March 2013 / Volume 65 / Issue 3|
Boost cutting efficiency with training
By Christopher Tate, Mitsubishi Power Systems, Savannah Machinery Works
Dynamic and aggressive cutting tool demonstrations are common at trade shows. Toolmakers present phenomenal displays, where chips spark and fly and machines move at feed rates that seem impossible. In other words, they demonstrate high-speed machining.
Few marketing tools are as successful as these demonstrations. Of course, the intent is to convince attendees that one tool is more capable than the next, and, by purchasing the more capable tool, they’ll achieve the same results, ultimately reducing cost through increased efficiency.
However, efficiency gains can be achieved without purchasing the newest products. Significant gains can be made with solid technical training and by applying that knowledge to the machining processes.
In my previous column, I pointed out how proper cutting tool application enhances profitability by prolonging tool life and boosting efficiency. It’s no secret that removing more material in less time is a common goal. Unfortunately, part manufacturers often rely on the cutting tool manufacturer’s application experts to be the source of knowledge for achieving efficiency gains with cutting tools. Cutting tool manufacturers should be viewed as partners because they can provide valuable resources to solve difficult problems, but even good partners are not always available.
The reliance on outside expertise comes from an inverse relationship between the development of machining technology and the dissemination of shop floor knowledge. As machining processes and cutting tools have evolved, the theories that drive many of the improvements have not been effectively conveyed to operators on the shop floor.
A more proactive way to increase efficiency is by establishing a robust training program that teaches chip-formation theory to machinists, engineers and programmers. It is common to encounter metalcutting professionals who cannot properly calculate speeds and feed rates—the most basic of machining calculations. Those who lack experience or training often rely on past practices by copying old programs or techniques, which propagates inefficiency.
Proper training can combat inefficiency by preventing this propagation and by providing the insight needed to identify inefficiencies. For example, at a previous employer I was the manufacturing engineer responsible for a dedicated machining cell that produced a family of 24 aluminum aerospace parts. The parts shared a common configuration and differed mainly in size. The first machining operation on each part was milling a circular boss from 2 " to 10 " in diameter. All bosses were cut with the same 3 " facemill tooled with PCD inserts.
I had not been on the job more than a few days when I noticed the cutting speed varied significantly from part to part. I asked around and no one could tell me why. In the part programs, I found several different speeds and feeds, but none in the range recommended by the toolmaker. After calculating the correct parameters using the median starting values from the tool catalog, I changed each program and documented more than $50,000 in annual efficiency savings. The total investment was about 8 hours of engineering time.
Had the previous machinists, engineers and programmers been given proper technical training, the company might have saved $500,000 during the life of that cell.
Every person who is held accountable for shop productivity should be taught the following key concepts.
■ How to calculate rpm for a given diameter based on the desired surface speed. The rotational speed of a tool directly impacts its life and cycle time, and, therefore, cost. Machinists, engineers and programmers should also be able to calculate the surface speed based on tool diameter and spindle speed to verify that older programs are correct.
■ How to calculate feed rates based on the desired chip load. Feed rate has less effect on tool life than rotational speed, but it can certainly alter the cycle time. As with rotational speed, end users should be able to work backwards by calculating the chip load per tooth using ipm and rpm.
■ How chip thinning, which is the basis for HSM, is related to feed rate. High-volume CAM packages derive their toolpaths primarily from algorithms based on chip thinning calculations. However, users can achieve productivity gains by exploiting chip thinning without purchasing software by simply learning when to change the feed rates to maintain proper chip thickness.
■ How to calculate expected surface roughness. Expected surface roughness can be easily calculated. Accurately predicting surface roughness can reduce development time when introducing new processes by reducing trial and error caused by the cut-and-measure cycle.
■ How edge geometry, chipbreakers and DOC interact when turning. I have witnessed many chip control problems in turning operations that could have been quickly eliminated had the machinist simply chosen a different edge prep, chipbreaker geometry or DOC.
These are the concepts I feel are most important to increasing productivity. It is not necessary to have graduate-level mastery of these calculations to realize benefits. Recognizing that complex relationships exist and information is available when needed should be the primary focus of a chip-formation training program. When machinists, engineers and programmers become familiar with these concepts, they can begin to recognize opportunities for improvement and develop a vocabulary that enhances communication when discussing problems and solutions.
In addition, providing operators with the skills needed to document their suggestions will give them confidence and pride in their work. That confidence will encourage more investigations and help drive improvements in part quality and machining efficiency.
Training costs are not prohibitive because most major cutting tool manufacturers are more than willing to provide it free of charge, either onsite at your machine shop or in offsite classroom settings. Manufacturers also provide productivity improvement tips in their free catalogs and technical guides, and are eager to get their printed and online materials in front of customers.
Providing shop personnel with instruction costs very little, instills confidence in the workforce and empowers frontline personnel to make significant improvements in efficiency and productivity. CTEAbout the Author: Christopher Tate is manufacturing engineering lead for machining at Mitsubishi Power Systems, Savannah (Ga.) Machinery Works, a global builder of gas and steam turbines. He has 19 years of experience in the metalworking industry and holds a Master of Science and Bachelor of Science from Mississippi State University. E-mail: email@example.com.
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