Wood machining and tooling research program provides real-world answers.

Industry-sponsored study take wood processing into the 21st century.

Whether you are machining solid or engineered wood, making dining room tables or medical cabinetry, quality and productivity both revolve around a single point -- where the metal meets the wood.

This is the focus of the Wood Machining and Tooling Research Program (WMTRP) at North Carolina State University's College of Forest Resources. The Program is a multi-disciplinary effort involving NCSU's departments of Wood and Paper Science, Mechanical and Aerospace Engineering, and Materials Science and Engineering.

The WMTRP's efforts are geared toward evaluating and improving wood machining methods and processes. Specific focus areas include cause-and-effect relationships in CNC router spindle vibration problems; the effect of carbide tool composition and edge quality on tool performance; developing a system for evaluating and quantifying machined surface quality; and on-line process monitoring in machining operations.

Program Director Dr. John Stewart says the program has received strong support from the woodworking industry in the form of grants, research contracts, donations of equipment, instruments, supplies, machining/fabrication services and technical assistance. The Wood Machinery Manufacturers of America (WMMA) was largely responsible for the founding of the program, and is still very active in its ongoing efforts.

"Through the WMMA's efforts, the International Woodworking Fair and a consortium of industrial firms interested in wood machining and tooling technology were able to join forces with NCSU to establish a program devoted to applied research and education," Stewart said.

"Our original intent was to develop something the industry can use; data with real-world applications," said Ken Hutton, executive vice president of the WMMA. This is one of the few programs in the country at a university level where ongoing research focuses on the machining of wood. Most programs focus on forestry management, which is certainly needed, but our members and their furniture-producing customers need information on wood machining."

"This 'wood engineering' approach is commonplace in Europe and Asia, but is unique in the United States," said Stewart. "A union like this is a crucial vehicle for realizing major technological gains in this important national industry."

The multi-disciplinary nature of the WMTRP facilitates the transfer of engineering methods and analytical techniques to wood machining and tooling applications. Examples are: computer modeling of tool tip temperatures from NCSU metalworking research; vapor deposition technology for diamond coating of cutting tools, from NCSU microelectronics research; and spindle/rotor finite element analysis technology, from high-speed aerospace machining applications.

High-speed spindle vibration

"Vibration is the enemy of a CNC router," said Todd Herzog, president of CNC router manufacturer Accu-Router Inc. in Morrison, Tenn. "Tool design and machine rigidity both play a large part in spindle vibration levels. Anyone involved in high-speed machining should be concerned about vibration; it affects machine and spindle bearing life, not to mention part quality."

"Research into this area has improved our understanding of the causes and effects of vibration on CNC router spindle performance," said Stewart.

This work has resulted in charts and tables indicating maximum safe speeds, in rpm, for router spindles at various levels of unbalance and chuck centering error. Tolerance limits have also been established for out-of-balance and chucking accuracy for various spindle and tool design combinations.

"The requirements are considerably more stringent than the tolerances typically found in many industrial tool and chuck applications," Stewart said.

"We're using the results of the program's tool balance research," said Steve Segal, chairman of the board of tooling manufacturer North American Product Corp., and one of the WMMA's driving forces behind launching the WMTRP. "We've tightened the balance specifications on the products we sell -- some acceptable tolerance ranges have been cut in half."

To help end users assess vibration characteristics when choosing a machine, the WMTRP's research has developed a single-number rating system, not unlike the energy-efficiency index for home appliances. This system allows direct comparison of spindles, and helps the user determine the tooling and chucking accuracies required to satisfactorily operate the spindles.

Safe spindle operating limits determined by WMTRP's research are used as parameters for vibration warning alarm systems, permanently mounted to the spindle, that alert operators to potentially damaging levels of spindle vibration. The alarm is part of a spindle vibration information system, which can perform on-line process monitoring of a machine's operation, detecting excessive vibration from cutting loads (excessive feed speeds, dull tools, etc.) in addition to tool unbalance and tool centering problems.

Further research has been focused on the development of computer models which aid in understanding the susceptibility of spindles to vibration, the spindle design requirements for avoiding resonant spindle conditions known as 'critical speed,' and the relationships between spindle housing vibration and forces and loads on the spindle bearings, Stewart said.

Herzog says spindle vibration research should also influence the quality standards for reground tools. "Users will go out of their way to buy a good tool, but they don't apply the same standards to the quality of the regrind. Getting high-tolerance regrinds and changing the tool as it begins to dull gives you better parts, less noise, more regrinds, reduces spindle stress and increases bearing life."

Carbide tooling research

"Our research on carbide tooling has focused on the effect of carbide grade and carbide edge quality on tool performance," Stewart explains. "Since different wood machining operations produce different wear mechanisms, special carbide grades have been designed to combat such problems as high temperature oxidation and corrosion of the carbide binder material.

"These special grades often contain relatively small amounts of binder and/or alloyed binder materials which require special brazing and grinding procedures," Stewart said.

The WMTRP's research has focused on identifying the effect of grinding on tool performance; procedures have been developed to measure both edge sharpness and edge strength.

"Grinding parameters such as wheel grit, direction of wheel rotation, orientation of grinding marks, coolant conditions and grinding feeds and speeds have been studied for conventional and special carbide grades," Stewart says. "While edge sharpness is controlled primarily by grinding parameters, research has shown that the quality of the edge cannot be determined entirely by optical inspection."

A knowledge of edge strength is especially important since tool edges that appear to be good may have been damaged during brazing or grinding, Stewart said, resulting in disintegration of the edge on contact with the wood workpiece.

"We've also found that precision ground carbide edges produce substantially better surface quality and last longer than conventionally ground carbide tool edges."

Research for the industry's future

Reliable evaluation of wood product surface quality is essential to research aimed at improved wood machining. The WMTRP is currently developing systems to measure surface defects such as torn and fuzzy grain, as well as surface waviness or tooth marks resulting from the machining process. The long-term objective of this research, Stewart says, is to provide the woodworking industry with on-line techniques for measuring and quantifying machined surface quality.

"We're looking forward to a new project that will determine the relationship between feed rates, cutting speeds, material and horsepower," says Segal. "When a customer is cutting a certain material at a certain feed rate and rpm, we want to be able to use established data to help determine the necessary horsepower."

Efforts are also underway to incorporate on-line process monitoring and control into CNC woodworking operations. Multiple sensors monitoring a range of process data (vibration, power, cutting forces, etc.) are being used in conjunction with a variety of signal processing methods to develop relationships between sensor outputs and cutting conditions.

"We're working to develop an adaptive learning system whereby machine control centers can establish these relationships automatically," Stewart said.

The WMMA said it supported the study because research in wood machining and tooling is of critical importance to the wood products industry. Productivity, efficient use of wood resources, and product quality are all closely tied to wood machining. Not only will the woodworking machinery and tooling industry -- not to mention wood products manufacturers -- benefit directly from technology generated by WMTRP research; they will also benefit from the pool of well-educated personnel who can turn technology into productivity gains and more profitable operation.