Performing Bench work

Department of EMMTLevel I (summer program)

Module trainerLemma Kiftaga(BSc in Engineering)

1. Introduction to engineering metals• We will group materials of similar types

together and discuss their properties

• Generally Materials can be classified :– metallic and ,non metallic material

• Metal:We can consider metals as substances that have a lustrous sheen when cut, are good conductors of heat, and are good conductors of electricity.eg. aluminum, copper and iron

• Non metal:These can be elements, compounds of elements and mixtures of compounds. They include wood, rubber, plastics, ceramics and glass.

Continued …• Some materials are compounds of metals and

non-metals. eg, naturally occurring abrasive grits, such as corundum contain between 70% and 90% of aluminium oxide (a compound of aluminium and oxygen).

1.1. Importance of metals

• Metal are the most important elements on earth that are mostly applicable in many industrial activities and construction sectors.

• A repair man repairs broken parts and manufactures replacements according to samples and blueprints.

1.2 Classification of metals• Metals can be classified as ferrous and non

ferrous metals.

• Ferrous metals: Ferrous metals and alloys are based on the metal iron.

• Iron is a soft grey metal and is rarely found in the pure state outside a laboratory

• For engineering purposes the metal iron is usually associated with the non-metal carbon.

Continued…i. Plain carbon steels:as their name implies,

mainly of iron with small quantities of carbon.

• There will also be traces of impurities left over from when the metallic iron was extracted for its mineral ore.

• A small amount of the metal manganese is added to counteract the effects of the impurities.

Plain carbon steel Contains

0.1% to 1.4% carbon.

Up to 1.0% manganese (not to be confused with magnesium).

Up to 0.3% silicon.

Up to 0.05% sulphur.

Up to 0.05% phosphorus.

Effect of carbon content on the properties of plain carbon steel

plain carbon steels can be grouped in to categories

i. Low carbon steels

(below 0.3% carbon).

ii. Medium carbon steels

(0.3% to 0.8% carbon).

iii. High carbon steels

(between 0.8% and 1.4% carbon).

i. Low carbon steels

• It is referred to as mild steels

• If the carbon content is kept between 0.1% and 0.15%, the steel is often referred to as ‘ dead mild ’ steel.

• This steel is very ductile and very soft, and can be pressed into complicated shapes for car body panels at room temperature without cracking

Continued…• It is used for the sub-strate of tin-plate and galvanized

steel. It is slightly weaker than the next group of low carbon steels to be considered

• Mild steel can be forged, rolled and drawn both in the hot and in the cold condition. It is easily machined with high-speed steel cutting tools.

• Because of its ease of manufacture and the very large quantities produced, mild steels are the cheapest and most plentiful of the steel products.

• Hot worked mild steel is available as structural sections for fabrication engineering (e.g. I-section beams, rolled steel joists, reinforcing rods and mesh for concrete, etc.), forgings, sheet, strip, plate, rods, bars and seam-welded tubes.

Cold worked mild steel

• also known as bright drawn mild steel is available as

bright drawn bars

rods

solid drawn tubes

sheet and strip

formed wire goods.

Medium carbon steels• There are two groups of medium carbon steels

From 0.3% to 0.5% carbon(can be heat treated to make them tough and strong)

From 0.5% to 0.8% carbon can be heat treated to make them fairly hard yet remain a degree of toughness (impact resistance).

• Medium carbon steels are harder, stronger and tougher than low carbon steels.

• They are also more expensive. They cannot be bent or formed in the cold condition to the same extent as low carbon steels without cracking.

Continued…• medium carbon steels hot forge well, but

close temperature control is required to prevent(burning and cracking)

Burning’ at high temperatures over 1150°C, as this leads to embrittlement. The metal cannot be reclaimed and the forging has to be scrapped.

Cracking when forging is continued below 700°C. Cracking is due to work hardening as the steel is in the ‘cold’ condition from a forging point of view.

Continued…• Medium carbon steels with carbon content in the

0.3% to 0.5% range are used for such products as drop-hammer die blocks, laminated springs, wire ropes, screwdriver blades, spanners, hammer heads and heavy duty forgings.

• Medium carbon steels with carbon content in the 0.5% to 0.8% range are used for such products as wood saws, cold chisels, forged blanks for connecting rods, crankshafts, gears and other stressed components such as high- ensile pipes and tubes.

High carbon steels• These are harder, less ductile and more expensive

than both mild and medium carbon steels.

• They are also less tough

• used for springs, cutting tools and forming dies.

• High carbon steels work-harden readily and, for this reason, they are not recommended for cold working.

Groups of high carbon steels

i. From 0.8% to 1.0% carbon where both toughness and hardness are required.

sheet metal pressing tools where the number of components to be produced does not warrant the cost of expensive alloy steels.

Also, cold chisels for fine work, some hand tools, shear blades, coil springs and high-tensile wire (piano wire).

