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How to Improve the Production Efficiency of Automatic Stamping Line?

At present, the application of high-speed automatic stamping line is in the popularization stage, but affected by the cost, many enterprises are still using more traditional stamping equipment. Although they are equipped with automation facilities such as manipulator and end pickup, which reduces personnel investment, the improvement of production efficiency is not very significant.

This post mainly introduces the ways to improve the efficiency of automatic stamping line around the three elements of press, die and manipulator.

With the increasing demand for automobiles in the market, the demand for stamping parts is also increasing at the same time.

However, due to the preparation before production, the long time of die commissioning, the uncoordinated operation of manipulator and press, the structural defects of end pickup, etc., the production efficiency can not be significantly improved.

Therefore, it is particularly important to shorten the mold change time, optimize the action matching between the press and the manipulator, and improve the structure of the end pickup.

The following takes the stamping production line composed of traditional mechanical press and six axis manipulator with manual die change as an example.

Shorten die change time

The die change process of the press includes:

① Workbench opening → ② ejector rod replacement → ③ mold positioning and installation → ④ lower mold clamping → ⑤ workbench opening → ⑥ sliding block descending and fine tuning to the lower dead center → ⑦ upper mold clamping → ⑧ adjustment of production parameters → ⑨ pressure test and re-inspection clamping → ⑩ formal production.

Through the above analysis, it can be found that the processes that take a long time in the process of die change are mainly ②, ③, ⑥ and ⑧.

The solution is as follows:

In view of the problem of process ②, most stamping plants generally purchase outsourced molds for production.

In order to facilitate production and use, the ejector rod and stretching pad are of split structure. The ejector rod is installed at which position needs to be installed, and each replacement takes a lot of time;

If the stamping dies used in the workshop are self-developed, make the ejector rod and stretching pad into an integrated structure or insert the ejector rod on the worktable, and only avoid the air on the die, which can greatly shorten the time for replacing the ejector rod.

For the problem of procedure ③, two positioning structures (V-shaped + plane positioning or 2 V-shaped positioning) can be added on the same side of the die body to facilitate the positioning work by only pushing with force during die installation.

Similar structures are shown in Fig. 1.

Schematic diagram of mold positioning structure

Fig. 1 Schematic diagram of mold positioning structure

When using this structure, it is necessary to ensure that there is a pin hole inserted by the positioning pin on the working table of the equipment.

If there is no pin hole on the table, the table can be modified.

For the problems of processes ⑥ and ⑧, the required parameters (such as mold mounting height, closing height, balancer air pressure, air cushion pressure, etc.) and operation specifications can be specified by compiling the on-site process card, and all production parameters can be monitored, observed and adjusted in time.

Optimization of press, manipulator and end pickup

The movement of the press and manipulator is driven by the signal output from the proximity switch installed on the die, but it is comprehensively affected by the die structure, press structure, PLC program, end pickup structure, manipulator deflection angle and running track.

In order to improve the production beat, we need to start from the following aspects.

Increase the safety distance between upper and lower molds

The safe distance between the upper and lower molds is the distance between the process part lifting from the mold surface to the position where the lower mold can be translated and the lowest point of the upper mold, as shown in Fig. 2.

Schematic diagram of safety distance between upper and lower molds

Fig. 2 Schematic diagram of safety distance between upper and lower molds

Increasing the safety distance is conducive to the manipulator entering the die in advance to grasp the parts.

Usually, because the stroke of the slider is limited by the equipment structure, it can only be realized by optimizing the die structure.

Taking the turnover die in Fig. 2 as an example, there is an inserting knife on the f surface of the upper die to drive the lower die pulley mechanism.

In order to increase the safety distance, it can be considered to move the inserting knife position to the side and avoid the movement track of the manipulator.

Height of model surface under unified full order

When the manipulator moves at the maximum speed, the height of the lower model surface between each process is basically the same, which can save the part handling time between adjacent processes.

Generally, during mold development, requirements can be made here, and the lower mold height shall be as low as possible;

In case of the mass production mold, when the height difference of the lower mold surface between processes is too large, the base plate can be added to the lower mold.

Reduce the change of stamping angle between processes

The change of stamping angle directly affects the change of manipulator trajectory.

Generally, the closer the stamping angle between two adjacent work sequences, the less the coordinated action of each axis and the smoother the operation of the manipulator in the process of picking and feeding.

If the parts are left-right symmetrical parts and the stamping angle changes greatly between processes, the clamping development of left and right parts can be considered.

Optimize the structure of end pickup

In order to facilitate the movement of the end pick-up between the molds, under the condition that the end pick-up structure meets the conditions of grasping parts, the main rod shall be close to the parts, and the included angle formed by the auxiliary rods on both sides of the main rod shall be as large as possible;

In order to ensure the reliability of grasping parts, the number of suction cups and reinforcing rods can be increased appropriately.

