What Is Die Cast Molding?

The die casting method is used to manufacture things like toy cars.

Used in a variety of industrial, commercial and consumer products, die cast parts can be found in many common items like cars and toys. Created by placing molten metal into pressurized steel molds the die cast pieces can be very complex, and because of the reliability of the technology, identical parts can be manufactured with great accuracy.

Die Cast History

The mid-1800's saw the development and use of pressure-injected die casting, but the technology was limited for the first 20 years to the production of printer's type and the use of tin and lead. By the end of the 1800's other shapes and parts, like phonographs, began to be produced using alloys like zinc, aluminum and magnesium. These, as well as magnesium and copper, remain popular die casting metals today.

Types of Die Cast Methods

There are two predominant methods of commercial die casting. The hot chamber and cold chamber methods both utilize injection systems, but in different ways. The hot system is used for metals with low melting points such zinc, copper and lead. The injection system itself is immersed in a bath of molten metal where it then fills with the liquefied metal. The cold chamber method is used for metals with higher melting points like aluminum. A manual or automatic ladle pours the molten metal into a cylindrical sleeve and is then sealed under pressure to cool.

Die Cast Advantages

The die casting technique is more useful than other production methods because it creates durable, identical materials and parts in more shapes and types than what is capable by other manufacturing processes. The accuracy of the die casting process, as well as the strength and easy assembly of its finished products, makes it an efficient commercial manufacturing method that is valuable in a wide range of industries.

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Chrome Vs. Nickel Plating

Chrome and nickel are metals used to plate machine parts, such as rollers and cylinders, with a scratch-resistant surface that protects them from wear and tear. They are also used on bathroom and kitchen fixtures.

1.                            Chrome

Chrome comes in standard and hard versions. It is applied in varying thicknesses according to the required purpose. Thinner coatings are used on objects that are not exposed to much abrasion. Thicker coatings offer more protection from abrasion and corrosion. If a machine part is frequently exposed to water, experts at Phoenix Electroplating recommend an undercoat of nickel plating, as chrome is porous.

Nickel

Nickel is used to prevent corrosion, particularly when applied prior to chrome plating on objects. It is also hard-wearing and is widely used on machine parts in the oil and gas industry, the automotive industry, in making molds for plastics and in food processing machines.

Bathroom and Kitchen Fixtures

According to Rejuvenation, suppliers of home fixtures, nickel was the standard finish for kitchen and bathroom fixtures made from the 1800s until the 1930s. Chrome then overtook nickel in popularity. Nickel is warmer in appearance and creates a more authentic, antique look, but Rejuvenation says the two finishes blend harmoniously in one room.

How to Clean Chrome Plated Plastic

Any chrome surfaces actually consist of an extremely thin layer of chrome plated onto another material. Regardless of what that other material is, from plastic to steel to aluminum, this chrome plated is what needs to be addressed when the time comes to clean it. You can always buy a special chrome cleaner, but there are several items in your home that work just as well and are far less expensive.

1.                            Toothpaste Method

1

Spread a thin layer of toothpaste on the surface of the chrome plating. Use the opaque white toothpaste, not one of the gel varieties.

2

Rub the toothpaste-covered chrome plating with a soft, clean cloth in small circular and swirling patterns. There is no need to apply a lot of force.

3

Take a fresh cloth and wipe away the toothpaste, revealing a shining, clean surface.

2.                            Vinegar Method

4

Pour undiluted distilled white vinegar into a spray bottle.

5

Spray the surface of the chrome plating with the undiluted vinegar.

6

Wipe down the surface with a clean cloth.

3.                            Baby Oil Method

7

Dampen a portion of a soft cloth with baby oil.

8

Rub the baby oil into the chrome plating in the same manner as you did with the toothpaste.

9

Wipe off excess baby oil with a fresh cloth or a still fresh portion of the same cloth.

10

Wipe down the newly cleaned area with soapy water to remove any greasy feeling from the baby oil, if desired.

