*The C4 Service Plan _ The Four C’s of Machine Tool Performance
Machine Tools today are complicated and expensive investments for any company. When purchasing a new or used machine it is a good idea to have a plan. Your plan should include how you intend to protect your investment in order to obtain positive return on investment. At MD Calibrations we embrace the “Cradle to Grave” philosophy. The overall objective is to maintain maximum performance and minimum downtime. This is achieved through applying C4, “The Four C’s of Machine Tool Performance”.
C2 _ Compensation
Today’s machine tool controls are equipped with the ability to optimize a machines’ linear and rotary positioning. At MD Calibrations we utilize the Renishaw XL80 laser system in order to accurately measure linear positioning. The XL80 laser in conjunction with the Renishaw RX10 or XR20 is used to measure rotary positioning. The XL80 Laser in conjunction with the XR20 and Renishaw OAR software is used to measure trunnion axes. The accuracy of the data acquired by these devices play a large role in the accuracy of the performance optimization. Proper compensation is a lot more than just entering correction data into a control. Establishing a proper pitch line for the product or products to be produced on the machine, proper evaluation of the environment, using the proper expansion coefficient, and controlling thermal drift play a very big role in obtaining accurate compensation data. If the machine is properly optimized it will operate at peak performance. Upon completion of optimization, the linear and rotary positioning data is the used to replace the “as found” data that was originally entered into our VEE form. This way we are able to quantize the improvements made by optimization. We have now established a baseline for future evaluation and calibration of the machine throughout its lifespan.
MD Calibrations can perform leadscrew compensations on all makes and models of machine tool controllers. Our proprietary algorithms enable us to establish, correct, or update control leadscrew compensation files quickly and efficiently for maximum linear accuracy.
It is important to note that most leadscrew compensation file updates are performed for completely the wrong reason. If you find in-house personnel or outside vendors updating machines' compensation files each time they are checked, there may be a flaw in the way they are obtaining and/or analyzing the data.
The International Organization for Standardization (ISO) clearly defines the requirements for fully documenting set-up instructions for machine tool calibration in ISO-230-2. These must include:
1. Location of all (non moving) machine tool axis positions
2. Location of the laser material temperature sensor
3. Location of the air temperature sensor.
4. The effective expansion coefficient used
5. Starting and ending temperatures of both the machine and
its surrounding environment
6. Location of the pitch line in the machine including:
Distance from the
spindle face to the pitch line
Distance from the
spindle centerline to the pitch line
Distance form the
work holding surface to the pitch line.
Armed with this information, a technician can quickly achieve repeatability and reproducibility when performing any subsequent calibration or certification of the same machine. However, the slightest variation or deviation from the documented setup and the user will acquire calibration data resulting in unnecessary leadscrew compensation file updates.
For instance, by varying the location of the pitch line, geometric errors in the machine affect the measured results. Varying the location of the temperature sensors or the expansion coefficient can cause thermal slope errors in the data. Using an incorrect expansion coefficient can significantly affect the results when air and material temperatures change.
The examples above are all operator setup errors, not machine performance errors, and should not play a role in the machine compensation tables. When MD Calibrations performs leadscrew compensation file installation, correction, or updates, all required information is supplied on our copyrighted Summary Report Form.
At MD Calibrations, we perform annual calibration certification for our customers, and we have not found it necessary to update the compensation file annually. Our customers realize a direct, significant saving because we eliminate the significant time required to perform unnecessary leadscrew compensation.
At MD Calibrations, we are so confident in our documentation and processes that we are often able to quote flat rates for annual calibration certification (after our initial service of a machine).
Without exception, leadscrew compensation files should be checked and updated whenever any part of the feedback and positioning loop (i.e. ball screw, CV coupling, drive motor, encoder, resolver, scale, block ways, linear guides, pre-amp, servo board, etc.) has been adjusted or replaced.
Contact MD Calibrations today to discuss your machine tool calibration needs and to find out how we can meet them.