This news article was originally written in Spanish. It has been automatically translated for your convenience. Reasonable efforts have been made to provide an accurate translation, however, no automated translation is perfect nor is it intended to replace a human translator. The original article in Spanish can be viewed at Selección rápida de una inyectora ajustada al molde

Software facilitates much work

Quick selection of a fuel transfer adjusted to the mould

Javierre, j. Aisa, a. Fernandez.TIIP unit associate C. CSIC-University of Zaragoza01/02/2002

This work presents a programme developed in the T.I.I.P. (workshop of injection of the industry of plastic, unit associated with the C.S.I.C) belonging to the area of engineering of the University of Zaragoza. The described software has as main objective the determination of the machines that can inject a certain mold. The tool works in Windows environment and has been programmed in Visual Basic in order to achieve a nice user interface. The program allows to manage databases of machines very easily and select which can inject the mold, which can not do and can with any restrictions (which can not injected it in conditions optimal).

The programme, to be able to take into account adequately all factors, carried out with a very small number of data, estimates of the strength of closing, injection pressure, time of cooling etc. and complemented through coefficients for different criteria to establish the suitability of a machine.

An important factor in the production of a piece of plastic injected is the suitability of the machine where is going to inject this mold. The selection must be made at an early stage that is considered the construction of a new mold.

To select the injection machine suitable for a particular mold is necessary to check many factors of a technical nature. A usual technique is to look at only the force of closure, and in any case the injection volume and dimensions of the mould. This can cause problems of injection that are not attributed to the machine.

In some cases it could have serious economic and technical problems either by the need of having to buy a new machine or for expenses incurred after injection during the duration of the project in order to obtain a valid piece for sale. This would involve a cost to the company unexpected and probably unacceptable, when considering the feasibility of injecting a piece of plastic.

The size of the machine

The characteristic of the machine that determines its size is its clamping force (force that performs the closure system to hold the mold closed during the injection). The clamping force is a parameter key, there a relationship between this and the rest of its features.

Because of the necessity of generating greater forces closing, to inject into molds which require it, it is inevitable to increase the size of the system and therefore of the machine in general. On the other hand a large machine can also be endowed of a greater unity of injection capable of inject and laminating greater amount of material.

How the program works

The following describes how the program works and the steps has followed for the proper conduct of the selection of the optimal machine (Figure 1).

Beginning of the selection process: after selecting the database machines desired, the program will allow us access to the selection process.

(a) data entry: the first part is a form that allows us to introduce nearly all of the necessary data for subsequent calculations.

(b) selection process: then you can access a new form where appear the factors against which conduct the selection process. By clicking on each one of them to access a new screen where we are called the conformity on already entered data on that factor or that we do now for the first time.

This gives us a first selection from a single factor and allows you to change values related to him if this was required by the user, and can return to again make this partial selection.

Finally, from the screen where all the factors are marked those with whom you want to make the final selection.

Final presentation of results: appears a form with the outcome of the selection where we can also see new parameters of the machines, order them to our own liking, deleting those that we want, direct access to the file of the machine or save results to a text file.

DATABASE

The database has information on the different machines. This database can be expanded or modified easily. The information associated with each machine is reflected in the following figure:

NTRODUCTION OF DATA OF THE MOLD

The data corresponding to the characteristics of the mold are introduced through the following screens:

The introduction of all the data is not essential program ask us later those essential which have not introduced or in some cases it will help us to calculate them. Each of the two leaves that comprise the data entry form has a button for help with a question mark icon. If you click on them, you will see a help screen showing a description of what each of the data we requested.

Selection of factors

After the input screen of data and have pressed start process access to a new screen where the fifteen factors on which we will carry out the selection of the optimal machine.Factors involved in the process of selection of the injection machine can differentiate between what can be considered as necessary and that without it, if they are recommended. Most of recounted specifications appear in the machine as those values that can withstand the machine. As a result any less than that maximum value may be used.

EXAMPLE OF APPLICATION OF FACTORS

Theoretical volume of injection

When this factor is selected the screen through which the program calculates the theoretical volume of the selected material, at the temperature of injection, injection mold.

Selection process:

• If the theoretical volume of injection of the machine is less than necessary, the machine is excluded because it is not able to inject parts of that size.

• If they are close, restricted its use, since the amount of material may be inadequate in parts that require precision.

• If the (V). theoretical machine is far higher than necessary, the dose to inject is too small it although it is possible to use is not recommended, as that can cause the degradation of the material that should go (long in proportion) plasticizing cylinder before being injected.

A partial selection of valid machines for the injection according to a given factor may be performed.

Clamping force

If you do not know its exact value approximations it from; material to inject, thickness of piece and projected average area.

Selection process

• Those machines whose clamping force does not exceed the necessary are excluded by not keep closed the template correctly.

• It is recommended to exclude those machines whose clamping force is much higher than the necessary to the be therefore using a machine oversize for the necessary characteristics which can also damage the mold.

