Broaching is a machining process that involves removing material using a special tool called a broach. The broach is a multi-toothed cutting tool that progressively increases in size, enabling it to cut different parts of a workpiece in a single pass.
This process is especially efficient for producing internal keyways, splines, and other complex shapes with high precision.
In this article, you will learn about broaching machines, types of broaching machines, Broaching operations, and Advantages.
What is a Broaching Machine?
Broaching is a method of removing metal by pushing or pulling a cutting tool called a broach, which cuts in a fixed path.
In a 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 surfaces, either internal or external. 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 called “drifts” were hammered in blacksmith shops through the work or pushed with an arbor press.
How Broaching Machines Work?
Although it can be performed by hand, most manufacturing companies use a machine when broaching a workpiece.
Typically powered via hydraulic pressure, broaching machines are used to hold and maneuver the broach, the cutting tool, as it pushes against or pulls through the workpiece.
There are several types of broaching machines, including horizontal and vertical. Vertical broaching machines are designed to push the broach against the workpiece, whereas horizontal broaching machines are designed to pull the broach through the workpiece.
Statistics show that vertical broaching machines are the most common, with horizontal broaching machines only accounting for roughly one in 10 of all broaching machines purchased and used by manufacturing companies.
Types of Broaching Machine
Following are the types of broaching machine
- Horizontal broaching machine
- Vertical broaching machines
- Surface broaching machines
- Continuous broaching machine
Broaching machines are the simplest of all machine tools. The broaching machine consists of a broaching tool, a work-holding fixture, a drive mechanism, and a suitable supporting frame.
Although the 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 machines have one or more rams depending on production demand.
Dual-ram models are arranged so that when one ram is 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.
#1. Horizontal Broaching Machine.
Horizontal broaching machines employ the pull-type broaching method, ideal for internal broaching as well as certain external applications.
These machines are commonly used for manufacturing keyways, splines, slots, round holes, and complex internal shapes. The configuration features an elongated bed, a broach pilot to align and guide the broaching tool, and a powerful drive mechanism.
This setup is optimal for machining long broaches and handling heavy workpiece requirements often found in automotive or heavy equipment manufacturing.
However, horizontal broaching machines require significant floor space in the production facility. They deliver high accuracy, repeatability, and allow quick changeovers for multiple part geometries.
#2. Vertical Broaching Machine.
A vertical broaching machine operates by pushing or, in some types, pulling the broaching tool vertically relative to the workpiece. These machines offer great versatility, enabling both internal and surface broaching.
With push broaching as the most common operation, vertical broaching machines are suited for the mass production of parts requiring accurate slots, holes, and other geometric features.
There are three primary types of vertical broaching machines: push down, pull up, and pull down, each with different capabilities for workpiece handling and broaching force.
Pull-up machines are especially prevalent in high-production manufacturing for their efficiency and quick loading/unloading of workpieces. Vertical broaching machines may be powered by hydraulic systems or electromechanical drives, with hydraulic models offering superior force control and reduced maintenance costs.
#3. Surface Broaching Machine.
A surface broaching machine is designed to remove excess material from the flat or contoured surfaces of a workpiece. The broaching tool, typically mounted on a reciprocating ram, traverses the workpiece, cutting multiple profiles or features in a single pass.
Surface broaching processes are highly efficient for producing complex contours, slots, or dovetails on components like turbine blades, pistons, and connecting rods.
These machines can be configured for horizontal or vertical operation, and duplex broaching machines (with two rams) increase production throughput for batch manufacturing and high-volume runs.
#4. Continuous Broaching Machine.
In continuous broaching (also known as chain broaching or production broaching), the workpiece moves steadily while the broach remains stationary. This process leverages a conveyor or chain-driven fixture to transport multiple workpieces in sequence through the cutting zone.
Continuous broaching is ideal for machining numerous identical parts such as automotive transmission components, small gears, or fasteners, maximizing productivity and part consistency in large-scale manufacturing environments.
The process can involve linear, horizontal, or circular movement, depending on the design and intended application.
Types of Broaching
Linear Broaching
In linear broaching, the broach moves linearly along the workpiece. This is a common method for cutting keyways and splines. Linear broaching can be classified into two main types:
Internal Broaching
Internal broaching focuses on creating precise internal features within a workpiece. Internal broaching is highly efficient, providing exceptional precision and accuracy in producing internal features, essential for various industries like automotive, aerospace, and machinery manufacturing.
The internal broach method significantly reduces the need for multiple machining operations, offering a streamlined and cost-effective solution for creating complex internal geometries with tight tolerances.
