Our eBook "An Introduction to Plastic Injection Molding" was developed with designers, engineers and downloading specialists in mind. It is written to provide a . This is the first in the Plastic Injection Molding (PIM) 4-volume series authored by plastics expert Douglas M. Bryce. This eBook covers it all and is an excellent. A resource guide to plastic manufacturing for designers, engineers and downloading agents.
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As of today we have 78,, eBooks for you to download for free. No annoying ads, no Design Guide Cover - Quality Plastic Injection Molding. We developed this eBook with designers, engineers and downloading specialists in mind. It is written to provide a basic understanding of plastic injection molding. Seminar on Productivity in Plastics Injection Moulding ( Shawbury, Thermoplastics and Injection Molding Conference Cincinnati, Ohio , 1 book.
It resembled a large hypodermic needle, with a heated cylinder through which a large plunger forced the gooey mass into a mold.
Today, the process is more complicated although, the basic principle of plastic being injected into a waiting mold is still the same. Also called polymers or resins, there are more than 20, unique formulations that can be injected into molds to produce parts with specific properties to be utilized for specific purposes.
Examples of common thermosetting plastics include polymers such as epoxy and phenolic. Common thermoplastics are nylon, polyethylene and polystyrene. Injection molding machines are fairly simple and straightforward, consisting of a hopper where raw material is placed, a heating cylinder and an injection plunger.
Molds are typically made from steel or aluminum. Major advantages to using plastic injection molding for the manufacture of parts include: Highly complex parts can be produced at a low cost. The only real disadvantage is the initial start-up costs. Each application requires a special manufacturing process that can mold the part based on specifications. This article provides a brief overview of the different types of molding and their advantages and applications.
Blow Molding — Well suited for hollow objects, like bottles The process follows the basic steps found in glass blowing. A parison heated plastic mass, generally a tube is inflated by air. The air pushes the plastic against the mold to form the desired shape.
Once cooled, the plastic is ejected. The blow molding process is designed to manufacture high volume, one-piece hollow objects. If you need to make lots of bottles, this is the process for you. Blow molding creates very uniform, thin walled containers.
And, it can do so very economically.
Compression Molding — Well suited for larger objects like auto parts The name of this molding method says everything. A heated plastic material is placed in a heated mold and is then compressed into shape. The plastic can be in bulk but often comes in sheets. The heating process, called curing, insures the final part will maintain its integrity.
As with other molding methods, once the part has been shaped, it is then removed from the mold. If sheeting plastic material is used, the material is first trimmed in the mold before the part is removed. This method of molding is very suitable to high-strength compounds like thermosetting resins as well as fiberglass and reinforced plastics.
The superior strength properties of the materials used in compression molding make it an invaluable process for the automotive industry. Extrusion Molding — Well suited for long hollow formed applications like tubing, pipes and straws While other forms of molding uses extrusion to get the plastic resins into a mold, this process extrudes the melted plastic directly into a die.
The die shape, not a mold, determines the shape of the final product. Injection molding - Well suited for high-quality, high-volume part manufacturing Injection molding is by far the most versatile of all injection molding techniques.
The presses used in this process vary in size and are rated based on pressure or tonnage. Larger machines can injection mold car parts. Smaller machines can produce very precise plastic parts for surgical applications. In addition, there are many types of plastic resins and additives that can be used in the injection molding process, increasing its flexibility for designers and engineers.
The process itself is fairly straightforward; however, there are many enhancements and customization techniques that can be used to produce the desired finish and structure. Injection molds, which are usually made from steel, contain cavities that will form the parts. Melted plastic is injected into the mold, filling the cavities.
The mold is cooled, and the parts are ejected by pins. This process is similar to a jello mold which is filled then cooled to create the final product. The mold making costs in this method are relatively high; however, the cost per part is very economical.
Rotational Molding Rotomolding — Well suited for large, hollow, one-piece parts This process uses high temperatures and rotational movement to coat the inside of the mold and form the part. The constant rotation of the mold creates centrifugal force forming even-walled products. Because it is ideally suited to large hollow containers, such as tanks, it is not a fast moving process. However, it is a very economical process for particular applications and can be cheaper than other types of molding.
Very little material is wasted using this process, and excess material can often be re-used, making it an environmentally viable manufacturing process.
Conclusion Each type of molding has its strengths and weaknesses. Designers and engineers need to understand these differences and the production options available.
There are always several approaches to a final manufacturing solution. The molding company who consults on a specific project should be able to provide additional insights into the applications and materials that are best suited to an individual project.
In fact, problems can be easily avoided from the very beginning as long you are working with a turnkey precision molding manufacturer. Some companies opt to use a separate firm to design the mold, then contract another vendor to build the mold often these are offshore mold builders and another to run the parts.
By separating these responsibilities, they often sacrifice control, accountability and quality. Mold Design Often problems arise at the very beginning of a project.
