Common Uses Of Extrusion Moulding
When using this method your outcome product will continuously have the same shape along the length of it. These can be things like straws or PVC pipes. These types of parts can be made at very high volumes because it can just keep producing the same shape without end.In comparison, this type of moulding is low cost because the equipment is fairly simple and can have high productivity. The downside to this method is that you are very boxed in when it comes to the variety of parts you can make.
Mix & Pour The Epoxy For The First Half Of The Mold
I purchased a quart of two-part epoxy from Tap Plastics . It comes in two 8 oz bottles marked Part A & Part B. I mixed equal parts of A & B, being careful not to introduce air bubbles into the mix. Tap also sells colorants that can be added to the epoxy. I added black colorant to better see the mold surface after curing.Then I carefully poured the epoxy mix into the mold frame to surround 1/2 of the tropical fish. Again, pour slowly to avoid creating air bubbles in the epoxy.
Extrusion Molding Flash And Pinch
It might seem as though extrusion molded flash is just a throwaway aspect of the molding process. However, the way flash is engineered is critical to maintaining the integrity of the molded container or part. Here are a few of the things that can go wrong:
- The flash pocket doesnt fill up enough, so there is too little pressure pushing plastic back toward the container to weld the pinch-off seam properly. This is characterized by a v notch at the pinch-off, which indicates a weak bond where the seam will probably split.
- The flash pocket is not big enough to hold all flash material, which produces too much pressure back toward the container. This causes a thick bump of plastic at the pinch-off. Depending on the properties of the plastic, cooling speed and other processing factors, this extra thickness might cool at a different rate, displace volume, and potentially crack.
- If processing conditions or mold pinch-off geometry are not correct for any reason, it can negatively affect the integrity of the parison bond at the pinch-off land, where edges of the two molds come together.
- Flash is removed manually or mechanically after molding. It must be handled carefully or containers/parts can be damaged, as with any post-molding process.
- Flash can have an impact on both appearance and functionality of a plastic container or part. Ragged or excessive flash is not visually appealing. Too much flash around the neck of a bottle can hinder proper operation of the lid or closure.
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Ways To Join Plastic: How Does Plastic Overmolding Compare
Plastics are extremely versatile, making them sought-after materials across a range of industries. For instance, in the United States the transportation/automotive and construction industries are two of the three major markets that account for the more than $31 billion spent annually on plastic components and products.1
With popularity and common use comes some challenges. For plastics, its reliably joining semi-finished plastic products to one another or to other materials. Several proven plastic joining solutions exist including plastic overmolding but the process best-suited for a specific project and budget isnt always readily apparent.
This brief overview of the main plastic joining methods provides fundamentals that will help guide your choices.
Types Of Plastic Injection Molding Machines And Processes
Image credit: The Rodon Group
Injection molding can use thermosets or thermoplastics. A machine heats and mixes the plastic until it is in a pliable molten shape, then a screw device turns to force the plastic into an outlet that leads to the mold. Once the plastic sets, the mold opens to eject the product.
Reaction injection molding uses only thermosets and involves a special curing operation that takes place within the mold. It is also slightly slower than standard plastic injection molding.
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How To Repair Molded Plastic
Molded plastic is a difficult plastic to repair because it does not bond easily and therefore does not glue back together. It requires a little extra work to fix or repair the molded plastic item. Even plastic adhesives are not always enough to keep it together and fix the problem, but there are ways to repair the plastic and avoid expensive purchases.
Pull the plastic back together. Hold it so it is shaped properly. Have a friend or family member help, if necessary, for larger items.
Clean the plastic with a cleaning cloth and a solvent. The solvent is a type of soap that removes dirt, oils and anything else that would create problems for bonding.
Sand the plastic with 200- to 400-grit sandpaper. Sand until the plastic is smooth and there are no rough edges.
Add flame to melt the plastic edges. This will make bonding easier. The size of the molded plastic item and damage will determine the best tool for adding heat. Small items need only a lighter, while a larger item will need a larger flame. Allow about one to two hours for the plastic to start cooling.
Apply a clear epoxy to the plastic material. This will keep it together and bond the plastic.
Sand the patch until smooth.
What Plastic Is Used For Injection Molding
Plastic part manufacturers most commonly use thermoplastics for injection molding. Thermoplastics are polymers that turn into molten under high temperatures and solidify under cool temperatures. Unlike thermoset plastic material, which burns if it is reheated, you can heat and cool the thermoplastics multiple times before it degrades beyond use.
Youll most often see thermoplastics in plastic pellet-form for injection molding purposes. You can mix plastic pellets with colorants, recycled material, and even glitter or other specialty additives.
