Copyright 2009 Society of Manufacturing Engineers. FUNDAMENTALS OF TOOL DESIGN Fixture Design - DF

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Theodora Patterson
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1 FUNDAMENTALS OF TOOL DESIGN Fixture Design - DF SCENE 1. DF26A, FTD87, 03:20:15:00-03:20:46:00 zoom out, milling operation DF26B, CGS: Milling Fixtures Lathe Fixtures Grinding Fixtures Broaching Fixtures IN ADDITION TO THEIR BASIC CONSTRUCTION FEATURES, FIXTURES ARE OFTEN CLASSIFIED BY THE MACHINE TOOL OR THE PROCESS FOR WHICH THEY ARE DESIGNED AND USED, WITH SOME OF THE PRIMARY TYPES INCLUDING: MILLING FIXTURES, LATHE FIXTURES, GRINDING FIXTURES, AND BROACHING FIXTURES. SCENE 2. DF27A, CGS: Milling Fixtures DF27B, FTD86, 01:14:46:00-01:15:06:00 milling DF27C, FTD88, 04:02:00:00-04:02:22:00 milling MILLING FIXTURES ARE THE MOST COMMON TYPE OF FIXTURE AND INCLUDE STANDARD VISES AND CLAMPS. HOWEVER, AS THE WORKPIECE SIZE, SHAPE AND COMPLEXITY BECOMES MORE SOPHISTICATED SO DOES THE FIXTURE. SCENE 3. DF28A, FTD90, 06:27:22:00-06:27:43:00 tombstone used on horizontal milling machine DF28B, FMP212, 01:01:39:00-01:01:51:00 tombstone with chucks TOMBSTONES, WHICH ARE COMMONLY USED ON HORIZONTAL MACHINING CENTERS, COME IN A WIDE VARIETY OF CONFIGURATIONS TO HOLD MULTIPLE PARTS ON UP TO FOUR SIDES OF THE FIXTURE.

2 SCENE 4. DF29A, FTD87, 03:06:01:00-03:06:13:00 t-slots THE T-SLOTS OF THE MACHINE TABLE ARE STANDARDIZED IN SIZE AND SPACING AND ARE THE PRIMARY MEANS OF HOLDING WORK AND FIXTURING DEVICES FOR MACHINING. SCENE 5. DF30B, FTD89, 05:10:08:00-05:10:13:00 t-slot bolt DF30C, FTD86, 01:20:00:00-01:20:08:00 step clamp DF30D, FTD87, 03:22:00:00-03:22:08:00 clamps FIXTURES ARE TYPICALLY MOUNTED TO THE TABLE USING A VARIETY OF ACCESSORIES SUCH AS CLAMPS, STRAPS, T-SLOT BOLTS, NUTS AND JACKS. SCENE 6. DF31A, FTD88, 04:06:24:00-04:06:48:00 zoom out, milling operation ACCURACY AND EFFICIENCY REQUIRES THAT THE MILLING FIXTURE DESIGN PERMIT AS MANY PART SURFACES AS POSSIBLE TO BE MACHINED WITHIN A SINGLE CLAMPING. SCENE 7. DF32A, FTD88, 04:37:08:00-04:37:20:00 part located on fixture LOCATORS MUST BE DESIGNED TO RESIST ALL TOOL FORCES. SCENE 8. DF33A, HSM08, 09:18:38:00-09:18:58:00 tool change during milling DF33B, HSM08, 09:20:54:00-09:21:05:00 loading parts to vises SUFFICIENT CLEARANCE SPACE MUST BE ALLOTTED TO ALLOW FOR TOOL CHANGES..., AND FOR THE LOADING AND UNLOADING OF PARTS. SCENE 9. DF34A, FTD92, 08:19:42:00-08:19:55:00 milling operation MILLING FIXTURES SHOULD ALSO BE DESIGNED AND BUILT WITH A LOW PROFILE TO PREVENT

