What is Injection Molding Process

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.

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Automotive Plastic Mold

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.

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Stripping reasons for the difficulties

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

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Introduce about Shell Moulding

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.

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High thermal conductivity copper alloy mould

High thermal conductivity copper alloy mould manufacturing plant can have higher production efficiency, both to save money, but also improve product quality. Some car bumpers and instrument panels manufacturing companies have used this kind of material the mould and has achieved significant production efficiency.

With the normal industrial / die steel compared to copper-based alloys due to the high cost of production in the mould, therefore, a lot of mould factory has yet to find a better way to make a rational use of high thermal conductivity copper alloy materials, But in fact, the use of high thermal conductivity of copper alloys to save time and efficiency benefits of such areas is very significant.

In this paper to explore the high thermal conductivity copper alloy is a copper-based materials, alloys and manufacturing techniques by the method of combining, it is necessary to keep copper inherent characteristics of the high thermal conductivity, but also it has a certain hardness to be able to let in a production environment for a variety of processing conditions.

The main advantage of copper alloy

In the injection mould in the use of high thermal conductivity of copper alloys include the following special advantages:

A, thermal diffusivity properties

Plastic in the mould of the injection moulding process, the high thermal conductivity copper alloy will absorb a large amount of heat, of course, its initial absorption of heat is a key factor, while the latter will rely mainly on thermal cooling system. In each plastic injection process, heat is absorbed the initial rate of high thermal conductivity copper alloy to play a role in a real place.

2, polished performance

In contact with plastic packaging used in the production process of high thermal conductivity copper alloy moulds, its excellent polishing performance has been proven in practice. In a highly polished high thermal conductivity copper alloy inserts in the future, you can create high-quality transparent plastic packaging, to meet the inspection through the packaging production needs. Practice has proved that this inserts polished steel inserts longer than the time required to finish four times faster, work cycle, but it can reduce 57%.

3, coating

In order to improve the wear resistance, high thermal conductivity copper alloy surface can be easily coated with a layer of non-plated nickel coating, hard chrome coating, PVD coating (physical vapor deposition layer), or CVD coating (chemical vapor deposition layer), so that the hardness of the surface coating to achieve 60 ~ 90 HRC. Non-plated nickel coating can make uniform the thickness of the coating to penetrate into every hole, but its essence is not as galvanizing process, as is also not as hard as chrome plating process. In order to facilitate the plastic mould release, non-plated nickel coating with PTFE (PTFE) or a combination of boron nitride materials. PTFE or boron nitride coated with non-plated nickel coating the surface of the mould parts are very smooth as if coated Feizao Mo in general, it will not make already-formed plastic pieces glued to the mould, the mould release very easily.

Of course, the use of high thermal conductivity copper alloy moulds, there are some limitations, such as eliminating stress or annealing (the only way to maintain the hardness of the material characteristics) should be placed in a long time to avoid mould temperatures above 900 F being.

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Mold temperature in injection mold Applications

1, the heat balance control of injection mold injection molding machine and mold thermal conductivity is the key to producing injection molded parts. Internal mold, made of plastic (such as thermoplastics) caused by thermal radiation heat transfer to the material and mold steel, heat conduction through the fluid circulating handed. In addition, the heat transfer by thermal radiation into the atmosphere and is mold. Thermal conductivity of the fluid is absorbed by the mold temperature to the heat away. Mold thermal equilibrium can be described as: P = Pm-Ps. Where P is the mold temperature away the heat; Pm plastic into heat; Ps emitted to the atmosphere to heat the mold.

2, the purpose of controlling mold temperature and mold temperature on the impact of injection molded parts injection molding process, the main purpose of mold temperature control of the mold is heated to one temperature, the second is to maintain a constant temperature in the mold temperature. The success of these two points do, you can optimize the cycle time, thereby ensuring the stability of high-quality injection molded parts. Mold temperature will affect the surface quality, liquidity, shrinkage, deformation and molding cycle aspects. Mold temperature too high or inadequate for the different materials will have different effects. Of thermoplastics, the mold temperature is usually a little higher will improve the surface quality and liquidity, but will extend the cooling time and injection molding cycle. Lower mold temperature will reduce the shrinkage in the mold, but will increase after the injection molding mold shrinkage. While thermosets, the higher mold temperature will usually reduce cycle time and cooling time from part time decision. In addition, plastic processing, the higher mold temperature will reduce the plasticizing time, reduce cycle times.

3, effective control of the preparation conditions of mold temperature control system consists of the mold temperature, mold temperature, heat transfer fluid of three parts. To ensure that heat can be added to the mold or removed parts of the system must meet the following conditions: first, in the mold inside the cooling channel surface area must be large enough in diameter to match the flow capacity of the pump (pump pressure). Cavity in the temperature distribution of parts deformation and internal pressure have a great impact. Reasonable to set the internal pressure of the cooling channel can be reduced, thus improving the quality of injection molded parts. It can also shorten the cycle time, reduce product cost. Followed by the mold temperature must be able to heat the fluid temperature constant at 1 deg -3 deg range, depending on the quality of injection molded parts required to be. The third is the thermal conductivity of the fluid must have good thermal conductivity, most importantly, it must be able to import or export in a short time a lot of heat. From the thermodynamic point of view, the water was significantly better than oil.

