Machining cell meets JIT production requirements

Manufacturing Engineering, Jul 1998

A big, twin-machine flexible machining cell at John Deere's Davenport, IA plant lets the company achieve build-to-order flexibility on just-in-time (JIT) scheduling for five different four-wheeldrive loader models. Two Cincinnati Milacron (Cincinnati) machines process between 10,000 and 11,000 tons (9000-9900 t) of parts annually, with just one operator each, three shifts a day. Two machines produce most of the large chassis parts: a TC-Bar horizontal CNC machining center with dual rotary worktables, live spindle, and nine CNC-controlled axes; and a Magnum 800 CNC horizontal machining center (HMC) with a six-pallet automated workchanger.

"The TC-Bar produces the loader's engine frame, which houses the engine, transmission, cab, rear axle-literally the entire back half of the articulated loader," says Deere supervising engineer Tom Roller. "Frames arrive as unwieldy, boxy steel weldments, weighing as much as 6000 lb (2.7 t) each. Everything takes place in a single setup. Once fixtured to one of two 63 X 80" (1.6 X 2 m), 360,000position tables, the operator starts the cycle." A probing operation tells the Acramatic 950 CNC which frame is on the pallet, and the machine does the rest. The two-table setup allows continuous machining, and the TC-Bar can run 24 hours a day, seven days a week, without interruption.

As well as an 80,000 lb (36.3 t) table capacity, the TC-Bar features a 432" (ll m) longitudinal column travel in the X axis. The 15 (4.5 m) swing diameter of the two tables accommodates Deere's biggest parts. "We rely on this capacity," says Roller, "and use every bit of it."

On the line, the Magnum runs a variety of loader parts, such as linkage parts, mounting pans, and axle support parts weighing from 20 to 800 lb (9-363 kg). Its front carousel workchanger moves constantly.

Six off-line pallet stations keep the Magnum's high-output, 50taper spindle running. Per-pallet loads as high as 4847 lb (2.2 t) and 45.3" high by 51.2" diameter (1.2 X 1.3 m) transfer in and out in seconds. Automatic pallet transfer on and off the Z axis is a speedy 1000 ipm (25.4 mn/min). The rotary workchanger brings a new pallet of parts into position for shuttle onto the pallet-forward Z axis. Pallet loading and unloading takes place during cutting. Cycle times range from 5 to 30 min.

"We do a lot of torque-controlled machining [TCM] in the cell, involving constant horsepower monitoring", says Roller. AcraSense builtin torque control software automatically monitors spindle load and changes the feed rate in-process, reducing broken tooling and optimizing metal removal and tool life. Software continuously compares measured cutting torque with programmed values, and automatically adjusts the cut for conditions such as gaps, workpiece hardness, hole break-through, cross and blind holes, and chip buildup. When a problem occurs, AcraSense automatically initiates a machine-feed hold, or users can program it to replace a broken tool in the case of redundant tooling.

"We analyze all related operating costs of our major equipment purchases over the entire life span of the machine," explains Roller. "Taken individually or collectively, the equipment and long-term costs may seem staggering, but in the context of value added to the end product, these costs are really quite reasonable." For more information on Cincinnati Milacron equipment, Circle 372.