Precautions and solutions for waste material loss during die stamping!

Principles of Scrap Material Handling

1. Basic Principles

1) Scrap material handling must be given high priority.

2) The user must confirm whether the scrap material slides outside the mold, outside the press table, or into the machine tool's scrap hole.
3) Scrap material should fall with each punching operation.

4) The angle of the scrap funnel should be at least 50 degrees for small holes and smaller scrap materials; 30° for the first-stage slide, 25° for the second-stage slide, and 15° for the raceway.

5) Sufficient height must be provided at the scrap cutter location to allow for funnel installation.

6) If the funnel installation height is insufficient, a scrap box can be considered.

7) Scrap material must be handled thoroughly and have sufficient space to be removed from the mold.

8) The dimensions of the openings (interfaces) of various scrap hoppers must be standardized.

9) When scrap material is required to slide out of the press table, the scrap funnel should be a two-stage, foldable type. 10) The scrap chute must be at least 30mm larger than the maximum size of the scrap (this can be slightly reduced except in special cases).

2. Basic Principles

1) The basic process of scrap handling is a cycle where the scrap naturally ejects to the drill bit.

2) The height of the scrap cutter holder should be considered when determining the height of the slide rail.

3) When handling scrap, the channel structure should have sufficient leeway both horizontally and vertically.

4) Generally, the scrap slide angle is 30 degrees inside the mold and 25 degrees outside the mold.

5) When manually feeding, pay attention to the scrap cutter arrangement and slide rail structure to ensure the scrap does not travel towards the operator.

6) If the scrap cannot eject naturally due to the relationship between the upper and lower cutters, forced ejection should be used.

Precautions to prevent scrap deformation:

1. Leave a 20mm clearance on the punch profile surface and a 2mm clearance behind it to reduce finishing work and prevent deformation of the scrap top.

2. Unnecessary protrusions should be optimized and removed to reduce machining and prevent scrap deformation.
3. Punch surfaces with protrusions and concave surfaces must be replicated; they cannot be removed.

4. Simulated operation checks are necessary. The punch cutting edge must contact the scrap before cutting; other parts should not interfere with the scrap, causing deformation.

Z-type scrap anti-jamming structure

1. The impact of scrap cutter arrangement on scrap discharge.

Precautions:
① The upper die punch should extend 1mm beyond the lower die cutting edge.

② Z-type scrap jamming mainly occurs when it gets stuck inside the scrap cutter of the lower die:

In the first case, both the high and low points of the Z-type scrap have cutting edges. A scrap ejector pin should be added to the side of the low point to allow the scrap to rotate and discharge along the purple scrap path. Otherwise, if an ejector pin is designed at the high point, the scrap may get stuck between the two cutters along the black scrap path.

The second scenario involves the Z-shaped scrap having its high point as the back of the cutter and its low point as the cutting edge. A scrap ejector pin is added to the upper die at the low point, allowing the Z-shaped scrap to slide out smoothly. Therefore, when designing, the scrap cutter arrangement should primarily choose scenario ②.

Standards for Regular and Irregular Scrap Discharge

1. Design of the Discharge Hole

① Direct Punching Type: As shown in the diagram, each step of the cutting edge discharge is 2mm larger on one side. If a scrap funnel is required, design according to the parameters shown in the diagram, where B > A + 30min. The flat cutting edge should be straight at 5 degrees and angled at 1.5 degrees (unless otherwise specified by the customer).

② Standard Insert Type: As shown in the diagram, the discharge step at the backing plate is 1mm larger on one side than the scrap hole of the insert, and each subsequent step is 2mm larger on one side.

③ For direct punching and opening type, as shown in the figure below, the material drop step should be 10mm on each side (except for special cases). If a scrap funnel is required, design according to the parameters shown in the figure, where B>A+30min. The flat cutting edge should be straight at 5 degrees and angled at 1.5 degrees (unless otherwise specified by the customer).

④ When designing, the foot pad should avoid scrap as much as possible. If it is impossible to avoid the foot pad due to insufficient space, a scrap trough must be machined. The scrap trough must have a straight body of at least 30mm and a 45-degree angle. If too little scrap falls on the foot pad, the angle of the trough can be at least 30mm, with a straight body and a 30-degree angle. In all cases, the diagonal of the material drop trough must be at least 30mm larger than the maximum outer dimension of the scrap to prevent the scrap from overturning and getting stuck during the fall. If the blanking space is insufficient, a reverse bevel groove can be machined at the bottom of the die base, as shown in the figure below:

⑤ When the blanking of the punch cannot directly drop scrap due to location limitations or when a funnel is used, the design can refer to the figure below. Note that the minimum blanking angle is 50 degrees. When designing the punching, pay attention to the depth of the punch. If the lower die blade is a wire-cut blade, use a 5mm straight blade with a 1.5mm bevel. If it is a standard part insert, a 5mm straight blade is preferred, unless otherwise specified by the customer or there is a difference in the height of the profile surface. Ensure that scrap is removed piece by piece after punching.

