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.

 

CONTENTS

• What is injection molding?
• Construction of an injection molding machine
• What injection molding processes are there?
• Thermoplastic injection molding
• Thermoset injection molding
• Elastomer injection molding
• What advantages does injection molding have?

 

 

1. WHAT IS INJECTION MOLDING?

How is injection molding done? Firstly, Injection molding is mainly used in plastics processing and uses to manufacture small parts and prototypes almost exclusively from plastics. Injection molding is the most common manufacturing method for prototyping and low-volume production of consumer parts.

In injection molding, a mechanism occurs where thermoplastic or thermoset polymers are injected into a cavity and then solidified as a finished part.

The solidified material is then ejected from the mold. With this injection molding process, molded parts can be produced economically in large quantities. An injection molding machine also produces these objects with high accuracy and in a short time.

Construction of an injection molding machine

How is injection molding done? Nowadays parts from a few tenths of a gram up to the two-digit kilogram range can be manufactured. In addition, the surface of the component can be selected almost freely in injection molding. The injection molding process uses to produce smooth surfaces, grains, patterns, and engravings.

After the plastic mass cools down in the injection molding tool, the tool can be opened to remove the plastic component.

When it cools down, the material returns to a solid-state. 

What injection molding processes are there?

How is injection molding done? The injection molding process makes economic sense for larger quantities. The costs for tool-making are a large part of the necessary investments. As a result, even with simple tools, the investment only pays off after a few thousand parts have been manufactured. The injection molding tool can use to produce up to a few million parts.

This makes injection molding the most common method for mass production of plastic objects. Injection molding is preceded by tool-making to produce injection molds for various injection molding processes.

The plastic injection molded parts are classified into categories as follows

How is injection molding done? Parts are very precise parts with the highest requirements, technical plastic parts with high requirements, or geometric simple moldings made of plastic with low requirements.

All categories have, among other things, the following essential quality characteristics: molded part dimensions and weight, surface structure, strength, and signs of warping.

Do you need further information on the subject of injection molding? Then simply contact us by the contact form on our homepage, telephone, or e-mail!

2. STRUCTURE OF AN INJECTION MOLDING MACHINE

How is injection molding done? The worm-piston injection molding machine basically consists of two parts. The injection unit or plasticizing unit plasticizes the plastic, prepares it, and doses it, and the closing unit closes, holds, and opens the mold.

The injection unit consists mainly of the plasticizing cylinder, a horizontal cylinder, and a screw located inside. At one end of the plasticizing cylinder, there is a hopper for filling with the raw material; at the other, there is a nozzle that can be either closable or non-closable. Furthermore, it locates between the plasticizing cylinder and the clamping unit and serves as a transition.

3. WHAT INJECTION MOLDING PROCESSES ARE THERE?

How is injection molding done? The material that is processed during injection molding can be divided into thermoplastics, duroplastics, and elastomers. Eventually, all three types of plastic can use for injection molding. However, the process most widely uses for plastic processing is thermoplastic injection molding, as it is the most economically important.

The injection molding process for duroplastics and elastomers works in principle like the process for thermoplastics and mainly differs in terms of parameters such as temperatures.

3.1. THERMOPLASTIC INJECTION MOLDING

How is injection molding done? The thermoplastic material trickles into the rotating screw as granules. The granules heat and melt by the heat in the tool. The melted granulate accumulates in front of the screw tip because the nozzle is still closed.

In the injection phase, the plasticizing unit moves to the closing unit, pressed with the nozzle and the screw pressurizes. Moreover, the molten plastic is pressed under high pressure through the open nozzle, which creates a cavity. The non-return valve prevents the melt from flowing back.

After the end of the pressing, the nozzle can close and the plasticizing and dosing process for the next molded part can begin in the injection unit. The material in the mold continues to cool down during the remaining cooling time until the core, the liquid core of the workpiece, has solidified and sufficient rigidity has been reached for demoulding.

3.2. THERMOSET INJECTION MOLDING

How is injection molding done? Compared to thermoplastic injection molding, thermoset injection molding is mostly cured by exposure to heat. After Duroplast has hardened, it can no longer melt again. However, thermosets can recycle.

The mass that has not yet hardened must therefore be injected into the mold at a lower temperature and then be hardened there at a higher temperature. With thermoset injection molding, parts with very large wall thicknesses of up to 50 mm can form.

Thermosets are typically used for vehicle headlights, among other things. Although the material price of duroplastics is generally cheaper, they usually lose out compared to thermoplastics in the comparison of economic efficiency.

3.3. ELASTOMER INJECTION MOLDING

How is injection molding done? Likes duroplastics, elastomers vulcanize under the influence of heat. The tool must therefore also be hotter than the molding compound during the injection process. The thermoplastic elastomers are an exception.

Elastomers can be drawn in by a special screw conveyor in the form of free-flowing powders or in the form of strips. The cylinder is usually heated to approx. 80 °C by means of water temperature control in order to avoid overheating. Since molten elastomers are very fluid, the effort involved in designing the tool is higher than with thermoplastic tools.

Apart from the special features, the injection molding process is basically similar to thermoplastic injection molding.