Cutting Clearance 321k1c
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CUTTING CLEARANCE
• Cutting clearance is the gap between a side of the punch and the corresponding side of the die opening when the punch is entered into the die opening. • Cutting clearance should always be expressed as the amount of clearance per side. • Proper cutting clearance is necessary for the longer life of the tool.
CUTTING CLEARANCE
• Quality of the piece part also depends on proper cutting clearance. • A visual examination of the punched component will indicate the amount of clearance and whether the punch and die have Optimum cutting clearance. Excessive clearance or In sufficient clearance or Misalignment
OPTIMUM CUTTING CLEARANCE
• •
When optimum cutting clearance condition exists a small edge radius is formed. The edge radius is the result of the plastic deformation (first stage of shearing).
OPTIMUM CUTTING CLEARANCE
• A highly burnished cut band results from the second stage (penetration). • The width of the cut band is approximately one third the thickness of the stock material. • The balance of the cut is the break resulting from fracture (third stage).
EXCESSIVE CUTTING CLEARANCE
• The gap between the punch and the die is comparatively more in this case. • The stock material reacts to the initial pressure on a manner approaching that of forming rather than cutting.
EXCESSIVE CUTTING CLEARANCE
• • • • • •
Therefore the edge radius becomes larger. It does not blend smoothly with the cut band. The cut band becomes smaller. The break shows greater irregularities. Heavy burrs are noticeable all along the cut contour. The burr results from the dragging of the material
INSUFFCIENT CUTTING CLEARANCE
.
• •
When cutting clearance is slightly less, the width of the cut band will be more. If cutting clearance is too less two or more cut bands will be formed.
INSUFFCIENT CUTTING CLEARANCE
•
Because of the steeper angle between the punch and the die cut edges the resistance of the stock material to fracture is increased. • The resulting pressure will cause the initial fracture to originate at clearance rather than at the cut edges. • Burr may be caused by compressive forces.
MIS AIGNMENT OF PUNCH AND DIE
• The cutting characteristics also indicate whether the punch and die openings are in accurate alignment. • Because of misalignment, clearance on one side increases and the other side decreases. • The component will show the corresponding difference on cut band.
BURR SIDE
• The burr side is adjacent to the break. Burr should be practically nonexistent If the cutting clearance between the punch and die is optimum. If the cutting edges are sharp. • The burr side of a blank or slug is always towards the punch (die starts shearing). • The burr side of a punched opening is always towards the die opening (punch starts shearing). • The characteristics of the blank or slug and the punched opening are inversely identical.
RELATIONSHIP OF PIECE PART SIZE TO PUNCH AND DIE SIZE
•
When pierced or blanked piece parts are measured, the measurement is made at the cut band.
BLANKING
• The actual cutting of the blank or slug is done by the cutting edge of the die opening. • Therefore the die opening determines the size of the blank or slug. BLANKING PUNCH SIZE = BLANK SIZE - TOTAL CLEARANCE. BLANKING DIE SIZE
= BLANK SIZE
PIERCING
• The actual cutting of the opening in the stock material is done by punch. • Therefore the size of a punched opening is determined by the punch. PIERCING PUNCH SIZE = PIERCED HOLE SIZE PIERCING DIE SIZE = PIERCED HOLE SIZE + TOTAL CLEAR
CUTTING CLEARANCE Clearance calculation. The ideal clearance can be calculated by the following formula Clearance = C x s x √ T max 10 Where C is a constant = 0.005 for very accurate component = 0.01 for normal components s = sheet thickness in mm T max = shear strength of the stock material in N/mm2.
WORKED OUT EXAMPLE -2
WORKED OUT EXAMPLE -2
WORKED OUT EXAMPLE -2
WORKED OUT EXAMPLE -2
WORKED OUT EXAMPLE -3
WORKED OUT EXAMPLE -3
WORKED OUT EXAMPLE -3
• BLANKING DIE DIMENSION IS SAME AS COMPONENT DIMENSION. • PIERCING PUNCH DIMENSION IS SAME AS THE PIERCED OPENING DIMENSION.
