How to Improve Your Bending Accuracy?

In the actual use of the bending machine, bending accuracy will be more or less error, sometimes it may be the mechanical factors of the machine bending accuracy is not high enough, may also be some external factors, such as bending tooling, bending plate material thickness, etc, and even some human operation factors. This article will analyse the factors affecting bending accuracy from a variety of aspects and propose solutions for some of the common situations.

● Common Factors

Mechanical Factors

1 bending machine slider clamping mouth straightness (Y direction and X direction).

2. The repositioning accuracy of the left and right sliders, and arbitrary positioning accuracy.

3. Bending machine slider and rack rail clearance are reasonable.

4. The verticality and internal tilt of the frame is reasonable.

5. The connection between the oil cylinder and the slider.

6. The strength and accuracy of the frame and slider.

7. The repositioning accuracy of the rear blocking system, the accuracy of arbitrary positioning (X direction and R direction).

8. Whether the computer system is adjusted in place.

9. Whether the hydraulic system is adjusted in place.

10. Matching of hydraulic system and computer adjustment.

Mold Factors

1. Whether the precision of the upper and lower molds is accurate.

2. mold deformation, damage, wear and other phenomena will have an impact on all aspects of bending and forming, once found to be promptly reported to amended.

3. The upper and lower molds on the knife different core will lead to bending size deviation, the knife should ensure that in place.

4. After the backstop, material left and right position movement, the relative distance to the lower die changes. Vernier calipers can be measured by the rear stopper screw fine adjustment.

5. Whether the lower die compensation device is accurate and whether the design of the frame matches.

6. The accuracy of the upper die jig should be high.

7. The size of the lower die V mouth and bending pressure is inversely proportional to length and thickness of the plate, the larger the V slot the smaller the pressure required, so the correct size of the lower die V slot should be used in accordance with the regulations when processing workpieces of different thicknesses.

8. At one end of the bending machine, i.e. when processing with a single side load, bending pressure is affected and is also a detriment to the machine tool and is expressly forbidden. The middle part of the machine should always be kept under pressure when matching the tooling.

Sheet Material Factors

1. Straightness of the datum of sheet metal.

2. The uniformity of stress on sheet metal.

3. The uniformity of the sheet metal thickness.

4. Insufficient parallelism between the workpiece and the lower die during bending, and rebound of the workpiece after the upper die is pressed down, affecting the bending dimensions.

5. Material characteristics and thickness will affect the bending angle, so each workpiece bending must be the first inspection and strengthen the sampling inspection.

Human Factors

1. People in the bending push iron plate left and right thrust are consistent.

2. The use of the system is not adjusted to the data errors within the system.

3. A bending angle is not enough when the secondary bending size will be affected.

4. The cumulative error of bending will lead to an increase in the size error of the workpiece profile. Therefore, it is particularly important to ensure the accuracy of single-sided bending.

5. The length and thickness of the workpiece requires different pressure, and the length and thickness of the plate are proportional to pressure. So the length and thickness of the workpiece has changed when bending pressure must be readjusted.

● Mold Maintenance Essentials

The above issues can be seen, the accuracy of the mold and the use of bending precision has a crucial impact on the use of bending machine for the possible problems of the upper and lower mold, we summarized the following mold maintenance essentials to share with you.

● Basic Maintenance of The Mold 

Continuous mold maintenance, must be careful, patient, step by step, do not blindly engaged. When repairing molds due to faults, a care tape should be attached to the mold to facilitate the awareness of the problem. Open the mold, check the condition of the mold against the care tape, confirm the cause of the fault, identify the problem and then clean the mold before dismolding.

For mold structures where the unloading spring is between the fixed plate and the unloading plate and where the unloading spring is directly on top of the inner guide pillar, the unloading plate should be removed in such a way that the plate is balanced and pops out. 

