module 1-1 - mwf applications

7/25/2019 Module 1-1 - MWF Applications

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2014 STLENot to be distributed, copied, or replicated without express written consent of STLE.


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1. Talk about how different customers look at and view cost.

1. A coolant may represent a small percentage of the manufacturing

budget when it is operating well. However, if the coolant is

contaminated with sediment or tramp oils, then tool life part quality

suffers. If the coolant is very bad, its possible that no machining cantake place and, in effect, literally shut down the process. Now that

coolant is very, very expensive.

2. Discuss the issue of Not in my budget! Coolants often show up as a

maintenance cost and not as a direct production cost.



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1. Often, its not the cost of the tool that is expensive, it is the downtime and scrap

rate related to the replacement of the tool. Often, a tool change is preceded by an

increase in out-of-spec parts or followed by out-of-spec while the new tool is

adjusted to the proper dimension.

2. Safety with any chemical that you are exposed to (externally and internally)becomes a personal issue. As a personal issue, it becomes an emotional decision.

3. Cost is not only the price per gallon of the metalworking fluid, it is also the impact

on tool wear, part microfinish, impact on measurement systems, and final disposal.

All too often, the lowest cost per gallon coolant translates into the highest cost of

manufacturing.



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1. 80 to 90% of all trials are decided by non-cutting issues and the $ per gallon

issue.

2. The reason for this is many trials are not capable of looking at the cutting

issues directly. As a result, the sensory issues (smell, feel, residue) become

the deciding factors.



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Different coolant chemistries enable different levels of robustness. In other

words, some metal working fluids are able to tolerate high levels of tramp oil

before there is an irreversible adverse effect on the machining performance. At

low concentrations, some fluids have good rust preventative qualities and

others dont.



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1. This is the current mantra of cutting tool suppliers and we will see why it

makes sense in some situations.

2. To run dry, the incoming blanks size and metallurgy (hardness and micro

structure) must be within a well controlled window and machine tool setup.

3. All things being equal, running dry will typically generate a cost ofmanufacturing about 20% higher than if a metalworking fluid was used.



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Repeating the main reasons for using a cutting fluid.



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This is a chip being separated from the blank.



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This is a close up of the previous chip. You can see the plane of deformation which is

where a chip is born.



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This is where the cutting tool was positioned in order to make this chip.



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Between the Part Finished Surface and the Tool Flank or Land, there is a clearance

angle. When the tool is sharp, the clearance angle exists right up to the cutting edge.

As the tool wears on the flank (land) the clearance angle is pushed backward and the

flat section of the worn tool drags on the machined surface.



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1. As the tool is forced through the part metal, the material directly in front of the tool

is compressed. This causes a slip plane called the Plane of Deformation.

2. The plane of deformation is where the metallic crystalline structure is wrenched

apart. The energy released during the peeling of the chip along the Plane of

Deformation accounts for about 60% of the heat generation of the machining process.3. A dimensionally longer Plane of Deformation required more energy required to make

the slip planes. As a result, the overall temperature of the chipmaking process

increases. This heat draws down the hardness of the edge of the cutting tool.



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These three cracks are residual stresses left in the part from the compressive force.



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The white arrow points out the affects of the cutting forces in that the part metallurgy

preceding the cutting tool edge is being affected. If the chip meets resistance as it

drags across the face of the tool, a plowing effect develops which increases pressures

on the tool face, increases the energy (increasing the process heat levels).



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Uptime or spindle time is a good barometer of the efficiency of a machine shop.



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1. The insert on the top has 8 individual cutting points. Two are shown here. One of

them has the BUE evidence remaining while the other edge has lost the BUE

evidence. The chipped edge was formed when the BUE was whisked away, taking

some of the tool substrate with it.

2. The tool on the bottom was used to machine titanium. Titanium is a difficult,squirmy material to machine and has a tendency to form a BUE. This photo is

looking directly at the face of the tool where the chip is formed.



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1. There are 14 fairly distinctive wear patterns that precede the tool failure mode.

2. Chips can be read to understand the nature of the chip curl and the pressure its

formation puts on the tool.

3. Vibration, especially in high speed (over 8,000 RPM) is an instant death sentence of

a cutting edge. The fluctuation in the pressures on the tool face and cutting edgecreate an audible signal that can be recorded, filtered and analyzed.