You may have drawings and even a prototype, but without the expert advice of design engineers who understand how to optimize an injection mold, you may experience costly defects and delays. This expertise helps to develop molds that will perform at the highest production levels.
The design team you choose to work with should conduct a Design for Manufacturability DFM analysis to ensure your parts meet the highest quality standards. Resin selection Choosing the right material for a project is one of the most important factors in creating perfect parts. The advances in polymer science have helped create a wide variety of resins to choose from based on the final application of the part. Reputable companies will have established strategic relationships with the best resin suppliers in the country.
They should have a great deal of experience using certified commodity and engineering resins that adhere to stringent manufacturing standards.
Mold Building and Testing Without careful attention to mold design, the end product may be non- conforming. It is important to create molds that accommodate enough draft for the selected resin and finish, for example. Plastic injection molders should create pre-production molds. These molds offer several benefits to the design and manufacture process. They are single cavity molds that are created using the same 3D software and tools as production molds; however they are made with less durable metal and steel.
Pre-production molds can be modified to help determine the best production solution for the project including finishes and coloration. Alternatively, SLA models can be created using 3-D printers, though these parts cannot be used as pre-production samples. Production and Quality Once the multi-cavity production molds are completed, a full cycle of samples are produced and checked for the quality standards outlined by the client.
Adjustments are made as required before full production begins. Quality checks continue throughout the part production process.
Our production molds are built to last, and we guarantee them for as long as we manufacture the parts. Our clients return year after year because our injection molds maintain their integrity. We use stainless steel on all of our molds, and our highly- trained operators insure each tool is properly maintained to maximize quality and output. Basics of an injection molding machine While plastic injection molders will help you determine the size of the machine needed to get the best results, a project designer or engineer can get a good estimate based on some basic information.
By knowing approximately what size machine will be required, you can better source a plastic injection molder that will meet your needs. Often plastic injection companies will provide a molding equipment list on their website.
It may look something like this: Plastic injection molding presses are classified or rated based on tonnage, or more specifically, the clamping pressure or force. Presses can run in size from less than 5 tons of clamping pressure to over The higher the press ton rating, the larger the machine.
A machine rated for 68 tons can deliver 68 tons of clamping pressure. This pressure keeps the mold closed during the injection process. Too much or too little pressure can cause quality issues. Too much or too little pressure can also cause flashing, where excess material appears on the part edge. Pressure also impacts the viscosity of the plastic being used in the project.
Plastic compounds react differently to pressure based on their MFI. The higher the MFI, the higher the pressure needed. There are many factors that are taken into consideration when determining the size of the press. The size of the part, the polymer being used and something called the safety factor.
The safety factor is an additional numerical percentage buffer that is added to the calculation to help avoid defects in the final part. As mentioned earlier, the MFI Melt Flow Index of the plastic compound will also impact the pressure needed to produce the part.
Many calculations include the platen size as well as the mold and part size, however, to get an estimate of the press size your project will need, we have simplified it even further. Many plastic injection professionals use a general rule of thumb of 2. So, if you have a part with 42 square inches than you would need a press size with tons of pressure.
A press size of tons would be able to accommodate your plastic injection molded product. Once you have an estimate of the press size you will need, you can identify plastic injection molding companies that will meet your requirements. In general, molders with a greater number and wider selection of press sizes will be able to accommodate the needs of your project.
If you are not working with a completed mold, look for a plastic injection company who can design and build the mold. They will have a better understanding of how to maximize the manufacturing process and will often offer tooling allowances.
This, in turn, will minimize the overall cost of your project. In the end, your plastic injection molder will determine which machine would be best suited for your project. Larger presses can accommodate larger molds and multi-cavity molds often reducing the cost per part. However, larger molds are more expensive. Choosing the right press size can balance the upfront tooling expenditures with long-term manufacturing costs. Molding systems Cold runner vs. Molds are classified into two main types, cold runner and hot runner.
Each has its advantages and disadvantages. Your plastic injection molder will be able to give you the costs and benefits of using these different systems. However, by understanding the key differences of these technologies, you can have a more educated discussion on the type of mold that would best fit your project.
The plastic is injected into the mold via the sprue and fills the runners which lead to the parts in the cavity. In 2 plate molds, the runner system and parts are attached, and an ejection system is used to separate the pair from the mold. For those of you who assembled a model car at some point in your youth, the runners and the parts were not separated. The child assembling the model was responsible for that final part of the process.
In 3 plate molds, the runner is contained on a separate plate, leaving the parts to be ejected alone. In both systems, the runner is recycled and reground, reducing plastic waste.
However, these processes can increase cycle time. Hot runner molding systems Hot runner molds consist of 2 plates that are heated with a manifold system. The manifold sends the melted plastic to nozzles which fill the part cavities. There are several types of hot runner systems, however, in general, they fall into two main categories; externally heated and internally heated. The externally heated systems are well suited to polymers that are sensitive to thermal variations.
