Basic Elements of Machine Tools

1. Machining Operations
Basic Elements and Mechanisms of
Machine Tools
Dr. Dalia Nabil

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Intended Learning Outcomes
• Introduction to Machine Tools and their productivity.
• Differentiate between the different elements of machine tools.
• Understand the function of each element of machine tools.
• Describe the different maintenance principles for machine tools.

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Contents
• Machine Tools
• Elements of Machine Tools
•Structures
•Guideway
•Spindle
•Driving system
• Maintenance of Machine Tools

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Machine tools
Compared to Forming ?
• Metal cutting machines (machine tools) are characterized by
higher production accuracy compared with metal forming
machines.
• They are used for the production of relatively smaller number
of pieces; conversely, metal forming machines are
economical for producing larger lots.
The productivity of a machine tool is measured either by:
• the number of parts produced in a unit of time,
• the volumetric removal rate,
• the specific removal rate per unit of power consumed.

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Machine tools
• Productivity levels can be enhanced using the following
methods:
• Increasing cutting speeds and feed rates
• Increasing the machine tool available power
• Using several tools or several WPs machined simultaneously
• Increasing the traverse speed of the operative units during
the non machining time.
• Increasing the level of automation for the machine tool
• Adopting modern control techniques such as NC and CNC
• Introducing jigs and fixtures that locate and clamp the work
parts in the minimum possible time

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Classification of Machine Tools
• During the use of general or special-purpose manual machine tools, product
accuracy and productivity depend on the operator’s participation during operation.
• Semiautomatic and automatic machine tools are best suited for large production
lots where the operator’s interference is minimized or completely eliminated, and
parts are machined more accurately and economically.
Machine Tools
General
Purpose
Turning
Drilling
etc.
Special Purpose
Gear Cutting
Thread
cutting
Semi-
Automatic
Automatic Computer
Numerically
controlled
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Machine Tools’ function
• The main functions of a
machine tool are:
• holding the WPs to be
machined,
• holding the tool, and
• achieving the required relative
motion to generate the part
geometry required.

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Elements of machine tools
Machine tools include the following elements:
1. A structure that is composed of bed, column, or frame
2. Slides and tool attachments
3. Spindles and spindle bearings
4. A drive system (power unit)
5. Work holding elements
6. tool holding elements
7. Control systems

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Requirements of machine tools
Machine tool, as whole, must have an adequate stability
and should possess the following general requirements:
1. High static stiffness of the different machine tool elements
such as structure, joints, and spindles
2. Acceptable level of vibration
3. Adequate damping capacity
4. High speeds and feeds
5. Low rates of wear in the sliding parts
6. Low thermal distortion of the different machine tool elements
7. Low design, development, maintenance, repair, and
manufacturing cost

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Elements of machine tools

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Contents
• Machine Tools
• Elements of Machine Tools
•Structures
•Guideway
•Spindle
•Driving system
• Maintenance of Machine Tools

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1) Machine tool structures
The main functions of the machine structure include:
1. Ability of the structure/bed to resist distortion caused by static and dynamic loads
2. Stability and accuracy of the moving parts
3. Wear resistance of the guideway
4. Freedom from residual stresses
5. Damping of vibration
Usually made from Cast Iron

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1) Machine tool structures

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1) Machine tool structures

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1) Machine tool structures
Chip disposal
Chip disposal, in the case of high-production machine tools, affects the construction
of the machine tool frame as shown in the following figure.

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Contents
• Machine Tools
• Elements of Machine Tools
•Structures
•Guideway
•Spindle
•Driving system
• Maintenance of Machine Tools

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2) Machine tool guideways
Features required by machine tool guideways:
• Accessibility for effective lubrication
• Possibility of wear compensation
• Restriction of motion to the required directions
• Proper contact all over the sliding area
• Wear resistance, durability, and rigidity

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2) Machine tool guideways
Sliding friction guideways
• Consist of any one or a combination of the flat, vee, dovetail, and cylindrical
guideway elements.
• For the sliding surfaces, the bulk of the load is carried on the metal-to-metal
contact. The load carried by the lubricating oil film is very small.
Types of guideways: (a) vee, (b) flat, (c) dovetail, (d) cylinder,(e) cylindrical–cylindrical,
and (f) cylindrical–flat

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2) Machine tool guideways
Friction condition and, consequently, wear of the
guideways are affected by:
1.material properties of the fixed and moving element,
2.surface dimensions of the guideways,
3.acting pressure, and
4.accumulation of dirt, chip, and wear debris
(maintenance).