4. Power or Horsepower is an indirect measurement of the tool wear and machine

tool setup.



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1. These pictures demonstrate 6 very different failure modes on tools.

2. Each wear pattern can be read to understand the conditions in the cutting zone.

1. Flank wear is from the finished workpiece surface dragging along the land

(flank) of the tool.

2. Thermal shock is a fatigue failure caused by rapid changes in the cuttingedge temperature. Intermittent coolant splashing will cause. Wet parts

introduced to a dry machining operation will create this wear pattern.

3. Diffusion wear is due to the Extreme Pressure film failing. The backside of

the chip is creating friction temperatures that exceed the film strength of the

EP additives.

4. A built up edge is caused by the workpiece material welding to the face of

the tool.

5. Chipping such as this pattern is usually related to high frequency vibrations.

These vibrations can be recorded, filtered and analyzed to determine if theyare generated by natural frequency, tool impact frequency, or looseness in

the part fixture or spindle.



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1. Clockwise

1. This is a tight curled chip indicating good chip formation

2. This is a small, stringy chip with poor chip formation with unpredictable tails

3. These stringy chips cause machining problems with fixtures and spindles.

They wrap around the tools and parts interfering with coolant flow andautomatic part handling equipment. They can also clog in-ground coolant

trenches.

4. This chip is showing the slip planes or planes of deformation.



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Acoustically speaking, the top graph indicates a smooth cut, while the lower graph

depicts a noisy vibration. Cutting edges of tools do not cope well with noisy vibrations.



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The horsepower needed to make the chip can be calculated. If the machine tool

cannot deliver the level of horsepower needed to meet the chip formation energy, the

machine will vibrate or stall. If there is vibration at lower RPM, some of the machine

tool horsepower is used to create this vibration, thereby decreasing the available

horsepower needed to make the chip.



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1. In 1906, Taylor presented his epoch-making paper, "On the Art of Cutting Metals,"

before the American Society of Mechanical Engineersas his presidential address. It

was the result of twenty-six years of experimentation during which time more than

800,000 pounds of steel and iron were cut up into chips with experimental tools.

Some 30,000 to 50,000 recorded experiments were carried out, in addition to manyothers not recorded. Aided golfers with subsurface irrigation techniques for greens.

2. Taylor developed this equation after controlled experiments of measuring

temperature in the cutting zone (via thermal dynamic analysis of heat travel in a

cutting tool) and the resulting tool life.

3. In a nutshell, there is an inverse, exponential relationship between the cutting edge

temperature and the life of the tool. In other words, a small reduction in the

cutting zone temperature results in a large increase in tool life.



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The reason tool life decreases as the cutting edge temperature increases is that tools

become softer at higher temperatures.



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Coolants impact the cutting zone in 3 ways. Next slide quickly.



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1. In the left picture, the drag zone where the tool land drags on the freshly machined

surface (number 1) doesnt exist as it does in the right hand picture. Thats because

the tool is sharp.

2. As the tool wears in the right hand picture, area #1 increases as the tool wears

down. This wear accelerates as you would expect as temperatures rise.



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1. We know that by changing the lubricity characteristics of the metalworking fluid, we

can affect the movement of the chip as it slides up the face of the tool

2. In the left picture, there is a high coefficient of friction (CoF) between the backside

of the chip and the face of the tool.

3. This drag forces the chip to back into itself creating a longer plane of deformation(as compared to the right hand picture with a low CoF.

4. The shear angle (that angle between the plane of deformation and the direction of

the tool) will become smaller with a HIGH CoF.

5. A longer plane of deformation simply has more metallic crystalline structure to

break apart and results in higher horse power requirements, higher heat generation

as the chip is wrenched from the part blank.

6. 80% of all machining problems are related to the coolant not getting into the

cutting zone. Coolant nozzles must force coolant up the land (clearance angle) and

up the face of the tool between the backside of the chip and face of the tool.Proper application will reduce the CoF, enabling a larger shear angle to develop.



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1. Both pictures are of the same tool, cutting the same material at the same surface

feet per minute. We are cutting M2 tool steel at 28 Rockwell C (Rc) and the tool

is made from M2 tool steel heat treated to 65 Rc.

2. The chip thickness on the left was generated with a lower Coefficient of Friction

compared to the chip in the right side picture.



