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Tips of better Use
Nomenclature & Tips of better Use:
Given below showing important feature of a Broaches

 Pull end -
This is the end of broach, which engages to the puller of the broaching machine

Front pilot -
This is the guiding portion of a broach, which serves a safety check to overload the first roughing tooth, and corrects axial alignment

Rise per tooth -
This is the progressive increase in diameter or the height from tooth to tooth of a broach. Usually rise per tooth is higher in roughing teeth than in semi finishing teeth

Pitch -
This is the linear difference from cutting edge of one tooth to the corresponding cutting edge of the next or previous tooth.

Roughing teeth -
These are the cutting teeth take first cut in broaching and generally have heavier rise per tooth than semi finishing teeth.

Semi finishing teeth -
These are cutting teeth, which have rise per tooth much smaller than roughing teeth.

Finishing teeth -
These are the cutting teeth that have no rise per tooth or those which have same height or diameter.

Rear pilot -
This portion just after the finishing teeth, which maintains tool alignment during broaching. Rear pilot is normally smaller than finishing teeth size.

Rear end -
This is the end of the broach which is engaged to the retriever of the broaching machine.

Length up to first tooth -
This is the sum of the pull end length and front pilot length and normally referred to the length from the end of the pull to first cutting teeth.

Overall length -
This is the total length of the broach.

Face angle -
This is the angle of the cutting edge of the broach tooth. Sometimes this is called Rake angle or Hook angle.

Face angle radius -
This is the radius just below the cutting edge, which blends in to the back of the tooth radius.

Back-of-tooth radius -
This is the radius on the back of the teeth, which blends to the back of cutting teeth.

Gullet -
This is the space between broach teeth, which accommodates chips produced during broaching. This sometimes called Chip space and includes face angle, face angle radius, and back-of-tooth radius.

Gullet depth -
This is the depth from the cutting tooth to the root or bottom of the gullet.

Tooth width -
This is the thickness of the top of the cutting tooth.

Back-off angle -
This is the top relief angle of the cutting edge of broach tooth.

Straight land -
This is a land on the top of the tooth having no back-off angle and is normally used for the finishing teeth to retain the finishing size after series of sharpening.

Chip breakers -
These are small notches created on top of the cutting teeth, which breaks up the chips facilitating their easy removal. In round broaches these help in preventing formation of solid rings in the chip gullet.

Shear angle -
This is the angle between the cutting edges of shear cutting teeth and line perpendicular to the axis of broach or the direction of the travel of the broach. This is also called helix angle.

Shear cutting teeth -
These are the cutting teeth, which are positioned at a shear angle to the direction of broach travel. Normally these appear on the surface broaches or external broaches which cuts with shear action, requiring maximum contact with component.

Tips for better Use of Broaches:

these appear on the surface broaches or external broaches which cuts with shear action, requiring maximum contact with component.

Setting of Broaches-
For most of the conventional operations it is possible to carry out the job with some change in tooling and standard clamping etc. However this is not feasible with broaching since the only variable is broaching speed and therefore all the other factors must be corrected during first use only, which helps in avoiding expensive failure. It is very important that broaching operation be entrusted to an engineer or Supervisor who has longer experience in using broaches, understanding the correct settings and maintaining the correctly sharpened broaches. However for a newcomer following steps will definitely help in getting improved life.

Internal Broaching-
In the first step it should be ensured that the ram, the faceplate and the work piece are in exact alignment. Next it should be ensured that work piece sits on faceplate exactly perpendicular to the direction of broach travel. This is particularly important since if the work piece is not

square, the broached component may not be accurate, the broach may also drift in bore or possibly the broach may break. Please refer to fig.2 given below. In case if the bearing surface of the work piece is not square with the bore to be broached then in such cases a hemispherical bearing can be used to overcome this problem. In the next it should be checked that the puller Clamps the broach properly, locking securely and releases easily. Before broaching the ram stops should be checked to ensure that these are positioned correctly and these are securely clamped. Finally, before broaching is stared it should be ensured that components fit over the broach pilot.

