Reprinted with permission from Modern Woodworking Magazine.
By David Welch
Manufacturers of CNC machines are pushing the envelope of technology, enabling wood product manufacturers to machine faster, change tooling instantly and produce quality finished products quicker than ever before. Nevertheless, there are still some industry sources who have some concerns about machine control, machine stability, fixture design, machine positioning speed and speed of the overall manufacturing process. Good information and on-site demonstrations will help you make an informed decision on purchases.
“Speed in the manufacturing process is critical today,” said Todd Herzog, president, Accu-Router Inc. “Customers demand faster deliveries. Machines must be faster in throughput and setup time, and must accommodate small lot sizes cost effectively. Just-in-time shipment of parts to assembly calls for more speed. Quicker product deliveries lead directly to more market share and new products have to be launched faster. The same expectations cover custom wood products. Faster machine throughput and output lead to faster investment payback.
“The machine tool industry is on a worldwide treadmill with a singular focus on more speed,” Herzog continued. “The ultra high speed machining systems will obsolete older, slower machines.”
Spindle speed technology continues to improve, according to John Park, general manager, Delmac Machinery Group. “There are a number of spindles out there today that have router speeds greater than 30,000 RPM,” he said. “On CNC machining centers you don’t see that kind of RPM, but you will start seeing it soon. RPM, machine stability, and tool and fixture design all impact speed. Fixture design is important because if you cannot hold your part securely, you will have vibration introduced into the process that will affect the quality of the cut. Also, the bulk of the motor can allow you to absorb more vibration in the cut enabling you to run faster.”
With increases in speeds comes the question of control. “You must be able to control the router so that when you can go fast, you do, and when it is impossible to cut at such speeds, the router slows down,” Park said. “For example, there is no way to rout very small arcs at 20 meters per minute. But if you have the ability to manage the speed, then you can optimize the cycle. You have to make sure that your speed is balanced to your conditions.”
More important than the speed at which a machine performs its cutting operations is the machine’s positioning speed, according to Park. “Positioning speed is the positioning of the machine head from the left hand zone to the right hand zone — or positioning the machine head between operations, for example between drilling and between routing,” he said. “A fast positioning speed would be between 100 to 115 meters per minute — or up to 377 feet per minute. However, you could never rout at that speed.”
Positioning speed on larger machines is especially important when pendulum processing is performed, according to Park. “Pendulum processing is running the left hand zone while the operator is loading the right hand zone — and vice versa.”
With spindle speeds over 30,000 RPM and positioning speeds of 377 feet per minute, have we reached the maximum CNC machining speeds? Herzog says no. “We thoroughly expect to witness a continuation of higher speed capability. New technologies such as custom-ball screw technology, massive spindle shafts with four ceramic bearings, spindles mounted on a cast iron platform for optimal rigidity and cutting capability, a 30,000 RPM spindle, built-in flotation ball motion system, latest CNC control technology with an emphasis on speed, and automatic cornering software will obsolete slower machines from a cost-to-produce viewpoint.
What About the Rest of the Process?
“Most woodworking operations waste eighty to ninety percent of the labor that they pay for,” Susnjara said. “Any labor that does not physically change the part is wasted. If a way could be found to totally eliminate that labor, the final product still would have the same value. All the material handling, loading, unloading, setup and inspecting does not add value to the part being produced.
“From this perspective, focusing on the cutting speed of a machine is focusing on the ten to twenty percent of the effort that is actually adding value to the product, rather than targeting the eighty to ninety percent of the effort that is being wasted.”
“The real danger in focusing only on machine speed is that any process that increases machine time but dramatically reduces unproductive labor is automatically rejected,” Susnjara said. “Because the market focuses on cutting speed, the CNC machine manufacturers focus on supplying the fastest machines possible. I believe that the real key to higher profits is to focus on the overall manufacturing system.”
For this industry to grow and prosper, methods must be found to produce products faster with fewer people, according to Susnjara. “Machines must be able to change tools quickly. They must be able to select from a large assortment of tooling and they must be able to automatically change to a sharp tool when the current tool dulls. This all needs to happen without operator assistance. As soon as the operator becomes involved in tooling selection and management, things slow down dramatically and mistakes start to happen.”
Set-up speed is an important area of improvement for a manufacturing process. “Electronic technology is getting better and better and will continue to get better,” said Mike Hawkins, marketing manager, IMA America. “No one will change Newton’s basic laws of physics. As electronics get better, they only can go so far with mechanics. I feel like there is a much larger window of opportunity to save time during set-ups than saving tenths of a second on a part because the machine cuts faster. One way to save time is to invest in a machine that will allow you to load/unload material while the machine is cutting a part.”
As important as the speed at which a machine performs its cutting operations is the machine’s positioning speed.
“I think we are closely approaching the maximum speed of machining,” said Park. “Systems being used today are similar to those being used in the metalworking industry and even they have a limit of maximum speed potential. The bigger input is developing the software that minimizes any unnecessary moves and maximizes the optimization of the part.”
Reprinted with permission from Modern Woodworking Magazine. Free subscriptions are available by completing an on-line Subscription Form.
