M. Rafi Raza

Investigation of Rheological Behavior of Low Pressure Injection Molded Stainless Steel Feedstocks

The purpose of this research is to investigate the influence of different powder loadings of 316L stainless steel (SS) powders on rheological behavior of feedstocks required for low pressure powder injection molding (L-PIM) process. The main idea consists in development of various formulations by varying 316L SS powder contents in feedstocks and evaluating the temperature sensitivity of feedstock via flow behavior index and activation energy. For this purpose, the irregular shape, spherical shape, and combination of both shapes and sizes (bimodal approach) of 316L SS powders are compounded with wax based composite binder. Moreover, the influence of elemental nanosized boron (B) addition (up to 1.5 wt.%) on rheological properties of irregular shape 316L SS powders is also evaluated using capillary rheometer method. It is observed that rheological parameters for solid powder loading of powder gas atomized (PGA) and bimodal powder P25/75 316L SS underwent sudden change from PGA-69 vol.% to PGA-72 vol.% and P25/75-67 vol.% to P25/75 316L SS 70 vol.%, respectively. Thus it is concluded that PGA-69 vol.% and P25/75-67 vol.% are optimal powder solid loadings corresponding to the lowest values of activation energies.

Rheological Behavior of Carbon Nanotubes / Copper Feedstocks for Metal Injection Molding

Metal injection molding (MIM) technology is known for its ability of producing near net shape components. This study presents the results of flow behavior of multi-walled carbon nanotubes (MWCNTs) reinforced copper composites mixes. The solid loadings in the copper mixes were investigated in the ranges of 55-61 V% using a binder. Copper mixes and copper/MWCNTs were compounded using a Z-blade mixer for homogenous dispersion of solids in the binder. Results identified a mix containing 59 V% copper suitable for substitution of MWCNTs. The flow properties were measured using a capillary rheometer in the shear rate range expected to occur during metal injection molding. An increasing trend in viscosity of the copper mixes with powder loading was noted. Copper/MWCNTs composite mixes showed viscosity more than 1000 Pa.s perhaps due to addition of MWCNTs and increasing trend in viscosity of copper/MWECNTs was recorded. The results of flow data showed that all copper composite mix containing up to 10 Vol.% MWCNTs were successfully injection molding and test samples were produced.

Flow Behavior of Cu/CNTs Feedstocks for Powder Injection Molding

Abstract— In this study, the flow behavior of multi-walled carbon nanotubes (CNTs) reinforced copper matrix feedstocks isp resented. The solid loadings in the copper feedstock were investigated in the ranges of 55-61 Vol. % using binder. Pure copper (Cu) and Cu/CNTs feedstocks were compounded using internal mixer machine for homogenous dispersion of solids in the binder. The flow behavior was measured using a capillary rheometer in the shear rate range expected to occur during powder II.injection molding. An acceptable increasing trend in viscosity of the copper feedstock with powder loading was recroded. Cu/CNTs composite feedstocks showed viscosity more than 1000 Pa.s which is most probably due to the addition of CNTs and increasing trend in viscosity of Cu/CNTs was noted as well. The results also identified that the feedstock containing 59 vol. % copper was most suitable for substitution of CNTs in Cu feedstock.

Defect Analysis of 316LSS during the Powder Injection Moulding Process

Austenitic Stainless Steel Has a FCC Structure at Room Temperature and the Temperature Range of the Austenite Phase Depends upon its Composition. 316L SS Is Widely Used in Medical, Marine, Industrial, Sporting and Aerospace Applications due to its Excellent Combination of Mechanical Properties and Corrosion Resistance. this Study Presents the Defects Observed during Optimization of the Processing Parameters for the Fabrication of Powder Injection Molding (PIM) of 316L SS Parts. in this Study, Five Formulations of Feedstock Containing 60-71vol% of Metal Powder Were Prepared Using a Wax-Based Binder. Green Samples Were Injection-Moulded, Followed by Binder Removal by Solvent and Thermal Means. Paraffin Wax (major Binder) Was Extracted at Various Temperatures in Order to Determine the Solvent Extraction Temperature. the Thermal De-Binding Was Performed Successfully at a Temperature of 450°C by Varying the Heating Rate from 1°C/min -10°C/min. SEM Results Showed Complete Removal of the Plastic Binder. Test Samples Were Sintered at Various Temperatures and Atmospheres. the Defects Observed during Solvent Extraction Were Swelling, Cracks and, at the Thermal De-Binding Step, Collection of Binder, Swelling and Holes. Sintered Samples Showed a Loss of Dimensional Control. these Types of Defect Were Considered to Be due to Inappropriate Heating Rates, Temperature and Dwell Time at each Process Step.

