Unit 6Manufacturing Processes:Machining and JoiningCUTTING, SHAPING METALS MACHINE TOOL OPERATIONS

Cutting Sheet Metal – Manual Shear

A bench shear, also known as a lever shear, is a bench mounted shear with a compound mechanism to increase the mechanical advantage. It is usually used for cutting rough shapes out of medium sized pieces of sheet metal, but cannot do delicate work. It mostly designed for a wide field of applications. Light weight and easy efficient operation, yet very sturdy in construction. The cutting blades fitted are carefully and accurately ground to give easy, clean quick cuts, and free of burrs. These special features help the operators save a great deal of their energy. But some shearing machines can cut sheet bar and flat bar up to 10mm.

Cutting Sheet Metal – Laser Cutting Sheet metal can be cut in various ways, from hand

tools called tin snips up to very large powered shears. With the advances in technology, sheet metal cutting has turned to computers for precise cutting. Many sheet metal cutting operations are based on computer numerically controlled (CNC) laser cutting or multi-tool CNC punch press.

CNC laser involves moving a lens assembly carrying a beam of laser light over the surface of the metal. Oxygen, nitrogen or air is fed through the same nozzle from which the laser beam exits. The metal is heated and burnt by the laser beam, cutting the metal sheet. The quality of the edge can be mirror smooth and a precision of around 0.1 mm can be obtained. Cutting speeds on thin 1.2 mm sheet can be as high as 25 m (82 ft) a minute. Most of the laser cutting systems use a CO2 based laser source.

Cutting Sheet Metal – Laser Cutting

http://www.youtube.com/watch?v=UeGVbtrrHjE&NR=1&feature=fvwp

Manual Press – Bending Sheet Metal

In press brake forming, a work piece is positioned over the die block and the die block presses the sheet to form a shape.Usually bending has to overcome both tensile stresses and compressive stresses. When bending is done, the residual stresses cause the material to spring back towards its original position, so the sheet must be over-bent to achieve the proper bend angle. The amount of spring back is dependent on the material, and the type of forming. When sheet metal is bent, it stretches in length. The bend deduction is the amount the sheet metal will stretch when bent as measured from the outside edges of the bend. The bend radius refers to the inside radius. The formed bend radius is dependent upon the dies used, the material properties, and the material thickness.

Bending Sheet Metal

http://www.youtube.com/watch?v=HiCZh_TFHCM&feature=related

Punching Sheet Metal

Punching is performed by placing the sheet of metal stock between a punch and a die mounted in a press. The punch and die are made of hardened steel and are the same shape. The punch just barely fits into the die. The press pushes the punch against and into the die with enough force to cut a hole in the stock. In some cases the punch and die "nest" together to create a depression in the stock. In progressive stamping a coil of stock is fed into a long die/punch set with many stages. Multiple simple shaped holes may be produced in one stage, but complex holes are created in multiple stages. In the final stage, the part is punched free from the "web".

Punching Sheet Metal

A typical CNC turret punch has a choice of up to 60 tools in a "turret" that can be rotated to bring any tool to the punching position. A simple shape (e.g., a square, circle, or hexagon) is cut directly from the sheet. A complex shape can be cut out by making many square or rounded cuts around the perimeter. A punch is less flexible than a laser for cutting compound shapes, but faster for repetitive shapes (for example, the grille of an air-conditioning unit). A CNC punch can achieve 600 strokes per minute.

A typical component (such as the side of a computer case) can be cut to high precision from a blank sheet in under 15 seconds by either a press or a laser CNC machine.

Punching Sheet Metal

http://www.youtube.com/watch?v=93IBQSUNWCU&feature=related

Tube Bending and Polishing

is the umbrella term for metal forming processes used to permanently form pipes or tubing. One has to differentiate between form-bound and freeform-bending procedures, as well as between heat supported and cold forming procedures.

Form bound bending procedures like “press bending” or “rotary draw bending” are used to form the work piece into the shape of a die. Straight tube stock can be formed using a bending machine to create a variety of single or multiple bends and to shape the piece into the desired form. This processes can be used to form complex shapes out of different types of ductile metal tubing.[1] Freeform-bending processes, like three-roll-pushbending, shape the workpiece kinematically, thus the bending contour is not dependent on the tool geometry.

