4. Press Brake Machine and Technical Capabilities

  1. Introduction to the bending process

Sheet metal forming is one of the most common metal manufacturing processes that can be used to produce complex parts with a high degree of dimensional accuracy and increased mechanical properties, along with a good surface finish. Bending is defined as the plastic deformation of sheet metal along a straight line. Bending is a commonly used sheet metal shaping process in various sheet metal industrial products (Tekiner 2004).  A bending operation is employed to fabricate parts such as braces, brackets, supports, hinges, angles, frames, channel and other non- symmetrical sheet metal parts which are used in automobiles, aircrafts, ships and various consumer products. There are two types of bending, V-bending and U-bending. The most common one is V- bending and this is subdivided into closed die bending and air bending (Tekiner 2004).

Lehtmetalli painutamisel surutakse materjal templi abil matriitsi, et saavutada soovitud painutusnurk. Painutusnurga määrab templi matriitsi tungimise sügavus. Standardsete painutusoperatsioonide puhul kasutatakse üldjuhul V-kujulise soonega matriitse. Nende ebatäpsus (mittekvaliteetsus) võib teha hea tulemuse saamise väga aeganõudvaks (kaasneb suur praagi hulk) või koguni võimatuks, mis tähendab parandamatu praagi tekke ja täiendavaid kulutusi ettevõttele

Painutamise teoreetiliste aluste tundmine on väga oluline, et arvestada nii tehnoloogilisi võimalusi kui ka piiranguid juba toote kavandamisel. Spetsiaalsete rakenduste jaoks on kasutusel  raadius-matriitsid,  U-matriitsid, serva voltimismatriitsid (hemming) jne. Esmapilgul  võib painutamine tunduda lihtsa protsessina, kuid tegelikult mõjutavad mitmed faktorid täpse tulemuse saavutamist. Rolli mängivad tööriistade mõõtmete valik, kasutatava painutuspingi tüüp,  painutamise liik, materjali tüüp ja kvaliteet. Kõik need avaldavad toote kvaliteedile koosmõju ja mingi teguri ebakvaliteetsus põhjustab reeglina kohe ka toote mittekvaliteetsuse. Näiteks on väga tähtis ka painutatava materjali omaduste konstantsus (sh ka materjali paksuse  püsivus kogu lehepaki ulatuses, jms

Painutuspingi ehituse ja kasutatavate tööriistade ning tehnoloogiate tundmine vähendab toodete tootmisse juurutamise aega ning võimaldab kasutada tootmises olemasolevaid tehnilisi vahendeid efektiivselt. Kuna operaatorid koostavad painutuspingil tihti programme ise (eelkõige väikeste seeriate puhul või väiksemate töömahtude juures)  või vähemalt viivad läbi korrektsioone lähtuvalt esimese detaili mõõtetulemustest, siis on heade baasteadmiste omandamine hädavajalik.

Painutustehnoloogia kavandamine ja teostus on komplekstegevus, kus igal etapil on oluline roll kogu tegevuse õnnestumiseks. Tulemuskriteeriumiteks on:

  • toote (pooltoote) omahind;
  • painutustsükli kestvus (suurte organisatsiooniliste ajakulude juures mõelda LEAN meetodite rakendamisele);
  • seadme häälestuseks kuluv aeg (suurete seadistusaegade puhul mõelda SMED´i   meetmete rakendamisele;
  • kvaliteedi tagamine (kvaliteedi probleemide puhul kindlasti tuleb koheselt välja selgitada tekkepõhjused)
  • tööohutusnõuete kindlustamine, mis väldib igasuguste tööõnnetuste tekkimise võimalused täielikult.
  1. Press-brake machine nature and classification

A press brake is a machine pressing tool for bending sheet and plate material, most commonly sheet metal.[1] It forms predetermined bends by clamping the workpiece between a matching punch and die.[2]. Typically, two C-frames form the sides of the press brake, connected to a table at the bottom and on a movable beam at the top. The bottom tool is mounted on the table, with the top tool mounted on the upper beam.[3].

