Plastic injection molding is used widely in the manufacture of everything from precision medical devices to children’s toys because of the many benefits it offers. Plastic is one of the most versatile materials used in modern manufacturing, given it can be molded into a wide range of durable products—everything from high-precision medical devices to widely popular kids’ toys. Injection molding offers numerous advantages over alternative manufacturing methods. Take a look. High rates of production Injection molding offers extremely fast cycle times—making it cost-effective for high-volume runs. Once a mold is complete, the process of molding molten plastic is quick, effective and highly scalable in output. The process also creates parts without the need for post-production refinement, a step involved with other manufacturing methods that costs time. Precision quality parts The process of injecting molten plastic into intricate molds under high pressure, creates complex, highly detailed designs with extremely tight tolerances of (+/-) .001”. This makes injection molding an ideal process for creating the types of high-precision parts and components required by the bioscience, automotive, electronics and aerospace industries. Mold very small to very large parts Plastic injection molding is highly versatile—offering the same quality and durability in everything from large-scale HVAC and plumbing units to micro components for high-precision applications like medical devices and wearable tech in which size and weight are primary factors. Prototyping capabilities Plastic injection molding for prototyping offers several unique advantages. Among them: It is a fast, efficient process that allows for designs to be in use early during product development, and the process is cost-effective enough to iterate multiple designs without causing budget-busting overruns. This type of tooling in the industry is considered as quick-turn mold or a bridge tool. Customizable (color, texture, material) Two classes of plastics are used in injection molding: thermoplastics and thermosets. Thermoplastics don’t undergo chemical change when heated, making them highly recyclable given they can be re-heated and re-molded repeatedly. Thermosets form irreversible chemical bonds during the curing process, making them less recyclable but more reliable in retaining strength and geometry even when exposed to high temperatures. Both classifications offer multiple materials options for plastic injection molding manufacture—making them highly customizable to meet the demands of any project. Cost-effective manufacturing with little waste Plastic injection molding produces very little if any waste byproduct, making it more cost-effective than other manufacturing methods. Whatever waste is created generally can be recycled for future use, resulting in significant cost savings. Improved mechanical/physical properties Through the use of additives and by altering heating and curing processes, plastic injection molding can improve the mechanical properties of component parts to address such things as tensile strength and flexibility, warpage and dimensional stability, and temperature- and fatigue-resistance. Ease of adding post-mold operations Plastic injection molding is ideal for post-molding services when customers require more than just a molded part. Pad-printing, hot stamping, painting, plating and shielding services are available for decorating and coating requirements. In addition, ultrasonic welding and heat-staking resources are available to accommodate molded joining needs. About Stelray Stelray Plastic Products is a leading global plastic injection molding company providing cost-effective solutions across a wide range of applications and industries. We have an outstanding supplier record of providing precision plastic molding, post-molding and prototyping services to an array of industries and Fortune 500 companies. We take pride in knowing that our customers rely on our team for consistent quality, superior service and on-time delivery. Get in touch to learn more about our custom plastic injection molding services.
In the development of a well designed and manufactured injection molded item, comes the decision-making process of determining what level of mold build you, or your company are willing to invest in. Some variables to consider are, your budget, part design complexity, number of parts required/life of project or life requirements for this phase, and plastic resin type that will be injected into the mold. To aid in this decision-making process, the toolmaking industry has developed standard classifications of molds to help sort through and designate mold classes available based on the molders and customer’s needs reflecting on the variables mentioned above that you will be assessing. Standard industry mold classifications go from class 101 through class 105, with class 102, 103, and 104 molds representing most molds being built today. Injection mold tooling and engineering involves an enormous amount of detail to the mold itself which can make the decision process as an outsider somewhat overwhelming. It is critical to at least be thinking about these standard mold classifications before going out for quotations and certainly have a mutual understanding with your molder/mold maker before getting your tool manufactured. As an example, certain molds have the durability to withstand 1 million cycles while others could last as few as 250 cycles. A class 101 mold would have higher production capacity, utilizing better grade tooling materials, and more robust construction overall. This higher class of mold build will translate typically in a better aesthetically looking part, dimensionally more accurate and overall, a higher quality product, and certainly longer lasting tool. Conversely, a class 105 mold has a very low production capacity and the intent for this mold would be for prototyping only, making this mold the least expensive out of all the classifications. As you work your way up the mold ‘classes’ to a class 101 mold you will find that the cycles, and production level will increase with each level offering a better-quality tool build and likewise a bit higher in cost. Choosing the right mold classification is essential for certain specifications. For example, when looking for a quality part with an anticipated life projection volume of 500,000 mold cycles, you will likely want to choose a class 102 mold. If you were to be looking to have a mold built for a plastic ‘cap’ that required 20,000 pieces per year, you could likely be fine specifying a class 104 mold. Several factors come into play when selecting the right mold; program volume, quality requirements, part size, and plastic resin being used. When going out for mold and product quotations, knowing what mold class to request for your company’s tooling application is a crucial step in the new mold sourcing/construction process. Do you have questions regarding mold classifications? Give us a call at (203)-735-2331.