WORKED OUT EXAMPLE -4
WORKED OUT EXAMPLE -4
WORKED OUT EXAMPLE -4
• BLANKING DIE DIMENSION IS SAME AS COMPONENT DIMENSION. • PIERCING PUNCH DIMENSION IS SAME AS THE PIERCED OPENING SIZE.
LAND AND ANGULAR CLEARANCE
LAND
WORKED OUT EXAMPLE -4
Land • The inner walls of the die opening are not usually made straight through. • If they are straight, the blanks or slugs tend to get jammed inside the die opening. • This may lead to the breakage of punch or die. • To avoid this, the die walls are kept straight only to a certain dimension from the cutting edge. • The straight wall is called as land. LAND = 3mm for sheet thickness up to 3mm and for thicker material equal to the sheet thickness.
ANGULAR CLEARANCE
ANGULAR CLEARANCE
• The die walls below the land are relieved at an angle for the purpose of enabling blanks or slugs to clear the die. • Soft material requires greater angular clearance than hard materials. • The normal value of angular clearance is 1.5° per side. • Dies for materials like silicon steel and stainless steel are provided with angular clearance from the cutting edge. (No land is provided). • These materials are abrasive in nature and tend to bell-mouth the die opening rapidly if land is provided.
DIE WITH EJECTOR WITHOUT ANGULAR CLEARANCE
• Tools employing ejectors to clear the blanks will have straight walls without any angular clearance.
GUIDE PLATE TOOL
GUIDE PLATE TOOL The guide plate tool consists of : Punch & Die Punch Holder Thrust plate (Back plate) Shank Top plate Stripper cum guide plate Bottom plate Stopper Screws & dowels APPLICATION • The guide plate tools are preferred when the shape of the component is simple. • The accuracy of the component is less. • Only a fewer number of components are required.
CUTTING FORCE • Cutting force is the force which has to act on the stock material in order to cut out the blank or slug. • This determines the capacity of the press to be used for the particular tool. Calculation of cutting force:
RELATIONSHIP BETWEEN SHEARING ACTION AND CUTTING FORCE
RELATIONSHIP BETWEEN SHEARING ACTION AND CUTTING FORCE
• The three critical stages of shearing action are related to cutting force. • Resistance begins when the punch s the stock material. • The load builds up rapidly during the plastic deformation stage. • It continues to increase while penetration takes place. • The accumulated load is suddenly released when fracture occurs.
RELATIONSHIP BETWEEN SHEARING ACTION AND CUTTING FORCE
• •
•
The curve levels off near the bottom. The last portion of the load curve represents frictional resistance developed, As the punch travels through the stock material As the blank or slug ing through the die. If proper cutting clearance condition exists between the punch and the die fracture will occur when cutting force equals the shear strength of the material.
METHODS OF REDUCING PRESS FORCE
• In some cases it will be necessary to reduce cutting force to prevent over loading press • A method to reduce press force is to grind the face of the punch or die at a small shear angle with reference to the horizontal plane. • This reduces the area of during shear at anyone time. • Providing shear angle also reduces shock to the press and smoothens out the cutting operation.
METHODS OF REDUCING PRESS FORCE
•
The shear angle should provide a change in punch length from 1 to 1.5 times the sheet thickness.
•
Double shear angle is preferred over single shear angle because it does not create lateral forces.
•
Double shear angled punches should be concave to prevent stretching the material before it is cut.
METHODS OF REDUCING PRESS FORCE
• To prevent distortion on the stock material for blanking operation the shear angle will be on the die member for piercing operation the shear angle will be on the punch member. • Another method to reduce cutting force is to step punch lengths. • Punches or groups of punches are made progressively shorter. by about one sheet thickness.
WORKED OUT EXAMPLE -1
WORKED OUT EXAMPLE -2
WORKED OUT EXAMPLE -3
WORKED OUT EXAMPLE -4
ASSIGNMENTS -1 CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE THE FOLLOWING COMPONENTS
ASSIGNMENTS -2 CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE THE FOLLOWING COMPONENTS
ASSIGNMENTS -3 CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE THE FOLLOWING COMPONENTS
ASSIGNMENTS - 4 CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE THE FOLLOWING COMPONENTS
• Cutting clearance is the gap between a side of the punch and the corresponding side of the die opening when the punch is entered into the die opening. • Cutting clearance should always be expressed as the amount of clearance per side. • Proper cutting clearance is necessary for the longer life of the tool.