A brake can be described by basic parameters, such as the force or tonnage and the working length.[1] Additional parameters include the stroke length, the distance between the frame uprights or side housings, distance to the back gauge, and work height. The upper beam usually operates at a speed ranging from 1 to 15 mm/s.[3] There are several types of brakes as described by the means of applying force: mechanical, pneumatic, hydraulic, and servo-electric.

In a mechanical press, energy is added to a flywheel with an electric motor. A clutch engages the flywheel to power a crank mechanism that moves the ram vertically. Accuracy and speed are two advantages of the mechanical press.[4]

Hydraulic presses operate by means of two synchronized hydraulic cylinders on the C-frames moving the upper beam.[3][4] Servo-electric brakes use a servo-motor to drive a ball-screw or belt drive to exert tonnage on the ram.

2.1 Classification principles

A press-brake machine is a machine tool for bending sheet and plate material, most commonly sheet material. It forms predetermined bends by clamping the workpiece between a matching punch and die.

According to a source of bending force the brake is divided into:

  • Mechanical press-brake
  • Pneumatic press-brake
  • Hydraulic press-brake
  • Servo-electric press-brake.

For the mechanical press brake, the vertical movement of the ram is driven by a crank mechanism, which is powered by the flywheel.

The pneumatic press-brake machines makes use of air pressure to move the ram.

Hydraulic press-brake utilizes the two  synchronized hydraulic cylinders to move the ram.

Servo-electric brakes use servo motor to drive a ball screw or belt drive to exert force on the ram to make it move vertically.

Today the hydraulic type of press-brake machines becomes most popular all over the world.

From another point of view, the press-brake can be divided into:

  • Manual press brake
  • Hydraulic press brake
  • CNC press brake

Figure 1. Manual press brake machine
 
 

Figure 2. CNC press brake machine

Manual press-brakes are required to adjust the bending dimensions and angles manually when used. It contains work-table, supporters and the clamping plate. The worktable is mounted on the supporters which consists of a base and a pressure plate.

Hydraulic press-brake, classified by synchronization, can be divided into:

  • Torsion synchronization press brake
  • Hybrid press brake
  • Electric-hydraulic synchronization press brake.

By movement they are classified:

  • Up-moving press brake
  • Down moving press brake

CNC press brake machines are going more and more popular. Their cost is also constantly decreasing compared to conventional equipment. They need less competent staff to deal with them.

CNC press brake consists of:

  • Machine frame
  • Ram (slider)
  • Workbench
  • Oil cylinder
  • Hydraulic proportional servo system
  • Position detection system
  • CNC controller
  • Electrical control system 

CNC press brake realizes bending function by controlling slider stroke and back gauge.

The main advantages of CNC press brake are:

  • It is featured with high precision synchronization, high bending accuracy, high repeat positioning accuracy.
  • Equipped with a hydraulic automatic clamp or fast clamp for the upper die and socket lower die based on customer`s requirement to reduce the labour intensity and improve production efficiency.
  • The back gauge of CNC press-brake can be extended to six axes.
  • The separated upper die which is in different lengths can be assembled into a certain width according to the requirements of the workpiece in order to meet the special needs of the fabrication.  

For more detailed understanding of press brake machines and bending technology,

see https://www.machinemfg.com/press-brake-ultimate-guide/

2.2.  Painutuspresside tehnoloogilised võimalused

Painutustehnoloogia kasutamise aluseks on painutuspinkide olemuse ja nende tehnoloogiliste võimaluste tundmine. Tööpingi tehnoloogilistest võimalustest sõltub suuresti antud tööpingi kasutamise võimalus toodete valmistamiseks. Kõige olulisemateks parameetriteks on tööpingi painutusjõud, üla- ja alatala vahekaugus avatud asendis ning töökäigu ulatus. Tootlikkusele mõjub töökiirus ning ülesliikumise kiirus. Toote valmistamise seisukohast on veel olulised maksimaalne lehe laius, mis mahub pinki ning juhitavate koordinaatide arv ja nende olemus. Painutuspresside ehitust ja juhitavaid koordinaate käsitletakse põhjalikumalt edasistes peatükkides.

