Broaching is an efficient, cost effective method of precision machining that can be performed on an external surface (round, flat or contoured) or the internal part of a shape or form. It is considered a metal removal service, and almost any material, from ferrous and nonferrous metals to plastic materials and wood are able to be cut through broaching, although softer metals are by far the most common material.
Various broaching methods are performed in broaching job shops to cut internal splines, gears and sprockets, as well as keyways, slots and serrations on the surface of a work-piece. These products are fabricated in high volumes, a process called production broaching, which takes place in a facility that specializes in broached parts. While broaching machines are specialized and have somewhat limited ranges of abilities, there are many different kinds that do different kinds of broaching, including spline cutting, keyway broaching using a keyseater machine and gear hobbing. Broaching machines work on the outside of a work-piece or create holes by internal broaching, which reaches all the way through the material. They are either horizontal or vertical machines, depending on the size of the work-piece and the involvement of the manual worker. Vertical broaching is used for higher volumes of products. The holes and grooves that are made with a spline shaft, which contains a series of successively larger teeth that are strong enough to cut through metals, may reach all the way through the work-piece, forming a hole, or make shallow indents that blind broaching produces. Rotary broaching is a popular method that spins the broach tool at high rotations and pushes or pulls it through the work-piece. Pot broaching inverses the machinery movements-the broach tool stays stationary while the work-piece moves through the broaching machine.
The broaching process produces many different parts and products, mostly for use within the industrial sector, and usually made of softer metals like aluminum, brass and copper, although harder metals like steel grades and other materials including plastic and wood are also able to be broached. The most common broached products are gears. A broaching process called gear hobbing forms their shape by externally broaching the grooves on the gear's external surface. Sprockets, pulleys, the heads and threading on fasteners like screws, nuts and bolts, smaller wheels, gun components, industrial machinery parts, tools like wrenches and bushings all get their shape from the broaching process, which doesn't generate or require any heat and therefore is less prone to error. During the broaching process, machines such as automatic lathes, CNC Swiss lathes and rotary transfer machines are used to push or pull a broaching tool with cutting teeth through or over a work-piece. The only limit to the process is the length and width of the part that is being machined.
The most common form of broaching services is done using hydraulic driven machines, since they require a large amount of power in order to operate continuously. There are three main methods to forming the holes and indents in the work-piece, including pull broaching, push broaching and pot broaching. When the broach cutting tool is pulled through the part in a single pass, this process is called pull broaching. The second most common type of broaching services used is push broaching. Broaching job shops most often utilize this service on short run jobs using a hydraulic press, or more commonly, a hand operated arbor press. Pot broaching, on the other hand, moves inversely-while the broaching tool remains stationary, the work-piece is pushed through it inside a hollow casing shaped like a pot. Broaching job shops can also perform broaching on a lathe, which spins at a high rotation. During rotary broaching, the tool must be held at a 1° angle to the work-piece. The cutting face of the broach should be positioned as close to the centerline of the work-piece as possible. The tool and part are stationary while the broach holder spins on a spindle. As the broach tool and the part come into contact, the tool moves in a "wobble" motion; thus, another name for this process is wobble broaching.
The entire broaching process takes a matter of seconds, and is fully automated. High production runs are possible, making broaching cost efficient, economical and fast. Broaching has many advantages, including high productivity, economical operation, accurate cuts over large runs, close tolerances, versatility and smooth finishes. Chips tend to accumulate in the broaching hole. Therefore they must be cleared periodically so that they do not cause damage to the broach tool. Also, the hole must be drilled as deep as possible to allow room for the chips to accumulate. Sometimes a pressure relief vent on the broach tool is necessary when broaching a tight hole if air, oil and coolant cannot escape. If enough hydraulic pressure is generated, the broach will be pushed back and could cause damage to the machine. A ventilation hole on the tool prevents this occurrence.
Broaching Services - VW Broaching Service, Inc.
Broaching Companies - Avon Broach and Production Company
Broaching Services - Avon Broach and Production Company
Broaching Companies - VW Broaching Service, Inc.
Broaching Services - VW Broaching Service, Inc.
Broaching Companies - VW Broaching Service, Inc.
