CNC mill turning machine slides. a detailed account of its introduction and basic concepts to understand the working and dependancies.

1. CNC Mill-Turn Center
CNC mill-turn center has the general configuration of a turning center; in
addition, it can position a cylindrical workpart at a specified angle so that a
rotating cutting tool (e.g., milling cutter) can machine features into the outside
surface of the part.
• An ordinary turning center does not have the capability to stop the workpart at a defined angular
position, and it does not possess rotating tool spindles.
• The additional capabilities of CNC Mill-Turn Center include
1. combining milling, drilling, and turning with grinding, welding, and inspection operations, all in
one machine tool
2. using multiple spindles simultaneously, either on a single workpiece or two different
workpieces
3. automating the part handling function by adding industrial robots to the machine
4. The terms multitasking machine and multifunction machine are sometimes used for these
products. 1

2. CNC Mill-Turn Center
CNC mill-turn center has the general configuration of a turning center; in
addition, it can position a cylindrical workpart at a specified angle so that a
rotating cutting tool (e.g., milling cutter) can machine features into the outside
surface of the part.
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3. Drilling Operation
Drilling is a machining operation used to create a round
hole in a workpiece.
• Drilling is different from boring operation, which can only be used to
enlarge an existing hole.
• Drilling is usually performed with a rotation cylindrical tool which has two
cutting edges on its working end, called as a drill or a drill bit.
• Drilling is usually performed on a drill press
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4. Cutting Conditions in Drilling
Drilled holes are either through holes or blind holes.
Through Holes: the drill exits the opposite side of the
work.
Blind Holes: The drill does not exit the opposite side of
the workpiece
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5. Cutting Conditions in Drilling (Cont.…)
The rotational speed in drilling is related to the surface
cutting speed at the outside diameter of the drill by the
equation:
𝑁 =
𝑣
𝜋 𝐷
Where:
• N = Rotational speed (rev/min)
• v = Cutting Speed (m/min)
• D = Drill Diameter (m)
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6. Cutting Conditions in Drilling (Cont.…)
The feed in drilling is generally expressed in mm/rev.
This feed can be converted to a linear travel rate in
mm/min by the formula
𝑓𝑟 = 𝑁 𝑓
Where:
• fr = feed rate (mm/min)
• f = feed (mm/rev)
Since there are (usually) two cutting edges at the drill
point, the uncut chip thickness, taken by each edge is
half the feed
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7. Cutting Conditions in Drilling (Cont.…)
The machining time required to drill a through hole can
be determined by the following formula:
𝑇𝑚 =
𝑡 + 𝐴
𝑓𝑟
Where:
• Tm = Time of Machining (min)
• t = Work Thickness
• A = Approach Allowance
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8. Cutting Conditions in Drilling (Cont.…)
The Approach Allowance accounts for the drill point
angle. It is the distance that the drill must feed out from
the opposite side of the workpiece, before reaching the
full diameter
is given by;
𝐴 = 0.5𝐷 tan(90 −
𝜃
2
)
Where;
• θ = drill point angle
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9. Cutting Conditions in Drilling (Cont.…)
The machining time required to drill a blind hole can be
determined by the following formula:
𝑇𝑚 =
𝑑
𝑓𝑟
Where:
• d = Hole depth = The distance from the work
surface to the ‘point’ of the hole.
By this definition the drill point angle allowance does
not affect the time to drill the hole.
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10. Cutting Conditions in Drilling (Cont.…)
The volumetric rate of material removal in drilling can
be determined by the product of drill cross section area
and the feed rate, as follows;
𝑀𝑅𝑅 =
𝜋 𝐷2 𝑓𝑟
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Where
• MRR = Material removal Rate (mm3/min)
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11. Operations Related to Drilling
Reaming: Reaming is used to slightly enlarge a hole, to
provide a better tolerance on its diameter, and to improve
its. The tool is called a ‘reamer’ and is usually has straight
flutes
Tapping: tapping is used to provide internal screw
threads on an existing hole. This operation is performed
by a tool called a ‘tap’.
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12. Operations Related to Drilling (Cont.…)
Counter Boring: Counter boring provides a stepped hole,
in which a larger diameter follows a smaller diameter
partially into the hole. A counter-bored hole is used to seat
bolt heads into a hole so the heads do not protrude above
the surface
Countersinking: This is similar to counter-boring, except
that the step in the hole is cone-shaped for flat head
screws and bolts.
