Injection molding equations

Really nice blog and great source of information. Sector Reports. Nice blog and attractive information. I like your blog and your work. Hii dear, Really its a very intresting news for all about injection molding. Injection Moulding, along with extrusion ranks as one of the prime processes for producing plastics articles. It is a fast process and is used to produce large numbers of identical items from high precision engineering components to disposable consumer goods. Thanks, high speed injection machine.

I find this fascinating and your tutorial is very helpful. I have been having a hard time with tonnage and calculating the tonnage required on a cincinnati milacron injection molding machine in our plant. I read your post and I really appreciate your experience. I will get good knowledge from there as well. Keep posting… Injection mold suppliers plastic injection molding plastic mold manufacturer.

Wow, what a challenging math formula, anyway such injection moulding helped produce plastic shapes such as the pallets in canada. Really its a very interesting thing I came to know about the calculation of cooling time in injection moulding. Nice Math formula will help to all mould industries. We are a Plastic injection mold supplier in China. We are a factory which integrates design, drawings, prototype samples, mold and production one-stop service.

Mould Cover. Nice tutorial and great source of information. Mould China. Plastic Injection molding is used in many industrial applications, from toys and model parts to furniture and building materials. It's amazing how much work goes into these moldings. I'm always just so impressed with how far engineering and technology has come. I'm excited to see where it goes 10 years from now!

Visit plasticmoldinchina. I didn't know the cooling process was so important. I learned a lot from this article. It was great learning more about something new. One of my friends is getting his own plastic moulder. The injector is going to be an interesting new toy. I'm glad there are guides like this, too.Injection molding cycle time is one of the biggest factors in the efficiency of your molding process, and, by extension, a major factor in the cost and bottom line implications of any injection molding project you tackle.

Cooling typically makes up 80 to 85 percent of the overall cycle time. When you consider that the cooling part of the cycle is the counterpart to the immense amount of heat required to liquefy the plastic resin during the injection process, this 85 percent figure makes a lot of sense. As you can see, the importance of the cooling phase should not be overlooked. The issue?

injection molding equations

Cooling time has a wide number of variables, including part thickness, material qualities, heating temperature, and injection and holding time.

Also, when factored with the thickness of a part, composes the bulk of the measure of cooling time. Thermal diffusivity can be calculated by dividing the thermal conductivity of a part by the product of its density multiplied by its specific heat the energy required to raise its temperature 1 degree.

Each of these values can be found on the spec sheet for the material in use, or by contacting the manufacturer. Once you know the thermal diffusivity of the part, you can plug it into the rest of the cooling time equation. First, divide the square of the part thickness by the product of the following: the square of the thermal diffusivity, multiplied by 6.

This number is then multiplied by a logarithmic equation. Of course, any injection molding partner worth its salt should be well-versed in these figures. As you can see from above, mold cooling plays a big factor in injection molding cooling time. Mold design is also a big factor here: Cooling channels can and should be designed into the mold whenever possible, to assist with more efficient heat dispersal.

The importance of efficient mold cooling is readily illustrated when you consider the pathway of heat in the cooling process: from the material, to the mold, to the ambient surrounding environment. Efficient mold cooling means efficient overall cooling. The most common scenario will be parts that have not yet solidified enough to hold their shape, which are then damaged by the firing of the ejector pins.

Improper or inefficient cooling — including poor mold design — can also lead to part errors such as warping, shrinking, sink and more. Consistent, well-engineered cooling time is one of the biggest steps you can take to raising the quality of your finished parts and reducing your number of defects.

A part should only be cooled to the point at which it will retain its shape and can be safely ejected from the mold. Any further cooling is not effective or is barely effective and will only lengthen cycle time needlessly.

Ultimately, mathematically estimating the proper cooling time for your part will help you avoid excessive cooling time just as much as insufficient cooling time. Understanding Injection Molding Cooling Times. Share on facebook. Share on twitter. Share on linkedin. Share on pinterest. Jacob Schwartz March 20, No Comments. Injection: The heated material is injected into the mold cavity or cavities. Packing and holding: Injection continues as some of the material that has already been injected begins to cool and shrink.

injection molding equations

Although material begins to cool as soon as it exits the heated injection nozzle and enters the mold cavity, cooling time should only be calculated as a separate phase, after packing and holding. At this point, the liquefied resin begins to re-solidify and hold the shape of the mold cavity. Ejection: Once the material has cooled and solidified to a point where it will hold its shape, the part can be ejected via the mold ejector pins.