3 DISTORTION OR DEFLECTION DURING MACHINING. SCENE 10. DF35A, FTD86, 01:19:22:00-01:19:43:00 milling with chips, fluid CHIP REMOVAL AND CUTTING FLUID CONTROL ARE BOTH IMPORTANT CONSIDERATIONS WHEN DESIGNING A FIXTURE. SUFFICIENT SPACE SHOULD BE ALLOTTED TO EASILY REMOVE CHIPS FROM AROUND FIXTURES. SCENE 11. DF36A, CGS: Lathe Fixtures DF36F, FTD12, 11:48:54:00-11:49:12:00 turning operation DF36D, FTD89, 05:02:16:00-05:02:22:00 c.u. milling DF36E, FTD87, 03:23:31:00-03:23:37:00 turning operation THE SAME BASIC DESIGN PRINCIPLES THAT APPLY TO MILLING FIXTURES ALSO APPLY TO LATHE, OR TURNING, FIXTURES, WITH ONE MAJOR DIFFERENCE. IN MOST MILLING OPERATIONS, THE CUTTING TOOL ROTATES DURING MACHINING, WHILE WITH TURNING, THE PART ROTATES. SCENE 12. DF37A, FTD04, 04:07:29:00-04:07:49:00 zoom out, boring operation on lathe THIS SITUATION CREATES ANOTHER CONDITION THE TOOL DESIGNER MUST DEAL WITH - CENTRIFUGAL, OR ROTATIONAL, FORCE. THE COMPLETED FIXTURE MUST RESIST ROTATIONAL FORCES, WHILE FOLLOWING A FEW BASIC DESIGN PRINCIPLES. SCENE 13. DF38A, FTD101, 11:35:42:00-11:35:55:00 zoom out, turning operation SINCE LATHE FIXTURES ARE DESIGNED TO ROTATE, THEY SHOULD BE LIGHT WEIGHT AND

4 WELL BALANCED. SCENE 14. DF39A, FTD87, 03:25:03:00-03:25:20:00 zoom in, turning on lathe WHENEVER POSSIBLE, PARTS SHOULD BE GRIPPED AND SECURED BY THEIR LARGEST DIAMETER OR CROSS SECTION. SCENE 15. DF40A, FTD21, 01:05:55:00-01:07:31:00 turning operation, edit at multiple points within clip THE PART SHOULD BE POSITIONED IN THE FIXTURE SO THAT MOST IF NOT ALL OPERATIONS CAN BE PERFORMED IN A SINGLE SETUP. SCENE 16. DF41A, FTD100, 10:07:00:00-10:07:15:00 part placed, secured in lathe chuck AVOID CLAMPING OVER AREAS TO BE BORED TO THIN-WALLED THICKNESSES AS THIS MAY RESULT IN PART WARPING OR DEFORMITY. SCENE 17. DF42B, FTD100, 10:32:17:00-10:33:06:00 setting up cutter on lathe, getting ready to turn part CUTTER SETTING SHOULD BE INCORPORATED INTO THE DESIGN AND TOOLS EASILY REMOVED. STANDARD LATHE ACCESSORIES SHOULD BE ADAPTED INTO THE DESIGN OF ALL TURNING FIXTURES. SCENE 18. DF43A, FTD100, 10:05:42:00-10:05:53:00 part mounted to chuck DF43B, FMP32, 01:21:54:00-01:22:00:00 collet DF43C, FMP34, 05:05:35:00-05:05:47:00 pan of between center workpiece DF43D, FMP33, 02:08:05:00-02:08:10:00 tailstock moved to support work DF43E, FMP34, 05:04:56:00-05:05:02:00 center mount in headstock spindle THE MAJORITY OF WORK ON THE LATHE IS HELD AT ONE END BY EITHER A CHUCK..., OR COLLET. LONG WORK MAY ALSO BE HELD AT BOTH ENDS BETWEEN CENTERS, WHICH ARE POINTED, CONICAL PINS THAT LOCATE INTO PREDRILLED

