As many of us in the machine industry are aware, Plastic Injection Molding is just as relevant and important as any other machining process. There are many things to consider when considering purchasing plastic injection molding equipment, such as: Shot Size, Tie Bar Spacing, Ejector Stroke, Platen Size, and Tonnage.
Shot Size
Shot size is best defined as the maximum amount of plastic that the injection molding machinery is capable of injecting into the molding cavity during one molding cycle. The amount is rated in ounces of “general purpose polystyrene” (GPPS) for U.S. machines, and cm3 for European and Asian machines.
When searching for a machine, it's always a best practice to look for a machine that is capable of producing 30-40% greater shot sizes than what your parts require.
Tonnage
In this case, I mean “clamp tonnage or clamping pressure.” This could be considered the same concept as when you're examining press brakes. With press brakes, tonnage capabilities are measured by how many tons of downforce the machine is capable of directing towards a workpiece. However, with plastic injection molding machines, tonnage is measured by how many tons with which the machine is capable of pressing together the platens, which hold the mold cavity and form the plastic that is injected into said cavity to produce the desired part.
Platen Size
The platen is the "table" or tool that holds the mold cavity. Spaced apart, the mold is inserted and clamped securely to the platens. Once the two platens come together and are held under the pressure of tonnage, the plastic is heated, injected under pressure, and then allowed to cool through a molding cooling cycle. Here, the plastic takes on its hardened, final shape while continuing to be kept in place with many tons of pressure to retain the desired shape.
Tie Bar Spacing
Tie Bar Spacing is defined as the space between the horizontal tie-bars on an injection molding machine. Basically, this measurement, along with the platen max spacing, determines the maximum size of molds that can be placed in the molding machine.
Ejector Stroke
Simply put, Ejector Stroke is the action of the machine pushing out (ejecting) the final workpiece from the platens using ejector pins. The ejector in the molding machine pushes against an ejector plate on the mold, Ejector "Pins" or rods are attached to this plate and perform a pushing operation on the molded part after the plastic has hardened and the mold has opened.
Once the action of molding the workpiece is completed, the mold opens and then the ejector pins slowly extend outwards, pushing (or ejecting) the finished part out of the mold cavity. Pin movement is timed with the mold opening—because pins that move too quickly could impact the plastic workpiece and damage the final product and pins that move too slowly may not fully eject the molded part.
At Southern Fabricating Machinery Sales, Inc. we have many Plastic Injection Molding Systems available and can assist you in selecting the right system for your part or application. Also, with equipment appraisers on staff we can help you evaluate and sell any excess plastics machinery you may have. Please call me directly at 813-444-4555 X113 to discuss your machinery needs.
Key 1: The nature of the injection product
There are certain ideas for plastic injection products, which can be simpler and clearer when choosing an injection molding machine. If you have any questions when purchasing an injection molding machine, you can directly ask the supplier of the machine according to the requirements of the product. You can provide ideas to discuss the actual product that is injected with the injection machine company. If there is no actual injection product, there will be more communication problems. For example, does the company have set the product to be produced with a plastic injection machine? Is it a general household item? Or are there special-purpose parts? Does the injection product have requirements for temperature, light transmission, softness, or weight? Should the product material use thermoplastic plastics (such as ABS, PE, PP, engineering plastics) or thermosetting plastics (FRP, LSR)? Is it necessary to make high-precision and high-density products to meet the needs of the product (such as automobiles, communications)? Should the product color be used for single-color injection or two-color injection? These are the questions that we often encounter from customers, so you must clearly understand your needs, and then determine the nature of the product is one of the very important homework.
Key 2: Mold size, product size
If we just want to shoot a small plastic doll, the size of the mold will naturally be smaller, but if we want to shoot a trash can today, the mold will be much larger. It can be known from this that if the product to be injected is larger, the mold will be larger, so the injection molding machine must be larger. In addition to understanding the size of the product to be developed, it is also necessary to know that the size of the mold that each injection machine can use is different. Therefore, instead of calculating the approximate size of the mold by yourself, it is better to consult a number of mold factories to understand the size of the mold, and then determine whether the inner distance, mold thickness, and size of the machine can be placed according to the mold size.