Quality assurance: Parts are spot-inspected for proper production and quality.Injection moulding U. Injection moulding can be performed with a host of materials mainly including metals for which the process is called die-castingglasseselastomersconfections, and most commonly thermoplastic and thermosetting polymers. Material for the part is fed into a heated barrel, mixed using a helical shaped screwand injected into a mould cavitywhere it cools and hardens to the configuration of the cavity.

Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers that do not melt during the injection moulding of some lower temperature thermoplastics, can be used for some simple injection moulds. Parts to be injection moulded must be very carefully designed to facilitate the moulding process; the material used for the part, the desired shape and features of the part, the material of the mould, and the properties of the moulding machine must all be taken into account.

The versatility of injection moulding is facilitated by this breadth of design considerations and possibilities. Injection moulding is used to create many things such as wire spools, packagingbottle capsautomotive parts and components, toys, pocket combssome musical instruments and parts of themone-piece chairs and small tables, storage containers, mechanical parts including gearsand most other plastic products available today.

Injection moulding is the most common modern method of manufacturing plastic parts; it is ideal for producing high volumes of the same object. Injection moulding uses a ram or screw-type plunger to force molten plastic material into a mould cavity; this solidifies into a shape that has conformed to the contour of the mould.

It is most commonly used to process both thermoplastic and thermosetting polymerswith the volume used of the former being considerably higher. Thermoplastics also have an element of safety over thermosets; if a thermosetting polymer is not ejected from the injection barrel in a timely manner, chemical crosslinking may occur causing the screw and check valves to seize and potentially damaging the injection moulding machine.

Injection moulding consists of the high pressure injection of the raw material into a mould, which shapes the polymer into the desired form. In multiple cavity moulds, each cavity can be identical and form the same parts or can be unique and form multiple different geometries during a single cycle. Moulds are generally made from tool steelsbut stainless steels and aluminium moulds are suitable for certain applications.

injection molding equations

Aluminium moulds are typically ill-suited for high volume production or parts with narrow dimensional tolerances, as they have inferior mechanical properties and are more prone to wear, damage, and deformation during the injection and clamping cycles; however, aluminium moulds are cost-effective in low-volume applications, as mould fabrication costs and time are considerably reduced.

When thermoplastics are moulded, typically pelletised raw material is fed through a hopper into a heated barrel with a reciprocating screw. Upon entrance to the barrel, the temperature increases and the Van der Waals forces that resist relative flow of individual chains are weakened as a result of increased space between molecules at higher thermal energy states.

Injection moulding

This process reduces its viscositywhich enables the polymer to flow with the driving force of the injection unit. The screw delivers the raw material forward, mixes and homogenises the thermal and viscous distributions of the polymer, and reduces the required heating time by mechanically shearing the material and adding a significant amount of frictional heating to the polymer.

The material feeds forward through a check valve and collects at the front of the screw into a volume known as a shot.One of the important process parameters to establish and record for any injection molded part is its injection or fill time.

Research research reveals the limitations of popularly taught methods of establishing this critical parameter. Fill Time appears to be a nearly straight line, due to the scale employed. The ability of two fill-time data points to generate the same curves as 12 fill-time points was found to be true for a variety of molds and materials.

The resulting two curves are very similar, though the slopes between data points are different due to the influence of pressure on the y-axis values 8A. But when the curves are shifted they overlay on top of one another very well 8B. This was consistent for all molds tested. As shown in this example, those curves in all cases closely matched the original RV curves for the other molds and materials. Today, that information can be supplemented with finite-element modeling of melt temperature throughout a mold cavity during fill 10B.

David A. Injection molding process methodologies have evolved over the decades from a seat-of-the-pants black art to a more structured approach. A number of schools, companies, and individuals provide a valuable service to the industry by teaching these structured methods, which have been labeled with terms such as Scientific Molding, Decoupled Molding, and 2-Stage and 3-Stage processes.

These approaches involve similar specific procedures that help establish a foundation on which to build a process. Among the procedures taught are a method for determining a fill time or fill speed using in-mold rheology curves a.

Math for Molders

These approaches also teach that the process must be documented in a manner that allows it to be transferred to other molding machines with the intent of achieving relatively consistent part quality. For example, if you are documenting the melt temperature you would document the temperature of the plastic coming out of the machine nozzle—not the barrel temperature settings on the machine controller. Fill time is an indication of how fast the plastic is injected into the mold. Any change in fill time may adversely affect the final molded part.

The key question is: How does one go about identifying an ideal fill time for a given mold? Ideally, every part would be evaluated for fill time using mold-filling simulation performed by a skilled analyst with plastics processing experience. Unfortunately this type of analysis data is not available for many plastic parts, so molders need a method to establish an ideal fill time that they can employ on the shop floor. This is where the Relative Viscosity RV test comes into play.