The most common types of thermoplastics are:
- Polyethylene is one of the most versatile plastics to use for injection molding. Polytheylenes high ductility, tensile strength, impact resistance, low moisture absorption, and recyclability make it an ideal material for plastic containers and bags.
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Frame For Holding The Epoxy
Epoxy is a two-part liquid that eventually hardens into a solid material. To create a mold from epoxy, you need need a frame to hold the liquid epoxy until it hardens. The mold will consists of two halves, so the frame must also be constructed as two halves that fit together.This is a pre-made aluminum mold frame that I purchased from LNS Technologies at –
I could have tried to make my own frame, but this one was affordable and already had steel alignment pins to align the two halves.
How Does Ultrasonic Welding Work
The two parts to be joined together are placed securely into a custom-made fixture. A vibrating tool called a horn then lowers and contacts the parts. Next, pressure and ultrasonic frequency, otherwise known as high-frequency pressure and sound waves, are applied. The horn transmits this pressure to the parts, usually at a frequency of 20 or 40kHz.
These pulses cause the two plastic parts to vibrate against each other. The vibrations then heat and fuse the parts together. This is the result of converting high-frequency sound energy into high-frequency mechanical energy. The heat and friction that melt the plastic flow together to create a solid weld.Once the parts are joined, there is a hold time to allow the material to harden. The horn then retracts and the welded part is removed.
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What Products Are Made From Injection Molding
Manufacturers all over the world use injection molding to mass-produce all kinds of goods. You can use injection molding machines to make anything from a large object like a garbage can to a small object like a mobile phone case.
The most widespread use of plastic injection molding is to make non-consumer parts used in situations where visual appeal doesnt matterlike mechanical partsbecause the injection molding process often leaves impurities behind on the plastic part. Why? Lets look at the process to find out.
Tire chains made from plastic injection molding
Plastic Molding Melt Temperature And Mold Temperature Considerations
Understanding how melt temperature and mold temperature work together to produce final part properties is essential.
In most cases a lower melt temperature combined with a higher mold temperature will produce optimal performance.
However, many button-pushing plastic injection molders do not have the technical expertise to implement and monitor these two critical aspects of plastic molding. Instead they see high melt temperature as the only solution for reducing resin viscosity.
Higher Melt Temperatures can Cause
Unfortunately, higher melt temperatures can result in:
- Resin Degradation
- Longer Cooling Cycles
- Increased Energy Consumption
Now, these plastic molders are forced to reduce the mold temperature in order to regain the lost productivity caused by long cooling cycles necessitated by higher melt temperatures. This high melt temperature to low mold temperature ratio often results in compromised part properties and an unstable part.
Instead, if they combined a lower melt temperature with a higher mold temperature they would likely create a part with better final properties and shorter cycle time, which would improve part quality and reduce costs.
*For information on defects caused by improper melt and mold temperatures and how to fix them see: Plastic Injection Molding: Temperature-Induced Defects & Solutions.*
U.S. Plastic Molding Company Specializing in Complex Projects for Mission-Critical Parts
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How To Calculate The Right Press Size For Injection Molding
To accomplish the highly technical process of injection molding plastic components, injection molding machines exert an extreme amount of pressure. The mold is subjected to two strong opposing forces, holding the mold open and forcing it closed. The pressure that pushes the mold together is called the clamping force, which is measured by tonnage. The strong opposing pressures are needed to keep the mold together during and after the molding material is inserted, while the opening pressure needs to be strong enough to hold the mold open while injecting the molding material. Each of these pressure types must be exerted to a specific factor, which needs to be carefully calculated before the injection process begins.
The History Of Plastic Molding
Plastic molding began in the late 1800s to fill the need for plastic billiard balls as opposed to the commonly used ivory billiard balls of the time. In 1868, John Wesley Hyatt invented a way to make billiard balls by injecting celluloid into a mold. Four years later, Hyatt and his brother invented and patented a machine to automate the process. This was the first plastic injection molding machine in existence and it used a basic plunger to inject plastic into a mold through a heated cylinder.
In 1946, the screw injection molding machine was invented by James Hendry, which replaced the plunger injection technique. This is the technique most commonly used today.
Modern rotational molding also has a rich history beginning in 1855 when rotation and heat were used to produce metal artillery shells in Britain.
Plastics were introduced into the process in the early 1950s, when rotational molding was first used to manufacture doll heads. And then in the 1960s the modern process of rotational molding that allows us to create large hollow containers with low-density polyethylene was developed. In recent history, process improvements, better equipment, and plastic powder developments have sped up the process of creating finished products which has caused rotational molding to grow rapidly in popularity.
