Trouble Shooting Presses

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zIwWt-

1988

MS88-200Trouble ShootingjMetal Stamping Presses

authorJEFFERY R. FREDLINEOperations ManagerP.R.E.S.S., IncorporatedMorristown, Tennessee

abstractThe major problems facing pressroom operations on a daily basis are discussed. Manyof the tricks of the trade are covered in laymans terms, allowing the reader to find prac-tical solutions, saving the company thousands of dollars.

conferencePredictive Maintenance for PressesOctober 2526, 1988Schaumburg, Illinois

index termsMetal StampingPresses

Society of Manufacturing Engineers l One SME Drive l P.O. Box 930Dearborn, Michigan 48121 l Phone (313) 271-l 500


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SME TECHNICAL PA PERSThis Technical Paper may not be reproduced in whole or in part in anyform including machine-readable abstract, without permission from theSociety of Manufacturing Engineers. By publishing this paper, SME doesnot provide an endorsement of products or services which may be discussed inthe papers contents.


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TROUBLE SHOOTING METAL STAMPING PRESSESMetal Stamping Presses-require on going attention, Just as anyother type of manufacturing equipment. Often, due to their sizesmany feel that they wl I I not be damaged, this Is a false premlse.Paralleltsms Effect On OperationThe Press BedPress manufacturers exercise great care to Insure that allsurfaces on the press bed are machined In a parallel condition.The bed of the press Is the maJor bufldlng block upon which themachine Is constructed. Press beds should be malntalned wlthlnthe fol lowlng I Imlts;LEVEL BED Parallel


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RIGHT TO LEFT OR FRONT TO BACK PARALLELISM

IF THE BED MEASURES: MAXIMUM OUT OF PARALLELISM:30 Inches .00254 Inches .002578 Inches e 003

102 Inches .0035126 Inches .004150 Inches * 0045174 Inches .005

The Bolster Plate effects Parallelism

The Bolster Plate Is the plate attached to the top of the pressbed having drilled holes or T slots for attaching the lower dleor dle shoe to the press.Normally there exist two common problems wfth Bolster Plates;1.0 PROPER SEATING ON THE PRESS BED.

In press operations It becomes extremely Important thatthe Bolster Plate be In proper contact with the bed of themachine. There should not exist any detectable clearancebetween the bed and bolster plate surface. This should bechecked wlth feeler gauges on a regular basls. Thefollowing are special problem areas that you should be onthe lookout for;1.1 Breathing between the bed and the bolster plate durlng

press operatlon.1.2 Dirt, slugs or scrapes between the bed and the bolster.1.3 Tlghtness of bolster plate tie downs.1.4 Burrs and dents In bottom face of bolster and top ofbed.


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2.0 SURFACE CONDITION OF THE BED.The surface condition of the bolster plate and top of bedare critical in maintaining the proper level and alignmentof tooling. Each time the plate is removed or the toolinginstalled there exists the possibllity of damage to thework 1 ng surface. Extreme care should be taken during theloading and unloading the tooling to minimize scraping thetooling over the machined surfaces. With each scrapematerial is removed thus resultlng in wear.

The Slides Effect On Parallelism

The Slide is the main reciprocating member of th,e press towhich the die shoe and sometimes the upper dle Is affixeddirectly. The face or bottom of the slide should be heldwithin .002 flatness. The slide way surfaces should beheld perpendicular with the face of the slide within.002 in 36 inches of length.

90 FLAT CIBSURFACE 45O GIB SURFACE

SLIDE FACE


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MS88-200-4

Proper checking of parallelism involves disassembly of themachine and component s being set up and indicated on a mill.Due to the excessive amount of time and money required toaccomplish thfs It Is necessary to find a Short Cut if youw9ll. This short cut Is known throughout the Industry asTracking the Slide. Please note the diagram on page 4.

Parallelism between the slide and bed should be maintainedwithin the following tolerances:(Thousands Per Foot).OOl AT BOTTOM DEAD CENTER

.003 AT MIDSTROKE (Quarter down and quarter up)

.005 AT MIDSTROKE 0.N THE BLANKHOLDER OF A DOUBLEACTION PRESS.

