manufacturing processes 1wec. cutting cutting is the separation of a physical object, or a portion...

MANUFACTURING PROCESSESMANUFACTURING PROCESSES

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WECWEC

Cutting Cutting is the separation of a physical object, or a

portion of a physical object, into two portions, through the application of an acutely directed force.

Cutting is a compressive and shearing phenomenon, and occurs only when the total stress generated by the cutting implement exceeds the ultimate strength of the material of the object being cut.

The simplest applicable equation is stress = force/area: The stress generated by a cutting implement is directly proportional to the force with which it is applied, and inversely proportional to the area of contact.

Hence, the smaller the area (i.e., the sharper the cutting implement), the less force is needed to cut something.

Cutting Tools In the context of machining, a cutting

tool or cutter is any tool that is used to remove material from the workpiece by means of shear deformation.

Cutting may be accomplished by single-point or multipoint tools. Single-point tools are used in turning, shaping, plaining and similar operations, and remove material by means of one cutting edge.

Milling and drilling tools are often multipoint tools. Grinding tools are also multipoint tools.

Each grain of abrasive functions as a microscopic single-point cutting edge

Cutting tools

Cutting Tool Requirements

Single point cutting tool – Tool Bit The term tool bit generally refers to a

non-rotary cutting tool used in metal lathes, shapers, and planers.

Such cutters are also often referred to by the set-phrase name of single-point cutting tool (one edge for cutting).

The cutting edge is ground to suit a particular machining operation and may be re-sharpened or reshaped as needed.

Various tool bits, carbide inserts and holders

Single point tool Geometry

Single point tool Geometry Back Rake is to help control the direction of the

chip, which naturally curves into the work due to the difference in length from the outer and inner parts of the cut.

Side Rake along with back rake controls the chip flow and partially counteracts or prevents the resistance of the work to the movement of the cutter and can be optimized to suit the particular material being cut.

Brass for example requires a back and side rake of 0 degrees while aluminum uses a back rake of 35 degrees and a side rake of 15 degrees.

Single point tool Geometry Nose Radius makes the finish of the cut smoother as it can overlap the previous cut and eliminate the peaks and valleys that a pointed tool produces. Having a radius also strengthens the tip, a sharp point being quite fragile.

All the other angles are for clearance in order that no part of the tool besides the actual cutting edge can touch the work.

The front clearance angle is usually 8 degrees while the side clearance angle is 10-15 degrees and partly depends on the rate of feed expected.

Tool Geometry

Multipoint Cutting Tools

Twist Drill

Twist drills are rotary cutting tools that normally have two cutting edges and two flutes which are grooves formed in the body to provide cutting lips, to permit the removal of chips and to allow coolant or cutting fluid to reach the cutting action.

It is made from a round bar of tool material , and has three principles parts: the point, the body and the shank. The drill is held and rotated by its shank. The point comprises the cutting elements while the body guides the drill in the operation. The body of the drill has two helical grooves called “ flutes”. The flutes from the cutting surface and also assist in removing chips out of the drilled hole.

Broach Broaching is a machining process that uses a toothed

(saw like) tool, called a broach, to remove material. A broach merely a long tool with multiple cutting

elements on it. A broaching tool may be pulled or pushed along a workpiece. It must be noted that each cutting element on the broach tool is slightly larger than the previous one.

There are two main types of broaching: linear and rotary. In linear broaching, which is the more common process,

the broach is run linearly against a surface of the workpiece to effect the cut.

In rotary broaching, the broach is rotated and pressed into the workpiece to cut an axis symmetric shape.

A rotary broach is used in a lathe or screw machine. In both processes the cut is performed in one pass of the broach, which makes it very efficient.

Tooling hardness and temperature

Tool Life Tool life is the time a tool can be constantly be

used for cutting before it must be discarded/repaired.

Looking at the three main machining parameters, speed, feed, and depth of cut, each has an effect on tool life. For best tool life:

Optimize ap (to reduce the number of cuts)

Optimize fn (for shortest cutting time)

Reduce vc (to reduce heat)

Tool Life There are three possible modes by which a cutting tool

can fail in machining:

Fracture failure: This mode of failure occurs when the cutting force at the tool point becomes excessive, causing it to fail suddenly by brittle fracture.

Temperature failure: This failure occurs when the cutting temperature is too high for the tool material, causing the material at the tool point to soften, which leads to plastic deformation and loss of the sharp edge.

Gradual Wear: Gradual wearing of the cutting edge causes loss of tool shape, reduction in cutting efficiency and finally tool failure in a manner similar to a temperature failure.