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1. Coolant is most often used as the tool to move chips out of the work area

and transport them.

2. Most central systems are cost justified based on chip handling not coolant

management.

3. This is unfortunate as there is a holistic system that is being overlooked.



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A freshly machined surface is chemically active ready to react with oxygen.



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Movie here



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Movie Here



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Reamers are used for generating very accurate diameters and surface finishes. They

are used to clean up a drilled hole and to size it within 0.0005 inches (0.0127mm) or

about 13 microns.



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This is a cutting tap. Notice the chip formation. The stringy chips may pose a

transportation problem if they are allowed to entwine and wrap around the tool.

These chips will be difficult to move through a trench. Thats why small broken chips

are preferred.



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Flat form threading does not create a chip, but actually compresses a threaded finish.



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Die threading is a means of generating a tapped thread on the outside diameter. Like

tapping an internal hole, only its done on the outside of a part. Pipe threading comes

to mind.



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There are two fundamentally different types of taps. Both make a thread, except one

does not generate a chip. The tap on the left is a cutting tap and makes a chip. The

form tap on the right does not make a chip, but requires more lubrication as it rolls or

slides through the hole. You can tell the difference by looking at the largest diameter of

the tool. The largest diameter on the form tap on the right isnt a cutting edge. On thecutting tap on the left, the largest diameter is a cutting edge. A formed thread is

typically much stronger and resists stripping and pull out better than a cut thread.



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Drilling describes several method of making a hole in a blank. Twist drills are very

common. Single point insert drilling is sometimes called boring (no pun intended).

Spade drills often have coolant fed through the tool for deep drilling operations.



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Movie Here



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Yes, we know its boring (pun intended here.)



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Grooving on a lathe doesnt mean its a groovy process. (Groan!)



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There are two ways to do milling, one is conventional milling where the cutter cuts the

chip upwards. Climb milling cuts the chip downwards. In conventional milling, the chip

thickness and tool load varies during the cut, while with climb milling the chip load and

pressures are constant. Climb milling is faster, but require more horsepower and a

more rigid spindle/tool/fixture set up.



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An end mill is not a drill, in spite of some similarities. Typically, an end mill has a flat

bottom. Some have a round bottom, but none have a pointed bottom as you would

find in a drill.



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It is called centerless since the workpiece is not held between centers, but allowed to

float. Centerless grinding is used when a round workpiece is required. The 3 point

positioning creates a round object. The regulating wheel spins the part which rests on

the work rest blade.



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Movie Here



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This grinding method is called cylindrical grinding. The workpiece is held between

centers. Notice the automatic gaging feelers. Good flooding is essential for keeping

the feelers free of swarf.



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Movie Here



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Movie Here



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This is surface grinding. Notice the spark stream when there is no coolant present.

When the coolant flood is turned on, the spark stream disappears. Whenever you see

a spark stream, even when there is coolant flowing, it means that the coolant is NOT

getting into the cutting zone. If you see a spark stream when coolant is flowing, it

means that the coolant is not entering the cutting zone with enough force or velocity topenetrate properly.

The spark stream means that the workpiece may burn, altering the surface quality and

condition. It also means that the wheel is running hot and that the binder that holds

the grit grains in place will fail faster than if it were cooled properly with coolant. In

extreme cases, the hot parts will change dimension when they cool, affecting part

quality and consistency.



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Lapping is very similar to grinding.



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Another way to look at lapping.



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Mass finishing is the same as vibratory finishing.



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Movie Here



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Superfinishing is not unlike honing.



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Movie here



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A lubricant is needed here to prevent the part from welding to the dies.



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Movie Here



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Lubricants are used here mainly for die sliding purposes. The blank is actually broken in

a controlled fashion.



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Movie Here



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Lubricants here are to protect the sliding die in the center from picking up (welding)

workpiece particles. Welded particles will leave score lines in the blanked part.



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Here, too, the lubricant is used to reduce wear on the die block.



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Lubricant here is used to enable the bent sides to slide without binding on the female

die.



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Lubricants are used here to facilitate the sliding of the tube around the forming die. It

is used to help prevent the tube from pinching.



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Lubricant is used here to prevent galling (metal pick up) of the workpiece material to

the upper and lower dies. Without a lubricant, the metal would tear or stretch, leaving

a thin wall region.



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module 1-1 - mwf applications

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