Features of injection molding

How does a plastic injection molding machine work? The principle of operation of injection molding machines for the production of plastics is to melt granular polymer material to a liquid state. Feed it under high pressure into a closed injection mold. Moreover, the product acquires the exact outlines of the internal cavity of the mold.

In addition, various types of raw materials can be good to use in production: polyethylene, polystyrenes, polyethylene terephthalates, polyvinyl chlorides, and polypropylenes.

However, machines are configured for certain parameters:

• Consistency;
• Degree of viscosity;
• Melting parameters.

The main criterion for choosing a material is the melt flow rate.

How does a plastic injection molding machine work? In addition, the strength, quality, and accuracy of product parameters depend on temperature and pressure values, which should be in the range of 80 to 200 MPa.

Moreover, it is important to strike the right balance, as low pressure can lead to cavities or underfilling, while too high pressure can lead to flashing.

Varieties of plastic injection molding methods

The determining factor in the choice of equipment is the melting methods, which are injection or intrusion.

1. The injection method is suitable for creating parts of complex configurations with walls of various thicknesses: from very thin to thick-walled. Moreover, a popular method is characterized by minimal shrinkage. However, the ability to use multi-cavity molds for plastic injection, and work with any polymers.
2. The intrusion method is suitable for creating three-dimensional parts with thick walls. In addition, by rotating the screw, the molten mass is fed into the injection mold and fills it. Then, under pressure, another small amount of solution is injected, filling all the cavities of the casting mold and compensating for the shrinkage of the cooling melt.

Stages and features of the process

Moreover, the creation of plastic products in injection molding machines takes place in several stages:

1. The polymer raw material is loaded into the receiving hopper of the injection molding machine.
2. Under the influence of their own weight, the granules enter the screw zone, where they are melted under the influence of high temperatures.
3. In addition, under high pressure, through the mouthpiece of the plasticizing module, the molten mass injects into the molds.
4. In the process of cooling, the pressure in the molds gradually decreases, and the products are taken out.
5. However, the entire casting process takes from a few seconds to 10 minutes. Moreover, it depends on the starting material, wall thickness, dimensions, and configuration of the parts.

In addition, plastic parts for cars, various containers, stationery, toys, household items, components for electronics, medical equipment, and other products are created by injection molding machines.

How does a plastic injection molding machine work? Types of molding equipment

 

The choice of mechanisms and equipment for plastic injection depends on the type, configuration, and dimensions of the manufactured parts.

In addition, machines operate in automatic, semi-automatic, or manual modes.

Extruders

Good to use for the production of sheet products, polymer films, plates, pipes, and window profiles.

Moreover, the raw material load into the mechanism and squeeze out under pressure through molds with predetermined proportions.

Machine tools include:

1. Pneumatic loading mechanisms;
2. Extruders with a filter system;
3. Blowing heads with coolers;
4. Calibration mechanisms;
5. Pulling and turning devices;
6. Stacking and winding modules.

In addition, extruders control automatically using special programs.

Injection molding machines

Good to use for injection molding of all types of products under pressure from polymeric materials. Moreover, in injection molding machines, parts of various shapes and configurations with walls of different thicknesses, hybrid, hollow or multi-colored products can create.

In addition, the production technology consists of the melting of polymeric raw materials and injection under high pressure into special molds.

Machine tools include:

• Loading bins
• Preparation and plasticization modules;
• Press forms;
• Closure nodes;
• Automatic control units.

By design, injection molding machines are:

• Electrical, electromechanical, and hydromechanical;
• With combined or separate plasticization;
• Piston, worm-piston, one- or two-worm.

How does a plastic injection molding machine work? In addition, they can have one or more options for plasticization and a different number of mold closure nodes.

Blow molding machines

Good to use for the manufacture of polyethylene containers and containers with thin walls: bottles, canisters, barrels up to five thousand liters.

Moreover, blow molding machines heat up polymer raw materials and create products by blowing them into molds of certain sizes.