4, mold temperature machine works by the water tank, heating and cooling systems, power transmission systems, level control system and temperature sensors, sprue and other device components. Typically, power transmission systems in the thermal fluid from the pump with built-in heater and cooler tank to reach the mold, and then die back from the water tank; temperature sensors measure the fluid temperature and heat transfer to the control part of the data controller; controller regulates the temperature of hot fluid, and thus indirectly regulate the temperature of the mold. If the mold temperature in the production, the mold temperature exceeds the set value the controller, the controller will open the solenoid valve connected into the water, heat until the liquid temperature, mold temperature back to set that value. If the mold temperature is below the set value, the controller will turn on the heater.

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Characteristics and Application of PPS

First, properties (1) General performance: PPS as a white appearance, high crystallinity, hard and brittle polymer, the relative density of pure PPS 1.3, but the modification will increase. PPS There water absorption is extremely small, generally only about 0.03%. PPS flame is good, its oxygen index is over 44%; compared with other plastics, it is a high fire-retardant plastic materials (PVC pure oxygen index 47%, PSF was 30%, PA66 to 29% MPPO to 28%, PC 25%).
(2) mechanical properties: the mechanical properties of pure PPS is not high, especially low impact strength. Glass fiber reinforced will greatly enhance the impact strength, from 27J / m increased to 76J / m, increased 3 times; tensile strength increases by the 6Mpa to 137Mpa, increased 1-fold. PPS rigid high, rare in engineering plastics. The bending modulus of pure PPS up 3.8Gpa, after modification of inorganic filling up 12.6Gpa, increased 5 times. And to rigid PPO known only 2.55Gpa, PC only 2.1Gpa.

PPS resistance to creep under load, good, high hardness; high wear resistance, abrasion when his 1000 transfer was only 0.04g, molybdenum disulfide filled F4 and will be further improved upon; PPS also has a certain self-Yun sex. The mechanical properties of PPS temperature sensitivity to small (3) Thermal Properties: PPS has excellent thermal properties, short term resistance to 260 deg, and can be 200 ~ 240 deg for long term; its heat resistance and the PI rather, second only in F4 plastic, which is also rare in thermosetting plastics.

(4) Electrical Properties: PPS electrical properties is very prominent, compared with other engineering plastics, the dielectric constant and dielectric loss tangent values are relatively low, and the larger the frequency, temperature and temperature range did not change large; PPS arc resistance, and can be comparable with the thermosetting plastics. PPS commonly used in electrical insulation material, the amount can account for about 30%.

(5) environmental performance: PPS is one of the best features of a good chemical resistance, chemical stability after the F4; PPS on the most acid, ester, ketone, aldehyde, phenol and aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons so stable, intolerance and oxidative chlorinated biphenyl acid, oxidants, concentrated sulfuric acid, concentrated nitric acid, aqua regia, hydrogen peroxide and sodium hypochlorite, etc.. Good radiation resistance of PPS.

Second, application

(1) Automotive: PPS for the automotive industry accounted for 45%, mainly for automotive functional parts; such as production of discharge pipe loop can replace metal valves and water pump impeller, such as pneumatic signal modem.

(2) Electronics: PPS can be used for electrical and electronic industry, 30%, which is suitable for ambient temperature higher than 200 high temperature electrical components; can produce generators and engines on the point of shabu, shabu electric brackets, starter coil , shield and blade; the TV can be used for high voltage shell and socket, binding post and terminal board; in the electronics industry, manufacturing transformers, choke ring and frame relay and housing, integrated circuit carrier; use high-frequency performance, manufacturing H-level routing frame and fine-tuning capacitors.

(3) Mechanical industry: for housing, structural parts, wear parts and sealing materials, specifically a pump, valve, bearing, bearing bracket, piston rings and gears.

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Selection of the three principles of mold

A) working conditions to meet the requirements of the mold
1, abrasion resistance

Blank in the mold cavity in the plastic degeneration, both the flow and along the cavity surface of the slide, so that the cavity surface and generates intense friction between the blank, leading to mold due to wear and failure. Therefore, wear resistance is the most basic mold, one of the most important performance.

Hardness of the main factors affecting the wear resistance. In general, the higher the hardness of the mold parts, the smaller the amount of wear, wear resistance is also better. In addition, the wear resistance of carbide materials with the type, quantity, shape, size and distribution of the.

2, strength and toughness

Most of the mold is very bad working conditions, often bear some of the larger impact load, leading to brittle fracture. To prevent mold parts sudden brittle fracture at work, die to have high strength and toughness.

Toughness of the mold depends on the carbon content of the material, grain size and organization of the state.