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2) Machine tool guideways
Wear of guideways can be minimized by:
1.minimizing the sliding surface roughness,
2.increasing hardness of the sliding surfaces,
3.removing the abrasive wear particles from the
guideways system,
4.reducing the pressure acting on the guiding
surfaces.

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Contents
• Machine Tools
• Elements of Machine Tools
•Structures
•Guideway
•Spindle
•Driving system
• Maintenance of Machine Tools

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3) Machine tool spindles
• Machine tool spindles are
used to locate, hold, and
drive the tool or the WP.
• These spindles possess a
high degree of rigidity,
rotational accuracy, and wear
resistance.
• Spindles of the general-
purpose machine tools are
subjected to heavier loads
compared with precision
ones.

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3) Machine tool spindles
• Machine tool spindles are supported inside housings by
means of ball, roller, or antifriction bearings.
• The geometrical accuracy and surface finish of the machined
components depend on the quality of the spindle bearings.

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3) Machine tool spindles
• Spindles are normally made hollow and provided with an
internal taper at the nose end to accommodate the center or
the shank of the cutting tool/WP fixation.
• A thread can be added at the nose end to fix a chuck or a
face plate.
• Hardened, tempered Medium carbon steel containing 0.5% C
is used for making spindles (40 Rockwell (HRC).

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3) Machine tool spindles
Spindle bearings must provide the following requirements:
1. Minimum deflection under varying loads
2. Accurate running under loads of varying magnitudes and
directions
3. Adjustability to obtain minimum axial and radial clearances
4. Simple and convenient assembly
5. Sufficiently long service
6. Minimum temperature variation throughout the speed ranges
7. Sufficient wear resistance

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Contents
• Machine Tools
• Elements of Machine Tools
•Structures
•Guideway
•Spindle
•Driving system
• Maintenance of Machine Tools

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4) Machine tool drives
Motion in M/C Tools
Primary
Cutting
Rotating
Straight
Feed
Continuous
Intermittent
Auxiliary
• To obtain a machined part using a machine tool, coordinated motions
must be imparted to its working members.
• Primary (cutting and feed) movements, which removes the chips from the
WP or
• Auxiliary motions that are required to prepare for machining and ensure
the successive machining of several surfaces of one WP or a similar
surface of different WPs.

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4) Machine tool drives
Rotary Motion
Stepped
Belt Slip
Gearing
Stepless
Mechanically
Hydraulic
Electrical
Stepped motions are obtained using belting or gearing.
Stepless speeds are achieved by mechanical, hydraulic, and electrical methods.

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4) Machine tool drives: Belting
• The belting system, shown in
the figure, is used to produce
four running rotational
speeds.
• Cheap and absorbs
vibrations.
• It has the limitation of the low-
speed changing, slip, and the
need for more space.

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4) Machine tool drives: Gearbox
• Provides speed and torque conversions from a rotating power source to another
device using gear ratio.
• The advantage of a sliding gear transmission is that it is capable of transmitting
higher torque and is small in radial dimensions.
• Among the disadvantages of these gearboxes is the impossibility of changing
speeds during running.

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4) Machine tool drives: Stepless
• The drive shaft rotates
at a constant speed n1
as well as the friction
roller of diameter d.
• The output speed of the
driven shaft rotates at a
variable speed n2 that
• Disk-type friction
stepless drive depends
on the instantaneous
diameter D

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Benefits of Stepless Speed Drives
• Infinitely variable speed (stepless) drives provide output speeds,
forming infinitely variable ratios to the input ones.
• Such units are used for main as well as feed drives to provide the
most suitable speed or feed for each job, thereby reducing the
machining time.
• They also enable machining to be achieved at a constant cutting
speed, which leads to an increased tool life and ensures uniform
surface finish.
• The easy and smooth changing of the speed or feed, without
stopping the machine, results in an appreciable reduction in the
production time, which increases the productivity of the machine
tool.

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Contents
• Machine Tools
• Elements of Machine Tools
•Structures
•Guideway
•Spindle
•Driving system
• Maintenance of Machine Tools

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Machine Tool Maintenance
• Machine tools cannot produce accurate parts throughout their working life if there is
excessive wear in their moving parts.
• Maintenance is classified under the following schemes:
• Corrective maintenance
• Preventive maintenance
• Predictive maintenance

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Lab Assignment 2: Due date: 24/2/2023
You are required to draw a proper block diagram for
different machine tools in the workshop. Label all parts
clearly, indicating the machine structure type, guideways
type, the spindle is used for workpiece or tool and the drive
system used.
1. Lathe machine
2. Drilling machine
3. Shaper
4. Planer
5. Vertical Milling Machine
6. Horizontal Milling Machine
7. Boring Machine