Marking the spot on off-highway pistons

  • 10-Sep-2008 04:03 EDT
Fig. 3.jpg
This marking machine features a two-part fixture that is manually rotated to place the piston in front of the dot-peen marking head. The electrical enclosure mounts the controller and keyboard, and a part-present sensor mounted above the fixture detects when a piston is in position for marking.

When Bharat Forging America was contracted to provide large piston forgings for a new off-highway engine, each part needed to be marked with specific information. The marking method preferred by the piston manufacturer was dot-peen because it imposes no perceivable stresses on the forgings and does not create any possible arcing situations that could occur with a laser marker.

The information required on the pistons included a heat lot identification number, the die set that was used, a part number, a Bharat supplier identification, and the customer’s logo. It was determined to place that information at two areas on the opposite sides of the wrist pin bore location, piston areas that would not be machined off.

Because of the amount of information, the total marking area became fairly large. That fact required a dot-peen marking machine with a large marking window and the ability to mark up to 17 0.25-in (6.35-mm) characters. Columbia Marking Tools provided a compact PM Micro AXL dot-peen marking unit that has a 200- x 80-mm (7.87- x 3.15-in) marking window that met Bharat’s requirements. It uses an extended carbide pin design with a protective debris shield that adequately protects the stepper motors and ball-screw drive of the marking head.

“Having the marking capability was just part of what we needed in a machine design,” said John Turner, Piston Program Manager, Bharat Forge. “The forging processing cell that we designed for the pistons required that the marking be performed on the factory floor in the inspection area located near the hot-forging presses.”

Columbia designed a stand-alone machine that had a rugged machine base and table, on which was mounted a manual load/unload rotating two-part piston locating fixture. The marking unit is mounted to the back of the machine base.

“The PM Micro CNC-controller is contained in an enclosure that is attached to the machine base and located at eye level. The enclosure also includes a keyboard for programming,” said Turner. “The standard unit interfaces with existing Microsoft Windows XP or Vista systems using Columbia’s software, which allows us to create the logos and special graphics required.”

The data entered by the keyboard can be viewed and edited on an LCD display before any marking is performed. The text can be fixed or variable, numbering can be sequential, and date coding can be set up to be automatic. The penetration depth is adjustable through a pressure regulator.

“Although some of the pistons that we are marking have different metallurgical makeup, their hardness is the same, so the penetration setup for the parts is also the same,” said Turner.

Because of its size, 5.5 x 7 x 7 in (140 x 178 x 178 mm), the dot-peen unit was easy to integrate into a production system. The movement for the marking head is provided by high-torque stepper motors and a ball-screw drive that runs at 300 mm/s (12 in/s), which can mark up to eight characters per second.

The electric motors for the X-Y axis require 110-V ac power; 30 to 75 psi (2 to 5 bar) is the operating range for the air-powered pneumatic dot-peen action. With onboard I/O and serial interface, the unit can receive information two different ways, regardless of the type of PLC. It can be designed for automatic, semi-automatic, or manual operation.

“As the production schedules for the piston program have expanded, we have found the Columbia equipment can easily handle our increased production requirements,” said Turner. “It’s the manual loading and unloading of the parts that is limiting the production cycle time. As a result, we are in the process of building a new manufacturing cell that will utilize three robots to present the parts to the marking station.”

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