Experimental studies on manufacturing of the complex shapes made from copper

The paper presents the manufacturing process of a complex copper electrode. To process complex copper shapes is difficult because the material is soft and very sticky. The paper presents the steps for processing this copper electrode at a high dimensional accuracy and a good surface quality. For this process a special tooling solution is needed, optimal process parameters, smart CAD/CAM software and precise CNC equipment.


Introduction
CNC milling technology is one of the most important methods used in industry to machine materials [1,2].It has various distinct advantages over the other cutting technologies, such as: high machining versatility, high flexibility and has been proven to be an effective technology for processing various engineering materials [3][4][5].
Current trends in the manufacturing industry require parts to be processed in a short time, with a good surface quality, high dimensional accuracy and complex 3D shapes [6,7].For manufacturing 3D complex parts are used a variety of CNC machines, such as: 3 or 5 axis milling machines, multitasking lathes, 6 axis robots, or even abrasive water jet centers [8][9][10][11].
To manufacture complex 3D parts is important to use CAD/CAM software.This kind of software must have various strategies for processing complex 3D shapes with fine details [12][13][14].
The electrodes which are used in electrical discharge machining are made from two materials graphite or copper.In this paper is presented the manufacturing process for a complex copper electrode.To obtain a good surface quality and a high dimensional accuracy for copper cutting are required dedicated tools for this type of application [15,16].
Using wrong combination between tool geometry and process parameters, an accumulation of material against the rake face (built up edge -BUE) can appear.The built up edge can generate in this case a poor surface finish or tool brake [17].

The 3D model
The study was started with a 3D model, as in figure 1.This 3d model represents a copper electrode, designed for processing a complex mould.

Tools and process parameters
Copper alloys are difficult to machine by using normal tools, because they are very sticky.For process this copper electrode was chosen a special type of end mill made by Guhring Company.
To avoid the built up edge was selected a tool geometry with sharp edge and polished rake face.The end mills are made out of carbide, with 3 flutes and a bright surface finish with radial coolant ducts.
For roughing operations an end mill with the code 3367/12.00 was selected, as in figure 2.  For finishing operations was chosen a ball mill with code 3015, as in figure 4. The processing width, Ae is an important parameter for finishing of 3D complex surfaces.It has a direct influence on the surface quality.
To calculate this parameter the next formula can be used: [18] In this formula the Hc parameter represents the height of the surface roughness.To convert Hc µm in the general parameter for surface quality Ra µm, table 1 can be used [18].Table 1.To convert Hc µm in Ra µm.
In our study the width of processing was calculated at Ae=0.05 mm.For this experimental study a 3 axis CNC Milling Centre was selected, HAAS VF2, with HAAS controller, from the Tehnical University of Cluj-Napoca.To fix the workpiece a special clamping device was developed, presented in figure 7.For clamping the tools was used a tool holder with ER32 collet chuck.The cutting process was using internal and external cooling with fluid (for 12 mm end mill).In figure 9 are presented different phases of the machining process.

Investigation results
The manufactured electrode is illustrated in figure 10.Using a surface roughness tester Mitutoyo Surftest SJ-210 was measured the surface quality (Ra max 0.18 µm).The maximum dimensional accuracy, 0.03 mm was obtained during the measurements.

Conclusions
This paper presents an experimental study for manufacturing a complex copper electrode.

Fig. 2 .
Fig. 2. The tool for the roughing operation.The process parameters for roughing operation are: • End mill 12 mm, code: 3367/12.000

Fig. 4 .
Fig. 4. The tool for the finishing operation.The process parameters for finishing operation are: ball mill 3 mm, code: 3015; Rotation speed: 11400 RPM; Feed Rate: 950 mm/min; Depth of cut: Ap=0.18 mm;The processing width, Ae is an important parameter for finishing of 3D complex surfaces.It has a direct influence on the surface quality.To calculate this parameter the next formula can be used:

Fig. 7 .
a.The clamping system b.Defining the work offset.Using a 3D Probing Device, the work offset of the part was taken and the required tools were measured (see figure 7).a. b.Fig. 8. a. Roughing operation, b.Finishing operation.