Tool Materials

High speed steel Tungsten carbide Cemented carbide Cermet Alumina ceramics Sintered polycrystalline diamond Cubic boron nitride

ASSIGNMENT # 2

WRITE DOWN THE PROPERTIES OF THESE TOOL MATERIALS?

Cutting Fluids – Types & Properties

Mill cutters

Milling cutters are cutting tools used in milling machines or machining centres. They remove material by their movement within the machine (eg: a ball nose mill) or directly from the cutters shape (a form tool such as a Hobbing cutter).

Milling Cutters

Features of a milling cutter Milling cutters come in several shapes and many

sizes. There is also a choice of coatings, as well as rake angle and number of cutting surfaces.

Shape: Several standard shapes of milling cutter are used in industry today, which are explained in more detail below.

Flutes / teeth: The flutes of the milling bit are the deep helical grooves running up the cutter, while the sharp blade along the edge of the flute is known as the tooth. The tooth cuts the material, and chips of this material are pulled up the flute by the rotation of the cutter. There is almost always one tooth per flute, but some cutters have two teeth per flute.

Often, the words flute and tooth are used interchangeably. Milling cutters may have from one to many teeth, with 2, 3 and 4 being most common. Typically, the more teeth a cutter has, the more rapidly it can remove material. So, a 4-tooth cutter can remove material at twice the rate of a 2-tooth cutter.

Features of a milling cutter Helix angle: The flutes of a milling cutter are

almost always helical. If the flutes were straight, the whole tooth would impact the material at once, causing vibration and reducing accuracy and surface quality. Setting the flutes at an angle allows the tooth to enter the material gradually, reducing vibration. Typically, finishing cutters have a higher rake angle (tighter helix) to give a better finish.

Center cutting: Some milling cutters can drill straight down (plunge) through the material, while others cannot. This is because the teeth of some cutters do not go all the way to the centre of the end face. However, these cutters can cut downwards at an angle of 45 degrees or so.

Features of a milling cutter Roughing or Finishing: Different types of

cutter are available for cutting away large amounts of material, leaving a poor surface finish (roughing), or removing a smaller amount of material, but leaving a good surface finish (finishing). A roughing cutter may have serrated teeth for breaking the chips of material into smaller pieces. These teeth leave a rough surface behind. A finishing cutter may have a large number (4 or more) teeth for removing material carefully. However, the large number of flutes leaves little room for efficient swarf removal, so they are less appropriate for removing large amounts of material.

Features of a milling cutter Coatings: The right tool coatings can have a great influence

on the cutting process by increasing cutting speed and tool life, and improving the surface finish. Polycrystalline Diamond (PCD) is an exceptionally hard coating used on cutters which must withstand high abrasive wear. A PCD coated tool may last up to 100 times longer than an uncoated tool. However the coating cannot be used at temperatures above 600 degrees C, or on ferrous metals. Tools for machining aluminium are sometimes given a coating of TiAlN. Aluminium is a relatively sticky metal, and can weld itself to the teeth of tools, causing them to appear blunt. However it tends not to stick to TiAlN, allowing the tool to be used for much longer in aluminium.

Shank: The shank is the cylindrical (non-fluted) part of the tool which is used to hold and locate it in the tool holder. A shank may be perfectly round, and held by friction, or it may have a Weldon Flat, where a grub screw makes contact for increased torque without the tool slipping. The diameter may be different from the diameter of the cutting part of the tool, so that it can be held by a standard tool holder.

An End Mill cutter with two flutes

Types of milling cutters

End Mill End mills (middle row in image) are those

tools which have cutting teeth at one end, as well as on the sides. The words end mill are generally used to refer to flat bottomed cutters, but also include rounded cutters (referred to as ball nosed) and radiused cutters (referred to as bull nose, or torus). They are usually made from high speed steel (HSS) or carbide, and have one or more flutes. They are the most common tool used in a vertical mill.


Slot drill Slot drills (top row in image) are generally

two (occasionally three or four) fluted cutters that are designed to drill straight down into the material. This is possible because there is at least one tooth at the centre of the end face. They are so named for their use in cutting keyway slots. The term slot drill is usually assumed to mean a two fluted, flat bottomed end mill if no other information is given. Two fluted end mills are usually slot drills, three fluted sometimes are not, and four fluted usually are not.


