BMFS 3373 CNC TECHNOLOGY Lecture 3

1
BMFS 3373CNC TECHNOLOGYLecture 3
2
Lecture Objectives

• At the end of the lecture, you will be able to
• Understand the engineering drawing terms and to
  interpret various projections
• Identify the various types of systems and
  practices used in basic blueprint drawing
• State the various tooling and their applications
  in milling and lathe operation
• Explain the meaning of tool speeds and feeds for
  milling operations
• Understand the difference between climb milling
  and conventional milling various cutting fluid
  application

3
Drawing Formats

• Title Block placed in the lower right-hand
  corner of the drawing form. It shows the
  companys name and address, drawing title, scale,
  drawn and checked by, etc.
• Part list also known as the Bill of Material
  (BOM) is located above the title block.
• Revision block placed in the upper right-hand
  corner of the drawing. Indicates the zone where
  the correction takes place and the description of
  correction.
• Notes block is located to the left of the title
  block. Contains Tolerances, Material, Finish,
  Next assy, Used on

4
Visualization

• 1. Parallel projection
• a. Multiview orthographic projection present the
  minimum views needed to
• completely describe a 3-D object
• Auxiliary views
• Sectional views
• Commonly used as working drawing
• b. Oblique projection
• c. Axonometric projection
• Isometric
• Dimetric
• Trimetric
• 2. Perspective projection

5
Drawing Codes

• Other aspect to be understood when reading a
  blueprint
• Dimensioning
• Tolerances
• Thread forms and dimensioning
• Surface finish symbols and notes

6
Tooling for Drilling

• Twist Drill
• Most important tool used is the twist drill.
• Comprise of 2 helical grooves/flutes that cut
  around a center (web), shank (straight/tapered)
• The web gives strength to the drill in resisting
  deflection.
• Accuracy tends to decrease when either the drill
  length or drill size is increased less
  stiffness and more torsional deflection.
• Metal cutting twist drills are made from a wide
  range of material ranging from carbon tool steel
  to solid carbide.

7
Tooling for Drilling
8
Tooling for Drilling

• Center Drill
• To better locate a hole center, center drills are
  used due to its short and stubby character as
  compare to twist drill.
• The initial work is used to guide the twist drill
  into the material
• Good practice the countersunk portion is approx.
  0.003 to 0.006 in. larger than the twist drill
  diameter

9
Tooling for Drilling
10
Tooling for Drilling

• Spade Drill
• Consists of a blade holder to which one of
  several different size drill point blades can be
  bolted in.
• The larger web of the spade drill ensures that
  during drilling penetration less flexturing
  occurs and thus more accurate hole results.
• Spade drills are designed to machine a hole from
  the solid in one pass - no need for center
  drilling or multiple pass drilling. However the
  hole depth is limited because flutes does not
  exist to carry out the cut chips.
• To fully utilize the cutting tool, a 50 or
  greater torque machine is required with increased
  machine rigidity.

11
Tooling for Drilling
12
Tooling for Drilling

• Indexable Insert Drill
• Made of carbide that helps penetration into the
  hardest of material.
• It offers a penetration rates of 5 to 10 times
  that of a twist drill or spade drill.
• However it requires a machine to have higher
  spindle horsepower, pressurized cooland system
  and rigidity

13
Tooling for Drilling
14
Tooling for Hole Operation

• Boring enlargement of existing hole accurate
  readjustment of the center location of the
  enlarged hole
• Reaming increase the accuracy of a hole
  dimension size
• Tapping cutting threads on the inside of a hole
• Counterboring enlargement of a hole to a depth
  slightly larger than the head of a specific
  bolt/pin to allow the head to burried below the
  machined surface.
• Countersinking enlargement of the top end of a
  hole in the form of coneshaped depression to
  allow a flat or oval head machine screw to be
  flush or slightly below the surface when inserted.

15
Tooling for Hole Operation
16
Cutting Parameters

• Cutting speed is defined as the speed of any
  point on the circumference of the tool (surface
  feet per minute/sfpm)

17
Cutting Parameters

• Cutting speed selected for a particular tool will
  depend on several factors, some of which are
• Type of hole operation, material hardness, hole
  depth
• Type of tool used and type of lubricant or
  coolant used
• Type of hold-down fixture and CNC machine used

18
Cutting Parameters

• Tool feed (Hole Operation) is defined as the rate
  at which the tool advances into the work per
  revolution (inch per revolution/ipr)

19
Cutting Parameters
20
Tooling for Milling

• End Mill
• 2 flutes vs 4 flutes
• Different hardness of material
• Plunging directly into center of solid material
• Suitable for rough drilling hole, counterboring
  and boring, as well as slotting and cavity
  cutting

21
Tooling for Milling

• End Mill

22
Tooling for Milling

• Shell End Mills
• Several cutter sizes can
• be fitted to one mounting
• arbor
• Facing uses this cutter

23
Tooling for Milling

• Carbide Indexable Insert End Mills

24
Cutting Parameters

• Cutting Speed for milling is the same as previous
  explanation
• Tool Feed for milling

25
Cutting Parameters

• Correct feed for milling also depends upon
  another parameter known as chip thickness. This
  is not the chip load (feed per tooth) but the
  actual thickness of chip resulting from a given
  feedrate
• For general purpose milling, the chip thickness
  must be within 0.004 to 0.008 in. or it will
  cause premature wear and breakdown of the carbide
  insert cutters.

26
Cutting Parameters
27
Feed Direction for Milling Operations

• Climb Milling (Down)
• The tool to make a chip of maximum thickness at
  the start of the cut at and near the part surface
• Less clamping and horsepower is required
• Recommended in order to get a more accurate
  roughing cuts with minimum machining marks and
  machining thin parts or parts that are hard to
  hold down
• Cutter are less prone to be dull as the chips are
  pushed behind and away
• Conventional Milling (Up)

28
Feed Direction for Milling Operations

• Conventional Milling (Up)
• The tool starts with a cut of chip of no
  thickness before attaining maximum thickness at
  the end of the cut near and at the part surface
• High clamping and horsepower is required
  especially for hard outer scales material.
• Recommended in cases where the a tool length used
  may cause unacceptable chattering of the cutter
  if using climb milling
• Cutter are prone to be dull as the cut can create
  high tool impact

29
Feed Direction for Milling Operations
30
Cutting Fluids

• Cutting fluids are essential in order to minimize
  the heat built up during the shearing action of
  the tool towards the workpiece.
• The phenomenon known as Built Up Edge (BUE) can
  result in the tools edges becoming dull.

31
Cutting Fluids

• Water based solutions of cutting oil are the 2
  most commonly used cutting fluids. They can be
  divided into 4 categories
• Nondilutable straight oils provides best
  lubrication but poorest cooling
• Water soluble oils provides both good
  lubrication and cooling
• Semi-synthetic fluids lubrication and cooling
  falls between synthetic and soluble oil fluids
• Synthetic fluids provides best lubrication and
  cooling of all fluids

32
End Chapter 3