Painutuspresside tootjaid on palju. Valiku puhul olulisteks kriteeriumiteks on tehnoloogiline võimekus, töökindlus, kasutamismugavus, hooldustingimused ja muidugi hind.  Euroopas pikaajalised ja tuntud tootjad on AMADA (www.aider.ee ), TRUMPF (www.trumpf.com ) ja PrimaPower (www.primapower.com ). Lisaks nimetatud tuntud ja tunnustatud tootjatele, on tekkinud hulgaliselt vastavaid seadmeid valmistavaid ettevõtteid Hispaanias, Türgis, Indias, Hiinas, ja mujal. Tööpinkide tutvustuseks on piisavalt palju materjale tootjate kodulehekülgedel ja võib leida Internetist ka toodete katalooge ja toodete detailsemaid kirjeldusi. 

Toote – painutuspressi valikul on kahtlemata esmalt kolm olulist kriteeriumi, mis ettevõtet huvitab:

  1. Seadme tehnoloogilised võimalused (pisut käsitletaks edaspidiselt)
  2. Seadme maksumus
  3. Tarnija tuntus, varasemad kogemused ja riigisisesed tugiteenused.

Otsustuse juures on esmatähtis, seadme kasutusotstarve ettevõttes. Millised on tootmismahud, kui suur on toodete varieeruvus ja kui keerulised ning täpsed valmistatavad tooted on. Lihtne põhimõte: lihtsad tooted, varieeruvad tootmismahud ja teatav ebarütmilisus – siis ka seade võiks olla vähempretensioonikas ja odavam. Ning vastupidi, kui on toodetel oluline nende teenistuslik otstarve ja kasutusvaldkonnad on näiteks autotööstus, lennukitööstus, meditsiinitööstus- peab väga kontsentreeritult planeerima ostetava seadme funktsionaalsust ja tarnijat.

Joonis 3. Kaasaegne painutuspress CNC juhtimisega

Jrk.nrTehniline parameeterVäärtus
1Painutusjõud1000 kN
2Üla- ja alatala vahekaugus avatud asendis470 mm
3Töökäik200 mm
4Lähenemiskiirus100 mm/sek
5Maks. Töökiirus10 mm/sek
6Maks. ülesliikumise kiirus100 mm/sel
7Telgede arv4
8*-detaili saab positsioneerida 590mm ülatuses590mm ülatuses
Tabel 1. Seadme tehnoloogilised võimalused

Oluline on kahtlemata ka lehe Laius, mis mahub painutuspressi kolonnide vahele ja sealt tulenevad ka valmistatava toote maksimaalsed gabariidid.

Suuremate tootmismahtude puhul on otstarbekas painutuse töökohta automatiseerida. Tervikliku automatiseerimise lahenduse pakub painutuspressi integreerimine robotiga üheks terviklikuks mooduliks. Näitena on joonisel 4 kujutatud integreeritud tootmismoodul koos painutusroboti Amada HG-Rm. Suuremate tootmismahtude puhul on kindlaks trendiks tootmismoodulite kasutamine (vt näiteks joonis 4), milliseid kasutatakse eraldiseisvate moodulitena või vahetult tootmisliiniga ühendatuna. Laia nomenklatuursusega ja väikeste partiidega tootmise puhul on enamlevinud variandiks eraldiseisvate tootmismoodulite kasutamine. Suurema tootlikkuse tagamiseks on sellised moodulid integreeritud materjalide laoga ja vahel ka valmistoodete automatiseeritud pakendamise ning lattu kohaletoimetamise lahendustega. Robotiga integreeritud painutusmoodul on kujutatud joonisel 4.