<Extended reading: What is the Corinthian Pillar? 〉
Key 3: Mold opening stroke
Generally speaking, a mold is divided into two parts: a male mold and a female mold. The product structure and appearance geometry we design is to design a film cavity in the male and female molds, and then inject the plastic materials into the film cavity. Here, after the plastic material is injected, the "mold opening" will be performed, which means that the male mold will be opened backwards, and then the finished product will fall out from the female mold, which is "demolding". The maximum distance that the male mold can be separated from the female mold is called "mold opening stroke". When purchasing an injection machine, in addition to the product size mentioned just now, how long the length of the mold opening stroke is, it is also a very important point, otherwise it may happen that the product cannot be taken out after injection into the mold.
Key point 4: Clamping force
After the injection machine injects the plastic into the mold, in order to keep the shape of the finished product, it will maintain a certain pressure on the product, and the plastic itself will also give a reaction force to the outside. Therefore, in order to prevent the mold from being completely opened and the phenomenon of supporting the mold, the clamping unit of the machine will give "clamping force". The clamping force can also be calculated according to the product area, size, material and other factors. However, if you want to know how much clamping force your product needs, it is recommended to consult a professional to avoid insufficient clamping force calculations. There may be burrs and glue overflow to the injected products.
〈Extended reading:
Is there any relationship between the flash of the product and the strength of the template? 〉
Key point 5: Injection volume
The injection volume will vary with the weight of the product, the material, the number of cavities of the mold, etc., but usually the larger the weight and volume of the product, the larger the tonnage of the machine, otherwise it may not be able to manufacture. This is related to the "screw" in the machine. The screw is horizontal in the machine. It pushes the melted plastic material to the injection port before injecting the plastic. It also melts, compresses, and mixes the plastic in the process. The longer the diameter and stroke of the screw, the larger the volume of the finished product that can be injected. So when choosing an injection machine, not only need to look at the tonnage of the injection machine, but also pay attention to the diameter of the screw by the way.
〈Extended reading:
Key point 6: Screw compression ratio
We just mentioned the screw in the injection machine, and explained what its work is. Let's explain the work of each section of the screw more clearly. The screw is divided into three sections. The order from feeding to injection is: feeding section, compression section, discharge section.
Feeding section
: the plastic pellets that have not been melted are transferred to the compression section, where some plastic pellets will be slowly melted.Compression section
: plastic is compressed and mixed.Discharge section
: the plastic will be completely melted, and the temperature and particle mixing should also be completely uniform.
The screw compression ratio stated in the title is about the groove depth of the feed section/the groove depth of the discharge section. There is no best number for screw compression ratio, because each type of plastic has different properties, so you should seek professional manufacturers to evaluate the compression ratio production to have the best production quality.
Point 7: Injection speed
When the injection machine is producing thin-shell products, the injection speed of the injection molding machine must reach a certain value before production can be produced to avoid the failure of production due to cooling when the filling is completed. In addition, it should be noted that the higher the injection speed, the mold exhaust and the higher the accuracy requirements, the overall planning is required.
Key 8: Other requirements for finished products
We often hear that customer products have relatively high standards for appearance, function, quality, etc. or other applications and requirements, such as gloss, surface brightness, fire rating, environmental protection rating, etc. Some factors are quite related with the plastic material, but some are also related to whether the injection machine itself can support this function, so if you have requirements for product quality, it is recommended to ask first to see if the injection machine can meet your needs. We are committed to helping customers solve problems and tailor-made professional companies for customized injection molding machines. If you have any questions, please feel free to ask.
