Tips for Buying An Injection Molding Machine

When you buy injection molding machine, the knowledge you need to know

What is injection molding machine?

The Wikipedia give the answer like this “An injection molding machine (also spelled as injection moulding machine in BrE), also known as an injection press, is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, an injection unit and a clamping unit.” Based on this general information, I would like to explain you more.

INJECTION MOLDING MACHINE

Generally, the injection molding machine consists of Clamping UnitInjection UnitMachine BaseElectrical Control System, and Hydraulic System (Electric Injection Molding Machine don’t have the hydraulic system).

The clamping unit function is to provide enough force to clamp the mould tightly, making sure the mould will not get apart while the materials injection into the mould cavity. About its design, there are two types, toggle clamping and hydraulic clamping. 

CLAMPING UNIT

The Injection Unit main function is to injection the material into the mould cavity and charge material into the barrel. In which, the key components are Screw&Barrel set, sometimes it’s main factor for successfully injection molding a perfect final product. Especially for some critical products or material, such as for molding optical lens and similar transparent materials. For different materials, usually the design of screw may be a little different. The screw steel is also very import, for some strong materials, like materials adding fiber glass, or metal powder, Bakelite powder, they must require the bimetallic screw, otherwise the screw will be worn out in couple of months. 

INJECTION UNIT

The machine base is the main frame, on which the injection unit, clamping, hydraulic and electrical control systems be installed. The main point of the base are just strong enough and the design should be reasonable. 

MACHINE BASE

The Electrical Control System is like the brain to a human. It controls the machine actions sequences. It has an HMI keyboard, from which you may check and input the instructions to let the machine work as you want by setting different parameters. 

ELECTRICAL SYSTEM

The Hydraulic System is the injection molding machine power source for all the machine actions. When the machine start, firstly the motor works and force the hydraulic oil into the main valve block through oil pipes, from the valve block the hydraulic oil will be guided into different cylinder controlled by each action valves, then each action works in sequence accordingly. For the electric injection molding machine, it does not have the hydraulic system, all the actions were driven by servo motors directly. 

HYDRAULIC SYSTEM
From different view, injection molding machines have different clarification.
 
From Mould closing direction difference, it could be sorted as: Horizontal Injection Molding machine, and Vertical Injection Molding Machine.  For horizontal machine, the clamping platen moves horizontally to close the mould, and the vertical machine vertically. 
HORIZONTAL INJECTION MOLDING MACHINE
VERTICAL INJECTION MOLDING MACHINE

From the machine power system, it could be shorted as: Hydraulic injection molding machine, Electric injection molding machine, and Hybrid injection molding machine. For hydraulic machine, both clamping force and injection force are powered by hydraulic system; the electric machine’s all action forces are driven by servo motors directly; for most hydraulic machines, clamping force by hydraulic system and injection unit by servo motor.   

ELECTRICAL INJECTION MOLDING MACHINE

From the special material the machine to injection molding, there will be too many sorts, such as Bakelite injection molding machine, BMC/DMC injection molding machine, LSR injection molding machine, MIM (Metal Powder Injection Molding), Rubber injection molding, etc.

Baktlite, BMC/DMC PRODUCTS

Typically, the injection molding machine’s working process (action sequences) is, 1. Close mould, 2. Inject material into the mould, 3. Products cooling/heating inside the mould, at the same time, the screw charging material for the next injection, 4. Open mould, 5 Eject out the finished product. Then start another cycle. 

INJECTION MOLDING PROCESS
What is cheaper injection molding or 3D printing? Maybe this will be your first question to ask. For answer this question, it will be better to analysis both of them from the view of cost, efficiency, developing time. 
 
The production cost. If the demands for the plastic parts is no more than 100pcs, definitely, the 3D printing is good choice. Because for injection molding, it requires to make the mould, which cost is much expensive, considering only making 100pcs products. If produce thousands or millions of products, when share the mould cost to each product, the mould cost could be ignored. 
 
Production efficiency. If make a product which size is big, the 3D may take couple of hours to finish it. But for injection molding, it will be no more than 3 minutes to get it done. So, when comes to mass production, more than thousands of pieces products, it’s for sure to use injection molding. 
 
