4 Advice to Choose a precision injection molding

China is recognized by the UN to have the world's most perfect industrial system, and the plastic machinery manufacturing industry is one of the traditional ones enjoying the most rapid development. 

Injection machines play an important role in such rapid development of the plastics industry, no matter by quantity or by type. For they can form in once plastic products of complex shapes, precise dimensions and fine quality, or even with metal inserts, injection molding machines have been widely applied in all sectors of people's daily life, including national defense, motor, automobile, transportation, building materials, packaging, agriculture, culture, education and healthcare. There are a variety of injection molding machines of different models and different uses on the market, so users have been always confused by how to select perfect injection molding machines:

Here are the notes that we should pay attention to when selecting injection machines: 

Tip 1: 
Technical parameters of injection molding machines 
A vertical or horizontal comparison can be made when selecting injection machines. A “vertical comparison” is to compare the main technical parameters of injection molding machines according to industry standards, and a “horizontal comparison”is to compare the technical parameters of domestic and foreign injection molding machines of the same type, which are both scientific works needing carefulness. 

The materials, shapes, structures of injection products and their applicable fields and scenarios, the structures, quality and precision of dies, the number of die openings, the types, shapes and dimensions of runners, and the daily, monthly and annual production capacity and automation degree of products, are all the parameters to be considered when selecting injection machines.

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Tip 2:
Working stability, reliability, safety and service life of injection molding machines 
The stability of injection machines is mainly reflected in whether the clamping mechanism and the injection system run smoothly in each looping cycle, without impacting noise and with noise not exceeding the industry standard, which are determined by mechanical manufacturing and assembly precision of machines, as well as reasonable design and structure of toggle links. 

Reliability and service life are mainly reflected in system rigidity of the clamping mechanism, which is determined by the shape, size, material and heat treatment process of templates, pull rods, links and pin shafts. The structure and manufacturing process of the injection system of an injection machine, containing the barrel, screw and tip of screw, as well as the check ring and the screw drive spindle, which are the main stress and wear parts, directly affect the machine's service life. 

Tip 3:
Safety of injection molding machines
Human and machine safety is determined by the reliability of the low-voltage protection system when the clamping mechanism is running. Injection molding machines are required to be equipped with an electrical-mechanical-hydraulic joint safety protection system to guarantee the safety of both dies and humans. Before mold closing, where the safety door is not properly closed, the clamping mechanism will stop working. During mold closing, where the safety door is not properly closed, the platen will stop working or open automatically. Where, during mold closing, any foreign matter, such as an insert, falls into the cavity by mistake due to vibration, or any foreign matter is inserted into the mold by mistake, the mold will stop closing, or will open automatically and alarm. 

Another safety system in injection molding machines is the cold start prevention of the pre-plasticized screw. Where screw materials fail to reach the specified temperature and holding time, it is forbidden to start, otherwise, it will alarm. Injection molding machines are also required to be equipped with protective devices at their nozzles to prevent burns caused by splashed materials. 

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Tip 4: 
High automation, complete functions and high production efficiency 
Modern injection molding machines can enable manual, semi-auto and auto operations. As long as a mold is reasonably designed, a modern injection machine can run fully automatically from injection to molding and to product ejection. It also enables unmanned operations if equipped with robots. Functions, including core pulling and plugging, hydraulic nozzle control and quick runner probe heating, can be programmed into the automatic process in the injection molding cycle for automatic loops. 

High production efficiency refers to a short molding cycle of products from each mold under normal injection process conditions. It reflects the comprehensive performance of mechanical, electrical and hydraulic systems of an injection molding machine, so in order to guarantee it, it is necessary to adopt high-quality hydraulic and electronic components and precise manufacturing techniques that can improve the sensitivity and repeatability of the systems of injection machines. 

Tip 5: 
Energy conservation and environmental friendliness, an important index to select a good injection molding machine  
Energy conservation refers to better water and electricity conservation of an injection machine than those of its type when its electromagnetic heating system, power drive system (containing the inverter and servo) and heat dissipation system are working under normal process conditions. 

An injection machine should be designed to be environment-friendly. That is, it should work quietly without causing noise pollution, hydraulic oil leakage or excessive noise, and it should be made of environmental materials as far as possible. 



Tip 6:

An injection molding machine should be easy to maintain and repair, and its mechanical, hydraulic, electronic and electrical components should be assembled to facilitate its maintenance and repair. Universalization and standardization of an injection molding  machine are also important factors to users. 

