metalchips

Chapter Seven, Cutting Tools

2010-03-11T22:34:00.000-08:00

Part One of Notes taken while studying Chapter Seven of Machine Shop Basics visit them at www.aubelbooks.com

Chapter Seven

Cutting tools

All machine tool operators need to have a basic knowledge of the cutting action of cutting tools.

Action of Cutting Tools

Cutting tools use a wedging action, the power used in cutting metal is expended in the form heat. When used to make heavy cuts a tool has a small ridge of metal directly over the cutting edge. This metal is much harder then the metal bring cut, coolants help absorb the heat from the cutting edge of the tool, in high-speed production work.

Materials

Here are some materials used for making cutting tools.

Carbon Tool Steel: Less expensive as other cutting tools, and can be used on some types of metal successfully.

High Speed Steel: The most popular cutting tool material, high-speed tools contain tungsten, chromium, vanadium and carbon.

Stellite: These bits can withstand higher cutting speeds then high-speed steel. Stellite is a non-magnetic alloy, harder than common steel (High-Speed) even if heated red hot by fiction, it will not lose its temper. Being harder than high-speed steel, Stellite is more brittle and is used for machining high steel cast iron and bronze.

Carbide: Tips of cutting tools are made of carbide for manufacturing operations where maximum cutting speeds are desired.

Tungsten Carbide: These cutting tools for machining cast iron, alloyed cast iron, bronze, copper, brass, Aluminum, Babbitt, and abrasive nonmetallic materials, hard rubbers and plastics. These tools are so hard they cannot be ground satisfactory on a regular grinding wheel.

Titanium Carbide: a combination of tungsten carbide and titanium carbide are interchangeable with tantalum carbide in its uses.

Shapes and Uses of Cutting Tools

Here are nine popular shapes of lathes cutter bits and their uses.

Left Hand turning tool-opposite of the right hand turning tool for turning in either direction, this tool is used in machine work from left to right.

Round-nose turning tool-used for reducing the diameter of a shaft in the center, this tool is for turning in either direction.

Right-hand turning tool-is the most common type of cutting tool for general lathe work used in machining work; this cutting tool travels from left to right.

Left-hand facing tool-opposite of the right hand tool, and is used for facing the left hand side of the work.

Threading tool- This tool is used to cut threads and the point is ground to a 60-degree angle.

Cutoff tool-is used where a regular turning tool cannot be.

Boring tool-is ground the same as a left hand turning tool; however, the front clearance angle is slightly greater. This is the heel of the tool will rub in the hole of the work.

Inside threading tool-is ground the same way as the screw-threading tool, except that the front clearance angle must be greater.

Terms Related to Cutting Tools

Base- Surface of the shank that bears against the support and takes the tangential pressure of the cut

Chip Breaker- this is to break chips into small pieces, can be an irregularity in the face of the tool or a separate piece attached to the tool or holder.

Cutting Edge- Portion of the face edge along which the chip is separated from the work

Face- Surface on which the chip slides as it is cut from the work

Flank- Surface or surface below and adjacent to the cutting edge

Flat- Straight portion of the cutting edge intended to produce a smooth machine surface.

Heel- Edge between the base and the flank immediately below the face

Neck- An extension of reduced sectional area of the shank.

Nose- A curved face edge

Shank- Portion of the tool back of the face that is supported in the tool post

Chapter Six, Cutting Fluids

2009-10-14T13:40:00.000-07:00

Notes taken while studying chap. 6 of Machine Shop Basics visit them at www.audelbooks.com

Chapter 6
Cutting Fluids

In machining operations, cutting fluids reduce temperature and adhesion between the chip and the tool. This avoids thermal expansion and provides easier handling; cutting fluids also keeps away chips from the machining area. Sometimes a lubricant is part of the cutting fluid; this provides a rust proof layer to the finished work piece.

Coolant

A coolant chief purpose is to absorb heat from the work and the cutting tool. Coolant is usually in a liquid form; water has the highest cooling effect of any cutting fluid.

Lubricant

A cooling lubricant is a cutting fluid with the additional property that enables it to act as a lubricant. These materials usually consist of both cooling and lubricating agents, such as soluble oil or glycerin mixed in proper proportions.

Applications of Cutting Fluids

A stream of soluble oil is increases the cutting capacity of an abrasive wheel by preventing it from glazing over, and by carrying off the heat generated by the friction of the wheel on the work. It is important to apply the coolant to the work. A large stream of coolant at slow velocity is preferable to a high stream at high velocity. The cutting fluid should make contact with the work at the exact spot where the cutting is taking place, not above or to one side of the cutting tool.
On machining tools, cutting fluids keep heat from softening the cutting edge of the cutting tool. Cutting fluids cool the cutting tool and make it cut more easily and smoothly. The use of fluids washes away chips, prevents friction and allows higher cutting speeds.

Types of Cutting Fluids
Commonly used cutting fluids

o Lard oil- One of the oldest and best cutting oils, providing excellent lubrication, increased tool life, and provides a smooth finish on the work while preventing rust. Primary used for cutting screw threads, drilling deep holes, and reaming. Its use is somewhat limited because of the expense, the tendency to become rancid, and can cause skin irritation.
o Mineral-lard oil mixtures- Mixtures of various proportions of lard oil and petroleum-base mineral oils use in the place of lard oil alone, they are more fluid, less expensive and almost as effective.
o Mineral oils-Petroleum-based oils- Added with chemicals improving lubrication and anti-welding qualities. They are less expensive than lard oil and mineral oil mixtures.
o Water-soluble oils- Limited to use in rough turning operations, they carry away heat better than lard and minerals oils; however, lubricating qualities are poor. They are mixed with water to form an emulsion and prove to be an excellent low-cost coolant.
o Chemical cutting fluids- These are mixed with water and generally do not contain any petroleum products. The chemicals used provide excellent lubricating and anti-welding properties.
o Low-viscosity oils- Kerosene and other types of oils are used for cutting tough nonferrous metals and alloys such as bronze, aluminum alloys and alloys containing a small percentage of iron such as Monel metal.

Solid Lubricants

Grease-type lubricants are used on band saws to lubricate the sides, back edge and guide bearing especially where high speeds are involved. Graphite is often combined with these lubricants and is supplied in tubes.
Wax and soap lubricants are combined with petroleum substances and are supplied in stick form. A good solid lubricant is recommended for sawing metals, hardwoods ect, where the use of a solid lubricant is preferred to a circulating type.