Reduce clutch start waiting time

In order to ensure that the sliding block does not collide with the manipulator when it goes down, in the PLC program of the press, the feeding signal will generally be transmitted to the press in the die to promote the delay of 500 ~ 1000ms before the clutch is started.

The delay time is gradually shortened through on-site attempt.

Adjust equipment safety parameters

When the manipulator controls the end pickup to “enter” and “exit” in the die, it is related to the equipment parameters “blanking angle” and “die protection angle”.

When the slider returns to the “blanking angle”, the press transmits a signal to the manipulator to make it enter the die for blanking operation;

When the slider moves from the top dead center to the “die protection angle”, but the manipulator has not moved out of the die, force the press clutch for emergency braking.

Combined with field observation, the press and manipulator can be operated in advance and the single operation cycle of the press and manipulator can be shortened by gradually reducing the “blanking angle” and increasing the “die protection angle”.

In order to ensure the operation safety of the manipulator automatic line, when multiple manipulators operate within the system coordinates, anti-collision safety protection procedures will be set to promote the manipulator to run in advance by modifying the manipulator procedures.

Estimation of production beat of the automatic production line

After the mold design is completed, in order to preliminarily evaluate the production beat of the automatic line, it can be estimated in the following ways. The specific methods are as follows:

(1) Using the safe distance X1 between molds, the distance x2 from the highest point of the end pickup to the workpiece and the slider stroke X3, calculate the displacement of the slider Y = X3 – (X1 – X2) (taking the lower dead center of the slider as the reference value 0) when the end pickup does not interfere with the lower mold and can be moved out of the mold.

(2) Using the calculated Y value, make a straight line on the running curve of each equipment slider to intersect the curve, and obtain the values W1 and W2 on the horizontal axis (which can be used as the reference values of “blanking angle” and “mold protection angle”).

(3) By calculating the difference U of W2 minus W1 of each equipment, take the same multiple V to divide the U value;

The horizontal axis of the sliding block operation curve of each equipment is divided equally by using the multiple V value, as shown in Fig. 3 and Fig. 4.

Stroke curve of slider of 2250t press

Fig. 3 Stroke curve of slider of 2250t press

Stroke curve of sliding block of 1000t press

Fig. 4 Stroke curve of the sliding block of 1000t press

(4) Draw the schematic diagram of manipulator operation, as shown in Fig. 5.

Operation diagram of the manipulator

Fig. 5 Operation diagram of the manipulator

(5) Set the corresponding values according to the layout of the stamping production line and equipment parameters, and use the same time axis to match the actions of the press and the manipulator.

For example, if the layout of the stamping line is 2250t + 1000t + 1000t + 1000t, the six-axis manipulator is connected, the press spacing is 7m, the maximum operating speed of the manipulator is 7m / s, and the maximum number of strokes of the automatic line slider is 10spm.

It can be assumed that the operating time of the press and the manipulator in each equally divided interval is about 0.5s (i.e. 0.5s for each displacement of I ~ XII; 0.5s for each displacement of KL and Mn).

Using the states of Fig. 3, FIG. 4 and Fig. 5 for analysis, then,

Single piece man hour = time of one stroke of the press + waiting time of the press at top dead center = 12 × 0.5+(6-2) × 0.5 = 8 seconds / piece

Production beat = 60 ÷ 8 = 7.5 pieces / min

Note:

① The first equipment is usually a multi link press, which runs slowly during forming, and the stamping production line is in linkage state, so the time taken for one cycle of actual production and operation of the first equipment is the production man hour of a single piece;

② The waiting time of the press at the top dead center is the time when the press stops at the top dead center and the upper feeding robot puts the materials into the mold and the press starts to move.

Improved effect

By improving the ejector rod structure, positioning mode and process standardization, the efficiency of die installation and commissioning is increased by at least 35%;

By optimizing the structure of end pickup, shortening the waiting time for clutch start and adjusting equipment safety parameters, the production capacity can be increased by about 5%;

In the mold development stage, the production capacity can be increased by about 15% by increasing the safe distance between molds, unifying the height of the lower mold surface and reducing the change of stamping angle between processes.

Conclusion

In order to pursue higher production efficiency, the industry also puts forward higher requirements for molds and equipment, such as selecting high-end press, increasing the slider stroke and punching times of press, shortening the layout between presses, increasing rapid die change system, adjusting the traditional 4-station layout to 5-station layout, using 7-axis manipulator and equipped with more advanced end pickup, etc.

With the rapid development of the economy, more advanced technologies will be applied in actual production to jointly promote the progress of the stamping industry.

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