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.

The Stages of Blow Moulding

today virtually all cast plastic parts are manufactured using blow molding technology.

Blow molding is a process used to cast plastic parts that are hollow. Since 1942 when the first polyethylene bottle was produced using blow molding technology, blow molding has become the standard manufacturing process for making cast plastic parts. Blow molding involves the fabrication of a tube made of molten plastic called parison. The next stage of the process is to shape the tube into the desired form using one of several blow molding processes.

Heating The Resin

The first step in any blow molding process is to heat the resin. Thermoplastic resin is heated to about 400 degrees. Once the resin reaches its molten state, it is extruded over a die head. The die head forces the thermoplastic resin to flow around it, thus creating a hollow center in the resin. The resin has now formed a tube called parison.

Molding

The parison is then placed inside a pre-determined mold. The interior shape of the mold cavity is what will ultimately determine the shape of the finished casting. The mold is then closed around the parison. At this point in the process, the parison is still very warm. The mold however, is cooled with water.

Inflation

Compressed air is then blown into the mold. The air fills the center of the parison tube and forces the sides to expand, thus conforming to the shape of the mold interior. The parison is still very warm at this point to allow it to expand without breaking. As the warm parison expands to meet the cold walls of the mold, it freezes off and becomes rigid.

Cooling

Once the warm parison has cooled off, it solidifies inside the mold. Once properly cooled, the parison will maintain the form in which it was cast. The mold can now be opened and the finished plastic component removed.

hinjection molding, mold shop tool maker :http://www.freetech-mould.com

How to Calculate Molding Machine Sizes

Producing quality plastic products requires a molding machine that has been properly sized.

Molding machines come in a wide variety of clamp tonnages. The clamp tonnage refers to the amount of force that the machine can exert on a mold while the molten plastic is being injected. The plastic is injected into the mold at high pressure in order to ensure that the mold is completely filled before the plastic hardens. The pressure of the injection when coupled with the surface area of the mold creates a force that must be counteracted by the molding machine. The molding machine must be sized to handle this force to produce acceptable products.

Instructions

1.                            Sizing a Molding Machine

1

Determine the surface area of the part that is being molded in square inches. If it is a multiple cavity mold, the surface area associated with each cavity along with the runners that feed each cavity should be included in the total surface area.

2

Determine the planned injection pressure in pounds per square inch (psi). The injection pressure will be a function of the material that you are using and the part wall thickness. A material supplier can help determine the injection pressure.

3

Determine the pressintensification ratio for the molding machine. This is a function of the machine's screw and the hydraulic piston that acts upon it. The machine supplier can provide this information if it is not already known.

4

Multiply the injection pressure by the intensification ratio. This provides the plastic packing pressure in psi.

5

Multiply the plastic packing pressure by the part surface area. This results in the total pounds of force that will be exerted on the mold in pounds.

6

Divide the pounds of force by 2,000 (2,000 pounds = 1 ton). This provides the tons of force required to be offset by the molding machine's clamp tonnage. This gives the minimum clamp tonnage size needed for a molding machine for the specific product in question.

http://www.freetech-mould.com

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."

http://www.freetech-mould.com/product.html

Research and Forecast of Injection Molding Machine Industry in China, 2014-2018

The injection molding machine belongs to the plastic machinery type that has the largest output and application volume in China, as well as being the main force of China's plastic machinery export. In 2013, the export volume of injection molding machines was 22,946 sets with the export amount of USD 932 million; in 2012, the export volume was 24,830 sets, so the export volume in 2013 declined, but the export value in 2013 increased 3.78%, which fully shows that the average price of export products of China's injection molding machines is gradually growing. With the increasing demand for plastics, plastic machinery industry has huge market potential. From the global perspective, the top three plastic machinery types are injection molding machine, extruder/extruder production line and blowing molding machine, which account for more than 80% in the plastic machinery total output value. Among them, injection molding machine accounts more than 50% of the total output value of these three main types of plastic machines. 

In 2013, the output of China's injection molding machines was about 82,000 sets, rising by 4.21% compared with 2012. On the whole, the growth of China's injection molding machine industry gradually slowed during the year of 2007 to 2013, but the output was still rising. During 2007 to 2013, the average growth rate of output of China's injection molding machines was 4.77%. 

As this report estimates, the market supply volume of China's injection molding machines will reach 86,175 sets by 2014, 89,612 sets by 2015 and about 101,095 sets by 2018

http://www.freetech-mould.com

what's color mold? double shot molding two shot mold double injection

Color mold : two on the same plastic injection molding machine , a two- molding, but the product just only in one mold die . In general, this is also called double injection molding process. it is usually done by a mold , and need specialized color injection molding machine . Color mold growing popularity on the market today , it can make the appearance of the product is more beautiful from the process, easy to change colors and no no painting, also expensive and high technically demanding .

1 two female molds are different , each forming one kind of products, and the two male molds are the same.

2 before the mold, the mold in the center of the rotation after 180o, must match. This inspection must be done during mold design , this points have high demand for the mold base positioning  process.

3 The total thickness of the front plate plus A plate must be not less than 170mm. Please carefully review the reference data of the injection molding machines. for example, the maximum and minimum thickness of the mold, KO -hole distance etc.

4 the gate of three plates mold preferably designed to automatically release action. Particularly pay attention to the gate release of soft part..

5 when design the second injection of the female die , in order to avoid secondary mold insert ( or rub ) the first part with good product molding, can make some clearance . However, the intensity must be carefully considered . During injection ,if there will be a big injection pressure , it will cause deformation , resulting in flash problem in the second injection ?

6 during the injection , the first injection molded product may be slightly larger size , so that it can be formed in the second well tightly, in order to achieve the effect of sealing compound .

7 pls note that in the second injection , the plastic flow will impulse the first product and cause part deformation ? If there is the possibility, must find ways to improve .

8 Before A, B plate clamping , pay attention to the mold slider or lifter ,if they will be reset and the crushed product ? So , we must find ways to make the A, B plates first clamping , then make the slide or lifters reset second.

9 the water of two female molds and the male mold transport as fully and balance as possible

10 99% of the injection molded hard plastic case is the first part of the product , and then injection molded soft part . Because soft part have deformation problem .