Abrasives/grinding Flashcards
Abrasives offer high metal removal rates, great precision and the ability to machine intricately shaped parts. Allows for tight tolerances and provides good surface finish. T or f
Truw
5 types of abrasives
-emery
-silicon carbide
-almunim oxide
-diamond
-CBN carbon boron nitride
___ also caller conundrum, is the best know if the natural abrasives and has been used for many centuries in the form of loose grain, coated abrasives and eventually grinding wheels
Emery
___ produces a very hard and sharp abrasive grain. Has black silicon for low strength material ie. Cast iron, aluminum and non metallic materials. And green silicon carbide for sharpening cemented carbide.
Made of silica sand and petroleum coke
Silicon carbide
___ is the most common abrasive. Used for cutting steel and other ferrous alloys. Found on most bench or pedestal grinders for sharpening twist drills, hss lathe tools. White or light gray in appearance
Aluminum oxide
The hardest abrasive. Used for finishing carbide and ceramic cutting tools. Used for cutting granite, concrete, glass and other similar substances. Typically used for non ferrous and non metallic materials
Diamond
___ is a synthetic abrasive second in hardness only to diamond. It is most useful for grinding hard and tough allot steels or tool steels having a hardness of 50 RC or more
CBN cubic boron nitride
4 types of abrasives and their hardness
Diamond- 7000
Cbn - 4700
Silicon carbide - 2480
Aluminum oxide- 2100
The American national standards institute (ANSI) has developed such a system and Canadians have adopted it. There is 1 numbering system for aluminum oxide and silicon carbide and another system for diamond wheels. T or f?
True
Aluminum oxide and silicon carbide wheels consist of these 5 standard elements
Abrasive 1st
Grains size 2nd
Grade 3rd
Structure 4th
Bond type 5th
Letter designation for aluminum oxide and silicon carbide
A for aluminum oxide
C for silicon carbide
Grit sizes are subdivided into 4 groups
Very fine
Fine
Medium
Coarse
The ___ of the grinding wheel is a measure of strength of the bond between the grains. A wheel with a strong bond is said to be hard, a weak bond releases the grain easily such a wheel is said to be soft
Grade or hardness
The grade of a wheel is specified by the third element in designation, which consist of letters A(softest) to Z (hardest) t or f?
True
Structure of a wheel refers to the size of the open spaces (or voids) between the grains. If these voids are large, the wheel is said to be open. If the voids are small the wheel is said to be closed or dense. T or f
True
The structure of a grinding wheel is specified by the fourth element in the designation, which consist of a number from 1-16 (1 having the highest density) t or f?
True
Bond type is identified by a letter standing as the fifth element in the designation, t or f?
True
Types of bonds and letters
Vitrified- V *most common
Resinoid -B
Resinoid reinforced- BF
Rubber- R
Rubber reinforced - RF
Shellac- E
Silicate- S
Metal-M
The designation for diamond wheels is similar to the designation used for aluminum oxide and silicon carbide wheels with these 4 differences
-7 elements instead of 5
-abrasives are identified by different set of letters
-fourth element identifies the concentration of abrasives
-seventh element identifies the depth of abrasive layer
5 shapes of grinding wheels
-straight
-tapered
-cylindrical
-straight cuo
-flaring cup
___ grinding wheels are used for surface and cylindrical, tool grinding, offhand grinding and snagging
Straight grinding wheel
___ grinding wheels have a taper on both sides and are used for snagging type operations
Taper grinding wheel
___grinding wheels are used on horizontal and vertical spindle surface grinders. Cutting takes place mainly on the face
Cylindrical grinding wheel
___ are used for both surface grinding, tool and cutter grinding. The edge may be plain or bevelled
Straight cup grinding wheel
___ are used almost exclusively on tool and cutter grinders. If the bond is resinoid, the wheel may be used for snagging
Flaring cup grinding wheel
___ is a process whereby a revolving grinding wheel is used as a cutting tool to produce either a flat surface or an irregular contour on a workpiece. The workpiece is passed under the grinding wheel at a controlled rate
Surface grinding
Surface grinders are classified according to the orientation of the spindle and the type of table motion. 4 types of surface grinders are
-horizontal spindle with reciprocating table
-horizontal spindle with rotary table
-vertical spindle with reciprocating table
-vertical spindle with rotary table
This is the most common type of surface grinder and is often referred to as a tool room grinder or simply a horizontal surface grinder
Horizontal spindle with reciprocating table
This surface grinder leaves the wheel in constant contact with the workpiece and leaves a circular pattern finish, which is desirable for metal to metal sealing of mating round parts
Horizontal spindle with rotary table
This grinder uses a cylindrical or straight cup grinding wheel mounted on a vertical spindle. The wheel cuts on its face and rim and the wheel can be tilted a few degrees to increase pressure on the rim where the wheel makes contact with the workpiece
Vertical spindle with reciprocating table
This surface grinder is used for grinding large plates flat and parallel and is considered to be the most efficient because the wheel is in constant contact with the work.
