IN-DIE TAPPING by Chandan kumar H.K.

IN-DIE TAPPING

IN-DIE TAPPING

IN-DIE TAPPING: "In-Die" tapping is tapping in a progressives die on a punch press. In-die tapping has become the only competitive alternative to secondary tapping.

IN-DIE TAPPING

Considerations for Combining Stamping and Tapping

INITIAL INVESTMENT LABOR REQUIREMENTS PRODUCTION RATES

IN-DIE TAPPING

INITIAL INVESTMENT

Cost of building a tapping die is generally less than that of building a secondary high-speed tapping machine.

Secondary tapping machines usually are dedicated to a single part, but a tapping unit can be changed from die to die, reducing the initial cost of subsequent tapping dies.

The cost of stamping parts with multiple tapped holes can be further reduced using a multi-spindle tapping unit. (Cost per hole 30% to 40% less than that of an individual tapping unit.)

IN-DIE TAPPING

INITIAL INVESTMENT

Multi-Spindle tapping units usually are dedicated to a single die, so they cannot be interchanged.

Tapping heads are compact.

IN-DIE TAPPING

LABOR REQUIREMENTS

Eliminating a secondary tapping operation also eliminates related handling and feeding costs.

In-die tapping enables the press operator to produce completed tapped parts in one operation.

Inspection is still required. New sensor technology can help reduce inspection costs.

IN-DIE TAPPING

PRODUCTION RATES

The size of the tap and the material (Hardness) being tapped determine the ultimate production rate of a tapped stamped part.

Some stampers are running modern tapping units close to 200 strokes per minute (SPM), producing millions of tapped stamped parts monthly.

These high production rates usually are limited to nonferrous metal parts and those with small-diameter tapped holes (up to M6).

IN-DIE TAPPING

PRODUCTION RATES

As the diameter of the tap increases, production rate decreases.

It can be difficult to convince a metal stamper to slow down the press to perform the tapping operation. Even with todays modern tapping units, some compromise in press speed may be necessary.

Part is finished in one operation with one operator.

IN-DIE TAPPING

PRODUCTION RATESExample: An automotive part with a 5/16-18TPI tapped hole required.

Alternative 1:Produce pre-tap hole at (Piercing) 90 SPM. Secondary tapping operation 30 to 40 SPM. 22 components / min.

Alternative 2: In-die tapping produce a completed part at a rate of 60 SPM.60 components / min.

IN-DIE TAPPING

WORKING OF TAPPING UNIT

Conversion of the vertical linear press motion to a helical tap movement requires a lead screw that will the cause rotation in a mating part, when axially loaded.

When driven down by the press ram, the lead screw drives a series of gears that convert the linear travel of the press ram to the required helical travel for a specific tap diameter and pitch.

IN-DIE TAPPING

WORKING OF TAPPING UNIT

The lead screw itself does not rotate, but it passing through a mating gear, causes the gear to rotate.

This rotation is transmitted to a tap cartridge, which produces a helical rotation for the tap.

The required tap travel, relative to ram travel, is obtained by selecting the correct gear ratio.

IN-DIE TAPPING

DIE IN OPEN POSITIONSHEET STRIPLEAD SCREW

IN-DIE TAPPING

DIE CLOSED POSITION

IN-DIE TAPPING

DIE CLOSED POSITION

IN-DIE TAPPING

PRESS WORKING CYCLE

IN-DIE TAPPING

TYPES OF IN-DIE TAPESTop-down TappingBottom-up Tapping Strip-following Tapping Servo-driven Tapping

IN-DIE TAPPING

TOP-DOWN TAPPINGTop-down tapping unitssingle or multi-Spindleare suitable for flat running parts with minimal strip travel.

Tap changes can be made in seconds

These units typically can be used in high-volume, high-speed applications and are capable of running at more than 200 SPM.

IN-DIE TAPPING

BOTTOM-UP TAPPINGAs strip lift begins to increase, (which is the distance the material has to lift above the lower die to clear for extrusions or forms to progress to the next station) tapping from the bottom up is one way to compensate for the increase in material movement.

IN-DIE TAPPING

BOTTOM-UP TAPPINGIn bottom-up tapping, the material is pushed down, allowing the tapper to thread the part.