Roughing end mill Roughing end mills quickly remove large

amounts of material. This kind of end mill utilizes a wavy tooth form cut on the periphery. These wavy teeth form many successive cutting edges producing many small chips, resulting in a relatively rough surface finish. During cutting, multiple teeth are in contact with the workpiece reducing chatter and vibration. Rapid stock removal with heavy milling cuts is sometimes called hogging. Roughing end mills are also sometimes known as ripping cutters.


Ball nose cutter Ball nose cutters (lower row in image) are

similar to slot drills, but the end of the cutters are hemispherical. They are ideal for machining 3-dimensional contoured shapes in machining centres, for example in moulds and dies. They are sometimes called ball mills in shop-floor slang, despite the fact that that term also has another meaning. They are also used to add a radius between perpendicular faces to reduce stress concentrations.


Slab Mill Slab mills are used either by

themselves or in gang milling operations on manual horizontal or universal milling machines to machine large broad surfaces quickly. They have been superseded by the use of carbide-tipped face mills which are then used in vertical mills or machining centres.


The side-and-face cutter The side-and-face cutter is designed

with cutting teeth on its side as well as its circumference. They are made in varying diameters and widths depending on the application. The teeth on the side allow the cutter to make unbalanced cuts (cutting on one side only) without deflecting the cutter as would happen with a slitting saw or slot cutter (no side teeth).


Involute gear cutter There are 8 cutters (excluding the

rare half sizes) that will cut gears from 12 teeth through to a rack (infinite diameter).


Hob These cutters are a type of form tool

and are used in hobbing machines to generate gears. A cross section of the cutters tooth will generate the required shape on the workpiece, once set to the appropriate conditions (blank size). A hobbing machine is a specialised milling machine.


Face mill A face mill consists of a cutter body (with

the appropriate machine taper) that is designed to hold multiple disposable carbide or ceramic tips or inserts, often golden in color. The tips are not designed to be resharpened and are selected from a range of types that may be determined by various criteria, some of which may be: tip shape, cutting action required, material being cut. When the tips are blunt, they may be removed, rotated (indexed) and replaced to present a fresh, sharp face to the workpiece, this increases the life of the tip and thus their economical cutting life.


Fly cutter A fly cutter is composed of a body into which

one or two tool bits are inserted. As the entire unit rotates, the tool bits take broad, shallow facing cuts. Fly cutters are analogous to face mills in that their purpose is face milling and their individual cutters are replaceable. Face mills are more ideal in various respects (e.g., rigidity, indexability of inserts without disturbing effective cutter diameter or tool length offset, depth-of-cut capability), but tend to be expensive, whereas fly cutters are very inexpensive.


Woodruff cutters make the seat for woodruff keys. These keys locate pulleys on shafts.


Hollow mill Hollow milling cutters, more often called

simply hollow mills, are essentially "inside-out endmills". They are shaped like a piece of pipe (but with thicker walls), with their cutting edges on the inside surface. They are used on turret lathes and screw machines as an alternative to turning with a box tool, or on milling machines or drill presses to finish a cylindrical boss (such as a trunnion).


Dovetail cutter A dovetail cutter is an endmill whose

form leaves behind a dovetail slot.

Tool Materials

Steels Originally, all tool bits were made of high carbon tool steels

with the appropriate hardening and tempering. Since the introductions of high-speed steel (HSS) (early years of the 20th century), sintered carbide (1930s), ceramic and diamond cutters, those materials have gradually replaced the earlier kinds of tool steel in almost all cutting applications. Most tool bits today are either HSS or carbide.

Carbides and ceramics Carbide, ceramics (such as cubic boron nitride) and

diamond, having higher hardness than HSS, all allow faster material removal than HSS in most cases. Because these materials are more expensive and brittler than steel, typically the body of the cutting tool is made of steel, and a small cutting edge made of the harder material is attached. The cutting edge is usually either screwed on (in this case it is called an insert), or brazed on to a steel shank (this is usually only done for carbide).

Tool Materials

High Speed steel (HSS)

Cemented Carbides

Inserts

Almost all high-performance cutting tools use indexable inserts. There are several reasons for this. First of all, at the very high cutting speeds and feeds supported by these materials, the cutting tip can reach temperatures high enough to melt the brazing material holding it to the shank. Economics are also important; inserts are made symmetrically so that when the first cutting edge is dull they can be rotated, presenting a fresh cutting edge. Some inserts are even made so that they can be flipped over, giving as many as 16 cutting edges per insert. There are many types of inserts: some for roughing, some for finishing. Others are made for specialized jobs like cutting threads or grooves. The industry employs standardized nomenclature to describe inserts by shape, material, coating material, and size.

