TOBB UNIVERSITY OF
ECONOMICS AND TECHNOLOGY
MAK 307
Design and Manufacturing
LAB # 2
THEORY OF METAL CUTTING
Experiment Information Sheet
1. INTRODUCTION
Machining is the one of the indispensable manufacturing methods. Nowadays, CNC machining
centers have become capable of carrying out many machining operations by means of single
machine tool with the development of technology. Process control parameters, cutting tool
properties and machine tool quality directly affect properties of the part. The process parameters
must be carefully selected for machining both for rough-cut and finish cuts, in order to improve
efficiency, minimize process time and meet with required tolerances and surface quality of a
part.
2. OBJECTIVE
The purpose of this experiment is to observe and understand effects of process parameters for
rough-cut and finish cut machining on a difficult to cut material such as steel, titanium alloy or
Inconel.
3. THEORY
CNC machine tools provide to give desired form by manufacturing metal, plastic and wood
materials. Operations in CNC machining centers can be divided into turning and milling
operations. Operations such as hole drilling, tapping, etc. can be included in the milling
operations because the working principle is the same.
3.1 TURNING OPERATIONS
Turning is the removal of metal from the outer diameter of a rotating cylindrical workpiece.
Turning is used to reduce the diameter of the workpiece, usually to a specified dimension, and to
produce a smooth finish on the metal. Often the workpiece will be turned so that adjacent
sections have different diameters. Sample workpieces are shown in figure 1. CNC lathes are used
in the manufacturing of cylindrical workpieces.
Figure 1. Turned Workpieces
3.3 SURFACE ROUGHNESS
Surface roughness is called in condition, which causes irregular deviations below and above the
nominal surface line. The parameters used to measure surface roughness are shown below.
Ra: Arithmetic average deviation
Rz: Average of 5 highest and 5 lowest point
Rt: The sum of the maximum height and the maximum depth for the entire measurement length
Rq: The square root of aritmetic average deviations
The most commonly used surface roughness parameter is Ra. Average surface roughness is the
arithmatic mean of the height variations measured from the average line. Ra values are calculated
automatically by the device to be used in the experiment.
(1)
The relationship between the average ideal surface roughness obtained with the single-tooth
cutting tool and the tool tip radius and feed is given in the following equation.
(2)
Ri : Ideal average surface roughness, mm
f : Feed, mm/rev
r : Tip radius, mm
4. EXPERIMENTAL METHOD
Figure 3. Rough-cut of the Test Specimen
Figure 4. Finish-cut of the Test Specimen
The test shall be carried out on a CNC turn-mill machine using stainless steel or similar difficult
to cut alloy. The exact kind of the material, dimensions of the rotational test specimen will be
specified during the experiment. On the rotational specimen, the rough cutting process by depth
of cut “d1” and “d2” in Fig. 3 and finish cutting process by depth of cut “d3” and “d4” in Fig. 4.
The following data will be measured by the students in two stages of the experiment:
1. Rough Cutting
1.
2.
3.
4.
Part Dimensions
Process control parameters
Chip thickness
Measured operation time
5. Measured Average Power load of the machine tool
2. Finish Cutting
1. Part Dimensions
2. Process control parameters
3. Measured surface roughness of the specimen
The aforementioned experiments will be carried out twice with different parameters so that
students will have change to compare and contrast effect of process parameters on operational
efficiency and part quality.