Leafly Mould Blog

The history of rotational molding began somewhere between 1940 and 1950 in the USA when the process was developed for a small number of plastics. By the late 1950s, when the rotational molding process was better understood, applications for other industries were developed including road cones, marine buoys, and car armrests. A process was developed in Europe in the early 1960s that enabled large hollow containers to be created in low density polyethylene (LDPE) by rotating (or rocking) a mold on a chassis, houses open gas jets, through 30 degrees which coated the inside of the mould with the polymer…

The history of plastic injection molding has seen steady industry growth since its beginnings in the late 1800s. The technique has evolved from the production of combs and buttons to major consumer, industrial, medical, and aerospace products. In 1868, John Wesley Hyatt invented a way to make billiard balls by injecting celluloid into a mould.

Plastic moulding is the process of shaping plastic using a rigid frame or mould. The technique allows for the creation of objects of all shapes and sizes with huge design flexibility for both simple and highly complex designs. A popular manufacturing option, plastic moulding techniques are responsible for many car parts, containers, signs and other high volume items.

Plastic Moulding Techniques

The underlying concept of plastic moulding is placing liquid polymer into a hollow mould so that the polymer can take its shape, often with various ranges of pressure and heat required. There are different plastic moulding techniques available to accomplish this including rotational molding, injection molding, blow molding, and compression molding to name just a few. Each technique has its benefits and is best suited for the creation of specific items.

Plastics are synthetically produced non-metallic compounds. It can be molded into various forms and hardened for commercial use. Plastic molding products can be seen everywhere. Examples are jars, protective caps, plastic tubes, grips, toys, bottles, cases, accessories, kitchen utensils and a lot more.

Even the keyboard and the mouse that you use are made through plastic molding. Even the plastic parts of the chair that you are sitting on are created this way.

The basic idea in plastic molding is inserting molten liquid plastic into a ready shaped mold, for example the mold of a bottle. It will be then allowed to cool, then the mold will be removed to reveal the plastic bottle.

Plastic molding can also custom-mold a wide variety of plastic products including: garden pots, cabinets, office trays and boxes, barriers, barricades and traffic signage and displays for product and marketing promotions.

If you are planning to go into plastic molding business, you should first know the different processes. Choose from a plastic molding process that fits your budget, your expertise, and your resources. Here are basic definitions of various methods of plastic molding.

The Plastic Molding Processes:

Injection Molding
In Injection Molding, melted plastic is forced into a mold cavity. Once cooled, the mold can be removed. This plastic molding process is commonly used in mass-production or prototyping of a product. Injection molding machines were made in the 1930’s. These can be used to mass produce toys, kitchen utensils, bottle caps, and cell phone stands to name a few.

Blow Molding
Blow molding is like injection molding except that hot liquid plastic pours out of a barrel vertically in a molten tube. The mold closes on it and forces it outward to conform to the inside shape of the mold. When it is cooled, the hollow part is formed. Examples of blow molding products are bottles, tubes and containers.
Equipments needed in setting-up a blow molding business are relatively higher than injection molding.

Compression Molding
In this type of plastic molding, a slug of hard plastic is pressed between two heated mold halves. Compression molding usually uses vertical presses instead of the horizontal presses used for injection and blow molding. The parts formed are then air-cooled. Prices of equipments used for compression molding are moderate.

Film Insert Molding
This plastic molding technique imbeds an image beneath the surface of a molded part. A material like film or fabric is inserted into a mold. Plastic is then injected.

Gas Assist Molding
Also called gas injection molding is used to create plastic parts with hollow interiors. Partial shot of plastic is then followed by high-pressure gas to fill the mold cavity with plastic.

Rotational Molding
Hollow molds packed with powdered plastic are secured to pipe-like spokes that extend from a central hub. The molds rotate on separate axes at once. The hub swings the whole mold to a closed furnace room causing the powder to melt and stick to the insides of the tools. As the molds turn slowly, the tools move into a cooling room. Here, sprayed water causes the plastic to harden into a hollow part. In this type of plastic molding, tooling costs are low and piece prices are high. Cycle time takes about 40-45 minutes.

