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Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. The Ceramic Samurai Ceramic Lathe.

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Presentation on theme: "Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. The Ceramic Samurai Ceramic Lathe."— Presentation transcript:

1 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. The Ceramic Samurai Ceramic Lathe Concepts by Roger Cortesi Alex Roger Precision Engineering Research Group Massachusetts Institute of Technology, Mechanical Engineering Department Phone: (518) Fax: (703) Room Massachusetts Ave. Cambridge, MA

2 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. There are many unanswered questions. Close collaboration with marketing and the customer will be required What follows are our ideas. These could be used as a starting point…

3 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. When designing a machine to grind ceramics there are two (2) major types. Machines that grind parts that HAVE been fired. and Machines that grind parts that HAVE NOT been fired

4 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. The Dry Machine and Wet Machine have sufficiently different requirements, that they have developed into separate machine concepts. Dry Machine Much lower accuracy since it will be rough turning parts while they are still green. No liquid coolants or lubricants to trap swarf and cause problems in firing the green part. Wet Machine A much higher stiffness and cooling requirement since it will turning finish parts to their 1 micron target accuracy. Liquid coolants and lubricants are not a problem since the part has already been fired. Roger underwater and wet (just like the wet machine) Roger in the desert and very dry (just like the dry machine)

5 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. We have ideas for both… However, our instinct is that there is a larger market for machines that grind the finished part. So we will stay focused on the wet machine for now.

6 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Basic Machine Requirements ( this is our guess as to what the customer wants) Turn Ceramic Parts of up to 15” diameter and 12” long Turn Ceramic Parts with a Maximum Weight of 100 kg Turn Inside and Outside Diameters Target Part Accuracy of 1 micron ( ”) Target Cost of LESS THAN $50,000 Robust with respect to Ceramic Swarf Minimal Assembly Last ?????? Cycles (5? Years)

7 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Initial Error Budget

8 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Concepts Considered for the Wet Machine

9 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Initial Double L Concept Con’s Low Natural Frequency Potentially Very Heavy Structure Alignment of Both Spindles w/ axis at COM is tricky but possible Pro’s Excellent Access to Part and Spindles Easy to Offer Multiple Configurations Simple Structure

10 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Double “C” Concept Con’s Lower Natural Frequency Potentially Very Heavy Structure Alignment of Both Spindles w/ axis at COM is NOT possible Pro’s Excellent Access to Part and Spindles Easy to Offer Multiple Configurations Simple Structure

11 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Alternate Double L Concept Con’s Low Natural Frequency Potentially Very Heavy Structure Pro’s Excellent Access to Part and Spindles Easy to Offer Multiple Configurations Simple Structure Alignment of Both Spindles w/ axis at COM is possible

12 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. “C” on Pipe Concept Con’s Low Natural Frequency Potentially Very Heavy Structure Complicated Structure Pro’s Excellent Access to Part and Spindles Easy to Offer Multiple Configurations Alignment of Both Spindles w/ axis at COM is possible

13 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. The Pipe Lath Concept It is difficult to get the 1 st Non-Solid Body Mode greater than 200 Hz with the Double L structure. This spawned the Pipe Lathe Concept The minimal pipe lathe structure (left) showing the workpiece pipe and tool carriage half-pipe. The pipe lathe with stiffening members and support plates (right). Workpiece carriage motion shown in blue-dashed arrow. Tool carriage motion shown in red-solid arrow.

14 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. More Images of the Pipe Lathe Grinding Wheel Workpiece Tool Carriage Hydrobushing Rails Workpiece Carriage Inside Pipe (not shown) This finger necessary to allow grinding the inside surface

15 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Components

16 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Major Component Costs The machine structure is NOT included in these estimates

17 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Linear Guide Selection Sliding Bearings Cheapest Ruined by Swarf Standard Replacement Part Rolling Element Trucks and Rails Ruined by Swarf High Stiffness Standard Replacement Part Aerostatic Bearings Non affected by swarf Low stiffness stiffness Affected by coolant Difficult to Replace (once installed) Hydrostatic Bearings Unaffected by swarf Very High Stiffness Not affected by coolant Star Linear™ Steel Truck Newway™ Aerostatic Bearing Pad Hydrobushing™ Pacific Bearing™ Sliding Bearing

18 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Actuators The machine should give the customer the option of being driven by Ball Screws or Linear Motors. The customer should be able to switch between them once the machine has been purchased. For example: If the ball screw is not meeting the customer’s accuracy requirement, then they could upgrade to the linear motor.

19 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Actuator Selection An open face linear motor Typical ballscrew assembly Ballscrew Cheap ($700 per axis w/o motor & encoder) Will be destroyed by ceramic swarf, therefore must be super easy to replace. Allows the use of cheap rotary position encoders Linear Motor More expensive ($2000 to $6000 per axis) Will not be destroyed by ceramic swarf May have to be protected against water Requires use of linear position encoder The image below is of an open face linear motor. These have a lot of cogging so they would not be used in the ultra precise version of the machine, rather a “closed face” linear motor, which has the coils run between a part of magnet tracks to eliminate the cogging.