The use of hot runner systems in plastic injection molding has been possible for nearly 50 years, but it’s only since the late 1990s that the use of a hot runner system surpassed cold runner systems in plastic injection molding. In a hot runner system, a manifold system heats the mold tool and sends melted plastic to nozzles which deliver the plastic to various cavities within the mold. Hot runner systems may be either internally or externally heated. External hot runner systems are excellent for use with polymers that may be sensitive to temperature fluctuations, but internally heated systems offer better flow control. In a cold runner system, the plastic injection occurs through the sprue. The plastic fills the runners leading to the cavity. Both hot and cold runner systems have advantages and disadvantages that may make one system more applicable to a certain plastic injection molding use case. Here’s a look at the pros and cons of each. Hot Runner System in plastic injection molding Advantages Eliminates runners and material waste Can assist in even melt flow Faster cycle times Assists with post mold automation processes Disadvantages Higher maintenance costs More potential downtime Higher tooling costs Slower color changes Not suitable for thermal sensitivity materials Higher part production volume to pay for higher mold costs Cold Runner System in plastic injection molding Advantages Can accommodate a wide variety of polymers, including specialty polymers Quick color changes Disadvantages Slower cycle times than hot runner systems Creates more waste from runners Deciding Between Hot and Cold Runner System for Plastic Injection Molding Since the cold runner system wastes the plastic that fills the runner, it may not be the best choice if the job calls for an expensive specialty plastic. If the product won’t be used in food or a medical device, scrap from the runner can often be reground and reused. However, the regrinding process is expensive in itself, as well as noisy and dirty. In most applications, the proportions of new to reground materials are strictly controlled, which can lead to a build-up of unusable material. With the hot runner system, there is little or no scrap, eliminating this additional cost. Hot runner systems often have faster cycle times, which reduces processing costs. Hot runner systems also produce less wear and tear on the equipment, helping to increase uptime and reduce maintenance costs. The ability to design mold channels to ensure that the material flows the same distance from each nozzle helps improve quality by moderating pressure and thermal variations This may be extremely important with certain resins that have limited processing margins. In addition to the speed, product quality and resin characteristics of the job, it makes sense to consider other factors that can affect overall costs. Consider the availability of engineering and design assistance that the supplier may provide to help you get the most from the system you choose. Also consider service costs—cold runner systems may be more reliable because of their simplicity.
When it comes to choosing the right resin for your plastic injection molding project, there are a number of considerations that should be kept in mind. After all, different plastic resins and materials have different properties that can (and often do) influence the performance of a part. The first and most important question to ask in a fundamental part assessment is: What is the application of the part to be injection molded? What will it do and how should it ultimately function? The below considerations are addressing this fundamental question. For example, you have made a shiny plastic part. When we ask what is the purpose of this part, your simple answer is a plastic case for a dental appliance. The below considerations explore of all the scenarios, expectations and possible future needs and options you anticipate for your plastic part. There are several considerations to review before making the final selection on which plastic resin works best for your part. Plastic resins come in many varieties and there may be additives available to help you meet specific needs. There are commodity resins and engineering resins. The choices can be endless from a very common ABS plastic to TPE a plastic material that looks and acts more like silicone than plastic. This article will review the most important considerations that you should keep in mind when deciding which plastic resin would work best for your project. Some key considerations in deciding the right plastic resin to use for your injection molding project include: Will your plastic product be exposed to temperature variation? Will your plastic product be disposable or be used over a long life? Is your plastic part more functional or aesthetic requirements such as a high gloss finish? Does the product need to be made from a flexible plastic or a more rigid plastic? What plastic product regulatory requirements have to be met? Is the part functional or strictly aesthetic? Will the plastic part be required to withstand a specific mechanical or physical load? Let’s review each of these factors. 1. Will your plastic product be exposed to temperature variation? There are a few reasons that temperature variation will come into play in impact your resin selection, largely tied to the environment your part will be used in and the purpose that it will fulfill. For example, if the product is for use outdoors, it may need to be able to withstand both heat and cold temperatures without compromising its integrity. There are products that are for use with applied heat or cooling. Nylon, for instance, provides excellent thermal resistance, making it an ideal engineering grade to choose from for a product that will withstand demanding performance needs. If you’re creating something that only needs to weather common environmental or household conditions, you might choose a commodity grade like ABS, which is weather resistant but can be damaged with extreme conditions. If you’re making something that’s unlikely to see extreme conditions in use, that wouldn’t be a concern. 