Most manufacturing industries-from industrial machinery to automotive, aerospace, or military equipment-all require broaching job shops and specialty broaching machines. Broaching, as a process, has evolved from internal keyway broaching to broaching sophisticated machinery. The process is considered expensive to other alternatives such as milling, boring, reaming, and shaping; however, broaching is still economically viable. The broaching process can be applied to high-volumes of machine parts with no extra finishing steps unlike other alternatives, which require additional finishing steps. Broaching produces final products that do not need additional processing.
Most manufacturers recognize that broaching can be expensive, however, most do not fully understand the basics of the broaching process. Therefore, the following paragraphs discuss the basics of this type of machining process and enable you to ask meaningful questions of broaching job shops.
What is Broaching?
Many dictionary definitions describe broaching as a process to remove material. This definition is quite ambiguous and does not address application-specific uses of the process. In broaching processes, a toothed machine-unlike a lathe or shaper-called a broach is used across internal and external machine surfaces. The broach is applied in various predetermined shapes from holes to square, to geometrically irregular shapes to gear hobbing. A broach machine, in comparison to other machining tools, is quite unusual based on its multiple cutting teeth which vary in length successively. Instead of cutting a single point, the broach includes a collection of single point cutting tools arranged linearly to cut or remove material.
What does the broaching process include?
The broaching process can be categorized based on the use, purpose and motion, construction and function being addressed. However, broaching can generally be classified as surface or internal based on the manufacturing use. In surface broaching, the simplest of all broaching processes, a work piece, which needs to be machined, moves while the broach remains stationary, or the broach moves against a stationery work piece to remove material.
Internal broaching is more complex because a work piece is clamped into a holder-the holder is known as a work holder and is a part of the broaching machine. Within the broach machine, the elevator moves the broach tool above the work holder, and the broach itself is moved through the work piece. Then the linear movement of the broach machines the part. Based on a specific need such as gun-barrel rifling or spiral splining, the broach also rotates.
What parts can be broached?
Consider the following points when determining which machine parts are appropriate for broaching. Broaching does have its limitations but can be controlled to ensure precision and process efficiency.
Why broaching is typically expensive?
Broaching, unlike other machining alternatives, is job specific. One type of broach can machine only one shape. Each broach is designed for a specific geometry. These limitations make it a highly specialized option for very limited use. In custom broaching, a completely new tool is developed only adding to manufacturing costs.
We all know broaching is an important process across industries that shape or machine highly precise work pieces for various purposes. However, most manufacturers are unaware that broaching is done in broaching job shops, which are specialized facilities for the metal removal involved in creating holes, profiles, and cut outs. At these facilities, specialized machines are used that makes broaching, a significantly expensive processing technique, more cost effective. Broaching machines are automated and work either horizontally or vertically.
Vertical Broaching Machines
Most of the broaching machines used in broaching job shops are vertical and either support external or internal broaching. These machines, as their name suggests, work vertically on a work piece and are driven by hydraulical presses. Based on their mode of operation, vertical machines are categorized as table-up, pull-up, and pull-down or push-down machines.
In vertical table-up machines, the broach remains stationery, and the work piece is mounted on a table that moves. These machines meet cell concept manufacturing needs, adding flexibility for manufacturing processes. They are designed for short-runs; and after one or two years, the machines can be re-tooled for different applications. Vertical machines also add flexibility in terms of portability, as they can be moved to another area. In vertical table-up machines, the stroke lengths vary from 30to 90 feet, whereas its capacity is 5 to 30 tons.
Horizontal Broaching Machines
These machines have a horizontal configuration and are gear or screw driven. They sometimes are exclusively used for finishing and roughing various engine blocks and can be powered hydraulically or mechanically. Horizontal broaching machines are returning as a favored design as the perform very long strokes and do not have limitations, like their vertical counterparts. Horizontal machines are further divided as horizontal internal broaching machines, horizontal surface broaching machines, and chain-broaching machines.
For modern production needs, chain-broaching machines are preferred, as these surface broaching machines have a continuous chain where work pieces are mounted, eliminating the need of a return stroke.