Tracking the Slide consists of determining the path of theslide as it goes through the stroke. It is a fast, reliablemethod finding out what is happening in the machine duringoperation. For you to be able to perform this check it isnecessary that you have a dial indicator, magnetic base, andprecision square. The following steps must be followed inorder to produce the desired results.1 .l1.2

1.31.4

1.5

Deburr top of bolster plate to remove any high spots orburrs.Measure the die space at bottom dead center to insurethat you have enough height to allow your precisionsquare to rest on top of the bolster plate through thestroke without being damaged.Attach the dial indicator to the face of the slide.Indicate to the face of the precision square andrun the machine through the stroke recording anymovement in both the front to back and left to rightpositions.Evaluate results.

NOTE : If the movement is more than .005, it is generallynecessary to make adjustments to the machine.


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MS88-200-5

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MS88-200-6

General Slide to Bed (Bolster Plate) Parallelism.As a general rule parallelism between the face of the slideand the top of the bed or bolster plate should be maintainedwithin the following tolerances:(The following are measured in thousands per foot)Bottom of Stroke . . . . . . . . . . . . . . . . . . . . . . . . . . . . .OOlMidstroke (Quarter Down or Quarter Up)...... :003Midstroke on a (Blankholder)................ .005Example: If the bed area of the machine is 120 left to rightthen the following tolerance would apply:

120 divided by 12 = 10 feet X ,001 = .OlO Thiswould be the maximum that the machine could be outand still be considered within normal running toler-ance. NOTE: Many precision operations may requiretighter tolerances than noted above.

Parallelism Control and AdJustment1.0 On single point or O.B.I. presses, parallelism is

controlled in both the front to back and left to rightpositions by the slide guiding. Please note thefollowing example:

ADJUST ADJUST


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Given that the slide is suspended within the frame by onepoint of pivot, you have the ability to move the slidein any direction necessary to obtain parallelism.2.0 On 2 point and 4 point machines the front to back para-llellsm is controlled by the slide guiding. You have theability to move the slide with the gibbing to bring theface parallel with the bed of the machine in the frontto back position of the slide. NOTE: Generally left toright parallelism is controlled by the adJustment of theconnecting rods.3.0 On four point machines the front to back and left to

right parallelism can be effected by both the slideguiding and the connecting rod adJustment.

Multiple Point Machine Parallelism

When dealing with two point and four point machines paralle-lism is affected by each of the following areas:1.1 Adjustment screw drive1.2 Drive train timing.1.3 Difference In the stroke lengths.1 .4 SI ide centering.1.5 Tie rod pre-stressing. .

We will take a look at each of the following areas of concern.Please note the following with regards to the diagrams whichfol I ow:

TDC- Position of slide at top,dead center.l/4 Down- Position of slide at 90 degrees.BDC- Position of slide at bottom dead center.l/4 up- Position of slide at 270 degrees.1.0 AdJustment Screw Drive.


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TDCl/4 DownBDCl/4 up

Left0000

Right

When one side of the slide remains higher than the otherside, without changing all the way through the stroke of themath ine. The problem is usually with the adJustment screwdrive. This condition is corrected by disconnecting thecoupling between the RH and LH adjustment assemblies andlowering the higher side to bring it back in parallel.

2.0 Drive Train Timing


Left Right0 00 +0 0+ 0

When the slide remains level at bottom and top dead center,then drifts up on one end at l/4 down and up on the opposi teend at l/4 up the problem is usually drive train timing.The machine timing needs to be checked at regular Intervals.The timlng can be changed on most machines by leveling thesl ide, removing -(l) key and rotating the pinion or gear to thepotnt that all the gear load Is evenly distributed throughthe machine. A key is then manufactured. This key isf itted, installed, and the timing is rechecked.


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!

3.0 Difference In Stroke LengthLeft

TDC 0l/4 Down 0

Right+0

BDC + 0l/4 up 0 0

When the slide is out of parallel at both bottom and top deadcenter. Then at l/4 down and l/4 up it is parallel, theproblem to look for is a difference in the two throws of thecrankshaft. This problem can also exist if you have an ec-centric driven press. This problem will evidence itself whenthe machine is new or returning from a rebulld. It is nota common problem and if it occurs, the only method ofcorrection is to rework the parts involved.