Joonis 4. Automatiseeritud painutusmoodul

Tootmismoodul HG-Rm on konstrueeritud keskmiste ja suurte detailide automaatseks painutamiseks, mille puhul painutusprotsess on ajamahukas ja nõuab operaatorilt märgatavat jõupingutust, seda eriti raskete detailide puhul, mille käsitlemisel kasutatakse kahte operaatorit. HG-1303 mudelil põhinevas lahenduses on kasutatud hübriidtehnoloogiat ja äärmiselt robustset konstruktsiooni, et vastata tootmise kõrgendatud nõudmistele. Painutuspress on ühendatud 7- teljelise robotiga ja mitmete nutikate seadmetega, mis hõlbustavad keerukate toodete ja suurte paneelide painutamist.

Tabel 2 Mooduli tehnilised parameetrid

Painutusjõud1300 kN
Töölaua pikkus3110 mm
Üla- ja alatala vahekaugus avatud asendis520 mm
Töökäik250 mm
Lähenemiskiirus220 mm/sek
Maks. töökiirus25 mm/sek
Maks. ülesliikumise kiirus250 mm/sek
JuhtsüsteemAmada 3i
LisaseadeBI-S painutusindikaator
Roboti telgede arv6 + 1 telg relsil
Roboti relsi pikkus8 m / 4.8 m
Roboti tõstevõime80 kg ( koos haaratsiga)
Detaili suurus100 x 500 kuni 1250 x 2500 mm ( pakus 0.5 – 6 mm )
Haaratsite tüübidIminappadega / Mehaaniline / Kombineeritud
Detailide laadimine1 laadimisala
Detailide mahalaadimine2 positsiooni ( alus )

References

 [1] Fournier, Ron; Fournier, Sue (1989), Sheet metal handbook, HPBooks, p. 37, ISBN 978-0-89586-757-5

 [2] Parker, Dana T. Building Victory: Aircraft Manufacturing in the Los Angeles Area in World War II, p. 29, 83, Cypress, CA, 2013. ISBN 978-0-9897906- 0-4.

 [3] “Press Brake Bending: Methods and Challenges”. Metalforming. Precision Metalforming Association. August 2008.

 [4] Tool and Manufacturing Engineers Handbook (TMEH), Volume 2, Forming. Society of Manufacturing Engineers, 1984.

Eestikeelsed materjalid painutustehnoloogia kohta on toodud kutseõppeasutustele mõeldud õpikus:

[5] Rein Pikner, Aleksei Saareväli. LEHTMETALLI TÖÖTLEMISTEHNOLOOGIAD

Õppematerjal kutsekoolidele.

3. Press-brake machine construction principles and technological capabilities

Press brakes are usually in the capacity range of 20 to 200 tons with bed lengths ranging from 4 to 14 feet (1.2 m to 4.3 m). They may be powered by mechanical, hydraulic or mechanical-hydraulic means. They may be “up- acting” or “down-acting,” depending on the direction of the ram’s power stroke. Figure 1 shows a down-acting CNC hydraulic press brake.

Press brakes may be equipped with one of several types of back gauges, including manually placed and adjusted gauges, pins which engage holes in the workpiece and computer numerically controlled programmable units which adjust settings after each stroke.

The axes’ orientation is best observed from the front of the press brake as shown below. The X-axis positions the gauge bar for the desired flange lengths. The R-axis controls the height of the gauge bar so the gauging surface can be positioned as needed. The Y-axis controls the stopping point of the press brake’s ram for the desired bend to occur. For hydraulic downacting press brakes, the Y-axis can also control the ram’s opening height and speed change point.

