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Mechanical engineering |Машиностроение

Lesson 7

Read the text: The rotary broach

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 wobbles broach. This type of tool is often used on rotating machines such as lathes, screw machines and turning machines.

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, and this leading edge of the tool is wider than the body. The broach is free to rotate within the tool holder, but the axis of rotation is inclined slightly to the axis of rotation of the work. A typical value for this misalignment is 1 degree. 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 work piece, but is driven by tool holder rotation. Since the axis of rotation is different, the tool holder appears to "wobble" with respect to the work. This illusion is the reason for the original term 'wobble broach', now commonly referred to as 'rotary broach'. If the tool is inclined at an angle of 1 degree to the work, the sides of the tool must have a 1 degree or greater draft. Ideally the tool advances at the same rate that it cuts. So a 1/2" diameter tool should advance at 0.009" per revolution.

If it advances any faster than that, then the tool becomes choked; if it advances any more slowly, then you get an interrupted or zigzag cut. Since all work material is elastic, you would actually cut a little less than the ideal rate, just to release the load on the non-cutting edge of the tool.

There is some spiraling of the tool as it cuts, so the form at the bottom of the work piece may be rotated with respect to the form at the top of the hole or profile. Spiraling may be undesirable because it binds the body of the tool and prevents it from cutting sharply. One solution to this is to reverse the rotation in mid cut, causing the tool to spiral in the opposite direction. If reversing the machine is not practical, then interrupting the cut is another possible solution.

In general, a rotary broach will not cut as accurately as a push or pull broach. However, the ability to use this type of cutting tool on high-production machinery such as a screw machine, and eliminate secondary operations, makes this a desirable manufacturing method.

 

1. Match the left part with the right:

 

1. The broach is free to rotate within the tool holder, but the axis of rotation

a. secondary operations, makes this a desirable manufacturing method.

2. If the work piece rotates, the broach is pressed against

b. a little less than the ideal rate, just to release the load on the non-cutting edge of the tool.

3. Since all work material is elastic, you would actually cut

c. it, is driven by it, and rotates synchronously with it.

4. The ability to use this type of cutting tool on high-production machinery and eliminate

d. is inclined slightly to the axis of rotation of the work.

 

2. Complete the sentences with the suggested words: tool holder; axis; pressed; rotate; value; broaching; shape; leading edge; wobble

Rotary_____requires two tooling components: a_____and a broach. The _______of the broach has a contour matching the desired final_____, and this leading edge of the tool is wider than the body. The broach is free to _____within the tool holder, but the axis of rotation is inclined slightly to the axis of rotation of the work. A typical _____for this misalignment is 1 degree. If the work piece rotates, the broach is_____ against it, is driven by it, and rotates synchronously with it. Since the _____of rotation is different, the tool holder appears to "_____" with respect to the work/