FABRICATION OF A JIG FOR HYBRID MACHINING PROCESS.
ABSTRACT : This paper aims to present the fabrication process of a jig as an assisted tool for the combination between milling and plasma arc cutting processes. The jig was fabricated to attach the plasma torch in front of the cutting spindle with the movement distance around 100 mm for z axis and 80 mm for x and y axis respectively. Mild steel material was used to fabricate the jig into 4 different parts that were assembled together to form an adjustable plasma torch holder. The jig was attached in front of the mini CNC milling machine before being tested to heat AISI D2 in a single plasma cutting process. The jig developed in this study was capable to heat the metal and performed consistent straight cutting movement throughout the work piece material surfaces.
Hybrid machining is a process where two or more manufacturing processes that combines together to perform material removal tasks. The advantages of hybrid machining process include having a better material removal capability and reducing some effects related to the respective single processes when they are applied individually . Some examples of hybrid machining are the laser assisted machining plasma assisted machining and heat assisted machining . The application of hybrid machining requires modification of the existing machine since there is no commercial hybrid machine available in the market. For instance in a plasma assisted machining a plasma torch should be installed in front of the mill cutter. The process requires special jig to hold the plasma torch in accordance to the cutting area.
Jig as an assisted tooling should be able to hold components and sub-assemblies according to the function requirements prevent undesired motion and avoid interference problems . In plasma assisted machining the jig is required as an assisted tool to combine the plasma arc welding and spindle/cutting tool in the whole system of milling machine.
A milling process is material removal process that shears a metal by using a rotating cutting tool. On the other hand plasma arc welding is a process where the metal is heated until it reaches a melting temperature before being cut by pressurized air on the plasma tip. The combination of both processes enable the material to be heated first by the plasma torch to obtain a softer surface condition before merging with the milling process to remove the softer material. Such process is capable to remove the material at an elevated hardness indicating that this process is capable to perform a better material removal with a significantly lower cost . This paper presents the development of jig for a hybrid machining process. The jig consists of several parts that are assembled together as a structure in order to hold the plasma torch in front of the milling machine spindle.
The jig was designed based on the flexible movement along x y and z axis to assist the machining process with better flexibility to control the plasma torch movement for safety and optimum process.
2.1 Concept Design of Jig
Fig. 1 shows the assembly drawing of the jig developed in this study. The design of every part of the jig was based on the axis movement during the cutting process. The jig was divided into four parts in which most of the parts were made by 6 mm thick metal for strong and portable structure (Figure 1(a)). Part 1 (Figure 1(b)) provides a major function to support the whole part of the jig by clamping the jig in front of the machining spindle. The function of Part 1 was also to hold and control the movement of Part 2 (Figure 1(c)) along the x axis by the distance of 80 mm long together with Part 3 (Figure 1(d)) for back and front movement. Part 4 was used to hold the plasma torch with 100 mm height adjustment along z-axis of the machine (Figure 1(e)).
It this study mild steel was used in every part of the fabrication. The mild steel was chosen because of its availability in the market low cost and ease of processing according to the current job specifications. This type of steel generally has low tensile strength high weldability formability and malleability as compared to the other alloys such as the high carbon steel and chromium steel. In this study the raw materials were ready in a large form of plate around 200 mm (width) x 200 mm (length) x 6 mm (thickness). During the fabrication process the designs of every part were exploded into plane-parts drawing to facilitate easy fabrication for each part. The parts then were cut by the laser cutting machine by referring to the drawing of the components (Figure 2). Then the smaller parts were assembled through the welding and fitting processes to produce the required shapes.
RESULTS AND DISCUSSION
3.1 Complete fabrication of the Jig
The idea behind the attachment of jig in front of the milling machine was to produce a hybrid process in which the milling and plasma cutting can be combined together . This hybrid system was tested as the jig was used to hold the plasma torch and produce a stable process of plasma cutting. For the current study only a single plasma cutting was applied to test the stability of the jig. Figure 3 shows the complete components of the jig development. Figure 4 shows the complete jig after the assembly process. The jig was attached in front of the mini CNC milling machine before it was ready to be applied to cut the suitable material (Figure 4(b)). The plasma torch was aligned parallel to the workpiece surface to facilitate better control during cutting process. Complete jig developed in this study provided an additional advantage of a hybrid machining process since the jig requires minimum space. It is also portable and suitable in most working conditions.
AISI D2 tool steel was used as a raw material for the cutting trial. The plasma was set at 30 A arc current 0.4 MPa air pressure and 200 mm/min feed rate. Fig. 5 shows some preliminary action of plasma cutting using the present hybrid machine based on the developed jig. The plasma torch heats consistently at the beginning of the cutting process where it demonstrated consistent plasma grooving around 30 mm cutting length. However there is a slight burr formation at the endof the machining process due to the molten metal formation as a result of excessive pressurized air from the plasma nozzle. Overall the machining trial shows that the jig developed in this study is capable to heat the metal and perform a consistent straight cutting movement throughout the workpiece material surfaces.
A jig that combines plasma cutting and milling processes for hybrid machining application has been fabricated. The method of fabrication involves the design of the product according to the job specifications identification of the suitable materials as well as measurement cutting and assembly processes by referring to the design of the component. The jig was fabricated in 4 different parts with the movement distance of 100 mm for z axis and 80 mm for x axis and y axis respectively. The jig was attached in front of the mini CNC milling machine before it was tested to heat AISI D2 in a single plasma cutting process. The jig developed in this study is capable to heat the metal and perform consistent straight cutting movement throughout the workpiece material surfaces. The jig fabrication in this study results in a better assisting technique for hybrid machining process. It also has better flexibility to control the plasma torch movement.
The authors would like to thank Ministry of Higher Education Malaysia(MOHE) Universiti Teknikal Malaysia Melaka (UTeM) and Malaysia Technical University Network (MTUN) for their support that enabled this work to be carried out through the Grant RAGS/201/FKP/TK01/1 B00012.
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 Mohd Hadzley Abu Bakar Muhammad Hafiz Samsudin MohdNajib Zamri Raja Izamshah Raja Abdullah Mohd Shahir Kasim and Abu Abdullah Development of 3 Axis Mini Milling Machine for Small Scale Production International Conference on Design and Concerent Engineering 22-23 Spetember 2014 unpublished.
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|Date:||Dec 31, 2014|
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