Reverse engineering of inserts and the analysis of issues of the injection mould

When such issues occur, #reverse engineering must be conducted very carefully, since maximum accuracy is required. The client wanted to be able to produce each spare part separately and thus to replace only one component of the mould.

Shema orodjaProblem definition

  • the client has no technical documentation nor a 3D model of the mould, which means that they cannot act quickly in case of failure of a component or the entire mould;
  • 3D scanning demonstrated uneven mould wear and certain inaccuracies in production.

 

Solution

The following steps have been implemented for the client:

  • 3D scanning of all mould inserts (accuracy of 0.01 mm);
  • reverse engineering (development of a precise computer 3D model);
  • preparation of 2D technical documentation for the production of spare parts;
  • analysis of the accuracy of models and identification of causes of insert wear;
  • #Simulations of injection moulding for an in-depth analysis of the issue (analysis of the core displacement).
The final result was a technological computer 3D model of all form inserts with the accompanying technological documentation.

 

Purpose and benefits for end customers

  • quick way to credible 2D and 3D mould documentation;
  • the actual condition of mould inserts suitable to replace only one worn/broken component;
  • detailed analysis of the discovered excessive wear of mould inserts.

 

Pictures and additional description of individual stages are provided below.

3D scanning

Five form inserts of a two-cavity mould were scanned (sliders, runner plate, sprue and stripper plate).

Skenirani modeli

Figure 1: Scanned (STL) models of mould inserts and an illustration of a detail

ATOS CS 5M was used for #scanning with the accuracy of 0.01 mm (the accuracy under 0.01 mm could also be achieved); all the smallest details were captured, including errors which were eliminated during the reverse engineering stage. Figure 2 illustrates a detail of scanned data of one of the mould sliders.

 

Detajl skeniranih podatkov

Figure 2: Detail of scanned data

Reverse engineering

Reverse engineering is a process of creating a surface or (in this case) solid CAD model on the basis of scanned data. As already mentioned, a functional model of all scanned elements had to be made, which means that surfaces had to be created with appropriate components (planes, cones, cylinders, etc.), whereby their relative positions had to be taken into consideration:

  • exact positioning of parting (i.e. contact) surfaces of inserts (slider to slider, sprue to both sliders and upper plate, etc.)
  • parallelism of planes of functional surfaces;
  • coaxiality of mating components (taper for locking the runner plate to the sprue axis, etc.)

 

Throughout the process, deviations of the developing CAD model from scanned STL models are repeatedly checked.

 

 Vmesna primerjava nastajajočih površin z STL-modelom

Figure 3: Interim checks of the accuracy of the CAD model when compared with the original STL model

The analysis of the problems of injection moulding

During the reverse engineering stage, several unexpected deviations were discovered. These are shown in figures below.

Oblikovni trn - nakazuje se zamik osi

Figure 4: Analysis of deviations of the sprue shows unsymmetrical wear and displacement of axis

 

Analiza obrabe dolivne plošče

Figure 5: Analysis of deviations in the runner plate confirms our suspicions regarding the top of the sprue - unsymmetrical wear of the contact surface

 

Vodilne površine čeljusti

Figure 6: Analysis of deviations of one of the sliders shows a significant displacement
of the guiding surfaces; the insert has been, however, produced very accurately

Injection moulding simulation

All the indicated problems are probably a result of unsymmetrical positioning of a runner on the side (visible in Figure 5). Therefore, the simulation of #injection moulding was performed with software package Autodesk #Moldflow Insight. Our main point of interest was the displacement of the core, but an analysis of cooling was also conducted.

slika12 nesimetricno fill

Figure 7: Illustration of the mould cavity filling - unsymmetrical filling or uneven distribution of material is clearly visible on one side

 

Deformacija jedra

Figure 8: Despite the fact that the core is locked on both sides, there is deformation in the mid-section, which is the thinnest; the size of deformation is 0.126 mm, which means that the wall of the product is thicker by 0.25 mm on one side - this may cause certain issues in the product's functionality

 

Tranzientna analiza hlajenja orodja

Figure 9: Transient analysis of cooling; the results show that the difference in temperature is bigger at the top of the core (~15°C); this is due to poorer cooling of the core, which is warmer in this case - this difference could be eliminated or reduced by extending the cooling hole or introducing conformal cooling

Final result

Shortly after the CAD model was created, the sprue in cavity 1 broke. The analysis of the conditions in the mould provided the possible reasons for this issue. It must be emphasized that this problem could result in a longer downtime were there not for the CAD models. In case of a single cavity mould, there would also not be any real representative model for the creation of replicas, since we would have to make use of the broken component.

It can therefore be concluded that, in addition to other frequently described benefits, precise 3D scanning of moulds can provide us with priceless information on the condition or wear of the mould. This information can then be used to identify causes of problems occurring during the operation of the mould. Without understanding the causes of problems in detail, it is very difficult to eliminate them completely.

 

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