IN-DIE TAPPING

BOTTOM-UP TAPPING

IN-DIE TAPPING

SERVO-DRIVEN TAPPING

In a servo-driven tapping unit, the threading operation functions independently of the press stroke, which can be beneficial when running large-diameter taps.

They can tap from the top down or bottom up and work in multitap applications.

IN-DIE TAPPING

PRESS CYCLE225135

IN-DIE TAPPING

STRIP FOLLOW TAPPING

Strip following tapping is used for high strip lift (may due to bending or flanging on the strip).

A strip-following tapping unit can begin to thread the part as soon as the material feeds into position.

After the sheet is piloted, the tapper starts to thread the sheet and move along with the sheet downwards.

IN-DIE TAPPING

STRIP FOLLOWING TAPPING

IN-DIE TAPPING

STRIP FOLLOWING TAPPINGLead screwTapping headSpring liftStrip

IN-DIE TAPPING

STRIP FOLLOW TAPPING

The following example demonstrates strip-following tapping unit, Given:Running in a 12-in.-stroke press. in. thick part with a 3/8-16TPI hole and 1 in. strip lift that needs approximately 9 tap revolutions.

IN-DIE TAPPING

STRIP FOLLOW TAPPINGA conventional tapping unit working from the bottom up with a 2:1 gear ratio (2 revolutions per 1 of press stroke) requires the stripper to hold the material for approximately 4.5 in (for 9rev of tap). This 4.5 in. window allows the press to run at 18 to 22 strokes/min.PRESS STROKETapping stroke

IN-DIE TAPPING

STRIP FOLLOW TAPPINGThe same part with a strip-following tapping unit with a 1:1 gear ratio allows the tapping window to increase from 4.5 to 9 in., which reduces the rpm of the tap by half so press speed can be doubled.Press can run at 36 to 44 strokes/min.

PRESS STROKETapping stroke

IN-DIE TAPPING

TAPPING STROKE VS SPM4.592244Tapping stroke in inchesStroke per min.

IN-DIE TAPPING

DESIGN CONSIDERATIONMaterialsMaterial lift Stripper Piloting Clearances for tapping unit Lead screw engagement Press stroke Gear ratio Tapped hole diameter

IN-DIE TAPPING

MATERIALS

Taps a full range of threaded hole diameters in popular materials including Stainless steel, Mild steel and Aluminum.

IN-DIE TAPPING

MATERIAL LIFT

When tapping from top down, material lift should be kept minimum.Less the material lift less the tap has to travel.

When the part requires a higher material lift, tapping from the bottom up or top down require Rapid Advance Lead Screw assembly to maintain the production rate.

IN-DIE TAPPING

STRIPPER

The stripper will have to hold the material the entire time the tapping process is taking place.

If the stock moves up and down during the tapping cycle, results in "pulled threads in the part.

Variables Such as material thickness (plus extrusions) or any forms will determine the actual stripper travel.

IN-DIE TAPPING

STRIPPERSpring strippers are the most common method used in tapping dies, though in many cases a bridge stripper (box stripper) may be used in relatively flat running parts.

If a bridge stripper is used it is still advisable to have spring pushpins located on either side of the tapping unit to hold the material down during the tapping operation.

IN-DIE TAPPING

STRIPPER

Air activated hold-downs located on either side of the tapping unit have also been a successful method of holding the material during the tapping process.

Whichever method is used it is important to properly calculate the length of stroke that is necessary to hold the part during the tapping operation.

IN-DIE TAPPING

STRIPPERTop half moving down (no strip holding)Strip is held before tapping beginstapping is continued with strip holding

IN-DIE TAPPING

STRIP HOLDING Strip should be held as nearer as possible to the tapping areaCOMPONENT

IN-DIE TAPPING

PILOTING

Hole location will aid in providing longer tap life.

Due to the longer stripper travel tapping dies usually require longer pilots.

It is always best to have the pilots enter the material prior to the tap entering the material.

In some cases it is not practical to use such long pilots, especially when they are a smaller diameter.

IN-DIE TAPPING

TAPPINGTAP EXTRACTIONFEED ANGLEPILOTINGPILOT EXTRACTION

IN-DIE TAPPING

PILOTING

It may be necessary to place the pilots in a guided stripper or in the lower die section.

Ideal situation is to have pilots immediately before and after each tapping unit station.

The stock is likely to move back and forth in the die by a few thousandths, can mean broken taps!