CHAPTER 5 OF MACHINE SHOP BASICS

2009-07-13T22:56:00.000-07:00

CHAPTER 5
GRINDING
NOTES TAKEN WHILE STUDYING CHP5 OF MACHINE SHOP BASICS
VISIT THEM AT www.audelbooks.com
Grinding
By definition, grinding is the process of disintegrating a material and reducing it into small particles of dust by crushing or attrition.
Manufacture of Grinding Wheels
Grinding wheels are made from sandstone, occurs in nature or from man-made abrasives. Natural grindstones are mostly used in glass, cutler, and woodworking edge-tool industries. However, manufactured abrasives wheels have largely replaced natural grindstones in these industries. Because manufactured grinding wheels can be operated at higher speeds, and the grain size, hardness and structure can be controlled.
Manufactured Abrasives Grinding Wheels
Most grinding wheels are made from aluminum oxide and silicon oxide, these are prepared in a similar way. The process starts out with ore from an electric furnace rough crushed into lumps about six inches in diameter. From there the next step is to the abrasive mill, the lumps are further reduced in size to about three fourths in diameter. The final step they are ran through a series steels crushing rolls, the pieces are reduced to grain size for use in grinding wheels and coated abrasive products.
Iron impurities are removed by using magnetic separators, fine abrasive dust and foreign particles are removed by washing with stream and hot water. Washing is important because clean grains mix uniformly with the bond, after washing the abrasive in then dried in continues rotary driers.
The abrasive grains are passed over a series of vibrating screens in the range of 10 to 600 this is the mesh size, which a particle grain will pass though. A screen having 10 mesh openings per linear inch is called a 10-grit size and will have 100 openings per square inch.
Abrasive grains are inspected as they come from the mill for capillary, uniformity of size, strength, and weight per unit volume. The grains are uniformly distributed throughout the bond in the wheel. The structure refers to relative spacing as dense, medium or open, depending on the percentage of abrasive or pores. Wheels of medium structure are best for hard, dense materials open structures are best for heavy cuts and soft, ductile materials that are easily penetrated and require good chip clearance.
Shapes of Grinding Wheels
Grinding wheels are manufactured in nine standard shapes and 12 faces

Straight
Recessed one side
Recessed two sides
Cylinder
Straight cup
Flaring cup
Tapered Two sides
Dish
Saucer

Twelve Standard Grinding wheel faces
Method of Mounting Grinding Wheels
Before mounting grinding wheels should be checked for balance and out of balance wheels cause excessive vibration, causing chatter marks on the ground surface and excessive wear on the bearings and spindle.
Truing and Dressing the Grinding Wheel
To be running true on its own spindle, a wheel should have enough of the cutting face removed in preparation for grinding. With use a wheel will become glazed or loaded then it needs to be dressed, this restores its original shape and clean cutting face. There are three types of wheel dresses used on precision grinding machines. The diamond tool, abrasive wheel and mechanical dresser, the common is the diamond wheel on all types of precision grinders.
Bond types in grinding wheels
The bond in the grinding wheel holds the grains together and supports them while they cut. The greater the amount of bond with respect to the abrasive, the heavier the coating of bond around the grains the harder the wheel. Hard and soft are terms that actually refer to the strength of the bonding wheel. The three types of grinding wheel bond are:

Vitrified
Organic (resinoid, rubber, shellac)
Silicate
Vitrified-Bond Grinding Wheels

Approximately two-thirds of the manufactured grinding wheels are made with a vitrified bond composed of clays and feldspars, and are selected for their fusibility. During the burning process manufacture, a temperature of 1270’f is reached, which is high enough to fuse the clays into molten glass condition. When cooling a span or post of this glass connects each abrasive grain to its neighboring grains to make a strong rigid grinding wheel.
Organic-Bonded Grinding Wheels
Organic-bonded grinding wheels are made from resinoid , rubber of shellac. Resinoid wheels are used in high-speed rough-grinding operations and are the largest percentage of organic-bonding wheels. Straight wheels are used on bench and pedestal grinding, cup wheels and cones are used for cleaning castings and for weld grinding with portable grinders. Reinforced cutoff wheels are used on both cutting-off machines, cutting bar stock and cutting concrete blocks and other masonry materials.
Grinding Wheel Markings
In 1944 a standard system for marking grinding wheels was adopted by grinding wheel manufacturers throughout the country. The markings consists of six parts arranged in this order

o Abrasive type
o Grain size
o Grade
o Structure
o Bond Type
o Bond Modification Symbols

Abrasive types: Abrasive types fall into two groups, letters are used to identify them

o A-Aluminum Oxide
o C-Silicon Carbide

Grain Size: Grain size in wheels range in size from 10 (course) to 600 (fine)
Grade: Grade is indicated by letters of the alphabet ranging from A to Z (soft to Hard)

Grade A to H Soft
I to P Medium
Q to Z Hard

Structure : Structure spacing or grain spacing in grinding wheels is indicated by a number from 1 to 12. The higher numbers indicates more open grain spacing
examples

3 in dense or close grain structure
8 is a wide grain spacing

Bond or Process: the following letters designate the type of bond.

V-Vitrified
B-Retinoid
R-Rubber
E-Shellac
S-Silicate

Bond Modification Symbols: These indicate a particular type of bond that distinguishes it as a variation from a basic bond.

VG (Norton G type of Vitrified bond)
B11 (Norton 11 type of resinoid bond)

Factors Affecting Grinding Wheel Selection
Six items need to be taken into consideration when selecting grinding wheels

1. Abrasive type
2. Grain size
3. Grade
4. Structure
5. Bond type
6. Manufacture’s Record

Hardness of the Metal to be Ground
Abrasive: Aluminum oxide is best suited for grinding steel and steel alloys.
Silicon Carbide grinding wheels are most efficient for grinding cast iron, non-ferrous metals, and non-metallic materials.
Grit Size: Fine grit is best for hard, brittle, and difficult to penetrate materials. Course grit is best for soft ductile, easily penetrated materials.
Grade: For very hard dense materials, use a relatively soft grade-grinding wheel. Hard materials resist the penetration of the abrasive grains and cause them to dull quickly. A soft grade wheel enables worn, dull grains to break away and expose newer, shaper cutting grains. Harder grade grinding wheels should be used for soft, easily cut materials.
Amount of Stock to be removed and Finish Required
Grit size and bond are important in the selection of a wheel depending on the amount of stock to be removed and the finish required.
Grit size: For rough grinding or rapid removal of stock, use a coarse grit. If a high finish and close tolerances are required, use a fine grit size.
Bond: A vitrified bond is best suited for a fast cutting and a commercial finish. Resinoid, rubber of shellac is best for obtaining a high finish.
Operation (Wet or Dry): Generally wet grinding permits the use of grinding wheels at least one grade higher than for dry grinding without danger of burning the work from heat of friction. Water speeds up the work and reduces dust.
Wheel speed: Grinding wheel speed is very important in selecting a wheel and bond as follows.
For speeds, less than 6500 surface feet per minute (sfpm) use vitrified-bonded wheels.
For speeds above 6500, sfpm use an organic-bonded wheel (resinoid, rubber or shellac).
Areas of Grinding Contact
The area of contact between the wheel and the work influences grit size and grade. In general the smaller the area of contact, the harder the grinding wheel should be. For a large area of contact, a coarse grit wheel should be used. If the area of contact is small then a fine-grit wheel should be used.
Severity of the Grinding Operation
Factors that influence the choice of abrasive:
Use a tough abrasive, “regular aluminum oxide for grinding steel and steel alloys under severe conditions.
Use a relatively mild abrasive for light grinding on hard steels.
Use a intermediate abrasive for grinding job of average severity

Abrasives

2009-06-24T21:07:00.000-07:00

CHAPTER FOUR
ABRASIVES

Notes made while reading Audel‘s Machine Shop Basics visit them at www.audelbooks.com
Grinding is relativity a new art with most of the development having taken place since the 1890’s. The definition of an abrasive is a substance (i.e. sandpaper, emery) used for grinding polishing etc. Before this, the only abrasives were prepared from sandstone. Because of harder metals and alloys, abrasives that are more efficient were needed.

