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Machine Tool Geometry
Transcript of Machine Tool Geometry
Machining would be very difficult, if not impossible, without the use of proper cutting tools. They are one of the most crucial elements in the process of machining any material, from plastic and aluminum or steel, to any of the various superalloys. There is a lot of information about cutting tools to go over. This presentation is just an overview of what you will learn in this class.
Cutting Tool Material
The workpiece material is one of the factors in choosing what type of cutting tool to use.
Single PoingTool Geometry
-Tool Geometry: The specific shape and orientation of a cutting tool in relation to the workpiece
-Remove the most amount of material in the least amount of time.
-Prolong the life of the cutting tool.
-Create the best possible surface finish.
-The goal is to find the tool geometry that best matches a particular machining operation.
Milling Tool Geometry
Carbide Tool Grade Selection
CARBON TOOL STEELS
FIRST TYPE OF TOOL USED IN MACHINING
LOW WORKING TEMPERATURE: SLOW
NOW USED FOR INEXPENSIVE TOOLS
TWO MAJOR TYPES: TUNGSTEN
NON FERROUS CAST ALLOY
-CANNOT BE HEAT TREATED... NO IRON
-CAST AND GROUND INTO SHAPE
-NO HARDER THAN HSS AT ROOM TEMP
-STAYS HARD AT HIGHER TEMP THAN HSS
-HARDER BUT LESS TOUGH THAN CARBIDE
CUBIC BORON NITRIDE
HARDER BUT LESS TOUGH THAN CERAMIC
WORKS AT 5X THE RATE OF CARBIDE
SINGLE CRYSTAL DIAMOND
POLYCRYSTALLINE DIAMOND (PCD)
HARDEST KNOWN MATERIAL
MOST COSTLY CUTTING TOOL
CAN NOT MACHINE FERROUS METALS
VERY VERY VERY BRITTLE
-CARBIDE IS A "CERMET" OR, A CERAMIC AND METAL ALLOY
-TWO MAJOR TYPES: TUNGSTEN CARBIDE
-MADE FOR MORE RIGID CNC MACHINES
-HARDER BUT LESS TOUGH THAN HSS
Back Rake Angle
SIDE RAKE ANGLE
Viewed down the length of the tool holder
Basic single point turning operation
FACE AND FLANKS
BASIC SINGLE POINT TOOL
viewed from the end of the workpiece
End Relief Angle
Side Relief Angle
Cutting Edge Angle
End Cutting Edge Angle
Side Cutting Edge Angle
Positive / Negative
All carbides are composites that combine ceramic particles in a metallic binder,
What is Carbide?
Because carbide tools effectively balance toughness with hardness, they can be used for both continuous and interrupted cuts. This is a distinct advantage over other tool materials. For example, HSS tools are not hard enough to be effectively used for continuous cuts. Ceramics are not tough enough for interrupted cuts.
Common Uses of Carbides
The original carbide cutting tools contained
(WC), which used cobalt as the metallic binder. Tungsten carbide tools are very hard, but they tend to crater if they are used to machine steel. Figure 1 shows a crater that formed on the face of the tool.
Eventually, manufacturers developed carbide tools containing
(TiC), which is very effective at resisting cratering. Pure titanium carbide tools are not as hard as tungsten carbide. Consequently, cutting tools are also made that contain a combination of both carbides in order to blend hardness with crater resistance.
Nowadays, manufacturers produce tools containing all sorts of different carbide combinations. Cobalt is still used as the metallic binder. A common carbide added to tools is
(TaC), which increases hot hardness. Other materials may be added as well. Manufacturers are continually tinkering with various carbide recipes to create cutting tool grades with improved properties.
Types of Carbide
Carbide cutting tools are made by a process called sintering.
(TiN) increases crater resistance and reduces the friction between the workpiece and cutting tool.
(Al2O3) helps to prevent the abrasive wear of the tool and allows higher cutting speeds.
(TiC) increases wear resistance and strengthens the bond between the coating and the material.
Titanium nitride (TiN) increases crater resistance and reduces the friction between the workpiece and cutting tool.
Aluminum oxide (Al2O3) helps to prevent the abrasive wear of the tool and allows higher cutting speeds.
Titanium carbide (TiC) increases wear resistance and strengthens the bond between the coating and the material.
C1 through C4 grades are best used to machine cast irons, nonferrous alloys, and materials yielding short chips. These tools contain tungsten carbide for improved wear resistance.
C5 through C8 grades are best used to machine the various grades of steel. These tools contain additions of titanium carbide and tantalum carbide to reduce cratering.
American National Standards Institute
P grades are best suited for the various steels. These tools operate at the highest speeds. Blue designates a P grade tool.
M grades are intermediate grades best suited for ductile irons, harder steels, stainless steels, and high-temperature alloys. Yellow designates an M grade tool.
K grades are best suited for cast irons and nonferrous metals. These tools operate at the highest feeds. Red designates a K grade tool.
International Organization for Standardization
Economics of Machining
Though tools made of high-speed steel often cost less than carbide tools, the improved material removal rate of carbide tools often makes them the most economical choice for many materials.
Drilling is a metal cutting process that involves rotating a cylindrical tool at high rates of speed in order to create a hole in a workpiece. A drill is designed to reproduce its own diameter by removing metal. A twist drill removes relatively more metal than any other cutting tool. Although precise work can be performed by drilling, it is often followed by finishing operations such as reaming, boring, and grinding.
is the end of a drill that is held in a chuck or collet and is rotated by a machine workhead during drilling.
is an optional flattened portion of the shank end that locks the drill into the driving mechanism of the machine tool. The tang allows more secure holding of taper shank drills.
of the drill is the end opposite the shank. The body diameter is usually about 0.003 in. smaller than the shank diameter.
The body has two helical flutes that act as passageways for coolant to get into the hole and for chip evacuation from the hole during drilling.
The angle of a flute is called the helix angle,
which varies from 10° to 52 degrees. The helix angle is measured from a flute down to a line parallel to the axis of the drill (Figure 3).
is the conical end of the drill opposite the tang and shank.
Hss works better with ductile stringy material, like stainless steel.
Harder grade of steel, tool steels, cast iron and super alloys require a harder tool, such as carbide, CBN, Ceramic, or diamond.
Carbide is by far the most common cutting tool material, because it balances the hardness and toughness necessary to cut most workpiece materials.
whatever your workpiece material may be, chances are there is a type of carbide that will cut it.