Automated Tube Polishing

Generally, round stock is what is used in tube bending. However, square and rectangular tubes and pipes may also be bent to meet job specifications. Other factors involved in the tube bending process is the wall thickness, tooling and lubricants needed by the pipe and tube bender to best shape the material and its also used in different ways e.g.( tube,pipe wires)

Automated Tube Bending

http://www.youtube.com/watch?v=k-F_az5nyAo

Machine Tool Operations

Basic Machine Tools

Metal Saw Operations Drill Presses Lathes Milling Machines

Basic Machine Tools

1. Metal Sawing Operations: Used to cut stock materials to

useable lengths for specific part manufacturing

Band Saws (Vertical) Figure 13.2, page 250 TB

Cutoff Saws Horizontal

Figure 13.5 and 13.6, page 251 TB Reciprocating – Also known as a

power hacksaw

Basic Machine Tools

2. Drilling Machines and Equipment

Primarily used for making holes, counterboring, spotfacing, reaming, and tapping.

Drill Presses Sensitive Upright Heavy Duty Radial Arm

Basic Machine Tools

2. Drilling Machines and Equipment Sensitive Drill Presses – Figure 13.7,

page 252 So named because the operator

“senses” or “feels” the cutting action of drill while holding the handle that feeds the drill into the work

Maximum hole size ~ ½ inch Sized by the largest diameter of a

circular piece in which a centered hole can be drilled

Basic Machine Tools

2. Drilling Machines and Equipment

• Upright Heavy Duty -- Figure 13.8, page 253 TB

Have power feeds and reversing capability

Most have tapping accessories Coolant pumps supply cutting

fluid Hole Sizes: ¼ to 3 ½ inches

Basic Machine Tools

2. Drilling Machines and Equipment Radial Arm – Figure 13.9, page 253 TB

Sized by the diameter of the column and length of the arm as measured from the center of the spindle

The drilling “head” can be positioned over the work and clamped in place

Coolant pumps supply cutting fluid Large holes made with flat spade drills

Cutting Tools: Drills

High Speed Twist Drills • Most Common• General purpose• Twisted flutes

provide for chip clearance and removal

Cutting Tools: Drills

Straight Flute Drills • Use for plastics,

brass, bronze• Zero “rake”

prevents material from “grabbing”

Cutting Tools: Drills

Spade Drills• Primarily for holes > 1

inch• Very rigid shank

allows for heavier cuts• Use stepped blade to

produce a bevel

Cutting Tools: Drills

Gun Drills• Capable of very

precise holes up to many feet deep

• Used for holes in automotive engine blocks

Cutting Tools: Special Tools

Counterbores Used to enlarge existing holesCountersinks Provided a bevel to receive

certain bolt headsSpotfacing Provides a machined seat for

bolt heads or nuts

Cutting Tools: Taps

Taps Hardened thread cutting

tools with flutes to collect chips. Taps are very brittle.

Taper Plug Bottoming

Basic Machine Tools

3. Turning Machines and Equipment

Engine Lathes (horizontal spindle)

Vertical Spindle Machines

Vertical Turret Machines

Basic Machine Tools

3. Turning Machines and Equipment

Engine Lathes – Figures 13.26, 13.29, 13.30

Principal Function: to remove unwanted material to form cylindrical and conical shapes

Accomplished in a “turning” operation using a single-point tool

Range in size from small jeweler’s lathes to machines that turn massive forgings

Basic Machine Tools

3. Turning Machines and Equipment

Engine Lathes Turning Operations on Lathes

Turning Cuts Facing Boring / Reaming Shaping Internal / External Grooves and Threads

Basic Machine Tools

3. Turning Machines and Equipment

Turret Lathes Similar to engine lathes, but are arranged for

repetitive, rapid production and are capable of performing several operations in succession

The “turret” is usually six sided and holds different tools (drills, taps, turning tools, knurling tools, etc.)

Operator moves levers to change tools Operators are usually less skilled than engine

lathe operators

Basic Machine Tools

4. Milling Machines and Equipment

Horizontal Spindle Mills – Figure 13.74, page 271

Use various milling cutters:

• Plain milling cutters for slab milling• Side milling cutters or staggered

tooth cutters for deep slots• Saws or slitting cutters for grooves• Face mills for milling flat surfaces

Basic Machine Tools

4. Milling Machines and Equipment Vertical Spindle Mills – Figure 13.75,

page 271• Very versatile• Utilize tools ranging from end mill

cutters to face mills and fly cutters• Used for drilling, reaming, and

boring operations• Usually numerically controlled for

precise drilling of hole patterns in flat or bar stock and other milling operations

Basic Machine Tools

4. Milling Machines and Equipment

Horizontal Spindle Mills – Figure 13.74, page 271

Use various milling cutters:

• Plain milling cutters for slab milling• Side milling cutters or staggered

tooth cutters for deep slots• Saws or slitting cutters for grooves• Face mills for milling flat surfaces

Basic Machine Tools

5. Shapers – Figure 13.78, page 272

A machine tool that utilizes a reciprocating motion of the cutting tool rather than the more common rotary motion to make repeated machining cuts.