5 CENTER HOLES ON THE ENDS OF THE WORKPIECE. SCENE 19. DF44A, FTD101, 11:44:55:00-11:45:26:00 zoom out, turning operation DF44B, FMP208, 01:02:57:00-01:03:10:00 part placed in 3-jaw chuck, starting to spin DF44C, FMP210, 03:03:48:00-03:03:53:00 6 jaw chuck holding part DF44D, FMP210, 03:07:53:00-03:08:00:00 4-jaw chuck turning non round part, stopping DF44E, FMP210, 03:14:45:00-03:14:53:00 2-jaw chuck holding non round part CHUCKS HOLD SHORT, LARGE DIAMETER WORK. THERE ARE MANY TYPES OF CHUCKS, AND THEY ARE EITHER MANUALLY OR POWER OPERATED. SELF-CENTERING THREE-JAW UNIVERSAL CHUCKS ARE THE MOST COMMON. ALL THREE JAWS MOVE IN TANDEM TO GRAB A ROUND WORKPIECE, CENTER IT, AND GRIP IT. SELF-CENTERING CHUCKS MAY ALSO BE 6-JAW. IRREGULARLY-SHAPED WORKPIECES MAY BE HELD IN EITHER FOUR-..., OR TWO-JAW CHUCKS, IN WHICH THE JAWS ADJUST INDEPENDENTLY. SCENE 20. DF45A, FMP216, 01:25:33:00-01:25:40:00 part in soft jaws DF45B, FTD100, 10:39:46:00-10:39:55:00 zoom out, soft jaws WHERE ACCURATE CONCENTRICITY WITH A PREVIOUSLY MACHINED DIAMETER IS REQUIRED, SOFT JAWS MAY BE USED. SCENE 21. DF46A, FTD100, 10:37:54:00-10:38:12:00 pan, multiple sets of soft jaws SOFT JAWS ARE USUALLY MADE OF ALUMINUM AND ARE PRODUCED TO HOLD A SPECIFIC PART OR FAMILY OF PARTS. SCENE 22. DF47A, FMP34, 03:06:56:00-03:07:23:00 collet placed in spindle, work placed in collet, collet tightened, multiple cuts DF47B, FMP33, 02:01:03:00-02:01:11:00 zoom out, multiple collets DF47C, FMP211, 04:06:11:00-04:06:16:00 square collet, part placed in it COLLETS, WHICH USUALLY SEAT IN THE SPINDLE OF THE LATHE, ARE HOLLOW CYLINDRICAL DEVICES WITH SLOTS ALONG

6 MOST OF THEIR LENGTH. A COLLET OPENS UNDER ITS OWN SPRING TENSION AND IS CLOSED SECURELY TO GRIP THE STOCK. THEY HOLD SMALL-DIAMETER WORK ON-CENTER. CHUCKS AND COLLETS COME IN MANY TYPES TO SUIT VARIOUS WORKPIECES. SCENE 23. DF48A, CGS: Grinding Fixtures DF48B, FTD95, 03:47:09:00-03:47:32:00 zoom in, surface grinding operation DF48C, FTD100, 10:53:49:00-10:54:03:00 zoom in, cylindrical grinding operation GRINDING FIXTURES ARE A FAMILY OF FIXTURES RATHER THAN A SINGLE CLASSIFICATION. THE TWO MAJOR TYPES OF GRINDING FIXTURES ARE THOSE USED FOR SURFACE GRINDING..., AND CYLINDRICAL GRINDING. SCENE 24. DF49A, FTD100, 10:47:52:00-10:48:08:00 parts fixtured to magnetic table THE MAGNETIC TABLE IS THE PREFERRED WORKHOLDING DEVICE ON SURFACE GRINDERS. SCENE 25. DF50A, FTD102, 12:03:53:00-12:04:08:00 zoom out, special fixture holding part during surface grinding DF50B, FTD100, 10:46:46:00-10:47:08:00 surface grinding WORKPIECES, OR FIXTURE ELEMENTS IN CONTACT WITH THE MAGNETIC TABLE MUST BE FERROUS IN COMPOSITION IF THEY ARE TO BE HELD SECURELY. IN EITHER CASE, THE WORKHOLDING BOND MUST BE STRONG ENOUGH TO PREVENT LATERAL OR TRANSVERSE WORKPIECE MOVEMENT DURING MACHINING. SCENE 26. DF51A, FMP127, 03:18:44:00-03:19:00:00 cylindrical grinding operation CYLINDRICAL GRINDING IS USUALLY A