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Agree with everything said so far, and will add these thoughts:

The hydraulics of the injection unit are typically balanced against the clamp capacity of the press. If you are buying new, there are typically several shot capacity barrels available for any given size press, but... the max amount of injection pressure available on the large barrels is less than the small barrel. High pressure on a large shot doesn't do you any good if the press can't keep the mold closed.

The really useful way to size a press is through the clamp tonnage. Rule of thumb is each square inch of "projected" mold cavity, projected meaning that it's aligned directly across the parting line, trying to force open the clamp, requires between two to seven tons of clamp pressure. The difference is the mold-ability of the material. So, you have a part that's 2" x 5" in plan view on the parting line, that's ten square inches, that you wanted to mold it in easy to mold polystyrene, you may be able to do it on a 20 ton press. If it's going to be polycarbonate, you may need a 70 ton press.

Once you've determined how much clamp you need, then figure out if the shot size is adequate to fill the part.

Dennis

Added comment: I own a 66 ton Battenfeld with a 3.17 oz. barrel, bought that way specifically because I do parts with a lot of fine detail, and need the injection pressure. There are some parts I can't run in my 75 ton, 4 oz. Cinncy; not enough injection pressure. Awesome info guys, I am hoping to setup a very multi purpose shop so it is good to know about the "flow molding", multi barrel setups for different shot size and how to calculate clamp force required. Quick second question, I have only been around an injection molding ship once and they had 10 or so machines with hydraulic part pickers to pull them out of the mold and drop them in a bin. Under what circumstance do I need that vs an ejection pin that drops it into a chute below and how much am I going to spend setting that part up if needed?

Seems almost too inexpensive when I look at these machines on ebay, so I assume there is a lot of extra's I just don't know about yet that is going to surprise me So for the sake of argument, if I grabbed a machine like this off ebay, other than feeding it pellets and getting my own mold, what else is missing to put it in operation? Do most all of them run on 3 phase, do they work ok with a converter if so, and I know this last question is stupid but how do you move a 20,000 lb machine? I haven't found a forklift with that capacity and not sure how else to move it once I am the lucky winner... Almost seems like the weight / size is what makes resell value so poor.

Awesome info guys, I am hoping to setup a very multi purpose shop so it is good to know about the "flow molding", multi barrel setups for different shot size and how to calculate clamp force required. Quick second question, I have only been around an injection molding ship once and they had 10 or so machines with hydraulic part pickers to pull them out of the mold and drop them in a bin. Under what circumstance do I need that vs an ejection pin that drops it into a chute below and how much am I going to spend setting that part up if needed?

Seems almost too inexpensive when I look at these machines on ebay, so I assume there is a lot of extra's I just don't know about yet that is going to surprise me So for the sake of argument, if I grabbed a machine like this off ebay, other than feeding it pellets and getting my own mold, what else is missing to put it in operation? Do most all of them run on 3 phase, do they work ok with a converter if so, and I know this last question is stupid but how do you move a 20,000 lb machine? I haven't found a forklift with that capacity and not sure how else to move it once I am the lucky winner... Almost seems like the weight / size is what makes resell value so poor.

What the previous poster said, also....

Part pickers still require ejector pins/strippers in most cases. A lot of injection moulding is done without pickers though. If you don't mind separating the sprues from the parts later, just eject the parts into the chute. We have 18 machines, all with pickers/robots, sometimes they pick the parts, and the sprues drop in the chute, and sometimes they pick the sprues and the parts drop, horses for courses. Of course we have a lot of hot runner moulds too, no sprues then.

Extras include a material dryer, in its simplest form a hopper with a hot air blower, essential for some resins, not necessary for others, and some resins require very fancy additional gear like dessicant driers to get them dry enough to run well, eg Polysulphone.
Water cooling system, both for the machine hydraulics (I am assuming you are not in the market for a full electric $$$), and for the mold. Either a refrigerated unit or cooling tower. For some resins though eg nylon, the mold is not chilled but kept at a constant, hotter than ambient temperature, for this you need an MTC, mold temperature controller, that heats or cools the water to and from the mold as necessary.

Getting a mold, have you made any enquiries in this respect? Ok if you are a toolmaker, or at miniumum a skillful machinist, but if you have to pay someone to make it... consider that molds can be worth more than the machine they run in.

