Match the process to the part

There’s more than one way to machine a part. The trick is to match the part’s complexity and volume requirements with an optimal production process. As a leading single-source contract manufacturer, Plouse Precision Manufacturing, Harrisburg, Pa., can choose from a wide range of production alternatives. The company’s capabilities include metal stamping, CNC machining, assembly, fabrication, grinding, wire EDM and welding. Part volumes range from single-digit prototypes to production runs of a few thousand. Such a diversified mix of capabilities and part volumes prompts careful consideration of processes and strategies to maximize accuracy and efficiency.

A good example was an approximately 1½ “×1¼ “×½ ” squared-off, U-shaped aluminum bracket Plouse machined for a medical equipment manufacturer. Lot size was about 300.

The bracket featured milling, drilling and tapping on six sides, which would require a minimum of five fixturings to complete on a horizontal machining center. For significantly higher-volume part runs, the HMC would have been a wise choice, as parts for subsequent operations would be set up while the prior ones ran nonstop.

However, for this relatively small part run, Plouse determined that the most efficient method was to perform the operations in a continual sequence on a multitask lathe. The Mori Seiki NL-2000SY machine chosen for the job has driven tools and, in addition to turning, the machine can mill, drill and tap in both the Z and X axes. The machine’s Y- and C-axis motion capability permits machining of off-axis features, and the option of feeding bar stock through the chuck minimizes load time.

The machine enabled Plouse to write one program, setup once and machine the part complete, eliminating refixturing time and the possibility of setup errors between operations.

Working from a customer-provided print, Plouse drew the part in SolidWorks and programmed it in Mastercam. The workpiece material, 36 “-long bars of 2 “-dia. extruded 6061-T6 round bar stock, was fed into the machine through the chuck about 2 ” at a time. “When most people see the part, they think rectangular bar stock,” said Darryl Smith, the company’s engineering services manager. “But it’s round.”

In the first and only turning operation, Plouse faced and rough-turned the bar’s OD to a diameter of 1.660 “. In the next operation, a ½ “-dia., 3-flute, solid-carbide endmill in a live toolholder approached the chuck in the Z-axis and milled and squared the round bar to 1.580 ” wide × 0.500 ” thick × 1.375 ” long (from the free end to where it attached to the bar stock) at a speed of 3,200 rpm and a 40-ipm feed rate. Smith said the parameters were the maximum possible without generating chatter.

Courtesy of B. Kennedy