What is Plastic Injection Mold

Plastic injection molds are metal forms created to produce a specific plastic item. These molds are the primary way that all plastic parts are manufactured. Heating and melting granules or pellets of plastic begins the process. The liquefied plastic is then forced, injected, into the closed split-die mold under high pressure and allowed to cool. The plastic injection mold is then opened to release the product.

Once a product has been designed, plastic injection molds are made, usually of either steel or aluminum, and precision machined to form the smallest feature of the plastic product. Often several plastic injection molds are used for a product that has numerous parts. Plastic injection molds have both core and cavity inserts, which will correspond to the shapes desired.

The material used for injecting into the plastic injection molds is derived from two different basic plastics: thermoplastic and thermosetting plastic. Most familiar plastic items are made from thermoplastics because these meltable plastics can be shaped and reshaped easily. Thermoplastics are used to make such common items as milk containers, soft drink bottles, pantyhose, styrofoam cups, plastic toys, etc. This type of plastic is easily recyclable as used products can be melted, injected into molds, and reformed into new items.

Thermosetting, or thermoset, plastics are rigid and set in a one-time pattern when they come out of the plastic injection mold. They cannot by recycled or melted for further use. Examples of thermoset plastics are automobile tires, appliance cases, electrical and electronic circuit boards, and electrical switches.

John Wesley Hyatt developed the first plastic injection mold, and the injection molding process, in 1868. He successfully injected hot, liquid celluloid, often called the first thermoplastic, into a split-die mold by the plunger method, a process that was little changed until James Hendry built the first screw plastic injection mold in 1946. Today, nearly all plastic injection molding uses the screw method.

To inject liquid plastic into a mold using the screw method, the screw below the molten plastic hopper is moved back to allow the material to flow into the mold. The screw assembly is then advanced to close the injection entry, using a non-return assembly to keep the material from backing up into the screw area. After allowing enough time for the plastic to cool, the mold is opened and the part removed, either by hand or by machine. The mold is then closed, the screw opened, and it is prepared to receive more material.

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What Are the Different Types of Cutting Tools

Cutting tools that are frequently used for metalworking include bandsaws, broaches, and drills. Other types of machining tools might include fly cutters and reamers. While some cutting tools require some type of human interaction to perform a function, others might be completely computer operated. Milling tools can be small enough to be bench or floor mounted but might also command a large space within a room. Cutting tools generally perform contouring, drilling, and desinking cuts along with possible surface planing.

While bandsaws are commonly associated with woodworking, metal shops also employ them. The machine gets its name from the circular metal blade that cuts by rotating around two or three wheels. These saws can be used in a horizontal or vertical position. The metal being cut might be placed in a vise with the saw blade descending onto the material, or the blade housing may be stationary, requiring the metal to be pushed toward the blade. Bandsaws typically make straight cuts, but materials can be rotated around the blade for angled or curved cuts.

Broaches generally use toothed bits that remove metal materials. The bits might look similar to drill bits, with cutting edges around the bit that run up and down the length of the tool. A combination of bits on one machine might each perform a cut in succession. One bit may accomplish roughing, another semi-finishing, and the last tool, the finishing cuts. Broaches operate as linear or rotary cutting tools, milling the exteriors and interiors of metal pieces.

Drill presses or radial arm drills are common pieces of machinery in a metalworking shop. Presses are typically located in a fixed position and are manufactured in a number of sizes. The drill spindle travels up and down and can be operated manually or mechanically. Drill bits are typically powered by electric motors that are equipped with variable speed transmissions. Attached to the end of a movable arm, radial drills may provide greater flexibility in the size of an established workspace.

Fly cutters get their name from metal extrusions that appear to fly around a central hub as it rotates. These cutting tools can also be used horizontally or vertically, either approaching or rotating around a stationary piece of metal. The bit might also be fixed, with a conveyor type of setup bringing the metal to the cutter. Fly cutters are usually used for internal boring or precise exterior cuts.