Developing time. For 3D printing, as long as the drawing finished, you can get the product immediately by 3D printing. But for injection molding, it needs to make the mould firstly according to the drawing, usually it will take 20-30 days to finish the mould. 
3D PRINTING

In conclusion, for mass production, the injection molding is much cheaper than 3D printing. 

How to choose your suitable injection molding machine?

Firstly, you need to know what’s your product material. Is it thermoplastic material? Like PP, PE,PS, PVC, ABS, PA, TPE, TPR, etc. The thermoplastic material is the most popular used ones.  Or is it the thermosetting material? Like Bakelite, BMC, DMC, UF, etc. The difference between the thermoplastic and thermosetting material is whether it could be used again for injection molding after recycled. Other than plastic material, the metal powder, liquid silicon and rubber could be also injection molded. 

When come to this point, many people may get confused and easily make mistake. I can say many client do not even know there is a vertical injection molding machine. 
 
For making 100% single color/material plastic parts without any other material inside the parts, it’s for sure to use the horizontal injection molding machine. Because for the horizontal injection molding machine, could be fully automatically produce by taking our the finished product by robot or just drop down outside of the machine. 

If the plastic product contains other materials, for example a piece of metal part inside, or injection molding material around wires (injection molding plugs), or over molding one material upon another plastic material to get a double color or 3-color products. To use the vertical injection molding machine will be a smart choice. It will not only improve the production efficiency dramatically, but also make the production easier and safer.  

When comes to the products to injection molding, there is no 100% correct answer for this question? But to special client, the 100% correct answer is there. For example, when a medical product making company, when the buy the injection molding machine, the first point they are thinking is the machine must be as clean as possible, since they have to put the machine into dust-free workshop. So, the electrical injection molding machine is the first choice. 
 
Here lists the advantage and disadvantage of each type. 
 
Electrical injection molding machine: the first advantage of it is clean, during production, there is no chance to get any oil leakage, since it does not have the hydraulic system; the second advantage is precise, very suitable to injection molding the micro precise parts.  The disadvantage of it is the price is very expensive. So, it is not suitable for injection molding very large plastic products.
 
Hydraulic injection molding machine: it is the most popular injection molding machine in the market. Because the price of it is much cheaper comparing with electrical machine. No matter as small as less than 15-ton machine, or as big as 6000ton machine, all available in the market. It is hard to find the disadvantage of it, the only thing is the client need to change the hydraulic oil in 1-2 years for machine good performance. 
 
Hybrid machine. Normally the hybrid machine is with hydraulic clamping unit and electric injection unit. It’s a middle category between hydraulic and electric machine. The price and performance are also between them. The hybrid machine has the precise advantage, and also balance its price. 
 
 

The machine tonnage 

          
When you plan to buy an injection molding machine, the first question come to you may be “How much do plastic injection molding machines cost?”. For answer this question, you need to ask the answer to another question “What size injection molding machine do I need?”. So, it comes to the key point, the injection molding machine tonnage. “What is machine tonnage?” and “What is meaning of ton in injection moulding machine?”
 
The injection molding machine size is mainly based on the machine clamping force tonnage. Take the hydraulic injection molding machine for example, the small injection molding machine is with small motor, so it gives small clamping force upon the mould, accordingly the injection unit could not be big, otherwise the mould will be get apart during injection. For sure, the small injection molding machine could not work big mould for molding big plastic parts. So, when you buy injection molding machine, you need to choose the suitable tonnage machine. 
 
Then another question comes:“How do you calculate injection mold tonnage?” or “How is tonnage calculated?” 
In order to make this question easy to answer, let’s not consider the very critical product, like thine wall product and the difficult material like Bakelite powder. 
 
Firstly, calculate your product area: A(area)=L(length)*W(width), or A(area)= πr². 
 
Then, you will calculate the product required clamping force.  Considering you measured the size by inch, the tonnage required will be T(tonnage)=A (area by inch) *3(tonnage required per square inch). The 3 tonnage is based on normal thermoplastic material, like PP, PS, PE (If for special material, please consult to the professor).  Remembering that, this is the one product required clamping force, if you have multi-cavity mould, need times to the cavities number and add the runner area.  
 
