MANUFACTURING PROCESS - SWAGING

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SWAGING

IN THIS PROCESS, THE DIAMETER OF A ROD OR A TUBE IS REDUCED BY FORCING IT INTO A CONFINING DIE. A SET OF RECIPROCATION DIES PROVIDES RADIAL BLOWS TO CAUSE THE METAL TO FLOW INWARD AND ACQUIRE THE FORM OF THE DIE CAVITY. THE DIE MOVEMENTS MAY BE OF IN – AND – OUT TYPE OR ROTARY. THE LATTER TYPE IS OBTAINED WITH THE HELP OF A SET OF ROLLERS IN A CAGE, IN A SIMILAR ACTION AS IN A ROLLER BEARING. THE WORKPIECE IS HELD STATIONARY AND THE DIES ROTATE, THE DIES STRIKE THE WORKPIECE AT A RATE AS HIGH AS 10 - 20 STROKES PER SECOND.

SCREWDRIVER BLADES AND SOLDERING IRON TIPS ARE TYPICAL EXAMPLES OF SWAGED PRODUCTS. 

IN TUBE SWAGING, THE TUBE THICKNESS AND / OR INTERNAL DIA OF TUBE CAN BE CONTROLLED WITH THE USE OF INTERNAL MANDRELS. FOR SMALL – DIAMETER TUBING, A THIN ROD CAN BE USED AS A MANDREL; EVEN INTERNALLY SHAPED TUBES CAN BE SWAGED BY USING SHAPED MANDRELS.


THE PROCESS IS QUITE VERSATILE. THE MAXIMUM DIAMETER OF WORK PIECE THAT CAN BE SWAGED IS LIMITED TO ABOUT 150 MM; WORK PIECES AS SMALL AS 0.5 MM DIAMETER HAVE BEEN SWAGED. THE PRODUCTION RATE CAN BE AS HIGH AS 30 PARTS PER MINUTE DEPENDING UPON THE COMPLEXITY OF THE PART SHAPE AND THE PART HANDLING MEANS ADOPTED.

THE PARTS PRODUCED BY SWAGING HAVE TOLERANCE IN THE RANGE ± 0.05 MM TO ± 0.5 MM AND IMPROVED MECHANICAL PROPERTIES. USE OF LUBRICANTS HELPS IN OBTAINING BETTER WORK SURFACE FINISH AND LONGER DIE LIFE. MATERIALS, SUCH AS TUNGSTEN AND MOLYBDENUM ARE GENERALLY SWAGED AT ELEVATED TEMPERATURES AS THEY HAVE LOW DUCTILITY AT ROOM TEMPERATURE. HOT SWAGING IS ALSO USED TO FORM LONG OR STEEP TAPERS, AND FOR LARGE REDUCTIONS.

SWAGING IS A NOISY OPERATION. THE LEVEL OF NOISE CAN BE, HOWEVER, REDUCED BY PROPER MOUNTING OF THE MACHINE OR BY THE USE OF ENCLOSURE.

WIRE DRAWING
WIRE DRAWING IS PRIMARILY THE SAME AS BAR DRAWING EXCEPT THAT IT INVOLVES SMALLER – DIAMETER MATERIAL THAT CAN BE COILED. IT IS GENERALLY PERFORMED AS A CONTINUOUS OPERATION ON DRAW BENCH LIKE THE ONE

LARGE COIL OF HOT ROLLED MATERIAL OF NEARLY 10 MM DIAMETER IS TAKEN AND SUBJECTED TO PREPARATION TREATMENT BEFORE THE ACTUAL DRAWING PROCESS. THE PREPARATION TREATMENT FOR STEEL WIRE CONSISTS OF:
  • CLEANING. THIS MAY BE DONE BY ACID PICKLING, RINSING, AND DRYING. OR, IT MAY BE DONE BY MECHANICAL FLEXING.
  • NEUTRALIZATION. ANY REMAINING ACID ON THE RAW MATERIAL IS NEUTRALIZED BY IMMERSING IT IN A LIME BATH. THE CORROSION PROTECTED MATERIAL IS ALSO GIVEN A THIN LAYER OF LUBRICANT.
TO BEGIN THE DRAWING PROCESS, ONE END OF COIL IS REDUCED IN CROSS SECTION UPTO SOME LENGTH AND FED THROUGH THE DRAWING DIE, AND GRIPPED.

