What Is Plastic Injection Molding

Plastic injection molding is a popular and economical industrial process for manufacturing a wide range of plastic consumer products. These include knobs, washers, valves, pulleys, gears, power tools, bottle caps, toys, car panels, computer monitors, keyboards, furniture and so on. These items are mass-produced using molding machines of various sizes and various specific requirements.

The process of injection molding was invented by John Wesley Hyatt. In 1868, he produced billiard balls by injecting celluloid into a mold. Later he built a plunger type injection molding machine to facilitate production. Another inventor, James Hendry, improved on Hyatt’s invention and built a screw injection molding machine in 1946.

Both plunger type and screw injection type molding machines are used in the modern plastics industry. The difference between the two is in the way the plastic is transferred to the mold. Screw injection types are more convenient and are more widely used.

In the plastic molding process, plastic resins are used in pellet or granular form. Choice of plastic type depends on the kind of product being made, its requirements and the overall budget. Of the hundreds of available plastics, only a few are safe for consumer use. Some of the ones used in the plastic injection molding process include polystyrene, polycarbonate, polypropylene, polyethylene, polyamide, polyvinyl chloride, Teflon®, Delrin®, and acrylic.

Plastics are non-degradable and therefore not environment friendly. The plastic injection molding process, however, plays a positive role in reducing waste. Plastics used in the process can be reused as often as required.

The plastic pellets or granules are poured into the feed hopper of an injection molding machine. The feed hopper is a large container that opens into a heating cylinder. In the heating cylinder, the pellets are subjected to intense heat until the plastic melts.

A plunger or a screw then pushes the molten plastic forward through a nozzle into a split-die mold. The mold is the reverse of the part to be made and can have one cavity or several to make more parts at the same time. Molds can be made of durable and expensive steel, or the more affordable, less-durable aluminum or beryllium-alloy metal.

As with selecting the right plastic type, selecting the mold metal depends upon product, cost and durability factors. Manufacturers often use a less expensive metal mold for prototype molding, and get the more long-wearing, precision-machined molds when the production demand increases.

The molten plastic cools in the mold, hardens and takes on the shape of the mold. The mold then opens and the part is ejected out. It is then either ready for packing or is prepared for any other secondary operations. The whole plastic injection molding process is completed within a few minutes and can be carried out automatically.

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Basic knowledge of plastic mold 2

injection molding is the most commonly used plastic processing method. The method is applicable to all parts of thermoplastics and thermosetting plastics, plastic products obtained large quantities unmatched by other molding methods, injection molding process as one of the main tools for plastic injection molds, precision in quality, manufacturing cycle and injection molding process in the level of production efficiency, etc., directly affect the product quality, yield, cost and product updates, but also determines the competition in the market responsiveness and speed.

injection mold by a number of steel plates with the various component parts, and basically divided into:
A molding device (die, punch)
B positioning device (guide post, guide sleeve)
C fixtures (the word board, code-mode pits)
D cooling system (carrying water hole)
E constant temperature system (heat pipe, heater)
F flow system (pump nozzle holes and flow channel grooves, flow hole)
G top of the system (thimble, top stick)

5, the system according to the different type of gating system can mold into three categories:
(1) large outlet die: the flow channel and gate at the parting line, with products in the mold with the mold release time to design the most simple, easy processing, low cost, so the more people using a large nozzle system operation.

(2) fine nozzle mold: flow channel and the gate is not the parting line, usually directly on the product, so much to design a set of outlet parting line, the design is more complex, more difficult process, generally used depending on the product requirements fine nozzle system.

(3) hot runner mold: This mold structure and fine nozzle substantially the same, the biggest difference is that the flow in one or more of a constant temperature of the hot runner plate and heat pump mouth, no cold material ejection, and the water flow port directly on the product, so the flow does not require stripping, this system is also known as non-outlet system can save raw materials for more expensive raw materials, products require a higher situation, design and processing difficulties, mold costs are higher.

Hot runner systems, also known as the hot runner system, mainly by the hot sprue bush, hot runner plate, temperature control electric box composition. The most common hot runner hot runner system has a single point and multi-point thermal gate two forms. Single hot runner gate is a single set of heat directly to the molten plastic injected into the cavity, it applies to a single gate single cavity plastic mold; more hot runner hot runner plate through the molten material to each branch sub-set of the hot runner and then go to the cavity, it is more suitable for feeding a single cavity or multi-cavity mold.