Surface broaching-
For surface broaches it should firstly be ensured that alignment of the ram and the travel of the ram is relative to the position in the fixture and are in the same plane. This is normally carried out using a dial indicator. When the broaches are fitted in the holder or bolster, great care has to taken to ensure that broaches sit properly, there is satisfactory space for removing chips and there are no burrs or foreign particles on broaches. If the broaches are made of several segments then the rise from the last tooth of each segment to the first tooth on the following segment should be checked to ensure that no incorrect or misfitting broach segment. In some cases segments are manufactured separately although these are designed in set, In such cases special care should be taken while setting so that there is no mismatch in the profile to be produced. It should also be ensured that the clamps are working efficiently, the work piece is correctly positioned and butting or holding surfaces are clean and free from chips and burrs. Some times it is essential that the fixture holding broaches (bolster) is also checked for clamping and alignment. Finally, the ram stops are to be checked to ensure that stroke of the machine is correct.

General precautions
During the broaching of first component special note should be taken of the reading of the pressure gauge or the ammeter. During subsequent broaching careful watch is to be carried out to ensure that increase in broaching pressure is not more than 35% of the initial pressure reading, which was noted during first use. If abnormal increase in pressure is observed it should be considered an indication that broach is worn out. After producing first component size and the surface finish should be checked thoroughly and it be checked occasionally during the whole broaching operation.

Setting of Broaches
In turning, milling and other operations some amount of wear on the tools can be tolerated but in broaches the cutting edges must be maintained in a sharp condition. Cutting with a worn-out broach may not only damage the cutting teeth but can cause the broach to drift in the hole and can destroy the accuracy by broaching in inclined axis. This phenomenon normally occurs due to non-homogenous nature of the component material. When a broach requires sharpening there are always sufficient indications. These can be poor be taken out from the machine immediately as further use can not only deteriorate the components but it can cause a damage to the broach which can be beyond repair and keep its first class condition. Please refer to fig.3

given below. You may note that in this correct form and contour of the broach are maintained very carefully, and the radius is accurately blended to prevent the interference with the chip curling. All the internal and the surface broaches are sharpened on the front face only and only just sufficient enough material is to removed to restore the original sharpness. Please refer to fig.4

This clearly shows a common mistake done during sharpening. As it is seen in this case the radius is not perfectly blended and a small groove has been created which can cause packing of the chips. This is a common cause of breakage. It should be clearly understood that under no circumstances broach be kept on benches from where it can be dropped or kept on the floor where other tools can strike and can cause irreparable damage. In some cases it is observed that the operator does not have sufficient knowledge how the broach is resharpenend on the finishing teeth. Many operators do sharpening of all the finishing teeth during each sharpening and result consumption of the straight-land, which is usually ground in original condition. Here, one must understand that the straightland provided on the finishing teeth gives consistency in the size produced by a broach and has to be consumed gradually. Usually the no. of finishing teeth on the broaches range from 3 to 9 and each tooth carries a straight land which may be constant or varying from first finishing teeth to the last one. Thus if just sufficient enough material is removed, the broach may be sharpened at least 2 to 3 times to consume the land of first finishing tooth. After consuming the land of first finishing tooth, the land of second finishing tooth is consumed and till that time the sharpening of second or subsequent finishing teeth may be avoided or a very light sharpening maybe carried out. Many times there is always a small amount of damage to a roughing teeth or the pairs of roughing teeth are damaged. If the damage is restricted to only one tooth it can happen that after sharpening the size of the tooth may reduce than the next tooth. This can cause double cutting pressure on this tooth, which can cause permanent damage to the same during broaching operation. Here the operator needs to adjust the rise per tooth, which many times very difficult to carry out since it is very skilled work. In such cases the sharpening of broach may be given to broach supplier or the person who has facility to grind adjusted rise per tooth and relief angle. In some cases it can happen that few teeth may have lost chip breakers. If observed so, these can be ground on the resharpening machine by using smaller thickness nicking wheel. This will help in avoiding the formation of annular rings in the gullet spaces. In few cases it is also observed that broaches are not correctly inspected before sharpening. This is very serious since without this it cannot be ensured as how much allowance is to be removed during sharpening. Before attempting the sharpening it the broach should be cleaned of all chips and the oil has to be removed. It is recommended that a brush is used to clean the chips from the cutting teeth. Similarly after carrying out sharpening the broach should be properly oiled and stored in a peelable plastic coating to give maximum protection during store.

