DJJ 1043 WORKSHOP TECHNOLOGY PDF

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DJJ 1043 WORKSHOP TECHNOLOGY INTRODUCTION  Drilling is the operation of producing circular hole in the work-piece by using a rotating cutter called DRILL.  The machine used for drilling is called drilling machine.  The drilling operation can also be accomplished in lathe, in which the drill is he...

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DJJ 1043 WORKSHOP TECHNOLOGY

INTRODUCTION  Drilling is the operation of producing circular hole in the work-piece by using a rotating cutter called DRILL.  The machine used for drilling is called drilling

machine.

 The drilling operation can also be accomplished

in lathe, in which the drill is held in tailstock and the work is held by the chuck.

 The most common drill used is the twist drill.

BENCH DRILL MACHINE

Radial Arm Drilling Machine

TWIST DRILL

GLOSSARY OF TWIST DRILL  POINT – The cutting end of a drill, made up of the

ends of the lands and the web. In form it resembles a cone, but departs from a true cone to furnish clearance behind the cutting lips.  POINT ANGLE – The angle included between the lips projected upon a plane parallel to the drill axis and parallel to the cutting lips.  LIPS – The cutting edges of a two flute drill extending from the chisel edqe to the periphery.

GLOSSARY OF TWIST DRILL  FLUTES – Helical or straight grooves cut or formed in the body of the drill to provide cutting

lips, to permit removal of chips, and to allow cutting fluid to reach the cutting lips.  WEB -The central portion of the body that joins the lands. The extreme end of the web forms the chisel edge on a two-flute drill.

GLOSSARY OF TWIST DRILL  SHANK – The part of the drill by which it is held and driven.

 TANG - The flattened end of a taper shank, intended to fit into a driving slot in a socket

TWIST DRILL SIZE Twist Drill sizes are designated under four systems; Fractional

1. •

The Fractional Drill sizes range from 1/64 inch to 1 inch and over.

Number

2. •

Numerical drill sizes, corresponding to wire gauge (the larger the number, the smaller the drill). Example: Starting with a # 80 drill and a #1 drill.

Letter

3. •

Drill size designed by letter range from letter A measures . inch to letter Z measures . inch .

4. Metric 

The metric sizes range from 0.4mm (measures .015 inch) to 50mm (measures 1.968 inch).

MEASURING THE SIZE OF A DRILL By using two methods : 1.

With a drill gauge

2. With a micrometers (taken measurements across the margin of the drill)

MATERIAL

 The two most common types are

1. High Speed Steel (HSS) drill - Low cost 2. Carbide- tipped drills - high production and in CNC machines  Other types are:

Solid Carbide drill, TiN (titanium nitrate) coated drills, carbide coated masonry drills, parabolic drills, split point drill.

STEPS OF MARKING OUT BEFORE DRILLING 1. 2.

3. 4. 5. 6.

A small dent is marked at centre of the hole by using prick punch. Draw two circles by using divider; one circle has same diameter with the hole and another one is smaller. Punch the small dent by using centre punch. Switch ON the machine and make sure the drill point is pointed to the centre of the hole. Check either the drill bit spinning at the centre of the hole or not. The location of the centre of the hole need to adjust if the drill bit is slide away from the centre. A groove is marked by using round chisel to indicate that the new adjustment has been made.

METHODS OF HOLDING A DRILL BIT  The different methods used for holding drill

in a drill spindle are By directly fitting in the spindle hole. By using drill sleeve By using drill socket By using drill chuck

DIFFERENT TYPES OF DRILL BIT 1. COMBINATION AND COUNTERSINK:

These double ended drills are also called centre drills. They are designed for drilling centre holes in the end of work pieces to be held between standard 60º centres. Also available in bell type with 120° chamfer to protect the centre hole.

DIFFERENT TYPES OF DRILL BIT 2. TWIST DRILL:

A twist drill bit is a metallic cylinder with helical grooves that spiral up the bit. Drills are used in a wide variety of projects and fields, from home repair to arts to large-scale construction projects.

DRILLS OPERATION

DRILL BIT GEOMETRY Point angle:  The larger the point angle on a drill bit with a specific diameter, the shorter its cutting edges. Reducing the length of the cutting edges improves the drill bit guidance and reduces the required contact pressure.  The smaller the point angle on a drill bit with a specific diameter, the longer its cutting edges. Increasing the length of the cutting edge makes drill bit guidance more difficult and increases the required contact pressure.

DRILL BIT GEOMETRY Lip Angle Clearance:

 Excessive clearance results in lack of support behind

cutting edge with quick dulling and poor tool life.  Clearance angle behind cutting lip for general purposes is 8º to 12º.

DRILL BIT GEOMETRY Helix Angle:  The helix angle on a bit is the angle between the cutting edge and a vertical line along the centre of the bit.  Bits with a moderate helix angle aid in chip ejection and are recommended for drilling of plastics.  Small helix angles interfere with chip ejection, increasing melting.  Helix angles, which are too large, can cause cracking around the hole edges.  Typically a helix angle of 15-30° is recommended.