Rheological study of copper and copper grapheme feedstock for powder injection molding

Heatsink is one of the solution to optimize the performance of smart electronic devices. Copper and its composites are helping the electronic industry to solve the heating problem. Copper-graphene heat sink material with enhanced thermal conductivity is the ultimate goal.Powder injection molding (PIM) has advantages of high precision and production rate, complex shape, low cost and suitabality for metal and cremics.PIM consists of four sub sequential steps; feedstock preparation, molding, debinding and sintering. Feedstock preparation is a critical step in PIM process. Any deficiency at this stage cannot be recovered at latter stages. Therefore, this research was carried out to investigate the injectability of copper and copper graphene composite using PIM. PEG based multicomponent binder system was used and the powder loading was upto 7vol.% less than the critical powder loading was used to provide the wettability of the copper powder and graphene nanoplatelets (GNps). Corpper-graphene feedstock contained 0.5vol.% of GNps . To ensure the homogeneity of GNps within feedstock a unique technique was addopted. The microscopic results showed that the feedstock is homogeneous and ready for injection. The viscosity-shear rate relationship was determined and results showed that the addition of 0.5vol.% of GNps in copper has increased the viscosity upto 64.9% at 140˚C than that of pure copper feedstock. This attribute may be due to the large surface area of GNps. On the other hand, by increasing the temperature, viscosity of the feedstock was decreased, which was recommended for PIM. The overall viscosity and share rate lies within the range recommended for PIM process. It is clear that both feedstocks showed pseudo plastic behaviour which is suitable for PIM process. In the pseudo plastic behaviour, the viscosity decreases with the shear rate. It may be due to change in the structure of the solid particles or the binder. The molding results showed that both copper feedstocks were successfully molded and free from the physical defects.

Experimental Investigation on Thermal Conduction of Carbon Nanotubes Reinforced Copper Matrix Composites

The performance of the micro-chip is affected by overheating and hence reduces the efficiency of electronic devices. The development of high thermal conductivity material can solve problems associated with dissipation of heat from the micro-chips. Thermal conductivity for carbon nanotubes (CNTs) are in the ranges of 1200-3000 W/moK which considered as the best candidate material for heat sink applications. This research investigates the fabrication of CNTs reinforced copper composites using powder metallurgy method. Copper powder and CNTs were ball milled to prepare mixtures and compacted at 600 MPa to fabricate test samples. The compacted test samples were sintered in argon atmosphere at 850oC. Sintered density of CNTs/Cu composites was measured and compared with theoretical density. Density data showed that 98% sintered density was achieved. Optical and scanning electron microscopic (SEM) examination of sintered compacts showed good grain growth, however porosity was also noted in sintered samples. Field emission scanning electron microscopy (FESEM) showed well dispersion of CNTs in copper matrix and interfacial bonding between copper particle and CNTs. In this experiment, the addition of 2 % vol. CNTs in copper matrix showed 9% increase in thermal conductivity approximately compared to thesintered pure copper.

Flow properties of Cu/CNTs feedstocks

In this study, the flow behavior of multi-walled carbon nanotubes (CNTs) reinforced copper matrix feedstocks is presented. The solid loadings in the copper feedstock were investigated in the ranges of 55–61 Vol.% using binder. Pure copper (Cu) and Cu/CNTs feedstocks were compounded using internal mixer machine for homogenous dispersion of solids in the binder. The flow behavior were measured using a capillary rheometer in the shear rate range expected to occur during powder injection molding. An acceptable increasing trend in viscosity of the copper feedstock with powder loading was recorded. Cu/CNTs composite feedstocks showed viscosity more than 1000 Pa.s which is most probably due to the addition of CNTs and increasing trend in viscosity of Cu/CNTs was noted as well. The results also identified that the feedstock containing 59 vol.% copper was most suitable for substitution of CNTs in Cu feedstock.

Quantitative Analysis of Fiber Fracture in Powder Injection Molded Metal Composites

In this study, metal composite feed stocks were prepared and test samples were produced by powder injection molding and Multiple Live-Feed Molding (MLFM) devices to investigate the effects of fiber content and macro-shear on the fiber fracture. Fiber-length was measured using an image processing system. The results showed that the fiber volume content increased fiber fracture by 9% and viscosity showed 10% increase in fiber fracture. Samples produced by MLFM devices showed a 1% higher fiber fracture compared to the test bars produced by injection molding. Tensile strength of composites was calculated using fiber contents and fiber length. Considerable increase in tensile strength was noted for metal composites with fiber length above a critical length.