Continued…ii. From 1.0% to 1.2% carbon for sufficient hardness for most metal cutting tools for example wood-drills, screw-cutting taps and screw-cutting dies.

iii. From 1.2% to 1.4% carbons where extreme hardness is required for wood-working tools and knives where a very keen cutting edge is required. For all of these applications the steel has to be heat-treated to enhance its properties

Properties of material

• Physical properties

• Chemical properties

• Thermal properties

• Electrical properties

• Magnetic properties

• Optical properties, and

• Mechanical properties

Layout• Selection of Materials: depends on the specific

task to be performed.

• Layout tool: Before you can shape or form work pieces, you have to mark them to the required dimensions.

• The following tools are used in laying-out.

scriber

Continued…

Continued…

Dot punch…

a. making out punches, b. making out dots , c. filling of removing metal, d. chamfering

The procedure making punched hole1.Mark out the centre.

2. Centre punches using the punch and a hammer

a) finding the position of the hole (b) punching (c) punched hole.

3. Bench work operations3.1 Cutting: In the metalwork shop, materials (especially metals) are cut to shape before filing. The numerous types of cutting operations.

Cutting using Saws(mishar) :Saws used for cutting purposes in the school workshop

The different type of saw are:

• Hacksaw

• The junior hacksaw

• The sheet saw

• The piercing saw

types of saw• Hacksaw

Points to watch when using the hacksaw1. Hold the work securely in the vice.

2. Grip the hacksaw firmly, using both hands

3. Use the same stance as for filing.

4. Use the full length of the blade.

Other saws…• The junior hacksaw: has a spring tension frame,

which takes a blade about 150 mm long and 6 mm wide. It is useful tool for small work.

• The sheet saw: is used for cutting large sheets of metal or other materials, and fitted with the standard hacksaw blade (32 teeth per 25mm).

• The piercing saw: is used for fine work, either for decorative patterns or for cutting circles in beaten metal work. To fix the blade, loosen one end and passing through a hole drilled in the work, then re-fix it in the frame.

KNIVES(mindi)• Most knives have cutting edges and are used to

cut, pare, notch, and trim wood, leather, rubber, and other materials.

Fig. Pocket Knife

Saddler knife

Rubber cutting knife

Putty knife

PIPE CUTTING• There are two sizes of pipe cutters.

• One size can cut from 1/8 to 2 inches

• while the other can cut from 2 to 4 inches. The pipe cutter has

1. a cutting blade

2. two pressure rollers which are adjusted and tightened by turning the handle

• Pipe cutters are used to cut steel, brass, copper, wrought iron, and lead pipe.

Continued…

Procedures to cut pipe• Measure from end of pipe and make a mark

where you want to cut

Continued…

• Fasten pipe securely in a pipe vice (2). Be sure mark is clear so that it can be cut. Pipe must be supported on both ends to keep it from bending.

Continued…• Open the jaws of the pipe cutter enough to

allow the pipe cutter to be placed around the pipe. Adjust so that the cutting blade (3) is on the line.

Continued…

4. Tighten the handle (4) until cutting blade

makes contact with pipe.

5. Then turn the handle (4) 1/4 of a turn more

clockwise.

6. Now turn the whole cutter one turn around the

pipe (counter clockwise).

3.2 Chipping Chipping metal (chiselling)

• You can chip the metal to produce grooves or to

reduce the width or thickness.

• Nowadays the grinder, shaper and miller are widely

used for this purpose, but if these machines are not

available, chipping is still an economical process.

Procedures to chip metal1. Hold the metal in the vice.

2. Hold the chisel at an angle of about 45° to the work.

3. Hammer to remove the chip

Chisels• It is used to cut cold metals and made of cast steel

or alloy steel.• The common types of chisels are

flat chisel: it used for general-purpose chiselling

cross-cut chisel: used for cutting grooves such as keyways, and for chipping;

half-round round-nosed chisel: used for cutting grooves (which are either curved or half-round).

diamond-pointed chisel: used for working into corners and cutting small grooves

Continued…• Chiselling is one of the methods of

cutting material.

• Working in Chisel is inaccurate, but still widely used in mechanical workshop.

• When it becomes difficult to use shears or a saw, you can use the chisel in cutting metal plate or sheet, the process is called chopping out.

3.3. Filling

• Filing is a method of removing metal,

and the file which is the most widely

used hand tool in the school workshop,

is used for this cutting operation. It is

made of carbon tool steel containing

about 1.3 per cent carbon.

• Filing is a skill that is difficult to learn.

It is not easy to explain how to use a

file.

principles of cross-filing

1. Hold the work firmly in the vice.

2. Allow a small part of the work to project from the vice and avoid vibration.

3. The work should normally be level with your elbow 4. Apply pressure in the forward stroke only.

5. Observe the correct methods for handling files, for

3.4. Drilling, boring, counter boring,

spot-facing• Drilling in engineering refers to cutting a

circular hole in a material.

• before reaming, holes should be drilled.

• Drilling and reaming are therefore not the

same process.

• Boring, on the other hand, is making an

existing hole larger.