Extrusion blow molding lines

They produce products by combining the methods of extrusion and blowing, which expands the possibilities and range of products.

In addition, extrusion blow molding machines produce:
Fuel tanks and bumpers for cars, various bottles, bottles for the cosmetic and medical industries, chairs, buckets, and toys.

Moreover, machines differ in the type of extrusion heads, the number of streams and posts, including:

• Extruders that heat up and prepare the polymer mass
• Molds with a closing mechanism for molding products;
• Heads of angular or direct-flow configuration, single or multi-strand, for forming sleeves or pipes;
• Blowing elements supplying compressed air at high pressure to molds with blanks.
• Extrusion blowing lines are equipped with compressors and coolers.
• Thermoforming complexes
• Good to use to create disposable plastic utensils or containers with thin walls.

In addition, the production technology consists in blowing products from a polymer film heated to a temperature of about 140 ° C, with a thickness of more than 100 microns. Moreover, finished products are punched out of the plate and packaged.

The process is controlled semi-automatically or manually.

Additional accessories

The production of plastics is equipped with various auxiliary devices:

• Dryers;
• Dispensers
• Mixers
• Conveyors
• Crushers;
• Loaders;
• Conveyors.

Mini machines for highly specialized enterprises

In addition, for the production of small batches of plastic products or experimental batches of goods, there are mini-machines on the market suitable for use in small, highly specialized enterprises.

Moreover, compact machines do not require large production areas and can be placed on a regular table. Craftsmen make such machines with their own hands to organize production at home.

1. The technique for plastic injection is characterized by the high precision of products and other advantages:
   The possibility of manufacturing products of any geometric shapes and sizes of impeccable quality.
   2. Use of any polymers.
   3. Mass production of identical parts.
   4. Lack of additional refinement of cast products.
   5. Profitability and quick payback of production.

Moreover, by injecting the molten mass under high pressure, the molds are evenly filled, including the smallest details and holes.

General structure

How many types of injection moulding machines? Injection moulding machines generally consist of two parts: the injection unit, which prepares the plastic granules and injects them under pressure into the tool, as well as the closing unit, which picks up the tool and opens/closes it.

Three-zone screw

The three-zone screw is often used in thermoplastic processing. In the so-call feed zone, the plastic granules are drawn in and conveyed to the next zone, the compression zone, where the plastic is plasticized and compressed (degassed).

The melt is then homogenized in the metering zone and finally pushed through the non-return valve in front of the screw, which moves axially backward as a result of the increasing dynamic pressure in the barrel.

Non-return valve

How many types of injection moulding machines? The reverse flow lock prevents the volume of mass in front of the screw from flowing back into the screw flights when injecting and squeezing so that the screw acts as a piston. The non-return valve is located at the end of the screw and usually consists of three parts:

During dosing, the melt presses the locking ring against the tip of the screw. It creates a gap between the locking ring and the pressure ring (locking ring stroke) through which the melt can flow.

How many types of injection moulding machines? When the fuel is injected, the locking ring presses against the pressure ring and thus closes the screw threads. The distance between the locking ring and the barrel is called the worm clearance.

Moulding machine Locking unit

The clamping unit usually consists of three plates, which are arranged vertically on one axis on a machine frame. The fixed platen carries half of the mold (nozzle side) and is the plate closest to the injection unit. The fixed platen has a hole in the middle through which the nozzle can pass and dock onto the tool. The second platen is the moveable platen.

The second half of the mold (ejector side) is mounted on it. It is movable and is pushed mechanically or hydraulically in the direction of the fixed platen.

How many types of injection moulding machines?

Since the two tool halves are pushed together, this is referred to as closing. Finally, the third plate is the front plate. It has a supporting function because the toggle lever or the hydraulic cylinder is for closing the clamping plates. It is located between the faceplate and the movable clamping plate.