Natural Abrasives

Emery and corundum are hard natural metals, naturally occurring in aluminum oxide, corundum has larger crystals and contains fewer impurities. These materials were used in grinding wheels until the turn of the century, since then more efficient man-made material started being used.

Manufactured Abrasives

As the need, grinding increases so did producing abrasives whose quality is controlled. Progress has made in the development of bonding materials when ceramic clays and pottery kiln used in grinding wheel manufacture.

Composition of Abrasives

At first emery was used in grinding wheels, it was not until silicon carbide, aluminum oxide, and diamonds were developed to replace emery that true progress was made. Silicon carbide is a mixture of clay and powered coke originally used to polish precious gems. Aluminum oxide or Bauxite was fused electrically into a hard material similar to emery and corundum. Its one advantage is it can be produced in uniform grade and higher purity, 93% to 94% Aluminum oxide. Today Aluminum oxide is used 75% of all grinding wheels of one type or another.

Diamonds

The ability to synthesize diamonds in the laboratory was achieved in 1955, prior to this natural diamonds were used in grinding wheels. The need for diamonds was created by tungsten carbide a material so hard ordinary grinding wheel would not work. Today diamonds wheels are used for grinding carbide, ceramics, glass, stone and some tool steels.
Use of Abrasives in Grinding Wheels

Grinding is the process of disintegrating a material and reducing it into small particles of dust by crushing or attrition. Here are some of the newer abrasives used in grinding wheels.
Silicon Carbide Abrasives

Silicon carbide is made of pure silica and carbon in the form of finely ground coke. When heated in an electric furnace silicon carbide crystals are formed, these are mainly used in a large variety of abrasive and refectory products. Here are some brand names

crystolon
carborundum
carbolon
carbonite
Aluminum Oxide Abrasives

The source of aluminum oxide (Al/2O/3) is Bauxite, which is aluminum, combined with water and varying amounts of impurities. Manufacture of aluminum abrasive is done with Arc-type electric furnaces. The finished product is called a “pig” of crystalline aluminum oxide. Here are some brand names of aluminum oxide abrasives:

Alundum
Aloxite
Lionite
Borolon
Exolon

Diamond Abrasive

Both natural and man-made diamonds have fields of application in which they excel. Diamond grinding wheels are made in the following three different bond types.

Resinoid
Metal
Vitritied

More Notes From Virtual Machine Shop

2009-04-19T04:34:00.000-07:00

Notes on Machinery’s Handbook

Source: Virtual Machine Shop

Introduction to the Machinery’s Handbook

The Machinery’s Handbook is necessary in any machinist’s toolbox to be referred to on a regular basis. Here is an example of manufacturing a part and the use of the handbook during the machining process.

The Blueprint

Look at this blueprint

The material on the blueprint to be machined is 4130 steel that has been tempered at 800 degrees. Tensile strength needs to be determined to select the appropriate cutting tool. Find the Hardness of the metal, done by a Rockwell C scale tester, to find this information look in the chapter called Properties, Treatment, and Testing of Materials. Look for 4130 steel tempered at 800 degrees, looking at the table, tensile strength is 186,000 Pounds per square inch. (See table 11b page 469) The next thing to do is find the hardness of 4130 on the Rockwell C scale. Note here that the Brinell hardness is 380, to convert Brinell to Rockwell C scale look at in the Hardness Testing section table 1. A 381 Brinell hardness number equals a hardness of 41 RC on the Rockwell C scale. The chose of a cutting tool a coated carbide cutter would be more suitable.

Cutting Speeds and Feeds

Now the machining can begin, at a point, two questions need asking, they are. What should be the feed rate, and RPM for a 3-inch diameter work piece? Look at table 1 in the chapter on Feeds and Speeds in the Machinery’s handbook. See where 4130 under Material AISI/SAE Designation; remember 4130 has Brinell Hardness of 380 BHN that gives a feed rate of .028 per revolution and a speed of 120 feet per minute. Use this formula to determine the correct RPM to use:

RPM= (CSx4)/Dia. or (125x4)/3

RPM= (500)/3

RPM=166

To find feed rate in inches per minute use this formula

Feed=RPM x IPR (inches per revolution)

Feed= 166 x .028 = 4.65 inches per minute.

Finding Major Diameter

Remember the drawing calls for 1-8 UNC-2A thread on this piece. Here is how to go about finding the major diameter, look on table 3 of Unified Screw Threads on page 1744. The class is 2A, the max diameter is .9980 and the minimum diameter is .9930.

Thread Depth and Compound Angle

The material is going to be machined on a conventional engine lathe, next it has to determined how much to feed the material in for a complete thread. Looking back at table 3 in the Unified screw threads chapter to find the pitch diameter, and the table states for a 1-8UNC-2A thread the pitch diameter has to be between .9168 and .91. Take the average value of these two numbers.

(.9168+.91)/2

(1.8268)/2

=.9134

With a major diameter of .990, a feed in rate of, .990-.9134=, .0766 Note here that four things control thread geometry, pitch, major diameter, pitch diameter and tread angle. The minor diameter is a byproduct of these, so a feed of .0776 will produce some minor diameter not shown in table 3.

We are almost ready to machine the thread; however, the compound slide is set to 29 degrees. The question is how many thousands must the compound be moved to achieve the .0766 depth required? To solve a right angle problem, turn to page 91 in the Machinery Handbook, Solution of Right-angled Triangles. The compound slide is set at 29 degrees use the formula:

Side b; angle A

c=b/coos A

Since the distance to dial in is .0766 and the angle of the compound is 29 degrees, .0766 is side b and 29 angles A, use the above formula and plug in the numbers:

c=.0766/cos29

c=.0875

Measuring Over Wires

To measure the thread pitch diameter use three wires, actually these precisely matched ground steel rods fit on the threads as shown on the stretch below.

Then a micrometer is used to measure over the wires, with this reading calculations determine the pitch diameter.

From table 3 in the Unified screw threads chapter it states that the pitch diameter has to be between .9168 and .9100. Look at the table on page 1896, Diameters of Wires for Measuring American Standard Threads, of the Machinery’s Handbook for selecting a working diameter of wires for the 1-8 thread. The table states use a wire set of .0700 diameters to .1125 diameters for this thread. This however would take a great deal of calculating to determine what the measurement over wires should be for a given pitch diameter and wire set. Now look on page 1901 of the Machinery’s Handbook, Dimensions over Wires of Given Diameter for Checking Screw Threads of (U.S. Standard) and the V-Form. The table selects a .090 diameter wire, note that this is within the limits of .0700 and .1125. Using all the noted tables a 1-8 thread with a pitch diameter of .9314 will measure from 1.0535 to 1.0806 over three properly placed .090 diameter wires.

