Sains Malaysiana 43(1)(2014): 123–128

Characterization of the Feedstock Properties of Metal Injection-molded WC-Co

with Palm Stearin Binder System

(Pencirian Bahan Suapan bagi Pengacuanan Suntikan WC-Co dengan Sistem Bahan

Pengikat Stearin Sawit)

SRI YULIS M. AMIN¹*, NORHAMIDI MUHAMAD², KHAIRUR RIJAL JAMALUDIN³, ABDOLALI FAYYAZ⁴& HENG SHYE YUNN⁴

¹Department of Engineering Mechanics, Faculty of Mechanical and Manufacturing Engineering

Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia

²Precision Process Research Group, Department of Mechanical and Materials Engineering

Faculty of Enginerring, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor Darul Ehsan

Malaysia

³Department of Mechanical Engineering, Razak School of Engineering and Advanced Technology

Universiti Teknologi Malaysia, International Campus, 54100 Kuala Lumpur, Malaysia

⁴Department of Mechanical and Materials Engineering, Faculty of Engineering

Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor Darul Ehsan, Malaysia

Diserahkan: 30 Mac 2012/Diterima: 18 Jun 2012

ABSTRACT

Feedstock preparation, as well as its characterization, is crucial in the production of highly sintered parts with minimal defect. The hard metal powder - particularly, cemented carbide (WC-Co) used in this study was investigated both physically and thermally to determine its properties before the mixing and injection molding stage. Several analyses were conducted, such as scanning electron microscopy, energy dispersive X-ray diffraction, pycnometer density, critical powder volume percentage (CPVP), as well as thermal tests, such as thermogravimetric analysis and differential scanning calorimetry. On the basis of the CPVP value, the feedstock, consisting of WC-Co powder, was mixed with 60% palm stearin and 40% polyethylene at an optimal powder loading, within 2 to 5% lower than the CPVP value. The CPVP spotted value was 65%. The feedstock optimal value at 61% showed good rheological properties (pseudoplastic behavior) with an n value lower than 1, considerably low activation energy and high moldability index. These preliminary properties of the feedstock serve as a benchmark in designing the schedule for the next whole steps (i.e. injection, debinding and sintering processes).

Keywords: Critical powder loading; metal injection molding; palm stearin; WC-Co

ABSTRAK

Penyediaan bahan suapan berserta dengan penciriannya adalah sangat penting dalam menghasilkan jasad sinter berketumpatan tinggi dengan kecacatan yang minimum. Serbuk logam keras, iaitu karbida terekat (WC-Co) yang digunakan dalam kajian ini diuji secara fizikal dan terma untuk mengkaji sifatnya sebelum proses percampuran dan pengacuanan suntikan dilakukan. Beberapa ujian telah dilakukan, antaranya mikroskopi elektron imbasan (SEM), serakan tenaga sinar-X (EDX), ketumpatan piknometer, jumlah peratusan serbuk kritikal (CPVP) manakala secara terma adalah analisis permeteran graviti haba (TGA) dan permeteran kalori pengimbasan kebezaan (DSC). Berdasarkan nilai CPVP yang diperoleh, iaitu 65%, didapati bagi bahan suapan yang mengandungi serbuk WC-Co yang dicampur bersama bahan pengikat stearin sawit sebanyak 60% dan polietilena sebanyak 40%, beban serbuk yang optimal berada 2-5% di bawah nilai CPVP tersebut. Seterusnya didapati sifat reologi bagi bahan suapan pada beban serbuk yang optimal, iaitu 61% mempamerkan sifat pseudoplastik, dengan menunjukkan nilai n kurang daripada 1, tenaga pengaktifan aliran yang rendah dan indeks pembolehacuanan yang tinggi. Kesemua ciri awal bahan suapan ini akan digunakan sebagai penanda aras dalam merangka jadual bagi proses yang berikutnya; iaitu pengacuanan suntikan, penyahikatan dan seterusnya pensinteran.

Kata kunci: Pembebanan serbuk genting; pengacuanan suntikan logam; stearin sawit; WC-Co

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*Corresponding author; email: yulis@uthm.edu.my