A “ram” moves back and forth holding the tool that cuts the stationary work-piece.

Basic Machine Tools

6. Broaching – Figure 13.78, page 272

The precision cutting of a material by a tool incorporating a series of progressively stepped teeth.

Flat surfaces, contours, internal splines, and external splines are some of the shapes produced.

Basic Machine Tools

7. Abrasive Machining

Grinding processes remove metal by using abrasive grains as cutting tools.

Figures 13.111, 13.112, 13.113, and 13.114 on page 283 of the TB are examples of different grinding machines.

Basic Machine Tools

8. Honing, Lapping, and Superfinishing

When smooth internal finishes are required (for example: tubing for hydraulic cylinders), Honing is a preferred method of finishing.

Honing is a finishing process that utilizes a rotating and oscillating abrasive tool.

Figure 13.125 shows the honing of a cylinder in an engine block.

Unit 6Manufacturing Processes:Machining and Joining

NONTRADITIONAL MANUFACTURING PROCESSES

Nontraditional Machining Processes

1. Electrodischarge Machining (EDM)2. Electrochemical Machining (ECM)3. Electrolytic Grinding (ELG)4. Laser Machining5. Ultrasonic Machining6. Water Jet Machining7. Electron Beam Machining (EBM)8. Plasma Cutting

Nontraditional Machining Processes

Electrochemical Machining (ECM) Essentially a reverse metal-plating

process The process takes place in a

conducting fluid called electrolyte that is pumped in under pressure between the electrode and the work piece.

As the work piece material is de-plated it is flushed away by the flow of electrolyte. The residue from the work piece is filtered from the electrolyte.

Nontraditional Machining Processes

Electrolyte A nonmetallic conductor, usually

a fluid, in which electric current is carried by the movement of ions.

The electrode and the work-piece are immersed in the fluid, the arc then creates a small glob of melted metal which is solidified and carried away by the fluid

Nontraditional Machining Processes

Plasma Technology Plasma Cutting is an extremely

fast process for cutting, welding, and machining nonferrous metals and stainless steel.

Plasma is created by passing a gas through an electric arc.

The gas is ionized by the arc, and an extremely high temperature ( can be > 40,000 degrees F )

Nontraditional Machining Processes

Plasma Technology When the superheated gas is

forced through a venturi, a high-velocity jet is created that instantly melts metals on contact and blows the molten material away from the cut.

Nontraditional Machining Processes

Plasma An ionized gas of extremely high

temperature achieved by passing an inert gas through an electric arc.

Plasma arcs are used in welding, cutting, and machining processes.

Joining Processes

Manufacturing processes commonly require assembly involving several different pieces made of the same or different materials.

In manufacturing, it is almost always necessary to join the materials at some point in the process.

Joining Processes

Joining processes can be divided into the following categories:1. Mechanical Fasteners2. Adhesive Bonding3. Welding4. Brazing and

Soldering

Joining Processes

1. Mechanical Fasteners Threaded fasteners Nails and Staples Rivets Stitching, Tying, Snaps Pins, Retaining Rings Pressing, Crimping

Joining Processes

2. Adhesive Bonding Natural Adhesives

Vegetable / animal glues and caseins

Sodium silicate Natural gums

Plastic Resin Adhesives Thermosets Thermoplastics

Joining Processes

3. Welding Processes Oxifuel Welding and Cutting Electric Arc Welding

Shielded Metal Arc Welding Inert Gas Shielded Arc Welding Gas Metal Arc Welding (GMAW /

MIG) Gas Tungsten Arc Welding

(GTAW/TIG) Submerged Arc Welding Plasma Arc Welding

Joining Processes

3. Welding Processes Resistance Welding

Stud Welding Induction Welding

Solid State Welding Processes

Forge Welding Ultrasonic Welding

Joining Processes

3. Welding Processes Flux: A solid, liquid, or gaseous

material that is applied to solid or molten metal in order to clean and remove oxides or other impurities.

Shield Gas: Usually an inert gas used to displace air from around a weld zone, thus keeping the weld uncontaminated.

Joining Processes

4. Brazing and Soldering Brazing processes use filler

material with a melting temperature above 840 degrees F and below the melting temperature of the base metal.

Soldering processes use filler material with a melting temperature below 840 degrees F and below the melting temperature of the base metal.