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frezowanie - parametry obróbkowe

Milling – selection of machining parameters

Milling in relation to turning is characterized by much greater variation. The following are the basic descriptions and dependencies of the machining parameters related to milling. This is the first of a series of articles about machining parameters.

This method is a machining in which the main rotary motion is made by a tool and the feed movement performs the workpiece. This machining process is characteristic of conventional milling machines (fig. 1).

frezowanie - parametry obróbkowe

Fig.1 Tool milling machine JFN 36 from JAZON.

In the case of CNC machining centers (fig. 2) one should speak about the relative motion between the tool and the workpiece. The work table moves with the workpiece and the carriage moves with the main drive spindle (with the tool) in relation to the work table. 5-axis CNC machining centers simultaneously use the carriage movement with the spindle and the movement of the working table.

In this machining method, the tool’s work is not continuous. The tool is a rotating solid body. Depending on the location (workmanship) of the blades, such cutters as: plain milling cutters, end milling cutters, face mill. Conical, spherical and shaped tools are also made. On the cylindrical surface, the blades can be made as straight or helical.

Non-continuous machining means that only part of the cutter blades are working at the same time. On the one hand, this is a beneficial feature due to cooling conditions. On the other hand, the thickness of the cutting layer (cross-section of the cutting layer) is variable, which affects the course of the cutting process. As a consequence, the load changes and the durability of the tool decreases.

Technological parameters

The technological parameters of milling include:

  • rotational speed n [rpm];
  • diameter of the tool Dc [mm];
  • cutting speed vc [m / min] – equation 1;
  • feed speed vf [mm / min] – equation 2;
  • feed per revolution ff [mm / rev];
  • feed per blade / tooth fz [mm / tooth] – equation 3;
  • width ae and depth of cut ap [mm].

Table 1 presents the basic computational relationships.

Table 1.
Number: Technological parameter: Equation: Component description:
(1) cutting speed vc frezowanie - parametry obróbkowe Dc – diameter of the tool
n – rotational speed
(2) feed speed vf  frezowanie - parametry obróbkowe ff – feed per revolution
n – rotational speed
(3) feed per tooth fz frezowanie - parametry obróbkowe ff – feed per revolution
n – rotational speed
vf – feed speed

 

milling - machining parameters

Fig. 2. CNC milling center (HASS – Abplanalp trade fair stand).

The width and depth of milling

Depending on the used cutter, it is necessary to correctly interpret the width ae and the depth of the cutting ap. This is shown in figure 3. In the following case, face milling (figure 3), the cutting width ae is equal to the diameter of the tool Dc.

milling - machining parameters

Fig. 3. On the left side face milling, on the right side – interpretation of the milling width and depth.

In the case of face milling the following types are distinguished: – figure 4: a.) full, b.) incomplete symmetrical c.) incomplete asymmetrical which results from the ratio of milling cutter diameter to cutting width ae and workpiece width in the case of machining the entire entire surface.

milling - machining parameters

Fig. 4. Face milling: a.) full, b.) incomplete symmetrical and c.) incomplete asymmetrical.

The presented above-mentioned issues do not fully cover the subject of milling. One of the technological parameters is the tool path. In the case of milling, the use of CAM software plays an important role.

Selection of machining parameters

The choice of machining parameters (fig. 5) is similar to turning.

milling - machining parameters

Fig.5 Diagram of selection of machining parameters for milling.

Differentiation of milling varieties prevents clear definition of general values of machining parameters. An example is a high-speed machining, whose defining process is multifactorial and in addition variable over time.

Workpiece material

In order to facilitate the selection of parameters, the ISO material groups are used. The same division applies to all machining methods. There are 6 material groups – table 2.

Table 2.
Workpiece material ISO marking Sample material:
steel P low-alloy steel
stainless steel M austenitic stainless steel
cast iron K grey cast iron, ductile cast iron
aluminum alloys N cast
heat-resistant alloys S high-alloys based on iron, nickel, cobalt
and titanium
hardened steel H hardened and tempered steel

Catalogs, whether in paper or electronic versions (eg Sandvik Coromant or ISCAR or SECO), constitute a significant user support in making the first choice and matching the tools and parameters to the individual technological task.

Tool path

The tool path in the case of surface machining with complex shapes (fig. 6) and also when machining pockets is a key issue of the technological operation. Milling is characterized by the necessity of dynamic changes of machining parameters during machining. CAM software plays a very important role in this machining method.

milling - machining parameters

Fig. 6. Example of machining surfaces with a more complex shape – MAZAK CNC center.

Sources
  • Materials by SANDVIK Coromant
  • ISCAR materials
  • SECO materials
  • Didactic materials of Warsaw University of Technology and Rzeszów University of Technology
  • Author’s own notes.

About author

morek

Born 1973. In 1993, I graduated from Technical Secondary School No. 1. In 1998, the Faculty of Mechanical Engineering and Automation (now Faculty of Production Engineering) - Warsaw University of Technology. 1997-2000 cutting tools manufacturer at VIS Precise Products Factory S.A. 2004. Unfortunately, this company no longer exists. PhD in gear technology. Production technologies and technological processes are my passion.

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