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Basic Knowledge of Plastic Mold

1,Introduction
Our everyday life and production used a variety of tools and products to the large to the machine base, the body shell, an embryo as small screws, buttons and various household appliances in the shell, all have a close relationship with the mold. The shape of the mold determines the shape of these products, the quality and precision mold processing will determine the quality of these products. Material for various products, appearance, specifications and use of different mold into the casting mold, forging mold, die casting, stamping die and other non-plastic mold and plastic mold.

In recent years, with the rapid development of plastics and general industrial and engineering plastics in the intensity and precision, continuous improvement, plastic products, also expanding range of applications, such as: household electrical appliances, instruments, construction equipment, automotive, Japan with hardware and other fields, the proportion of plastic products is rapidly increasing. A well-designed plastic parts can often replace the more traditional metal parts. Plastic household products, industrial products and the trend is increasing.

2, the general definition of the mold: in industrial production, mounted by a variety of presses and press the special tools, through pressure or non-metallic materials, the metal shape of the required parts or products, this special tool referred to as mold.

3, the injection molding process Description: Mold is a tool for the production of plastic products. It consists of several groups of components parts, the combination of the successful mold cavity. Injection, the injection mold clamping in injection molding machine, molten plastic is injected into the mold cavity forming and cooling in the cavity shape, and then separated from the upper and lower mold through the top of the system will be products from the top of the left mold cavity, the mold is closed again, the last the next injection, the injection molding process is conducted in cycles.

4, the general categories of mold: Mold can be divided into plastic and non plastic mold:
(1) Non-plastic molds are: die casting, forging die, die stamping, die casting molds.
A. Casting mold – faucets, cast iron platform
B. Forging Die – Auto Body
C. Stamping die – computer panel
D. Die casting mold – super alloys, cylinder

(2) Plastic mold production technology and production based on the different products are divided into:
A. Injection Molding – TV cabinet, keyboard buttons (the most common)
B. Blow mold – drink bottles
C. Compression Molding – bakelite switch, science bowl dish
D. Transfer Molding – IC products
E. Extrusion die – glue tubes, plastic bags
F. Hot Forming Die – transparent shell molding packaging
G. Rotary molding – soft toy doll

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History of Plastic Injection Molding

The injection molding has seen steady growth since its beginnings in the late 1800’s. The technique has evolved from the production of combs and buttons to major consumer, industrial, medical, and aerospace products.

In 1868, perhaps in response to a request by billiard ball maker Phelan and Collander, John Wesley Hyatt invented a way to make billiard balls by injecting celluloid into a mold. By 1872, John and his brother Isaiah Hyatt patented the injection molding machine. The machine was primitive yet it was quite suitable for their purposes. It contained a basic plunger to inject the plastic into a mold through a heated cylinder.

Revolutionizing the plastics industry in 1946, James Hendry built the first screw injection molding machine with an auger design to replace Hyatt’s plunger. The auger is placed inside the cylinder and mixes the injection material before pushing forward and injecting the material into the mold. Today, almost all injection molding machines use this same technique.

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The Plastic Injection Molding Process

Because of its high viscosity, in order for plastic injection molding to be successful melted polymer must be injected into a hollow mold with a large force.

Preparing the Mold
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Feeding the polymer resin (pellets) down to the auger (screw) is a large open-bottomed container. An electric (or hydraulic) motor is responsible for turning the auger inside a heated cylinder which feeds the pellets up through the grooves of the auger. A gate before the injection mold cavity restricts the flow of the melt into the mold and limits backflow. The pressure created by pushing the forward through the grooves up to the gate also produces heat on the inside of the cylinder which helps to melt the polymer and prepare it for injection into the mold.

Injection of Polymer Melt Into the Mold

As the auger moves forward it injects polymer melt into the mold at high pressure (typically 10,000 – 30,000 psi), holds it, and adds more melt to ensure the contraction due to cooling and solidification does not leave gaps in the final product. Eventually the gate solidifies and isolates the mold from the injection cylinder.

Cooling the Mold

Molds are typically air or water cooled. Sometimes small holes are bored into the mold that allow a cooling liquid (such as water) to be circulated. Injection mold cooling consumes about 85% of the cycle time for the entire process.

