then used to bring the temperature down significantly.
Once the ultra low temperature is achieved, the excess material is blasted with small media pellets. In some cases, the pellets are not used and the parts are only thrown in a tumbler to achieve the intended result.
How deep cryogenic treatment works
Deep cryogenic processing works by bringing down a metal’s temperature to below -300⁰F. From there, the metal is left in a cryogenic cooler for 24 hours or more, depending on the metal and the application.
This has the effect of altering the crystalline structure of a given metal to permanently relieve any stresses that the manufacturing process may have instilled in the metal.
It’s important to do that as the temperature needs to be brought down gradually. In deep cryogenic treatment, it’s also possible to regulate the temperature and increase the amount of cryogenic material in the cooler as per the needs of the job.
At such low temperatures, the crystalline structure of the metal undergoes significant change. The next step is to slowly bring up the temperature in order to make these changes permanent.
With this stage, the stresses that were introduced in the metal in the machining process are released, thereby increasing the durability of the material.
Advantages of deep cryogenic treatment for plastic molding
There’s a lot of benefit to be had by using cryogenic processing for plastic molding. This particular industry is very competitive and with razor-thin margins, those competing in this business can’t afford any delays caused by worn components, eroded gates, and seized pins.
To minimize these issues, it’s vital to get the steel or other metallic molds cryogenically treated. This will significantly increase their wear resistance, allowing you to reproduce plastic products through the molding process with far fewer issues.
Since deep cryogenically treated metal has more consistent hardness, it’s easier to polish and this helps save both time and money in producing and maintaining the molds.
These molds will also be more resistant to abrasive materials like glass which leads to a reduction in runner wear, cavity wear, and gate wear.
The ejector pins that are deep cryogenically treated are also more stable in size and shape, thus solving problems which may be caused by pins getting stuck.
Since the metal is also more stable, any change in size due to the conversion of retained austenite during the heating and cooling cycling experienced during the molding process is minimized which helps reduce potential quality problems.
Controlled Thermal Processing Cryogenics can help you stay on top of your game in the competitive plastic molding industry. We are leaders in the cryogenics industry with almost four decades of experience.
Many of our customers who have taken advantage of our proprietary deep cryogenic treatment process have seen two to three times the life on their molds, pins, and other parts.
We’ll be happy to provide you with a free quote for the cryogenic treatment of your molds. Reach out today and we’ll be happy to discuss the specifics of the job with you.
CTP Cryogenics provides its wide range of services to customers from all over the country through its three processing facilities located in the United States.