Study of Orientation of Triangular and Square die hole profiles on Extrusion Load in Multi-hole Extrusion process

. The multi-hole extrusion process is an extrusion process with a die having more than one hole. The multi-hole extrusion process is used to extrude more than one product from the same billet with less extrusion load. Different die profiles are used to get different extruded profiles as per the need. Different profiles such as circular, triangular, square etc., are used. The symmetric die hole profiles are easy to fabricate on the extrusion die but the location and positioning of other types of hole profiles like triangular and square need attention as they cause different material flow behavior during material flow. In the present study, triangular and square dies of 2-hole, 3-hole and 4-hole with different orientations of apex and edges have been used to study the extrusion load behavior. Both finite element analysis and experimental study reveals that square hole dies need less extrusion load than that of triangular ones.


Introduction
The extrusion process is widely used in metal-forming industries to produce metallic and non-metallic products.With the improved mechanical properties of extruded components and low wastage, the extrusion process is widely accepted in metal shaping industries.In the extrusion process, a billet is passed through the die opening by applying an external load on the punch and the extruded product takes the shape of the die opening.In multi-hole extrusion, the billet is passed through a die having several orifices, and more than one extruded product from a single billet is produced.*Corresponding author: ritasahufme@kiit.ac.inMulti-hole extrusion is widely used to get a higher production rate, the required extrusion load is less than that of the single-hole extrusion and suitable for the use of the lowcapacity press.Small-dimensioned products manufactured through multi-hole extrusion are many and used in the aviation, healthcare, and automobile sectors.In this competitive era, the multi-hole extrusion process is a better option to achieve higher productivity at a low cost.
Research works multi-hole extrusion process is decades old.The first reported work on multi-hole extrusion was on the extrusion of lead through one, two and three-hole dies with 0.86 reductions and further extended to multi-hole extrusion experiment taking three different reductions with dies i.e. 0.75, 0.86, 0.938.The experiments were carried out on dies containing one and two holes, symmetrically placed and for three and four holes dies arranged radially along the diameter [1].The extrusion load depends on the total reduction and arrangement of the holes.Experiments were carried out with a multi-hole extrusion process by taking the different sizes of holes and spacing between them to find the root cause of cracks in the extruded bars [2].The distribution of die opening and die land length significantly affect the exit velocity of the extruded product and the length of the die land affects the profile of the extruded products [3].In multi-hole extrusion, the metal flow is very complex and affects the mechanical properties of extruded products, extrusion load, and surface finish of the products.Different process parameters related to the die such as the number of holes on the die die land length, die pockets and their geometry and extrusion speed were studied and mechanical properties like tensile strength, hardness and microstructures were evaluated [4][5][6][7][8][9][10].Other parameters such as friction condition and location of holes on the multi-hole dies were investigated to determine the extrusion load and extruded product profiles [11][12][13][14].The bending of exit profiles of extruded products also depends of the velocity distribution [15].The literature reveals that the previous research findings on multi-hole extrusion are limited to circular profile products except for some exceptions.Production of different profiles of extruded products using multi-hole extrusion is not well explored.Before extruding different profiles, it is worth discussing the position of the holes at a particular pitch circle diameter on the die.For circular holes on the die, there is no issue in positioning them because of symmetry.However, in the case of other hole profiles like triangular and square, the location of the edge and apex are important.The current research work is to study the effect of the orientation of triangular and square holes in the multi-hole extrusion process.Finite element simulations have been carried out followed by experimentation to find out the variations in the requirement of extrusion load for changing the orientation of triangular and square holes on the die.

