Machining

Several weeks ago, my wife and I attended a dinner party at her sister's home. One of the guests heard I was in manufacturing and introduced himself. He's 48, married and has five children and a mortgage. He's a pleasant individual, and we spoke about his trials and tribulations over the last few years. He lost his job during the Great Recession and has since been struggling to find a steady job. Unemployment checks and odd jobs, as well as assistance from their church and friends, have helped his family muddle along. His experience is in customer service and sales.

Real-time measurements during metalcutting can offer significant insight into machine tool performance. The parameters to be measured include position, velocity and acceleration of the axes; cutting force; sound; temperature; and acoustic emission, which is not the same as sound, but rather a high-frequency, structure-borne vibration.

All metals are not created equal. Therefore, neither are the machine tools for cutting them. Parts for extreme aerospace applications, such as in engines, landing gear and flap tracks, must be made of a heat- and corrosion-resistant metal, which typically has a high Young's modulus of elasticity and is difficult to machine. These include titanium, stainless steel and high-nickel alloys.\r\nThe “hard metal” machines that process the parts must be stiff, typically requiring a large mass, and have a large servomotor to create lots of thrust. They also need a high-torque spindle to effectively move the cutter through the material and a high thrust load on the axes of the ballscrews, which often have a low 8mm pitch, to offer an effective mechanical advantage, according to Scott Walker, president of machine tool builder Mitsui Seiki USA Inc., Franklin Lakes, N.J. He explained that the machines are built that way because aerospace customers typically run them slower than 600 rpm, require around 2,000 ft.-lbs. of torque and take maximum chip loads from 0.002 to 0.006 ipt. “So you build this big, rugged machine,” Walker said.

The U.S. economy appears to be on the mend. In January, the Manufacturers Alliance for Productivity and Innovation gave a tentative thumbs up to sustained business expansion through the first half of 2013. And the Institute for Supply Management's manufacturing index rose again in January, painting an optimistic picture. Maybe it's time to buy that machining center you've been thinking about.\r\nBefore you whip out your checkbook, though, some homework is in order. There's a lot more to machining centers than spindle speeds and rapid traverse rates. Sure, you've had good results over the years buying machines based on that, but that might be the wrong criteria in this brave new manufacturing world. You're facing growing competition from overseas and down the street, so you owe it to yourself to take a look at what's changed in the years since you bought your tried and true 20"×40" vertical machining center.

High-performance cutting tools can provide increased efficiency and productivity, but they can also be a drain on tooling budgets. Cost-justifying these tools often requires regrinding and reconditioning them when they are worn or damaged. A successful reconditioning program reduces tooling costs by extending life as long as possible.

Continuing and concluding the theme of my previous two columns, this month's installment provides additional tips for enhancing the operation of a manual milling machine.

Prevent sealed bearings from overheating in a live tooling head. A live tooling head with coolant-fed bearings.

Enhance PCD cutting tool design while decreasing processing times. SOLUTION: A 6-axis rotary erosion machine.

Provide centerless grinding machines that can produce parts with continually tightening size and surface finish requirements. Customized coolant filtration equipment.

Milling sounds range from loud to quiet, and experienced machinists <br />often use those sounds to judge what is occurring in the cutting zone. It is difficult to position a sensor such as an accelerometer or a displacement probe close to the cutting zone, and it is often a challenge to see the cutting zone, but the sounds are pervasive.