Rotary broaches are used to cut precision hexagon, square and other polygon forms in metal parts. The rotary broaching process is popular for manufacturing blind holes on most turning machines, including lathes, mills and machining centers. Due to various form sizes and part materials, Polygon Solutions Inc. offers a variety of broach materials.
Although form sizes typically range from those considered micro up to about 3/8", larger sizes can be broached, but may result in poor broach life. Upgrading the broach material can provide customers with tougher or harder broaches that will last longer when broaching larger sizes. Customers who choose to use pilot-hole diameters that are very close to the flat-to-flat dimensions may also see improved tool life when upgrading broach materials.
Another factor to consider is material of the work piece. The machinability of aluminum makes it ideal for rotary broaching. Polygon Solutions customers have reported broaching 1000's of small parts using a single broach. However, alloy steels, stainless steels and other tougher metals will cause the same broach to wear much faster. Upgrading the broach material can also provide customers with tougher or harder broaches that will last longer when broaching tougher materials.
Polygon Solutions Inc. presently offers (4) different materials for all standard and custom made broaches. These high speed tool steel materials include:
This tungsten molybdenum tool steel has high wear resistance and bending strength. M-2 is the standard material used for all broaches by Polygon Solutions Inc. and is suitable for most work piece materials.
Powdered metal has a super-fine grain size and carbide microstructure resulting in an extremely versatile high speed steel which provides a unique combination of high wear resistance with high impact toughness. Polygon Solutions recommends PM M-4 for broaching stainless steel and improving tool life in general.
M42 is a molybdenum chromium vanadium tungsten high speed steel alloy with an additional 8% cobalt composition. M-42 is recommended by Polygon Solutions Inc. for challenging broaching projects including titanium alloys and other materials used in the medical and aerospace industries.
This powdered metal also has a super-fine grain size and improved tempering due to its cobalt composition. Polygon Solutions Inc. recommends PM T-15 for broaching harder grades of stainless steel and most materials where chipping is the failure mode and a harder broach material is required.
Upgrades to rotary broach materials require more than simply choosing a harder tool steel. Complex combinations of rotary and axial stresses affect each material differently. Although one variety may technically be harder, it may also be more brittle. Broaching speeds and feeds can also affect performance. The recommendations here are meant to be starting points, and a means of continuous improvement in optimizing your rotary broaching process.
Ordering rotary broaches with the various material options mentioned in the article is easy to do. Polygon Solutions Inc. has an online store (www.buybroaches.com) with pull-down menus for specifying broach materials. Technical support is also available by phone or email, which is also published on the company's website.