Fits

The other callout on the drawing is for a 2.00 Class RC7 fir. Find table 8a American National Standard Running and Sliding Fits page 659 of the Machinery’s Handbook. For a shaft of 2-inch diameter, the tolerance is from -5.8 to -4 thousands of an inch. Therefore, the diameter must be between

2.-.0058=1.9942 minimum

2-.004=1.9960 maximum

More notes on Planning a CNC program and setup

2009-03-07T23:42:00.000-08:00

Planning a CNC Program
When writing a CNC program planning all the steps ahead of time is very important. The machine that is used and the operations done on that machine is the first step in the process.

Consider things like the size of the part to be machined, required horsepower, number of tools needed and the availability of the machine.

The Part and the Tools

The blueprint or drawing of the part is the basis for writing a NC program; dimensions from the drawing are converted directly into a program. A plan has to be developed for each operation on the part that allows for the sequence of tools to be used and the operation each tool will perform.

The use of extra tooling, using the same tool more the once, or having the tools programmed in the wrong order are things to be avoided. Fixtures and holding devices should be planned for early in the process; pay close attention to clamp locations in order to program around them.

Writing the Program
Planning out each operation on the part allow the machinist to prepare the sequence of tools and the operation each tool will perform before actually writing out the program.
In a nutshell a program is simply a series of commands written in the order they are to be executed. The controller interprets, and then acts on these commands one at a time without stopping.
With the operations defined, the tools selected, and the feeds and speeds calculated the last step is to write the program. This can be done on paper or with the aid of a computer; a part set-up sheet is developed with a tool list. Now the machine can be set-up and the parts machined.
Tool Length Offsets on the Mill
What is an Offset?
With a program written for multiple tools it is crucial that there a method accounting for the difference in tool length of each tool used is relayed to the controller. If these differences are not taken into account crashes will happen.
G43
The introduction of the G-code G43 (tool length offset code) is the solution to tool length compensation. G43 “talks “to the CNC controller to look in a special place within its memory for the length of the tools being used. During the setup of the program, the setup person or operator would have “touched off” each tool used in the program, input the value traveled from the tool change position to the Z-zero plane of the part. When M6 tool change is encountered the controller will make all the additions or subtractions necessary that the programmed value of Z0.0 will be adjusted for the tip of each tool to rest perfectly on the Z-zero part plane.

CNC Notes, Introduction to CNC code

2009-02-22T00:19:00.000-08:00

Introduction to CNC Code

With Computer Numerical Control (CNC) a machine controller manages the operation of the machine. This includes table motions, spindle speeds, tool changes, and other machining functions. A program written in NC code is how these functions are accomplished. The coded instructions use letters, numbers and symbols (+,-,/…. and so on) to create a program.

A Character

An NC code is the language that is read by the CNC machine’s controller. To insure accuracy there is specific structure to this language, and consists of characters, words, blocks and programs.

Here are the nine character types used in CNC programming

1. letters A thru Z

2. a number or combination of numbers 0 thru 9

3. + plus sign

4. – minus sign

5. . decimal or period

6. : colon

7. ; semi-colon

8. / slash

9. % percent

A Word

Here are some examples of NC words and what they mean, these are used to provide specific commands to a machine.

NC Word Description

F as in F12.0 Feed rate at 12.0 inches per minute

G as in G1 Tool movement in linear interpolation while under feed control

M as in M6 Miscellaneous function in this instant a tool change

N as in N100 Block sequence number

R as in R.25 Arc radius 0.25 radius

S as in S1250 Spindle speed at 1250 RPM

T as in T3 Selection of tool number 3

X as in X2.5 X-axis coordinate, 2.5 inches in the X direction

Y as in Y4.75 Y-axis coordinates 4.75 inches in the Y direction

A Block

A series of words defining a single instruction is called a block, and a block is made up of a word or a combination of words. An end of block character terminates a block, the EOB can be either visible or invisible. Here are some examples of both.

N89 M30 (two word block)

N11 T01 M06 (three word block)

N05 G80 G90 G17 (four word block)

N9 G01 X3.0 Y1.7 F4.0 (Five word block)

With an EOB

N400 G0 X0.2 (three word block with “;” used as an EOB)

N5005 G90 G1 F20 X5 Y2 Z4$ (seven word block with “$” used as an EOB)

A Program

A program is a complete set of coded instructions made up of a series of block needed to completely machine a part.

A program and all of its parts can be equated to the English language as follows:

A character is the same in both CNC Code language and the English language

A word is the combination of characters in both the CNC language and the English language.

A block in CNC Code Language is equivalent to a sentence in the English language, conveying specific thoughts, commands and has punctuation that ends them.

A program in CNC Language is equivalent to complete memo of letter in the English Language. They both are a combination of sentences/blocks that convey complete ideas (English) or completed parts (NC Code).

Address Words

Address codes are a single letter character (A-Z) at the beginning of each word that defines what the computer should do with the numerical data that follows. There are address code for Milling and turning, two address codes are considered major codes they are G-codes and M-codes.

Address codes for Milling and Drilling

A Angular dimension around the X axis

B Angular dimension around the Y axis

C Angular dimension around the Z axis

D Cutter compensation register number

E Angular dimension for special axis

F Feed rate

G Preparatory function (G-codes)

I X axis arc center location

J Y axis arc center location

K Z axis arc center location

L Loop count repeat for canned cycles

N Block number

O Program number or subroutine number

P Dwell time

Q Canned cycle repeat dimension

R Arc radius Or z-axis retract distance

S Spindle speed

T Tool selection number

X primary X motion dimension

Y primary Y motion dimension

Z primary Z motion dimension

Address codes for Turning

A Fourth axis rotary motion

B Linear B axis motion

C Fifth axis rotary motion

D First pass cut depth for threading

E Feed rate

F Feed rate

G Preparatory function (G-codes)

I X axis arc center location

J Canned cycle data

K Z axis arc center location

L Loop count repeat for canned cycles

N Block number

O Program number of subroutine number

P Dwell time

Q Canned cycle repeat dimension

R Arc radius or z-axis retract distance

S Spindle speed

T Tool selection number

U Incremental Z axis motion

V Marco parameter

W Incremental Z axis motion

X primary X motion dimension

Y primary Y motion dimension

Z primary Z motion dimension

G Words

G words or G codes as they are commonly called are the major address codes for preparatory functions involving tool movement and material removal. This includes lineal and circular feed moves, rapid moves, canned cycles and dwell. Here are some of the more commonly used G-codes

G-codes for Milling

Rapid positioning (G00)

Interpolation (G01, G02, G03)

Dwell (G04)

Plane selection (G17, G18, G19)

Automatic Reference Returns (G28, G29)

Cutter compensation (G40, G41, G42)

Tool offset (G43-G49)

Work Coordinate Offset (G52-G59)

Unit Input (G20, G21; or G70, G71)

Fixed canned cycles (G80-G89)

Positioning Input (G90, G91)

Set Work Coordinates (G92)

Return Points (G98, G99)

G-codes for lathes

Rapid positioning (00)

Interpolation (G01, G02, G03)

Dwell (G04)

ZX plane selection (G18)

Unit Input (G20, G21)

Automatic Reference Return (G28, G29)

Tool Nose Radius Compensation (G40, G41, G42)

Work coordinate offset (G52-G59)

Fixed cycles:

Finishing Cycle (G70)

Turning Cycle (G71)

Facing Cycle (G72)

Peck-drilling (G74)

Grooving Cycle (G75)

Threading Cycles (76, G92)

O.D./I.D. turning cycle (G90)

Constant Surface Speed (G96, G97)

Free Rate unit (G98, G99)

M Words

Miscellaneous functions that perform instructions that do not involve tool movement are called M words or more commonly M-codes. Included in this is spindle on and off, tool changes, coolant on and off, along with similar other functions. Here are the more commonly used M-codes

for Milling and Lathes.