The faceplate is therefore necessary to build up the force. The ejector is also located on the movable clamping plate; these are hydraulic cylinders that actuate small metal pins in the mold when the mold is open, which then presses the molded part out of the mold.

There are also connections for core pulls here. This can be used to actuate slides in the tool; these are movable areas in the mold in order to be able to produce undercuts.

The forces acting on the clamping unit are defined (according to DIN 24450) as follows:

• Closing force
• locking force
• Buoyancy
• (Maximum) Mold opening force
• Ejector force

Moulding machine Process

How many types of injection moulding machines? The process depends on many things. However, there is always a basic scheme in which further steps can be integrated as required.

At the beginning of the cycle, the mass volume is metered, and the mold is open. First, the mold is closed and the injection unit is moved up to the mold. Then the moulding plastic is injected. After a certain waiting time for the moulding compound to cool down or react, metering is carried out, and the injection unit is lifted off again.

Types of injection moulding machines

How many types of injection moulding machine? Another difference is the way in which the force in the clamping unit (clamping force) is built up. A distinction is made between hydraulic machines, in which the mold is built up and held by large hydraulic cylinders, and toggle machines, in which a large, double-acting toggle presses the tool together.

The toggle lever itself is in turning and also moved either by a hydraulic cylinder. In the case of an electric machine, by an electric motor, the mechanics of the lever require significantly less force to hold the mold together than with exclusively hydraulic systems.

How many types of injection moulding machines?

There are also some special forms, such as the two-platen clamping unit. Here the tool is not pressed together from behind but pulled together hydraulically. Due to the special structure, special, large tools can be used.

There are also electric series in which the closing force is generated by electric motors. However, this is only possible on machines with very low clamping forces, since electric motors cannot provide a good compromise between power and speed.

Injection moulding machine Special types

How many types of injection moulding machines? Multi-component injection moulding machines offer the possibility of producing the frequently required complex molded parts from different colors or types of plastic in a single process. In addition to the classic multi-color and hard-soft combinations, various special processes can also be implemented with multi-component machines.

Another type is the electric injection moulding machines, in which all axes are driven electrically. The clasps are built as toggle levers.

Size information about moulding machine

How many types of injection moulding machines? The information that can be used to evaluate and assess the size of an injection moulding machine is specified in the standard.

Since an injection moulding machine consists of two parts, the injection unit, and the clamping unit, clear parameters are given there. After that, an injection moulding machine is characterized by:

The closing force with which the tool is compressed, specified in kN (kilo- Newton)

The calculated stroke volume of the injection unit in cm³ is based on an injection pressure of 1000 bar. In other words, the amount of moulding compound is that the injection unit can inject into the clamping unit at a pressure of 1000 bar.

What is plastic injection molding?

What is plastic injection molding? Plastic products are increasingly popular and diverse in daily life as well as in the industrial field. The strong development of the plastic industry led to the development of the design and processing of plastic injection molds.

Designing and processing plastic injection molds play an important role in creating beautiful, convenient, and useful plastic products.

So what is a plastic injection mold, what types of plastic injection molds are there, what is the process of designing and processing plastic injection molds and where is the processing?

Let’s learn together with Tip-Top Molds in this article.

What is plastic injection mold?

• A plastic injection mold is a metal tool (equipment) used to shape products according to the shaping method. Each mold is typically made and used for a certain number of molding/pressing cycles, which can be one or more times.
• A plastic injection mold is a group of assembled parts, where the plastic is injected, cooled, and then ejected.
• The texture and size of the mold depend on the size, shape, quality, and quantity of the product to be created.

Each plastic injection mold has a common structure including the following main parts:

 What is plastic injection molding? Mold body: where the mold cavity locates, the mold body is divided into two halves, a stationary half and a movable half. As well, the stationary half is mounted on the fixed plate of the injection molding machine and the movable half is mounted on the movable plate of the injection molding machine. 

