Video basic understanding of injection mould

I found a great video from youtube, although it was on youtube a while, but this video deserves to be given the thumbs.
in this video can be seen clearly how the process of formation at the injection mold part to work, well we'll find out in detail the process of melting and movement of the screw on the injection machine

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rapid heat cooling system on injection mold

rapid heat temperature, is actually an old method that is often used to eliminate the weld line, the front cover products such as TV, is an example of the most frequently used method, but its use is now developed further, as demand for products with low cycle time and quality of surface nice sharp increase lately, covering progress being made is that the control system is used, so the heat on the heating rod is held constant, the only heating occurs during the process of filling, so filling process stops, and the cooling process is done, no heating rod heating process.

Advantage

Trim cycle times up to 20 %

A new unit combines rapid heating and cooling and mold-temperature control in one unit as a means to trim cycle times by up to 20% and reduce energy cost. It is the result of a collaboration between Wieder GmbH International of Germany, a supplier of pulsed mold heating/cooling systems, and Regloplas of Switzerland, a maker of fluid temperature-control units

Reduce Weld line

because during the process of filling, the mold is heated, especially at the regional meeting of the plastic, this led to the solidification of the material evenly, so that the weld line can be minimized.

injection mold is rapidly heated to a high temperature, usually higher than the glass transition temperature of the polymer material, before melt-injection and rapidly cooled down to solidify the shaped polymer melt in mold cavity for ejection. Since the elevated mold temperature can eliminate the unwanted premature melt freezing during filling stage, the melt flow resistance is greatly reduced and the filling ability of the polymer melt is also significantly improved. As a result, plastic parts with excellent surface appearance can be obtained.

Improve Appearance

rapid heat cycle method is also shown to improve the quality of the surface, this is because the process of filling with stable temperatures ranging from the gate to the end product, or it could be said to be due to differences in temperature in the cavity is not much different.

Reduce Cost

I was not sure whether this method can reduce the cost of production, when production is carried out is to a large scale, of course, 10-20% reduction in cycle time will bring a lot of meaning to the cost of production, but when the scale of SMEs, given the initial price for the application of this method expensive, I think this method will not reduce production costs.

Heating Method

various types of heating methods research has been carried out

1. use of the insulation layer, An insulation layer is coated onto the mold base then a heating layer is applied to the insulation layer as the cavity surface, for Increasing the mold surface temperature in the filling process, a coating on the cavity surfacewith TiN and Teflon has reduced the heat transfer from the melt to the mold material, the which Increased the temperature on the cavity surface.

2. the use of steam. difficulty of this method is the first installation costs are expensive, and slow increase in temperature,

3. Infrared radiation on the surface, this method has also been investigated, and are able to reduce cycle time by 20%

4. electric heating rod, this method is the method most commonly used in industry because of the installation, maintenance, repairs are relatively easy. but the price per Kw electricity is relatively expensive, because it takes a minimum of 300 watts for a heating rod.

Reference

1. S.C. Chen, H.S. Peng, J.A. Chang, W.R. Jong, Simulation and verification of induction

heating on a mold plate, International Communications in Heat and Mass Transfer

31 (7) (2004) 971–980.

2. P.C. Chang, S.J. Hwang, Simulation of infrared rapid surface heating for injection

molding, International Journal of Heat and Mass Transfer 49 (21–22) (2006)

3846–3854.

3. G.L. Wang, G.Q. Zhao, H.P. Li, Y.J. Guan, Research of thermal response simulation

and mold structure optimization for rapid heat cycle molding process,

respectively, with steam heating and electric heating, Materials and Design 31

(1) (2010) 382–395.

4. X.P. Li, G.Q. Zhao, Y.J. Guan, M.X. Ma, Optimal design of heating channels for rapid

heating cycles injection mold based on response surface and genetic algorithm,

Materials and Design 30 (10) (2009) 4317–4323.

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Cooling Layout and Cooling method between core/cavity and mold base

Cooling is most important parameter when talking about cycle time reduce, some of my friend who very interest in injection mould still confuse how to design cooling system in injection mould, before talking about optimal design, first we must be familiar with the term and design standard that will be used.

Basic Cooling Layout

in principle, the more uniform temperature in the cavity, the better the resulting product, the more uniform and rapid heat transfer processes during the process of solidification occurs, the faster the cooling process, and of course the faster the cycle time that happened.when designing, to keep the cooling process is rapid and uniform cooling channels should be sought closer to the wall of the product, especially for regions of high and thick walls. therefore the cavity cooling channels is essential.

in the image above, is an example of basic connections cooling layout, its parts are
A. cavity colored with blue
2. green is mold base
3. yellow is cooling joint plug
4. white is hose connection to connecting cooling joint plug

on the left side of mold in above picture, we see that two pcs of cooling joint plug (yellow color) in that side, is for input and output of cooling mold base and cooling channel from the machine.

Rectangle Like Layout
depend one cooling layout is a favorite around the product, because the drilling process should be straight, then the shape is rectangle, except in the form of circular gear will be retained.

