Production Machining - Your access to the precision machining industrial buyer.
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Helping Precision Machine Shops Be More ProducƟ ve and Profi table 20 PRODUCTION MACHINING :: SEPTEMBER 2017 What Machinability Means Depends on Where You Are Continued from page 17 On the Machine In my experience, the machinist has a more expected defi nition of machinability, and that is ease of producing a chip with consistent dimensions and surface without leaving a burr, while making a part to print. This is characterized by higher speeds, feeds, effi ciency and shorter cycle times and consistent tool life. When discussing machinability with the machinist, surface feet per minute is usually one of the fi rst ideas to be discussed, but if the depth of cut and feed per revolution are wrong for the material, excessive downtime for tool adjustment, regrind or replacement will affect their ability to make conforming parts at the rate quoted. At the machine, the SFM, feed rate (IPR) and depth-of-cut factors enter the conversation, as they are considered against the particular demands of the operation and their interaction with the tooling selected (base material, coatings and geometry), the metalworking fl uid used, and the level of maintenance on the machine and its workholding. In the Estimating/Engineering Offi ce This is where making sense of the material has to take place if the shop wants to be successful. The engineer/estimator gets out the calculator and determines, using those speed, feed and depth-of-cut factors, the machining time needed to produce each and every feature on the part. It's simply how many revs at what removal rate per rev is needed to create this feature. Move to next feature and repeat. If only it were so simple! The reality is the estimator/ engineer has the experience and tribal knowledge to apply pragmatic adjustments based on their experience with all of the above. The estimator/engineer might think, "If the material comes in from supplier A, the bars are straighter and the dimensions are consistent, so we can use the high side speed and feed," or, "That runs on the machine that has the sloppy spindles, so we can't push it. If we had better workholding, we might be able to get that job running even faster, but the order quantity is too small to justify higher precision collets." And frankly, that is just to quote. If the customer accepts the quote, now we have to make it work! The Boss's Seat As a supplier of bars to thousands of customers, I've seen the view from the boss's seat. "Your bars are burning up my tools, which is bad machinability," is the view from the boss's seat. The fact that his new machine operators hadn't changed a rough form in two weeks and only changed the fi nish form tools when they were close to failing were somehow a machinability factor of my product. Or, the fact that his team had been used to machining an inexpensive, high-nitrogen, mini-mill steel, but because of delivery or price incentives, his buyer chose to buy my low residual, low nitrogen BOF steel, which cuts totally different. Well, somehow that is a machinability problem, not one of purchasing or engineering. But the message was still important. The boss wants to see those bars turned into conforming parts in the time we quoted with minimum fuss throughout his operations. What is the proper defi nition of machinability for our organizations, or the defi nition that applies wherever we are in our organization? I would suggest that machinability is promoted by the decisions that best align the properties of the material with the priorities of the operation to assure minimum issues with unexpected variation, providing consistent predictable performance and minimized downtime. It is not necessarily the cheapest, nor must it be the most expensive material. It is, I am certain, a product of consistent sourcing from companies with consistent and in-control processes and practices. And it is not just speed, surface feet per minute, or the percentage of 1212, though those can be factors. But if the tooling, workholding and machine maintenance are merely up to standard, tell me, how can you expect better than standard performance from the material and from your machinists? Aligning every position in our companies to make decisions that optimize production, reduce variation and minimize downtime is the real job of the person in the boss's seat. I hope this article gives you some ideas regarding the conversations you need to have.