DEFINITIONS AND CALCULATION

 Cutting Speed (v): )t’s the peripheral speed of the drill v = Π*D*N where D = diameter of the drill in m N = Speed of rotation in rpm  Feed Rate (f): )t’s the movement of drill along the axis rpm  Depth of Cut (d): The distance from the machined surface to the drill axis d=D/2

DEFINITIONS AND CALCULATION  Material Removal Rate :

)t’s the volume of material removed by the drill per unit time MRR = ( D2 / 4) * f * N mm3 / min  Machining Time (T) :

It depends upon the length (L) of the hole to be drilled , to the Speed (N) and feed (f) of the drill t = L /( f * N) min

SELECTION OF CUTTING SPEED AND CUTTING FEED  The selection of cutting speed and cutting feed is

influenced by: Types and condition of machine. Accuracy and work finishing. Toughness of work holding device. Usage of coolant Drill bit material

COOLANT  Cutting fluids are very important in machining 

   

processes. They are used to reduce the effects of friction. They are also used to carry away heat in machining operations. Excessive heat can damage the microstructure of metals. Proper use of coolants can make higher metal removal rates possible. Coolants can also help improve part quality and dimensional accuracy.

TYPES OF COOLANTS  Straight Cutting Oils

 Active Straight Cutting Oils

 Inactive Straight Cutting Oils

 Chemical Fluids  Emulsions

 Special coolant

FUNCTIONS OF COOLANT  to cool the tool

 to cool the work piece

 reduce friction at the sliding contacts,

 prevent or reduce the adhesion on the

contact edges.  to flush chips away.

BENEFITS OF USING CUTTING FLUID  Improve part productivity.

The use of cutting fluids reduces friction and heat.

The removal of the heat prevents the work piece from expanding during the machining operation, which would cause size variation as well as damage to the material’s microstructure. • Reduce tooling cost.

Proper use of cutting fluids increases tool life, which

reduces the tooling costs. Increased tool life also reduces tool changes and downtime which decreases labour costs.

BENEFITS OF USING CUTTING FLUID  Increase Cutting Speeds and Feeds

Cutting tools reduce friction and heating a

machining operation. This allows high speeds and feeds to be used to achieve optimal cutting conditions  Improved Surface Finishes

Effective use of cutting fluids helps remove the

chips. This prevents the chip from being caught between the tool and work piece where it causes scratches and a poor surface finish

BENEFITS OF USING CUTTING FLUID  Reduces Bacterial Growth

Bacteria can drastically affect cutting oils. Bacteria

growth can turn a cutting fluid rancid. Additives in coolants help reduce the effects of bacteria, but it is important that pure water is used for coolant mixing.

• Rust and Corrosion Prevention

Cutting fluids should protect the tooling, machine,

and work piece against rust and corrosion. Cutting fluids should leave a small residual film that remains after the water has evaporated.

MACHINE AND DRILL BIT MAINTENANCE  Machines should be cleaned after use.  Chips should be removed using brush.  T-slots, grooves, spindles sleeves, belts, pulley should

be cleaned.  Machines should be lightly oiled to prevent from rusting.  Use suitable cutting speed.

SAFETY DURING DRILLING OPERATION  Do not support the work piece by hand – use work   

  

holding device. Use brush to clean the chip No adjustments while the machine is operating Ensure for the cutting tools running straight before starting the operation. Never place tools on the drilling table Avoid loose clothing and protect the eyes. Ease the feed if drill breaks inside the work piece.

WHY THE WORKPIECE IS NEEDED TO CLAMP SECURELY? 1. Workpiece will loose from workholding 2. 3. 4. 5. 6.

device. The hole drilled become large. Drill bit will broken. Hole drilled will not meet specification. Waste material and drill bit. Waste time to replace the new material and drill bit.

WORKHOLDING DEVICES • Machine table vice

WORKHOLDING DEVICES

METHOD TO DRILL A LARGE HOLE  Drill a small pilot hole on the spot with a smaller bit if you will be drilling a large hole. This will help ensure that the hole will be straight when you use

the larger bit.

THE IMPORTANCE OF PILOT DRILL  Pilot hole will allow you to centre the tip of

the larger diameter tool and then accurately drill your final size hole.  This often keeps the larger tool from jumping all over the surface when it first touches the material.

THE IMPORTANCE OF CENTRE DRILL  Centre drills are an progression to improve

productivity.  They combine the countersink with a small pilot drill.  Centre drills are intended for putting in centres for turning on a lathe.

TYPES OF JIGS  Plate jigs or channel jig.  Angle plate jig.  Box jig.

 Leaf or latch jig.  Sandwich jig.  Trunnion jig.  Template jig

 Universal Jig

FUNCTIONS OF DRILL JIGS  A drill jig is a type of jig that expedites repetitive hole

centre location on multiple interchangeable parts by acting as a template to guide the twist drill or other boring device into the precise location of each intended hole centre.

End of Chapter [Assignment 1] QUESTION 1  a) List TWO (2) tools that are used as marking tool.    

(2 marks) b) List FIVE (5) types of hammer. (5 marks) c) State THREE (3) major hazards which may arise from the use of electrical equipment and their causes (6 marks) d) List SIX (6) ways on how to care for a file. (6 marks) e) i) Draw a chisel (2 marks) ii) State the uses of a chisel (2 marks) iii) Explain the differences between a hot chisel and a cold chisel (2 marks)

QUESTION 2  a) State FIVE (5) procedures of maintaining a

micrometer. (5 marks)  b) Name THREE (3) types of micrometer and their uses. (6 marks)  c) State THREE (3) disadvantages of using a micrometer. (6 marks)  d) Draw a vernier calliper and label SIX (6) main parts. (8 marks)

QUESTION 3  a) Define of mandrel. (2 marks)  b) Name THREE (3) important parts of a lathe

machine. (3 marks)  c) State THREE (3) effects on a drill bit and a work piece if the work is carried out without using any coolant. (6 marks)  d) Calculate the cutting speed if the twist drill diameter is 18 mm and the rotation per minute is 993. (6 marks)  e) State FOUR (4) types of manufacturing lathe machines and their functions. (8 marks)...