Plastics are the most common materials for producing end-use parts and products, for everything from consumer products to medical devices. Plastics are a versatile category of materials, with thousands of polymer options, each with their own specific mechanical properties. But how are plastic parts made?
A variety of plastic manufacturing processes have been developed to cover a wide range of applications, part geometries, and types of plastics. For any designer and engineer working in product development, it is critical to be familiar with the manufacturing options available today and the new developments that signal how parts will be made tomorrow.
This guide provides an overview of the most common manufacturing processes for producing plastic parts and guidelines to help you select the best option for your application.
Consider the following factors when selecting a manufacturing process for your product:
Form: Do your parts have complex internal features or tight tolerance requirements? Depending on the geometry of a design, manufacturing options may be limited, or they may require significant design for manufacturing (DFM) optimization to make them economical to produce.
Volume/cost: What’s the total or the annual volume of parts you’re planning to manufacture? Some manufacturing processes have high front costs for tooling and setup, but produce parts that are inexpensive on a per-part basis. In contrast, low volume manufacturing processes have low startup costs, but due to slower cycle times, less automation, and manual labor, cost per part remains constant or decreases only marginally when volume increases.
Lead time: How quickly do you need parts or finished goods produced? Some processes create first parts within 24 hours, while tooling and setup for certain high volume production processes takes months.
Material: What stresses and strains will your product need to stand up to? The optimal material for a given application is determined by a number of factors. Cost must be balanced against functional and aesthetic requirements. Consider the ideal characteristics for your specific application and contrast them with the available choices in a given manufacturing processes.
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There are several processes that play an important role in plastic injection molding projects, and one of the most important here is tooling. Referring to the process of producing custom molds that will go into the cavity and be injected with plastic to create your parts, tooling is often the single most involved part of injection molding for clients – and should be considered carefully.
At EnviroTech Custom Injection Molders, we’re happy to offer high-quality plastic injection molding services for a wide range of products and industries, from automotive needs to chemical processing, marine solutions and numerous others. Here are some of the most important things to be thinking about during the tooling process for any part you’re in the process of designing.
First and foremost, consider the physical and chemical properties of the plastic you’ll be using during molding. This can have a direct influence on tool design, as different features may need to be taken into account depending on the type of plastic – such as shrinkage rate, flow characteristics or other features.
For instance, let’s say you’re using a glass-filled plastic. This type of reinforced plastic has glass fibers added to make it stronger, but it can wear down tools more quickly. As such, tooling may need to account for these wear and tear factors. Being aware of your plastic choice and how it may impact tooling is key.
One key part of the tooling design process involves planning out the wall thicknesses of your molded parts. Thicker walls may require more robust tools and longer molding cycle times, while thinner walls can be more delicate to work with. Finding the right balance of strength and speed is important here.
Furthermore, many molds will require different wall thicknesses within the same product. This requires planning for where thicker and thinner areas will be placed and how that will impact tooling. Close collaboration with your molding team is key to getting these details right.
As plastics cool from a molten state, they will shrink to some degree. The amount of shrinkage depends on the specific resin being used, but it’s important to account for this shrinkage in the tooling design. Adding additional material to account for shrinkage, using ribbing or other structural elements, and planning for how shrinkage may impact fit or function are all important considerations here.
For many molded parts, ribbing is used to add structural integrity while also reducing material usage and cycle times. However, it’s important to find the right balance of ribbing for your needs. Too much ribbing can lead to longer cycle times and increased wear on tools, while too little ribbing may not provide enough strength. Working closely with your molding team to determine the ideal rib balance for your product is key.
Your rib height is another key factor here. Rib height should be less than three times the part thickness to avoid overly long cooling times and potential defects. By keeping rib height in check and finding the right balance of ribbing overall, you can optimize both tooling and part performance.
Cooling is a major factor in any plastic injection molding project. Molds need to be designed to allow for even, efficient cooling so that parts can be ejected from the mold at the right time. Things like incorporating cooling lines, leaving adequate space around the molded part, and using materials that conduct heat well are all important for tooling. Not allowing for proper cooling can lead to longer cycle times, defects, or other issues.
Near the end of the molding process, parts must be ejected from the mold. As such, ejection pins and mechanisms are incorporated into the tooling design to push parts out once they have cooled and set. The size, number, and placement of ejection pins will depend on the specific part design. However, they must be placed in areas that will not impact the final part appearance or function. Including ejection mechanisms in the initial tooling design and testing them out is important to ensure smooth part ejection.
For new or complex tooling and molded parts, it is often a good idea to have prototype tools made to produce initial samples. This allows you to test out the tooling design, make sure parts are being produced correctly, and address any issues before the full production tooling is made. While there is added cost and time involved here, it can save time and money in the long run by identifying and solving problems early on.
As you can see, there are many important factors to consider with tooling for injection molding. By working closely with an experienced molding team and keeping all elements of the tooling design in mind, you can achieve high quality molded parts as efficiently and cost effectively as possible.
At EnviroTech Custom Injection Molders, our experienced team can help you navigate all aspects of tooling design and ensure your project is a success. Contact us today to get started!