Rebuilding only where necessary

Rebuilding only where necessary

DaimlerChrysler was machining 150,000 pump housings/yr for an electronic, four-speed automatic, rearwheel-drive transmission using a line that included nine automated and palletized HMCs and two vertical turning centers. Unfortunately, the housing design

Through machine tool evaluations, DaimlerChrysler had only those machines that needed it rebuilt to handle a new automotivetransmissionpump-design.

U.S. Equipment redesigned palletized tombstones to accommodate a new transmission-part size and correct deficiencies that caused diaphragm cracking.


DaimlerChrysler was machining 150,000 pump housings/yr for an electronic, four-speed automatic, rearwheel-drive transmission using a line that included nine automated and palletized HMCs and two vertical turning centers. Unfortunately, the housing design changed, making the part 5 lb heavier and 2 in. longer with a tighter tolerance of 1.67 Cpk.

To run the new parts, the company had to reprogram the machine tools, install new cutting tools, and develop workholding fixtures for the HMCs on twosided tombstones and chucks for the turning centers. But the most important part of getting the line running was to make sure the machines could meet the moreprecise tolerances.

Rather than retool the line and then find out that machines couldn't meet tolerances, the company worked with U.S. Equipment Co., which proposed evaluating the HMCs' and turning centers' capabilities relative to the process and statistical-runoff requirements. This would allow it to repair and rebuild only where necessary to meet customer requirements instead of completely rebuilding each machine. The evaluations and not having to rebuild all machines saved $1.5 million for the new part changeover.

Evaluations included static, dynamic, and load (circle, diamond, square) tests for each machine to establish its baseline condition. For static tests, U.S. Equipment examined axes for backlash, positioning, and repeatability as well as machine alignment. Also checked were power-supply output, servomotor-drive electrical data, and each CNC's functions. The company then checked the high-speed automatic toolchagers.

For dynamic testing, the company conducted vibration analyses to measure frequency response and amplitude through speed ranges, spindles, motors, and pumps, while also inspecting hydraulic pumps for vibration, noise, output, and leakage. Testing then involved evaluating electrical motors for smooth operation and quietness and machine cutting repeatability and accuracy.

In other examinations, U.S. Equipment examined lubrication, coolant, and filtration systems; visually checked hydraulic hoses, electrical cabling, power tracks, push-button panels, and overall cleanliness; and inspected main hydraulic pressure and all electrical peripherals.

"We found from the machine tool evaluations that the HMCs were basically in good condition," reports Paul Simon, president of U.S. Equipment. "However, one spindle had been crashed prior to the shutdown and needed replacing. Another required realigning. In addition, many machines needed preventative maintenance, and because of a contaminated air supply at the facility, we installed dryers on the machines and flushed and recharged the spindles." The company also installed Renishaw probe systems on six of the nine HMCs.

The evaluation also found six of the line's workstations (two/cell) were underdesigned and so loose in their tolerances from wear that when the AGV set tombstone pallets on them the pallets wouldn't seat properly on four positioning cones.

Because of this, workset stations weren't accurately receiving the tombstones from the HMCs, causing faults with the machine cell.

The palletized tombstones used hydraulic-diaphragm chucks to clamp parts. During the rebuild and changeover, U.S. Equipment redesigned them to accommodate new parts and correct deficiencies causing diaphragm cracking. After redesigning the first chuck, the company simulated workholding and ran it over 150,000 cycles to make sure the new diaphragm material was flexible enough.

Each VMC in the line was out of square and no longer met OEM specs. They needed complete rebuilding, which was done at U.S. Equipment's facility. Also, a washer in the line was repaired and reconfigured for the new parts and a CMM was recalibrated and reprogrammed.

"We wrote new programs and provided three sets of toolholders and perishable tooling," adds Simon. "The tool pockets still functioned and were reused, and we provided program management and application engineering that included the processing, cycle times, programs, and runoff with program debugging."

U.S. Equipment Co.
Detroit

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