CUTTING CLEARANCE
• Quality of the piece part also depends on proper cutting clearance. • A visual examination of the punched component will indicate the amount of clearance and whether the punch and die have Optimum cutting clearance. Excessive clearance or In sufficient clearance or Misalignment
OPTIMUM CUTTING CLEARANCE
• •
When optimum cutting clearance condition exists a small edge radius is formed. The edge radius is the result of the plastic deformation (first stage of shearing).
OPTIMUM CUTTING CLEARANCE
• A highly burnished cut band results from the second stage (penetration). • The width of the cut band is approximately one third the thickness of the stock material. • The balance of the cut is the break resulting from fracture (third stage).
EXCESSIVE CUTTING CLEARANCE
• The gap between the punch and the die is comparatively more in this case. • The stock material reacts to the initial pressure on a manner approaching that of forming rather than cutting.
EXCESSIVE CUTTING CLEARANCE
• • • • • •
Therefore the edge radius becomes larger. It does not blend smoothly with the cut band. The cut band becomes smaller. The break shows greater irregularities. Heavy burrs are noticeable all along the cut contour. The burr results from the dragging of the material
INSUFFCIENT CUTTING CLEARANCE
.
• •
When cutting clearance is slightly less, the width of the cut band will be more. If cutting clearance is too less two or more cut bands will be formed.
INSUFFCIENT CUTTING CLEARANCE
•
Because of the steeper angle between the punch and the die cut edges the resistance of the stock material to fracture is increased. • The resulting pressure will cause the initial fracture to originate at clearance rather than at the cut edges. • Burr may be caused by compressive forces.
MIS AIGNMENT OF PUNCH AND DIE
• The cutting characteristics also indicate whether the punch and die openings are in accurate alignment. • Because of misalignment, clearance on one side increases and the other side decreases. • The component will show the corresponding difference on cut band.
BURR SIDE
• The burr side is adjacent to the break. Burr should be practically nonexistent If the cutting clearance between the punch and die is optimum. If the cutting edges are sharp. • The burr side of a blank or slug is always towards the punch (die starts shearing). • The burr side of a punched opening is always towards the die opening (punch starts shearing). • The characteristics of the blank or slug and the punched opening are inversely identical.
RELATIONSHIP OF PIECE PART SIZE TO PUNCH AND DIE SIZE
•
When pierced or blanked piece parts are measured, the measurement is made at the cut band.
BLANKING
• The actual cutting of the blank or slug is done by the cutting edge of the die opening. • Therefore the die opening determines the size of the blank or slug. BLANKING PUNCH SIZE = BLANK SIZE - TOTAL CLEARANCE. BLANKING DIE SIZE
= BLANK SIZE
PIERCING
• The actual cutting of the opening in the stock material is done by punch. • Therefore the size of a punched opening is determined by the punch. PIERCING PUNCH SIZE = PIERCED HOLE SIZE PIERCING DIE SIZE = PIERCED HOLE SIZE + TOTAL CLEAR
CUTTING CLEARANCE Clearance calculation. The ideal clearance can be calculated by the following formula Clearance = C x s x √ T max 10 Where C is a constant = 0.005 for very accurate component = 0.01 for normal components s = sheet thickness in mm T max = shear strength of the stock material in N/mm2.
WORKED OUT EXAMPLE -2
WORKED OUT EXAMPLE -2
WORKED OUT EXAMPLE -2
WORKED OUT EXAMPLE -2
WORKED OUT EXAMPLE -3
WORKED OUT EXAMPLE -3
WORKED OUT EXAMPLE -3
• BLANKING DIE DIMENSION IS SAME AS COMPONENT DIMENSION. • PIERCING PUNCH DIMENSION IS SAME AS THE PIERCED OPENING DIMENSION.