 

● Maintenance of The Upper And Lower Molds 

When dismantling the upper and lower molds, the original condition of the molds should be noted, so that they can be easily recovered during subsequent mold assembly. When replacing the upper die, try to insert the unloading block and see if the lower die is smooth and if the gap between the insert and the lower die is even. If the upper die is shortened after resharpening and a shim needs to be added to achieve the required length, check that the effective length of the upper die is sufficient. To replace a broken upper die, identify the cause and check whether the corresponding lower die has a chipped edge and whether the edge needs to be ground. To assemble the upper die, check that there is sufficient clearance between the upper die and the fixing block or plate, and if there is a press block, check that there is a margin of movement. The lower die should be placed horizontally and then the flat iron block should be placed on the face of the lower die and knocked into place with a brass rod, not at an angle. After assembly, check that the lower mold surface is level with the mold surface. After the assembly of the upper and lower molds as well as the cores, the necessary checks should be made on the care belt to see if the parts are wrongly fitted or reversed, whether the lower mold and the lower mold gasket are reversed, whether the drop hole is blocked, whether the new parts need to be stolen, whether there is enough material to steal and whether the parts of the mold that need to be locked are locked tight. Pay attention to the locking confirmation of the stripper plate screws. When locking, the screws should be cross-locked from inside to outside with balanced force, not locking a certain screw first and then another screw, so as not to cause the stripper plate to be tilted, resulting in the upper mold breaking or the mold precision being reduced. 

 

● Adjustment of Mold Clearance 

The die core positioning holes are worn due to frequent combination of die cores, resulting in large clearance after assembly (loosening after assembly) or uneven clearance (positioning deviation), which will cause poor shape of the section after punching, easy breakage of the upper die and burr, etc. Proper clearance adjustment can be made by checking the condition of the section after punching. When the gap is small, the cross section is small, when the gap is large, the cross section is large and the burr is large, so the gap should be shifted to obtain a reasonable gap, and after the adjustment, proper records should be made, and marks can also be made on the lower die edge, etc. For subsequent maintenance work. The original mold tape should be collected and kept in good condition for daily production, so that it can be used as a reference for mold overhaul if subsequent production is not smooth or if mold variations occur. In addition, auxiliary systems such as ejector pins for wear and tear, guide pins and bushings for wear and tear should be checked and maintained.

 

● The Causes of Common Failures in The Mold And Countermeasures 

In actual production of bending machines, bending accuracy for the problem must be specific analysis, to take effective countermeasures to fundamentally solve the problems that occur, so as to reduce production costs and achieve smooth production. The following common bending accuracy phenomenon in the production of its causes and treatment countermeasures are analyzed below for your reference and use. 

Punching Edge

Causes:

1.knife mouth wear.

2.Gap is too large after training knife mouth effect is not obvious.

3.Knife mouth chipping angle.

4.Gap unreasonable up and down offset or loose.

5.Mold up and down misalignment. 

Countermeasures: 

1.Training of the cutter.

2.Control of the machining accuracy of the upper and lower die or modification of the design gap.

3.Training of the cutter.

4.Adjustment of the punching gap to confirm problems such as wear of the cavity holes of the template or machining accuracy of the molded parts.

5.Replacement of the guiding parts or reassembly of the die. 

Jumping Chip Crushing 

Causes: 

1.Large clearance.

2.Improper feeding.

3.Stamping oil dripping too fast, oil sticking.

4.Die not demagnetised.

5.Upper die worn, chips pressed onto the upper die.

6.Upper die too short, insufficient length inserted into the lower die.

7.Hard material, simple punching shape.

8.Emergency measures. 

Countermeasures: 

1.Control the processing accuracy of the upper and lower dies or modify the design clearance.

2.Trim the material belt and clean the die in time when sending it to the appropriate position.

3.Control the amount of oil dripping from stamping oil or change the oil type to reduce the viscosity.

4.Must demagnetize after training (even more attention must be paid to punching iron materials).

5.Train the upper die cutter.

6.Adjust the length of the upper die edge into the lower die.

7.Change the material and modify the design. Eject or bevel the upper die edge (note the direction). Reduce the surface area of the upper die edge and the chip.

8.Reduce the sharpness of the lower die edge, reduce the training volume of the lower die edge, increase the roughness of the lower die straight edge surface (covered), and use a hoover to absorb the scrap. Reduce punching speed to slow down chip jumping. 

