Modular fixtures for inspection in CMM

A modular fixturing system is a versatile alternative to a single–purpose, dedicated fixture used along with CMM.

1. MODULAR FIXTURES FOR INSPECTION SURESH LAL S R Assistant Professor Department of Mechanical Engineering Government Engineering College, Wayanad

2. Contents Introduction to jigs and fixtures Principles of location Modular fixtures Components Applications Merits and demerits

3. Jigs and Fixtures Jig Fixture Fixtures - are strong and rigid mechanical devices which enable easy, quick and consistently accurate locating, supporting and clamping , blanks against cutting tool(s) and result faster and accurate machining with consistent quality, functional ability and interchangeability . Jig - is a fixture with an additional feature of tool guidance.

4. Elements of Jigs and Fixtures Base and body or frame with clamping features. Locating elements for proper positioning and orientation of the blank. Supporting surfaces and base. Clamping elements. Tool guiding frame and bushes (for jig ). Indexing plates or systems, if necessary. Auxiliary elements. Fastening parts.

5. Principles of Location Any rectangular body may have 12 degrees of freedom. 4 along each axis;2 translational and 2 rotational . By properly locating, supporting and clamping the blank, its all degrees of freedom are to be arrested.

6. Principles of Location The basic principle used to locate the points is the six point location of a rectangular block (3-2-1 principle). Provide a rest to work-piece on three points on the bottom XY plane. This will stop the movement in the - Z axis, rotation with respect to the X axis and Y axis (five motions). Rest the work-piece on two points of side surface (X-Z), this will fix the movement of work-piece along +Y axis and rotation with respect to Z axis (three motions). Provide a support at one point on the adjacent surface (Y-Z) that will fix the movement in –X direction (one motion). The remaining movements are restricted by a clamping device (3 motions ).

7. Principles of Location One or more surfaces (preferably machined) and / or drilled / bored hole(s) are to be taken for reference Locating should be easy, quick and accurate A minimum of three point must be used to locate a horizontal flat surface The locating pins should be as far apart as feasible V-block and cones should be used for self-locating solid and hollow cylindrical jobs. Holes provide an excellent method for locating . Eleven motions can be restricted using a pin locator along with a diamond pin locator to accommodate tolerance on the distance between the holes and their diameters

8. Limitations of Fixtures Can have complicated designs. High initial set up costs (and time ). Can use a lot of material and be bulky. Loading , unloading and reloading of the same parts, is time consuming. Can wear away over time.

9. MODULAR FIXTURES

10. Modular Fixtures A modular fixturing system is a versatile alternative to a single–purpose, dedicated fixture. Constructed from a kit of interchangeable components, the modular fixture is easily reconfigured for any work holding application . The modular fixture will hold the component of different configuration, size and shape without much efforts to locate, align and clamp the component on the fixture.

11. Modular Fixtures Modular systems are ideal for intermittent or one–time use. They are commonly used to: Stage parts for CMM inspections Hold work pieces during machining Position parts when bonding or assembling The modular system saves time and reduces cost. When not in use, the fixture can be dismantled for convenient storage.

12. Fixturing Principles A set of fixturing principles should be followed to ensure the part is stable enough to allow for repeatable and reproducible measurements The principles are:- 3 point of support 3 point nest Part clocking Part holding Adjustability

13. The photo shows a sculpted part in a simple 3-2-1 nest, with 3 base datum locators and the overhead clamp force applied inside the triangle formed by the three base locators. The two pins clock the rotation, and the end-stop provides the final locator . The opposing pin standoff is used to force the part against the front two pin standoffs.

14. Positioning of Part in the Fixture - Manually Determine the part position according to the measurement needs. The features to be presented for measurement. Accessibility of CMM probe to these features. Immobilization of parts. 3-2-1 location principle (3 support points, 2 orientation points, 1 stop point) and clamping. Out of three support points one is fixed and other two are adjustable. Rough determination of difference of height between supports. Mounting the fixed support. Mounting the adjustable supports. Vertical and horizontal adjustment of part using spirit level or dial gauge. Lockup the part with clamps.

15. Positioning of Part in the Fixture – Software Based FixtureBuilder is a 3D-modelling software package designed to allow the creation and documentation of fixturing set-ups. The software can be used with a CAD model of the inspected part, which is imported into FixtureBuilder , so that the fixture can be built around it. The entire set-up, along with the inspected part, can then be exported into inspection programming software . FixtureBuilder supports most CAD formats including IGES, SAT and STEP. A translator add-on module is available for Pro/E and CATIA.

