Alongside many other factors, the optimum interaction between tool and press is a crucial and often underestimated factor when it comes to stably functioning production. Unfortunately, this factor generally goes unheeded due to the organizational separation of tool and press maintenance. Responsibility for errors and faults is unclear, and the bigger picture over all interfaces is not considered.
Press table: think elastic!
Often in tool design, one assumes that the press table is rigid and the top and bottom remain in parallel with one another – as in the CAD-System. Yet this is not the case in reality: according to VDI standard 3145, a load case of ¼ nominal force, by ¼ eccentricity of the table width, allows a tilt of the press table by up to 1.9 mm/m! The vertical dislocation with the nominal load can amount to up to 5.5 mm!
Of course, fineblanking presses are built to be significantly more stable than normal punch presses, but this shows what the standards actually would permit.
Nevertheless, the conclusion from these theoretical assumptions should be: The press always behaves elastic to a certain extent and interacts accordingly with the tool via the load and deformation.
If you are aware of this interaction between press and tool and take it into consideration, then maximum capacity and process stability can be achieved.
The insert ring, an interface that shouldn’t be underestimated
The insert ring represents an additional interface between tool and press. It’s basically the foundation upon which the tool and, most importantly, the active elements in the middle of the tool are supported.
Beside the task of supporting the tool, the insert ring has also pressure-pins for the transfer of the counter-holder and vee-ring forces. That means, on one side, that the insert ring must be stable in order to provide support, and on the other it must have holes for the pressure-pins. This is the first contradiction that emerges at this interface.
The other contradiction arise from the situation that, fineblanking is characterized by smooth and perpendicular blanked surfaces. In order to achieve this, in addition to the actual blanking tonnage, counter-holder and vee-ring pressure must also be applied, which increases the overall load on the ram and press frame significantly.
However, the very small clearance is a crucial element of fineblanking, and essential to obtain a tear-free blanked surface. Hence, higher compressive stresses are reached in the blanking zone and thus the force requirement is further increased relative to conventional blanking too. This rises one of the great challenges for fineblanking installations and tools:
extreme forces that lead to deformation vs. very small clearance!
Bending cannot be avoided, since steel is elastic, the 210,000 N/mm2 are by nature. Also important here, keeping in mind that concentrated high forces will always deform the tool somehow, be it for example through deflection, bending or tilting. Only if you take the elastic deformation into account, you can achieve the maximum parts precision and process stability.
In general, we try to counter the bending and tilting by designing a more stable tool or reinforcing the active elements as far as possible. If that reaches its limits, however, then a more stable solution can be achieved with weakening at the right point. With tilting, for example, a one-sided weakness can be countered and thus parallel deflection of a punch achieved.
Stronger isn’t always better!
Looking to the future with the “press control system” interface
If you want to stand out from the competition and overcome the limitations of conventional fineblanking with new tool concepts, then you will also need a press with the necessary functions.
This means, for example, that for the latest tool concepts such as out-of-strip and rotary transfer, you will need a press with additional hydraulics. The advantages of out-of-strip concepts are clear after introduction from the tilting of the press table. Beside the possibility of integrating more steps than in a strip solution, the most convincing point is the option to apply a tool concept with a complete symmetrical arrangement, well balanced across the entire press stroke. Eccentric load, one of the major disruption parameters of stable production, are thus entirely eliminated. In addition, with these two modern tool concepts, it is also possible to incorporate operations such as deburring and subsequent bending operations effectively. This means integration of subsequent operations.
But be aware, what is considered new today will be standard tomorrow. The presses need to meet the standard of tomorrow too and therefore must boast functions such as additional hydraulics as a minimum.
Look to the future, and be ready!
The challenge of kinematics
For tool solutions such as the speed concept, you also need presses that permit precise and synchronous regulation of the counter-holder and vee-ring hydraulics. Rapid and precise proportional valves permit exact reproducibility and finer coordination of the operations. These two elements maximize process stability and capacity too.
Tool concepts that permit high stroke rates also require a correspondingly precise calibrated drive. However, more speed brings new challenges with it. Hence with high stroke rate, suddenly the reaction times and inertia play a role where previously they were irrelevant.
Fineblanking at 200 strokes per minute – today a novelty, tomorrow a standard!
The final interface: parts removing
Analyses with FEINmonitoring show that tool safety is by far the most frequent reason for stoppage of machines, and errors in parts handling are also among the top reasons for interruptions.
Correspondingly, parts and slug handling concepts are necessary, and this facilitates optimum parts creation in the combination of press and tool. One example of this is the removal technology, which is a guarantees for stable processes. With removers, parts and slugs are ejected in a controlled way and the probability of interruptions due to hung-up slugs is significantly reduced. Fixed, in-built removal-arm drives simply coordination for the ram movement.
Controlled removing creates process stability and thus greater OEE!
Those who take the numerous interfaces into account can avoid faults and thus operate more efficiently. Well trained employees and a strong partner that manages the interaction between the press and the tool are a further success factor that needs to be considered. In order to be armed for the future, it’s worth taking a forward-thinking approach to long-term investments in a press – with this in mind: Think elastic, also outside the press table.
Share your experiences: At which interfaces were you already able to optimize or where do you still see potential?
I look forward to your comments.