SMALL DIAMETER WIRE IS GENERALLY DRAWN ON TANDOM MACHINES WHICH CONSISTS OF A SERIES OF DIES, EACH HELD IN WATER – COOLED DIE BLOCK. EACH DIE REDUCES THE CROSS SECTION BY A SMALL AMOUNT SO AS TO AVOID EXCESSIVE STRAIN IN THE WIRE. INTERMEDIATE ANNEALING OF MATERIAL BETWEEN DIFFERENT STATES OF WIRE MAY ALSO BE DONE, IF REQUIRED.

WIRE DRAWING TERMS:

FOR A SINGLE COLD – DRAWING PASS, THE PERCENT AREA REDUCTION THAT CAN BE DONE DEPENDS UPON MANY FACTORS. THESE INCLUDE THE TYPE OF MATERIAL, ITS SIZE, INITIAL METALLURGICAL CONDITION, THE FINAL SIZE AND MECHANICAL PROPERTIES DESIRED, DIE DESIGN AND LUBRICATION EFFICIENCY. THE PERCENT OF AREA REDUCTION PER PASS CAN RANGE FROM NEAR ZERO TO 50%.

DIE PULL
THE FORCE REQUIRED TO PULL THE STOCK THROUGH THE DIE (UNDER FRICTIONLESS CONDITIONS) CAN BE COMPUTED AS FOLLOWS. 


WHERE F = DIE PULL, I.E. THE FORCE REQUIRED TO PULL THE STOCK THROUGH THE DIE
YAVG = AVERAGE TRUE STRESS OF THE MATERIAL IN THE DIE GAP
AO, AF = ORIGINAL AND FINAL AREAS OF CROSS SECTION OF MATERIAL.
ALTERNATIVELY, THE FOLLOWING EXPRESSION CAN BE USED 
                                                                    F = C ST (AO - AF


WHERE C IS A CONSTANT WHOSE VALUE IS IN THE RANGE 1.5 TO 3.0 DEPENDING UPON THE % AREA REDUCTION, (LOWER VALUE FOR HIGHER % REDUCTION), AND ST IS TENSILE STRENGTH OF MATERIAL BEFORE DRAWING.

THE PULL FORCE DETERMINES THE MACHINE CAPACITY NEEDED.

TUBE DRAWING
THE DIAMETER AND WALL THICKNESS OF TUBES THAT HAVE BEEN PRODUCED BY EXTRUSION OR OTHER PROCESSES CAN BE REDUCED BY TUBE DRAWING PROCESS. THE PROCESS OF TUBE DRAWING (FIG 3.5) IS SIMILAR TO WIRE OR ROD DRAWING EXCEPT THAT IT USUALLY REQUIRES A MANDREL OF THE REQUISITE DIAMETER TO FORM THE INTERNAL HOLE.

TUBES AS LARGE AS 0.3 M IN DIAMETER CAN BE DRAWN. 


DRAWING EQUIPMENT
DRAWING EQUIPMENT CAN BE OF SEVERAL DESIGNS. THESE DESIGNS CAN BE CLASSIFIED INTO TWO BASIC TYPES; DRAW BENCH, AND BULL BLOCK. A DRAW BENCH USES A SINGLE DIE AND THE PULLING FORCE IS SUPPLIED BY A CHAIN DRIVE OR BY HYDRAULIC MEANS. DRAW BENCH IS USED FOR SINGLE LENGTH DRAWING OF ROD OR TUBE WITH DIAMETER GREATER THAN 20MM. LENGTH CAN BE AS MUCH AS 30 M. THE DRAWING SPEED ATTAINABLE ON A DRAW BENCH RANGES FROM 5 M/MIN TO 50 M/MIN. DRAW BENCHES ARE AVAILABLE HAVING CAPACITIES TO PROVIDE PULL FORCE OF UPTO 1 MN.

BULL BLOCK OR ROTATING DRUM IS USED FOR DRAWING RODS OR WIRES OF VERY LONG LENGTH. 

References :- www.nptel.iitm.ac.in/








5 comments:

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  3. see, you learn something new every day. I don't ever intend to be doing any greasing but this is a good tip to keep your hands clean so you can take more progress photos

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