In a broader context, high-speed stamping represents an intricate balance of machinery, technology and processes, harmonized to produce high volumes at breakneck speeds without compromising quality or safety. It’s a testament to advanced engineering and refined operational practices.
A classic instance of high-speed stamping in action can be found in the production of the myriad of tiny components that nestle inside of smartphones. Given the minuscule thickness of the metal strip used, the stroke length is brief, demanding minimal press tonnage and straightforward, lightweight tools. Coupled with enormous production demand, this scenario epitomizes the ideal use case for high-speed stamping.
A Look into the Mechanical Aspects
Let’s look at a few ram-drive mechanisms of typical high-speed stamping presses. Historically, the industry relied heavily on single connecting-rod pushers. However, technological advancements have rendered these less common, giving rise to two-push-rod press designs. Recently, the industry has noticed a shift toward link-motion presses, which employ lever systems to modify ram motion.
Link-motion designs integrate ram adjustment within the main drive system. A mechanical counterbalance is fundamental to this system. Here, the lever movement within the link-motion system is crucial—it modifies ram motion to decelerate at the bottom of the working stroke. This reduces impact force and provides a critical extended timeframe for forming. However, it introduces a challenge: a marked increase in system acceleration, with potential operational implications.
The transversal-shaft system has distinct attributes. Its eccentric drive, combined with the lever system, offers a clear advantage. It ensures harmonic and consistent motion. Additionally, this mechanism efficiently distributes force toward the exterior of the press frame. A notable feature of this system is its ability to separate ram adjustment from the primary drive, although the design inherently restricts the maximum stroke length.
On the other end of the spectrum, longitudinal-system presses embody simplicity and durability. They can manage effectively longer strokes, but their design doesn’t support adjustable-stroke systems and introduces certain operational challenges, such as lateral forces and a tipping moment on the ram.
Understanding the Physics
When these presses operate at peak speeds, the energy dynamics undergo a transformation. Three distinct types of energy are of importance: kinetic, thermal and impact.
Of these, kinetic energy—associated with mass movement—is vital. Its relationship with speed is not linear but exponential. A twofold increase in speed leads to a fourfold increase in energy. If the speed is augmented tenfold, expect kinetic energy to surge one-hundredfold. This stark relationship underscores the pivotal difference between traditional and high-speed stamping. When delving into the kinematics and dynamic forces at play in stamping, it becomes evident that the size and weight of the die introduce considerable complexities. Essentially, a heftier die implies a greater mass in motion, and the forming process is extended over a more protracted distance.
It is crucial to account for the thermal distortion that manifests within the press frame. This heat originates from two primary sources: the drive mechanism and the die itself. As the temperature escalates, it causes an elongation of the press columns, which in turn impacts the depth of punch penetration. Initially, this leads to a marginal reduction in shut height. However, as the frame’s temperature continues its upward trajectory, it counteracts this reduction, leading to an opposite effect. To mitigate these effects, a proactive approach involves consistently monitoring the press-frame temperature and ram penetration. By calibrating the ram-guiding system, we can accommodate thermal expansion. It’s noteworthy that a more substantial ram results in a greater extent of expansion that requires absorption. To further regulate these thermal variations, we deploy chillers or coolers, ensuring that the temperature remains within the desired range. Additionally, heaters can be utilized at the start of a run, serving to elevate the press to an optimal working temperature. This strategy proves pivotal in narrowing the temperature differential as the operation progresses.
Increasing the operational speed results in notable effects. This causes increased accelerations that the press structure experiences at top- and bottom-dead centers (TDC and BDC). Concurrently, we see a spike in impact velocity, contingent on stroke length. The industry guideline is unmistakable: for optimal stamping processes, the shortest stroke always is preferred for two key reasons: curtailing impact velocity and reducing press-frame acceleration.
To provide empirical evidence, Fig. 2 presents data from a test machine, showcasing potential deflections in a press as speed escalates. The red and blue curves, representing presses with 13-mm and 32-mm strokes, explain the discrepancies in forces exerted on the ram drive system and the inherent deflections within the press frame. Both parameters amplify with speed.
Beyond the inherent impact energy, the press imparts vital working energy to the forming process. This energy is quantified in the tonnage rating point, a gauge of the energy on hand when operating at the standard speed. However, many high-speed stamping presses possess the ability to function at fluctuating speeds. Consequently, it’s imperative to evaluate the energy capacity at the diverse operational speeds intended for part formation, and to understand that as speed mounts, the energy allocated to each stroke diminishes. Concurrently, the energy that the press requires to operate surges, resulting in a diminished energy pool for the stamping process at peak speeds. This presents two pivotal stages: one at the lower spectrum, where flywheel energy is scant, and the other at ultra-high speeds, where the energy drain from the press-drive mechanism is accentuated, leading to a dip in the available energy/stroke.