Unloading / Demolding

After solidification, the clamp holding the two halves of the mold together closed is opened allowing the part to be removed. The injection molding process can then be repeated.

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Plastic injection mold design features of the slider

Slider is a plastic injection mold to complete the side core pulling an important part, it is mainly connected with the forming core, with the angle pin lead for core pulling.

Under normal circumstances, it is core to form with the lateral side of the slide core, called the modular side of the slider. In the side of the core is simple and easy processing of cases, can also side slider and side core made ​​of one, called the integral side of the slider.

Slant-hole slider for cooperation with the bevel pillar, in line with the same time to make single 0. 5MM the gap, so the moment there is injection mold in a small space travel, the slide core is not tic and activities before the mandatory plastic extrusion die or punch, and to lock the block from the first slider, and then the pumping cell. Slider structure, depending on the mold side core pulling force structure and size of the decision.
With generally slide the slider and guide, to enable a smooth slide-led core for core pulling and accurate, must be fixed template template or guide chute opened, the slider and the guide chute to be a good match and lead slip in the slide after the completion of the action, still remain in the guide chute, the stay in the lead trough the length of the slider block length should not be less than 2 / 3, guide chute structure there are two commonly used species, rectangular-shaped guide dovetail guide chute and chute.

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Progressive stamping

Progressive stamping is a metalworking method that can encompass punching, coining, bending and several other ways of modifying metal raw material, combined with an automatic feeding system.

The feeding system pushes a strip of metal (as it unrolls from a coil) through all of the stations of a progressive stamping die. Each station performs one or more operations until a finished part is made. The final station is a cutoff operation, which separates the finished part from the carrying web. The carrying web, along with metal that is punched away in previous operations, is treated as scrap metal.

The progressive stamping die is placed into a reciprocating stamping press. As the press moves up, the top die moves with it, which allows the material to feed. When the press moves down, the die closes and performs the stamping operation. With each stroke of the press, a completed part is removed from the die.

Since additional work is done in each “station” of the die, it is important that the strip be advanced very precisely so that it aligns within a few thousandths of an inch as it moves from station to station. Bullet shaped or conical “pilots” enter previously pierced round holes in the strip to assure this alignment since the feeding mechanism usually cannot provide the necessary precision in feed length.

The dies are usually made of tool steel to withstand the high shock loading involved, retain the necessary sharp cutting edge, and resist the abrasive forces involved.

The cost is determined by the number of features, which determine what tooling will need to be used. It is advised to keep the features as simple as possible to keep the cost of tooling to a minimum. Features that are close together produce a problem because it may not provide enough clearance for the punch, which could result in another station. It can also be problematic to have narrow cuts and protrusions.

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What Is Die Casting

Die casting is a process in which various metals can be cast from molten states into a mold. These molds are called “dies” in many foundry environments. The die is filled with typically non-ferrous metals, such as zinc and aluminum. It is filled in a high-pressure application that ensures that the density of the die-cast material is at the desired level.

The metal is injected into a specific cavity or mold that has been created. This is then machined to create two opposing steel dies. After the cooling process is completed, the casting is then removed from the mold. It is next burred or buffed to create a product that has been manufactured to exact specifications.

The process of die casting has evolved since its original inception to become much more efficient, in terms of both production and a decrease in the creation of scrap materials. When the molten metal is injected into the mold, this shot uses between 1,500 pounds (680.39 kilograms) to over 25,000 pounds (11,339.08 kilograms) per square inch of pressure. This is to ensure that the entire mold is filled with material to create consistent and full mold shots. The term shot refers to each mold being injected, since there can be multiple molds within a mold casing, and multiple castings produced within a shot.

Die casting has long been a valuable means of producing hardened metal products, such as engines. Many other items are also cast into molds from molten states, such as cast-iron pots and pans, and other car parts. This method of production has been used in industrial settings to create a multitude of different products, mainly because the casting process is able to produce parts of virtually any size and shape, depending on the mold that has been created for the metal to be poured or injected into.

Virtually any part that is needed for a specific application can be cast from almost any metal. One of the most popular, however, is aluminum. The low melting point and the ease of machining applications with aluminum make it an easily manipulated material to work with. This, in turn, results in a lower cost of production.

