Search results

The purpose of this paper is to provide a demonstration of the application of techniques for robust optimization for improvement of the injection moulding processes in an injection moulding small and medium sized enterprise (SME).

A critical to quality characteristic (CtQ) which is connected to assembly problems is the subject of investigation. The CtQ is not directly measurable. The variation in a dimension of a product, which is correlated to the CtQ, is studied using design of experiments (DoE) and Taguchi methods. A two-cavity mould is used in the injection moulding process. To evaluate the robustness of the process using signal-to-noise analysis, the data were transformed to compensate for the systematic differences between the mould cavities.

The initial results showed that finding optimal process parameter settings commonly valid for both cavities was impossible. After a modification of the mould, the experiments were rerun and optimal settings could be found.

Applying DoE techniques in small and medium-sized injection moulding companies is far from common practice. This case study demonstrates a method to apply DoE with five process parameters which can serve as a standard method to prepare production when a new mould is used for the first time.

The originality is connected to the combination of the applied methods and, in the context of the case study, carried out in an SME unfamiliar with the power of the applied methods. The value of the paper is to demonstrate the power of the most powerful technique in quality engineering to improve an injection moulding process within the context of SMEs. The authors would accentuate the point that the true power becomes visible when this powerful technique is introduced into an organization with very little understanding of the technique. In addition, the case study is valuable to practitioners because it proposes a new scientific and systematic approach to understand and optimize the start-up of the moulding process.

This paper aims to explore the influence of the materials used in moulding blocks of hybrid moulds on the injection moulding setup and the properties of the mouldings.

An instrumented (pressure and temperature) hybrid mould with exchangeable moulding blocks, produced by rapid prototyping and tooling techniques (RPT), was used to produce polypropylene tubular mouldings. The configuration of the mould was varied with combinations of moulding block materials, namely, an epoxy resin composite processed by vacuum casting and steel. The processing conditions were adjusted to obtained steady processing conditions. The mouldings were assessed in terms of the microstructure and the shrinkage.

Due to the properties of the moulding block obtained by RPT being different from tool steel, the injection moulding processing conditions and the plastics parts properties are different when hybrid moulds are used. The cycle time depends on the moulding block properties and must be adjusted to the desired running temperature. The morphology of the mouldings is strongly affected by the thermal properties of the moulding block materials. When different materials are used in the core and the cavity asymmetric structures develop in the part. The shrinkage of the mouldings, when resin cores are used is also affected by the deformation of the core caused by the injection pressure.

This paper makes a contribution to understanding the morphology of semi‐crystalline mouldings obtained using hybrid moulds and enhances the importance of the core deformation on the shrinkage of the mouldings.

Advances in rapid prototyping and machining have resulted in reduced lead times for injection moulding tooling. Comparisons between aluminium and stereolithography (SL) tools are made with regard to the ejection forces required to push mouldings from the tools, heat transfer through the tools and the surface roughness of the tools. The results show that ejection forces for both types of tools are increased when a longer cooling time prior to ejection is used. The ejection forces required from a rough aluminium tool are considerably higher than those from a smooth aluminium tool. SL tools do not appear to be subjected to any smoothing as a result of moulding polypropylene parts. The rubber like nature of the tool’s surface is as a direct consequence of the low glass transition temperature and low thermal conductivity of the tool material. Further potential benefits of the low thermal properties of the tool are discussed.

In this work, the changes to stereolithography (SL) resin mechanical properties during the injection moulding process were evaluated. A multi‐impression SL mould was built and used to inject a series of small flat mouldings. The fixed half SL tool insert included recesses to accommodate tensile test specimens. Tensile test specimens made from SL resin were positioned in these recesses and plastic parts were injected. After injecting a predetermined number of mouldings, tensile tests were performed using the tensile test specimens. The results from the tensile tests show that the thermal cycling encountered during the injection moulding process did not significantly affect the mechanical properties of the resin. Observations indicate that decrease in the temperatures encountered in the tool may lead to longer tool life.

Robots have been used on plastic injection moulding machines for many years. Linear robots account for the vast majority of applications but there is a small increase in use of six‐axis articulated arm types for certain applications. This paper discusses the pros and cons for the various types being used and describes the downstream processes that can be incorporated within the automated cell.

The purpose of this study is to demonstrate and characterise a soft-tooled micro-injection moulding process through in-line measurements and surface metrology using a data-intensive approach.

A soft tool for a demonstrator product that mimics the main features of miniature components in medical devices and microsystem components has been designed and fabricated using material jetting technique. The soft tool was then integrated into a mould assembly on the micro-injection moulding machine, and mouldings were made. Sensor and data acquisition devices including thermal imaging and injection pressure sensing have been set up to collect data for each of the prototypes. Off-line dimensional characterisation of the parts and the soft tool have also been carried out to quantify the prototype quality and dimensional changes on the soft tool after the manufacturing cycles.