20 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Encoder Selection Must not be affected by coolant or swarf A Rotary encoder on ballscrew allows high resolution and low cost linear position encoder is needed if linear motors are used, more expensive We need more cost data We need estimates on how much variation in ballscrew length due to force loading and thermal effects (hollow ballscrew?)

21 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Linear Encoder A rotary position encoder on the ball screw will NOT detect expansion in the ball screw. Internal cooling of the ballscrew may be needed to minimize the thermal expansion of the ballscrew. A linear encoder on the carriage with the scale on a Super Nilvar plate will detect and correct changes due expansion of the ballscrew. This means that an internally cooled ballscrew is not needed. Star Linear™ Integrated Measuring System

22 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Minimizing Motion Errors The motive force for the two axis can be applied through the COM for each axis. This minimizes errors as the carriages are accelerated. The Ballscrew and Ballnut/Drive Motor Assembly is designed to be removed straight from the end of the machine, making it very easy to replace when the swarf kills it. A similar implementation could also be used for a coreless linear motor in place of the Ballscrew (eliminating the wear problem) Ballscrew acting on spindle carriage COM

23 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. The Importance of Error Mapping The machine MUST be designed for easy error mapping. Especially if ballscrews or contact bearings are used. (since these will have to be replaced and the machine remapped) Pitch and Yaw Mapping are easy Straightness and Roll Mapping require the use of a straightedge and take more setup and work. Mapping Fixturing MUST be included in initial design. Mapping yaw errors on the Axtrusion required minimal fixturing. Mapping vertical straightness errors on the Axtrusion required more fixturing (cap. Probe and straightedge).

24 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Spindle Questions I have about a million spindle question that I need help with before the design can go forward

25 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Thermal Management The Thermal Errors is the largest source of error in the error budget. The method of thermal management will affect the following subsystems: Base Structure Actuator selection and design Position Encoders Techniques for thermal management include: Thermally Centered Base Aluminum Oxide Base (same  as part) Internally Cooled Base Internally Cooled Ballscrew Linear Position Encoders (measuring actual carriage pos.)

26 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Error Analysis

27 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. The Double L Machine Abbe Errors Other Benefits Better dynamic stability due to heavy (and varying) workpiece mass mounted between rails It is easier to integrate wheel “dressing” station, since grinder is moving orthogonal to its axis. Abbe Errors are Eliminated in: Work Carriage Roll & Tool Carriage Pitch (Because the axis of error motion is collinear with axis of workpiece and tool rotation.) Tool Carriage Roll is in a Non-sensitive Direction Minimizing the Effects of carriage roll allows for faster mapping of motion errors. Yaw is the sensitive error motion for both carriages!

28 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Double L Machine Evolves… So an Alternate Double L is designed to allow the tool carriage to travel more inboard (direction of red arrow). Alternate Double L without Fillets Alternate Double L with Fillets The original Double L configuration does not allow the tool to center on the workpiece (due to not enough travel in tool carriage).

29 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Modal Analysis

30 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Double L Machine Modal Analysis The Double L structure was the best at minimizing Abbe errors of the structures considered to date! Were its resonant frequencies high enough? ( greater than 200 Hz)? Lets find out…

31 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Alternate Double L Modal Analysis When the base was sized to accommodate the maximum workpiece size it became very heavy and didn’t have a very high modal frequency. Modes 7 and 8 are the first nonsolid body modes. Mode 7 for a Cast Iron (40) Alternate Double L with fillets

32 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. More Alternate Double L Modal Analysis By making the walls thinner and making the base from Aluminum Oxide the base is 1/5 the weight and improves the resonant frequency. These results are for the base alone. Analysis shows that adding the carriages can cause the resonant frequency to go up or down. The thinner walled Alternate Double L configuration. Path of tool carriage red-solid arrow, workpiece carriage blue-dashed arrow.

33 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Pipe Lathe Modal Results 244 Hz325 Hz 321 Hz424 Hz These results are for the base only, when the workpiece carriage is installed (filling a portion of the tube) the tube will be prevented from collapsing and the frequency for modes 8, 9, and 10 should all increase.

34 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Pipe Lathe Basic Structure 16” OD Steel Pipe for workpiece tube 18” OD Steel half-pipe with ½” steel plate for tool half-pipe There is a dramatic improvement in resonant frequencies

35 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Proposed Plan of Action Work with customer Coors-Tech to determine machine specs Work with Hardinge Marketing to determine market size. Build and test a 1  m/$50K machine Build and test a machine to validate interchangeable concept

36 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Our Crude Market Estimate Coors-Tech buy or rebuilds 100 cheap lathes per year.