4.0 Slide Centering


When the slide is not

(FrontLeft

000+

to Back Shaft Machines)Right

0+00

properly centered in the press frameor there exists excessive wear on the locating flangesof the drive mechani sm you will experience a problem whichappears to be timing. Particularly on front to back shaftedpresses the slide must run on the center line of themachine to function properly. This problem can be correctedby replacing the thrust surfaces which are worn or in somecases by adjustment of the gibbing which locates the slideback on center.


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M888-200-10

5.0 Tie Rod Pre-StresslngThe tie rod is the main support structure for the machine.It Is the long bolt which holds the different component s ofthe machine together. Tie rods are installed on the machine,heated, and PRE-STRESSED. It 1s necessary to always pre-stressall (4) tie rods at the same time. When a machine stickson bottom it Is the tendency to heat only enough rods to getthe machine off bottom. THIS IS NOT AN ACCEPTABLE PROCEDURE!In order to maintain an even load on all (4) corners ofthe machine the rods must be pre-stressed the same amount.It is possible to calculate the proper amount of PRE-STRESSusing the following formula:T = Number of degrees of turn on the nut.L = length of the rod in inches between the nuts.t = Number of threads per Inch on the rod.

T = (L x t1 Divided by 4Please note the following diagram

l-f?Ii 1I I II _ It II j! Ii Ii I/i I/ /I ,I 1-

5 IHREAASPER INCHt 175 X 5T = = 218.75 or4

219" Degrees

175"

6% I21 Degrees


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M888-200-U

THE PERIODIC INSPECTIONProper machine maintenance requires periodic Inspecttons.Press lnspectlons as part of the preventative malntenaceprogram allow you to schedule down time, and many timesstop problems before they progress to a critical stage.There are two types of press Inspections; The Informaland The F.ormaI Inspect ion.The Informal InspectionThe informal inspection is performed on a daily basis andconsists of checking the machine systems to insure properfunction at the control center. In addition to checkingthe math ine systems, many things can be noted by a visualand audio check of the machine. Is there any new vibrationor noise? Does there appear to be any part of the machinewhich is loose? Is there oil or grease leaking which wasnot evident before? Many times the floor sweeper andthe operator are the best informal inspectors. Each dayas they work with and around the machine they hear thesame sounds. One day however there is a new sound comingfrom the machine. Now is the time to check it out, becausesomething has changed within the machine. Its betterto have 1 day of down time now, than 1 week tommorrow.

The Formal InspectionThe formal inspection is a complete examination of ail themachine componen ts at regular intervals by competentpersonnel. A formal record keeping system should also existallowing maintenance management to keep track of the conditionof each machine in question. Formal machine inspectionsshould be performed at regular intervals i.e. quarterly, semi-annually or at least annually.The following areas and procedures should be followed whenperforming inspections. PLEASE REMEMBER SAFETY.1.0 Check all control and motor functions to determine ifthe proper control and safety features exist and functionproperly.2.0 Locate the machine at bottom or top dead center in thestroke cycle. Disconnect machlne and lock out controlsystem to prevent unauthorized start up.


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3.04.05.0

6.0

De-Energize flywheel.Exhaust counterbalance system.Begin Inspection. Note: You will need the followingequipment to perform the inspection; (11 Jack (Largeenough to lift the weight of the slide and drivetrain combined. (1) Dial indicator and magnetic basewith one inch of travel. Inside micrometersThe Following items should be checked and recorded sothat they can be compared with previous inspectionresults.6.1 Vertical Stack clearances, Main Bushing clearances,

Connection Rod clearances, Connection Headclearances, Wrist and Pin Clearances, and AdJustingScrew and Housing Clearances.6.2 Counterbalances, Check air pressure settings, Rodconditions, and Air seal leakage.6.3 Lubrication System, Condition of grease or oil,f I lters, I ines, fittings, and pumping system.6.4 Level and Alignment of Bed and Slide. Adjust asnecessary.6.5 Condition of Bolster Plate. Is it tight on the bed?is it level? Does it need to be resurfaced?6.6 Gib Clearances, Check and adjust as necessary.6.7 Flywheel Bearings, Lubricate and check for smooth-ness of rotation.6.8 Visual fractures or other damage. Are there anycracks in the frame components or slide? Locat ionand size.

SPECIAL ATTENTION AREAS.

Special attention should always be given to the followingareas of your machine .1.0 Clutch/Brake Assembly2.0 Counterbalance Assemblies3.0 Die Cushions


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.

