Broaches can be categorized by Use : Surface broaches & Internal broaches

Surface broaches

• Slab broaches are simple tools for producing flat surfaces come closest to being truly general-purpose broaches. A single slab broach can be used to produce flat surfaces having different widths and depths on any workpiece by making minor adjustments to the broach, fixture, and / or machine.

• Slot broaches are for cutting slots but are not as general purpose in function as slab broaches. Adjustments can easily be made to produce different slot depths, but slot widths are a function of the broach width. When sufficient production volume is required: however, slot broaches are often faster and more economical than milling cutters. In broaching, two or more slots can often be cut simultaneously.
• Contour broaches are designed to cut concave, convex, cam-, contoured, and irregular shaped surfaces.
• In pot broaching, one or more workpieces are generally pulled or pushed up or pushed down through the bore of a pot broach subholder that is normally stationary on a vertical machine. There are three basic types of pot broaches having internal cutting tooth configurations: ring, stick, and combination ring and stick.
• Straddle broaches use two slab broaches to cut parallel surfaces on opposite sides of a workpiece in one pass. This type of broaching holds closer tolerances than if the two cuts were done independently. It is named after the fact that the broaches “straddle” the workpiece on multiple sides.

Internal broaches

Internal broaches are either pulled or pushed through a starter hole. The machines can range from fully automated multi stationed verticals to horizontal pull types to simple presses.

Rotary-Cut Broaches
Rough forgings, malleable~ iron castings with a hard skin, and sand castings with abrasive surface inclusions are cut with one of three types of rotary-cut broaches.

• Solid broaches are the most common type; they are made from one solid piece of material. For broaches that wear out quickly shellbroaches are used; these broaches are similar to a solid broach, except there is a hole through the center where it mounts on an arbor. Shell broaches cost more initially, but save cost overall if the broach must be replaced often because the pilots are on the mandrel and do not have to be reproduced with each replacement.
• Modular broaches are commonly used for large internal broaching applications. They are similar to shell broaches in that they are a multi-piece construction. This design is used because it is cheaper to build and resharpen and is more flexible than a solid design.
• A common type of internal broach is the keyway broach (C & D). It uses a special fixture called a horn to support the broach and properly locate the part with relations to the broach.
• A concentricity broach is a special type of spline cutting broach which cuts both the minor diameter and the spline form to ensure precise concentricity.
• The cut-and-recut broach is used to cut thin-walled workpieces. Thin-walled workpieces have a tendency to expand during cutting and then shrink afterward. This broach overcomes that problem by first broaching with the standard roughing teeth, followed by a “breathing” section, which serves as a pilot as the workpiece shrinks. The teeth after the “breathing” section then include roughing, semi-finishing, and finishing teeth.

Broaches can be categorized by many means:

• Use: internal, or surface

Surface broaches
The slab broach is the simplest surface broach. It is a general purpose tool for cutting flat surfaces.

Slot broaches (G & H) are for cutting slots of various dimensions at high production rates. Slot broaching is much quicker than milling when more than one slot needs to be machined, because multiple broaches can be run through the part at the same time on the same broaching machine.
Internal broaches
Solid broaches are the most common type; they are made from one solid piece of material. For broaches that wear out quickly shell broaches are used; these broaches are similar to a solid broach, except there is a hole through the center where it mounts on an arbor. Shell broaches cost more initially, but save cost overall if the broach must be replaced often because the pilots are on the mandrel and do not have to be reproduced with each replacement.

• Purpose: single, or combination

• Motion: push, pull, or stationary

• Construction: solid, built-up, hollow or shell

• Function: roughing, sizing, or burnishing

• Equipment MLS:horizontal or vertical

Horizontal units are easily adjustable, and the user can readily reach any of its parts.

Vertical machines save room and last longer.

If the broach is large enough the costs can be reduced by using a built-up or modular construction. This involves producing the broach in pieces and assembling it. If any portion wears out only that section has to be replaced, instead of the entire broach.