Conclusion
The above 8 points are the key considerations when choosing an injection molding machine. Of course, there are many considerations and attentions in the injection molding process, such as mold making and plastic selection. The customers often encountered affected the finished product because of the wrong shape or material selection of the product itself. Later, after repeated communication to modify the mold in the injection machine, or to change the material to solve it. We are a professional injection machine expert who has been operating for many years in the local area. We care most about is the "quality" of the product. If you want to learn more about our expertise, please continue to pay attention to our blog. We are happy to share more about plastic knowledge of injection molding to everyone.
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Are you looking for a new injection molding machine for the company's new products, or want to upgrade the injection molding machine in your factory, but you don't understand a bunch of proper terms on the Internet? What is "mold opening stroke"? What is the "Tie-bar"? How to judge whether the "screw diameter" is suitable for your product? In this article, we have sorted out 8 key points and selection suggestions for you to teach you how to select the injection machine correctly, so that you can purchase accurately and save costs. The following are our key points:There are certain ideas for plastic injection products, which can be simpler and clearer when choosing an injection molding machine. If you have any questions when purchasing an injection molding machine, you can directly ask the supplier of the machine according to the requirements of the product. You can provide ideas to discuss the actual product that is injected with the injection machine company. If there is no actual injection product, there will be more communication problems. For example, does the company have set the product to be produced with a plastic injection machine? Is it a general household item? Or are there special-purpose parts? Does the injection product have requirements for temperature, light transmission, softness, or weight? Should the product material use thermoplastic plastics (such as ABS, PE, PP, engineering plastics) or thermosetting plastics (FRP, LSR)? Is it necessary to make high-precision and high-density products to meet the needs of the product (such as automobiles, communications)? Should the product color be used for single-color injection or two-color injection? These are the questions that we often encounter from customers, so you must clearly understand your needs, and then determine the nature of the product is one of the very important homework.If we just want to shoot a small plastic doll, the size of the mold will naturally be smaller, but if we want to shoot a trash can today, the mold will be much larger. It can be known from this that if the product to be injected is larger, the mold will be larger, so the injection molding machine must be larger. In addition to understanding the size of the product to be developed, it is also necessary to know that the size of the mold that each injection machine can use is different. Therefore, instead of calculating the approximate size of the mold by yourself, it is better to consult a number of mold factories to understand the size of the mold, and then determine whether the inner distance, mold thickness, and size of the machine can be placed according to the mold size.
What are injection molding machines? What are the types?
We just mentioned the screw in the injection machine, and explained what its work is. Let's explain the work of each section of the screw more clearly. The screw is divided into three sections. The order from feeding to injection is: feeding section, compression section, discharge section.The screw compression ratio stated in the title is about the groove depth of the feed section/the groove depth of the discharge section. There is no best number for screw compression ratio, because each type of plastic has different properties, so you should seek professional manufacturers to evaluate the compression ratio production to have the best production quality.When the injection machine is producing thin-shell products, the injection speed of the injection molding machine must reach a certain value before production can be produced to avoid the failure of production due to cooling when the filling is completed. In addition, it should be noted that the higher the injection speed, the mold exhaust and the higher the accuracy requirements, the overall planning is required.We often hear that customer products have relatively high standards for appearance, function, quality, etc. or other applications and requirements, such as gloss, surface brightness, fire rating, environmental protection rating, etc. Some factors are quite related with the plastic material, but some are also related to whether the injection machine itself can support this function, so if you have requirements for product quality, it is recommended to ask first to see if the injection machine can meet your needs. We are committed to helping customers solve problems and tailor-made professional companies for customized injection molding machines. If you have any questions, please feel free to ask.The above 8 points are the key considerations when choosing an injection molding machine. Of course, there are many considerations and attentions in the injection molding process, such as mold making and plastic selection. The customers often encountered affected the finished product because of the wrong shape or material selection of the product itself. Later, after repeated communication to modify the mold in the injection machine, or to change the material to solve it. We are a professional injection machine expert who has been operating for many years in the local area. We care most about is the "quality" of the product. If you want to learn more about our expertise, please continue to pay attention to our blog. We are happy to share more about plastic knowledge of injection molding to everyone.