Precise Control Of The Large 600-Ton Flexion Machine

• 1
  What A Large 600-Ton Flexion Machine Pushes At The Ram
• 2
  Ram Guidance And Deflection On A Large 600-Ton Flexion Machine
• 3
  How The Control Loop Holds Depth On A Large 600-Ton Flexion Machine
• 4
  Tooling, Springback And Material Limits
• 5
  Where Bending Ends And CNC Machining Begins
• 6
  When A Large 600-Ton Flexion Machine Fits

Tonnage ratings on a press brake are usually quoted at the bottom of the stroke, not at the top. A large 600-ton flexion machine can push roughly 600 metric tons near bottom dead center, and that number falls as the ram rises because the hydraulic advantage changes. Size a job from the nameplate alone and you will overestimate what the machine can do at mid-stroke.

The practical figure is tonnage per meter of bend length. Spread 600 tons across 4,000 mm of plate and you get about 150 tons per meter. Bend a short 500 mm part and the same ram delivers far more force per unit length than the tooling or the plate can survive. On a large 600-ton flexion machine, the limit is rarely total tonnage. It is tonnage per meter and the die opening underneath it.

Air bending force scales with the square of thickness and inversely with die opening width. Going from 10 mm to 20 mm plate does not double the force, it roughly quadruples it. That is why a large 600-ton flexion machine handles 20 mm plate over a few meters but not over eight. The same arithmetic tells you when a smaller machine is the better call.

Bottoming and coining change the picture. Coining needs three to five times the air-bend force for the same thickness, so a job that looks comfortable in air bending can sit outside the machine envelope once the drawing calls for a sharp internal radius. Check the bend method before you check the tonnage.

• 1
  Rate at bottom dead centerNameplate tonnage is a near-bottom figure, not a full-stroke figure.
• 2
  Think in tons per meterDivide total tonnage by bend length before comparing machines.
• 3
  Coining costs 3–5×A sharp internal radius raises required force sharply.

Two things bend when you form thick plate: the plate and the machine. The ram and bed deflect under load, and the upper beam tries to rotate against its guides. On a large 600-ton flexion machine the deflection across a 4,000 mm bed can reach several tenths of a millimeter at full tonnage. That is enough to open the bend angle at the middle of the part while the ends stay closed.

Crowning systems compensate by lifting the bed or the ram in the center. A hydraulic crowning table with several independently controlled cylinders lets the operator match the compensation curve to the actual load. Mechanical wedges do the same job with less adjustability. Either way, the compensation is a number you set per job, not a fixed machine property.

Ram guidance decides how much of the load becomes tilt instead of bend. Roller guides with preload hold the upper beam square to the bed and reduce side-to-side wander. Worn guides show up as inconsistent bend angles along the length of the part, not as a single bad angle at one end. If one end of a long part is always off, look at leveling first. If the middle is off, look at crowning.

Frame stiffness matters for repeatability more than for the first part. A heavily ribbed frame returns to the same position after unloading. A lighter frame creeps, and the operator chases the angle all shift. For thick plate work, this is the difference between holding ±0.5° and holding ±1.5° across a batch.

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  Middle open, ends closedClassic sign of missing or wrong crowning compensation.
• 2
  One end always offCheck ram leveling and guide preload before touching the program.
• 3
  Stiff frame, stable angleFrame stiffness shows up in batch repeatability, not the first part.

Depth control on a modern press brake is a closed loop. A linear encoder or glass scale reads the actual ram position, and the controller compares it to the target depth tens or hundreds of times per second. The valve opens or closes to close the error. On a large 600-ton flexion machine, the moving mass is heavy, so the loop has to be tuned for a slower, more damped response than on a 50-ton machine.

Hydraulic valves set the ceiling on how fast the loop can react. Proportional valves give smooth motion but respond slowly. Servo valves are faster but sensitive to oil cleanliness. A contaminated servo valve does not fail cleanly; it drifts, and the drift shows up as gradual angle change through a shift. Oil filtration and temperature control are part of precision, not maintenance overhead.