• The space between the stationary half and the mobile half is the void that will be filled by molten plastic, then the plastic is cooled to shape and then removed from the mold cavity.
• Mold base: clamp the mold firmly into the machine table when processing.
• Guide and positioning system: responsible for keeping the correct working position of the mold body when assembled.
• The system of leading plastic into the mold cavity: responsible for supplying plastic from the injection machine to the mold.
• Product ejection system: responsible for pushing the product out of the mold when pressing is complete.
• Exhaust system: responsible for bringing out the remaining air in the mold cavity, helping the plastic fill the mold cavity. The product does not leak air or burn.
• The cold mold-making system has the effect of cooling after we finish machining.

What is plastic injection molding? In a mold part, the recess determines the outer shape of the product (also called the cavity), and the protrusion determines the inner shape of the product called the core. Moreover, a mold set may have one or more cavities and cores. The part of contact between the cavity and the core is called the parting surface.

The mold cavity (negative mold) and core (positive mold) are in a closed state.

Classification of plastic injection molds

Classification based on the number of layers of the mold cavity:

• 1 tier mold
• Multi-layer mold

Sort by runner:

• Mold using hot channel
• Mold using cold channel

Sort by channel layout:

• Two-plate mold
• Three-plate mold

Sort by the number of plastic colors that make up the product:

• Mold for single color products
• Mold for multi-colored products (Integrating many different molds on one set of molds).
• Among the types of molds mentioned above, the two-plate mold is the most common and common form.

Mold material

• Steel is a metal commonly used to make molds and plays an extremely important role in determining the quality of molds and products.
• Steel material for plastic molding.
• The quality of the steel is the decisive factor in precision mold machining.

In addition, ordinary steels have low hardness, easier machining, less tool wear, and easy cooling, but the surface will not achieve a high gloss. Meanwhile, high-quality steels, with higher hardness will give a perfect product surface and good mechanical properties such as impact resistance; good wear resistance, high-temperature resistance for a long time, anti-rust, and increase durability for molds.

The choice of steel to make molds depends on factors such as:

• The type of plastic that will spray the mold because there are resins that are harmful to the mold steel.
• Surface gloss, complexity, the function of plastic products.
• The number of products requires.
• The resistance to abrasion and chemical corrosion.
• The weld ability and detail resilience

MOLD DESIGN AND PROCESS

In order to make molds that meet the technical requirements such as mold making to ensure the accuracy of the shape and size of the product, and the product to be removed from the mold easily, the mold must have reasonable structure, and not too complicated to suit the purpose of use, etc., the mold design and processing are very important factors determining the quality of the mold.

Furthermore, the mold design and manufacturing process are very important. Precise mold design and manufacturing process helps to produce high-quality plastic products.

Mold design process:

In general, the mold design process at Tip-Top Molds for plastic products includes the following steps:

• Step 1: Receive mold design requests from the customers.
• Step 2: Discuss with customers to agree on requirements such as mold material, mold characteristics, product material, and product shape and size… in order to control mold quality and the cost of designing & processing suitable molds.
• Step 3: Review the parameters and requirements of the customer provided.
• Step 4: Eventually, preliminarily determine the mold structure to send to the customer, waiting for the customer’s feedback to come to a final agreement on the design plan.
• Step 5: Conduct mold design on the software…
• Step 6: Hand over the design to the customer, wait for the customer’s feedback, and make adjustments to come to the final solution.
• Step 7: Acceptance with customers.

Mold processing:

What is plastic injection molding?  Lastly, the manufacturing process of plastic molds at Tip-Top Molds carries out according to the following steps:

• Step 1: Get standard parts, cast steel, plan, and make a production diagram.
• Step 2: Design and create machining data on CAD/CAM.
• Step 3: Process surfaces and details with simple shapes by 2D shaping machining methods.
• Step 4: Assemble the mold plate together into blocks.
• Step 5: Machining complex surfaces.
• Step 6: Polish the mold details.
• Step 7: Inspect and test the mold.