If you’re like me, you scan every issue of this magazine and read the first few sentences of each article in order to quickly discern if reading the whole thing is worth the time. If your company is broaching parts, or considering doing so, then reading this article is well worth the 10 minutes it will take—and that’s a promise.
The focus is the importance of proper cutting tool sharpening. Re-sharpening is often an afterthought for most companies trying to scramble through a launch, P-pap, paperwork, and then troubleshooting daily production heartburns. It is of course impossible to optimize the process without a good cutting tool design, quality steel, and proper tool processing, surface treatments, or coatings, as well as all the other attributes inclusive to the broaching process. The machine is also a very big factor. Newer machines are using technology and software to reduce the cost per part and improve speed and quality, and all these things definitely make a difference. After it’s up and running, however, it quickly comes back to re-sharpening, and then its “off to the Milky Way” as W. Edwards Deming—the father of modern management thinking—was fond of saying. Figure 1
Regardless of whether your sharpening is done in-house or your company is using a vendor to re-sharpen your broach tools, the process will only be optimized if the tools are sharpened on a CNC tool grinder. We understand that it may be more convenient to send broaches out to a local sharpening guy who will handle anything that needs sharpening. Figure 2 Many times these local guys offer free pickup and delivery, and they do it quickly. But very few of these local shops have dedicated CNC broach tool re-sharpening equipment. It might alternatively seem tempting to utilize internal personal that have some manual sharpening ability. On the surface it seems this would be lower in cost; after all, who doesn’t want to keep it local or in-house? Nothing could be farther from the truth. If your broach tools are not CNC made and CNC sharpened throughout their life, your company is wasting money in every case. The following is a list of the benefits of CNC sharpening, and after reading it you will intuitively know what you need to do in order to get double the life from your broach tools. Figure 3
Broach Tool Benefits
Even stock removal from each tooth: With the use of a tooth edge probing system, encoders, and/or scales, the exact tooth pitch can be recorded and the machine can be set to remove precise amounts from each tooth. This is important for several reasons that impact the tool’s life. Maintaining the pitch maintains the cut per tooth per the design. Thin teeth are similar to the weakest link in a chain; once a tooth is too thin and breaks, the tool’s life is over. When tools are manually sharpened, each tooth has a different amount of stock removed. This removal is predicated by the operator’s hands and eyes.
The use of coolant while grinding: Coolant serves two main purposes in this application: cooling during the grind prevents burning—if you burn an edge, it’s soft as a result, and soft is bad—and lubricity, to improve wheel cutting life. We have all seen the brown edges on manually sharpened broach tools. Figure 4
Consistent geometry every time: Even the very best operator has a bad day. A CNC grinding machine never has a bad day. This is important for several reasons that impact tool life. Maintaining the geometry per the design allows the tool to work as it was designed, and it provides stable results for design improvement considerations.
Smooth surface finish with proper blending: This allows chips to fall out easily.
Thin burrs that are easily removed before broaching: CNC sharpening will produce thin sharpening burrs that are easily removed before broaching. Manually ground tools typically have a thick burr, and when it is removed micro-chipping occurs at the cutting edge, which really reduces tool life.
Reduced tool warping and bending during grinding: CNC grinding under coolant will reduce tool bending during grinding. Manual dry grinding introduces heat into the tool, and bending is unavoidable. Bent tools do not broach accurate parts.
More regrinds per tool: It’s an absolute fact that tools that are CNC re-sharpened get more regrinds per tool, many times double the number. The thinnest tooth on the broach is similar to the weakest link in a chain, and with hand grinding variation is inevitable.
More parts between each resharpening: Normally we see 10 percent more parts between each sharpening when tools are CNC sharpened. In one recent extreme case, the improvement was 500 percent! Figure 5
Faster than conventional grinding: CNC sharpening is faster than manual grinding. If an average tool takes one hour to sharpen manually, it will take 40 minutes on a CNC, including setup and programing. The difference is that the operator on the CNC walks away for 30 minutes of this cycle.
Repeatable results: The results are repeatable with CNC grinding. If I had a dollar for every service call on a broaching machine where I found an improperly sharpened broach tool to be the root cause, I would be smiling large.
Process predictability: Process predictability is so important, and if you want process control then CNC grinding is a must.
Less labor intensive: Spend an hour watching someone sharpen a broach tool manually, and then watch a CNC grinder operator set up and start a CNC grinder, and then walk away. It’s easy to see why everyone would agree that CNC re-sharpening is less labor intensive.
Operator friendly, easy to run: We can’t speak to every grinder, but the American Broach CNC grinders are operator friendly and easy to run. Figure 6
Considered “best practice” globally: CNC sharpening broach tools is considered “best practice” around the world. To date American Broach has designed, built, and delivered over 50 CNC broach tool grinders.
The goal for American Broach & Machine Company is to provide a value added service to all of our customers. We do this every day by offering best practice advice, as well as providing a reliable source for world-class innovative broaching machines, quality broach cutting tools that perform, and turnkey CNC broach tool grinders or grinding services for our customers. We do this with the goal of eliminating hassles and reducing the cost per part. CNC broach tool sharpening is a key critical component of any broaching process, so don’t overlook it or it will cost your company money. Figure 7
The best tool life—and the key to “getting double the life from your broach tools”—lies in optimizing the entire broaching process, which is impossible without the use of CNC manufactured and sharpened broach tools. We also strongly suggest the use of metrics to visually display the value of CNC sharpening to process controls and resulting cost savings both monthly and annually. This really drives home the value to your entire team, and makes CNC re-sharpening broach tools seem as necessary as breathing. Please feel free to contact me at the number or e-mail address listed at the end of this article if you would like to schedule a site visit to observe the CNC broach tool resharpening process firsthand, or you can view the process on YouTube. American Broach & Machine Company is the only broach tool manufacturer America making a CNC broach tool grinder.