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New Developments in Broaching
High Speed Broaching :
This is the first outcome of the research, which was carried on different type of materials with different cutting speeds. The components were broached beyond the conventional barrier of 6 meters/min. cutting speed. The experiments were done with different cutting geometries to get maximum possible output. The variations of the coolants also helped in achieving the maximum possible production rate at higher cutting speeds. The acceptance of a higher cutting speed was basically due to the better surface finish obtained in the components.
It was observed that suitable finish is poorer at lower cutting speeds and gradually gets improved at higher cutting speeds. This however, remains not much affected for broaches with lower rise per tooth. It is now quite clear that higher cutting speeds can be recommended however this requires good rigidity of the broaching machine and the fixture holding the component
Helical Broaching :
The development of automatic Gearboxes can be regarded as the development of helical broaches. Gears with helical teeth are still popular today which can he produced by helical broaches only. By virtue of the components, helical broaches are divided into two types:
Those which have helical teeth but produces spur type splines in the Components and
Which have helical teeth and also produces helical splines in the components.
Helical broaches are most preferred for components having smaller broaching length and requiring high accuracy in splines. Helical broaches can be designed with plain. combination and interspaced cutting teeth similar to broaches with spur teeth.
Helical broaches, which require producing helical splines, can be used only on special broaching machines having attachments/fixtures to provide helical movement. Helical broaching is carried out by rotating the component either by self rotating support or by the helical nut in the component support which guides the broach through it's lead. The use of lead bar, which is provided either at bottom side or the topside, can also give rotary motion directly to the broaching tool. There can be provision of separate lead bar coupled with the broaching tool with gears at the bottom.
Hard Broaching :

The desire to control the transmission losses in the transmission units and other units of automotives can be considered the reason for development of hard broaching. The transmission losses can be controlled by providing the best attention to the dimensions at gear shaft connections, the better concentricity between outer and inner profiles of components etc. Earlier, these were controlled by modifying the dimensions at green stage and more attention was paid to the method of hardening. This, however. did not improve the quality required in the components. The concept of hard broaching at this stage was then later developed

The application of hard broaching is possible in following areas:
  • Components where bearing area is important such as gears with shafts.
  • Components, which require automatic joining in assembly lines for transmissions of torque.
  • Components requiring precision concentricity of internal splines.
  • Components having very delicate shapes.

  • Gears with shafts meant for transferring the power usually have press fitment. It is necessary to have their bearing area in 1OO% contact within limited dimensions. This requires control over dimensions in a narrow range, which is very difficult to achieve due to heat treatment deviations. It is, therefore, Hard Broaching by which the final dimensions in the gears can be controlled to a very tolerance and also with better quality. In hard broaching major dia., minor dia., and flank all can be broached to a very close tolerance.
    Components requiring automatic joining require very precise inner profile. Hard broaching helps in achieving this and therefore can be considered a process of very high reliability. The biggest advantage of this process is that it is simple to control it by simpler statistical technique on the broached splines.
    Gears, which are engaged between external and internal teeth, require very high degree of concentricity of profile with respect to minor/root dia. The distortions due to hardening cannot permit such close accuracies and therefore, it is only hard broaching which can broach with accurate profile and within close tolerance the internal and external splines.
    Some components have very delicate and indifferent shape, which also contribute difference in profile dimensions. Such components when hardened cause large amount of distortion, poor concentricity and run out. In such components, by trial and errors the effect of contractions is minimized by adjusting a portion of error at soft stage or by adjusting the procedure of hardening. Hard broaching in such components permits only required portion of deviation in the components as required for easy assembly with mating parts.
    Hard broaching was uneconomical in the beginning however, today with improved coating process and the modified coatings, this operation is very successful and economical too. There are several advantages to the user of hard broaching, these are as below:
    a) Process Reliability:
    By Hard broaching, it is possible to have consistency in achieving the tightened tolerances and reliable rate of
    production with the components.
    b) Short processing time:
    The processing time is very less (< 15 sacs) due to very high cutting speeds. It also offers broaching more than one piece, which can affect cost effectiveness.
    c) Better Surface Finish:
    Surface finish obtained is far better than the finish obtained by green stage broaching. The normal surface finish obtained is Rz <2.5/ Mu and Ra <0.6 Mu.
    d) Improved quality:
    The Components produced are with very small portion of distortion than the distortion at green stage. Thus there is significant Improvement in the quality of component. The rejection rate is almost zero.
    e) Cost effective:
    The life of 100,000 components without sharpening the broach indicates the cost of hard broaching per component.
    Full Form Mono Block Broaching :

    In order to reduce the profile errors, which are caused by drifting of the broach, high precision components such as "Ring Gear" are broached with a special broaching shell, which is attached to the main broach at the end of finishing teeth. This shell calibrates the rough profile produced by the portion before the shell .The procedure for profile cutting is quite complicate. This shell with special design is known as Full Form Monoblock broach.
    It is to be noted that in this type of broaching, each tooth has a flank rise in Microns in addition to the increase in core dia. which cuts the bore. The flanks have the original profile and therefore, Full Form relieved. Here, since roughing and finishing full form cutting teeth are provided, the errors in the profile are most minimum. Due to this, the component has problem free entry into mating parts. Further, in this case, since each tooth is cutting on form, there is no chance of premature wear, which happens due to drifting.

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