Reamers bore holes into metal. The spindles can rotate and travel horizontally on a lathe type of machine or they may move up and down similar to a drill press. The reamer cutting tools might include a drill type bit, which has cutting edges around and along the length of the tool. Other versions might have cutting edges located only on the distal end of the bit.

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What Is a Milling Machine

A milling machine is a tool found primarily in the metalworking industry. In general, these machines are used to shape solid products by eliminating excess material in order to form a finished product. Milling machines can be used for a variety of complicated cutting operations – from slot cutting, threading, and rabbeting to routing, planing, and drilling. They are also used in diesinking, which involves shaping a steel block so that it can be used for various functions, such as molding plastics or coining.

A milling machine is usually capable of cutting a wide variety of metals, ranging from aluminum to stainless steel. Depending on the material being cut, the machine can be set to move at a faster or slower pace. Softer materials are generally milled at higher speeds while harder materials usually require slower speeds. In addition, harder materials often require smaller amounts of material to be milled off at one time.

Generally, a milling machine operator runs the machine by feeding the material over a device called a milling cutter. As the material is fed past the cutter, the cutter’s teeth slice through the material to form the desired shape. Using gadgets like precision ground slides and leadscrews, the movement of the material as well as the cutter can be kept to less than 0.001 inches (about 0.025 millimeters) in order to make the cut exact.

In addition to a cutter, a typical mill machine contains a spindle axis, which is a device that holds the cutter in place. The cutter revolves around the spindle axis, and the axis can usually be adjust to varying speeds. Most machines also come with a worktable that can be used to support and feed the material. The worktable generally moves in two directions, and most modern worktables are power-operated. Additionally, a modern milling machine is typically equipped with a self-contained electric drive motor and a coolant system.

From micro, mini, and benchtop to floor standing, large, and gigantic, a milling machine can be found in a variety of sizes. Milling machines can have flat, angular, curved, or irregular surfaces. In addition, they can have a vertical or a horizontal orientation. A vertical milling machine has a spindle axis that faces vertically while a horizontal machine’s spindle faces horizontally.

Milling machinery can be operated manually or digitally using device called a computer numerical control or CNC milling machine. In addition to the traditional X, Y, and Z axes found in a manual machine, a milling CNC machine often contains one or two additional axes. These extra axes can allow for greater flexibility and more precision. CNC machines eliminate the need for a machine operator, which can prevent possible accidents as well as save on labor costs.

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What Is Machining

Machining is a form of manufacturing used to create objects out of metal. During this process, workers cut away materials to alter the appearance and shape of a product. Machining serves as an alternative to other forms of production processes, including molding or casting. It is one of the most effective methods of creating very fine, detailed objects, which are often not feasible through casting and molding techniques. Machining can be used to make everything from steel fasteners to metal jewelry, as well as larger objects like hand tools and automotive components.

This metalworking technique actually involves many types of processes that can be used to give metal the desired shape and finish. These techniques are often divided into four categories, and may be used together to produce a single product. Drilling is one of the most basic types of machining. During the drilling process, workers use a metal bit to cut holes in the metal. For example, drilling may be used to cut holes for fasteners in a metal kickplate used to protect a door.

Turning is another form of machining used to shape metal. During turning, metalworkers place the material on a piece of equipment known as a lathe. The lathe rotates the metal so that it can be shaped or cut using hand tools or specialty bits. This type of process can be used to create a threaded screw or similar fastener.

During milling, workers use a piece of equipment known as a milling machine. This equipment uses metal bits to cut material out of the surface or face of an object. The tool or bit is fixed in place, and the machine guides the metal around these cutting tools. This type of machining process may be used to cut a logo into a steel plate, or to form special tools.

Grinding is the final category of machining techniques. This relatively simple process involves using a stone-grinding wheel to shape or polish metal. This technique may be used to sharpen a metal hand tool or to give metal building materials a satin finish.