37 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. A marketing idea…

38 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Bicycle Marketing Model When buying a bike the you can… Choose from a variety of frames and A variety of components to To get a bike that meets your needs within your budget. Lets apply this same idea to a machine tool…

39 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Machine Combinations ALO 2 Base Polymer Concrete Base Cast Iron Base Aluminum Base Bearings Hydro- Bushing Aero- Static Rolling Truck & Rail Sliding Truck & Rail Actuators Closed Face Linear M. Open Face Linear M. Ballscrew Encoders Lin Pos. w/ Super Nilvar Lin Pos. Rotary on Ballscrew Controllers High End Low End (PCI based) Other Controlled Temp Bath Dressing Station Single Point Turning These options alone could provide several hundred possible machines. But some combinations would not make sense. Not shown above are spindle options, and size variations…

40 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Likely Machine Combinations ALO 2 Base Cast Iron Base Aluminum Base Hydro- Bushing Aero- Static Rolling Truck & Rail Sliding Truck & Rail Closed Face Linear M. Open Face Linear M. Ballscrew Lin Pos. w/ Super Nilvar Lin Pos. Rotary on Ballscrew High End Low End (PCI based) BaseBearingsActuatorsEncodersControllersOther Controlled Temp Bath Air Purge System High Accuracy, Long Life, Ceramic Working High End Dry Machine For “green” parts High End ALO 2 Base Low End Dry Machine For “green” parts High Accuracy for Metal Working Ballscrew Lin Pos. w/ Super Nilvar High End Controlled Temp Bath The configurations listed above are only to give an idea of how a family of bases and components could spawn a series of specialized machines. When Marketing these variants of the machine the customer must be provided with accurate data on: cost, final part accuracy, machine lifetime, etc. so they can make an informed decision.

41 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Machine Accuracy Map 1.2 micron envelope 0.8 micron envelope Part of this marketing method involves giving the customer real performance data that is a function of which machine components they choose.

42 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Background Slides

43 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. The Double L “Wet” Machine Ballscrew Ballnut and Drive Motor Assembly Hydrobushing Hydrobushing Rail

44 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Thermally Centered The part and base are kept at the same temperature by flooding both with coolant. If the part and base are both Aluminum Oxide they will expand at the same rate. If they are of different materials the difference in expansion causes a radial error. Radial thermal errors as function of increase in part and base temperature for granite or cast iron bases An Aluminum Oxide Base has the same  as the part, therefore no radial errors due to uniform heating and cooling

45 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Preliminary Work on a Dry Machine

46 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Axtrusion Based Concept Con’s Large Error Gains (Abbe Errors) Potentially Very Heavy Structure Pro’s Simplest Structure Excellent Access to Part and Spindles Easy to Offer Multiple Configurations

47 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. The Dry Machine and the Axtrusion The Axtrusion is a linear motion concept developed and implemented by Prof. Slocum and Roger Cortesi. It uses porous air bearings and linear motors to make an easy to assemble, non-contact linear motion system. Because it is a non-contact air system it will should be very robust with respect to the ceramic swarf

48 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Axtrusion Components Not Shown: Position Encoder and Position Encoder Scale

49 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. How the Axtrusion™ Works The attractive force between the motor coil and magnets preload the air bearings. Changing the values of , y m, and z m the values for F side, F top1, and F top2 can all be set independently

50 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. 2 nd Generation Sketch of Dry Machine Rough Error Abbe Errors were calculated for this design with the following assumptions: Average errors in Prototype Axtrusion used for the work piece and grinder carriage’s pitch, yaw, and roll errors. –No MAPPING CASE: Error magnitude is the actual error in prototype, 10  radians (2 arc sec) –PERFECT MAPPING CASE: Error magnitude is the repeatability of prototype 2.5  radians (0.5 arc sec) No errors in spindles Rough machine size based on a 15” dia. by 12” long work piece All Magnitude Abbe errors are added for a worst case Maximum Total Abbe Error With NO Error Mapping Radial 13  m (0.0005”) Axial 10  m (0.0004”) Maximum Total Abbe Error With PEFECT Error Mapping Radial 3.2  m ( ”) Axial 2.5  m (0.0001”)

51 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission. Notes on the Dry Machine Concept The previous error estimates are for an Axtrusion with a permanent magnet linear motor. A coreless linear motor would dramatically reduces these error motions further. Estimated Total Abbe Error With NO Error Mapping Radial 9.8  m Axial 7.4  m Estimated Total Abbe Error With PEFECT Error Mapping Radial 2.4  m Axial 1.8  m Total RMS Abbe Error With NO Error Mapping Radial 6.6  m Axial 5.0  m Total RMS Abbe Error With PEFECT Error Mapping Radial 1.6  m Axial 1.2  m


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