⑥ When the punching position is far from the scrap hole, the following method can be used:

Standard for scrap removal with the back of the blade and standard for scrap removal with the back of the blade

1. Method of cutting blade and blade edge

2. Scrap size requirements

① To ensure that the scrap can be dropped smoothly, the length of the scrap should generally be within 300mm, unless otherwise specified by the customer.

② Does the support rib of the scrap cutter reach the bottom? If not, can it be lengthened as much as possible or can a large bevel bevel be made on the side wall (without affecting scrap removal)?

3. Scrap Removal Details

4. Scrap Removal with the Back of the Blade: The scrap cutter should be 5mm lower than the mold surface, and the step-by-step cutting facilitates scrap removal.

Scrap Removal Methods

1. For scrap longer than 300mm and with a relatively gentle slope:

Preferred Method 1: For scrap longer than 300mm and with a relatively gentle slope, a silver steel rod needs to be added to the funnel to reduce the contact area between the scrap and the funnel, thereby reducing friction and removing the scrap faster. See Figure 1:

Method 2:

① When the scrap removal angle is greater than or equal to 30°, an angle iron funnel can be used directly to discharge the scrap outside the mold.

② When the scrap removal angle is between 25° and 30°, a mesh plate can be used as a scrap funnel to discharge the scrap outside the mold.

③ If the scrap needs to be reused, MISUMI rollers should be added to prevent product scratches. When the scrap angle is below 25°, rollers (as shown in the diagram) or a vibrating funnel can be used to discharge the scrap outside the mold.

2. U-shaped scrap
In this cutting method, scrap will accumulate on the lower die cutting edge:

① Ensure the punch is straight or flush with the cutting edge so that scrap is cut off piece by piece.

② Add ejector pins in corners where scrap is prone to getting stuck; add more as needed.

③ Design the cutting edge lines on both sides in a V-shape.

3. L-shaped scrap

Precautions: When L-shaped scrap falls, it will stand upright in the width direction. The heavier end falls first and hits the scrap hole edge, while the lighter end is supported by the end that might be blocked. Regulations: When encountering L-shaped scrap, confirm the center of gravity position, simulate the falling process based on the center of gravity, and avoid areas that might be blocked. A should be greater than the maximum value of the scrap falling to this location by 30mm. Use scrap simulation software to simulate the process.

4. Figure-eight shaped scrap

Precautions: When falling with a figure-eight shaped scrap, if the smaller end falls first, the scrap will get stuck on the cutting edge. Ensure the larger end falls first. Regulations: When encountering this type of figure-eight shaped scrap, the punch at the larger end must enter at least 1.5T first, and then the smaller end should cut in. Anti-stick ejector pins should be placed at the larger end. The scrap hole on the lower die base should be optimized into a regular, easily machined hole, as shown in the figure.

5. S-shaped, 8-shaped, Z-shaped, U-shaped, U-shaped side-cut, large undulation drop, scrap with hooks in the falling direction, double-sided back-cutting surfaces, etc. scrap

Precautions: ① Ensure no scrap is stacked; increase the punch depth or reduce the cutting edge length.

② Process optimization, adjusting the angle of the cutting edge on both sides. ③ Perform dynamic simulation of scrap removal.

As shown in the diagram above, precautions for removing scrap:

1. Dig down the cutting edge to avoid steps and chamfer the radius, ensuring strength.

2. Scrap length A+4MIN in the scrap avoidance groove B.

6. General Scrap

Precautions:
① The funnel angle should preferably be above 45 degrees, with a minimum of 30 degrees.

② Scrap removal space as shown in the diagram: BA+30.

③ In special cases where the funnel angle is ≤25 degrees, a filter screen is required.
④ Both sides of the funnel should be flush against the casting surface to prevent scrap from getting stuck.

1. Method 1:

2. Method 2:

Method: When the B value cannot reach at least 30 greater than the A value, a silver steel branch should be added to one end to allow one end to drop down first, preventing the scrap from standing upright and getting stuck.

7. Curved Scrap

① Anti-jamming Structure for Curved Scrap

The image above shows curved scrap. A common characteristic of this type of scrap is that it tends to get stuck on the upper die cutting edge. This is because after the scrap is cut away from the product, the stress is released during sheet metal forming, causing the scrap to open up. The higher the sheet metal strength, the greater the force exerted by this curved scrap on the upper or lower die cutting edge. Therefore, we need to pay attention to the jamming problem in the design for similar curved scrap.

② Problem of Curved Scrap Dropping When Cutting Along a Curve

In this cutting method, the curved scrap will get stuck on the upper die cutting edge. We need to add strong spring-loaded elements at both ends of the curve. The higher the sheet metal strength and the thicker the sheet metal, the greater the force required for our spring-loaded elements. For this type of scrap, we stipulate: the upper die ejector element uses a heavy-duty spring plunger of M12 or higher, and the upper die punch has a 20mm straight body, with the remaining portion having a 2.0mm clearance. When the scrap tilt angle is greater than 30°, the spring plunger is removed to prevent it from being broken by lateral force.