Image courtesy of Wikipedia
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Phase I: Cleaning Plastic And Setting
For our first phase, well outline some steps so that you understand how to set-up your weld, and clean your plastic. Well cover each step in more detail below.
Step #1: Create Your Workspace
First, youll need to focus on setting up your workspace. Youll want to use a ventilated area so that you dont breathe in anything harmful .
Keep in mind that there are a few safety concerns that youll need to review before you start any weld.
If possible, try to work outside, or at least make sure you have a sound ventilation system around you. Also, open up any nearby doors as well as windows, and put some fans around you so that you are airing the fumes away from your workspace.
Youll also need to wear a dust mask and some welding glasses or a welding helmet when you start cleaning the plastic.
Make sure that you tell other people to stay out of your area while you are welding. You want as few issues as possible surrounding you when you weld, and you especially want to make sure that you arent endangering other people.
#2 Dress Yourself in Heat-Resistant Gloves and Protective Clothing
Next, youll need to ensure your safety by putting on some heat-resistant gloves and wearing long-sleeved clothing or a welding jacket to protect your body.
Check out some of our recommended welding gloves here.
#3 Clean the Plastic
After your plastic is clean, get a lint-free cloth and dry off your pieces.
Plastic Welding With Heat
If you have two separate pieces of plastic that need to be joined or if you have a crack, then youll need to do some plastic welding. The basic idea is to apply heat to the edges being joined in order to melt the plastic until it is liquid enough to blend the edges together. Additional plastic can be melted into the groove to create a stronger bond, but depending on the situation this wont always be necessary.
There are tools specifically made to do plastic welding jobs, with attachments for each step in the process, but for small or one-time repairs, a cheap, low-wattage soldering iron will be sufficient. The video above from Delboys Garage demonstrates the technique and also shows how to embed small metal wires to stitch cracks in plastic together.
Important: Melting plastic can be toxic, so do this in a well-ventilated area.
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Common Uses Of Compression Moulding
The most effective use for this method is when you want to make plastic replacement parts for broken metal parts. The reason for this is because the high-temperature method makes for a very strong and durable end product. Even though it is plastic, it is a strong and low-cost replacement for the metal parts.
The cost-effectiveness of this moulding method depends on factors like the complexity of the design, the number of
cavities and the surface finish. When you are mass producing then this method is ideal because the cost per part will be very low.
What Is Made By Injection Molding
InjectionSurface Cut
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Common Uses For Blow Moulding
Blow Moulding is mostly responsible for producing products like plastic bottles, drums, cases and even fuel tanks. If your required number of parts is around the hundreds of thousands then this method is perfect for you .
This is a fast and economical friendly option with the mould prices ranging somewhere in between injection moulding and rotational moulding.
What Is Plastic Molding
Molding, also sometimes spelled moulding, is the process of manufacturing by shaping liquid or pliable material using a rigid frame called a mold or matrix.
When molding plastics, a powder or liquid polymer such as polyethylene or polypropylene is placed into a hollow mold so the polymer can take its shape. Depending on the type of process used, various ranges of heat and pressure are used to create an end product.
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Injection Molding Design Fundamentals: Snap
Michael Paloian | Nov 15, 2019
One of the greatest disadvantages of plastic materials is their flexibility and relatively low stiffness. One of the greatest advantages of plastic materials is their flexibility and low stiffness. Your perception of which of these statements is true depends on how you, as a designer, optimize the inherent properties of plastic materials. I personally prefer the latter statement, especially when I am designing products to be aesthetically appealing and easily assembled with minimal hardware.
At one time, all products required hundreds of screws to be assembled, which demanded extensive amounts of labor and parts. The aesthetics of the final design were often compromised by numerous exposed screws and fasteners. Todays industrial designers dont want exposed fasteners compromising the aesthetics of their product designs, and manufacturing engineers are being pressured to produce high-quality goods more efficiently. The solution to this apparent paradox is utilizing snap fits as a means of assembling parts that is ideally suited for plastic materials. The remainder of this article will be dedicated to discussing all the considerations associated with properly designing snap fits.
Before I discuss the types of snap fit designs and their associated design parameters, Id like to focus on some basic functional requirements for snap locks, which are listed below.
Annular snap lock
Torsional snap lock
Cantilever snap lock
Annular snap
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Why Is Injection Molding Good
Plastic manufacturing is one of the fastest growing manufacturing industries in the United States. From 1980 to 2015, employment in plastic manufacturing, which includes employment in plastic injection molding, outpaced the entire manufacturing sector by 1.5% each year on average. There are many reasons why manufacturers in the US love plastic, especially plastic injection molding.
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