2. Will your plastic product be disposable or be used over a long life? Another consideration in your material choice is the lifespan of the product. If you’re creating a part that works inside of a mechanical setting—for instance, medical grade equipment—there’s a definite need to make sure that the durability of the material matches the purpose of the product. However, you wouldn’t need to create such durability for a piece that will be used in packaging, such as disposable water bottles or casings for consumer goods which will be thrown away when the product is finished. The balance point here is in using the right material for the right purpose. You want disposable goods to be easy to recycle. You also don’t want them to cost more in production than they’re worth in price point. On the flip side, you need your long life goods to withstand the environment they’re created to perform in. If you were making a food container that’s disposable, you might choose something like Polypropylene because it’s a lower-cost material that will work for your purpose. But if you were making medical grade products, you may look at lower grade engineering resins such as PC(Polycarbonate), POM(Acetal ) or PET(Polyester) or a higher grade engineering resin PEEK(Polyether ether ketone) might be a more appropriate material because the strength of this resin is very high and you can sterilize it, which is obviously important in the medical field. It’s also quite a bit more costly than materials like ABS, but that cost is necessary for the product. 3. Is your plastic part more functional or are there color requirements/aesthetic requirements such as a high gloss? Some parts are simply functional and not seen by the consumer such as the inside of car versus other parts are mainly for aesthetic such as a faceplate for a wall switch. This is a determining factor for the deciding which type of resin would work best. Color matching might seem like a small portion of the process, but many products are made for consumption by consumers, and this means that consumer appeal is important. Ultimately, this can make color and aesthetics a big concern, especially in areas where consumers will use these products for a long time. An important consideration when thinking about color and plastic choice is: what is the use of the product? In some cases, parts that go into larger mechanisms may not need a wide color variety. In these cases, you can likely let other factors—such as strength, durability, and cost—influence your decision more than the color capabilities of a plastic. In other cases, though, color and other aesthetic elements may be of greater concern. Resins used for car interiors, toys, and other products that people purchase for the visual appeal will need careful consideration aesthetically such as in regards to texture or high polish. Texture and high polish would also reference back to mold cavity specifications – not just the raw material. The plastic you choose in these cases will need to be a balance between performance factors as well as aesthetic elements such as a particular plastic’s color-lasting or matching capabilities. 4. Does the product need to be more of flexible plastic part or more of a rigid plastic part? Flexibility and rigidity requirements are also important factors to take into consideration when choosing a plastic for your project. This requirement will often be considered along with the strength of the product—does it need to replace a machined or die-cast metal part in a machine? Will it be load bearing? Does rigidity compromise its lifespan or add to the lifespan? Some resins, such as Polycarbonate (Lexan), are naturally more rigid than others. Some, such as Polyethylene, are more flexible and may work better for your flexible injection molded part. Some, like PVC, might be made rigid for certain uses and flexible for other uses. 5. What plastic product regulatory requirements must be met? Almost any industry you might create a part or product to accommodate has its own regulatory requirements that you will need to meet. These requirements are integral to the creation of your products. Regulatory needs may vary, but it’s important to research individual compliance issues before choosing your resin. Of special importance will be requirements around durability and strength, depending on the end use of the product or part. Some regulatory bodies you may need to work with include: The FAA, FDA, REACH, NSA, and the EPA. 6. Will the plastic part be required to withstand a specific mechanical or physical load? It is important to look at properties of a resin such as impact and strength for those plastic parts whose primary purpose is for function versus aesthetic. These parts include parts inside your printer, under-the-hood automotive applications, or motor brackets for example. Some plastics inherently handle mechanical or physical load better than others and, in some cases, there are additives to assist in meeting load or strength requirements. See our reference tables for density values and abbreviations for common resins. Weighing All of Your Options Ultimately, choosing the right plastic resin for your plastic injection molding project will come down to balancing multiple considerations against others. How does your need for strength and durability balance against your budget? How does your desire for certain aesthetic qualities balance against performance needs? Etc. Answering these questions can help you settle on the best plastic for your particular needs.
