MAY 2017

Techspex provides metalworkers free research and analysis tools to help them find the right machine for their job.

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I S I T T I M E T O M O V E U P T O A N H M C ? 6 percent of all horizontals come with an APC Tombstones are upright fixture blocks with two or more sides onto which parts can be mounted for machining. They are also known as pedestal-type fixtures, tooling towers or tooling columns. These fixture blocks can be configured with two, three, four or six sides. The basic idea of a tombstone is to hold multiple parts per side. Typically, tombstones are made from aluminum or cast iron, and have bolt holes for attaching fixtures and clamps to hold the parts. The tombstone can be mounted on a moveable pallet to be shuttled in and out of the machine. Single-sided angle plates can also be mounted on an HMC, with or without the use of a tombstone, to machine parts made from flat plate. FIXTURING With an HMC, you have to be more creative when it comes to fixture designs. Fixtures may require more sophistication than those for a VMC, depending on part size. While it's often easy to get by with using vises on a VMC, vises are less useful on a horizontal. Common tooling items used on HMC fixturing include edge clamps, toe clamps and wedge clamps. While fixturing on an HMC might seem complicated, it also provides considerable flexibility. HMCs can use hydraulic or pneumatic fixturing. Some machines have the option to plumb hydraulic or pneumatic lines through the pallet which can then be incorporated into the fixturing. M codes are used in the CNC program to apply clamping pressure into fixtures in the machining zone. Although you can do the same on a VMC, it's more convenient on an HMC, because the pallet can be shuttled to the unload station while the clamps are still engaged. Hydraulic and pneumatic lines are usually fixed on a VMC, but on a horizontal, the lines are usually integrated in the pallet. This feature gives you the ability to use multiple hydraulic or pneumatic fixtures across multiple pallets without having to remove and replace hydraulic lines or fittings. PALLET POOLS Pallet pools enable more than two pallets to be used for continuous operation. Without a pallet pool, there are only two pallets and they must run one after the other. A pallet pool interfaces directly to the APC, enabling a pallet to run in any order you decide. For example, if you have four different jobs lined up on the machine and one job runs out of material, production of the other three can continue. Typically, pallet pools consist of six or more pallets, making around-the-clock, lights-out operation possible. Even if you buy an HMC with no intention of running all night, you still gain savings by automatic loading and unloading without interrupting the spindle of the machine. The uptime created by this method accounts for increased spindle utilization, which can be as high as 85 percent. CHIP EVACUATION HMCs are designed to run long periods without interruption. What happens to all those chips? With a high-pressure, through-the-spindle coolant system, chip evacuation on an HMC is easier than on a VMC. With a horizontal spindle, chips naturally drop into the conveyor. Another benefit of gravity and high-pressure coolant on an HMC is that deep-pocket milling or drilling causes less wear on the tool and preserves the surface finish. Chips have a tendency to fall out of a pocket as they form rather than remain in the bottom to interfere with cutting action. Select the best kind of chip conveyor based on the type of work you plan to do with the machine. For example, if you will be doing

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