All but the smallest machines are three phase. An RPC may not help as the issue is as much the total power required, most of this goes in to the melting of the resin. A 60 tonner will need more than 50A per phase depending on what you are making.

Forklifts exist that large that can fit on a low loader. Most injection molding machines I have commissioned arrived on the front of the low loader, the forklift on the back, the riggers did the lot. I have also hired mobile cranes to unload off the truck, and moved the machine into position with load skates.

Whay are used machines cheap? When a mold shop is running with all it's overheads, staff, rent, electricity, water, ancillary equipment and so on, the space that a machine occupies has to make the maximum return for the operation to be competitive, newer machines with their fine control, reliability, efficiency and high speed give you the best shot at this. Everone knows this so older machines get scpped or go to a small operater such as yourself.

But don't be discouraged. If you are using a resin such as polyethylene, one of the most common, no dryer is necessary, no mtc is necessary, it melts at a lower temp so less power is needed. If your water supply is not metered, you could cool the machine and mould with mains water an run it to waste, have seen it done, but wouldn't do it myself, terribly wasteful of a precious resource.

I worked for a guy who had a 350, 70, 50, and a 40 ton machines running under his house on a suburban street, had to get extra cables in the feed it all though. Used the cooling water to heat the swimming pool, meaning he had no cooling tower.

I would suggest getting a smaller machine, 20 to 50 ton first, get the hang of it, then look for a bigger one if you are still keen.

Awesome info guys, I am hoping to setup a very multi purpose shop so it is good to know about the "flow molding", multi barrel setups for different shot size and how to calculate clamp force required. Quick second question, I have only been around an injection molding ship once and they had 10 or so machines with hydraulic part pickers to pull them out of the mold and drop them in a bin. Under what circumstance do I need that vs an ejection pin that drops it into a chute below and how much am I going to spend setting that part up if needed?

Seems almost too inexpensive when I look at these machines on ebay, so I assume there is a lot of extra's I just don't know about yet that is going to surprise me So for the sake of argument, if I grabbed a machine like this off ebay, other than feeding it pellets and getting my own mold, what else is missing to put it in operation? Do most all of them run on 3 phase, do they work ok with a converter if so, and I know this last question is stupid but how do you move a 20,000 lb machine? I haven't found a forklift with that capacity and not sure how else to move it once I am the lucky winner... Almost seems like the weight / size is what makes resell value so poor.

If you've only been around injection presses once in your life, please go get a job running presses for a year or so. That will help answer many of your questions about presses, dryers, chillers, grinders, molds, etc.. There is a ton to learn. I've been working around injection molds and molding for 32 years, and basically feel like I've just scratched the surface as far as learning goes. I learn something new every day. One of my customers runs 10 or 12 medium sized electric presses, and IIRC has 800amps of 480-volt power, so you will need lots of power depending on your machines. Nice looking work.

You mentioned silicone, are you thinking of injection moulding silicone rubber? We do a lot of it here, mainly medical, it is a different game all together from thermo plastics. I can give you some tips, but like a lot of LSR moulding companies, we keep the finer details to ourselves, you may have to do a lot of your own development there.

Seeing what you are making now I see why you are looking for the shot size a 60 ton offers. What you are making is a pretty thick section for injection moulded thermoplastic, and therefore your shot weight is higher than normal for the projected area. If you use a standard resin without a filler or foaming agent you will not get a very nice result, lots of sinks and distortion. Injection moulded parts are designed thin and with uniform section to avoid this. Seeing your application
you are stuck with this and will need to work with the resin supplier to get what you need.

FWIW the 20k to build a mold for the teeth does not sound expensive if it is made well and from durable materials. Are there 24 unique cavities? polished? Irregular partlines? I have been builing molds for 20 years, for my self and others, simple washers to complex medical components, every time I quote a price I cant believe how much the total is, and often I still have not quoted enough. In industry some things take a long time but with low overheads, and some things have high overheads but happen quickly. Mold tool work has high overheads and happens slowly.

Once again do not be discouraged, you are obviously smart and skillful enough to pull it off, but it will take a lot of time to get there. Fortunately for you you are serving an industry that seems comfortable with spending money.
For you, if you decide to work over a weekend, say 20 hours, and your time as a toolmaker with all the expense that goes with it is worth say $75.00/hr, you just saved yourself $, do that for 13 weekends and you have your 20K mould complete.