Machining is just a single part of a larger manufacturing process. Metal manufacturing begins with design, then proceeds through manufacturing and production. Machining may be used to shape the metal and create the object, or may serve only as a method of finishing the metal to give it the desired appearance. After machining is complete, the object must be finished and assembled before it is ready for sale.

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What is Injection Molding

In the 1967 film The Graduate, Mr. Robinson offered a single word of career advice to Benjamin Braddock, the character played by Dustin Hoffman: “Plastics.” It would seem that Robinson had the right idea. The industrial science of transforming plastic resins into useful things through the process of injection molding, has had a tremendous impact on industry and on most of our lives.

The injection molding process was first designed in the 1930s and was originally based on metal die casting designs. Injection molding offers many advantages to alternative manufacturing methods, including minimal losses from scrap (since scrap pieces can be melted and recycled), and minimal finishing requirements. Injection molding differs from metal die casting in that molten metals can simply be poured; plastic resins must be injected with force.

The process uses large injection molding machines, which advance the resins through six major processes to produce everything from computer parts to plastic Halloween spiders. Although an injection molding machine is a complex piece of equipment, it consists of two basic elements, the injection unit and the clamping unit.

The process starts with a mold, which is clamped under pressure to accommodate the injection and cooling process. Then, pelletized resins are fed into the machine, followed by the appropriate colorants. The resins then fall into an injection barrel, where they are heated to a melting point, and then injected into the mold through either a screw or ramming device.

Then comes the dwelling phase, in which the molten plastics are contained within the mold, and hydraulic or mechanical pressure is applied to make sure all of the cavities within the mold are filled. The plastics are then allowed to cool within the mold, which is then opened by separating the two halves of the mold. In the final step, the plastic part is ejected from the mold with ejecting pins. The completed part may contain extraneous bits called runners, which are trimmed off and recycled. The entire process is cyclical, with cycle times ranging from between ten and 100 seconds, depending on the required cooling time.

The injection molding process requires some complex calculations. Every different type of resin has a shrinkage value that must be factored in, and the mold must compensate for it. If this value is not precisely determined, the final product will be incorrectly sized or may contain flaws. Typically, this is compensated for by first filling the mold with resin, holding it under pressure, and then adding more resin to compensate for contraction. Other complications may include burned parts resulting from the melt temperature being set too high, warpage resulting from an uneven surface temperature, or incomplete filling due to a too slow of an injection stroke.

Injection molds themselves can be surprisingly expensive, sometimes upward of $100,000. If the desired part quantity, however, is great enough, the mold cost becomes relatively insignificant, and the resulting plastic parts are very reasonably priced. Some molds are made with more than one cavities; these multicavity molds cost more than their single cavity counterparts, but due to increased production efficiency, the cost per part is minimized.

Injection molding can be used with a variety of plastic resins. The most popular resins for this type of molding include: polypropylene (PP), polyethylene (PE), and ABS. Each resin has its own set of advantages and disadvantages and are chosen based on the desired characteristics of the final part.

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What is CNC Machining


Computer numerical controlled (CNC) machine tools are the best tools to use for automated machining. The machines can be as simple as a drilling machine that drills a hole repeatedly or they can be huge complex devices that can machine large cylinder blocks in multiple designs.


CNC machines can be operated either unmanned or with a few operators manning a production cell of many machines. Once the program that is used to give the machining detail and the tools to be used, etc. is given, then the machinery can run by itself. They will change the tools in the ordered sequence; turn the component around so that a fresh face is exposed, and so on. Because these machines can run by themselves for hours at a time, they save you manpower. Usually roughing operations are done on other machines to save on productivity.


Because they are computer programmed, CNC machining is more accurate, consistent and precise than human operated machining as this system doesn’t require human adjustment for its settings. There are no errors in CNC machining as the machinery operates exactly as the computer programs it to. This enables complicated machining tasks to be performed repetitively and the finished product will be the same each time.