16. Fixture Plate/Base Plate Base plates are precision ground within tight tolerance that are key to the quality of the modular fixturing system. Base plates are available in standard and custom sizes with a choice of threaded holes: M4, M6, M8. Cast aluminium base plates are coated with hard coat anodise to resist wear and scratching and are available in sizes upto 1500 mm X 3000 mm. The base plates are made Thermally stable High wear/ abrasion resistant Low friction surfaces.

17. T–Slot Base Plates Provides infinite adjustability in multiple axes. Laser engraved reference scales and alpha identified T-slots facilitate repeat setups. A cross-slide assembly is included in the kit. The cross-slide allows infinite positioning of components between the T-slots. It can also be set at any XY angle. The lockdown clamps are used with a thumb-screw and locknut, which attach to a T-nut in the t-slot.

18. Modular fixture components Standoffs Adjustables Magnets Clamps Towers Miscellaneous Suction cup Trays

19. Standoffs Standoff - to elevate and locate part. Pin standoff – to elevate and locate the part against the pin. Spring loaded pin standoff – to locate within a hole or slot of a part. Standoff adaptor – for step clamps Rotator standoff – to secure parts against stops/supports.

20. Standoffs - Application

21. Adjustables Adjustable jack stand - to allow height variable up to 22 mm. Adjustable slide – to place components in between holes on the plate Adjustable angle plate – ideal for holding the components at an angle Adjustable V – post – for holding the cylindrical parts. Adjustable pivot joint – for positioning the component at any angle

22. Adjustables - Application

23. Magnets Plane magnet – for holding the steel or iron parts Pin magnet – for holding and locating parts. V magnet – for holding cylindrical parts and bent tubing.

24. Magnets - Application

25. Clamps Tension clamp - for quick and easy clamping. Screw pusher clamp – for pushing and holding a part against stops. Tension clamp bracket – to hold a tension clamp at an angle. Three jaw clamp – for holding round parts at one end or at middle, allowing the probe around the part without interference. Hold down clamp – for more clamping force

26. Clamps - Application

27. Towers To hold a part vertically

28. Miscellaneous Cone – to rest a part on a rounded point for a single-point contact. Resting pin – to rest a part on rounded point. Vertical base plate – for holding components vertically.

29. Miscellaneous - Application

30. Suction cups For holding plastic, glass, polystyrene and other non-ferrous parts

31. Fixturing kit

32. Vision fixtures Modular fixturing for vision systems or multi sensor machines. It create a faster and repeatable way to fixture the part for consistent and accurate inspection. Each vision fixture is made with a precision acrylic base plate that allows for backlighting and a clear, clean view of the part. Fixturing component can quickly be threaded into the base plate and arranged in any configuration.

33. Vision fixtures Renishaw offers two vision fixturing options. Quick load corner (QLC) Interchangeable vision fixture – for vision systems 450 mm x 450 mm or larger.

34. Advantages of Modular Fixtures Quick and easy to use. Repeatable and reproducible. To save time, multiple parts can be fixtured on a plate at one time or sub-plates can be used to automate the inspection process even further.  Document the part setup. Can reduce fixturing costs. Improves productivity . Better access to the entire part – unobstructed probe path. Eliminate the need of traditional fixtures.

35. Applications Inspecting parts for - Aerospace Automotive Electronics Industrial Medical Along with- CMMs Vision systems Non-contact scanning Optical comparators

36. Manufacturers

37. References Farhan U and Tolouei -Rad M., Design of modular fixtures using a 3D-modelling approach, 19 th International Congress on Modelling and Simulation, Perth, Australia (2011), pp 405–411 Liu Cheng- liang , A systematic Conceptual Design of Modular Fixtures , International Journal for Advanced Manufacturing Technology (1994) pp 9:217-224 Kumar KN , Naveen and AswathNarayan M S, Design and fabrication of Modular Fixture for CMM Inspection, International Journal of Research in Engineering and Technology, sep 2015, pp 406-411 Renishaw CMM modular fixtures, Technical specification, H-1000-0078-02-A Renishaw Vision modular fixtures, Technical specification, H-1000-0079-02-A Renishaw Equator modular fixtures, Technical specification, H-1000-0057-02-A R&R Fixtures brochure_20131 Alukeep Modular Fixturing System Product Brochure

38. THANK YOU