1 Machining Operations Part 1: Chapters 21, 22 Manufacturing Processes, 1311 Dr Simin Nasseri...

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Machining OperationsPart 1: Chapters 21, 22

Manufacturing Processes, 1311

Dr Simin Nasseri

Southern Polytechnic State University

Manufacturing ProcessesProf Simin Nasseri

Material Removal Processes

A family of shaping operations, the common feature of which is removal of material from a starting workpart so the remaining part has the desired geometry.

Material Removal

Machining – material removal by a sharp cutting tool, e.g., turning, milling, drilling.

Abrasive processes – material removal by hard, abrasive particles, e.g., grinding.

Nontraditional processes - various energy forms other than sharp

cutting tool to remove material, e.g. electrochemical and thermal energy

processes.


Reasons to MachineVariety of work materials can be machined.

Most frequently used to cut metals.Variety of part shapes and special geometric features possible,

Screw threads. Accurate round holes. Very straight edges and surfaces.

Improve dimensional accuracy of: Castings, forming, or shaping processes.

Produce features that cannot be produced by forming and shaping processes. External and internal profiles. Sharp corners. Flatness.

Remove distortion & discoloration from heat-treatment.Reduce manufacturing costs (usually small quantities).Apply special surface characteristics or textures.


Machining Limitations

Wasteful of material

Chips generated in machining are wasted material, at least in the unit operation

Time consuming

A machining operation generally takes more time to shape a given part than alternative shaping processes, such as casting, powder metallurgy, or forming

More expensive for mass production.

Consumes more energy.

Can have adverse effects on surface quality & properties.


Rotational - cylindrical or disk‑like shape

Nonrotational (also called prismatic) - block‑like or plate‑like

Figure 22.1 Machined parts are classified as: (a) rotational, or (b) nonrotational, shown here by block and flat parts.

Classification of Machined Parts


Machining Operations and Part Geometry

Each machining operation produces a characteristic part geometry due to two factors:

1- Relative motions between tool and workpart

Generating – part geometry determined by feed trajectory of cutting tool

2- Shape of the cutting tool

Forming – part geometry is created by the shape of the cutting tool

Or combination of the two.


Figure 22.2 Generating shape: (a) straight turning, (b) taper turning, (c) contour turning, (d) plain milling, (e) profile milling.

Generating Shape

Part geometry determined by feed trajectory of cutting tool.


Figure 22.3 Forming to create shape: (a) form turning, (b) drilling, and (c) broaching.

Forming to Create Shape

Part geometry is created by the shape of the cutting tool.


Figure 22.4 Combination of forming and generating to create shape: (a) thread cutting on a lathe, and (b) slot milling.

Forming and Generating

Part geometry determined by feed trajectory of cutting tool and is also created by the shape of the cutting tool.


Machining Processes

• Turning

• Milling

• Drilling

• Boring

• Reaming

• Shaping

Ultrasonic Electrical Discharge Electro-arc Optical Lasers Electrochemical Chem-milling Abrasive Jet Cutting Electron Beam Machining Plasma Arc Machining

Traditional Chip Removal

Sawing Broaching

Planing Grinding Honing Lapping

Nontraditional Machining

In the following slides, guess the machining processes based on the information given!

11

Conventional Machining


Single point cutting tool removes material from a rotating workpiece to form a cylindrical shape

Figure 21.3 Three most common machining processes: (a) turning,

Turning


Used to create a round hole, usually by means of a rotating tool with two cutting edges

Figure 21.3 (b) drilling,

Drilling


Rotating multiple-cutting-edge tool is moved across work to cut a plane or straight surface

Figure 21.3 (c) peripheral milling (Axis of the tool is parallel to the surface), and (d) face milling (axis of the tool is perpendicular to the surface).

Milling

Two forms: peripheral milling and face milling


This process is performed using a multiple tooth cutting tool. The tool is moved linearly relative to the work.

Broaching

Broaching operation.The tool is called a broach. The machine is called the broaching machine.


Used to slightly enlarge a hole, provide better tolerance on diameter, and improve surface finish.

Figure 22.14 Machining operations related to drilling: (a) reaming

Reaming


Internal turning operation which is performed on the

inside diameter of an existing hole (Turning is performed on the outside diameter of an existing cylinder)

Boring!

Figure 22.12 A vertical boring mill – for large, heavy workparts.

Boring


Counterboring

Provides a stepped hole, in which a larger diameter follows smaller diameter partially into the hole.

Figure 22.14 Counterboring


Compare!

ReamingCounterboring Boring


Figure 22.14 (b) tapping. Tool is called a tap

Tapping

Used to provide internal screw threads on an existing hole


Sawing

Cuts narrow slit in work by a tool consisting of a series of narrowly spaced teeth.

Typical functions:1. Separate a workpart into two pieces. 2. Cut off unwanted portions of part.

Sawing Tool is called a saw blade


Shaping & Planing

Shaping:

Tool has a linear speed motion. Work has occasional feed motion. Planing:Work has a linear speed motion. Tool has occasional feed motion.

Figure 22.29 (a) Shaping (, and (b) planing.

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Machinery

In the following slides, guess the name of each machine based on the machining operation!


Figure 22.7 Diagram of an engine lathe, showing its principal components.

Engine Lathe

Turning:


Figure 22.12 A vertical boring mill – for large, heavy workparts.

Vertical Boring Mill

Boring:


Upright drill press stands on the floor

Bench drill similar but smaller and mounted on a table or bench

Figure 22.15 Upright drill press

Drill Press

Drilling:


Large drill press designed for large parts.

Figure 22.16 Radial drill press (photo courtesy of Willis Machinery and Tools).

Radial Drill

Drilling:


Figure 22.23 (a) Horizontal knee-and-column milling machine.

Horizontal Milling Machine

Axis of the tool is parallel to the surface of the part.

Milling:


Figure 22.23 (b) Vertical knee‑and‑column milling machine

Vertical Milling Machine

Axis of the tool is perpendicular to the surface of the part.

Milling:


Figure 22.30 Components of a shaper.

Shaper

Shaping:The shaping machine is used to machine flat metal surfaces especially where a large amount of metal has to be removed.

Other machines such as milling machines are much more expensive and are more suited to removing smaller amounts of metal, very accurately.

As the disc rotates, the top of the machine moves forwards and backwards (reciprocating motion), pushing a cutting tool. The cutting tool removes the metal from work which is carefully bolted down.


Figure 22.31 Open side planer.

Planer

Planing:


Two operations which are similar. Both use a single point cutting tool moved linearly relative to the workpart. A straight, flat surface is created in both operations Interrupted cutting

Subjects tool to impact loading when entering work Low cutting speeds due to start‑and‑stop motion Typical tooling: single point high speed steel tools

Figure 22.29 (a) Shaping (, and (b) planing.

Shaping and Planing


Figure 22.35 (a) Power hacksaw

Power Hacksaw

Sawing:

Linear reciprocating motion of hacksaw blade against work.


Figure 22.35 (b) Bandsaw (vertical)

Band Saw

Sawing:

Linear continuous motion of bandsaw blade, which is in the form of an endless flexible loop with teeth on one edge.


Figure 22.35 (c) Circular saw

Circular Saw

Sawing:

Rotating saw blade provides continuous motion of tool past workpart.


Figure 22.27 CNC 4‑axis turning center (photo courtesy of Cincinnati Milacron);

CNC 4‑axis turning center

Capable of turning and related operations, contour turning, and automatic tool indexing, all under computer control.

Date post:	17-Dec-2015
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