3, fatigue fracture properties

To mold the work process, in the long-term effect of cyclic stress, often leading to fatigue fracture. The form of a small number of energy impact fatigue fracture, fatigue fracture of contacts stretching and bending fatigue fracture fatigue fracture.

Fatigue fracture properties of the mold depends on their strength, toughness, hardness, and material content of inclusions.

4, high temperature performance

When the mold into the higher operating temperature, hardness and strength will decrease, leading to early wear or mold the plastic deformation and failure. Due to mold material should have high resistance to tempering stability, to ensure that the mold in the temperature, the higher the hardness and strength.

5, anti-fatigue properties of hot and cold

Some die in the course of repeated heating and cooling in the state of the cavity surface tension, the pressure change the role of stress, causing surface cracking and spalling, increased friction and hinder plastic deformation, reducing the dimensional accuracy, resulting in die failure. Hot and cold is hot die fatigue failure of the main forms of help such mold should have a high resistance to thermal fatigue.

6, corrosion resistance

Some molds, such as plastic mold at work, because there are plastic chlorine, fluorine and other elements, heat decomposition of precipitation hci, hf and other strong corrosive gases, eroding the surface of the mold cavity, increasing its surface roughness, increased wear failure.

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Two-color plastic injection molding process

Two-color or process color plastic injection molding products is the same raw materials were mixed into two different colors prepared by the two same structure, same size, plastics injection molding machine were two colors melt, and then injected through a nozzle molding die within. Molded plastic products with color separation, and blending, or is irregular pattern, and its effect is the appearance of ordinary injection molding and surface modification are not received. Two different specifications melt plastics injection molding machine nozzle injection completed by alternating from the plasticizing cylinder and the nozzle control valve is between the process control. This two-color injection molding machine structure, plastics injection, two plastics injection unit to the same time, with the feeding quantity, the same pressure, with the injection rate to two different colors, melt through the nozzle with a rotating mandrel injected into the molding mold , the way, can be obtained by injection of different patterns on products . The same two sets of specifications, the structure forms the same equipment and plastics injection mold device is composed. This structure follows the working methods of injection molding machine. Plastics injection unit also completed two after the first injection, two sets of the same structure forming mold around the center axis 180 for, and then the second injection unit by two different colors melt into the molding die within. With this completed in two different colors melt into the same molding die within the movement, get two-color injection molding products .

Two-color injection molding products, process characteristics are as follows.
(1) two-color injection molding machine by the two structures, exactly the same specifications as plastics injection device group. Nozzle according to production needs should have a special structure, or with transposition of the structure can rotate two sets of identical shape mold . Plastics injection, require two sets of plastics injection device in the melt temperature, injection pressure, injection melt feeding quantity and other parameters the same two sets of devices to minimize fluctuations in the difference between the process parameters.

(2) two-color injection molding plastic products, plastic injection molding with the ordinary product comparisons, when the melt injection temperature and injection pressure have a higher value of the parameter. Main reason is two-color injection molding mold flow longer, more complex structure, a larger injection melt flow resistance.

(3) two-color injection molding plastic products to choose good thermal stability, low melt viscosity of the raw materials, in order to avoid the high melt temperature, residence time in a long flow path and decomposition. Application more plastic is polyolefin resin material such as polystyrene and ABS.

(4)color plastic products, injection molding, in order to melt two different colors can be good in the molding in the mold of welding, to ensure injection products, molding quality, should be a higher melt temperature, higher mold temperature, the higher the injection pressure and injection rate.

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Plastic Injection Mould Process

With the modern industrials development, the plastic products industry, agriculture and daily life, and other fields are widely used; quality requirements have become more sophisticated. Plastic products, the production and quality of mold design, advanced mold manufacturing equipment and reasonable processing, mold quality materials and modern equipment are molding quality plastic parts forming an important condition.

In the Injection plastic mould process, hot molten plastic is forced under pressure by a hydraulic ram into a closed mold. The mold is cooled to freeze the plastic in the desired shape, and no chemical reaction takes place.

Plastic injection mould Process, including pressure plastic, blow, extrusion, etc., plastic injection mould processing is the most commonly used methods, apply to all parts of thermoplastic and thermosetting plastics. With the injection mold industry, mold cavity mold and shape the increasingly complex, precision die increasingly high demands, the production cycle requirements become increasingly short.

Plastic injection mould process demands precise control of melt temperature, melt viscosity, injection speed, injection follow-up pressure, switch over point from speed to pressure, cycle time. It is found that different polymers have different characteristics and different limitations in processing. Shear rate and shear stress influence melt temperature, viscosity, density and flow behavior of polymer. Some polymers are hygroscopic, some polymer have limited thermally stable time which is different at different temperature. Such polymers have limited residence time. The changes in each parameter has its own influences on other parameters.

Plastic injection mould process includes a number of factors, some of them are important. They play a decisive role for the quality in the plastic injection mould processing. Such as freezing time and injection time; maximum injection speed; maximum injection pressure; injection power; plasticizing rate; etc.

And plastic injection mould machine application shaping products directly affect the efficiency of production, quality and cost.

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