Selection of correct Coolant
There are no real secrets or off-the-shelf recommendations for a perfect coolant. The coolant that is excellent for broaching high-alloy steel may be very poor for broaching stainless, and vice versa. The action of a coolant in reducing friction depends entirely upon the chemical properties involved, and the coolant must be tailored and adjusted with the correct amount and types of additives. Too weak a reaction and the lubricating film may not form. Too strong a reaction, and both the tool and the work piece may be chemically attacked and worn down. At low cutting speeds, coolants vary greatly in their ability to reduce chip-to-tool face friction.
However, at faster cutting speeds, there is less time for coolant to penetrate, less time to react, and therefore, less friction-reducing ability. Good cooling and wetting abilities are much more important at faster speeds since the time for chemical reactions to form adsorbed films is measured in milliseconds.
Thus the main functions of a broaching coolant can be as below:
Dissipate heat generated by the cutting action.
Lubricate the tooth surfaces and chips to facilitate chip flow
Flush the chips from between the teeth
Fortified petroleum coolants are used most often, (these are known neat cutting oils) but some of the new heavy duty water soluble coolants have excellent ability to dissipate heat, are cleaner to work with, and reduce fire hazards while, in some cases, allowing broach speed to be increased. However some have proven to reduce broach life.
If the component material is not varying with the jobs available for broaching it is advised that a reputed manufacturer may be contacted for the latest developed coolant. The supplier is normally more experienced and proven to suggest the most suitable coolant. There are very popular brands developed by leading coolant manufacturer viz. Castrol, Shell, Tidewater & oil etc. Who can readily offer the services at their cost.

Reasons of broach breakage
If the broach is designed by experts, manufactured properly and used with correct care it should definitely last long. However after grinding many times it becomes no longer capable of sustaining the broaching load. If this type breakage takes place it can only be result of careless or improper handling. Following are the basic reasons of broach breakages:
1 Overloading -
In many cases the broach drawings mention the pulling load or the broaching pressure in Kgs. or Tones, which should considered for setting of the broaching machine. In case if this is not mentioned, the pulling load observed during first component broaching should be noted. For Steel components having normal hardness this load may be allowed to increase up to 30 to 35% over the first component-broaching load. Any further increase in pulling load may cause the overloading of the broach and can be prime cause of breakage. Following are some basic reasons for overloading of the broach:

a) Permitting excessive wear on the cutting edges. This can be by allowing the
broaching of components of higher hardness than the one for which the broach
was designed.
b) Permitting internal broach to pass through the guiding bush or the face plate.
This increases the pulling load of the broach since broach has now to cut a
longer broaching length or face width.
c) Incorrect sharpening.
This can be due to the uneven rise per tooth maintained during sharpening.
d) Too low component hardness.
Lower component hardness can cause material pick up on the cutting edges
making the broach overloaded.
e) Insufficient rake angle
This can also increase pulling load since the cutting action will not be suitable
to the actual component material being broached.
f) Untrue locating surfaces
This can cause drifting of the broach causing increase in broaching length and
thereby increasing the pulling load.
2. Reversing the broach when work piece is still in the fixture.
If the broach is reversed without removing the component ill fixture it will not allow the
broach to come out of the component and can cause buckling of the broach, which can
ultimately break the broach.
3. Dropping the broach or dropping something on it.
This can be due to improper handling of the broach during storage.

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