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 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

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 tool’s 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