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How to Chrome Plastic Parts

How to Chrome Plastic Parts

1

Take the part down to the bare plastic. You can do this by etching the parts with strong chromic acid, according to Atlas Chrome. This will give you a basic surface to begin working on.

2

Repair any cracks or splits in the plastic part. You can do this by using epoxy glue purchased at your local auto supply store.

3

Dip the plastic parts with silver so that that they will conduct electricity.

4

Layer a conventional plating process such as copper, nickel or chrome onto the plastic parts in several layers. You will most likely need to lightly sand and buff the plastic parts prior this process as well.

5

Apply the chrome plating to the plastic parts for the final revamp. Do this by soaking them in a chrome plating solution for about five minutes

How to Make a Two Part Mold

There are several different ways to make molds. The most common mold types are one-part and two-part molds, with the complex three-part molds used a little less often. One part molds are best suited to flat-backed designs, as they typically require one side of the mold to be completely open at all times. Two part molds are used for most other projects, as they can be taken apart to retrieve a cast object. Three part molds are like two part molds, but have an added inner piece that makes the casting hollow.

Instructions

1

Coat your model with mold release, so that the mold material does not stick to the model.

2

Create an open-top box that will hold your liquid mold material. You can make the box out of pieces of thick cardboard or even wood, although cardboard will be easier to take apart later. Make sure that the box is at least 1/4 inch bigger than the model in all dimensions.

3

Seal the corners, edges and bottom of the box with modeling clay, so that none of the mold material leaks out of the box.

4

Mix together a batch of your mold-making material. Typically, two-part molds are made from either plaster or rubber. Make sure to take the appropriate safety precautions for the material you have chosen.

5

Pour the mold material into the box. Stop pouring once the box is half-filled. Discard the rest of the mixture.

6

Let the mold material sit for several minutes to firm up slightly. When the material is ready, press the model into it so that half of the model has sunken into the material. Let the other half of the model sit above the surface.

7

Let the mold material harden completely. If you have used plaster or rubber, this will set in 12 hours.

8

Coat the top of the mold, which has the model sticking out of it, with mold release. This will make the mold easier to separate later.

9

Make another batch of your mold material. Pour the material into the box, covering the model completely. Fill the box.

10

Let the mold material harden completely. When the material has hardened, take the box apart.

11

Pull each side of the mold apart and remove the model from the inside. Fit the mold back together.

12

Tie the mold together with rubber bands or cording. Carve a hole in the mold, at the seam, that reaches the inside cavity. Use this hole to pour your casting material.

How to Generate Runner Sizes for Plastic Injection Mold Design

The runner feeds the molten plastic from an injection machine into the mold to form the desired plastic part. The length of the runner is completely dependent on the part design, so there are no specific rules regarding overall length. It is the diameter of the runner that impacts part quality and cost and therefore it should be sized with some care. Once the runner freezes, no more plastic can be injected into the part. The runner should be sized to make sure that part receives sufficient plastic without excessive fractional heating, while freezing quickly enough to minimize cycle time.

Instructions

1.                            Calculating Runner Diameter

1

Determine thickest cross-section of the desired part.

2

Where part design allows, locate runner nearest to the thickest cross section of the part. If the part is of a uniform thickness, locate the runner near the center or along the longest edge, as part design allows.

3

Runner diameter should be between 75% to 100% of the part thickness where the runner is located.

4

Based on your injection machine type, determine the acceptable pressure drop for an injection cycle.

2.                            Calculate Injection Pressure Drop

5

Calculate runner volume. V = pi x r^2 x L, where pi = 3.14159, r = runner radius and L = runner length.

6

Calculate volumetric flow rate (Q) based upon your pre-determined fill time. The fill time is a function of material type, part thickness, and desired cycle time. The molder must know this independent of this exercise. Q = V/t, where t = seconds of fill time.

7

Calculate shear rate (S). S = 4Q/(pi x r^3)

8

Calculate the pressure drop (P). P = (S x m x 2L)/r, where m = melt viscosity of the plastic. The melt viscosity is a function of S, melt temperature, and the material. The molder must know this independent of this exercise, although many plastic suppliers can help with this.