Positioning accuracy and repeatability are different claims. A machine may position the ram to ±0.01 mm once, yet repeat only to ±0.05 mm across a thousand strokes, because of oil temperature rise and valve hysteresis. For production, repeatability is the number that keeps your scrap rate down. Ask for the repeatability figure over a warm machine, not a cold one.

Mechanical stops and depth-based control are not the same thing. A hard stop sets a fixed bottom position, so the angle depends on material thickness and springback. Depth control with a measured target lets the controller compensate when the plate runs a little thick. For mixed batches, that flexibility is worth more than a slightly tighter single-position number.

• 1
  Position vs repeatabilityOne accurate stroke is not the same as a thousand identical ones.
• 2
  Oil temperature drifts the loopWarm-up and temperature control change the angle you get.
• 3
  Hard stop vs depth controlStops fix position; depth control adapts to thickness variation.

Springback is the reason a bend never comes out at the angle you command. Steel with a yield strength of 350 MPa springs back more than mild steel at 250 MPa, and high-strength plate above 700 MPa springs back enough to need overbending or a bottoming operation. The controller can apply a springback correction, but the correction is only as good as the material data behind it.

Punch tip radius and die opening set the inside radius of the bend. A rule of thumb for air bending puts the inside radius at roughly one-sixth of the die opening. Force the punch tip into a smaller radius than the material wants and you get cracking on the outside of the bend, especially on thick 7075 aluminium or high-carbon steel. Match tooling to material before you match it to tonnage.

Die opening width also sets the minimum flange you can form. A short flange will not sit properly on the die shoulders and tends to slip into the opening. As a working guide, the minimum flange is around 70 percent of the die opening for air bending, and it grows for thicker plate. Long, narrow flanges on thick stock are a common reason a part does not fit the machine even when tonnage is fine.

Tool wear changes the bend over time. Punch tips round off, die shoulders polish, and the effective radius creeps. On thick plate the wear is slower but the consequences are larger, because every worn tool stroke is a heavier load. Track bend angle on a schedule rather than waiting for a rejected batch.

• 1
  Springback grows with yieldHigh-strength plate needs overbend or bottoming.
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  Inside radius ≈ 1/6 die openingAir-bend rule of thumb; smaller radii risk cracking.
• 3
  Minimum flange ≈ 70% of die openingShort flanges slip into the die and form badly.

A 600-ton press brake produces a formed shape, not a finished geometry. Holes, slots, counterbores, threads and sealing faces come from machining. The order of operations matters: bend first, then machine, because forming moves the material and relieves residual stress. Machine first and your carefully placed hole moves when the plate is bent.

On thick plate, the bend also changes the local material condition. The outer fiber stretches, the inner fiber compresses, and the neutral axis shifts inward. Hardness near the bend rises on strain-hardened alloys. If a hole sits within a few thicknesses of a bend line, drill it after forming and check the wall thickness on the outside of the radius, where thinning is worst.

At GreatLight we machine formed parts on 127 high-precision CNC machines, including 16 simultaneous 5-axis machining centers and a Ø400 mm rotary table. Maximum processing size is 4,000 mm, which covers most large bent brackets, chassis rails and structural plates after forming. Tolerance is held to ±0.005 mm and surface finish to Ra 0.8–1.6 μm on machined faces.

The reason to machine after bending is datum integrity. A bent part has no flat reference until the bend is made, so any fixture built on the flat stock is unreliable. Once the bend exists, we pick up the formed surfaces and machine from there. That sequence keeps hole-to-bend relationships inside tolerance instead of fighting them.

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  Bend, then machineForming relieves stress and moves hole positions.
• 2
  Check thinning near radiiOuter fiber thins; wall thickness drops at the bend.
• 3
  Datums come from the formed partFixture the bent shape, not the flat stock.