What is broaching?
Broaching is a manufacturing process that uses a broach, a multiple point linear cutting tool that removes material used to create holes, slots and cutouts. It is one of the most reliable and fastest machining processes. Broach may be used to create internal and external features. It is conventionally used to cut keyways and to create internally splined features. The concept of broaching as a genuine machining process can be traced back to the early part of the nineteenth century. Early broach applications involved cutting keyways in gears and pulleys. By the nineteen thirties, broaching allowed tolerances to be tightened and the cost of the process to reduce considerably, making it one of the most cost efficient machining processes. Today, almost any material can be broached.
Vestavia can offer one of the largest horizontal broaching facilities in Baltics, with which leads to a speedy completion of customer components.
Cutting force up to 40 ton
Types of Broaches
- Hex
- Spline
- Square
- ‘D’
- Double D
- Oval
- Circles
Broaches can also be categorized by:
- Use – Internal or External (surface) spur gears
- Function – Burnishing and roughing
- Motion – Stationary, push or pull
- Construction – Solid, hollow or shell or modular type
- Purpose – Single or combination
Depending upon the type of work-piece that has to be processed; broach material can vary from cast iron which is a low hardness material to very high hardness material like cemented carbide. Based on their working, broaches are classified as progressive cut, rotor cut, and burnishing broaches.
Types of Broaching Procedures
There are two types of broach procedures:
- Internal Broaching – This requires a starting hole or an opening in the work-piece so the tool or work-piece can be inserted. Then, work-piece is clamped into a special holding fixture called work holder which is inbuilt in the broaching machine. Elevator of the broached machine moves the broach above the work holder and then lowers the broach through the work-piece. Internal broaches include spiral teeth broaches that involve a continuous engagement of teeth. This process is used to produce irregular shapes, spline broach, key-way cutting or hole-configuration. Internal broaching can be done on a multi station machine, completing up to three or four parts per machine cycle. It is also used for making internal gears and in particular, smoothing of gun barrel bores.
- External Broaching – External cutting machines (which we don’t have) are used to process external surfaces of work-pieces. In this, broach tools may be pulled or pushed across a work-piece surface or the surface may move across the tool; this procedure is known as contour broaching. It involves preparation of concave or convex surfaces or any other shape with extremely close tolerances. Broaches which are used to cut externally require a starting hole and are also known as surface broaches.
The Process of Broaching
The process starts by clamping the work-piece into a special holding fixture such as the work holder, which mounts in the broaching machine. The broach needs to be mounted and clamped carefully in the tool holding device of the cutting machine. The part of the machine that moves the broach above the work holder, the broaching machine elevator, lowers the broach through the work-piece. After this, the machines’ puller, essentially a hook, grabs the pilot of the broach. The elevator releases the pilot and the broach is pulled through the work-piece, entirely. The work-piece is then removed from the machine and the broach is raised back up to reengage with the elevator. The broach almost always moves linearly. In process, the work order remains fixed and the broach travels while offering cutting velocity.
Most broaching machines are hydraulic. Electro – mechanical drives are also used for work that involves high speed but with light cuts. Machines are distinguished by whether their motion is horizontal or vertical-
(i) Horizontal broaching machines – They are the most flexible in utilization and performance and are employed for numerous types of production. These machines are used for internal broaching processes but they can also be used for external processes. They occupy large floor space.
(ii) Vertical broaching machines – Unlike horizontal broaching machines, vertical machines occupy lesser floor space and are used for the purpose of external cutting. They are more rigid and ram is supported by the base.
Broaching machines are specified by –
- Type – Horizontal and vertical
- Maximum stroke length
- Maximum working force (pull or push) or maximum cutting velocity
- Power
- Footprint
Advantages and Limitations of Broaching and its Applications
Advantages –
- Suitable and highly economic for mass production volumes.
- With single stroke of a cutter, surface can be roughed and finished.
- Design, construction, operation and control are simple as it is only used for a single motion cutting.
- High production rate.
Limitations –
- Requires a separate broach, whenever shapes of job change.
- Economic only when the production volume is large.
- Cutting speed cannot be high.
- High tool costs – Expensive to manufacture and re-sharpen.
- Usable only for light cuts.
Broach has tremendous potential for applications in these niche industries –
- The Aircraft Industry
- The Automotive Industry
- The Energy Industry
