Introduction to Machining and Machine Tools

• Machining is removing or separating metal using a cutting tool on a Machine Tool, also known as "Subtractive Manufacturing."
• The term "Machine Tool" describes machining equipment like mills, lathes, and Drill Presses.
• The cutting tools are called “Tool steels"
• An area that houses machine tools is called a “Machine Shop"

Machine Tool

• It is any tool that is used to remove material, typically metal.
• Anything that drills, mills, turns, grinds, etches, or cuts is considered a machine tool.

Common Machine Tools

• Milling Machines
• Lathe
• Drill Press
• Band Saw

Common Ways of Machining or Metal Removal

• Machine tool: Metal removal uses a cutting tool
• Sawing: Metal removal uses a blade to cut
• Filing: Metal removal uses a file to remove material
• Grinding: Metal removal uses abrasives to remove
• Non-Traditional machining: Metal removal uses other than mechanical energy to remove material

Material Removal Processes

• Material Removal Processes fall into three groups: Conventional Machining, Abrasive Processes, and Non-Traditional Machining
• Conventional Machining involves turning and related operations, drilling and related operations, milling, and other machining operations
• Abrasive Processes involve grinding operations and other abrasive processes
• Non-Traditional Machining involves mechanical energy processes, electrochemical machining, thermal energy processes, and chemical machining

Conventional Machining Operations

• Material removal uses a sharp cutting tool.
• Milling
• Reaming
• Planing
• Turning
• Tapping
• Broaching
• Boring
• Sawing
• Drilling
• Shaping

Conventional Machining: Milling

• Milling covers versatile machining operations using a milling cutter.
• Traditional Milling Operations include facing, 3D machining, boring, pockets, side milling, tapping, slots and Drilling and Reaming

Conventional Machining: Turning

• Turning means the part is rotating while it is being machined using a cutting tool.
• The starting material typically is a workpiece which has been produced by other processes, such as casting, forging, and extrusion.
• Turning and facing operations are performed on all types of materials.
• It requires Skill labor.
• It has a low production rate, but medium to high rates can be achieved with turret lathes and automatic machines

Conventional Machining: Boring

• Uses internal surfaces or profiles, with similar characteristics produced from turning
• Stiffness of boring bar is important to avoid chatter.
• Typically used to increase accuracy; requires the use of skilled labor.

Conventional Machining: Drilling

• Drilling is used for making round holes of various sizes and depths.
• It requires boring and reaming for improved accuracy.
• High production rates.
• The labor skill required depends on hole location and accuracy specified

Conventional Machining: Tapping

• Not suitable for mass production
• External and Internal Threads

Conventional Machining: Shaping

• Used for flat surfaces and straight contour profiles on relatively small workpiece.
• Suitable for low-quantity production.
• Skill labor required depends on part and shape.

Other Macining Operations: Broaching

• Operations include Chip gullet; Rake or hook angle; Land; Pitch; Back-off or clearance angle; Cut per tooth; Workpiece and Root radius

Conventional Machining: Sawing

• Used for straight and contour cuts on flats or structural shapes.
• It isn't suited for hard materials unless the blade has carbide teeth or is coated with diamonds.
• It has a low production rate and only requires low skilled labor

Important Questions About Machining

• What is the cutting speed and why is it important?
• How do we calculate rpms?
• What is meant by hardness and what is toughness?
• How we make precise holes - what tools are needed?
• What types of equipment do we use in a metrology lab and why?
• Why are tolerances important in machining?
• What are implied tolerances?
• How do tolerances affect the cost of a part?
• How do tolerances affect how the part is made?

Disadvantages of Machining

• Wasteful of material because chips generated in machining are wasted material.
• Time consuming: A machining operation generally takes longer to shape a given part than alternative shaping processes.
• Costly: Machining is expensive and minimized for large production runs

Factors of Machining

• Machining is an expensive operation, which is often secondary in manufacturing.
• It is performed after basic manufacturing processes, such as casting and forging.
• Other processes create the general shape of the starting work part.
• Machining provides the final shape, dimensions, finish, and special geometric details that other processes cannot create

Abrasive Machining

• Primarily a Finishing Process
• It is followed up from a conventional operation,typically used for high dimensional finish and surface finish, typically used when the work piece is either too brittle or to hard

Abrasive Machining Tolerance

• Abraisive and Precision Measurements have .0001 in tolerance, this differs from more traditional Macining tolerance of .001 in

Abrasive Wheel chart

|Abrasive Wheel |Applications |

• -- | --- | Aluminum Oxide|Good for Steel and Aloys, Low Cost and High Volume options| Silicon Carbide | Good for cast iron and Non Ferrous Metaerials and Low cost| Diamond | Natural or man-made, best for carbrides and some non metalic materials and very High cost| Cubic Boron Nitride | Superior and Long life for high speed Steel and cutting very high cost

Types of Abrasive Machining

• Includes Grinding and Sand Blasting

Non-Traditional Machining

• Includes Chemical Machining, Electro-Chemical Machining, Electro Discharge Machining, Wire EDM, Laser Beam Machining, Plasma Arc-Cutting,and Abrasive Water-Jet Machine

Non-Traditional Machining: Chemical Machining (CM)

• Was developed on the observation that chemicals attack metals and etch them, that way removing minimal materials from a surface
• CM is the oldest of the non traditional machining processes, and has been used to engrave metals and hard stone
• Examples are the production of printed-circuit boards and microprocessors.

Non-Traditional Machining: Electro Discharge Machining (EDM)

• The principle is based on the erosion of medals by spark discharge
• it can be used on any material that is an electrical conductor, so the hardness, strength and toughness of the work piece do not necessarily influence the overall rate

Non-Traditional Machining: Laser Beam Machining

• Highly focused high density energy melts and evaporates portions of the work
• commonly used for drilling, cutting a variety of metallic and nonmetallic materials, ceramics and composites.
• Laser Beams are also used for Welding, Heat Treating, and Marking.

Non-Traditional Machining: Plasma Arc-Cutting

• Similar processes as laser beam machining
• Much cheaper but not as accurate

Non-Traditional Machining: Abrasive Water-Jet Machining

• The water acts as a saw to cut a small groove in the material
• Operations perfomred such as cutting holes, slots or inaccurate patterns using abrasive particles and hard brittle and non-metallic materials.
• Process allowing the use to cut holes as small as 3 MM in diameter with very accurate tolarenaces
• changes mechanical properties of materials, while a Water Jet Cutting Machine ranges in between $150,000-$300,000 dependin on size and capability.