Form tools

A form tool is precision-ground into a pattern that resembles the part to be formed. The form tool can be used as a single operation and therefore eliminate many other operations from the slides (front, rear and/or vertical) and the turret, such as box tools. A form tool turns one or more diameters while feeding into the work. Before the use of form tools, diameters were turned by multiple slide and turret operations, and thus took more work to make the part. For example, a form tool can turn many diameters and in addition can also cut off the part in a single operation and eliminate the need to index the turret. For single-spindle machines, bypassing the need to index the turret can dramatically increase hourly part production rates.

Form tools

On long-running jobs it is common to use a roughing tool on a different slide or turret station to remove the bulk of the material to reduce wear on the form tool.

There are different types of form tools. Insert form tools are the most common for short- to medium-range jobs (50 to 20,000 pcs). Circular form tools are usually for longer jobs, since the tool wear can be ground off the tool tip many times as the tool is rotated in its holder. There is also a skiving tool that can be used for light finishing cuts. Form tools can be made of cobalt steel, carbide, or high-speed steel. Carbide requires additional care because it is very brittle and will chip if chatter occurs

Form tools

A drawback when using form tools is that the feed into the work is usually slow, 0.0005" to 0.0012" per revolution depending on the width of the tool. Wide form tools create more heat and usually are problematic for chatter. Heat and chatter reduces tool life. Also, form tools wider than 2.5 times the smaller diameter of the part being turned have a greater risk of the part breaking off. [1] When turning longer lengths, a support from the turret can be used to increase turning length from 2.5 times to 5 times the smallest diameter of the part being turned, and this also can help reduce chatter. Despite the drawbacks, the elimination of extra operations often makes using form tools the most efficient option.

Form tool

Factors which effect tool life & Tool life relationshipTool Wear Tool wear describes the gradual failure of

cutting tools due to regular operation. It is a term often associated with tipped tools, tool bits, or drill bits that are used with machine tools

Types of wear include: flank wear in which the portion of the tool in

contact with the finished part erodes. Can be described using the Tool Life Expectancy equation.

crater wear in which contact with chips erodes the rake face. This is somewhat normal for tool wear, and does not seriously degrade the use of a tool until it becomes serious enough to cause a cutting edge failure.

Factors which effect tool life & Tool life relationshipTool WearCan be caused by spindle speed that is too low or a feed rate that

is too high. In orthogonal cutting this typically occurs where the tool temperature is highest. Crater wear occurs approximately at a height equaling the cutting depth of the material. Crater wear depth ~ t0 t0= cutting depth

Built-up Edge in which material being machined builds up on the cutting edge. Some materials (notably aluminum and copper) have a tendency to anneal themselves to the cutting edge of a tool. It occurs most frequently on softer metals, with a lower melting point. It can be prevented by increasing cutting speeds and using lubricant. When drilling it can be noticed as alternating dark and shiny rings.

Glazing occurs on grinding wheels, and occurs when the exposed abrasive becomes dulled. It is noticeable as a sheen while the wheel is in motion.

Edge Wear, in drills, refers to wear to the outer edge of a drill bit around the cutting face caused by excessive cutting speed. It extends down the drill flutes, and requires a large volume of material to be removed from the drill bit before it can be corrected.

Effects of Tool Wear

Some General effects of tool wear include: Increased cutting forces Increased cutting temperatures Poor surface finish Decreased accuracy of finished part Reduction in tool wear can be accomplished

by using lubricants and coolants while machining. These reduce friction and temperature, thus reducing the tool wear.

Tool Life Expectancy The Taylor Equation for Tool Life

Expectancy provides a good approximation.

Crater Wear

Temperature Considerations At high temperature zones crater

wear occurs. The highest temperature of the tool can exceed 700 °C and occurs at the rake face whereas the lowest temperature can be 500 °C or lower depending on the tool.ram

Energy Considerations

Energy comes in the form of heat from tool friction. It is a reasonable assumption that 80% of energy from cutting is carried away in the chip. If not for this the workpiece and the tool would be much hotter than what is experienced. The tool and the workpiece each carry approximately 10% of the energy. The percent of energy carried away in the chip increases as the speed of the cutting operation increases. This somewhat offsets the tool wear from increased cutting speeds. In fact, if not for the energy taken away in the chip increasing as cutting speed is increased; the tool would wear more quickly than is found.

Temperature gradient of tool, workpiece and chip during orthogonal cutting. As can easily be seen, heat is removed from the workpiece and the tool to the chip. Crater wear occurs around the 720 degree area of the tool.

manufacturing processes 1wec. cutting cutting is the separation of a physical object, or a portion...

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