9

Compare pressure drop to predetermined acceptable pressure drop. If improvement is desired, change the runner diameter and repeat the exercise. Repeat calculation until an acceptable runner diameter is found.

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Two Different Types of Injection Molding

Injection molding is a manufacturing process for producing high volumes of finished parts at a low cost per part. Various plastic or rubber parts are produced in a wide range of colors. The injection molding machine injects heated molding material to the part mold through input channels. The two principal types of injection molding machines use either a cold runner channel or a hot runner channel.

Cold Runner Machines

Cold channel injection molding machines cool the entry channel, or runner, after each part is molded and ejected. During each molding cycle a part is produced with material in the runner channel. After the part is ejected, the runner is waste material and must be separated from the molded part. Runner waste is reground and reused or thrown away. Disposed material affects part cost. Reground and reprocessed material may affect part quality. Changing part colors in a cold runner machine is fairly easy since each ejected parts carries the material with it. Cold runner machines offer the advantages of cheaper mold designs, lower maintenance costs and lower operator skills.

Hot Runner Machines

Hot runner injection machines keep the runner portion of the mold hot. This reduces or eliminates runner scrap material, which may reduce part costs. Hot runnermachines are more expensive than cold runner machines. Hot machines require more skilled operators and require costly maintenance. Changing colors in hot runner machines is difficult because material is hard to remove from the runners. Hot runner machines eliminate wasteful runner scrap and the need to separate them from molded parts.

Changing Injection Molding Technology

Until recently, all injection molding machines were hydraulic devices. Newer machines are operated by an all-electric process or a hybrid combination of both technologies. Each injection molding process has an advantage. Hydraulic injectors offer high injection rates. Electric injection machines produce precision parts accurately and consistently. Hybrid machines are best suited to part positioning accuracy and repetitive parts. In a paper presented in May of 2008 to the Energy Technology Conference at New Orleans, Amit Kanungo and Eric Swan, senior engineers for RLW Analytics stated, "though it is a challenge to choose a right machine for molder's processing needs, by most accounts in the near future, all-electric machines will dominate the injection molding industry in the U.S."

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What’s hot runner mold?

  It use an assembly of heated components in plastic injection molds that inject plastic into the cavities of the mold. There are two general types of runnerless molds  - the insulated system and the hot runner system. Hot runners mold retain the advantages of the insulated 
  runner system over conventional cold runner system and eliminate a number of the disadvantages. Hot runner system is one of the more important enhancements you can incorporate into a mold to improve molded part quality, reduce production times and remain price competitive

  Injection Mold with Hot runner Solution will use reliable hot runner system and mold design tools. Our engineering department work harder and quicker than any other supplier to offer you new design ideas and mold concepts using any kind of hot runner system.with long history of experience and reliability for plastic injection molding and hot runner mold manufacturing,  we can deliver the best solutions. 
  Although there are many hot runner manufactures , a few major components is same:
  1. Hot runner plate (MANIFOLD)
  2. Nozzle

3. Temperature Controller
  4. Auxiliary parts

  Advantage of hot-runner mold in injection molding industry  

 Why some many customer select hot runner to make injection mold .This is mainly due to such injection mold has following salient feature:

  Less plastic raw materials: in the age of expensive oil and raw materials . hot runner technology is the effective way to reduce the materials cost.

  Quickly cycle time for injection molding, Due to no cooling time constrains runner system.

  Plastic can be more uniform state injection into each cavity, the result is consistent quality
  parts. Such injection molding components of good quality and low residual stress after ejection part distortion. reduce product costs, improve product quality

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Types of Plastic Injection Molds

Plastic injection molds create objects when melted plastic is forced into mold cavities. They often are used in mass-manufacturing operations to create products such as toys, kitchen utensils, bottle caps and cell phone stands. You can spot items constructed using an injection mold by the "flash lines" of extra plastic around the seams. Here are four major types of injection molds commonly used.

Cold Runner Molds

Cold runner molds are the most common type of plastic injection molds. These molds use a sprue and runner to inject plastic into each cavity. However, the sprue and runner harden along with the part once it solidifies. Workers then cut these pieces off and recycle them. This can create a problem with waste, which may make them less economical to use.