Vertical spindle with rotary table
A surface grinding table is traversed manually with the ___ and crossfed manually with a ___
Table traverse hand wheel
Crossfeed hand wheel
2 types of magnetic chucks are
Electromagnetic
Permanent
An ___ uses electricity to produce the magnetic field necessary to hold the workpiece. The major drawback of electromagnetic chuck is that if the power fails, the grinding wheel throws the wp off the table
Electromagnetic chuck
On a ___ the holding power is provided by a series of permanent magnets fastened in a silicon iron grid separated by grid conductor bars
Permanent magnetic chuck
5 magnetic chuck accessories
Adapter plate
Magnetic chuck blocks
Magnetic blocks
Magnetic sine chuck
Magnetic vise clamps
3 types of grinding fluids
Soluble oil and water- used for light to moderate stock removal
Chemical grinding fluids- for moderate to heavy stock removal where surface finish us required
Straight grinding oil- lacks cooling ability of other fluids but offers superior accuracy, finish and permits grinding of very hard material
3 methods od delivering coolant on a surface grinding machine
-Flood cooling system
-through wheel cooling system
-mist cooling system
___ grinding is used for any surface that is not flat, such as angles, radii or irregular profiles. It involves dressing the wheel to the mirror image of the desired contour
Form grinding
__ grinding is capable of much higher metal removal rates than other types of grinding. A very large depth of cut sometimes in excess of 1inch is combined with a very low feed rate
Creep feed grinding
The purpose of a cylindrical grinder is to finish a shaft to a precise size and shape and to impart an excellent surface finish. 2 main types of cylindrical grinders are
Center and centerless
Center type of grinders are for custom, one off work and are the type most commonly used in a general purpose machine shop. Centerless grinders are for production work, t or f?
True
There are 2 types of center grinders
-plain center grinder - used primarily for manufacturing
-universal center grinder- more versatile since both wheel and headstock can be swiveled to allow the grinding of tapers
__ grinding uses the face of the wheel to grind a steep taper or irregular profile I to the workpiece. The wheel head is fed straight in
Plunge grinding
___ grinding is performed on cylindrical and centerless grinders with specially dressed wheels matching the shapes if the threads. Threads produced by grinding are the most accurate of any manufacturing process and have very fine surface finish
Thread grinding
Common problem when internal grinding when the stone first enters the work
Bell mouth shaped hole
The purpose of ___ is to restore the cutting qualities of the wheel by removing worn or loaded grains
Dressing
The purpose of ___ is to ensure the grinding wheel is round and concentric with the machines spindle axis and to shape the face of the wheel
Truing
3 tools used for dressing and truing wheels
-star wheel dresser
-abrasive stick and wheels
-diamond dresser
A ___ is a quick means of dressing and truing a wheel, although it is not an accurate means. Used on off-hand rough/grinding machines and not on precision grinding machines
Star wheel dresser
An __ is guided across the face of the wheel by hand and is typically used to shape wheels on tool and cutter grinders. Made of silicon carbide with a hard bond
Abrasive stick and wheels
A ___ is used for surface, cylindrical and internal grinders and consists of either a single diamond point or a cluster of small diamonds. Most precision grinders have a built in dresser with a feeding mechanism
Diamond dresser
Do NOT use a diamond dresser on a diamond wheel or CBN wheel, t or f
True
5 steps to installing a grinding wheel
-inspecting
-mounting
-balancing
-truing/dressing
-secondary balancing and truing
Many cracks are too fine to be seen during a visual inspection. Perform a ___ to check for these cracks.
Ring test
There should be approximately 0.005in clearance between the bore of the grinding wheel and the spindle adapter. If it’s too tight, scrape the bore, too loose, install a sleeve. T or f
True
The flanges on a grinding wheel should be the same size as each other and not less that 1/3 diameter of the wheel, t or f
True
A ___ is a piece of paper fitted between the grinding wheel and flanges
Blotter
___ is a machining operation that uses a long, straight, multi toothed cutting tool. It is guided past or through a workpiece, leaving a precise, smooth and often intricately shaped surface. Has teeth like a file but wirh each tooth a little higher than the one before it
Broaching
Most broaching is ___ , meaning that it takes place inside a pre drilled hole
Internal broaching
4 advantages of broaching
-High production rate
- very precise. Up to .0005 tolerance
-produce surface finish as fine as 32
-certain tasks can’t be done any other way ie small internal gears
2 limitations of broaching
-cannot be used on a blind hole or cut up to a shoulder
-cannot be used for one off xustom work. The cost of the broach can be justified only for high volume work or for often repeated tasks
Besides the common shop application of cutting internal keyway with a broach and arbor press, machine broaching is used for mass production. Common in automotive/aircraft industry. T or f
True
There should always be atleast 2 teeth in contact with the workpiece when broaching. T or f
True
The overall length of a broach is the length of the cutting area plus the shank at each end of the broach, t or f?
