After a new injection mold is construction is finished, the mold maker need to set up the injection mold to do test or molding plastics. Setting an injection mold is more than loading and fixing the mold to injection machine, there are many other important things to do after you clamp the injection molds.
This article will give you a comprehensive explain of how to setup an injection mold, and the critical checklist you should pay attention to.
Injection molding is one of the most important processing methods to produce plastic parts. Plastic injection molding techniques have been used and developed for a long time.
Look around you, the case of your laptop, the case of intelligent cell phone, water filters, food containers, wash machines and quite a few components in your car... yes, we are living in a world that are full with plastic parts, most of the common plastic parts are made by injection molding. This article will show you the basics of plastic injection molding advantages and disadvantages.Injection Molding Basic Process
Feeding raw material from the hopper into the barrel, the plunger start to push, the plastic raw materials are pushed into a heating zone and then through the bypass shuttle, the molten plastic through the nozzle into the injection mold cavity, then water or oil run through the designed cooling system to cool down the injection mold to get a plastic article.
Some glossary of terms related with plastic parts design, mold making and plastic injection molding.
Antistatic Agent: Additive used to help eliminate or lessen static electricity from the surface of the plastic part.
Boss: Protuberance on a plastic part designed to add strength, facilitate alignment, provide fastening, etc.
Clamping Plate: A plate fitted to a plastic mold and used to fasten the mold to a platen.
Co-injection Molding: A special multilateral injection process in which a mold cavity is first partially filled with one plastic and then a second shot is injected to encapsulate the first shot.
An injection mold is a precision tool and also must be strong enough to withstand thousands of high pressure molding cycles, so the material of the injection mold must be carefully; it's normally special and expensive steel, The way of manufacturing injection mold have been changed along with modern technology developing, main steps are CNC milling, drilling, EDM, wire-cutting, CAD/CAE/CAM technology utilized in a wide range make the lead-time of mold making shorter and shorter.
Mold flow analysis is widely employed in mold making
industry, utilizing data simulation software, the injection molding process can be simulated and presented on the computer, you can improve part design or mold design base on the out put results. Moldflow, Moldex3D are very popular mold flow analysis software used by many mold makers.Advantages of mold flow analysis
Mold flow analysis will advise if the cavity is fulfilled, it can also provide other useful information such as the required injection pressure and clamping pressure.
You can know whether the filling problem exists. Many filling problems, such as short shot, bubbles and imbalances, can be predicted by a careful analysis of the filling curve. Mold flow analysis allows you to change the position of the gate, injection speed, and other processing conditions, so you would know if these problems can be improved or corrected.
Undercuts: in plastic injection molding industrial, it refers to part features that prevent straight ejection at the parting line, which cause much mold complexity and lead to higher mold construction and maintenance costs. Whenever it's possible, redesign the part to avoid undercuts. Minor part design changes can often eliminate undercuts in the mold. For example, adding through holes can give access to the underside of features that would otherwise be undercuts, simple modifications enable the mold to form a hole in the sidewall rather than with a side-action mechanism. See below figure.
Soft tool is the tool made of pre-harden steel, it is an economic solution for a small volume production. It has advantages of low cost and fast turn around, but pre-harden steel is a lower grades steel that process lower hardness and wear resistance, so the soft tool can only stand molding cycles no more than 500k shots, it's also difficult to maintain tight tolerances.
Hard tool is a high quality tooling for mass production, it's made of the best quality steel, like H13,420 etc. Hard tool requires more procedure and longer time to manufacture.
Two plate mold is the easiest injection mold structure and has many advantages. It's consist with A side and B side 2 main parts, when it is load in ejection machine to do molding, A side is fixed and held still, B side is movable.
Usually 3 plate mold is not recommended as there are some disadvantages, it's not just because of a much more complex structure but much higher scrap rate, it's also lack of stability because of complex mechanism. It's random to use for high volume production because it required longer cycle time and bigger injection molding machine as the run distance is longer comparing with 2 plate mold.
When considering the secondary mold function, ie that of a heat exchanger it is not achieving uniform temperature across the injection mould which is important. The amount of heat energy absorbed by the mould varies dependent on the flow of material through the cavity. Around feed points there will be maximum heat generated due to material flow and shear. At the end of fill the material temperature will have reduced and the surface of the injection mold will absorb less heat energy.
Physical restrictions which restrict size of cooling channels such as small inserts, deep sections, etc have to be considered in each case. Also don't forget that whatever size your cooling channels, when you come to connect them to supply and return pipes you will have a reduction in area, due to the need to fit connectors.