No fasteners, no adhesives, fewer components and simplified assembly – that’s the beauty of ultrasonic welding. A proven technique for joining plastic parts, it’s fast, cost-effective and reliable. However, as with any manufacturing process, getting the best from it means designing appropriately. In the paragraphs below we’ll share some advice on ultrasonic welding of plastic parts. Consider these your ultrasonic welding plastic part design guidelines. Ultrasonic Welding Basics Ultrasonic welding, also referred to as 'sonic welding', uses friction to heat plastics to a temperature high enough that they’ll bond together. This frictional heat is applied through high speed vibration generated in a sonotrode and delivered by a welding “horn.” Ultrasonic welding machines look similar to spot or resistance welders. A horn pushes against the parts being joined, applying pressure and energy until they fuse together. With modern industrial controls it’s a fast and repeatable process. When and Why to Use Ultrasonic Welding Consider ultrasonic welding whenever the design calls for joining separate plastic pieces. One common reason is because it’s not feasible to mold the pieces as one unitary part. Another is that the pieces must be assembled around another part or parts. (Think motor housings or enclosures.) Sonic welding can simplify part design. There’s no need for large flat areas or holes and it’s possible to create hermetically tight enclosures. By eliminating fasteners it reduces piece count and weight, saving time, money and factory space. It’s also cleaner than adhesives with none of the mixing, storing and dispensing challenges. Ultrasonic Welding Part Design To use ultrasonic welding in assembly plastic parts must be designed appropriately. This means considering both the materials and the joint design. Review common materials and their effectiveness in different ultrasonic welding applications with this free guide. Material Considerations Ultrasonic welding works best on plastics that soften gradually over a temperature range. Typically these are thermoplastic materials with an amorphous structure. Their melting behavior is characterized by a “glass transition temperature” or Tg. Among the easiest plastics to weld ultrasonically are polyphenylene oxide (PPO) and acrylonitrile butadiene styrene (ABS). In contrast, a semi-crystalline structure makes polyvinyl chloride (PVC), cellulose acetate (CA/B/P) and polyolefin materials difficult. Dissimilar Plastics The easiest situation is where parts being joined are molded from the same material. At the other end of the spectrum are assemblies where the component parts are molded from plastics with different properties. (Note that semi-crystalline plastics can in general only be welded to themselves.) Gauging the weldability of dissimilar thermoplastic materials entails considering Tg, chemical compatibility and melt flow index (MFI). As a rule, the Tg of two dissimilar plastics should be within 40°F for them to fuse successfully. Chemical compatibility is a complex topic that comes down to the proportions of radicals within the polymers. Compatibility exists when these values are similar within the two materials. Melt Flow Index is a measure of how easily a plastic flows as it transitions to a liquid state. For any given material the MFI can be found in the manufacturers literature and is given as a single number. For best results plastics being joined should have similar MFI’s. Joint Design In ultrasonic welding it’s important to focus the energy in as small a region as possible. This means incorporating an “energy director” into your sonic welding plastic design. An energy director is a raised region with a triangular cross-section. The triangle tip is pressed against the mating plastic part and ultrasonic energy applied. With friction occurring over a very small area the local temperature rises quickly. As it goes through the Tg melting begins and the plastic components join together. An energy director design is used with almost all ultrasonic welding plastic part designs, except when the materials are semi-crystalline. As these have a narrow glass transition temperature range they tend to move quickly into a liquid state rather than the “gummy-ness” typical of amorphous plastics. To address this, such parts are designed with shear joints. Shear joints are formed when the side walls of opposing parts are pushed together. Common Types of Energy Director Designs The main types of energy director designs are: 1. Butt Joint Image Source: Emerson Here one surface is flat while the other has the triangle shape. Keeping the triangle point as sharp as possible maximizes energy transfer. 2. Step Joint Image Source: Emerson The mating surfaces have a stepped design that minimizes lateral movement while the triangle point presses against a flat surface. (This simplifies part location for assembly.) 3. Tongue and Groove Image Source: Emerson The energy director is on a raised tongue that fits into a groove in the mating part. This provides good alignment of the two parts and minimizes flash. 4. Criss-Cross Image Source: Emerson Both surfaces have energy directors but are aligned perpendicular to one another. This yields stronger welds but can also produce a lot of flash. To achieve an air-tight seal configure the crossing energy directors as a sawtooth. 5. Textured Surface Texturing the non-energy director surface is an effective way of increasing weld strength. 6. Perpendicular Image Source: Emerson In this design the energy directors run perpendicular to rather than parallel with the joint faces. This reduces flash. 7. Interrupted Image Source: Emerson Here energy directors are kept short. This reduces the energy needed to make the weld. 8. Chisel Image Source: Emerson A variation of the step joint, by putting the energy director along the mating wall this enables welding of thinner sections. Considerations for using energy directors Smaller initial contact area reduces the energy needed, so only put energy directors where needed. The exception is when a hermetic seal is needed, in which case an energy director is needed on all of the mating surface. Parts must be aligned before welding. Step or tongue and groove joints can be useful for this. Shear Joint Considerations Image Source: Emerson Shear joints require side walls with an interference and their strength is proportional to vertical direction of overlap. They work better for regular/symmetrical parts than those with irregular shapes. Design for the Process For many plastic assemblies ultrasonic welding is a better joining method than fasteners or adhesives. It produces a strong joint while avoiding any mess or additional components. The key to successful sonic welding is appropriate material selection and part design. Use these plastic part design guidelines as a starting point, but don’t hesitate to ask a specialist for more detailed advice.