TOOL ROOM II - BROACHING

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BROACHING MACHINE: TYPES, OPERATIONS, ADVANTAGES AND DISADVANTAGES BROACHING METHODS

In this article you will learn about broaching machine, Types of broaching machine, Broaching operation and Advantages.

Broaching

Broaching is a method of removing metal by pushing or pulling a cutting tool called a broach which cuts in a fixed path.

In broaching machine, the tool of the machine is pulled or pushed through the surfaces to be finished. With the help of broaching, finishing is done on flat or contoured and either internal or external surfaces. Broaching is limited to the removal of about 6mm of stock or less.

The term broaching may have derived from an ancient Roman word braccus, which means an object having projecting teeth. The operation itself dates only to the 1850s when broaching tools when called “drifts” were hammered in blacksmith shops through the work or pushed with an arbor press.

Types of Broaching Machine

Following are the types of broaching machine

• Horizontal broaching machine
• Vertical broaching machines
• Surface broaching machines
• Continuous broaching machine

Read also: Lathe machine and its types

Broaching machines are the simplest of all machine tools. Broaching machine consist of a broaching tool, a work-holding fixture, a drive mechanism, and a suitable supporting frame. Although the component parts are few, several variations in design are possible.

There are two principal types of broaching machines: horizontal and vertical.

In addition to these standard types, there are special and continuously operating machines. Both horizontal and vertical types of machine have one or more rams depending on production demand.

Dual-ram models are arranged so that when one ram in on the cutting stroke, the other is on the return stroke; the return stroke is performed quickly to gain time, which is used to unload and load the machine.

Broaching machines usually pull or push the broach through, or past a workpiece that is held in a fixture. On some machines, however, the workpiece is moved past a broach that is fixed in its position. Most broaching machines are hydraulically operated to secure a smooth, uniform cutting action.

Horizontal Broaching Machine

Nearly all horizontal machines are of the pull-type. They may be used for either internal or external broaching, although internal work is the most common.

A horizontal broaching machine is shown in the figure. It consists of a bed or a base a little more than twice the length of the broaching stroke, a broach pilot and the drive mechanism for pulling the broach. The horizontal broaching machine is shown in the figure below

Horizontal broaching machines are used primarily for broaching keyways, splines, slots, round holes, and other internal shapes or contours. They have the disadvantage of taking more floor space than do the vertical machines. However, long broaches and heavy workpieces are easily handled.

Vertical Broaching Machine

The vertical types may be obtained in either push or pull type. The push-type is the most popular. Vertical machines are used in multiple operations since they are convenient to pass work from one machine to another. Of the three models available, pull down, pull up, and push down, the pull-up type is most popular. Vertical machines require an operator platform or a pit and are economical of floor space than the horizontal type. The vertical broaching machine is shown in the figure below:

Modern vertical broaches are offered with both hydraulic and electro-mechanical drives. But hydraulic drives are the most common because they cost less. A vertical hydraulic broaching machine is illustrated in above figure.

Surface Broaching Machine

Surface broaching machines have their broaching tools attached to a ram or rams forced in a straight path along guideways past the workpiece. On some surface broaching machines, the ram travels horizontally, on others ram travels vertically. When two rams are used, the machines is called a duplex broach.

Continuous Broaching Machine

For mass production of small parts, the highly productive continuous-broaching method is used on rotary or horizontal continuous-broaching machines.

in the rotary continuous broaching machines, the workpiece is loaded on the table which rotates continuously. During the operation the broach is stationary.

In the horizontal continuous broaching machines the workpieces travel as they are carried by an endless chain. The workpieces are loaded into work holding fixtures mounted on the continuously moving chain. During the operation, the broach is stationary as before. Such machines are used for broaching small parts.

Read also: Shaper machine and its types

Broaching Methods

Following are the classification of broaching methods:

1. Pull Broaching
2. Push Broaching
3. Surface Broaching
4. Continuous Broaching

Pull Broaching

In the pull broaching the work is held fixed and the broach is pulled through the work. Usually, broaches are very long and are held in a special head. Pull broaching method is used for internal broaching but it also used for some surface broaching.

Push Broaching

In the push broaching the work is fixed and the broach is pushed through the work. Hand and hydraulic arbor presses are commonly used for push broaching. This method is used for sizing holes and cutting keyways.

Surface Broaching

In surface broaching either the work or the broaching tool moves across the other. This method has become an important means of surface finishing. Many irregular or intricate shapes can be broached by surface broaching, but the tools must be specially designed for each job.

Continuous Broaching

In continuous broaching the work is moved continuously and the broach us held stationary. The movement of work may be either straight horizontal or circular. The continuous broaching method is mostly used for broaching a number of similar works at the same time

Broaching Machine Operations

Broaching is applied for machining various internal and external surfaces, for a round or irregular shaped holes from 6 to 100mm in diameter, for external flat and contoured surfaces.

Certain types of surfaces, for example, spline holes, are machined at the present time only by broaching due to the exceptional difficulties in machining such surfaces by other methods.

A number of important broaching operations are illustrated below. Some operations are done in one pass, but some operation arranged for repeated cuts to the design of the broach.

The teeth of a gear or spline may be broached all together or one or a few at a time. A comparatively simple broach can be made to cut one or a few tooth spaces. After one pass, the gear blank is indexed and more of its teeth are cut. Successive passes are made until all the teeth are finished.

Advantages and disadvantages of broaching of Broaching

ADVANTAGES OF BROACHING

1. The rate of production is very high.
2. Skill is required from the operator to perform a broaching operation. In most cases, the operator merely loads and unloads the work-piece.
3. High accuracy and a high class of surface finish are possible. A tolerance of ±0.0075mm and a surface finish about 0.8 microns (1 micron=0.001mm) can be easily obtained in broaching.
4. Both roughing finishing cuts are completed in one pass of the tool.
5. The broaching process is used for internal and external surface finishing.
6. Any form or shape that can be reproduced on a broaching can be machined.
7. Cutting fluid may be readily applied where it is most effective because a broach tends to draw the fluid into the cut.

DISADVANTAGES OF BROACHING

1. High tool cost. A broach normally makes only one job and is expensive to make and sharpen.
2. Very large work-piece cannot be broached.
3. The surface to be broached cannot have an obstruction.
4. Broaching cannot be used to remove a large amount of stock.
5. Parts to be broached must be capable of being rigidly supported and must be able to withstand the force that set up during cutting.