Papers by Author: Mohd Halim Irwan Ibrahim

Abstract: Metal injection moulding (MIM) is a cost-effective technique for producing small, complex, precision parts in high volume. Each step in MIM process plays a vital role in order to achieve high quality final product. To have a good understanding of the MIM process and successful in manufacturing, characterisation of the material feedstock is essential. This paper presents the characterization of MIM feedstock consisting titanium alloy (Ti-6Al-4V) powder mix with binder 60 wt% of palm stearin and 40 wt% polyethylene. The characterisation of Ti-6Al-4V alloy powder, binders and feedstock includes scanning electron micrograph (SEM), thermo gravimetric analysis (TGA), differential scanning calorimeter (DCS) and rheological test were established. Rheological results exhibited pseudoplastic or shear thinning flow behaviour, where its viscosity decreased with increasing shear rate. The feedstock viscosity also decreased with increasing temperature and was found to be suitable for moulding.

Abstract: Sintering is a key step in the metal injection moulding (MIM) process, which affects the mechanical properties of the sintered part. The mechanical property of the sintered compact is resulted from tremendous sintered part densification. The paper presents an optimisation of the sintering parameter for the best flexure strength of the fine SS316L water atomised powder compact. The L9 (34) orthogonal array is used in the study and four replication of the flexure strength has been recorded at each experiment trial. The analysis of variance (ANOVA) signifies the sintering variables are highly significant to the flexure strength, α = 0.005. The study demonstrates that the cooling rate is the most influential variable that contributes to the best flexure strength, followed by heating rate, dwell time and sintering temperature.

Abstract: Sintering is a key step in the preparation of metal foams. The present work focuses on the sintering effects on the properties of titanium foam prepared using the slurry technique. Sintering affects the density as well as the mechanical properties of the sintered parts. To achieve a high density of the titanium alloy foam, the effects of various parameters including temperature, time profile and composition have to be characterized and optimized. This paper reports the use of the Taguchi method in characterizing and optimizing the sintering process parameters of titanium alloys. The effect of four sintering factors: composition, sintering temperature, heating rate and soaking time to the density has been studied. The titanium slurry was prepared by mixing titanium alloy powder, polyethylene glycol (PEG), methylcellulose and water. Polyurethane (PU) foam was then impregnated into the slurry and dried at room temperature. This was later sintered in a high temperature vacuum furnace. The various factors were assigned to an L9 orthogonal array. From the Analysis of Variance (ANOVA), the sintering temperature was found to give the highest percentage of contribution (34.73) followed by the composition of the titanium alloy powder (26.41) and the heating rate (0.64). The optimum density for the sintered titanium alloy foam was 1.4873±0.918 gcm-1. Confirmatory experiments have produced results that lay within the 90% confidence interval.

Abstract: The L27 (313) Taguchi orthogonal array is used in the experiment while the injection pressure, injection temperature, powder loading, mold temperature, holding pressure and injection speed are optimized in this study. A grey relational grade (GRG) obtained from the grey relational analysis (GRA) is used to solve the titanium alloy powder injection molding operations with the multiple performance characteristics such as strength and density. From the analysis of variance (ANOVA), the injection temperature has the highest contribution at confidence level 90% to the quality of green part followed by powder loading. The others factor such as mold temperature, holding pressure, injection pressure and injection rate and all the interactions are not significant even though it give contribution during injection molding but the confidence level are less than 90%.

Abstract: This paper investigates the characteristic important to metal injection moulding (MIM) process via rheological behavior of MIM feedstock. A gas atomized spherical ZK60 magnesium (Mg) alloy powder and the binder of 60wt.% palm stearin (PS) + 40wt.% low density polyethylene (LDPE) were used in this investigation. Prior to mixing process, critical powder volume percentage (CPVP) was determined and subsequently four different feedstocks with powder loading of 62, 64, 66 and 68vol.% were prepared. The properties of the feedstocks were then analyzed rheologically. Here, the flow behavior index n, the flow activation energy E and the mold ability index αSTV of the Mg alloy MIM feedstocks were determined. Results show that feedstock with 64% powder loading has the best rheological properties and therefore it is considered to be the best for the injection moulding process.