External Broaching
Unlike internal broaching, which focuses on internal features, external broaching involves cutting material from the external surface of a workpiece using a specialized broach tool. This process allows for the creation of flats, contours, or other external profiles with high precision in a single pass.
The broach, equipped with cutting edges or teeth, is carefully guided along the external surface of the workpiece, gradually removing material to form the desired shape.
External broaching is highly efficient and ideal for applications requiring accurately machined external features, contributing to improved component functionality and fit in industries such as automotive, aerospace, and general engineering.
Rotary Broaching
Rotary broaching is a specialized machining process that involves the simultaneous rotation of both the cutting tool and the workpiece. Unlike traditional linear broaching, where the broach moves linearly through the workpiece, rotary broaching imparts a rotary motion to both the broach and the workpiece.
This process allows for the efficient creation of intricate shapes and forms with a single pass of the broach.
The key component in rotary broaching is the rotary broach tool, which typically has a polygonal or contoured shape. The tool is designed to produce specific shapes, such as hexagons, squares, or other polygons, and it can also be customized for more complex forms like gears or splines.
Rotary broaching offers several advantages including single-pass operation, improved tool life, and overall versatility.
Surface Broaching
Surface broaching is employed to cut flat surfaces on a workpiece. It is commonly used in applications where a smooth and precise finish is essential.
Pull Broaching
Pull broaching involves applying force to the broach tool in the opposite direction of the cut, drawing the broach through the workpiece. This method is more common and widely used in vertical broaching machines.
Pull broaches typically have a hydraulic or mechanical system that pulls the broach downward or vertically through the workpiece that is fixed on a sturdy fixture or work table.
Push Broaching
Push broaching, on the other hand, applies force in the same direction as the cutting motion. This method pushes the broach upward or forward through the workpiece.
Push broaching are less common and often used in specialized applications. They apply force from the bottom of the workpiece to push the broach upwards.
Keyway Broaching
Keyway broaching is specifically designed for cutting keyways, which are slots that accommodate keys or other mating components.
Broaching Machine Operations
Broaching is applied for machining various internal and external surfaces, for round or irregularly shaped holes from 6 to 100mm in diameter, and for external flat and contoured surfaces.
Certain types of surfaces, for example, spline holes, are machined at present only by broaching due to the exceptional difficulties in machining such surfaces by other methods.
Some important broaching operations are illustrated below. Some operations are done in one pass, but some operations are 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 of broaching
- High production rate and low cycle. The broaching operation is faster than other metal-cutting operations. Then the price per piece will be low for broaching.
- Many operations are replaced by broaching. A single stroke of a broach can do both rough cutting and finishing operations.
- Broach has a long life because each tooth takes only one small cut in a single operation.
- The temperature of the workpiece is fairly constant, thus avoiding the error due to thermal stress.
- The cutting force on the workpiece acts in the clamping direction, assisting in holding/ clamping the workpiece firmly in position.
- Broach can be used for both internal and external cutting operations.
- Good surface finish. High dimensional accuracy and close tolerance.
- The broaching operation is simple and does not require a highly skilled worker.
- The application of cutting fluid is very easy.
Disadvantages of Broaching
- High initial cost for a customized broach.
- Design, restoration, and sharpening of a broach is expensive.
- Surface to be machined should not have an obstruction in the way of the broch travel.
- Broaching is useful only for low chip loads or light cuts. It can not be used for heavy work. Broaching is not used for delicate and very light jobs.
- One broach can use to one procedure only. A separate broach is required whenever the geometry of the job changes.
- It is economic only for mass production.
- Only used for machining through holes and linear surface cuts.
Application of Broaching
The broaching process is utilized across various industries that demand high accuracy and efficiency. Some of the main industrial applications include:
- Automotive Machining: In the automotive machining industry, broaching is used to produce a wide range of parts, including gears for transmissions, keyways for shafts, spline shafts for power transmission, and internal and external profiles for various components.
- Aerospace Components: The aerospace sector greatly depends on broaching to manufacture parts such as turbine blades, engines, wing spars, and landing gear components.
- Metal Fabrication: Broaching is a versatile tool in metal fabrication. It creates a wide variety of parts, including bushings, bearings, and shafts. It is particularly valuable for high-volume production of parts with consistent dimensions and fine surface finishes.
- Medical Devices: Accuracy is essential in the medical field, and broaching is used to produce intricate, high-quality parts such as surgical instruments, implants, and medical device components.