Press Controls and Their Impact
Modern press controls for high-speed operations have evolved significantly. Beyond basic functions such as motor and clutch management, they now offer advanced speed control with closed-loop feedback and precise ram-position adjustments. And, in high-speed stamping operations, specialized safety provisions are mandatory.
The electronic signal indicating crank angle is of major importance. It orchestrates a multitude of functions within the press, necessitating a resolution often less than 1 deg. To put this in perspective, a high-speed press operating at 2000 strokes/min. translates to 12,000 pulses/sec. or 83 msec/pulse.
Another salient feature is the ability to discern diverse signals emanating from the press at varying intervals. This includes sensory input as well as any anomalies or occurrences. The control system stands as a reliable sentinel, notifying us of components crafted below optimal speed or outside of set thresholds. This ensures that such components either are discarded or rerouted, or the system makes on-the-fly adjustments by tweaking parameters, such as press velocity.
In certain instances, metal formers embed a measurement device on the ram, to discern the ram’s position relative to the bolster plate and to subsequently relay signals to the control, prompting process adjustments. Analogous feedback-driven modifications can be initiated based on assessments conducted within the tool. These either can be temperature readings or distance evaluations to perceive any elongation variations attributable to thermal factors.
Further, the press control undertakes the crucial role of supervising and orchestrating a myriad of processes within what often can be a multifaceted forming environment. These meticulous operations encompass tasks such as measuring cylinder pressures, identifying acoustical patterns, and monitoring press tonnage and temperature. Many of these activities recur cyclically—stripper-plate detection is a good example. Post-production, it becomes feasible to examine and confirm part quality directly at the press in real time, enabling an immediate stop of the process, if needed, to curtail the production of non-conforming parts.
Building on our understanding of the press’ intricate operations, it’s important to note that the dynamic forces influencing the press also significantly impact the coil feeder. These forces primarily are generated by the indexing of material or components into the die; feed accuracy varies in tandem with the press and feed adjustments. The synergy between the press and feed system is undeniable. It’s crucial to recognize that even if both components are of the highest caliber, their peak performance only is achieved through proper installation.
Timing in the feed process is paramount across the entire speed spectrum. Consistency is key, especially when considering the pressure applied to grasp the raw material or the components. In the case of a roll feeder, the upper and lower feed rolls must be operational. When operating at high speeds, minimizing backlash becomes imperative to guarantee precise alignment and optimal performance.
In the domain of high-speed stamping operations, a pressing concern that often surfaces is the sturdiness of synchronization, particularly in the face of power interruptions. Given the intricacies—especially when considering independently regulated devices—it becomes immensely challenging to maintain equilibrium for press lines operating at such elevated velocities.
ecelerating a high-speed press demands more than a singular full stroke to reach a total stop. However, it’s worth noting that the inherent flywheel energy can function as an electronic counterbalance or even as a generator, supplying the requisite power to the servo-feed axis. This ensures a sufficient window to methodically decelerate the entire system without compromising the synchronization between the press and feed line prior to a complete power termination. It’s a standard protocol for controls to be fortified with battery-powered backups, often interconnected with the feed mechanism.
More Than a Technological Upgrade
Within the metal forming industry, a significant transition awaits: the shift from traditional metal-stamping methodologies to the advanced realm of high-speed operations. More than a mere technological upgrade, this transition represents a profound strategic decision with ramifications across the production landscape.
Central to this transition is an understanding of the metal former’s existing operational culture. Decision makers must rigorously assess the organization’s capacity and willingness to adapt. The world of high-speed stamping demands more than just new machinery; it necessitates a wholesale cultural and operational recalibration. There are instances where such initiatives have been undermined, not due to technological inadequacies but because of internal resistance within the production ranks or gaps in decisive leadership.
Success hinges on cohesive strategy formulation and execution. Every stakeholder, from technicians to top-tier executives, must be aligned with the overarching vision. The significant capital required for this transition highlights the necessity of informed, data-driven decisions from senior leadership.
Moreover, the intricate nature of high-speed stamping suggests two critical operational pillars: adaptability and system flexibility. The complex dynamics of these operations require an elevated threshold of automation proficiency.
An often-understated aspect of this transition: the post-press phase of handling the stamped parts and the resultant scrap. This calls for a well-planned and executed strategy to ensure that every phase of the material’s journey is optimized for efficiency and precision. MF
View Glossary of Metalforming Terms
See also: Sangiacomo Presses Americas, LLC
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Wednesday, September 6, 2023