Chip Blockage 

Causes: 

1.Small leak hole.

2.Large leak hole, chips tumbling.

3.Wear of the cutter, large burrs.

4.Stamping oil dripping too fast, oil sticky.

5.Rough surface of the lower die straight edge, powder chips sintering attached to the edge.

6.Soft material.

7.Emergency measures. 

Countermeasures: 

1.Modify the leakage hole.

2.Modify the leakage hole.

3.Sharpen the cutting edge.

4.Control the amount of oil dripping and change the oil type.

5.Surface treatment, polishing, pay attention to reducing the surface roughness when processing; change the material.

6.Modify the punching clearance.

7.Repair the slope or arc on the end face of the upper die edge (pay attention to the direction), use a hoover and add blowing air at the pad drop hole.

Variation in The Size of The Off-set of The Lower Material 

Causes: 

1.Wear of upper and lower die cutters, resulting in burrs (large shape, small bore).

2.Improper design size and clearance, poor machining accuracy.

3.Offsetting of upper die and lower die insert, etc., with uneven clearance.

4.Wear of guide pins, insufficient pin diameter.

5.Wear of guide parts; f. Feeder feed distance. Pressing material. Improper adjustment of relaxation.

6.Improper adjustment of the die closing height.

7.Wear of the press position of the unloading insert, no press (strong pressure) function (small punching holes caused by material traction).

8.Strong pressure of the unloading insert is too deep, large punching holes; j. Variation of the mechanical properties of the stamping material (unstable strength and elongation).

9.Dimensional variation caused by the traction of the punching force on the material when punching and cutting. 

Countermeasures: 

1.Train the cutter.

2.Modify the design and control the processing accuracy.

3.Adjust the position accuracy and punching clearance.

4.Replace the guide pin.

5.Replace the guide pillar. 

6.Readjust the feeder.

7.Readjust the height of the closed die.

8.Grind or replace the unloading insert, increase the strong pressure function and adjust the pressure material.

9.Reduce the strong pressure depth.

10.Replace the material and control the quality of the feed material.

11.Repair the slope or arc of the edge end of the upper die (pay attention to the direction) in order to improve the force condition when punching and cutting. If permitted, the lower part of the die is equipped with a guide function on the unloading block.

Stuck Material 

Causes: 

1.Feeder feed distance. Compression. Improper adjustment of the feeder.

2.Variation of the feeder distance during production.

3.Feeder failure.

4.Material arcs, widths exceedingly poor, large burrs.

5.Abnormal die stamping, sickle bending.

6.Inadequate guide aperture, upper die pulling material.

7.Bending or tearing position of the upper and lower unloading.

8.Improper setting of the unloading function of the guide plate, with the material on the belt.

9.Thin material, warping in the feed.

10.Improper erection of the die, and The vertical deviation of the feeder is large. 

Countermeasures: 

1.readjust.

2.Adjust and repair.

3.Replace the material and control the quality of the feed.

4.Eliminate the sickle bend of the material belt.

5.Train the upper and lower die for punching the positive hole.

6.Adjust the power of the stripping spring, etc.

7.Modify the guide plate to prevent the material belt.

8.Add upper and lower pressure material between the feeder and the die, add upper and lower squeeze material safety switch.

9.Re-erect the die. 

Upper Die Breakage And Chipping 

Causes: 

1.Chip jumping. Chip blockage. Jammed die, etc.

2.Improper feeding, cutting half material. 

3.Insufficient strength of upper die.

4.Size of upper die too close to each other, material traction when punching and cutting, triggering breakage of small upper die.

5.Upper and lower die too sharp angle.

6.Small punching clearance.

7.No stamping oil or strong volatility of stamping oil used.

8.Uneven punching clearance. 

9.Poor accuracy or wear of the unloading block, loss of precision guiding function.

10.Inaccurate guiding of the die. Wear.

11.Improper selection of upper and lower die materials, improper hardness.

12.Wear of guide parts (pins).

13.Improper shim setting. 

Countermeasures: 

1.Solve chip jumping. Crumb blockage. 

