Increasing Machine Tool Productivity With CNC Technology

When purchasing a new machine tool it is easy to focus solely on the capital cost of the equipment, without taking into account the recurring costs necessary to run and maintain the machine.

Manufacturers are being constantly challenged to increase productivity while lowering costs, and CNC technology may help them accomplish this by increasing throughput. According to CNC manufacturer FANUC FA America, two metrics that should be tracked are the total cost of ownership (TCO) and the mean time between failure (MTBF).

By tracking these items, a manufacturer can gain a true understanding of cost per part, machine utilization, and uptime.

Like developments in the personal computing industry, the rate of CNC advancement also has accelerated. Similarly, it is no longer acceptable for a CNC manufacturer to have a computing platform linger for a decade or more.

One byproduct of this improvement in computing power is in the reduced cycle times.

Reducing Cycle Time

"Using the latest CNC technology that integrates a high-speed CNC [with] drive system hardware containing servo and spindle motors featuring ultrasmooth rotation, accurate current detection, and high-resolution feedback devices helps to reduce cycle time," said FANUC FA America Director of Marketing and Business Development Karl Kleppek.

Although, he added, further reduction in cycle time often requires minimizing machine shock and vibration.

For example, FANUC CNCs have a suite of motion control software functions that reduce cycle times.

Bell-shaped acceleration/deceleration minimizes machine shock and reduces movement time. This can be applied to rapid, contouring, and tapping motions.

Some other functions that can affect cycle time are:

• AI Contour Control. This function looks ahead in the part program to eliminate the acceleration/deceleration and servo delays that limit feed rates when cutting short line segments or contours. It also eliminates machining trajectory errors in corners and small radii.
  
  
• Nanosmoothing. Nanosmoothing converts CAM-generated line segments into nonuniform rational basis splines (NURBS) curves for faster execution while at the same time improving surface finishes.
  
  
• Jerk Control. By reducing the rate of change of acceleration, vibration is suppressed as is machine shock and the associated machining errors.
  
  
• Autofollowing High Response Vector (HRV). These servo and spindle drive filters suppress mechanical resonance even when the frequency changes.
  
  
• High-speed Smooth Tool Center Point (TCP). Specifically for high-speed machining (HSM), this function creates a NURBS curve through programmed points, smoothes tool vectors, and controls unwanted acceleration/deceleration to reduce cycle times.

"In addition to control technology, there are many third-party accessories that you can add to your machine tool to increase accuracy and throughput while decreasing run-time," said Kleppek. "Adaptive control is an example of added technology that can assist in increasing productivity. The purpose is to reduce cycle time by way of dynamically optimizing cutting feed rates in order to reduce chatter and keep a constant chip load on the cutting tool."

Tool identification is another example of a machine tool enhancement that can decrease downtime by scanning toolholders to automatically pick up tooling parameters and input that information directly into the machine tool's offset register, eliminating operator error.

Improving Surface Finish

Today's CNC systems typically offer submicron resolution or nanoresolution throughout, from internal calculations and stored values through to the interpolator, the drive system, and back through the position feedback devices.

High-resolution count-per-revolution feedback devices create superior surface finish quality when contouring. According to Kleppek, this minimizes the need for secondary operations, reducing delivery times and part cost.

Reducing Cost per Part

"When referring to cost per part, there are many factors in the manufacturing process that contribute," said Kleppek. "When purchasing new equipment, it is easy to fall into the trap of focusing on the one-time acquisition cost while not fully appreciating all of the recurring costs to run and maintain this equipment."

In today's just-in-time manufacturing environment, equipment availability, reliability, and productivity all are true cost factors, as are the more traditional energy, operation, and maintenance costs. It is very important to consider the cost of a machine over its lifetime of operation.

"Cycle time, surface finish, and cost per part directly affect a manufacturer's bottom line," said Kleppek. "CNC reliability, efficiency, and innovation can help to reduce cycle time, increase surface finish, and thereby reduce the overall cost per part."

A reduction in downtime can also yield major dividends in terms of cost per part.

One recent development in FANUC's controls is that the hardware itself can monitor for errors in data exchange. If an error is found in the data flow on the CNC, it is automatically corrected by an error correction code (ECC).

"The purpose of this is to drive more reliability in addition to higher processing," said Kleppek. "Additionally, we continue to make improvements in predictive maintenance with new software that can signal a machine failure before it happens. For example, for crash protection, an unexpected torque disturbance control allows torque limits to be set so that the axis will stop or retract when a collision is detected, reducing damage to the machine."

Importance of Ergonomics

Fagor Automation Corp. released two new controls, the 8055 FL and 8055 Power, that combine improved platform capabilities and ease of use, the company states.

"R&D has discovered that [ergonomic] improvements contribute to improved operator concentration and help reduce visual fatigue, including even a reduction in headaches," said Fagor Automation Marketing Manager Todd Drane. "For operators who spend large amounts of time in front of the CNC, this subtle improvement would be noticeable in time."

The most important goal in the development of any new CNC, however, is improved machining performance. Faster cycle times and better part finishes are two key areas that developers are trying to enhance.

"By using a new high-performance microprocessor, coupled with improved machining algorithms, we have effectively doubled and even tripled our processing speeds. Our testing has revealed dramatically faster cycle times, yet also a smoother and more accurate part finish," Drane said.

The 8055 First Line (FL) can control up to four axes for milling, turning, grinding, or general-purpose applications in small and midsized machining centers. The 8055 Power is a modular platform for applications up to seven axes.