Types of drilling machine include

Continued…• hand drill is used to hold drill bits up to 5 mm for

light hand operations.

• electric hand drill is used in the same way as the

hand drill, but it is electrically powered and

controlled.

3.5. Lapping

• Sheet metalwork involves bending, cutting and joining of such materials as tinplate, aluminium, brass and galvanized mild steel.

• Hand shears (also known as tin man's snips) are made of tool steel

Stakes

• Stakes may be referred to as small anvils, as

you use them for similar operations.

• The hatchet stake is usually used to turn

edges more than 90°.

• The brick iron is used for cylindrical and

conical work.

• The half-moon is used for turning edges of

circular or curved work.

Continued…

• The funnel stake is used for forming conical and cylindrical work.

• The round-bottom stake is used for shaping the circular or curved bottoms of circular work.

• The tin man's anvil is used to true flat work.

• The creasing iron is used for preparing beaded and wired edges.

Mallets and Folding bars • Mallets are used for flattening and bending sheet

metalwork

• The heads are usually made of wood, hide or

plastic. Common types include the tin man's mallet

and the bossing mallet

• Folding bars come in lengths of 250-300 mm, and

are used for bending sheet metal at right angles.

• Groove Punch also known as a seaming tool, has

semi-circular or rectangular grooves. It is used for

fixing wired and folded seams in position.

Soldering bit…• It is made of copper. The two main shapes are

hatchet and straight. The bits are used in soft soldering.

• They are heated in soldering stoves before melting the solder. There are also electric soldering bits.

• The soldering iron is heated in the tin man's stove (gas soldering stove).

• Heat the bit until the green flame shows: this is an indication that the correct temperature has been reached.

Joints

• Types of Joints

Bending

Reaming• Reamers are used to enlarge and true a hole

• They are also used to remove burrs from the inside diameters of pipes and drilled holes.

(1). body the (2).shank (3). blades

SOLID TAPER-PIN REAMER

SOLID STRAIGHT-HOLE REAMER

Expansion reamer

ADJUSTABLE-BLADE REAMER

Pipe reamer

USING A SOLID STRAIGHT-HOLE REAMERI. Secure the work in a vice so that the hole to

be reamed is perpendicular to the top of the vice jaws.1 Secure the work in a vise so that the hole to be reamed is perpendicular to the top of the

vise jaws.

ii. Using a tap wrench (1), tighten the handle to the square end of the reamer shank (2).

2 Using a tap wrench (1), tighten the handle to the square end of the reamer shank (2).

iii. Position the reamer (3) at the top of the hole. Turn the wrench clockwise very slowly until the reamer is centeredin the hole. Straight-hole reamers (4) have a slight taper at

the end so they will fit into the hole easily.

iv. Turn the wrench clockwise with a steady, firm pres-

Thread cutting• Screwing is a temporary method of

fastening parts together

• Methods for cutting screw threads include the use of the centre lathe.

• For bench work, however, taps and dies are used.

Taps and dies• Tapes are the tools used for cutting internal

(female) threads. The term for cutting internal threads by hand is tapping

Procedure for tapping

1. Drill a hole that has about the same diameter as the core of the tap.

2. Hold the work firmly in the vice.

3. Grip the first tap in the tap wrench or holder

Continued…4. Insert the tap squarely in the hole and turn it clockwise to start threading

5. Turn anti-clockwise about a quarter-turn to break the sward.

6. Apply cutting oil through the flutes, to ease cutting and 'wash' away the chippings.

7. Repeat operation 5 until the entire length of thread on the tap has gone through (if it is a through hole).

Dies

• Dies are made either of high-carbon steel or of high speed steel. Unlike taps, dies are used for cutting external (male) threads).

procedure for cutting external threads

• Square the end of the work and chamfer it (using a file, grinding machine or centre lathe) for an easy start (Figure 3.31).

Continued…

• Grip the die, held in the stock, firmly and squarely on the work.

• Turn clockwise, about a quarter-turn, and ease back to remove chippings.

• Apply a good supply of oil (lubricant).

• Make adjustments of the screws after making a full cut until the depth required is achieved

3.8.Grinding

• Grinders are mechanical devices which allow you to reshape, form, and sharpen metal cutting tools or other tools.

BENCH GRINDER

Bench grinder…

SHARPENING STONES• Sharpening stones usually have one coarse

face and one fine face.

3.9. Replacing Broken tools

• Maintenance is one of the most important jobs you will do in the Navy.

• preventive maintenance is not done properly, or not done at all, your equipment may be put out of commission until it can be repaired.

• NEVER USE DAMAGED TOOLS

4. Clean up

4.1 Work area

• Keep your working area, especially the floor, clean and free from any unnecessary items that can cause slipping or stumbling

• Materials should be properly stored in a material rack

• Protect the floor against spilled cutting oil.

4.2 Tools and equipment• The tools and equipment's should be

cleaned after the required activities are performed.

• At last they should be stored in the recommended area based on the specifications from the industries they are manufactured to give the expected services.

END OF THE MODULE

2005 E.C