Pressure specified in injection.

If you do not know its exact value approximations it from; material to inject, thickness of piece, filling time and length of flow.

Selection process

• Are excluded those machines are not able to produce the necessary pressure, as this implies does not perform the correct filling of the mold.

Theoretical flow of injection

Selection process

• Those machines whose flow-injection rate is below the minimum flow are excluded for not being able to inject the material at the time.

• Machines whose flow-injection rate is greater than the minimum are suitable for injection but only those that are above the optimal flow will do so properly.

Flow of plasticizing

For optimal development of the process, the machine must have sufficient plasticizing capacity to carry out the phase of dosing (preparing to injection dose) during the time of cooling of the piece.

Selection process

• Is not an exclusionary factor, if a machine is not able to prepare the fast enough material there will be a delay, with the consequent economic cost, but does carry the correct injection of the piece.

Power of injection

We can find in the situation of not being able to inject a mold or end of fill it under the desired conditions without having reached the maximum values of pressure and flow of our machine, by the fact that the power required (power = flow x pressure) is greater than the available.

Selection process

• Not an exclusionary factor to be able to increase the power of the machine through the use of a more powerful bomb or thanks to a battery that provides great amount of oil for a short time, allowing you to reach the power maximum more rapidly than with a bomb.

Maximum opening/light race

This distance has to be enough to allow for the expulsion of the piece and its subsequent manipulation, by an operator or an articulated arm. Considered that it must be greater than 2.5 times the depth of the piece, which is the width of the projection of the piece on a plane perpendicular to the partition of the mold.(Distance between the two sides further away from the piece measures on the perpendicular to the plane of partition).

Selection process

• In machines with mechanical lock (knee) system use the career of maximum aperture which indicates the position that the system of links is fully reflected. Excluding the machines whose career of opening does not exceed 2.5 times the depth of the piece.

• In machines with hydraulic locking system where the mobile plate does not have the above limitation and can scroll to the part end of the machine, use the luza maximum, excluding those machines whose maximum light is not greater than the sum of the thickness of the mold over 2.5 times the depth of the piece.

Maximum/minimum thickness of mold

Selection process

• Are excluded those machines whose maximum thickness is less than our mold. This factor is only applicable to machines with mechanical closure to have limited the maximum size of mold by need have extended their articulated links to realize the clamping force.

• The minimum thickness is not a factor precluding there is always the possibility of placing a few residual dishes that allow us to reach this minimum size.

Distance between columns useful

Selection process

• The useful distance between columns must be such as to enable the mounting of the mold without interfering with the plates or other elements type time that can stand out from him to the be mounted machine either from the top or side.

Type of nozzle open/closed

Working with certain materials such as PA, PVC and POM, because gases generated at the temperature of injection is necessary open nozzle to allow their escape.

Selection process

• The choice of an open nozzle is not exclusive as nozzles locking system can remain open.

• If you choose closed nozzle, excluding those machines that only have open nozzles.

Automation

Some machines are you can attach a jointed-arm robots or other industrial robot, which is responsible for handling the piece once this has been ejected from the mold. In this way is automates the production, although it is not always advisable or necessary, either the machine is not endowed with this element.

Selection process

• It is an exclusionary factor, if so determined by the user. Automation reduces production times.

Machine with numerical control

Selection process

• Is an exclusionary factor or to be determined by the user, which is a great advantage over the conventional machines for allowing to optimize the process bringing it to our mold needs.

Monitorizable

The current machines are equipped with various entries where probes are connected to collect information on the injection process, such as pressure and temperature values.

Monitorizables are those machines that have the software necessary to show the operator of the machine the graphics and data collected by the probes.

Selection process

• Those not monitorizables machines have the possibility of using an external computer to perform these functions, so this process is not exclusive.

Number of controllable cores

Selection process

• If a machine is not able to control the number of required cores, there is the possibility of using a hydraulic switchboard to control them by what this factor does not exclude the use of any machine.

Once made the selection of independently for each of the desired factors, mark the screen selection of factors those which we involve in the final selection process.

Click selection end > and we accede to the final selection screen.

In the final selection we have machines that are able to inject the mould according to the factors considered relevant. This final list reflects possible restrictions of each factor and can be ordered according to various characteristics.

SEE DETAILS OF THE MACHINE

By "double-clicking" on the machine you want (on the row), and after giving our agreement will open the window where the file of the machine

Finally we save the result, obtaining the following file:

CONCLUSIONS

The developed program allows to select the machines capable of injecting a mold of quickly and easily, indicating which can inject it optimally and which without difficulty. For this he considers numerous factors. To be able to do this from a small number of data calculate approximate values of force closing, injection pressure, injection volume, cooling time... The program also works as a database of machines, storing and giving access to the information of the same quick and easy, so as a first step to a possible adaptation of the needs in plant.