Due to the increased initial cost for the die casting equipment and the facilitation of a die casting operation, most of the industrial environments that have these types of productions take place do so on a large or heavy production scale. This is especially true in the automotive industry. There, the bulk of many automobile engines are made out of cast metal parts.

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What is Injection Mold Design

In the fast paced world of plastic molding, injection mold design is one of the most interesting and challenging jobs to be found. You will draw upon all of your creative abilities as you develop the design for new products.

It might look easy because of the powerful CAD programs, but in reality, they are just tools to help you. In the field of injection mold design you often must develop new and original methods of plastic molding. This sometimes requires a lot of creativity and inventiveness. What is a typical day like for injection mold design? Most injection mold designers follow a schedule similar to the mold makers. Because their mold designs are soon going to be manufactured by the mold makers, there is a very close relationship between these two.

A mold designer spends most of his time at his computer, using powerful CAD programs such as Unigraphics, AutoCAd, SolidWorks, MasterCam and many, many others. Nowadays, the programs are incredibly fast and powerful.

Very often the mold designer will be required to communicate with the various mold makers, CNC programmers, WEDM operators, etc.. This rapport is critical for a successful career as an injection mold designer.

Usually the designer does not work quite as many hours per week as the mold maker. Often mold designers have a shop background and help out in the mold making shop as well. This is especially common if there is a slowdown in design and a lot of work in the shop. How do you become an injection mold designer? Essentially, there are two paths in the USA. One is to learn on the job and the other is to learn at a design school. Both are common and work well.

Many plastic molding designers come from a mold making background. This is especially helpful to provide a realistic approach to mold design. There is no substitute for practical experience!

Several tech schools and universities offer excellent courses on plastic injection mold design. A background in mechanics, spatial relationships, ability to visualize 3D parts, and mathematics are all essential.

Is there a future in injection mold design?

Like everything else associated with the plastics industry, the answer is yes and no. Yes, because the plastics field is growing all the time and skilled designers are in high demand and low supply.

No, because the field is so competitive on a global scale. In this electronic age the designer does not even need to be in the same country as the mold maker. I had this experience at one shop; the designer was in Canada and we were in the USA. It worked well, but required considerable phone time on the part of the project manager. Conclusion Working in injection mold design is challenging, interesting, secure, well paying and in demand. Anyone interested will find many good courses available and companies seeking qualified designers.

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How Plastic is Molded

Plastic has, quite literally, become the cornerstone of our society. We make so many things from plastic that it is hard to imagine what our lives would be like if it was never invented. With so many of our everyday products being made of plastic, it is easy to understand why plastic injection molding is such a huge industry.

Approximately 30% of all plastic products are produced using an injection molding process. Of this 30%, a large amount of these products are produced by using custom injection molding technology. Six steps are involved in the injection molding process, after the prototype has been made and approved.

The first step to the injection molding process is the clamping of the injection mold. This clamping unit is one of three standard parts of the injection machine. They are the mold, the clamping unit and the injection unit. The clamp is what actually holds the mold while the melted plastic is being injected, the mold is held under pressure while the injected plastic is cooling.

Next is the actual injection of the melted plastic. The plastic usually begins this process as pellets that are put into a large hopper. The pellets are then fed to a cylinder; here they are heated until they become molten plastic that is easily forced into the mold. The plastic stays in the mold, where it is being clamped under pressure until it cools.

The next couple of steps consist of the dwelling phase, which is basically making sure that all of the cavities of the mold are filled with the melted plastic. After the dwelling phase, the cooling process begins and continues until the plastic becomes solid inside the form. Finally, the mold is opened and the newly formed plastic part is ejected from its mold. The part is cleaned of any extra plastic from the mold.

As with any process, there are advantages and disadvantages associated with plastic injection molding. The advantages outweigh the disadvantages for most companies; they include being able to keep up high levels of production, being able to replicate a high tolerance level in the products being produced, and lower costs for labor as the bulk of the work is done by machine. Plastic injection molding also has the added benefit of lower scrap costs because the mold is so precisely made.

However, the disadvantages can be a deal breaker for smaller companies that would like to utilize plastic injection molding as a way to produce parts. These disadvantages are, that they equipment needed is expensive, therefore, increasing operating costs.

Thankfully, for these smaller companies, there are businesses that specialize in custom plastic injection molding. They will make a mock up mold to the exact specifications, run it through the complete process and present the completed piece along with an estimate to complete the job to the customer.

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