IN-DIE TAPPING

CLEARANCES FOR TAPPING UNITThe tapping unit requires two clearance holes in the die set, one in the upper die shoe and one in the lower die shoe.

The upper die shoe requires a clearance hole for the complete tapping unit.

The clearance hole in the lower die shoe will be for the lead screw.

IN-DIE TAPPING

CLEARANCES FOR TAPPING UNIT

By providing these two clearance holes the shut height between the two die shoes will be lowered to accommodate the basic tapping unit.

If less shut height is required then additional clearance for the housings themselves can be provided.

It is helpful to provide hand clearance to allow for removal of the tapping unit assembly.

IN-DIE TAPPING

CLEARANCES FOR TAPPING UNIT

Vertical clearance will be needed under the tapping unit equal to the press stroke for the lead screw in the lower die shoe, this is standard in all models.

IN-DIE TAPPING

CLEARANCES FOR TAPPING UNITClearance for tapping headClearance for lead screwParallel blocks

IN-DIE TAPPING

PRESS STROKE AND GEAR RATIO

Tapping dies will usually require a minimum of three inches of press stroke.

Higher press stroke may be necessary on dies with higher material lift.

Tapping units are available with different gear ratios, which will compensate for very high tap movement on long stroke presses.

Tapping units have four standard available gear ratios 2:1, 3:1, 4:1 and 5:1.

IN-DIE TAPPING

GEAR RATIOGear ratio refers to the number of revolutions that the tap will make per one inch of press stroke.

Example: 5:1 gear ratio in a 4 inch stroke press will make 20 revolutions clockwise and 20 revolutions counter clockwise per press cycle. As a general rule, lower stroke presses will use higher ratio tapping units. Once the number of required revolutions for a particular tapping die is determined press stroke and gear ratio can be calculated.

IN-DIE TAPPING

TAPPED HOLE DIAMETERProper tapped hole diameter is crucial for maintaining long tap life. one or two thousandth difference in hole diameter will make a major difference in the over all performance of a tapping die.

Example: for 10-32TPI form tap, tap drill sizes

As a general rule, a tapping die will run best when the lowest expectable thread percentage is used.

IN-DIE TAPPING

IN-DIE TAPPING

LEAD SCREW ENGAGEMENT

It is always important to maintain proper lead screw engagement.

No mating parts become disengaged during the press cycle.

Minimum engagement at TDC should be at least 1.5 times the diameter of the drive lead screw.

IN-DIE TAPPING

LEAD SCREW ENGAGEMENT

A higher stroke tapping unit can always run in a lower stroke punch press.

A lower stroke tapping unit in a higher stroke punch press, it will be necessary to purchase a lead screw designed equal (or more) to the stroke of the press.

IN-DIE TAPPING

FEED ANGLEA portion of crank rotation (in degrees) on the press, which is used to actually feed the stock forward one progression.

Tapping angle needs to remain as large as possible because more time allotted for tapping keeps the ratio of the tapping unit lower.

A lower ratio translates into a lower tap RPM.

This allows the stamper to run the press faster.

IN-DIE TAPPING

FEED ANGLEThe smaller the window for tapping, the faster the unit must turn the tap to get it into, and back out of, the part.

Faster tap RPM means Slower press speeds.

IN-DIE TAPPING

TAPPINGTAP EXTRACTIONPILOTINGPILOT EXTRACTIONAs small as possibleAs large as possibleFEED ANGLE

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STANDARDSHUTCHISON TOOL SALES Ltd.

IN-DIE TAPPING

COSTS

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Video of in-die tappingPlay

IN-DIE TAPPING

REFERENCESNEW CONCEPTS OF IN-DIE TAPPING, John s. Douse division supervisor/pronic, USA.COMBINING OPERATIONS TO COMPETE IN THE GLOBAL MARKET, By William Pfister, October 12, 2004. IN-DIE TAPPING CUTTERNT TECHNOLOGY AND EXPERIENCE, By Graham J. Clarke, Product Manager, Danly IEM, Chicago, ILIN-DIE TAPPING UNIT PAID FOR ITSELF WITHIN A YEAR,Brauer Coley,Manufacturingtalk Editorial Team on 24 May 20045)www.Hutchisontool.com6)www.mate.com/easytap 7)www.metalformingmagazine.com8)www.Thefabricator.COM

IN-DIE TAPPING

Thank you

IN-DIE TAPPING