Finite Element Analysis
Several researchers have employed the finite element method for analyzing forming process.For the present study, the FEM analysis has been carried out in DEFORM 3D V-6.1.The different die designs were prepared in CATIA software and saved in .stlfile format.The .stl die design files were then transferred to the Pre-processor of DEFORM software.The material property of billet (Lead) was selected from the material library of the software.The container, punch and die all were considered as rigid plastic whereas billet is taken as deformable material.For analysis, the billet has meshed with 20000 tetrahedral elements.For the process, shear friction is considered as 0.3, and ram speed is taken as 1.2 mm/min to avoid strain hardening effect.The extrusion process simulation was continued till the 2/3 rd height of the billet gets extruded.For all the simulation process extrusion load was measured at steady state conditions.For this study multi-hole dies (2 holes, 3 holes, 4 holes) of different profiles i.e., triangular, and square were used with different orientations of holes.Details of the die design are given in Table 2.1.The area of each hole whether it is a triangular or square hole is kept fixed.The Centroid of each hole is placed on a 10 mm pitch circle diameter (PCD) of the 20 mm die face.In this work, two types of orientation have been considered.In one case apexes of all the holes are oriented towards the centre and in another case, the edges of all the holes are placed towards the centre.A schematic diagram of this type of orientation is given in Fig. 2 The finite element analysis has been carried out for the extrusion of billet and the extrusion loads obtained are studied.Figures 2.3 and 2.4 show the extrusion load obtained from the finite element study with triangular and square dies with edges and apex towards the centre respectively.It was observed that the variation in extrusion load is not significant.During extrusion process, for 2-hole dies with edges towards centre, the fluctuations were due to the difficulty of material flow while passing along the edges.However, when the apex is towards centre, easy material flow leads to less fluctuation in extrusion load.The degree of fluctuation decreases with an increase in the number of holes on the dies and is due to the ease in the flow of billet material through the die holes.The orientation of die hole profiles gets less effective to an increased number of holes on the die.load An experimental study also has been carried out for 4-hole triangular and square profiles.Table 2.2 shows the extrusion load for the different hole profiles when the apex is towards the centre.The extrusion load obtained for the extrusion through a circular hole profile is less than triangular and square hole profiles.The increase in the number of holes on the die also helps in the reduction of extrusion load.The extrusion loads obtained during the experiment are of higher values than that of the simulation results.The ideal conditions of simulations with considered parameters remain the same in the entire process of simulation.However, the billet and die contact parameters changed during the experiment, especially the friction and lubrication conditions.This may be the main reason for an increase in extrusion load in the experiment as compared to that of simulations.

Experimental setup and Procedure
To validate the simulation process, experiments were carried out by taking a 4-hole triangular die and a 4-hole square die.For each type of profile again two orientation of the hole has been taken i.e. one is apex towards the centre and the other is edge towards the centre.The dimensions of both triangular and square holes are taken so that their area will remain the same.The centroid of the holes is placed radially on a 10 mm pitch circle diameter (PCD).The punch, container & die are made up of H13 material.The holes on the extrusion dies were cut by using an EDM machine for a better-quality hole.Copper electrodes of triangular & square cross sections were used in EDM to cut the holes.
The billet was prepared by using lead material (commercially available).Lead was first melted and then cast in a cast iron permanent mould.Machining was done on the casting piece to get cylindrical billets of size 20 mm × 20 mm.Thereafter, the machined billets are treated in boiled water for 30 minutes and allowed to cool to remove any types of residual stresses.Before the experiment container, punch, die, and billet was cleaned and lubricated with MoS2.Dies used in the experiment are given in Fig. 2.5.Extrusion experiment has been carried out in Universal Testing Machine (Make: Fine Spray associates & Engineers Pvt Ltd, Model -TUF-C 1000).The extrusion speed has been controlled below 1.2mm/min to avoid any kind of strain hardening during the experiment.The experiment is carried out up to 50% of the billet length.After the extrusion, extruded parts are cut carefully and kept for further study.

Result of experiments
An experimental study also has been carried out for 4-hole triangular and square profiles.The extrusion load obtained from experiments with four holes triangular and square dies are shown in Fig. 2.6.It was observed that for the square hole die there is no significant change in extrusion load but in the case of the triangular hole die a variation of the load is there.The die with the edge towards the centre shows the low requirement of extrusion load.The resistance to the material flow in triangular hole profile die is more than that of square hole profiles.

Conclusions
In the present study, both finite element analysis and experimental study have been carried out to study the effect of triangular and square hole profiles on the extrusion load.The area of triangular and square holes has been kept the same as per the circular holes of 3 mm diameter.The results of circular hole profiles have been published elsewhere.The orientation of the apex and edge of the triangular and square profiles has been changed and the FE analysis has been carried out.The extrusion load decreases with an increase in the number of holes on the die because of the decrease in the extrusion ratio.The die with square holes needs a higher extrusion load as compared to triangular holes in MHE.The square and triangular hole profiles restrict the flow of material.

Fig. 2 . 5 .
Fig. 2.5.Orientation of edge and apex of holes of Triangular, Square dies used for experiment.