Abstract: In this paper, titanium alloy was used to prepare titanium foam using the slurry method. The compressive strength is the most important properties to be considered to produce a good sample. To achieve a high compressive strength of the titanium alloy foam, the effects of various parameters including temperature, time profile and composition have to be characterised and optimised. This paper reports the use of the Taguchi method in optimising the processing parameters of pure titanium foams. The effects of four sintering factors, namely, composition, sintering temperature, heating rate and soaking time on the compressive strength has been studied. The titanium slurry was prepared by mixing titanium alloy powder, polyethylene glycol (PEG), methylcellulose and water. Polyurethane (PU) foams were then impregnated into the slurry and later dried at room temperature. These were next sintered in a high temperature vacuum furnace. The various factors were assigned to an L9 orthogonal array. From the Analysis of Variance (ANOVA), the composition of titanium has the highest percentage of contribution (64.64) to the compressive strength followed by the soaking time of sintering factor (6.01). The optimum compressive strength was found to be 38.03 MPa for this titanium alloy foam. It was achieved with a 750% composition of titanium, sintering temperature of 1250oC, a heating rate of 1.5oC/min and 120 minutes of soaking time.

Abstract: Nowadays, micro metal injection molding has become among the promising method in powder metallurgy research to produce small-scale intricate part at an effective process and competitive cost for mass production. This paper investigated the optimization of highest green strength which plays an important characteristic in determining the successful of micro MIM. In this paper, stainless steel SS 316L with D50 = 5.96µm was used with composite binder, which consists of PEG (Polyethelena Glycol), PMMA (Polymethyl Methacrilate) and SA (Stearic Acid). Feedstock with 61.5% with several injection parameters were optimized which highly significant through screening experiment such as injection pressure(A), injection temperature(B), mold temperature(C), injection time(D) and holding time(E). Besides that, interaction effects between injection pressure, injection temperature and mold temperature were also considered to optimize in the Taguchi’s orthogonal array. Analysis of variance (ANOVA) in terms of signal-to-noise ratio (S/N-larger is better) for green density was also presented in this paper. Result shows that interaction between injection temperature and mold temperature(BxC) give highest significant factor followed by interaction between injection pressure and mold temperature(AxC). Single factor that also contributes to significant optimization are mold temperature(C) and injection time(D). This study shows that Taguchi method would be among the best method to solve the problem with minimum number of trials.

Abstract: In this paper, the titanium alloy powder of Ti-6Al-4V is mixed with binder 60wt% of palm stearin and 40wt% of polyethylene for metal injection molding (MIM) process. Injection molding parameters has been optimized using Taguchi method of L27 (313) orthogonal array. Highest green density has been identified as the green part quality characteristic or as an output for this study. Parameters optimized are the injection pressure, injection temperature, powder loading, mold temperature, holding pressure and injection speed. Besides those, interaction of the injection pressure, injection temperature and powder loading were studied. The analysis of variance (ANOVA) is employed to determine the significant levels (α) and contributions of the variables to the green density. Results show that the injection pressure has highest significant percentage followed by injection temperature, powder loading and holding pressure.

Abstract: The Grey-Taguchi method was adopted in this study to optimize the injection molding parameters for the MIM green compacts with multiple quality performance. A Grey relational grade obtained from the Grey relational analysis is used as the quality performance in the Taguchi method. Then, the optimum injection molding parameters are determined using the parameter design proposed by the Taguchi method. The result concluded that the mold temperature (D) is very significant, by the fact that the ANOVA shows its contribution to excellent surface appearance as well as strong and dense green compacts is 38.82%.

Abstract: This paper presents the rheological properties of SS316L water atomized MIM feedstock. Coarse and fine SS316L water atomized powder is mixed with a composite binder consisting of PMMA and PEG to form a homogenous paste, termed as feedstock. The feedstock is loaded with SS316L water atomized powder ranging 62 v/o, 62.5 v/o, 63 v/o, 63.5 v/o and 64 v/o. However, due to the morphology of the water atomized powder which is not spherical compared to the gas atomized ones, fine powder feedstock is unable to produce any significant rheological result due to the powder loading being more than 63.5 v/o. Results show that the fine powder feedstock demonstrates a higher viscosity if compared to the coarse powder feedstock. It can be established that binder separations are likely to occur in the coarse powder feedstock, especially, at high temperatures. The investigation concludes that the fine powder feedstock has its best rheological properties at 62 v/o while the coarse powder feedstock lies between 63 v/o and 63.5 v/o.