Cutting Edge Article – Broaching 1

When discussing a topic to write about in our monthly publication, I broached the topic of broaching with a few people. (I try to add levity and humor when possible and often fall short, I will apologize now) I found that some people utilize the broaching process and are happy to share their thoughts and approach to it and others just don’t use it at all. Broaching in the steel rule die making industry is the process of reducing the thickness of the rule, typically within a few thousandths of an inch from the cutting bevel, to allow the die maker to create a very small radius. This is typically done to prevent cracking or edge distortion of the steel rule when bending a small radius. When bending a tight radius without a broach, the rule is compressed on the inside and stretched on the outside. This compressed steel needs to go somewhere which is typically down, in the form of a small bump causing a high spot in the rule that can flatten the edge very easily during the make-ready process. With the latest technology in rule processing, automated benders can now bend to a very tight radius. This stressing of the rule combined with the excessive stretching can cause the rule to crack or the bevel to distort. When using side bevel rule, there are different applications that may benefit by bending with the bevel in or bevel out depending on the application. Broaching may help in cases of side bevel bending especially when tight tolerances are required. This is probably more important to those folks outside of the folding carton industry making dies for gaskets, overlays, labels and other tight tolerance tooling.

(t-6 here)

There are a few different methods for broaching steel rule. One is with a grinding wheel and the other is using a series of teeth to progressively scrape away the side of the rule to within a specific distance from the bevel. Broaching can be done with special offline equipment also with newer technology and can be accomplished inline on a rule bender, saving time and money. With the scraping method of broaching, I learned that adding a radius to the broaching tools can add to the life of the tool by giving it more strength. The idea behind creating the broach with a radius cut can also help guide the bend to the middle of the broach for better bending accuracy. This could be a big benefit for tooling with very tight tolerances. This can also allow for a faster and easier make-ready on the die cutter, especially if you are using the die for kiss cutting. Broaching the tight radius areas can also allow the rule to be inserted into the die board a little easier by having less material to fit into a small area. 

(t-5 here)

For die makers, understanding the customer’s goals is very important to making the right tool for the job. If a faster make-ready and longer die life is a goal, broaching might be one way to help them save some time in make-ready as well as increase die life. Looking at the folding carton industry, we see press manufacturers focused on helping their customers run machines to their full potential. We also see those customers working toward faster make-ready times and longer die life. Taking the time to broach areas with tight bends may help prevent a high spots in the die allowing for faster make-ready by reducing patch up time but also extending the life of those knives by not slamming them into the cutting plate.

(t-7 here)

Another area where broaching may help is in tight gullet areas to replace or eliminate side grinding or a miter. It’s the same old story…the job was designed and approved with very small gullet areas or a not so friendly single knife layout and now there are a few departments that have to figure out a way to successfully make a good carton quickly. By bending the rule to a very tight radius or broaching a “T” intersection to eliminate an additional miter might just help you with stripping. I am sure you have all seen a broken miter or an area with a side grind open up. This is a potential nightmare in the stripping process. With more and more converters taking advantage of Dynamic stripping methods that are available, eliminating the possibility of a natural nick could be huge when trying to strip a small piece of scrap. Broaching a small hairpin or gullet area could give you a superior outcome with Dynamic stripping methods especially in those very tight areas. 

(t-2 here)

There are several benefits to broaching specific jobs depending on the outcome you desire from the die. A more accurate die in some cases can be a big benefit to the customer depending on what they are cutting and the tolerance they are trying to hold. In the gasket and label industry, there are some very tight tolerances that converters are expected to hold. Improved make-ready is also a benefit, with the improved tolerances of die cutting equipment this could save time in make-ready and add life to the customers die. If the die will be used for kiss cutting, this could be a huge benefit especially if the end user will not accept parts with cut through the liner. With the multitude of materials that can be kiss cut, broaching could make or break the job for your customer. 

After discussing this topic with a few different people, I found there are different thoughts and approaches to broaching. While there are reasons and benefits to broaching, the process is not always an exact science. It may take some time and finesse to get it just right. One suggestion was to test the rule you are using for its ability to broach and bend a tight radius before you begin. This will keep you from having to possibly mix and match different types of rule in one job. It was suggested to make a few sample pieces and evaluate them under magnification, looking for small cracks in the body and bevel of the rule. It was also suggested that in some cases you may need to make 20 of the same piece just to get 10 good parts. Also, make sure the broaching is to the correct depth, too shallow or too deep could cause an issue later in the cutting process.

(t-4 here)

The other part of successful broaching is the maintenance of the broaching tools. If your tools are not properly maintained, you could find yourself struggling trying to troubleshoot the issue. Of course, then you can always blame the rule….! (Ok I tried, it’s hard to find humor in broaching.) All kidding aside, die makers are trying to make a quality tool with very tight deadlines and very high expectations. With all the tools a die maker has to work with, if they are not well maintained it is hard for them to produce a quality product.

Is Broaching needed on all jobs? Are there cases where Broaching can help with the cutting and stripping process? That is for the Die Maker and their customer to determine.