For example, your product is an PP basin, one cavity mould, and the area is 100 square inch, T=100*3=300. Then you need a 300 ton injection molding machine. 
          
                 

Injection Capacity / Shot Weight

 
For choose the suitable injection molding machine, other than the clamping force, the second important factor is the shot weight (or called injection capacity). It will be easy for you to know this. You just put your products on the weighting device, then you know the single product weight. If multi-mould, just time the cavity number and adding the runner weight, you will know how much shot weight of machine you required. 
 
 

What auxiliary machines required during injection molding?

 
Hopper Dryer, which is the standard auxiliary machine you required, if you want to get your products well injection molded. This device helps to make the plastic material dry before material goes into the barrel to melt. 
 
Here lists the advantage and disadvantage of each type. 
 
Electrical injection molding machine: the first advantage of it is clean, during production, there is no chance to get any oil leakage, since it does not have the hydraulic system; the second advantage is precise, very suitable to injection molding the micro precise parts.  The disadvantage of it is the price is very expensive. So, it is not suitable for injection molding very large plastic products.
 
Hydraulic injection molding machine: it is the most popular injection molding machine in the market. Because the price of it is much cheaper comparing with electrical machine. No matter as small as less than 15-ton machine, or as big as 6000ton machine, all available in the market. It is hard to find the disadvantage of it, the only thing is the client need to change the hydraulic oil in 1-2 years for machine good performance. 
 
Hybrid machine. Normally the hybrid machine is with hydraulic clamping unit and electric injection unit. It’s a middle category between hydraulic and electric machine. The price and performance are also between them. The hybrid machine has the precise advantage, and also balance its price. 
 
 

The machine tonnage 

          
When you plan to buy an injection molding machine, the first question come to you may be “How much do plastic injection molding machines cost?”. For answer this question, you need to ask the answer to another question “What size injection molding machine do I need?”. So, it comes to the key point, the injection molding machine tonnage. “What is machine tonnage?” and “What is meaning of ton in injection moulding machine?”
 
The injection molding machine size is mainly based on the machine clamping force tonnage. Take the hydraulic injection molding machine for example, the small injection molding machine is with small motor, so it gives small clamping force upon the mould, accordingly the injection unit could not be big, otherwise the mould will be get apart during injection. For sure, the small injection molding machine could not work big mould for molding big plastic parts. So, when you buy injection molding machine, you need to choose the suitable tonnage machine. 
 
Then another question comes:“How do you calculate injection mold tonnage?” or “How is tonnage calculated?” 
HOPPER DRYER

Auto Loader, which is also an important auxiliary, if you do not want your workers always clamping on the injection molding for adding materials into the hopper. The auto loader will detect the material’s level in the hopper. If less material in the hopper, it will automatically such the material to hopper from the material container keeping on the ground (if no material in the ground container, auto loader will alarm). 

AUTO LOADER

Robot or sprue picker, for efficiency production and decrease the labor cost, the robot/sprue is very necessary. Actually, most of the big factories, one worker managers dozens of injection molding machine working, all of the injection molding machine works automatically.

ROBOT/SPRUE PCKER

Color mixer, when you want to get your products have special color, like green, blue, red, etc, you will ask, how is Colour added to plastic? If so, you need to add color master batch into the raw material to get what color you want. In order to make sure the color master batch and the raw material have good mixing, you need this device. If you want to have much accuracy mixing, the best choice is to use color masterbatch machine.  

COLOR MIXER
Crusher/Grinder, for thermoplastic material injection molding. The runner/sprue could be recycled to use again by crushed the runner/sprue into small pieces. These years, the most popular crusher is slow speed mute crusher. It is placed just beside the injection molding machine, each cycle injection molding finished, the sprue/runner be through into it, after grinder, material will be automatically suck back to the hopper for injection molding. 
 