Machine details
 
Bending force – declared bending force for the press brake as the max. obtained force for the bend. Bending force is calculated according to the thickness of the part, material and bend requirements.
Bending length – declared bending length as the length of the table and the max. possible length for the tooling installation. Bending length usually shows the possibility of length to be bend with the press brake. Bending length could be standard (usually declared) or inside the columns (which the same as the distance between the columns) for the parts which require the deep positioning inside the throat.
Moveable beam,  traverse – normally top beam of the machine which is moved together with the punch towards to the die to perform the bend. Beam has the controlled move with the hydraulic or electric systems.
Stroke of the press brake – declared stroke of the beam to move from the top position. Stroke of the bend together with the details and sizes of the punch and the die are necessary for the study of the bend possibilities.
Opening of the press brake, daylight – the max. possible distance from the top position of the beam and the bottom table without the installed tooling.
Back gauge of the press brake – back gauge is the main system at the rear part of the press-brake which is used as the stopper or fixation of the position of the part during the bending. Back gauge is the complex unit with the separate movements from manual to the servo-drived up to 6 moveable axis with CNC control for complex parts and programs.
Crowning, deflection – press brake because the construction has the internal structure deflections during the bend which are calculated and the subject for the elimination for the precision of the bend. Depends of the construction of the press brake the compensation of such deflections could be construction integrated, handwheel manual, hydraulic with CNC control etc.
Clamping, fixation of the tool – units and systems to clamp punches and dies with the beam and the table of the press brake. There are various systems of the tool clamping and fixation depends of the model and manufacturer, machine possibilities etc. Clamping is connected with the punch holder and die holder units as the middle part of the connection. In general clamping is the manual but could be replaced with pneumatic or hydraulic units.

Painutuspressi ehitus

Painutuspress koosneb jäigast raamist, mis kannab kõiki seadme komponente. Raami suur jäikus on oluline, et konstruktsioonis ei tekiks deformatsioone, mis võivad painutus­täpsust mõjutada. Eespoolt vaadates on näha seadme ülatala ja alatala. Üks taladest on vertikaal­suuna liikuv, et avaldada matriitsi ja templi vahele paigutatud detailile vajalikku painutusjõudu. Kui liikuv on alatala, siis on tegemist nn alatoimelise painutuspressiga ja liikuva ülatala puhul ülatoimelise painutuspressiga. Enamik kaasaegseid painutuspinke on ülatoimelised ehk painu­tus­operatsiooni ajal liigub ülatala alla. 

Raam  koosneb paksust materjalist valmistatud ülatalast (5), alatalast (6), külgplaatidest (1 ja 1’), ülemisest ühendustalast (3) ja tugiplaatidest (2), millele painutuspink toetub. Külgplaatidesse on tehtud C-kujulised väljalõiked, mis võimaldavad suurendada painutatavate detailide pikkust (külgplaatide vahekaugus on reeglina üla- ja alatala pikkusest väiksem).
Kuna ülatala on kinnitatud ainult otstest, siis painutamise ajal painduvad üla- ja alatala vastassuunas. Selle tulemusena tungib tempel töötsooni keskosas vähem matriitsi ja seal ei suudeta saavutada nõutud painutusnurka.

Ala- ja ülatala läbipaine

Antud probleemi kõrvaldamiseks paigaldatakse alatala keskosasse hüdrosilindrid, mis annavad vastusurve. Vajalik vastusurve (vt. Joonis) CNC painutuspinkidel arvutakse automaatselt. Teine lahendus antud probleemi kõrvaldamiseks on toestada alatala keskosast (alumine Joonis, punktid A ja A’) ja jätta alatala otsad kinnitamata (nn elastne alatala). Sellisel juhul järgib alatala ülatala kuju. Toode jääb sirge, kuna paindumine on nii väike, et materjali elastsuspiirist üle ei minda – peale jõu eemaldamist taastab toode oma sirgsuse.

4. Control axes of the press-brake machine 

The basics: X-R axes

A press brake is equipped with a back gauge, a motorized structure to which backstops (also called “fingers”) are attached. By resting the metal sheet to the fingers, we determine the bending line. Movement of the back gauge along the machine depth (i.e. perpendicular to the ram) is called X axis. Vertical movement is called R axis, and is useful when we have profiles with multiple bends.