Clutch/Brake AssemblyThe Clutch/Brake assembly is the main driving unit onyour math Ine. There are (3) major problem areas; SingleTrip Rate, Adjustment, and Air Pressure Setting. Eachof these areas will be discussed below.

Single Trip Rate: The single trip rate Is the maximumnumber of times that a clutch/brake assembly can beactuated per minute and remain able to dissipate anyheat build up. Each machine is designed to operateat a specific speed, 30 SPM, 40 SPM etc. Mostmachines are designed with a 70% to 75% single triprating. Please note the following example:You have a 300 Ton Press. This machine is designedto run at 50 SPM in the contfnuous mode of operation.This machine has a 70% single trip rating which wouldallow you to operate the machine at 35 SPM in thesingle stroke mode of operation.

Adjustment of Clutch/Brake Travel: Most clutch/brakeassemblies are deslgned to be operated with a specificamount of travel. This information will be containedin your manual or is available from the manufacturer.Excessfve travel in the clutch/brake -unit createsextra stress on the parts which can contribute topremature fa I I ure.Air Pressure Setting: Most clutch/brake assembliesare designed to operate in a range between 55 and 65PSI. The air pressure rating is critical to theproper operation and longevity of the unit. Operatlngthe unit without sufficient air pressure will allowIt to sl ip, thus causing premature failure of linings.

Counterbalance Assemblies: The counterbalance assembliesare perhaps the single most Important factor in theoverall longevity of the machine. Their primany func-tions are to take up gear backlash, reduce drive trainI oad, improve safety, reduce noise levels, and assistin the slide adjustment of the machlne.

Gear Backlash: The backlash is the amount of runningclearance in the gearing. As the gearlng begins towear, excessive clearance develops. The counterbalance assists In keeping the load evenly distributedthrough the gear train.


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Reduce Drive Train Load: By reducing the backlash andassisting in the lifting of the slide after bottomdead center, the counterbalance reduces the load onthe gear train.Improves Safety: When the slide is properly counter-ba I anced, the air pressure should be adjusted upwardan additlon 3 to 5 PSI. This allows for protectionagainst the slide falling in the event of a connectionrod fa 1 I ure. Thus optimum safety is achieved.Reduce Noise Levels: When the counterbalance isadjusted properly, excessive backlash is removed fromthe gearing. The double hit effect is also removeddue to the vertical stack clearances being taken up bythe cyl lnders. This results in a reduced noise levelof the machine.Assist in AdJustment of Slide: The counterbalance isimportant in reducing the load on the slide adjustmentmotor. Some presses will not allow you to adjust theshut height without the counterbalances being set.

3.0 Die Cushions: Die cushions are probably the most widelyabused component on a press. They are located under thebolster pl ate, in the bed of the machine. No one wantsto crawl under the machine to work on them, thus manyproblems go undetected until you experience a failure.A few of the problems die cushions experience are;eccentric loading, lubrication, wet air, and poorexternal guiding.

Eccentric Loading: Die cushions are designed fordistributed loading. An off center or eccentric loadon the cylinder causes premature wear on the sidesof the cylinder and external guiding. As the pistonwegrs into the side of the cylinder the packingsac,6 destroyed and the air seal fa9 Is.Lubrication: Due to the location of the cylindersIt Is difficult to determine If the cylinders arereceiving proper lubrication. Many times thereexists a line with a zerk in the bed of the machine.The shop oiler my very well be performIng hls duties,he is greasing the machine regularly. However if thelubrication line is broken, the grease may simply befilling up the pit under the machine. Care should betaken to insure that this condition does not exist.


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Wet Air: Just as surge tanks collect excessive waterand oil In the I ines, so die cushions also serve as acollection point. Excessive water and contaminationIn the grease can lead to the break down of the lubri-cant. Thus causing failure due to lubrication fault.Poor External Guiding: Poor external guiding as wellas eccentric loading can cause premature failure ofthe cushion unit. External guiding of the cylinderhelps to protect it against off center loading. Asthe wear plates become worn, the cylinder begins torun unevenly, causing both cylinder and packingfal lure.

InstallIng a few of the tips given above In your existingmaintenance program can save your company both money andextensive down time.

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Trouble Shooting Presses