Chiller, while the injection molding machine working, cooling water is required to keep the hydraulic oil at the temperature 40-50 ℃ for good performance, also to keep the mould cool fast. The chiller function is to cool the cycling water for this purpose.

Mold Temperature Controller (MTC), for some special mould, it requires the MTC to keep the mould at a special temperature for working. For injection molding the Bakelite material, it must be required to keep the barrel at 70-80 ℃. 

Mould/mold 
 
To get your products molded, other than the injection molding machine, the mould must be required.  The injection molding machine is common machine, all moulds, as long as the mould size suitable, material suitable, could be loaded on the machine to injection molding any products as you like. But the mould is unique. Special products require special mould/mold. 
 
The mould/mold could be hot runner or cold runner. Cold runner mould has the sprue/runner, but the hot runner mould do not have. The hot runner mould price is much higher than cold runner, because the hot runner mould has separate temperature control system.
The mould/mold could be 3-plate or 2-plate. For the 3-plate mould, when mould get open, the sprue/runner will get apart from the finished product. Then the sprue picker will take away the sprue/runner, and the products be ejected out and drop down. For 2-platen mould, the sprue/runner is linking with the product, need to cut off and separate them later. 
 
The mould/mold could be soft mould or hard mould. The difference between them is the hardness. The soft mould could be hard by heat treatment. The hard mould life cycle could be as much as 500K to 5 million, but the soft mould only around 10k-20k cycle lifetime. Normally the soft mould only used for trial production for new product development.

From where should I buy an injection molding machine?

For answer this question, let’s see firstly where the injection molding machine be made around the world?  Generally, there are 3 main group injection molding machine manufacturers for your choice: European/American Machine, Japanese/Korean Machine, and Chinese Machine. 
 
European/American injection molding machines, such as ARBURG, ENGEL, KRAUSS-MAFFEI, BATTENFELD, etc. These companies are making excellent machines. Also the price is also the highest, if the budget is not an issue, it’s for sure to buy an European/American injection molding is good choice. 
 
Japanese/Korean injection molding machine, such as WOOJIN, SHIMITOMO, JSW, TOYO, SODICK, FUNUC, etc. The injection molding machines made by these companies are also very nice. Personally opinion, to buy electrical injection molding machines there is good choice.
 
Chinese injection molding machine. From the sales volume in the injection molding machine industry all of the world, China is the top one, you may refer to the UN trade record to check the HS CODE 847710, you will find it out. Because from China, you may find any range of injection molding machines, from vertical to horizontal, from hydraulic to electric, from smallest tonnage 3ton to as large as 6500ton, all available in the market. 
 
Even with this information, you may still not sure from which company you should buy your injection molding machine, right?  There is a simple way if you want to save your time and energy, find a professional people for consultant. If you do not have such a professional around you, you may contact with me:
 
The mould/mold could be soft mould or hard mould. The difference between them is the hardness. The soft mould could be hard by heat treatment. The hard mould life cycle could be as much as 500K to 5 million, but the soft mould only around 10k-20k cycle lifetime. Normally the soft mould only used for trial production for new product development.

Commercial process

Normally, you need communicate with the salespeople clearly and make sure they understand fully about your all detail requirements. Then you make around 30% advance payment (depends on different factory), the factory the machine manufacturer. After the machine finished, you make the balance payment and get your machine to delivery. 

Logistic process

Since the machine is a heavy equipment, normally the transportation is by sea. For the transportation, it is better you find a forwarder in your local to arrange the machine shipping for you. Your forwarder can contact the machine factory to make your job done.  

Installation and start production

The final step before you use your injection molding machine, you may ask “How do I start my injection molding machine?”
 
For injection molding machine less than 400ton, the machine could be delivery in whole machine, when you received them, just connect power, cooling water, load the mould onto the machine, you start your production. 

For the machine between 500ton to 1000ton, the machine will be disassemble into two pieces, injection unit and clamping unit. It is not difficult to assemble them together, just follow the factory’s instruction manual, you can make them together and start your production.  

For the machine bigger than 1500 ton. Normally you need the factory send an engineer to your factory for installation, because such big machine, it could not put into the container in whole machine or two pieces. They will be disassembled into small parts.