Internally heated systems offer better flow control. The hot runner process eliminates runners entirely, so recycling and regrind which can only be done with virgin plastics do not impact cycle times.
A variation of this system is called an insulated runner. The insulation, rather than heat, keeps the plastic in a molten state. This system can only accommodate a few types of plastics, specifically semi-crystalline polymers which have a low thermal conductivity.
Cold runner systems Advantages -Comparatively cheaper to produce and maintain -Accommodate a wide variety of polymers, both commodity and engineered -Color changes can be made quickly -Fast cycle times if the systems include robotic assist in removing runners Disadvantages -Cycle times are slower than hot runner systems -Plastic waste from runners if they cannot be reground and recycled 22www.
Advantages and disadvantages continued Hot runner systems Advantages -Potential faster cycle times -Eliminates runners and potential waste -No need for robotics to remove runners -Can accommodate larger parts Disadvantages -More expensive molds to produce -Color cannot be easily changed -Higher maintenance costs and potential downtime -May not be suited to certain thermally sensitive materials Professionals in the field of plastic injection molding should be your primary resource for determining the best injection molding system for your project.
Look for injection molders who are familiar with all types of plastics processing. Injection molds represent the greatest expense in upfront production costs.
And, there are many factors that go into determining the cost. With any custom injection molding project, your injection molder will be able to give you the final price tag. In this article, we will review the variables that can impact the cost so that you can be better informed in making a mold downloading decision. Not all quotes are created equal Procurement and downloading managers have the unenviable task of obtaining quotes from a few mold makers for each project.
Depending on the input in terms of drawings, prototypes or sample parts , the cost quotes can vary greatly. Designers should look at all of these inputs and determine the best molding solution. They may re-design the part to maximize manufacturing efficiency and increase the number of parts that can be made with each molding cycle. Generally, molds made with tighter tolerances, more cavities and a longer production life will take longer to build and will cost more upfront.
The savings with a high-quality mold are long-term. These molds require less maintenance and last longer than lower quality molds. Here are some variables that impact the cost of a plastic injection mold. The core metal. For shorter production runs, some mold makers will use molds made from aluminum. This is a perfectly reasonable choice if you will not need the mold to perform long-term. However, if a project requires that a mold lasts for several years, an aluminum mold may cost more in the long- run.
The number of cavities. It is pretty intuitive when you think about it. Fewer cavities in a mold require less tooling work and time and ultimately less cost. A reputable experienced molder will be able to maximize cavitations in the mold to maintain the highest level of productivity.
In general, most molders recommend creating one mold per part versus creating a family mold. Family molds are created with various cavities for assorted parts. They tend to produce inferior products and have more downtime due to maintenance issues. Mold base. Think of the mold base as a case that holds all of the mold cavities, inserts and components together.
The cost of the base is estimated based on the size of the mold and the type of steel used to make the base as well as the customization required. Most mold bases come in standard sizes and are further machined to meet the requirements of a specific project.
All molds must also be customized. Customization includes the placement of cores, cavities, ejectors, cooling lines, etc. The steel used in the tool also impacts cost. Hardened steel molds lasts the longest and are more expensive to machine. Once done, however, they have a long production life. Part complexity. Just as the number of cavities plays a role in determining the cost of the mold, so does part complexity. This includes the surface finish of the final part as well as the number of undercuts required.
Parts, which demand tight tolerances, also contribute to the mold complexity. Turnkey or vertically integrated injection molders. Some mold builders also manufacture the parts. This type of integration can help defray the mold building cost. Often full service molding manufacturers will subsidize a portion or all of the cost of the mold based on the full term and value of the manufacturing contract.
They will amortize the cost of the mold so they can maintain profit margins while providing the lowest possible per piece cost to their clients.
The cost of a quality injection mold is certainly a major expense. However, tight- tolerance, precision molds that are made from the best steel available should last for years to come. The upfront cost must be calculated or amortized into the lifetime value of the project. Will these parts be in production for several years or several months?
Does the project require a high-volume of parts? Are faster cycle times required? If you answered yes to these questions, then the initial investment in a quality mold will lower the per part cost and will end up saving money in the long-run.
Common parts defects When downloading injection molded parts, it is important to understand some of the common problems and defects that impact product quality. Being familiar with these imperfections and their causes can help you work with injection molders to insure the highest quality part production is achieved. Most defects in plastic parts can be traced back to three sources: The material being used to make the part 2.
The processing of the material in the mold 3. Search BizReport. White Papers. Engineering Introduction to Plastic Injection Molding Ebook Injection molding is the most common plastic molding process and is used to create a huge variety of complex parts of different size and shape. You may also be interested in the following White Papers: Latest Headlines Reports: How banks can build stronger API Reports: Chatbots, personalized content driving conversions Top 5 tips to improve password safety Study: Businesses focused on ecommerce, pushing social for engagement Expert: How ethics in AI could impact data privacy Study: More people opening phones with no destination in mind Expert: How 5G could neutralize Net Neutrality More