With the continuous development and progress of the automotive industry, the production of stamping parts from the original manual feeding production gradually changed to automated production, automated production greatly saves labor costs and has obvious advantages in terms of production efficiency and operational safety.
In recent years, major auto OEMs and processing plants have introduced stamping automation production lines.
Then there has been a problem that the original manual line old molds will not be able to directly match the use of automatic line production.
The investment in redeveloping automation molds is large and the cycle is long.
Therefore, how to automatically transform the existing manual line mold to meet the requirements of automatic line production is particularly necessary.
Retrofit feasibility analysis
The shape, process and original mold structure of the pressed product directly affect the throughput and efficiency of the automated production.
Not all hand-loaded molds are suitable for automated retrofits. Before deciding whether to renovate, you need to understand the basic requirements of the automated renovation of products and molds, and conduct feasibility analysis to avoid the loss of blind investment.
Product shape analysis
In general, large and medium-sized outer coverings with relatively smooth surface shapes are more suitable for automated retrofitting.
However, some frame parts and small, medium-sized structural parts are not easy to arrange end-pick suction cups due to many hollow surfaces and narrow, complicated shapes, which makes it easy to be unstable.
There are also some parts with deep drawing depth, which are likely to cause insufficient pickup space and affect the normal production cycle of automation.
Therefore, it is not recommended to automate such parts.
Automatic line equipment analysis
Take an automated line of a car company as an example, there are 5 presses in the whole line, the first double-acting 1500t, and the subsequent 4 sets of 800t.
The first part of the line contains sheet metal destacking, automatic oiling, and automatic centering technology.
The workpiece transmission is automated by 8 ABB six-axis robots.
Product process analysis
(1) Considering the number of processes, in the case of the automatic line is 5 stations, the number of processes of the modified parts should preferably be equal to the number of machine stations arranged in the automatic line.
If the modified parts are less than 5 sequences, consideration needs to be given to putting in matching empty workstations.
If it is greater than 5 sequences, then sequential turnaround production needs to be considered.
(2) Considering the stamping direction, the stamping direction of the workpiece in each sequence of die bore in automatic line production is as consistent as possible, and there should not be too much rotation, and the change of the tilt angle of the parts in the adjacent process should not be too large.
The control rotates within ±10° around the Y-axis and ±15° around the X-axis (X direction is the logistics direction). In the case of two-piece production, the tilt angle of the left and right parts must be consistent with the adjacent process, otherwise the entire line beat will be greatly affected, and even automated production will not be possible.
Analysis of the spatial structure of the mold
The press stroke must be considered in conjunction with the parameters of the automatic line machine, and the press stroke must be considered on the premise that the tonnage, sealing height and table size is satisfied.
The travel of the press and the structure of the die together determine the rotation space of the part between the upper and lower die, which is the effective opening height, i.e. the distance from the highest point of the lower die to the lowest point of the upper die.
The effective opening height directly affects the flexibility of the end picker feeding and picking and the production rhythm of the whole line, the correlation is shown in Figure 1.
Figure 1 Schematic diagram of the mold
A – part depth
B – lower die safety distance
C – end picker height
D – upper die safety distance
G – space required to pick up parts
As can be seen from Figure 1, pick up space G = 2A + B + C + D, automatic transformation requirements of the press stroke must be greater than G value, the larger the machine stroke, the larger the effective opening space, the more conducive to automated production beats.
It should be noted here that the front and back of the mold try not to have large guide mechanism, oblique wedge, lifting wedge device, will affect the robot pick up trajectory.
If so, the height of this structure can be equal to the depth of the part added to the calculation, if the calculation of the space required to pick up parts G value is too large, greater than the machine stroke, then there is no space to pick up parts, not recommended for automated transformation.
Modification of mold installation method
(1) Modification of the mold alignment structure.
The installation of automated molds has more stringent requirements than ordinary molds, and must ensure that the relative position of the molds and the machine table is consistent each time.
This ensures that the robot can accurately and repeatedly grip the workpiece, so the automated mold mounting method must consider mold-to-neutral.
There are generally two types of alignment, the centering key-way form and the cylindrical positioning pin form. In this case, an automatic transformation mold adopts the center key way, and the processing size is 32mm wide and 20mm deep through-groove design.
In the actual renovation, the position of the middle groove maybe just on the main bar of the mold or the bottom surface of the nitrogen spring interference, can not be forced to process the original mold function and strength.
It is possible to reduce the requirements without machining the through-slot to ensure that the effective length of the key-way at both ends is more than 60mm, and can also meet the function of the centering, but the use of the centering key requires manual adjustment of the use of the position.
It can also be solved by adding a pad in the upper and lower plane of the mold and machining a centering slot in the pad.
If the transformation mold is a double-acting drawing die, the centering groove transformation process of the upper die and the blank holder should also be considered to match the need for rapid alignment of the inner and outer slider pads of the double-acting machine tool.
The center bond is machined to a length of 120 mm, hardened to 38-42 HRC, and locked with countersunk bolts. The specific requirements are shown in Figure 2.
Figure 2 Key alignment diagram
(2) Modification of the mold platen groove.
The automated wire die clamping device has an automatic fast clamping mode and several points need to be taken into account in the modification：
- The space structure of the mold near the platen groove needs to avoid the maximum size of the clamp, while leaving a certain space to ensure that the clamp can freely enter and exit without interference;
- The depth of the platen groove shall be the same as the thickness of the clamping device.
- The conductor surface of the upper die clamp needs to be machined to ensure that the conductor is in place.
In the actual transformation, the transformation of the mold platen groove may not find a suitable space position.
It is necessary to mill the ribs and increase the installation space, which will inevitably affect the strength of the mold.