Other than these machines, specialized turn-broaching or rotary broaching machines are available for creating different shapes that vary from linear to circular to spiral. These machines efficiently cut and machine steel and cast iron crankshafts. To perform different functions, peripheral cutters are assembled in segments, and have standardized components to rough and finish work pieces.
Selecting the Most Appropriate Broaching Machine
There are majorly two factors that determine the type of machine to be used for a specific job such as broaching of cold headed parts, screw machine products, keyway broaching, spline shafts, blind broaching, and gear hobbing. The first factor is the type of broach cutting tool required-internal or external. The second factor is the production requirement, such as the number of pieces required over the whole run of production or per hour. Together, these factors directly determine which machine will work efficiently for a given job. Where an internal broaching machine is concerned, the ratio of length of the broach to its diameter may determine if a pull action machine is more appropriate. The other factors include type of drive, whether hydraulic or electromechanical, and automation and convertibility.
Have you ever been intimated by the engineering jargon surrounding the process of broaching? The following paragraphs describe several broaching terms and put them in simple terms that can be understand by all manufacturing stakeholders. You can use these terms and their definitions in working with broaching job shops and broaching professionals. Moreover, these terms will help you to understand specifications of machines in case you are ever looking to buy one.
Front pilot ensures the axial alignment of the broaching tool and the starting hole. Basically, front pilot works as a check on the starting-hole size. Similarly, there is a rear pilot, which also checks the alignment of the tool but is placed at the rear end.
The cutting teeth on the broach are not of the same size; instead, they are divided into three separate sections. The first section consists of roughing teeth, which are followed by semi-finishing teeth, and the final section has finishing teeth. The roughing teeth are smaller and the size of teeth height increases progressively.
The tooth land gives support to the cutting edge as it goes through various processes stresses.
The distance between teeth is called tooth pitch. The length of the cut determines tooth pitch or length between. However, sometimes pitch is influenced by the type of material, like steel or aluminum.
As a tooth enters a work piece, a fixed thickness of material is chipped, and this is called chip load. The type of the broach tool used in a machine determines the chip load.
There are notches on broach tools called chip breakers that get rid of chip by facilitating its removal. The semi-finishing and roughing teeth section of the broach has chip breakers which are parallel to the axis of the tool.
Teeth on the broach designed at an angle are called shear angle, which improves the ultimate surface finish. Shear angle also brings tool chatter down significantly. Shear angles become important when an adjacent work piece surface is being cut concurrently, as the shear angle moves chips, made from broaching, away from the intersecting corner. If not done properly, this can lead to the crowding of chips at the intersection and overall machine damage.
As slots are broached, the motion leads to substantial friction because the sides of the broach teeth rub the sides of the slot. This friction can cause rapid tool wear and tear, therefore, a clearance is provided, which is called side relief. A relief angle is grinded, therefore, on both sides of each tooth.
You will come across these terms while researching about broaching processes such as keyway broaching, spline shafts broaching, blind broaching, gear hobbing broaching, and rotary broaching.
If you want to learn more about the broaching, read our other blogs and articles, where we have detailed the broaching process, as well as the types of machines employed.
- A metal cutting tool with a series of
- The space between the teeth on a broach that accumulates chips during the cutting operation.
- A broach that cuts along the external surface of a workpiece.
- The angle of the cutting edge of a broach tooth.
- Teeth for finishing a surface that are arranged at a constant size at the end of a broach.
- Another name for "chip space."
- Another name for a tooth's "face angle."
- A broach that is pulled or pushed through a hole in the workpiece in order to bring the hole to a desired size and shape.
- The length of a broach tool.
- The measurement from the cutting edge of one tooth to the same point on the next.
- A type of broach that is pulled through or over the surface of the workpiece during an operation.
- A type of broach that is pushed through or over the surface of the workpiece during an operation.
- The teeth that cut first in a broaching operation, with heavier cuts than semi-finishing teeth.
- A broach with a circular section.
- On surface broaches, the angle between the cutting edge of a shear tool and the line perpendicular to the broach axis or line of travel.
- A type of tooth used on surface and external broaches, positioned so that it does not make a right angle with the direction of broach motion.
- An external broach that is used to cut a flat or contoured surface.
- From the root to the cutting edge, the height of the tooth or broach gullet.