M-codes for Milling

Program Stops (M00, M01)

End of Program (M02, M30)

Spindle control (M03, M04, M05, M19)

Tool Change (M06)

Coolant Control (M08, M09)

Clamp Control (M10, M11)

Sub-program Control (M98, M99)

M-codes for Lathes

Program Stops (M00, M01)

End of Program (M02, M03)

Spindle control (M03, M04, M05)

Coolant Control (M08, M09)

Clamp Control (M10, M11)

Turret Rotation (M17, M18)

Tail Stock Control (M21, M22)

Sub-program Control (M98, M99)

More on Cnc and G-codes

2009-01-17T22:48:00.000-08:00

CNC CONTROL-OPEN AND CLOSED LOOP CONTROL

Motor drive controls the position and velocity of the machine axes in a CNC system, with each axis being driven separately, and follows the command signal generated by the NC control. The open-loop and closed-loop systems is how the servo drives are activated

The continuous –path control system is also known as the contour method. It can synchronize the axes of motion to generate a predetermined path such as a line or arc and everything in between.

CNC Control-: Open and Closed Loop Control

Motor drives are required in CNC systems to control position and velocity of the machine axes. NC generated signals drive separately each axis this is accomplished by the open-loop or closed-loop system activating the servos.

Open Loop – The input device feeds programmed instructions into the controller; the signals then are converted into electrical pulses by the controller. These signals then are sent to the servo amplifier which in turn energizes the servo motors. The number of electrical pulses will determine how far each servo will travel, while the pulse frequency determines the velocity.

There is a draw back to the open-loop system primarily being there is no feedback system to determine if the program position and velocity have been achieved. Load, temperature, lubrication, or humidity could affect the actual output of the machine causing it to be different from the desired output.

Because of this point to point systems generally use the open loop system where accuracy is not that critical.

Closed Loop-A feedback system that monitors the actual output and corrects any discrepancies from the programmed input is what is different with the closed loop system. The feedback system can be analog or digital, with the analog system measures the variations of the physical variables such as position and the velocity in terms of voltage levels.

FIXED CYCLES ON THE MILL

Fixed cycles on a CNC mill are used for the drilling of holes or hole machining. This includes center drilling, countersinking, drilling, reaming, counter boring, boring, right hand tapping, and left hand tapping. Holes can be a ¼ inch diameter hole drilled though the part, more complicated as a blind hole, low tolerance, or a stepped hole.

FFixed or canned cycles, as they can be called, allow programs to be shorter, faster to program, easy to

understand, easy to read, easy to troubleshoot, and less chances of error. Here is an example of the usefulness of canned cycles when drilling four holes drilled in a plate. ORIGIN 2 4 3

Here is an example of drilling four holes in the plate above without fixed cycles in the program.

Z-1 drills though

G90 Z.05
G00 X2Y2
GO1 Z-1F20.
G00 Z.05
X2Y8
G01 Z-1
X8Y8
G01 Z-1
G00 Z.05
X8Y2
G01Z-1
G00 Z.05

Here is the same program with a G81 canned cycle

G90
G81 X2 Y2 Z-1. R.05 F20. G99
X2Y2
X8 Y8
G80

Notice how simpler the program is.

G CODES

Using a canned cycle starts a mini-program already in the controller memory, and different canned cycles work beat for different hole machining operations. Here are the “G” codes used in these machining operations.

o G73 PECK DRILLING BREAK

o G74 LEFT HAND TAPPING

o G76 FINE BORING

o G81 DRILLING

o G82 COUNTER BORING

o G83 PECK DRILLING DEEP HOLE

o G84 RIGHT HAND TAPPING

o G85 REAMING

o G86 BORING

o G89 COUNTER BORING FOR BAR

RULES

A programmer needs to use the proper code words for a canned cycle to operate correctly.

This is an example of G81 correctly written.

G81 X1. Y1.Z-.50R. 1F6. G99

Here is how the five words used in this block of code are used

1. G defines the type of cycle

2. X and Y indicate the hole location

3. Z is the depth of the hole

4. R is to set the rapid plane

5. F is the feed rate

Rapid Plane-Can also be called the retract plane, it is the plane above the work piece where the cutting tool has cleared the top surface. From this position the tool can move the a new position without touching the work piece; however, this is not what is called the initial plane

Initial Plane-In machining the initial plane is the Z height of a tool when a canned cycle is initiated. This also may or may not be at a tool change position. G98 is often used in the canned cycle block insuring the tool returns to Z where it began without movement in X or Y axis. This to ensure the tool does not strike fixtures or jig before moving to a new location.

Feed Rate-A unit distance divided by a time scale that a tool travels while machining, with the unit distance in inches and the time scale in minutes. This is expressed in “inches per minute” (I/m IPM) or “feet per minute” (f/m or FPM).

The use of “words” is derived from the EIAS word address programming protocol, the original NC programming language. To retract the tool to the initial plane G98 is used.

The initial plane is the Z level when the canned cycle was called, and not the rapid plane. Using G98 is a good way to avoid clamps as long as the initial Z is higher than all tooling and clamps. To retract the tool to the rapid plane when the cycle is finish G99 is used. G98 and G99 can be used interchangeably in the program code.

Canned cycle are modal meaning once they are turned on they stay on until the cycle is cancelled. Once started every block of code is interpreted as being a part of that canned cycle process. G80 is the command to cancel a canned cycle, if not used every movement after the intended hole/s is more unwanted holes may be drilled or the machine may crash.

This is what a canned cycle will do:

1. Rapid to specific X and Y location;

2. Rapid to the Z rapid plane specified;

3. Machine the hole to the G code specified.

4. Exit the hole.

This is an example of a properly written G81 canned cycle to drill four holes.

o N008 G81 X1. Y1. Z-.2 R. 1 F6 G99

o N009 X1.25 Y1.25

o N010 X1.5

o N012 G80

G73-Peck Drilling Cycle

What the peck drilling cycle does is rapid to the XY coordinates and then to the R plane where it begins to feed down in increments of Q at a feed rate of F to a depth of Z. At the end of every Q increment the drill will back off .005 to break any possible stinger chips and continues to the next increment of Q. The controller calculates the number of pecks till the programmed Z depth is reached, when complete G99 return the drill to the initial plane.