The general procedure for this commonly taught method is presented below.

Math Makes You a Better Molder

Though some consultants and trainers may add other steps or teach it a bit differently, essentially the approaches are very similar:. Record the fill time and pressure at transfer. Reduce injection velocity and record the fill time and pressure at transfer. Repeat Step 3 until the fill time is over 10 sec. Graph relative viscosity y-axis vs. The results of one RV test are shown graphically in Fig. When you graph a number versus its reciprocal, the shape of the curve shown in Fig.

If the change in pressure were directly proportional to the change in fill time, the graph would show a straight line.

However, this test demonstrates that as plastic flows faster higher shear rateits viscosity is reduced and becomes fairly consistent over a wide range of injection rates. The non-log-log graph in Fig. The RV test has been widely taught and adopted by many molding companies to help select a fill time for a given mold.

Company procedures have been written to include the test as part of their process standards. Thus, there is a great deal of material, labor, and machine time spent each day on running the RV tests in hopes of identifying optimum fill times based on a structured approach that a process technician or engineer can use on the shop floor.This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.

Registered in England and Wales. Number Part 1 of this article covered shear rate and some of its effects in actual case studies. I n the first part of this series last month immnet. This article shows how to go about calculating shear rates g. These calculations were used in the case studies presented at the end of the first article. How do you calculate shear rate? Two formulas are generally used, one more commonly than the other, but there are many formulas available.

Do you want to model the entire range of viscosity vs.

Avoiding and solving injection molding problems using shear rate calculations—Part 1

This formula is called the true shear rate formula, the non-Newtonian shear rate formula, or the shear-thinning formula. It says that, as shear increases, the material flows easier. It is different for different materials.

NEW - Lesson 5-HD - Molding Machine Timer, Temperature and Clamp Controls

Polycarbonate is an example. If you want PC to flow better, you turn up the temperature. PC has an n of about. On the other hand, PP responds well to faster filling by flowing better. It is more shear sensitive. It has an n of about. The viscosity vs. Almost all molding happens in the region between the two vertical lines, especially the gates. The shear-thinning formula presented here is valid for this region.This page introduces formulas for calculating basic parameters necessary for injection molding.

The figures obtained from the calculation are for reference only. The conditions for machining depend on the machine tool you are using. Use the optimal conditions according to your actual machining circumstances. This formula is used to calculate the force required to clamp the mold halves during injection molding. The total projection area is the total of the projected areas of the cavities and runners in relation to the parting surface.

Therefore, this value varies depending on the number of items molded and on the runner layout. This formula is used to calculate the molding shrinkage from the mold dimensions and the product dimensions.

Plastic materials expand in volume under high temperatures and shrink under low temperatures. For this reason, the molds are designed to be larger than the molded products.

The difference between the dimensions of the molded product and those of the cavity of the mold is expressed by the molding shrinkage ratio. This formula is used to calculate the pressure loss in a sprue, runner, or gate.

The equation shows an example of calculating the pressure loss with the assumption that the resin is a Newtonian fluid. You can see that pressure loss is largely attributable to the thickness and diameter of the cross-section. Injection Molding Formulas This page introduces formulas for calculating basic parameters necessary for injection molding.

What is Cutting? Plastic Forming. What is Plastic Forming? Injection Molding. What is Injection Molding? Peripheral Equipment. Cutting Tools Holders Dies molds. Machining Formula Collection. Improve productivity just by changing the measurement system!

Get more information.Walk through the examples below and take note, it may save you a lot of money and downtime some day. Math for molders saves time and money. This same 1.

Later you move the same tool above 4. What would the shot sized be to maintain the 4. The diameter of the injection cylinder is 7 inches, the diameter of the screw is 2 inches, what is the Intensification Ratio? Once you know the intensification ratio of a Hydraulic Machine, you can multiply it by any hydraulic pressure to calculate the plastic pressure ppsi.

Our new mold is two cavity hot runner, the part is round 8 in diameter with a. At three tons per square inch, how many tons are needed to support this mold minimally and we will be using a ton machine?

The tool maker was asked to open the round gate from 0. What was the effect on the area of the gate? You are running a machine with a 1. What percentage of the shot are you using? You are running a 2. How fast is it actually injecting if you f time is. Featured Articles. Meet Brad, our Technical Support Manager, as [ As a larger manufacturing company, if you are shutting down production for a temporary period [ Rapid Raptor DUO, the combination of [ The goal is to make sure that your mold will fit, the screw will work [ The goal is to make sure the robot fits your molding machine, then to make [ Remember me Log in.


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