The data collection and analysis methods presented here enable the evaluation of the quality of the moulded parts in real-time from in-line measurements. Importantly, it is demonstrated that soft-tool surface temperature difference values can be used as reliable indicators for moulding quality. Reduction in the total volume of the soft-tool moulding cavity was detected and quantified up to 100 cycles. Data collected from in-line monitoring was also used for filling assessment of the soft-tool moulding cavity, providing about 90% accuracy in filling prediction with relatively modest sensors and monitoring technologies.

This work presents a data-intensive approach for the characterisation of soft-tooled micro-injection moulding processes for the first time. The overall results of this study show that the product-focussed data-rich approach presented here proved to be an essential and useful way of exploiting additive manufacturing technologies for soft-tooled rapid prototyping and new product introduction.

The purpose of this study is to compare the overall performance of the injection moulding process by using metallic inserts produced by both conventional technologies and selective laser melting (SLM).

A systematic methodology is proposed for prior evaluation of the effectiveness of conformal cooling channels to reduce cycle time and/or to reduce the scrap rate.

The mould was reengineered considering the SLM process and manufactured. Injection trials were carried out to validate expectations provided by injection simulations, which resulted on good quality parts and a significant decrease on cooling time, and, consequently, on the overall cycle time. The minimisation of scrap provided energy savings and time-to-market reduction.

The initial costs for AM tools still pose some doubts on decision-makers. The challenge of this study is to implement the methodology on a small-scale production and still ensure that benefits are achieved.

The case study selected for this research work is based on a parking sensor housing, which is a plastic part assembled on the vehicle’s front and rear bumpers, therefore, with aesthetics concerns. The part produced with the conventional mould exhibits surface defects that, to be minimised (not eliminated), require a longer packing time to diminish the sink marks.

The economic impact of the use of SLM is relevant despite the low batch size for the case study presented. Energy savings are achieved due to scrap reduction and shorter cycle time.

The systematic methodology proposed for prior evaluation of the advantages of conformal cooling is possible to be applied both on small scale and high production series.

This paper gives a review of the finite element techniques (FE) applied in the area of material processing. The latest trends in metal forming, non‐metal forming, powder metallurgy and composite material processing are briefly discussed. The range of applications of finite elements on these subjects is extremely wide and cannot be presented in a single paper; therefore the aim of the paper is to give FE researchers/users only an encyclopaedic view of the different possibilities that exist today in the various fields mentioned above. An appendix included at the end of the paper presents a bibliography on finite element applications in material processing for 1994‐1996, where 1,370 references are listed. This bibliography is an updating of the paper written by Brannberg and Mackerle which has been published in Engineering Computations, Vol. 11 No. 5, 1994, pp. 413‐55.

This paper aims to present a comparison between selective laser sintering and injection moulding technology for the production of small batches of plastic products.

The comparison is based on analysing the time–cost efficiencies of each manufacturing process regarding the size of the series for the selected product sample. Both technologies are described and the times and costs of those individual processes needed to create a final product are assessed when using each of the manufacturing processes.

The study shows that the time-cost efficiency of the selected laser sintering technology increases according to the complexity of the product and decreases with increasing series size and product volume.

The study and absolute values of the presented results are limited to a selected plastic product, but the series size-focused efficiency analysis could be expanded to general cases.

The presented analysis could be used as a general guideline for a decision-making process regarding the more efficient manufacturing method. In addition, the results show the viability of using selective laser sintering during the early stages of production when fast product availability is required, regardless of the series size. Also, some complementary effects of using both technologies in the serial production of the same part are discussed.

Polymer rapid tooling (PRT) inserts can be used as injection moulding (IM) cavities for prototyping and low volume production but lack the robustness of metal inserts. Metal inserts can withstand high injection pressure and temperature required, whereas PRT inserts may fail under similar parameters. The current method of parameter setting starts with using the highest pressure setting on the machine and then fine-tuning to optimize the process parameters. This method needs modification, as high injection pressures and temperatures can damage the PRT inserts. There is a need for a methodical process to determine the upper limits of moulding parameters that can be used without damaging the PRT inserts.

A case study analysis was performed to investigate the causes of failure in a PRT insert. From this, a candidate set-up process was developed to avoid start-up failure and possibly prolong tool life. This was then tested on a second mould, which successfully avoided start-up failure and moulded 54 parts before becoming unusable due to safety issues.

Process parameters that are critical for tool life are identified as mould temperature, injection pressure, injection speed, hold pressure and cooling time.

This paper presents a novel method for setting IM process parameters for PRT inserts. This has the potential to prevent failure at start up when using PRT inserts and possibly extend the operating life of the PRT inserts.