G74-Left Hand Tapping Cycle

The left hand tapping cycle rapids to the XY coordinates and to the R plane where it begins to feed the spindle down and counterclockwise at a feed rate of F to the depth of Z. The spindle then reverses and feeds upward at the same federate to the R plane, G99 will rapid to the initial plane.

G76-Fine Boring Cycle

With this cycle no witness marks are left behind, this is done by moving the tool away from the bored surface before retracting. The tool feeds down to the bottom of the bore; the spindle then stops and orients itself to the M19 position. Next the tool retracts from the wall of the bore and rapids out of the hole. I and J are introduced here, I and J are simply clones of X and Y. Depending on the tool orients itself, they determine how to move the tool away from the bored surface. I-.002 tells the controller to move the tool .002 in the X direction, J.002 tells the controller to move the tool in the +Y direction. Here is an example of G76 code: G76 X1. Y1. Z-1.R. 1 I-.002 F5 G98.

G81-Standard Drilling Cycle

This cycle has many uses such as center drilling, drilling, reaming, and rough boring. It travels down at a set feed rate and then rapids out of the hole. When drilling deeper holes, another cycle is recommended, either G73 or G83, as chips can clog in the flutes and break or overheat a drill.

An example of G81 code: G81 X1. Y1 Z-.2 R. 1 F3 G99

G82- Counter Boring cycle

The counter boring cycle causes the tool to feed to the bottom, pause if needed, and then rapid out of the hole. This pause is programmed in milliseconds, and allows the tool time to cut the bottom of the hole. Tool pressure is relieved, this is important when counter bore holes have a tight tolerance.

An example of G82 code: G82 X1. Y1. Z-1.R.1 P500 F7 G98

G83-Deep Hole Drilling Cycle

When drilling deeper holes G83 can be used, this cycle clears away chips and curls from the hole, as an excess of chips in a deep hole can cause a tool to break. The cycle drills a Q peck distance at the F (feed rate) then retracts at rapid speed back to the R (rapid plane) to clear out the chips, and then starts the cycle over again. Then the specified Z depth is reached it retracts at rapid. Here is G83 code: G83 X1. Y1. R.1 Q.1 F6 G99

A parameter in the controller controls the distance between the end of the rapid plunge and the new material to be drilled after the completed peck.

G84-Right Hand Tapping Cycle

This cycle goes to the XY coordinates, then to the R plane and begins to feed the spindle down and clockwise at a feed rate of F to a depth of Z. The spindle then reverses and feed upward at the same federate to the R plane. G99 will rapid to the initial plane.

Here is G84 code: G84 X1.Y1.Z-.8 R.400 F30 G99

G85-Reaming Cycle

This cycle is used for reaming and it feeds in and out of the hole at the set feed rate. Here is G85 code: G85 X1. Y1. Z1. R. 1 F5 G99

G86-Boring Cycle

This cycle feeds the tool in and at the bottom it stops the spindle, and then the spindle orients and rapids out.

G86 code: G86 X1. Y1. Z-1. R. 1 F7 G98

G89-Counter Boring Cycle

This cycle is half G82 and half G86 canned cycle, the tool feeds into the hole and pauses at the bottom; at that point the spindle stops and the tool will rapid out. The pause is necessary to relieve tool pressure for very accurate depths, and this cycle will leave a witness mark.

G89 code: G89 X1. Y1. Z-1. R. 1 P800 F10

CNC notes

2009-01-13T10:50:00.000-08:00

Lately I have been reading up on Cnc, G codes and the like, here are some notes I made while studying the subject from Virtual Machine shop.

CAD/CAM, computer aided design and computer aid manufacturing, along with CNC, computer numerically control, is the basis of how parts are machined in a modern machine shop. CAD is essentially an engineering drawing on a computer, changes can be made immediately if needed also, with modern software, and the part can be tested, and analyzed before manufacturing. Now that the part is drafted and is in a computer file CAM comes into play, this aids in the actual manufacturing process. In this case a CNC part program can now be generated which includes a tool path, tools to be used, feed rates, work holding and coolant. In using a CAD/CAM system the steps are

CAD, computer assisted drafting
CAM, computer assisted manufacturing
NC, G & M CODE generation
Shop Floor, CNC machine controller

CNC Control- Point to Point

A CNC controller is made up of two systems, mode of the control, and the type of control loop. The mode of control can be either point-to-point or continues path, and the type of control loop can be closed-loop or open-loop. The mode of control controls the tool as it moved to position or along the cutting path. The point-to-point system can also be referred to as the positioning system; its function is to move a tool from one point to another specified point. This is to perform such operations as drilling, punching, boring, reaming and tapping. There are three paths that the tool can follow to move from point to point; the Axial Path, the 45 degree path, and the linear path. With the axial path the tool moves in a right-angle path parallel to the two positioning axes, X and Y. The tool moves first moves along the X axis till it reaches a specified point, then along the Y axis till it reaches a specified point. Because one axis is moved at a time this is the slowest method.

The 45 degree path moves the tool at a 45 degree angle until x one of the axes is lined up with its new position. Then the tool moves along the axes to the specified coordinate position. At first both X and Y move at once till one of the specified coordinates is reached then the tool moves in an axial path mode to the specified coordinate position.

In the Linear Path mode the controller can synchronize the motion in both axes thus generating a linear path. This is the quickest method for moving point to point; however, more sophisticated equipment is needed to coordinate the speed of each axis so a straight line can be maintained.

More notes from Chp3 of MachineShop Basics

2008-12-22T08:09:00.000-08:00

This posting is about nonferrous metals used in the Metalworking Industry
NONFERROUS METALS
These are metals other than iron, important nonferrous metals are
o copper
o zinc
o tin
o antimony
o aluminum
Copper
Copper is a very useful metal in its pure form and its various alloys such as brass and bronze. Copper has a reddish brown color, it is very ductile and malleable; also it is very tenacious and is an excellent conductor of heat and electricity. At 1980 degrees Fahrenheit pure copper melts and it is1940 degrees Fahrenheit for commercial copper.
Zinc
At ordinary temperatures zinc is brittle; it becomes ductile and malleable at temperatures between 212 and 300 degrees Fahrenheit, then brittle again at 410 degrees Fahrenheit. Some of the uses of zinc are
o lining cisterns
o coating water pipes
o eaves
o gutters

Tin
Tin has a low melting point, that of 450 degrees Fahrenheit, it is very ductile and can easily be drawn into wire at 212 degrees F or rolled into very thin sheets.
Antimony