2.Pay attention to the feeding, timely trimming of the material belt, timely cleaning of the mold.

3.Modify the design, increase the overall strength of the upper die, reduce the size of the lower die straight edge, pay attention to the upper die edge end to repair the slope or arc, the small part of the back cut.

4.Small upper die length grinding short relative to the large upper die a material thickness or more.

5.Modify the design.

6.Control the upper and lower die machining accuracy or modify the design gap, the small part of the punching gap. 

7.Adjust the amount of oil dripping from the stamping oil or replace the oil type.

8.Check the accuracy of each forming part and adjust or replace it to control the processing accuracy.

9.Train or replace it.

10.Replace the guide pillar. Guide sleeve, pay attention to daily maintenance.

11.Change the material used, use the appropriate hardness.

12.Replace the guide parts.

13.Correction, the number of shims can be as small as possible, and the use of steel pads, the lower die under the shims need to be padded under the pad. 

Bending Deformation Size Variation 

Causes: 

1.Wear of guide pins, insufficient pin diameter.

2.Poor precision of the bending guide part. Wear.

3.Bending upper and lower die wear (pressure loss).

4.Insufficient die let.

5.Material slippage, bending upper and lower die no guide function, bending is not applied to the pre-pressure.

6.Die structure and design size is not good.

7.Punching parts burr, triggering bad bending.

8.Bending part of the upper die. Lower die with more shims, resulting in dimensional instability.

9.Material thickness dimensional variation.

10.Material mechanical shape energy variation. 

Countermeasures: 

1.Replace the guide pin.

2.Re-grind or replace.

3.Re-grind or replace.

4.Check, correct.

5.Modify the design, add guide position and pre-pressure function.

6.Modify the design size, decompose the bending, add bending shaping, etc.

7.Train the lower die.

8.Adjust, use the whole steel pad.

9.Replace the material, control quality of the feed.

10.Replace the material, control quality of the feed. 

Punching Parts High And Low (In Case of Multiple Parts in One Mold)

Causes: 

1.Punching parts with burrs.

2.Punching parts with crush injuries and chips in the die.

3.Upper and lower die (bending bit) crush damage or injury.

4.Turning material when punching and shearing.

5.Wear of the relevant pressing parts. 

6.Inconsistent tearing size of the relevant tearing bit and wear of the cutter.

7.Inconsistent pre-cutting depth of the relevant easy-to-break bit and wear or chipping of the upper and lower dies.

8.Chipping or more serious wear of the upper and lower dies of the relevant upper part.

9.defective die design. 

Countermeasures: 

1.Train the lower bit cutter.

2.Clean the mold to solve the problem of chip floating.

3.Retrain or replace with new parts.

4.Train the punching cutter, adjust or add strong pressure function.

5.Check and implement maintenance or replacement.

6.Repair or replace to ensure consistent tearing condition.

7.Check the condition of the pre-cut upper and lower dies and implement maintenance or replacement.

8.Check the condition of the upper and lower dies and implement maintenance or replacement.

9.Modify the design by adding height adjustment or additional shaping stations. 

Improper Maintenance 

Causes: 

1.molds without anti-dulling function, negligence when forming molds resulting in the opposite direction. 

2.Molds without anti-dulling function, negligence when forming molds resulting in the opposite direction. Misalignment (referring to different stations), etc.

3.Inserts that have been shifted through the gap are not restored to their original state. 

Countermeasures: 

1.Modify the mold to increase the anti-stalling function.

2.Make a mark on the mold and do the necessary checks on the care belt after the mold has been set up. Confirmation, and make a written record for reference. 

In the production of bending, bending accuracy is not high enough is likely to be a problem, for this kind of problem we can first find out the reasons according to the above comparison, and then according to the actual situation to solve. In addition, we should pay attention to the daily maintenance of the bending machine is essential, that is, daily attention to check whether the bending machine and molds are in normal condition, such as bending machine of each axis is working properly; whether there is deviation in the system; molds on the machine before the inspection; each part of the locking confirmation, etc., so that many sudden accidents can be avoided. When starting work, we must first think and then act, and carefully record the accumulated experience.