Monday, February 2, 2015

Balance Cutting Tool Life With Productivity

By Chad Miller, Product Manager – Turning and Advanced Materials

When it comes to cutting tools, machinists often find themselves torn between maximizing tool life and increasing productivity. But it really doesn’t have to be a choice. By understanding and following a few basic rules, it’s possible to achieve a balance of long life and high productivity from the same cutting tool.

1.  Tweak speed slowly within the recommended range.
Speed is the single biggest factor affecting cutting tool life – the higher the speed, the lower the tool life.  Unfortunately, machinists looking to increase productivity often make the common mistake of just cranking up the speed. They may even turn on the machine override and start running at speeds that are 20 or 30 percent higher. While this may increase the number of parts produced, it will drastically reduce the tool life. In fact, we’ve seen that increasing the speed by 50 percent can cause tool life to go down by as much as 90 percent. It’s best to stick within the tool’s recommended range for cutting speeds, tweaking speeds carefully along the way to find the best maximum that gives you both longer tool life and a higher level of productivity.

2.  Increase depth of cut to improve cutting tool productivity.
Increasing depth of cut can have an enormous impact on productivity. At the same time, a larger depth of cut does not have much effect on cutting tool life.  When machining a component that will have numerous passes with an insert, increase the depth of cut to reduce the number of passes thereby increasing productivity. 

3.  Increase feed rate to get more productivity out of the same inserts.
When it’s not possible to decrease the number of passes by increasing the depth of cut, the next best thing is to consider increasing the feed rate. When I am with a customer on his or her shop floor, the first thing I look at is how to increase feed rate without sacrificing surface finish. If we can increase the feed rate and still achieve the desired quality and precision, we can reduce processing time.

4.  Take a closer look.
One of the best ways to find the balance between the variables affecting tool life and productivity is to study how the tool is behaving during operation. Let’s say you’re currently getting about 100 parts per edge and you want to increase productivity to 125 per edge. Stop machining and pull the tool after about 80 pieces or 80 percent of the tool life and look at the edge wear under high magnification. This closer inspection will give you a good idea of what is going on with that insert – its condition or changes that have occurred– and allow you to adjust speed, feed or possibly change to a different grade or chip breaker to be able to increase throughput.

5.  Choose the strongest insert geometry.
Using the strongest possible insert geometry for the application gives you an opportunity to increase productivity by pushing feed rate and depth of cut. According to ISO standards, round insert geometries are going to be the strongest, followed by square, C, P and then V, respectively.

Machinists in different industries view the importance of tool life compared with productivity differently. Machinists in the automotive industry, for example, are often more concerned with achieving a higher volume. They need to get a lot of parts through the door very quickly and tend to run the inserts a bit faster in feed and speed. 

On the flip side, machinists in the aerospace industry are generally more concerned with tool life and quality. When machining high precision parts such as jet engine components, they want to make sure the insert completes the part. They absolutely do not want to have to pull the insert out in the middle of machining, so we see them running at more conservative speeds to extend the life of the tool.  

The most important tip of all is to use the insert within the recommended guidelines for speed and feed. Following these recommendations should result in good tool life. To learn more about how to balance tool life with productivity or discuss a specific challenge, please feel free to contact me.

About the Author
Chad manages Seco's turning and advanced materials product lines, including all CBN and PCD products. When he's not helping customers implement advanced metalcutting solutions, you can find him training for and running 5K, 10K and 1/2 marathon races and triathlons. 

1 comment:

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