7 SECONDARY OPERATION AFTER TURNING. OFTEN THE SAME CENTER HOLES USED FOR BETWEEN CENTERS TURNING MAY BE USED FOR GRINDING THE PART. SCENE 27. DF52A, FTD100, 10:52:39:00-10:52:53:00 zoom out, cylindrical grinding operation AS WITH LATHE FIXTURES, CYLINDRICAL GRINDING FIXTURES MUST BE PERFECTLY BALANCED FOR ACCURACY. SCENE 28. DF53A, FMP129, 05:07:41:00-05:07:51:00 pan, cylindrical grinding machine WHENEVER POSSIBLE, STANDARD CYLINDRICAL GRINDING ACCESSORIES AND ATTACHMENTS ARE PREFERRED OVER CUSTOM FIXTURES. SCENE 29. DF54A, FTD100, 10:49:38:00-10:50:04:00 zoom in, cylindrical grinding operation CAREFUL CONTROL OF FRICTION IS MORE SIGNIFICANT IN GRINDING THAN IN ANY OTHER MACHINING OPERATIONS. FOR THAT REASON ADEQUATE SPACE MUST BE PLANNED FOR COOLANT AND SWARF REMOVAL FROM THE GRINDING ZONE. SCENE 30. continue previous shot DF55A, FMP128, 04:21:39:00-04:21:50:00 truing of grinding wheel DF55B, FMP129, 05:11:58:00-05:12:13:00 truing of grinding wheel ADDITIONALLY, WITH ANY GRINDING MACHINE, WHEEL DRESSING AND TRUING SHOULD BE INCORPORATED INTO THE FIXTURE DESIGN IF NOT BUILT INTO THE MACHINE ITSELF. SCENE 31. DF56A, CGS: Broaching Fixtures DF56B, FTD20, 22:01:03:00-22:01:33:00

8 zoom in, broaching operation BROACHING FIXTURES HOLD AND LOCATE THE PART IN RELATION TO THE BROACHING TOOL. BROACHING FORCES REQUIRE THAT THE COMPLETE FIXTURE BE BUILT MORE SUBSTANTIALLY THAN WITH OTHER PROCESSES. SCENE 32. DF57A, FTD18, 18:25:36:00-18:26:01:00 2 cycles, internal broaching operation INTERNAL AND EXTERNAL BROACHING REQUIRES DIFFERENT APPROACHES TO THEIR RESPECTIVE DESIGNS. INTERNAL BROACHING REQUIRES LESS CLAMPING SINCE THE PROCESS TENDS TO KEEP THE PART FIRMLY SEATED ON THE FIXTURE. SCENE 33. DF58A, FMP781, 20:10:42:00-20:10:54:00 pot broaching of external gear teeth DF58B, FMP781, 20:02:53:00-20:03:02:00 zoom in, pot broaching tool teeth EXTERNAL BROACHING REQUIRES RESISTANCE TO BOTH PULL AND PUSH FORCES THAT ARE EXERTED ON THE PART, REQUIRING MORE SOPHISTICATED FIXTURING. SCENE 34. DF59A, FTD18, 18:03:56:00-18:04:23:00 zoom in, broaching operation THE PRINCIPLE PURPOSE IN EITHER CASE IS TO HOLD THE PART IN PROPER RELATION TO THE TOOL AND TO PREVENT MOVEMENT.

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