Categorization of Failures in Polymer Rapid Tools Used for Injection Molding

Your work addresses an important research topic which is very relevant to the real world  manufacturing problems. The categorization and analysis of the failure  modes are useful to the readers who are considering or trying to use  3DAM polymer insert for rapid prototyping. 

Thank you for this positive comment.

In  addition to addressing your questions, some further minor changes have  been made to tidy up the language and clarify the results. All changes  are shown in red text in the manuscript.

I have some questions about the experiment.  

When were the failures occur? How many molding cycles did these PRT inserts experience before they were inspected?  

The different failures observed in the PRT inserts occurred at different times during the moulding cycle. In the  text  we identify  the shot number during which we first observed the signs of each failure type. See new text in Table 5. 

Each part was inspected to detect failures, and likewise the tool.  While the tool damage was minor (surface deterioration, surface scalding, bending,) we continued the moulding process until catastrophic tool failure.  

Text to the above effect has been added to Method in section 2.  

Did those failures be observed in all the molded parts after certain shots? 

The failures occurred differently, as follows:  

Surface Deterioration: A small area of  deteriorated surface could be seen on the 7th shot of WHICH PART. The surface deterioration worsened after each shot. part. (Text added to section 3.1.1). 

Surface Scalding: This type of failure was observed only in Case 3, which  did not have any venting provided. This failure was evident after 12  moulding shots, this was a catastrophic failure as in the 13th shot it started to remove tool surface material from the tool. (Text added to section 3.1.2). 

Avulsion/Delamination: This is a catastrophic failure which we attribute to the combination  of  surface deterioration and surface scalding. Avulsion was observed on  the inserts once surface deterioration/scalding reached a critical  stage. This type of failure was evident on all the parts, as they had  fragments of mould material attached to them. Avulsion worsened after  each shot and reached a critical stage within 5 shots. 

Shear Failure: This was a critical failure as it occurred in the runner wall and we could not produce any further parts from the mould. (Text added to section 3.3.1) 

Bending Failure: This  feature on the tool was supposed to create a hole on the part, but  the  boss feature was broken off the tool after 5 shots and all the parts  moulded after it had a thick section instead of a hole. Although this  made the part functionally defective, it was not considered a critical  failure as it was still safe to operate the tool. 

Edge Fractures:  In  case study-3 the tool survived the initial process parameter setup  phase and the edges deteriorated progressively from the 9th to the 13th  shot. During the ejection of the 14th shot a large shard  of material was pulled out. After this shot the tool was flashing due  to failure of the edge which was on the parting line of the tool.  Surface erosion was seen on all the edges along the flow path and  chipping was only seen on edges which had no draft. At the end of the  19th shot the fracture was about 5mm wide, and this was the final  failure on the tool. (Text amended in section 3.3.3). 

These questions relate to the feasibility of using these 3DAM insert in injection molding. In my opinion, the failure analysis may only become meaningful for those  "useful" process. 

Correct.  

The  failure analysis shown here is only relevant to 3D printed tools. Such  tools are increasingly being used in industry, but generally for molding benign materials (low melt temperatures) not the more demanding material shown here. (Text added to limitations in 4.3) 

The  authors conducted these experiments as a part of feasibility study. We  wanted to study the feasibility of: (a) Using PRT inserts to mould  resins with melt temperatures above 250°C, (b) The size of the parts  that can be successfully moulded using PRT insert, (c) The variety of  features that can be safely moulded using a PRT insert, (d) the number  of parts that can be moulded before failure, and (e) the quality control  of the moulded parts. 

In  this study we were able to answer point (a), it is feasible to mould  resins with high melting temperature of up-to 350°C, and we can expect about 25 parts from the mould before failure if the process parameters used are properly set. 

(Text added to Conclusions, section 5). 

The  authors studied the failure mechanisms of Polymer Rapid Tools 3 Used  for Injection Moulding. The work is well written and the methodology and  results are sound. 

Thank you for this positive comment. 

In  addition to addressing your questions, some further minor changes have  been made to tidy up the language and clarify the results. All changes  are shown in red text in the manuscript. 

I only have few suggestions I would like to raise. 

 It  will be good to highlight the effect of the 3D printing process such as  layer thickness, nozzle speed and infill density on the quality of the  insert and how the parameters and potential changes in the failure  mechanic 

The authors recognize this as a limitation in the work and also as an implication for future research. 

In  this study we used only the recommended settings from the machine  manufacturers (3D systems and Stratasys). We did not experiment with  changing the settings for layer thickness, nozzle speed and infill density. (Text added to limitations in 4.3).