GASPARINI

Working with bending stations or different lengths: Z1-Z2 axes

Working with bending stations or different lengths: Z1-Z2 axesBack gauge fingers are at least 2 in order to keep the piece in position. Their repositioning is usually manual, but can be motorized to facilitate working with bending statons or with pieces of different lengths. Movement is along the Z axis (parallel to the bending line), hence each of the backstops is named Z1, Z2, etc.

Conical bends or edges with different depths: X5-X6 axes
With Z1-Z2 axes we can only bend parallel to the backstop fingers. In order to make conical bends we need to bring one of the fingers closer or farther to the bending line, that is along the X axis. We can either use a manual movement, or a CNC-controlled motorized positioning. Axes are called X5 and X6. With just one motorized backstop we can make tapered bends up to 75°; with both axes we reach 80°. X5-X6 axes are useful also if you have sheet edges at different depths.

Conical bends or edges with different depths: X5-X6 axes

With Z1-Z2 axes we can only bend parallel to the backstop fingers. In order to make conical bends we need to bring one of the fingers closer or farther to the bending line, that is along the X axis. We can either use a manual movement, or a CNC-controlled motorized positioning. Axes are called X5 and X6. With just one motorized backstop we can make tapered bends up to 75°; with both axes we reach 80°. X5-X6 axes are useful also if you have sheet edges at different depths.

Conical bends or edges with different depths: X5-X6 axes
With Z1-Z2 axes we can only bend parallel to the backstop fingers. In order to make conical bends we need to bring one of the fingers closer or farther to the bending line, that is along the X axis. We can either use a manual movement, or a CNC-controlled motorized positioning. Axes are called X5 and X6. With just one motorized backstop we can make tapered bends up to 75°; with both axes we reach 80°. X5-X6 axes are useful also if you have sheet edges at different depths.

AXIS explanation

1 AXIS BACK GAUGE (based on MAZAKPOWER)

When we come to 1 axis back gauge, actually we mean 3+1 axis,1 axis back gauge is X axis. MAZAKPOWER press brake are provided are equipped with BGA-1 CNC back gauge constituted by a solid structure in order to assure the best repetitiveness and high precision in axes. For positioning X -axis the press is equipped with HIWIN linear guide and ball screw. In additional, there is equipped Z-axis with manual linear guide. Fingers can be moved manually and fixed in desired place. Z1, Z2 axis are adjusted manually and can be fixed in place. The single axis  X-axis back gauge drives by the DELTA servo motor which controls the finger depth (flange depth).

2 AXIS BACK GAUGE

Also 2 axis back gauge (BGA-2) the X, R-axis are used. MAZAKPOWER fast and precise 2-axis CNC controlled back gauge that automatically adjusts the X (depth) and R (height) axes to ensure the material is always positioned accurately, resulting in higher quality finished parts. Axis movements are driven by AC motors and drivers. Using the best components, such as HIWIN (TAIWAN) ball screws, the back gauge movements are fast and precise, with X-axis speeds up to 500 mm/sec and stroke to 750 mm. high accuracy up to 0.01 mm.

4 AXIS BACK GAUGE4 Axis CNC back gauge (X-R-Z1-Z2), means 6+1 axis CNC press brake usually equipped with DELEM DA58T 2D graphical controller with PC-Profile-T2D software. Y1, Y2 precision ram positioning, X, R precision servo-driven back gauge drives by servo motor.

6 AXIS BACK GAUGE

6 Axis CNC back gauge (X1-X2-R1-R2-Z1-Z2), means 8+1 axis CNC press brake usually equipped with DA66T Touch 3D graphical control, auto crowning deflection compensation, the 6-axis back gauge offers you the highest degree of flexibility with highest production speeds. All 6 axis can be positioned independently of each other. Fingers can be independently located three dimension (X,R,Z) in the space. Control unit calculate finger positions on each axis. Stable finger position for asymmetrical work pieces, no setup times for back gauge adjustment.