For further information on the capabilities of VPI visit Assessment Process.
Capability Study
Many companies in today’s manufacturing arena are conducting capability studies to determine the exact extent of their tolerance potential. In other words, the need for closer tolerance and consistent repeatability at a smaller value has driven the requirement for these studies. Many major manufacturing companies are beginning to require that capability data be provided in order to obtain, or maintain in some cases, supplier certification. One element in determining the capability of any manufacturing company is to know the condition of the machine tools that are performing the work. This can be measured in several ways, but in order to isolate the machine tools contribution to the overall manufacturing capability it must be measured independently. This eliminates all other factors such as process, tooling, programming, etc., from skewing other capability data one way or another.
Predictive Maintenance
The data obtained through these measurements can be used for predictive maintenance by allowing service or maintenance personnel the opportunity to obtain the repair parts before the repair project begins. For example, the data has revealed that there is excessive wear on the X-axis ballscrew and it must be replaced. Often times this can require tremendous lead times and therefore the machine is down awaiting parts. Since this is a known condition it is easy to determine what parts the machine is capable of running until the repairs are completed. In other words the capability has been determined and only those parts, which can be successfully machined, will be ran on that machine. After the repairs are made, the capability is improved and therefore those parts with tighter tolerances can once again be successfully machined. Another example is after reviewing the data it is determined that the cost of the repairs is too excessive. This information allows your planning staff to make educated decisions about what steps to take in upgrading or replacing machine tools.
New Machine Purchase
It’s time once again to go through the grueling process of purchasing new machines for your manufacturing facility. You talk with several salesman and application engineers and each one assures you of their machine tool accuracy, reliability, and so forth. It is agreed that the parts for which the machine is purchased will be used in a run off test to determine the machine tools accuracy. You then watch as the applications engineers manipulate the program and or process in order to achieve the prescribed tolerance. Afterwards the machine is released to production and suddenly those tolerances are no longer there. What happened!!!!! I am not trying to make light of this scenario at all but this sort of thing happens much too often. Here is a different approach worth considering:
Send out a request for quote to at least four machine tool OEM’s and ask them for performance data measured in accordance with the ANSI / ASME B5.54 or B5.57 standard depending on machine type, i.e. machining center or lathe. The OEM responds and says our tolerance is this or that. Well, that may be the case but those tolerance numbers were obtained using methods that are in most cases unique to that OEM and therefore do not allow direct comparisons to be made with other OEM’s machine tools. The ANSI method does not prescribe a tolerance. The ANSI standard only prescribes a method. This allows each machine to be measured in exactly the same way so that the tolerance is revealed in the data itself and direct comparisons can now be made from one machine manufacturer to another. Again, your planning staff now has the tools to make educated decisions about which machine will meet the criteria required for the job at hand and beyond.
Reduced Scrap
Up to now most manufacturers are using data from the CMM to determine what offsets or changes are required to bring the parts within the prescribed tolerance. This technique does not isolate the machine tools contribution to part quality and sometimes requires several adjustments to machine offsets in order to achieve the desired result. This approach also is time consuming when considering the soak time required for the part before inspection and the number of parts ahead of yours waiting to be inspected. We know that the machine tool condition contributes at least 50% of the part quality and therefore the reduction of scrap can be directly influenced by machine calibration. Case in point: A leading aerospace manufacturer was producing parts from two identical machines with a scrap rate of 98%. The cost of these parts was in excess of $80,000.00 by the time they reached these two machines. The machine tools were measured, aligned, repaired and calibrated. The scrap rate was reduced to 2%. This is a true story and it can happen at your facility as well.
Improved CpK
Here is another example of improved part quality, there are several others that we could mention but space is limited.
Through the efforts of machine tool calibration at a large manufacturing facility in Lafayette, Indiana, CpK values have increased as much as 3 times. These achievements resulted from machine calibration and nothing else. These results have been so dramatic at this particular facility that production management is promoting this effort on every CNC machine in the facility. They even request machine tool calibration services each time a problem is revealed knowing that the source of the problem can be identified and corrected through this process. Once again, the benefits of this service more than justify the cost.
Be not slothful in business, but fervent in Spirit, as serving the Lord…