At this time, it is necessary to comprehensively consider the size of the impact according to the specific structure of the mold, and add auxiliary strengthening measures, such as adding an overall mold backing plate.
Figure 3 Schematic diagram of each station
(3) Change of mold F direction.
According to the different automatic manipulators of the stamping line, the direction of the in and out of the mold will change, which is related to the different rotation angle of the stroke of the manipulator.
Therefore, it needs to be considered in the mold transformation to change the original mark of the mold to prevent the wrong direction of the mold when producing.
In this case, the automatic line is a five-station machine, the first of which is a double-motion machine, so there is a need to turn the workpiece between OP10 and OP20 (180 degrees around the Y-axis), and two robots need to be set up to dock the feed.
The entire line is equipped with 6-axis robots, each robot will rotate 180 degrees around the Z-axis during workpiece transfer, so the F-direction of the OP30 and OP50 molds need to be changed during mold modification, that is, the original inlet and outlet direction need to be reversed, as shown in Figure 3.
After changing the F direction, you have to pay attention to the corresponding electrical circuit connector, and also need to adjust to the side near the machine tool air source and power supply.
Mold positioning method modification
The positioning of the automated mold requires not only accurate positioning of the workpiece, but also a reliable guiding function to ensure that the robot can automatically find the alignment when the material is discharged and ensure the consistency of the spatial position when the workpiece is ejected.
This is why positioning bars need to be installed in the automation retrofit.
The positioning rod needs to be compactly arranged, the height should be moderate, the upper half has a guide R angle with the angle between 35 ° and 45 °.
Automatic electrical modification of molds
Electrical transformation needs to add signal detection and transmission functions on the mold, and sensors and aviation plugs need to be installed in the transformation.
(1) Selection of sensor installation location.
Try to choose a diagonal position in the mold, as far apart from each other as possible.
Try to use the weight-reducing holes in the original mold structure for the signal line routing.
The original gas passage through the hole, there is really no suitable place to slot, pay attention to the wiring can not interfere with the waste slot.
The OP10 sensor uses standard parts, and the feed detection switch is shown in Figure 4.
Installed at the diagonal position of the two adjacent sides of the blank, as far as possible, in order to accurately detect whether the blank is placed in place.
Proximity switches are selected after OP20, as shown in Figure 5. It is generally arranged at the lowest part of the part and under the non-hollow plane of the workpiece.
The mounting bracket can use a steel plate no less than 2.3mm thick, meanwhile, the installation must be solid and reliable.
Figure 4 Feeding detection switch
Figure 5 Proximity switch
(2) Requirements for the number of sensors.
- When there is only one part in a pair of molds, please arrange at least 2 sensors.
- When there are two parts in a die (pulling part, double-die part, etc.), it is determined by the situation.
- If the two pieces have not been separated, please arrange at least 2 sensors and make sure there is 1 on each piece.
- If the two pieces have been separated, at least 4 sensors need to be arranged, 2 on each part.
⑶Installation place of aviation plug.
The tool is connected to the machine cable via an aerial plug for the purpose of identifying the tool and part.
Choose different aviation sockets according to the different power supplies provided by the press itself.
The installation position is placed on the side of the lower mold base near the power interface of the machine tool.
Similar to the pneumatic interface of the mold, the mold body cannot be protruded. Prevent bump damage during lifting and storage.
Disposal of mold waste
The problem of mold waste discharge is a major difficulty in the automation transformation.
Once the waste of the automatic production process is not smooth, it will not be discharged outside the machine table after the accumulation, and it needs a temporary shutdown for manual intervention.
This can affect production schedules and, in severe cases, damage parts and molds causing production accidents.
Several ways to improve waste discharge are described below.
(1) Modification of scrap skateboards to assist in discharge.
1) Increase the tilt angle of the waste skateboard. The angle of inclination is as large as possible under the conditions allowed by the structure of the mold, generally more than 25 degrees to ensure that the scrap will slide smoothly under the weight.
2) Add a secondary skateboard. Some of the mold scrap slides smoothly out of the mold, but not out onto the machine table. At this point consider adding a secondary skateboard, which generally requires an angle greater than 20 degrees.
3) Add an auxiliary slide mechanism at the skateboard. Replace the stencil, for example, to reduce the coefficient of friction of the slide. Add rollers, round steel bars, balls, etc. (see in Figure 6).
Figure 6 Roller-assisted discharge example diagram
(2) Add a poppet pin to assist in unloading.
(3) Forced discharge by using cylinders (Figure 7).
(4) Forced discharge by using barbs (use with caution, it’s not easy to control the direction of ejection of waste).
(5) Forced discharge by using an electric belt machine (Figure 8).
Figure 7 Example of forced discharge of a cylinder
Figure 8 Example of forced discharge from a belt machine
(6) Adopt vibration-assisted discharge. A vibration device is installed under the waste skateboard to reduce friction through vibration and accelerate the downward discharge of waste.
Automated modification of molds is different from mold making. Modified molds are those that implement changes to already formed molds, and the mold structure is not as flexible as the new design manufacturing.
There are a number of conditions that restrict the modification of the mold, and the original strength and service life of the mold must not be compromised as much as possible.
In terms of schedule, the transformation of the mold is normal production and sales of the model, the schedule requirements are relatively tight, the need to consider in advance the transformation cycle and in the system of construction and storage, can not affect the normal production supply.
Mold remodeling is difficult and risky, but it also brings great benefits.
The successful transformation of a pair of molds can save the company the cost of designing and manufacturing new molds.
In this article, the case project completed a total of 224 old mold automation transformation, if converted into new mold manufacturing costs will be a huge expense.
Therefore, the automatic transformation of old molds is of great significance to stamping companies in terms of function, duration and cost.