Two-Plate Cold Runner Molds

Two-plate cold runner molds are so named because they feature two plates that fit together. There is only one parting plane, and that is where the runner must be located. This is the simplest type of cold runner mold.

Three-Plate Cold Runner Molds

Three-plate cold runner molds have three pieces, which means there are a pair of parting planes. The three pieces are the runner plate, the moveable plate and the floating plate. The runner plate contains the sprue and half the runner. The moveable plate contains the part's ejector system and half the part's geometry. The floating plate contains the other halves of the runner and geometry. The system can be located at either parting plane, and the piece can be gated anywhere on the surface to provide flexibility.

Hot Runner Molds

Hot runner molds deliver plastic in a different way. While cold runner plastic injectors cool along with the part, the runners in hot runner molds are situated inside the mold and kept at a temperature higher than the plastic's melting point. This means the sprue and runner never have the chance to harden. This also reduces the amount of wasted plastic. However, hot runner plastic injection molds require more skill and maintenance and have a higher baseline cost. However, they often pay for themselves based upon the material savings.

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What Is Injection Molding Used for?

Injection molding is used for manufacturing plastic, rubber and metal. Materials are fed through a heated barrel in the machine and forced into a mold where it will cool and take its shape. An injection molding machine can stamp out metal car shell parts, rubber valve steam seals, and even plastic toys for kids.

 

Plastic

Injection molds uses plastic to make toys for children, milk containers and movie cases. It also makes other plastic products such as combs, kitchen utensils and dust pans.

Rubber

Injection molds make many rubber automobile parts. It makes valve steam seals and oil seals for the engine. It also makes earplugs, rubber hoses and telecommunications items.

Metal

Injection molds can stamp out small to large items. It can stamp out automobile parts from spark plugs and floor pans to ball bearings. It also can stamp out items like TV hangers and knitting needles.

 

 

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injection molding （2）

injection molding

 

Injection molding is a plastic manufacturing process whereby granules of plastic are heated until they melt and are then forced into a specially designed mold. Once in the mold the plastic is allowed to cool and hardens into the form of the mold. Injection molding is widely used in industry to produce plastic artifacts like computer casings, toys and cookware.

Barrel

·                                 The key part of an injection molding tool is the barrel. This is a metal cylinder that houses the reciprocating screw. The plastic granules are emptied into the barrel via the hopper and while in the barrel a combination of heat from the heaters and friction from the reciprocating screw liquidizes the plastic pellets. At the end of the barrel is an injection nozzle, through which the molten plastic is injected into the mold.

Reciprocating Screw

·                                 The reciprocating screw sits inside the barrel of the injection molding device. This tool rotates and forces the plastic pellets through the barrel and into the mold. In appearance, the reciprocating screw is roughly cylindrical, tapering slightly to a point at one end. Its outer surface is shaped into a screw thread.

Hopper

·                                 The hopper is a tool used to store the plastic granules before they enter the barrel. It consists of a large funnel into which the plastic granules are deposited before they enter the barrel.

Heater

·                                 The heaters sit around the barrel and raise the temperature of the plastic granules to the point at which they melt. This enables the molten plastic to be injected into the mold. The heaters sit wrapped around the cylinder and are powered by electricity.

Mold

·                                 The mold and the corresponding mold cavity determine the final shape of the injection molded artifact. There are certain limitations on the design of the mold and the design of the molded artifacts caused by the necessity of being able to remove the artifact once it has solidified.

Mobile Platen

·                                 The platen is a mobile flat plate that is used to push the mold and the mold cavity together. This ensures that the molten plastic migrates to every part of the mold and mold cavity. The platen is held in place against the mold by a clamp.

Clamp

·                                 The purpose of the clamp is to hold the mold and the platen as close together as possible while the molten plastic is setting into the final shape of the injection molded artifact. The clamp is often adjustable so the pressure on the platen can be increased to ensure that the molten plastic has reached every part of the mold cavity.

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