“Back in the day,” screw machine shops were easily identifiable. They were shops focused primarily on turning of high volumes of parts from relatively simple screws and fasteners to more complex hydraulics and pneumatic valves and bodies.
Most of the machines were actuated by mechanically using precision CAMs to move the cross-slides and end-slides as well as various accessories. The CAM department in these shops was equivalent to the programming department in a CNC shop. Often, shops could set up a Swiss automatic or multi-spindle CAM machine and run a single job for a year or two—volumes were that high.
What was common then is increasingly rare today. As manufacturing has always been migratory, seeking places where costs are lower, the European screw machining industry was hit earlier than that of the United States with a drying up of relatively simple, very-high-volume work that was the hallmark of the screw business for many years. For European companies, much of this work headed to countries in the former Soviet Bloc with cheaper labor; for U.S. companies, it was Asia.
The industry’s response to these emerging competitors came in the form of technological investment in machine tools, cutters, software and process refinements to wring out production costs and increase productivity. The historic cycle time per part metric was being replaced with throughput time and sales volume per employee. Faster, cheaper and better is what the customers demanded.
Shops retooled themselves to make lower volumes of more complex and higher-value-added workpieces. The need to perform change-overs on the CAM-actuated Swiss and multi-spindles led more shops to look at CNC as the actuation method of choice. CAMs still have their place—they are very fast—but setup times from job to job are very long.
The migration from screw machining to precision machined parts production has been a sea change for this industry. And it’s one that continues to evolve.
One of the hottest machine tool categories in the past few years has been CNC Swiss. These machines represent the ability to complete complex workpieces for the medical, aerospace and electronic industries in a single handling.
By eliminating multiple operations, throughput is greatly increased. With the application of automation devices such as magazine bar feeders, tool sensing and broken tool detection, these machines are well-suited to unattended machining.
Swiss-type CNC machines have evolved well past their origins in the watch industry. The century-plus-year-old sliding headstock mechanism, when coupled with servo controlled Z-axis motion, has broadened the appeal of these machines beyond the historic screw machine demographic to more general metalworking shops.
As use of the Swiss-type has proliferated, many applications that would not be considered “Swiss-type” parts, specifically parts with more than three time length-to-diameter ratios, are being applied to take advantage of the machine’s production capabilities. In response, the machine builders have begun to offer the option of using a guide bushing for long, slender parts or removing it for parts that don’t need the support. This is something to look for if your shop runs many different kinds of work.
In the multi-spindle world, CNC has found a place as well. These machines offer all of the programmability of a CNC lathe multiplied by six or eight spindles on a single platform. They use a progressive machining technique that breaks down a part’s operations into smaller steps so a complete part is dropped with each index of the spindle drum. Cross-slides on these machines are compound, which enables single-point turning.
If you are looking for a multi-spindle machine at IMTS, something called a “bridge machine” may be for you. These machines use traditional CAM actuation on most of the spindles, and then incorporate a CNC slide or compound slide on the final spindles for higher tolerance and better surface finish. These CAM/CNC machines are being used more in shops that are seeing work being reshored to the U.S.
And here’s a scoop: A new concept in multi-spindle design is debuting at IMTS. It combines the Swiss sliding headstock motion on a CNC multi-spindle. All six spindles move independently in the Z axis.
Software is a key to the transition from CAM actuation to CNC. Most CAD/CAM companies have specific packages to help automate programming of the complex, multi-axis Swiss-type machines. Many of these seats include simulation for off-line toolpath verification and to aid in collision avoidance.
Unfortunately, space doesn’t permit itemization of all the emerging technology trends for the precision machined parts industry that are on display here. Just go around and see for yourself, which is the fun part of attending a show like IMTS.