MAY 2017

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Page 4 of 23 | The Machine Tool Search Engine 3 Is It Time to Move Up to an HMC? The horizontal machining center is a fundamentally productive, versatile machine. Shops should consider the benefits of horizontal machining. By Barry Rogers In general, shops should consider using an HMC for prismatic parts on which multiple sides or surfaces must be machined. Good examples are valve bodies or aircraft components. Typical applications for an HMC include high production volumes, parts smaller in size or jobs with longer run times. That's not to say flat or plate stock cannot be machined on an HMC, because it can. However, this type of work must overcome some minor challenges of gravity by using appropriate fixturing. In short, horizontals can offer more flexibility than vertical machines. The first thing that jumps out at anyone considering buying an HMC is the cost. HMCs typically have three times the purchase cost of a VMC: around $375,000, compared to $15,000 for the average VMC. Notice that I didn't say three times the cost, but three times the purchase cost. You can easily spend $1 million if you want to purchase the most technologically advanced HMC available on the market today, including desirable options and accessories. WHY BUY A HORIZONTAL? The simple answer is productivity and profit. Horizontals can easily do three times the work of a comparable VMC. This assertion assumes that the workload to keep the machine busy is available. Without question, you can get more done in far less time using an HMC. With the increase in production, shop throughput is greatly improved. Because multiple operations can be done in a single setup on an HMC, less work in process must move around the shop, increasing efficiency. An HMC can readily replace three to four verticals in many applications. This means one HMC operator can do the work of three VMC operators, thus reducing labor costs. While the monthly finance payment for an HMC may be $4,800 higher than that for a VMC, the monthly labor cost for one HMC may be $7,200 less than that for the same amount of production on VMCs. Also, because HMCs usually have more associated automation, the operator can devote less attention to it, enabling him or her to run another cell, operate other equipment or perform inspection. SPINDLE UTILIZATION Making money on any CNC machine requires keeping the spindle running so that it is making chips with the least amount of operator intervention. A survey conducted by university researchers found that, "on average, VMC utilization, as measured by spindle run times, is 25 percent. HMC utilization is routinely 85 percent." A shop proficient with its VMCs may have 30 to 35 percent utilization, yet this is still substantially below the utilization rate of an HMC. In a typical eight-hour shift, the HMC cuts for about seven hours, whereas the VMC cuts for about two hours a shift. In a five-day week, the HMC gets 35 more hours a week of

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