Antimony resembles tin and hard and brittle metal, and it is used in forming alloys as it combines easily with other metals.
Lead
Lead is the heaviest of all the common metals, and melts at 621 degree F, it is malleable, ductile, and it can be cut with a knife. Also lead is not a good conductor of electricity, and has low tensile strength.
Bismuth
Is a unique metal in that its specific gravity decreases under pressure, and it expands on cooling. Bismuth has a melting point of 520 F, and is frequently added with antimony in type metals because it fills the molds completely on solidification.
Aluminum
Is made by the aid of electricity from cryolite and bauxite, and is ductile and malleable. It is a good conductor of heat and electricity, and is the lightest of all metals.
Refractory Metals
With melting points above 3632 F, tantalum, tungsten, and molybdenum are called refractory metals. These metals are made by powder metallurgy rather than smelting.
Tungsten and Molybdenum
Tungsten and molybdenum are extensively used of the ten refractory metals, with tungsten having the highest melting point of all metals. The use of these two metals is due to their high melting points, and the ability to retain strength and stiffness at high temperatures. Tungsten and molybdenum is used extensively in the electrical and electronic industries.
Tantalum
Is almost completely resistant to corrosion and chemical attack also it has the ability to immobilize residual gases in electronic tubes at high temperatures. Other properties are its high melting point, low vapor pressure, thermal expansion and the ease of fabrication. Tantalum has the ability to form highly stable anodic films.
Columbian
Is a sister metal to found in the same ore as tantalum, and its properties are somewhat similar to tantalum; Tantalum and Columbian are malleable and ductile as mild steel.
Nonferrous Alloys
Two or more metals combined that contain iron, here are some of the more important alloys.
Brass
Brass comes in many varieties, and is composed of copper and zinc in various proportions. Also small percentages of tin, lead and other metals are included tin, lead.
Bronze
Bronze is an alloy of copper and tin.
Aluminum
There is no limit to the number of alloys and aluminum the can be produced. Elements used in the casting of aluminum are copper, silicon, magnesium, nickel, iron, zinc and manganese.
Babbitt metal
Discovered by Isaac Babbitt in 1839, it is an alloy of tin, antimony and copper.
Other Nonferrous Alloys
Monel metal: this alloy is made up of copper, nickel and a small percentage of iron. It has a melting point of 2480 f also it can be forged between 165 degrees, and 1100 degrees F. Monel metal is used in ships propellers.
Muntz metal: this alloy is made up 60 percent copper and 40 percent tin, and used for applications in which hard sheet brass is needed.
Tobin bronze: this alloy contains 58 to 60 percent copper, 40 percent tin with small percentages of iron tin and lead.
Delta metal: this alloy is very similar in composition to Tobin bronze.
White metal: used in bearings, this alloy is made of zinc, and tin of zinc, tin and lead.
Tantung: Is the name for alloys made of cobalt, chromium and tungsten with either tantalum or Columbian carbide, and other components added. These alloys have great hardness, strength, toughness, and resistance to wear, heat, impact, corrosion, and erosion even at extremely high temperatures.

2008-11-15T10:41:00.000-08:00

I have been reading other material as well, these notes are from the U.S. Army Machining Course at http://opensourcemachine.org/us-army-courses.

NOTES FROM US ARMY MACHINE COURSES

FUNDAMENTALS OF MACHINE TOOLS

CHAPTER 1
INTRODUCTION TO THE MACHINE SHOP

MACHINE SHOP WORK

SCOPE
Work in a machine shop includes all cold-metal work by an operator using hand tools or power tools for the removal of material to a specified shape or form. This does not include sheet metal work or coppersmithing.

LAYING OUT WORK
Laying out is a shop term, it means to scribe lines, circles, centers, and so forth on the surface of material that serves as a guide in making the finished work piece. These lines must be scribed out with the greatest accuracy or the part will be of no use.
SCRIBING LINES OF METAL
Layout dye is used in the scribing of lines on metal, it is blue in color, and provides excellent contrast between metal and the layout lines. Before applying the dye clean the work surface of all oil and grease or the dye will not adhere to the metal.
COMMON LAYOUT TOOLS
SCRIBER: A scriber is the layout tool used to produce lines, it is made of hardened steel and is kept clean by honing on an oilstone.
DIVIDER: A divider is used to layout circles, arcs, and radii. The legs of the divider must be kept shape, and to the same length. Use a steel rule in setting the needed dimension to be scribed on a work piece.
TRAMMEL: When circles, arc, and radii are to large to use a divider a trammel is used. The trammel is made up of three parts: a beam, two sliding heads with scriber points and an adjusting screw
HERMAPRODITE CALIPER: IS A TOOL USED TO LAY OUT LINES PARALLEL WITH THE EDGES OF A WORKPIECE. Also it can be used to locate the center of an cylindrical shaped work piece.
SURFACE GAGE: Has many uses and is most often used for layout work, it can scribe lines at any distance parallel to the work surface. A square and a surface plate are needed to set the surface gage at the desired dimension
Surface Plate; Provides a true smooth pane surface, from which dimensions are measured, usually they are made of granite.
Vernier Height Gage: The height gage is a special caliper on a special foot block for use on a surface plate. Common sizes are 10, 18, and 24 inches. It uses various attachments to scribe lines; a dial indicator can be mounted to make precision measurements.

Combination Square Set: is used in a number of layout operations. The square consists of a blade, square head, protractor and center head. Here the that parts that make up a square set.
The Blade is designed to allow different heads to slide along the blade and be clamped in any desired location.
The Square Head is designed with a 45 and 90 degree edge and can be used as a try square and miter square as well as a depth rule. With a split level in the head it can also be used as a square.
The Protractor Head has a revolving turret graduated in degrees from 0 to 180 of to 90 and can be used to lay out and measure angles to and accuracy of 1 degree.
The Center Head is used to locate and layout the center of cylindrical workplaces.

Bevel Protractor has an adjustable blade with an graduated dial, the dial is marked out in degrees through a complete circle of 360 degrees
STEPS IN MAKING A LAYOUT
o Study the shop drawing or blueprint before cutting off stock, allow enough material to square the ends if required.
o Remove all grease and oil from the work surface and apply layout dye.
o Locate and scribe a base line, all measurements are made from this line. If the work piece has one true edge that can be used as a base line.
o Using the base line as a reference line, locate and scribe all center lines for each circle, radius of arc.
o Mark the points where the center lines intersect using a sharp prick punch.
o Scribe all circles, radii and arcs using a divider or trammel.
o Using the correct type protractor, locate and scribe all straight and angular lines.
o Scribe all lines for internal openings.
o All layout lines should be clear, sharp and fine, reapply layout dye to all messy, wide, or incorrect lines and rescribe.
JIGS AND FIXTURES
Aid in the manufacturing of parts, accurate and interchangeable.
MECHANICAL DRAWINGS AND BLUEPRINTS
Mechanical drawings are made with special instruments and give a true representation of the object to be made, including size, description, material used, and method of manufacture.
WORKING FROM DRAWINGS
A detail print shows the individual part to be made, with two or more orthographic (straight-on) views of the part, and in some cases shows an isometric projection. An isometric projection shows what the part will look like when complete. Every drawing has a number, and a title box which shows the part name, the scale used, the pattern number, and the material required. Also shown is the assembly or subassembly print number to which the part belongs, the job order number the quanity and the date of the order. Along with the name of the person who drew, checked and approved the drawing. Building a part to the print depends on the following:
o Correctly reading and observing all the data on the drawing.
o Using the correct tools and instruments for laying out the job.
o Using the baseline method of locating the dimensional points during the layout.
o Observing all tolerances and allowances
o Accurate measuring of part throughout the fabricating process
o Allowing for expansion of the work piece by heat generated by cutting and machining operations
Limits of Accuracy

Properties, Identification, and Heat treatment of Metals
GENERAL
METAL CLASSIFICATION
Metals are ferrous or nonferrous, iron being the main element in a ferrous metal. A metal can contain less than 50% iron if it contains more iron than any other metal.
FERROUS
Ferrous metals include cast iron, steel and various steel alloys. The only difference between iron and steel is carbon content. Cast iron has more than 2% carbon, while steel has less than 2%.