WORKED OUT EXAMPLE -4
WORKED OUT EXAMPLE -4
WORKED OUT EXAMPLE -4
• BLANKING DIE DIMENSION IS SAME AS COMPONENT DIMENSION. • PIERCING PUNCH DIMENSION IS SAME AS THE PIERCED OPENING SIZE.
LAND AND ANGULAR CLEARANCE
LAND
WORKED OUT EXAMPLE -4
Land • The inner walls of the die opening are not usually made straight through. • If they are straight, the blanks or slugs tend to get jammed inside the die opening. • This may lead to the breakage of punch or die. • To avoid this, the die walls are kept straight only to a certain dimension from the cutting edge. • The straight wall is called as land. LAND = 3mm for sheet thickness up to 3mm and for thicker material equal to the sheet thickness.
ANGULAR CLEARANCE
ANGULAR CLEARANCE
• The die walls below the land are relieved at an angle for the purpose of enabling blanks or slugs to clear the die. • Soft material requires greater angular clearance than hard materials. • The normal value of angular clearance is 1.5° per side. • Dies for materials like silicon steel and stainless steel are provided with angular clearance from the cutting edge. (No land is provided). • These materials are abrasive in nature and tend to bell-mouth the die opening rapidly if land is provided.
DIE WITH EJECTOR WITHOUT ANGULAR CLEARANCE
• Tools employing ejectors to clear the blanks will have straight walls without any angular clearance.
GUIDE PLATE TOOL
GUIDE PLATE TOOL The guide plate tool consists of : Punch & Die Punch Holder Thrust plate (Back plate) Shank Top plate Stripper cum guide plate Bottom plate Stopper Screws & dowels APPLICATION • The guide plate tools are preferred when the shape of the component is simple. • The accuracy of the component is less. • Only a fewer number of components are required.
CUTTING FORCE • Cutting force is the force which has to act on the stock material in order to cut out the blank or slug. • This determines the capacity of the press to be used for the particular tool. Calculation of cutting force:
RELATIONSHIP BETWEEN SHEARING ACTION AND CUTTING FORCE
RELATIONSHIP BETWEEN SHEARING ACTION AND CUTTING FORCE
• The three critical stages of shearing action are related to cutting force. • Resistance begins when the punch s the stock material. • The load builds up rapidly during the plastic deformation stage. • It continues to increase while penetration takes place. • The accumulated load is suddenly released when fracture occurs.
RELATIONSHIP BETWEEN SHEARING ACTION AND CUTTING FORCE
• •
•
The curve levels off near the bottom. The last portion of the load curve represents frictional resistance developed, As the punch travels through the stock material As the blank or slug ing through the die. If proper cutting clearance condition exists between the punch and the die fracture will occur when cutting force equals the shear strength of the material.
METHODS OF REDUCING PRESS FORCE
• In some cases it will be necessary to reduce cutting force to prevent over loading press • A method to reduce press force is to grind the face of the punch or die at a small shear angle with reference to the horizontal plane. • This reduces the area of during shear at anyone time. • Providing shear angle also reduces shock to the press and smoothens out the cutting operation.
METHODS OF REDUCING PRESS FORCE
•
The shear angle should provide a change in punch length from 1 to 1.5 times the sheet thickness.
•
Double shear angle is preferred over single shear angle because it does not create lateral forces.
•
Double shear angled punches should be concave to prevent stretching the material before it is cut.
METHODS OF REDUCING PRESS FORCE
• To prevent distortion on the stock material for blanking operation the shear angle will be on the die member for piercing operation the shear angle will be on the punch member. • Another method to reduce cutting force is to step punch lengths. • Punches or groups of punches are made progressively shorter. by about one sheet thickness.
WORKED OUT EXAMPLE -1
WORKED OUT EXAMPLE -2
WORKED OUT EXAMPLE -3
WORKED OUT EXAMPLE -4
ASSIGNMENTS -1 CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE THE FOLLOWING COMPONENTS
ASSIGNMENTS -2 CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE THE FOLLOWING COMPONENTS
ASSIGNMENTS -3 CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE THE FOLLOWING COMPONENTS
ASSIGNMENTS - 4 CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE THE FOLLOWING COMPONENTS
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