Structural Foam Molding
Structural foam molding is a process of plastic molding usually used for parts that require thicker walls than standard injection molding. Inserting a small amount of nitrogen or chemical blow agent into the plastic material makes the walls thicker. Foaming happens as the melted plastic material enters the mold cavity. A thin plastic skin forms and solidifies in the mold wall. This type of plastic molding can be used with any thermoplastic that can be injection molded.
Thermoforming

In this plastic molding process, sheets of pre-extruded rigid plastics are horizontally heated and sucked down into hollow one-piece tools. When the hot plastic solidifies, its shape conforms to that of the mold.

Tooling costs are usually low and piece prices vary on the machinery.

Plastic molding is a very technical process. It needs experts in this type of manufacturing business for it to be competitive in the market. Therefore, a very scientific and systematic study should be first made before going into this endeavor.

Injection molding is often ranked as the one of the commonly used processes in the production of plastic items. The popularity of plastic injection molding is often due to the fact that it is a fast process which can be used to produce vast quantities of identical plastic items ranging from disposable consumer goods to high precision engineering components.

Typically Produced Products
The majority of thermoplastics, such as nylon, polystyrene and polycarbonate are produced through the injection molding process, as are the majority of all plastic products ranging from micro parts to large components such as wheelie bins. Also, the fact that this process can produce items that range greatly in shape and size has resulted in the extension of the boundaries of plastic design and enabled significant replacement of traditionally used materials in part due to light weighting and freedom of design.

The Basic Process
The basic process involves the introduction of a material, via a hopper, into the injection molding machine. This molding machine consists of a heated barrel, equipped with a reciprocating screw (which is driven by a hydraulic or electric motor), which itself feeds the molten polymer into a temperature controlled split mold through a channel system of runners and gates.

The reciprocating screw plasticises (melts) the polymer as well as acting as a ram during the injection phase. The shearing action of the screw on the polymer also provides additional heating during this part of the process and the polymer is then injected into a mold which is created according to the required dimensions of the finished product.
The pressure used when injecting the polymer into the mold is very high and (depending on the material being processed) this pressure could even reach one thousand atmospheres.

The tools used in the plastic injection molding process are typically made out of steel (as it can be hardened and plated if required) and alloys of aluminium to allow increased cutting and hand polishing speeds. The costs associated with the production of the tools required in this process mean that injection molding tends to lend itself to high volume production of plastic products and components.

There is a large number of companies which specialise in the production of plastic components and products via injection molding and the supply of molds for the process. The fact that the service provided by these companies is demanded by a wide range of customers (including those in the defence and aerospace industries) shows the importance of this process and the necessity of its products.

vehicle body stampings broadly divided into panels, beams, parts and general stampings. Able to image features clearly indicated that car is the automotive panel stamping. Classification of automotive plastic mold many ways, in accordance with the method of molding plastic parts can be divided into different categories:

Compression mode: compression mode, also known as mold or adhesive mode suppression. This mold is characterized by the molding process the plastic material directly added to the open mold cavity, then close the mold, the plastic under heat and pressure in the molten state was after the cavity filled with a certain pressure. At this point, the molecular structure of plastics chemical cross-linking reaction, and gradually harden stereotypes. Compression mode used for thermosetting plastics, the molding of plastic parts for the electrical switches are mostly shell and daily necessities.

Extrusion die: also known as extrusion die extrusion die. This section of the mold can be the same shape as the continuous production of plastic, such as plastic pipe, bar, sheet and so on. Extruder heat and pressure of the device and the device the same injection machine. Molten plastic through the nose to form a continuous molded plastic parts, especially high production efficiency.

Injection Mould: injection mold, also known as injection molding. This mold is characterized by the forming process will be placed in the injection machine plastic raw materials, heating the barrel. Heated molten plastic in injection molding machine screw or plunger driven by the nozzle and the casting mold system into the mold cavity, the plastic in the mold cavity by heat, pressure, cooling, curing. As heat and pressure devices can play a role in phases, not only molding injection molding of plastic parts of complex shape and high efficiency, good quality. Therefore, in the plastic injection molding parts account for a large proportion of molding, plastic mold injection mold accounted for more than half. Machine is mainly used for thermoplastic injection molding, in recent years have gradually molding for thermosetting plastics.

