J. G. Kovács

55485170700

Publications - 7

Laser powder bed fusion and casting for an advanced hybrid prototype mold

Martin Zobač I. Fekete J. G. Kovács B. Zink István Hatos Dániel Török Tatyana Ageyeva Róbert Boros H. Hargitai

Publication Name: Journal of Manufacturing Processes

Publication Date: 2022-09-01

Volume: 81

Issue: Unknown

Page Range: 748-758

Description:

One of the factors limiting the throughput of injection molding is cooling time, which is the most significant part of the total cycle time. The cooling efficiency of molds can be considerably improved with additive manufacturing techniques. A 3D printed injection mold with conformal cooling channels reduces cooling time by 30–40 %. However, the cooling efficiency of these molds can be further improved with a multi-material approach and the use of materials with excellent thermal and mechanical properties. In this study, we propose a hybrid mold insert made of steel and copper, produced with the combination of Laser Powder Bed Fusion (L-PBF) and casting. The steel shell that contains conformal cooling channels was printed by L-PBF. Then this shell was cast with copper. We found that the hybrid mold insert we developed has lower residual cooling time and heat extraction is more uniform than the conventional printed steel insert. The developed hybrid mold insert enables a reduction of residual cooling time by 15 %.

Open Access: Yes

DOI: 10.1016/j.jmapro.2022.07.034

Surface modification and wear properties of direct metal laser sintered hybrid tools used in moulds

I. Fekete J. G. Kovács T. Ibriksz Mária B. Maros István Hatos H. Hargitai

Publication Name: Journal of Mechanical Engineering

Publication Date: 2018-01-01

Volume: 64

Issue: 2

Page Range: 121-129

Description:

Injection moulding is one of the most productive plastic forming processes. Product development and the reduction of production time require new solutions in tooling design and manufacturing. Direct metal laser sintering (DMLS) allows moulds to be built with special cooling systems, which offer curved cooling lines that can follow the geometry of the part (conformal cooling). One disadvantage of DMLS, its high cost, can be dramatically reduced with the building of hybrid structures. With conventional tool steels as the base plate and only the special geometry of the part sintered on the top, the final geometry can be manufactured after sintering by conventional process technologies. We produced hybrid structures by direct metal laser sintering maraging steel (MS1) powder onto the surface of commercial mould steels and studied the effect of different heat treatments on porosity, tribological behaviour and the microstructure. The transition zone was also characterized.

Open Access: Yes

DOI: 10.5545/sv-jme.2017.4942

Characterization of internal stresses in hybrid steel structures produced by direct metal laser sintering

J. G. Kovács István Hatos H. Hargitai

Publication Name: Materials Science Forum

Publication Date: 2017-01-01

Volume: 885

Issue: Unknown

Page Range: 196-201

Description:

In this study hybrid structures were produced by direct metal laser sintering of maraging steel (MS1) powder onto the surface of commercial mold steels. The over-sintering method should be analyzed to find the optimum pre- and post-heat treatment to minimize the internal stresses. The internal stress is directly proportional to the deformation if the solid thick part is reduced to thin plate like parts. Based on this recognition the deformation of the plates over-sintered with MS1 could be analyzed in order to explore the internal stresses and the effect of different pre- and postheat treatments were examined.

Open Access: Yes

DOI: 10.4028/www.scientific.net/MSF.885.196

Enhanced injection molding simulation of advanced injection molds

N. K. Kovács A. Suplicz J. G. Kovács T. Tábi B. Zink István Hatos H. Hargitai F. Szabó

Publication Name: Polymers

Publication Date: 2017-01-01

Volume: 9

Issue: 2

Page Range: Unknown

Description:

The most time-consuming phase of the injection molding cycle is cooling. Cooling efficiency can be enhanced with the application of conformal cooling systems or high thermal conductivity copper molds. The conformal cooling channels are placed along the geometry of the injection-molded product, and thus they can extract more heat and heat removal is more uniform than in the case of conventional cooling systems. In the case of copper mold inserts, cooling channels are made by drilling and heat removal is facilitated by the high thermal conductivity coefficient of copper, which is several times that of steel. Designing optimal cooling systems is a complex process; a proper design requires injection molding simulations, but the accuracy of calculations depends on how precise the input parameters and boundary conditions are. In this study, three cooling circuit designs and three mold materials (Ampcoloy 940, 1.2311 (P20) steel, and MS1 steel) were used and compared using numerical methods. The effect of different mold designs and materials on cooling efficiency were examined using calculated and measured results. The simulation model was adjusted to the measurement results by considering the joint gap between the mold inserts.

Open Access: Yes

DOI: 10.3390/polym9020077

Methodology development for through-plane thermal conductivity prediction of composites

A. Suplicz J. G. Kovács H. Hargitai

Publication Name: International Journal of Thermal Sciences

Publication Date: 2016-02-01

Volume: 100

Issue: Unknown

Page Range: 54-59

Description:

The prediction and tailoring of thermal conductivity of two-phase composites is essential. In this work a new semi-empirical model was developed, which was derived from the rule of mixtures. Furthermore, a new methodology was developed to determine the thermal conductivity of the fillers and the maximum achievable filler content. To validate the new model, polypropylene-based composites were prepared with different fillers, such as talc, boron-nitride and graphite, with 20, 40 and 60 vol% filler content. The results obtained from the proposed model are in good agreement with the experimental data. Various other theoretical models were also introduced and compared to the experiments, but in most cases those underestimate or overestimate the thermal conductivity of composites.

Open Access: Yes

DOI: DOI not available

Thermal simulations and measurements for rapid tool inserts in injection molding applications

N. K. Kovács A. Suplicz J. G. Kovács T. Tábi B. Zink H. Hargitai F. Szabó

Publication Name: Applied Thermal Engineering

Publication Date: 2015-06-25

Volume: 85

Issue: Unknown

Page Range: 44-51

Description:

apid prototyping (RP) is a widely used process in the industry to shorten development time. Another advantage of this technology is the ability to create conformal cooling systems, thus not only cooling time and cycle time can be shortened, but also shrinkage, thus warpage can be decreased. The main disadvantage of Rapid prototyping materials is their low thermal conductivity, which strongly influences cooling properties and warpage. The research based on a special developed injection mold for novel rapid prototyping based mold inserts with cooling systems. A method has been introduced to determine the most important thermal parameters for injection molding simulations using rapid tools. Those parameters, which can be measured such as the specific heat and thermal conductivity of the mold materials, are directly implemented into the software. The heat transfer coefficient between the polymer melt and the rapid tool insert surface cannot be measured in a reasonable way, thus simulation software was used to determine that based on indirect calculation derived from real measurements. In the paper, the method was proved with Fused Deposition Modeling (FDM) and Polyjet mold inserts.

Open Access: Yes

DOI: 10.1016/j.applthermaleng.2015.03.075

The analysis of injection molding defects caused by gate vestiges

N. K. Kovács A. Suplicz J. G. Kovács T. Tábi B. Zink H. Hargitai F. Szabó

Publication Name: Express Polymer Letters

Publication Date: 2015-04-01

Volume: 9

Issue: 4

Page Range: 394-400

Description:

Issues of product safety are the most serious problems of an injection molded product due to their risk to human health. Such a safety problem can be the needle-shaped vestige at the gate zone of injection molded products, called a gate vestige. Only observations of the formation of gate vestiges can be found in the literature, but the processing parameters influencing their dimensions, especially their height have not been studied yet. Our goal was to study the effect of various injection molding processing parameters and gate constructions on gate vestige formation.

Open Access: Yes

DOI: 10.3144/expresspolymlett.2015.37