Types of Broaches

Types of Broaches

Types of Broaches - There are three general categories of broaches

(i) Solid type

(ii) Shell type

(iii) Insert type.

Within these three categories, broaches can be further classified by the type of cut i.e.,

1. .Internal broaches

2. External broaches

Further classification can be on the method of actuating the broach i.e.,

x. Push type, or

y. Pull type broach.

Another classification of broaching tools may be with regard to the function they perform e.g.

(a) Round broach

(b) Helical cut broach

(c) Burnishing broach

(d) Straight Spline broach

(e) Angular Spline broach

(f) Serration Spline broach

(g) Keyway broach

(h) Combination broaches

(i) Square, hexagonal and rectangular broaches.

Of the various types of broaches, the solid pull broach probably is the most commonly used.

Solid broaches are one piece broaches produced from bar stock. They can be provided with greater dimensional accuracy and concentricity than shell broaches. The chief disadvantages of solid broaches lie in the difficulty of repairing broken teeth and in the cost of replacement when wear necessitates it.

Shell broaches consist of a main broach body    (usually the roughing and intermediate broach sections) and an arbor section over which a removable shell fits. The removable shell is the finishing section. A broach may have one or more removable shells.

A shell broach has the advantage that worn out sections can be replaced easily. A shell broach is capable of floating, which is helpful in maintaining alignment. Solid broaches possess more accuracy and concentricity as compared to shell broaches.

Insert type broaches are made up of a tool holder and insert of high speed steel or carbide which do the cutting. Carbide inserts can be brazed to the tool holder just as it is brazed on a lathe tool.

Disposable inserts having triangular or square shape have largely replaced brazed carbide inserts, because they save the toot cost considerably. Insert type broaches find main use for broaching large fiat surfaces, such as the machined face of automotive engine blocks.

Internal broaches are used to enlarge and finish a wide variety of holes previously rough formed by casting, forging, drilling etc. Fig. 13'9 shows some internal broaches.

External broaches are used for producing external shapes. Such broaches may be of one-piece construction when used for small, short surfacing application or they may consist or a series of segmented sections, assembled end to end.

Pull broaches are pulled through or against the surface or the workpiece. Most internal broaching is done with pull broaches. Push broaches are pushed through the hole in the workpiece. Push broaches are used to broach blind holes or for multiple station broaching machines wherein several short broaches, rather than a single long broach, are used; to reduce the time required for a given operation.

Push broaches, for internal broaching, are necessarily shorter than pull broaches, because of their problem of bending under load. One most used type of broach is the round broach with circular teeth. Deep holes are broached by helical cut broaches fed through the workpiece with a translational motion.

A burnishing broach has no sharp cutting teeth, it has a series of radius type buttons called burnishers which conform to the contour being broached and are used for compressing and smoothing the surface being machined.

Spline broaches are mostly of the generation cutting type. With respect to the kind of splines they are designed for. They are classified as straight Spline, angular Spline e) and serration Spline broaches. Keyway broaches are used to produce keyways of various shapes in previously machined holes.

Combination broaches are used to machine different surfaces of a Spline hole in a single stroke. The first section broaches a round hole (minor diameter) and the second broaches the splines. Therefore, the first section will have round teeth, and the second will have teeth of the shape of the Spline hole.

Polygonal holes are broached by square, nexagonal, rectangular and other broaches. One feature of their design is the provision of several groups of teeth along their length with different cuts per tooth.