Stripping reasons for the difficulties

A mould from the groove
2 stripping slope less than
3 mould finish is not high

II. Related Knowledge

1 As the stripping slope failure caused by lack of very common during the product design, mould must be marked in surface slope, stripping slope is usually in the range 1 to 2 degrees, in this context much good as far as possible, allow for special occasions, more than 0.5 degrees
2 If the injection pressure is too high, products closely aligns with the mould too closely, it becomes difficult to mould
3 in order to successfully make the products from the mould, silicone mould release agents containing generalists, but only when using a thin coating of release agent layer. If the coating is too thick to wipe hard. Well as release agent to the role of the print markings on the products of secondary processing becomes very bad, once the coating on the mould release agent attached to the products on the wipe is quite difficult to think of.

II. Related Knowledge

1 As the stripping slope failure caused by lack of very common during the product design, mould must be marked in surface slope, stripping slope is usually in the range 1 to 2 degrees, in this context much good as far as possible, allow for special occasions, more than 0.5 degrees
2 If the injection pressure is too high, products closely aligns with the mould too closely, it becomes difficult to mould
3 in order to successfully make the products from the mould, silicone mould release agents containing generalists, but only when using a thin coating of release agent layer. If the coating is too thick to wipe hard. Well as release agent to the role of the print markings on the products of secondary processing becomes very bad, once the coating on the mould release agent attached to the products on the wipe is quite difficult to think of.

III. Solution

An instant: decreased injection pressure, shorter dwell time, lower temperatures reduce the ejection speed of the mould, spray release agent
2 Short-term: to improve the finish of the mould cavity
3 Long-term: increase the stripping slope, increase the number of ejection pin

IV. Material Differences

1 is heavy and hard materials, such as GPPS, due to lack of slope hat thing common cause product damage. Of both sticky and soft materials like PE, has the potential to block the root of certain products were cut

In recent years, the financial crisis makes the slump, but the portable electronic products in the day and night to practitioners, but a lot of people are in short supply. Short and thin portable electronic products, pay attention, when shell thin to almost 1 mm, or less than 1 mm, the material suppliers, product and mould designers, mould factory, moulding plant and machine equipment manufacturer and subsidiary is a challenge. In this paper, shell moulding from material selection, product and mould design, CAE analysis, mould forming machine and equipment settings to choose the highlights. Period to initiate a total creative machine.

Fixed electronic products, the shell enable cost reduction, cycle time, thus increasing productivity. For portable electronics, the lighter weight shell allows the size reduction. Demand for portable electronic products grew by 30% per year, growth will be faster the next decade. With this product were also very few – less than 5% in the United States, less than 1% of the world – the market is amazing.
Typical shell thickness ratio of flow length on the range of 100:1 to 150:1 or more. To achieve such a high ratio without increasing the gate, they have high melt temperature, high injection pressure and the high rate of fire.
C-Mould simulation of injection moulding using the Cross-WLF model viscosity is as follows:
This model can be moulded in a wide range of conditions appropriate description of viscosity, one of the benefits is a better deal viscosity on the temperature and pressure sensitivity (viscosity The sensitivity of the pressure increases as temperature decreases). In the Cross-WLF viscosity model, the pressure on the viscosity to D3 show. In the traditional moulding conditions, the pressure had no significant effect on the viscosity, D3 can be set to 0. Under high pressure, the pressure on the viscosity becomes important, D3 must decide to make the simulation results can capture the effects of stress. D3 to obtain a reasonable value, the viscosity of special test procedures and data analysis is necessary.
Without taking into account the impact of pressure on viscosity, when the system pressure increases, the forecast error will be greater and greater pressure. The figure of the flat plate model is a good example of non-zero entry pressure on the viscosity of D3 can improve the filling and post-filling simulation of pressure prediction. Flat plate with polycarbonate (PC) material, the average thickness is 1mm, flow length is 170mm. Pressure on the viscosity of item D3 into the calculation, the predicted pressure was significantly increased, and quite consistent with the measured pressure.
Through the sprue gate, pin point gate, the second hot runner poured directly into the gate so thin, you should use the gate well, in order to reduce gate stress, to help fill, and products in time to the gate damage to a minimum. When the wall thickness less than 1.2mm, the diameter often greater than the thickness of the gate used to help flow, and coagulates in the gate before the completion of the appropriate tamping.
In order to have enough pressure to fill the thin cavity, flow pressure drop preferably not more than the machine can provide 15% of injection pressure. Great use of more traditional flow from 1.25 to 1.4 times the flow. Select more entrants with valve gate hot runner to effectively reduce the pressure to expectations.