Keywords:Cold embossing Assembly accuracy Geometrical defect Filling ratio Bulging The precision of cold forging parts becomes critical because the process depends on many factors such as the size and complexity of the parts。 Defects negatively affect the assembly accuracy and the performance of the parts。 Therefore, defects must be detected and prevented as soon as possible before the manufac- turing process begins。 The paper intends to investigate the geometrical defect of the cold embossing pin head, which may result in an inaccurate assembly of the blade。 In this paper, defect formation was studied using DEFORM-2D based on material flow pattern and stress distribution。 The defect was measured in terms of incomplete filling and geometries of the bulging。 The effect of the distance to the edge (DTE) is significant to the formation of defects。 The size of the bulge is reduced and the filling ability shows better performance as the DTE increases。 The FE results are in good agreement with the experimental result。83518

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1。Introduction

Assembly accuracy depends on part quality, but defects damage part quality and its accuracy [1]。 Accuracy is very crucial in man- ufacturing near-net or net-shape parts with complex profiles。 The main goal of net-shape manufacturing is to achieve the assembly of the components without secondary processes such as machin- ing [2]。 Therefore, it is essential to detect and prevent the defect during the production process。 Cold forging, one of the net-shape manufacturing processes, is governed by many factors such as fric- tion, part geometry, die shape, and temperature setting of the die and workpieces。 Hence, the cold forging process has a high ten- dency to form defects。 Arentoft and Wanheim [3] classified forging part defect into six: fold, shear defect, surface defect, form defect, crack, and structural defect。 Causes of defects include die deflection, yielding or wear, and eccentricity or buckling due to flow imper- fection。 Kimura et al。 [4] evaluated component assembly based on shape error。 Lin and Lin [5] studied the folding defect during the cold extrusion of aluminum。 The relationship between defect and geometrical shape were studied based on the radius ratio。 A similar approach was employed to investigate the barreling for- mation during cylinder upsetting with hollow die [6]。 Metal  flow

imperfection related defect has attracted the attention of many researchers。 Chan et al。 [7] proposed a dynamic change of tooling geometry to control the most common flow-induced defect such as folding。 Other defects such as die filling and barrel formation during the lateral extrusion process have been discussed by Tahir [8]。 Sim- ilarly, Liu et al。 [9] studied the under-filling problem in the rotary rolling of a flange。 On the other hand, Narayanasamy et al。 [10] stud- ied the reaction of various metals to barreling during the cold upset- ting process。 In his study, un-lubricated truncated cone billets were used as a case study, and the relationship between the measured radius of curvature of the barrels and the stress ratio parameter was established。 In addition, Baskaran and Narayanasamy [11] applied white grease as a lubricant to determine the dimensions such as height, contact, and bulge diameter at different stress-ratio param- eters。 Yilmaz et al。 [12] conducted an experimental investigation of conventional closed-die forging to study the effect of aspect ratios and indentation to the forging load and die filling。 Lu and Zhang [13] found that forging defects are caused by improper die dimen- sion。 Their study was carried out, taking into consideration the temperature dependency of the thermal and mechanical properties of materials。 Song and Im [14] studied the effect of process design parameters to the formation of under-filling and folding defect dur- ing closed-die forging of bevel gears。 In another study, by proposed optimizing process sequence, the surface defect can be solved [15]。 On the other hand, Qamar investigated the effect of shape com- plexity and dead metal zone to the quality of cold extruded part [16]。 In addition, Sheu and Yu [17] introduced a new type of die design to solve the folding defect during the orbital forging process。