Most broaches are made from high speed steel (HSS) or an alloy steel; TiN coatings are common on HSS to prolong life. Except when broaching cast iron, tungsten carbide is rarely used as a tooth material because the cutting edge will crack on the first pass.

Broaching machines are relatively simple as they only have to move the broach in a linear motion at a predetermined speed and provide a means for handling the broach automatically.

A broaching machine is a specialty machine designed for machining, or finishing, the surface of metal parts. It consists of a work table or some other fixture to hold the part in place, a broaching tool and a drive mechanism.

It has cutting teeth arranged in one or more rows, according to Encyclopaedia Brittanica. A broaching machine is typically used to finish metal surfaces in commercial industries.

A typical broaching machine works by keeping the metal piece stationary and cutting its edge while rotating around it, according to Global Spec. Broaching machines work quickly. A job usually takes only seconds.

Parts of a Broaching Machine

• Work Table

  The work table, or fixture, serves to tilt and hold the part in place for broaching. The center of the part and the center of the broaching tool are typically aligned with an offset of 1 degree, which creates a scalloping effect on the metal surface.

• Broaching Tool

  A broaching tool is a cutting tool with graduated cutting teeth arranged in a row. Each of the cutting teeth removes only a fraction of an inch from the surface of the metal, but, as the teeth become progressively higher, more and more metal is removed.

• Drive Mechanism

  The drive mechanism of a broaching machine is typically hydraulic or electromechanical. In either case, its purpose is to push or pull the broaching tool across the surface of the part. The part, itself, remains stationary.

• Types

  Broaching machines are either horizontal or vertical, according to Equipment MLS. Horizontal units are easily adjustable, and the user can readily reach any of its parts. Vertical machines save room and last longer.

• Applications

  Broaching machines are common tools in the electrical, automotive and aerospace industries. They must meet industry specifications. Manufacturers use them to make metal stampings, for forging and casting processes and to make machine parts.

A somewhat different design of cutting tool that can achieve the irregular hole or outer profile of a broach is called a rotary broach or wobble broach.The rotary broaching process takes just seconds and is capable of producing forms with an accuracy in excess of 0.0005-inch. The process can be performed at the same time as other operations, increasing the speed and profitability of production.

Rotary broaching requires two tooling components: a tool holder and a broach.

The leading (cutting) edge of the broach has a contour matching the desired final shape.

The broach is mounted in a special tool holder that that allows it to freely rotate.

The tool holder is special because it holds the tool so that its axis of rotation is inclined slightly to the axis of rotation of the work.

A typical value for this misalignment is 1 degree.

This angle is what produces a rotating edge for the broach to cut the workpiece. Either the workpiece or the tool holder is rotated. If the tool holder is rotated, the misalignment causes the broach to appear as though it is “wobbling”, which is the origin of the term “wobble broach”.

For internal broaching the sides of the broach are drafted inward so it becomes thinner; for external broaching the sides are drafted outward, to make the pocket bigger. This draft keeps the broach from jamming; the draft must be larger than the angle of misalignment. If the work piece rotates, the broach is pressed against it, is driven by it, and rotates synchronously with it. If the tool holder rotates, the broach is pressed against the workpiece, but is driven by the tool holder.

Ideally the tool advances at the same rate that it cuts. The ideal rate of cut is defined as:

Rate of cut [inches per rotation (IPR)] = (diameter of tool [inches]) × sin(Angle of misalignment [degrees])

Types of Rotary Broach ToolsThere are many types of rotary broach tools available. These include adjustment-free Swiss types that are designed for smaller European machines, where clearance is a concern. The standard, adjustment-free type is designed to accept a wide variety of forms and is easy to use while the heavy-duty type is built for speed and designed for larger forms. There is also a large form type designed for accuracy on larger forms.
Internal Hexagonal Rotary Broaches

The internal hexagonal rotary broaches from Polygon Solutions have a shank diameter of 0.315 inch (8 mm) and an overall length of 1.25 inches. These broaches range in dimension, from 0.0510-inch across the flats and a broach depth of 0.102-inch, to 0.4775-inch across flats and a depth of 0.650-inch.