CNC machine operation is relatively easy to learn and to set up as you just have to enter the instructions into a computer program. You can also recall the machine’s previous settings instantly. This process allows you to save time as lengthy manual changeovers are not required.


CNC machines have two tables and an automatic pallet changer. This saves valuable time as it allows components to be machined on one table while a fresh component can be loaded on another. There are various types of CNC machines available such as: turning; drilling; grinding; and machining centers that perform milling, drilling, boring, tapping, and contour operations.

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What is Polyvinyl Chloride (PVC)

A major thermoplastic material with a very wide variety of applications, the essential materials for polyvinyl chloride are derived from oil and salt. The vinyl chloride monomer (VCM) is formed by combining ethylene (obtained from oil) with Chlorine (produced from the electrolysis of salt water). VCM molecules are polymerized to form PVC resin, to which appropriate additives are incorporated to make a customized PVC compound.

Chemical Composition

The vinyl chloride molecule is C2H3Cl

Vinyl Chloride Monomer (VCM)
Polyvinyl Chloride Polymer



The symbol for polyvinyl chloride developed by the Society of the Plastics Industry so that items can be labeled for easy recycling is:


A highly versatile polymer, PVC is compatible with many additives. It can be plasticized to make it flexible for use in flooring or unplasticized (PVC-U) for use in building applications and window frames.

Physical Properties: Value:
Tensile Strength: 2.60 N/mm2
Notched Impact Strength: 2.0 – 4.5 Kj/m2
Thermal Coefficient of Expansion: 80 x 10-6
Max. Continued Use Temperature: 60 oC (140 oF)
Melting Point: 212 oC (413 oF)
Glass Transition Temperature: 81 oC (178 oF)
Density: 1.38 g/cm3
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What is Polypropylene

Polypropylene is a plastic polymer, of the chemical designation C3H6. It is used in many different settings, both in industry and in consumer goods. It can be used both as a structural plastic and as a fiber.

Polypropylene is often used for food containers, particularly those that need to be dishwasher safe. The melting point of polypropylene is very high compared to many other plastics, at 320°F (160°C), which means that the hot water used when washing dishes will not cause polypropylene dishware to warp. This contrasts with polyethylene, another popular plastic for containers, which has a much lower melting point. Polypropylene is also very easy to add dyes to, and is often used as a fiber in carpeting which needs to be rugged and durable, such as the carpet one finds around swimming pools or paving miniature golf courses. Unlike nylon, which is also often used as a fiber for rugged carpeting, polypropylene doesn’t soak up water, making it ideal for uses where it will be constantly subject to moisture.

Research is ongoing with polypropylene, as makers experiment with different methods for synthesizing it. Some of these experiments yield the promise of exciting new types of polypropylene, with new consistencies and a different feel from the fairly rigid version we are all used to. These new elastic versions of polypropylene are very rubbery, making them even more resistant to shattering and opening up many different uses for an already pervasive plastic.

Polypropylene is not as sturdy as polyethylene, but it has benefits that make it the better choice in some situations. One of these situations is creating hinges from a plastic, such as a plastic lid on a travel mug. Over time, plastics fatigue from the repetitive stress of being opened and shut, and eventually will break. Polypropylene is very resistant to this sort of stress, and is the plastic most often used for lids and caps which require a hinging mechanism.

Like many plastics, polypropylene has virtually endless uses, and its development has not slowed since its discovery. Whether used for industrial molds, rugged currency, car parts, or Tupperware, polypropylene is one of a handful of materials the world is literally built around.

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What is Polyethylene

Polyethylene is a type of polymer that is classified as a thermoplastic, meaning that it can be melted to a liquid and remolded as it returns to a solid state. As the name implies, polyethylene is chemically synthesized from molecules that contain long chains of ethylene, a monomer that provides the ability to double bond with other carbon-based monomers to form polymers. Polyethylene is known by other, non-official names, such as polythene in the United Kingdom. In addition, it is sometimes spelled as polyethylyne, or abbreviated to simply PE.