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13. Operations Related to Drilling (Cont.…)
Centering. Also called center drilling, this operation drills
a starting hole to accurately establish its location for
subsequent drilling. The tool is called a center drill.
Spot facing. Spot facing is similar to milling. It is used to
provide a flat machined surface on the workpart in a
localized area.
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14. Types of Cutting Tool
There are two main types of cutting tools;
1. Single Point Cutting Tool
2. Multi-Point Cutting Tool
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15. Multi Point Cutting Tool (MPCT)
A Multi point cutting tool have more than one cutting edge and
usually achieve their cutting motion by rotating.
such as a drilling, reaming, tapping, and milling cutting tools
Many of the principles that apply to single-point tools also apply
to the multi point cutting tools, simply because the mechanism of
chip formation is basically the same for all machining operations.
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16. There are many types of MPCT, however following two types are
most important to study
• The Drill
• The Milling Cutter
Types of MPCT
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17. The Drill
Various cutting tools are available for hole making, but
the twist drill is by far the most common.
Drills come in diameters ranging from about 0.15mm
(0.006 in) to as large as 75 mm (3.0 in).
Twist drills are widely used in industry to produce holes
rapidly and economically.
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18. • The most simplest of MPCT is the Twist Drill.
• Understanding the Drill geometry would help in studying other
rotating cutting tools
The Drill Geometry
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19. The Drill Geometry
• Flutes: The body of the drill has two spiral flutes. The flutes act as
passageways for extraction of chips from the hole.
• Helix Angle: The angle of the spiral flutes with respect to the axis of
rotation is called the helix angle, a typical value of which is around 30.
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20. The Drill Geometry
• Web: It is desirable for the flute openings to be large to provide
maximum clearance for the chips, However the body of the drill must be
supported over its length. This support is provided by the web, which is
the thickness of the drill between the flutes.
• Cutting Edges: Connected to the chisel edge are two cutting edges
(sometimes called lips) that lead into the flutes.
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21. The Drill Geometry
• Point Angle: The point of the twist drill has a conical shape. Typical
value for the point angle is 120o.
• Chisel Edge: At the beginning of the operation, the rotating chisel edge
tends to wander on the surface of the workpart, causing loss of
positional accuracy. Various alternative drill point designs have been
developed to address this problem. One of them is Chisel Edge, which is
used widely in the drill making
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22. The Drill Cutting Action
• The rotation and feeding of the drill bit result in relative motion
between the cutting edges and the workpiece to form the chips.
• The cutting speed along each cutting edge varies as a function of
the distance from the axis of rotation. Accordingly, the efficiency of
the cutting action varies, being most efficient at the outer diameter
of the drill and least efficient at the center.
• The relative velocity at the drill point is zero, so no cutting takes
place a that point.
• However, the chisel edge of the drill point pushes aside the material
at the center as it penetrates into the hole. But for doing this, a large
thrust force is required to drive the twist drill forward into the hole.
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23. The Drill Cutting Action
• The cutting action takes place inside the hole, and the flutes must provide
sufficient clearance throughout the length of the drill to allow the chips to
be extracted from the hole.
• As the chip is formed it is forced through the flutes to the work surface.
• There are two types of friction involved in the drilling operation:
– the usual friction in metal cutting between the chip and the rake face of
the cutting edge.
– The rubbing between the outside diameter of the drill bit and the newly
formed hole.
• These tow friction operations increases the temperature of the drill and
work.
• Delivery of cutting fluid to the drill point to reduce the friction and heat is
also difficult, because the chips are flowing in the opposite direction.
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24. The Drill Cutting Action
• Because of these reasons the drilling operation is considered
difficult and the twist drill is normally limited to a hole depth of about
four times its diameter.
• Some twist drills are designed with internal holes running their
lengths, through which cutting fluid can be pumped to the hole near
the drill point, thus delivering the fluid directly to the cutting
operation.
• An alternative approach with twist drills that do not have fluid holes
is to use a ‘‘pecking’’ procedure during the drilling operation.
• In this procedure, the drill is periodically withdrawn from the hole to
clear the chips before proceeding deeper.
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