2008-10-29T14:22:00.000-07:00

With a blog that goes by the name of metal chips I need postings about materials and Metals, here is a start.

Chapter 3 Materials

Materials are classified as metallic and nonmetallic, metallic is divided into ferrous and nonferrous. Here are some examples.

FERROUS

1. IRON

2. STEEL

3. VARIOUS ALLOYS

NONFERROUS

1. COPPER

2. ALUMINUM

3. TITANIUM

Nonmetallic materials such ceramics, glass, and graphite are inorganic materials; wood, rubber, and plastics are organic materials.

PROPERTIES

A material has certain properties that define behavior and characteristics under various conditions

Desirable Properties

Static strength and dynamic strength are desirable in any material, along with low cost. Some materials are used even if they have some poor characteristics, an example would be in casting materials the following is desirable.

o Low melting point

o Good fluidity when melted

o A minimum of porosity

o Low shrinkage

Definition of Properties

o Brittle, Breaks with a clean break, the harder a metal is the more brittle it is.

o Cold short is the name given to a metal that can not be worked under a hammer or rolling and can not be bent cold without the edges cracking. It must not be worked under a pressure of dull red.

o Ductile: Easily drawn out, pliable, material is ductile when it can be extended by pulling,

o Elastic limit: The greatest strain that a substance can endure and still completely spring back to the original shape when the strain is released.

o Fusible: Capable of being melted of liquefied by the action of heat.

o Hardness: The ability to resist damage.

o Homogeneous: Of the same kind or nature

o Hot short: more or less brittle when heated.

o Melting point of a solid: The temperature which a solid becomes a liquid or gas. Melting points range from -39 degrees F to 3000 degrees F.

o Resilience: The act or quality of elasticity, the property of springing back , or recoiling upon removal of a pressure (as with a spring).

o Specific gravity: The weight of a given substance relative to an equal bulk of some other substance, which is taken as a standard of comparison.

o Strength: The ability of a substance to resist force without breaking or yielding, solidity or toughness.

o Tensile strength: The greatest longitudinal stress that can be applied to a substance without tearing it apart.

o Toughness: A substance having the ability to resist great strain, and absorb energy without failure.

Metals

Is any element (silver, iron, etc) that carries a positive charge when dissolve in acid solution and seeks the negative pole in an electric cell. Metals are good conductors of heat and electricity, and can be melted, formed or machined.

Ferrous Metals

Ferrous metals are those metals that contain iron, usually they are magnetic, and can be pure iron or an alloy.

IRON

Pure iron is crystalline in structure, and is a relativity soft metal. There are three temperatures that affect iron, they are 2782 degrees F, the temperature iron solidifies, 1648 degrees F, and 1416 degrees F. Here are the four solid phases of iron.

Alpha iron- is soft, magnetic and incapable of dissolving carbon from atmospheric temperature to 1416 degrees F.
Beta iron -is feebly magnetic, hard, and brittle, it occurs from 1416 to 1648 degrees F.
Gamma iron- takes up carbon, and occurs between 1648 and 2554 degrees F. There are elements that effect gamma iron, carbon; nickel and manganese help prevent it passing into alpha iron. Chromium, tungsten, aluminum, silicon, phosphorus, arsenic, and sulfur helps in the passage from hard beta iron to soft alpha iron.

Delta iron- This type of iron has very little use, reaching 2554 to 2782 degrees F indicates that the internal structure of the metal has changed from gamma to delta iron.

Pig Iron

Pig iron is combined with carbon, silicon, sulfur, phosphorus, and manganese, with carbon making up 2 to 4.5 percent of the content.

Cast Iron

Is really remelted pig iron, it is not malleable, the carbon content is over 2 percent, and cannot be formed, shaped, rolled or drawn into shapes of any use. In industry cast iron is used for castings, and there are four types.

o Gray cast iron- mostly used in castings, has a high percentage of graphite, and is tough with low tensile strength. The carbon content is from 2.5 to 3.5 percent.

o White cast iron- is a casting of extreme hardness and brittleness, with a lower carbon content of 2.0 to 2.5 percent.

o Malleable cast iron- castings made of hard, brittle white cast iron and then annealed, which transforms it to a form of steel.

o Wrought iron- is actually a form of low carbon steel which contains a large amount of slag, up to 1 to 2 percent. What is called the puddling process removes this slag.

STEEL

This general term describes an alloy in which iron is the base metal, and carbon, is the most important added element anywhere from 0 to 2.0 percent. This is a form of what is called pure steel, and has never been made in large quantity. Manganese is the third alloying element of plain carbon steels along with small quantities of silicon, phosphorus, sulfur and other elements. Plain carbon steels contain a few hundredths to 1.4 percent carbon; properties depend on carbon content and heat treatment.

Low carbon steels are used in the rolled or the annealed condition; contrast this with high carbon steels are used where hardness is needed. Increasing the carbon content of steel to a certain percent increases its strength. Mild steel with a content of 0.1 percent carbon has a tensile strength of approximately 50,000 psi, increasing the carbon content to 1.2 percent then the tensile strength is 140,000 psi. A carbon content of 2.0 percent is the theoretical upper limit for steel.

Other elements are added to steel as well, they are as follows, and their effects.

o Phosphorus- enhances the hardness of steel and is able to better resist abrasion; however, it makes steel weak against shocks and vibrations.

o Sulfur- increases brittleness, content should not exceed 0.02 to 0.05 percent

o Manganese- increases strength, hardness and soundness of steel

o Nickel- increases strength and toughness of steel

o Aluminum- improves soundness of ingots and castings

o Vanadium- makes steel nonfatigable, ductile, high tensile strength, and high elastic limit; also resistant to shocks

o Molybdenum- is used in crankshafts, propeller shafts, gun, and rifle barrels also boilerplates

HIGH SPEED STEELS

Can be used as cutting tools for they retain hardness at high temperatures, even if the edges becomes red hot. High speed steels contain 12 to 20 percent tungsten, 2 to 3 percent chromium, and 1 to 2 percent vanadium along with cobalt which is sometimes added. Carbon content is low from 0.65 to 0.75 percent. The two most commonly used high speed steels are 18-4-1 and 14-4-2; the numbers refer to tungsten, chromium and vanadium.

STAINLESS STEELS

When properly heat treated and finished stainless steel resist oxidation and corrosion although they are not absolutely corrosion resistant. Medical and dental instruments contain 12 to 14 percent chromium.

CAST STEEL

Is stronger than cast iron when used in castings, stainless steel casting resist oxidation at temperatures up to 1800 degrees F. Cast steel does not pour as sharply as iron and shrinkage is greater.