True
Most vertical broaching machines pull the broach because a pulled broach is less likely to break, distort or be misaligned. The most common type of vertical broaching machine pulls the broach up and is called a ___ type machine
Pull up
___ broaching machines have a much longer stroke than vertical broaching machines and theu generally pull rather than push. Better suited for operations requiring a very long broach
Horizontal
A rotary broaching tool is also called a __ broaching tool, for cnc lathes, mills and screw machines is a precision method for producing internal and external polygon forms at an extremely fast rate
Wobble
Rotary broaching produces a very accurate form. Although the broaching tool is held at a 1deg angle, the incline is so slight that the resulting dimensional accuracy matches the cutting tool. Can hit .0005 tolerance. T or f
True
__ are grooves running along a shaft. These grooves matecup with similar grooves in a hub or bore ro provide a positive drive. Is much stronger than a keyed assembly
Splines
2 main types of splines
Involute splines
Straight sided splines
An ___ spline is so called because the teeth have an involute shape, just like teeth on a spur gear. The most widely used standard is the American national __ series
Involute
3 advantages of involute spline over straight sided splines
-can transmit more torque
-can be cut in a similar manner as standard involute gear teeth
-self centering
Involute splines are usually formed by hobbing, rolling, broaching or on a gear shaper. T or f
True
An __ spline is so called because the teeth have an involute shape, just like teeth on a spur gear. Most used standard for it is the American Involute series
Involute spline
3 advantages of an involute spline
-transmit more power
-require specialized cutters but can be cut in similar manner as standard involite gear teeth
-are self centering
Straight sided splines have the advantage of being easier to make and design than involute splines. Straight sided splines are not as standardized as involute splines, t or f?
True
Most common straight side spline is the SAE type, which is available in 4 series..what are the 4
-4 spline
-6 spline (3/4-3in dia)
-10 spline
-16 spline (3/4 - 6in dia)
On a ___ spline, the sides of the teeth contact each other. Clearance exists between the top and bottom of the mating teeth
Side fit
On a ___ fit spline, no clearance exists between the major dia of the external spline and the major dia of the internal spline, the sides of the teeth act as drivers. Only used with 30deg pressure angle
Major diameter fit
3 standard pressure angles on splines
30 - most common
37.5
45
The ___ denotes the radial distance from the pitch circle to the major diameter of the external spline or distance from the pitch circle to the minor diameter of an internal spline
Stub pitch
A spline is identified by the # of teeth. For example, a spline having 6 teeth is called a six spline, t or f
True
Some precautions should be taken when manufacturing long splines. Do not attempt to machine splines to finish size one at a time. Always take roughing and finishing cuts and mill on opposite sides, t or f?
True
The purpose of a ___ is to make production work faster and more accurate, it quickly positions a workpiece in relation to the cutting tool, thereby eliminating the need for a layout
Fixture
Fixtures does not guide the cutting tool, although some fixtures have a ___ for aligning the tool with the workpiece. Fixtures are typically used in milling machines, lathes and grinders
Setting block
3 advantages of using a fixture
-Semi skilled operates can mass produce parts using fixtures
-parts in a fixture are interchangeable
-skilled machinist can use a fixture to hold a wp that may be difficult or impossible to hold any other way
A __ locates and holds the workpiece and guides the cutting tool. Typically used on drill presses
Jig
The purpose ofna fixture is to prevent the workpiece from moving or rotating in space. There are 6 ways an object can move called the ___
Degrees of freedom
The ability to move in a straight line along an axis is called a ___. There are 3 axis to move along (x,y,z) so there are 3 __
Freedom of translation
The ability to rotate around an axis is called ___. There are 3 axes to rotate around so there are 3 ___
Freedom of rotation
Sometimes a workpiece can be put into a fixture more than one way. If so, use a ___ or other similar feature to make it impossible to load the wp incorrectly
Fouling pin
3 parts of a fixture
-base aka frame
-locators
-clamps
The ___ also known as a frame, is the underlying structure of the fixture. Can be custom made from cast iron or a general purpose one can be purchased from a catalogue
Base
___ ensure the workpiece is held in it’s correct orientation. They can take many forms, depending on the nature of the wp
Locators
___ hold the workpiece in place against the locators. Like bases and locators, it can be custom made or bought from a catalogie
Clamps
The most efficient way to locate a workpiece is to use a __ in a cylindrical feature on the wp such as a reamed hole
Cylindrical locator
A __ is used for locating against outside diameter of a cylindrical feature on the workpiece
Vee locator
Irregular workpieces like castings and forgings can be positioned by visually lining them up with a ___
Sighting plane
A __ or 2 point clamp is designed to clamp 2 wp at the same time
C- clamp
Single or plain fixtures hold only 1 wp at a time and multiples fixtures hike several identical wp at the same time
T or f?
True
A ___ fixture holds several workpieces in a line so they can all be machined in 1 pass of the cutter.
String milling fixture
Most turning and boring fixtures are mounted on the faceplate of a lathe, but few are mounted directly to the spindle, t or f?
True
___ fixtures are used on cylindrical grinders, surface grinders, tool and cutter grinders
Grinding
