BMFS 3373

CNC TECHNOLOGYLecture 3

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

Drawing Formats

Title Block: placed in the lower right-hand corner of the drawing form. It shows the company’s 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

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

Drawing Codes

Other aspect to be understood when reading a blueprint:

DimensioningTolerancesThread forms and dimensioningSurface finish symbols and notes

Tooling for Drilling

Twist DrillMost 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.

Tooling for Drilling

Tooling for Drilling

Center DrillTo 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

Tooling for Drilling

Tooling for Drilling

Spade DrillConsists 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.

Tooling for Drilling

Tooling for Drilling

Indexable Insert DrillMade 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

Tooling for Drilling

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 holeCounterboring : 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.

Tooling for Hole Operation

Cutting Parameters

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

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

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)

Cutting Parameters

Tooling for Milling

End Mill:2 flutes vs 4 flutes :Different hardness of materialPlunging directly into center of solid materialSuitable for rough drilling hole, counterboring

and boring, as well as slotting and cavity cutting

Tooling for Milling

End Mill:

Tooling for Milling

Shell End Mills:Several cutter sizes can be fitted to one mounting arborFacing uses this cutter

Tooling for Milling

Carbide Indexable Insert End Mills:

Cutting Parameters

Cutting Speed for milling is the same as previous explanation

Tool Feed for milling

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.

Cutting Parameters

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 surfaceLess clamping and horsepower is requiredRecommended 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)

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

Feed Direction for Milling Operations

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 tool’s edges becoming dull.

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

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