Yes, in addition to standard production in HSS, we can supply sintered + coated tools suitable for broaching very hard materials (max. 28/30 HRC).
For hexagons, pre-drilling 5% more than the inscribed diameter is recommended. Example: Hexagon 10 - pre-drill 10,5. For squares, 10% more is recommended.
If broaching is done correctly, the slot or outer profile will be identical in shape and size to the section of the tool used in machining. Theoretically zero tolerance.
Preferably cutting oil but emulsifiable oil can also be used.
Certainly yes. As the cutting edge wears down (rounding off), the machining effort increases considerably, making it easier to break the tool.
Given that it should not break but only 'wear out', the most frequent causes may be: - imperfect coaxiality with the workpiece - insufficient pre-hole depth - screwing during machining when the drive lever is not used
The rotary broaching orientation lever is used to index the broach to the workpiece. In lathe application the equipment syncronized the rotation of the broach and the working piece while the tool holder stationary against the stop rod as the tool holder body rotates.
Many factors affect speeds and feeds, including material, pre-broach drill diameter and form being broached. It is good practice to set the rotation speed between 50 and 100 RPM in the initial phase of contact between the working piece and the tool (the feed can be the same as the machining). Maintain these rotational speeds until the broach perimeter has fully entered the workpiece (consider that 0,5 mm depth is sufficient for a 10 mm hex). Then you can set the machine tool to the recommended RPM. This will avoid hopping on the surface of the working piece and will reduce the risk of chipping or breakage of the tool. Contact Poliangolar for the best solution on your specific application. A better finish of the working piece is obtained by reducing the feed. Use rapid movement when retracting the tool keeping the same RPM.
This guide provides some basic rules and tips for successfully producing forms using the rotary broaching process. Rotary broaching requires two components: a rotary broach tool holder and a broach. Rotary broaching can be performed in almost any turning center: lathe (manual or CNC) or mill. The only difference is that in a lathe the tool holder is stationary and the part is turning whereas in a mill, the rotary broach tool holder is rotated in the machine spindle and the part is stationary.
The Poliangolar tool holders have completely sealed bearings. Therefore, there is no need for constant greasing. Poliangolar tool holders are completely adjustment-free. Alignment between the rotary broach to the centre of the workpiece is extremely important. Broken rotary broaches or uneven form configuration can result from improperly centered broaching. As long as the toolholder block on your turret (or machine spindle on a mill) is centered with your workpiece, simply insert the tool holder and clamp it down.
Fluids play a minor role in rotary broaching being, generally, a low heat operation. However, the use of cutting oil is recommended as an alternative conventional water-based coolant.
A pre-broaching drill hole is required for internal rotary broaching. It is strongly recommended to make hole diameter larger than the minor diameter of the form being broached. See below the formulas for recommended pre-broach drill hole diameters for hex, square and torx forms. When broaching forms with serrations or splines, it is recommended to pre-drill a hole 2-3% larger than the minor diameter of the form. These percentages may be reduced for free cutting material and increased in materials with tougher machinability.
The depth of the pre-drill hole must be greater than the broaching depth to allow for swarf to accumulate and avoid excess build up. It is recommended to have a pre-drill depth of 1.3-1.7 times the depth of broached area. If swarf must be removed after broaching, it can be done by drilling out. If possible, an undercut at the bottom of the pre-broach drill hole will allow the swarf to break cleanly. The undercut diameter should be larger than the major diameter of the broach.
Pre-turning the diameter of the workpiece is required for external broaching. The pre-turned diameter must be smaller than the major diameter of the broach. It is recommended to turn the workpiece diameter to the smallest allowable diameter so the broach will clear on the major diameter. Allowing for more clearance will reduce the required broaching pressure and increase tool life.
A back chamfer or undercut will allow swarf to break cleanly.
With difficult machining, it may be useful to use tools with a specific coating, which a specific coating, which in most cases can be TIN-PVD. The use of one of these coatings is recommended as the tools become more resistant to the heat produced by the machining and to wear and as a result extend their life. The TIN-PVD coating reduces wear and the tendency for seizing and produces an anti-adherent effect during machining, and is recommended for soft materials such as aluminium alloys. The Poly x Inox coating can also support grater thermal loads and better results have been obtained when machining abrasive (superalloys, cast iron) and harder (steel alloys, stainless steel and titanium) materials.
The most frequent causes of breakage or chipping of the tool edges are:
When machining square profile keep in mind that the quantity of material to be removed is more than double the amount for a hexagonal slot, for this reason the machine is stressed more, therefore these procedures normally require a very rigid and powerful machine. When possible, and especially with a square greather than 20mm, a few masures can be implemented:
Broach is bouncing off the face of the workpiece at initial contact.
Reduce the speed to approx. 50-100 RPM during initial contact into the part (maintaining feed rate). Then, increase the speed back to the recommended RPMs once tool is about 1 mm into part. Consider leaving extra stock on workpiece and clean-off after broaching.
Workpiece not held thight.
Use a serrated collet to hold the workpiece.
Swarf may be cleared out from the bottom of the part by going back in with the same drill used to pre drill the pilot hole. A small undercut may be added at the end of the broaching depth prior to broaching the form.