The first laboratory creation of polyethylene occurred in 1898 by accident at the hands of Hans von Pechmann while applying heat to another compound the German chemist previously discovered — diazomethane. Ironically, the synthesis of polyethylene via extreme heat and pressure in an industrial setting was again made by accident, but 35 years later. A few years later, another chemist employed by the same England-based chemical company devised a method to consistently produce polyethylene under the same conditions. As a result, polyethylene became the primary source of low-density polyethylene (LDPE) production in 1939.

While polyethylene is essential to the economic health of the plastics industry, most consumers readily recognize the role it plays in everyday life. In fact, this substance is found in many ordinary household items, such as food wrap, shampoo bottles, milk containers, toys, and the common plastic bag used to tote groceries home from the store. However, polyethylene is also present in numerous other products that contain plastic components. For instance, it is used to manufacture artificial knee and hip replacement parts, bulletproof vests, and even glassy flooring for ice skating rinks.

Polyethylene may fall under one of several types. The distinction between them is determined by its molecular weight and branching, which is affected by its crystallization. LDPE is an example of branched polyethylene since its carbon molecules are attached to long chains of polyethylene instead of hydrogen. Otherwise, a linear structure of carbon to hydrogen occurs, which is known as high-density polyethylene (HDPE). However, further variances in structure and molecular weight produce other forms, such as ultra high molecular weight polyethylene (UHMWPE), medium-density polyethylene (MDPE), or very low-density polyethylene (VLDPE).

While polyethylene may help to make numerous useful and durable products possible, its environmental impact is cause for concern. For one thing, it does not readily biodegrade and can reside in a landfill for hundreds of years. However, diligent recycling may significantly reduce this problem. In addition, scientists are exploring the possibility of employing Sphingomonas, an aerobic bacteria shown to shorten biodegrading of some forms of polyethylene to just a few months. Environmental preservation efforts have also led to the development of bioplastics, with the aim of synthesizing polyethylene from ethanol obtained from sugarcane.

Continue reading “What is Polyethylene” »

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What is Nylons

The term “nylons” refers to the group of plastics known as polyamides. Nylon is used in the production of film and fiber, but is also available as a moulding compound.

There are many types of nylon available (e.g. nylon 6, nylon 66, nylon 6/6-6, nylon 6/9, nylon 6/10, nylon 6/12, nylon 11, nylon 12). The material is available as a homopolymer, co-polymer or reinforced. Nylons may also be blended with other engineering plastics to improve certain aspects of performance. Nylon is well suited for processing via injection moulding, rotational moulding, casting or extrusion into film or fiber.

Chemical Composition

Its properties are determined by the R and R’ groups in the monomers. In nylon 6,6, R’ = 6C and R = 4C alkanes, but one also has to include the two carboxyl carbons in the diacid to get the number it donates to the chain.


Polyamides, PA


The majority of nylons tend to be semi-crystalline and are generally very tough materials with good thermal and chemical resistance. The different types give a wide range of properties with specific gravity, melting point and moisture content tending to reduce as the nylon number increases. Nylons can be used in high temperature environments. Heat stabilized systems allow sustained performance at temperatures up to 185oC.

Physical Properties: Value:
Tensile Strength: 90 – 185 N/mm2
Notched Impact Strength: 5.0 – 13.0 Kj/m2
Thermal Coefficient of Expansion: 80 x 10-6
Max. Continued Use Temperature: 150 – 185 oC (302 – 365 oF)
Melting Point: 190 – 350 oC (374 – 662 oF)
Glass Transition Temp. (Nylon 66): 45 oC (113 oF)
Density: 1.13 – 1.35 g/cm3
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