8. Problem of scrap falling off curved ends

In this cutting method, curved scrap can get stuck on the cutting edge of the upper or lower die. ⑴ We need to add strong ejector elements at both ends of the curved shape. The higher the strength and the thicker the sheet metal, the greater the force required for the ejector elements, and the greater the stroke of the ejector elements. For this type of scrap,

we stipulate:
① The upper die ejector element uses a heavy-duty spring plunger of M12 or higher;

② The stroke of the ejector element at the higher position is at least 10mm smaller than that of the lower position.

(2) Scrap Material Falling Off: After the upper die cutter edge, the scrap material will still be stuck in the lower die.

We need:
① The cutter edges at both ends of the curved scrap material should be outwards (V-shaped), with a horizontal angle of 10 degrees on each side;

② The upper die cutter edge should extend at least 1mm beyond the lower die cutter edge after penetration;

③ Sufficient clearance should be provided at the lower die cutter edge.

"If the above methods cannot guarantee scrap material falling off, the material strip process can be optimized as shown in the right figure. The scrap material can be cut in half lengthwise in the preceding steps to eliminate its springback force."

9. Standard for Slender Scrap Material Falling Off

Note: To ensure the scrap material falls off smoothly, the length should generally be within 300mm, unless otherwise specified by the customer; A: Due to the slender punch, punch reinforcement is required in the design to ensure strength. B: To ensure the scrap material falls off safely and is not carried off the die surface by the punch, ejector pins should be added to the reverse side of the punch, with a minimum ejector pin length of 6mm (except in special cases). C: To reduce punching force and noise during punching, a draft angle H=1T (T is the material thickness) needs to be machined on the reverse side of the punch.

The following are the punch specifications.

The following are the specifications for slender scrap cutting edges:

1. Scrap lengths exceeding 250mm require separate cutting edges, as shown in the figure: Casting and steel plate die cutting edge specifications.

2. The blanking method for the lower die cutting edge is shown in Figures A and B. Either method can be chosen depending on the situation unless otherwise specified by the customer.

10 Scrap Box

The selection principle for scrap boxes: Due to their low production efficiency, they should not be used unless specifically requested by the customer. If their use is necessary due to special circumstances, formal approval from the customer is required. Design considerations:

1. The minimum height of the box should be 80mm to ensure sufficient scrap storage capacity.

2. The box should be designed to fit snugly against the casting surface, allowing for adjustment of sliding fit clearances.
3. The box must ensure smooth loading and unloading.

11 Casting Slides

Design considerations:

1. The slide should be angled at a minimum of 50 degrees.

2. The bottom of the chute should extend 10mm beyond the blanking hole of the punch press, table, or pallet to prevent steps from affecting scrap material discharge.

3. When the chute angle is small, a funnel should be considered.

4. The scrap discharge space in the chute should be greater than the scrap material A + 30mm.

12 Vibrating Funnel

Selection Principles of Vibrating Funnel:

1. Used when a general funnel cannot be used due to lower die height limitations.

2. Used when required by the customer.

Design Considerations:

1. Design specifications should be based on the customer's brand and parameters. The design must ensure the vibrator can be easily disassembled.

2. Because the vibrating funnel needs to pass through the entire width of the die, the die strength must be guaranteed (refer to the die base strength standard for castings).

Regulations for Vertical Cutting and Trimming Conditions

① Trimming parallel to the maximum inclination line of the inclined plane

Note:

1. The minimum inclination angle θ° of the scrap cutter in the shaping section is 5 degrees.

2. This value is for reference only; the specific value should be based on the material strip.

② When the tilt angle exceeds the tolerance, wedge cutting is required for vertical cutting.

2. Method for determining the stroke of the vertical cutting pressure plate:

3. Schematic diagram and considerations for vertical cutting scrap removal:
① Ensure that scrap is removed one piece at a time at the bevel or curved blade edge, and the punch must pass the blade edge with a straight body (except in special cases, no more than 3 pieces).

② The straight body of the bevel blade edge is 5mm, the specific value depends on the stroke of the stripper plate (unless otherwise specified by the customer).

③ When the pressure plate just contacts the product, the distance between the punch and the product should be at least 10mm. The pressure plate stroke calculated under this condition is the minimum stroke of the pressure plate.

④ The punch entry angle and radius (R angle) can be adjusted appropriately, depending on the shape of the scrap. Step 1: Measure 1mm off the lower edge and 2mm off the upper edge of the punch's bevel to ensure more efficient punch cut.

Step 2: Cut the product position first with the punch.

Step 3: Mold closed and locked.

4. Case studies of problems with vertical cutting:

① Incorrect vertical cutting method

② Correct vertical cutting method
Standard for side punch scrap removal

Precautions:

The following methods must consider the punch cut depth. Scrap from side punches tends to accumulate and form columns, easily damaging the mold. A scrap deflection structure needs to be designed.

1. Design a scrap crusher type.

2. Design a scrap deflection hole type (Note: Utilize the scrap discharge hole for deflection. The scrap rotates and falls out along the side wall of the hole. An observation hole of at least Φ8mm is required on the front of the discharge port. If the punch angle is above 30°, the scrap slides down and an observation hole is not required).

3. Insert a self-made deflection insert type.

4. Directly machine a beveled scrap discharge hole type on the mounting base.