Manufacturing large ultra-precision parts for the New BIPM Watt Balance

Transcription

1 Manufacturing large ultra-precision parts for the New BIPM Watt Balance ABSTRACT Because of our unique set of skills and equipment we ve developed over the past 60 plus years we were asked recently to manufacture some of the critical parts for the new BIPM Watt Balance currently being built by the Fraunhofer Institute in Aachen. Dave Arneson Professional Instruments Company Hopkins, Minnesota, USA FIGURE 3. Our largest CNC machining center, a Haas VF-3, was used to machine details on the outside of the Housing. FIGURE 1. BIPM magnet assembly MACHINING One of the biggest challenges this job came from the large size and substantial weight of some of the parts. Fortunately, we have an extensive job shop background and so are well equipped to handle the machining of such large pieces. FIGURE 2. The nature of the project required us to do some of the rough machining ourselves. Here we are roughing out the Housing on a large Monarch engine lathe FIGURE 4. Our SIP 6A was required to machine some of the features on the inside of the Housing.

2 GRINDING We originally developed air-bearing spindles for our own manufacturing, and now use them extensively in our shop. Most of our grinders have been retrofit with our spindles and therefore are capable of achieving extremely high accuracies. The parts for the Watt Balance were some of the most challenging we have ever attempted because of the material, (Supra- 50), the size and the precision required. FIGURE 7. Roto-grinding the Housing on a 10R Block-Head in a Brown & Sharpe surface grinder we retrofitted with an air bearing wheel spindle. FIGURE 5. Grinding the Outer Core segments in our Moore #3 Jig Grinder using a belt driven oil hydrostatic Block-Head spindle on a large sine table FIGURE 6. Angled section of the Inner Core being ground on our Parker Liberty, CNC cylindrical grinder, equipped with an oil hydrostatic work spindle and an air bearing wheel spindle. Figure 8. ID grinding the Housing in an old Landis 12x36 cylindrical grinder, we retrofitted with an air bearing wheel spindle and a 10B Block-Head work spindle with a belt lift to allow us to grind the Housing which weighs a whopping 91 kg.

3 INSPECTION It is one thing to make the parts right, but inspecting such large precise parts is also quite difficult. We continue to upgrade our inspection capabilities, so we can continue to be able to take on tough jobs such as this one. FIGURE 9. Roto-grinding the Outer Core segments on a 10R Block-Head spindle in an Okamoto 1224 DX surface grinder FIGURE 11. Inspecting the Outer Core segments in our Zeiss Contura CMM. FIGURE 10. Outer Core segments being ground on a Brown & Sharpe #2 cylindrical grinder with air bearing work and wheel spindles FIGURE 12. Measuring the size of the Core while it is still in the grinder. Using one of our Reed-Mik Comparators and a CEJ ¼ Micron resolution Mikrokator

4 FIGURE 13. Inspecting the Core in our Moore #3 UMM equipped with 4R Block-Head roundness tester using software developed at Penn State s Machine Dynamics Research Laboratory by Professor Eric Marsh and his graduate students FIGURE 15. To measure the bore diameter of the Housing we used our Zeiss Contura CMM with a VAST XT probe. FIGURE 16. Diameter measurements of the Housing from our Zeiss Contura CMM FIGURE 14. Measuring roundness and squareness on the Housing using a Moore UMM equipped with a 4R Block-Head roundness tester and Penn State developed software. FIGURE 17. Diameter measurements of the Core from our Zeiss Contura CMM

5 FIGURE 18. Roundness traces at different heights on the outside diameter of the Core. Note that they are all better than 350 nanometers. FIGURE 19. Roundness traces at different heights on the inside diameter of the Housing. Note that they are all better than 1/3 of a micron.

6 CONCLUSION Parts of this size represent a unique challenge for traditional manufacturing techniques and equipment. Fortunately at Professional Instruments we are used to getting more out of our equipment than it was originally built for. These kind of jobs are very important to take on from time to time as they help us develop new skills and techniques that will help us in our core business; making ultra-precision air bearing spindles. This particular job pushed us to the limit of what is possible but given the great importance of the project it was worth the extra effort. REFERENCES [1] Rachel Courtland. (May 2012). The Kilogram, Reinvented. Available from: [2] Brumfiel, G. Kilogram Adjustment Courts Controversy. Nature. January [3] Weighing a Kilogram. Economist. January 2011.