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Injection Mould Venting System, a little part of design that have big effect on part quality

venting is a small part of the mold design, on the design process also requires a very short time, perhaps only 10% or less of the total time required in designing.sometimes is frequently neglected until molding trials indicate mold inadequacies related to venting. if we understand the purpose and function of vents, it's can assists mold designer to design where clearly additional vents required.

when the cavity space injected by plastic material, automatically empty space on the cavity will be filled with plastic material, the air in the cavity will be shifted to another place, what would happen if the air can not move, the air will experience a high pressure , so the temperature rises even higher, resulting in plastic that fills the cavity will be burning, the defect is called a burn, because of the importance of venting a lot of products that fail due to not properly inject the gas vent, especially for products that have a rib that thin and tall, as compared to thick products.

source : Plastic Today


The main function of the venting is
A. compressed air release
when compressed air is not expelled from the cavity, the plastic flow is inhibited, the result will be formed on a short shot of the product
2. compressed air will produce a gas with high temperature and burn the plastic around it, resulting in a defect burn marks, the product looks like a burn, this will greatly affect the look of the product.
3. when the gas mixed with plastic, the plastic will generate an uneven structure, which will reduce the strength of the product / mold parts produced, stress concentration also common in this region, which occurs due to the plastic notch.

for more detail about effect of adequate of venting on injection mold, please see on picture below

part of venting, can divide on 2 section, land and groove, land is always contact with plastic melt, it's deep about 0.01 mm until 0.02 mm, depend on viscosity of material, relief of vent or gas land is about 1 mm until 2mm, but you must remember for rubber all the number above can't applied, gas vent on rubber material is very special, because rubber has low viscosity.
when designing the gas vent / venting on injection mould, make sure that all of the groove must have exhaust groove that connect to atsmosfer.

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collapsible core for demolding/ejection system of internal screw undercut

one common way used in the ejection system for an internal screw is used collabsible undercut core, which requires collabsible core product generally has the undercut on the inside, for example an internal screw, pipe fittings, elbow pipe, use collabsibe core is not only on the core course , undercut the slider is also often used collabsible cores.
video below gives a simple explanation of how Collapsible cores working

http://www.die-moldtool.com/

Main Component
The three units are a Collapsible Core, center pin, and a positive collapse sleeve.

cenTer pin
The Center Pin serves to expand the segments of the Collapsible Core to their molding position and holds them at this diameter. A hole is provided inside the pin for cooling. The center pin is manufactured of a high alloy Type D-6 steel hardened to 60 to 65 Rockwell C or use SKH 51, SKD 11. Refer to the pin grinding instructions for machining directions. In use the pin must incorporate two design features. The pin must protrude beyond the face of the collapsing core segments by certain amounts. This protrusion keeps material from flowing under the face of the collapsing segments to ensure they properly collapse. A radius must be applied to the outside corner at the front of the center pin. The sharp edge resulting from cutting the pin to length will gall and subsequently destroy the inside surfaces of the collapsing core segments
collapsible core
The Collapsible Core is manufactured from A.I.S.I. Type A-2 steel hardened to 51 to 57 Rockwell C. It is designed to collapse independently when the center pin is withdrawn. The fit between segments is controlled to permit flash free molding. The location of the core on its pin is critical. The distance between the back of the core flange and the front of the center pin flange (Head Space) is critical and must be maintained.
If the Head Space (1.938 ±.005 on a CC 202 PC) is not maintained, unsatisfactory operation will result, or the core may be permanently damaged.
posiTive collapse sleeve
The Positive Collapse Sleeve (PC sleeve) is designed to function when the Collapsible Core fails to collapse independently upon withdrawal of the center pin. In normal operation, the PC sleeve is not functioning. It is essential to have such a unit for maximum safety and reliability in automatic and semi-automatic operation. Under no circumstances should a mold be placed into automatic operation without the use of the PC sleeve.

picture above shown collapsible core and the component, detail explanation about CC we can find it in DME standard part http://www.dme.net/dme/resources/FAQs/collapse_cores.html

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Runner Design in Injection Mold,

in designing the runner, first-time we must consider items that affecting  runnersize, some of which
- Volume of part, the greater the volume takes a larger diameter runners anyway.
- Weight of part, the heavier parts, it takes a larger diameter runners.
- Plastic materials, plastic materials with low viscosity, aqueous requires a smallerdiameter runner.
- Wall thickness, the thicker the greater the diameter of the runner is needed.
- Length of flow path, the longer it takes the flow of large diameter runner.

picture above shown some factor that we must consider before choosing right diameter of runner, 

Cross Section Area

various cross section area use on the market, It depends on the heat loss, machining requirement, but the most popular cross section area are circular, parabolic and trapezoid section area, picture below shows three

Diameter

to determine the diameter, based on the type of material and wall thickness, the following chart can help, for similar materials PP, PA, POM, PC, PE can use the following graph, first select the appropriate thick wall thickness and look heavy parts, and then pull the line down, the approximate diameter required will be obtained

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