Punching Machine

How a Punch Press Acts Like a Press Brake

Upgraded tools, machines and software have made formation of complex parts more possible than ever.

Some avoid using formation tooling on punching presses, in particular those creating tall shapes like flanges. Avoiding this is well reasoned. Formation through an old mechanical punching press caused troubles, mostly due to handheld adjustment required for tools. Besides, not all formation opportunities were available, as this mechanical machine ran through flywheels and no ways were provided to hold the ram downwards.

Situations when tooling pulls materials up at the return strokes occurred quite often. This resulted in the failure to gain the desired precise forms. The idea underlying the molding tools was (and remains) really nice, since they eliminate secondary molding operations that demand additional costs. Yet, as soon as your tooling crashes permanently during the main punch process, many of these savings become insensible.

Punch machine designs as well as their tooling have achieved a lot more precision during these years. The hydraulic system of punching presses allow controlling the tool positioning and programming hovering heights needed for different formations. Since punching presses are not required any longer to complete the full backstroke, formation of complex shapes becomes more reliable whether through wheel, hinge or bend tools. (Fig.1) For example, a punching press descends the wheel tooling to its precise positioning demanded for flange formation, then using a rolling tool you may form flares at a hole or in other areas in accordance with accurate heights needed. 

Fig. 1

The shift from a mechanical punch to the hydraulic one happened not long ago, and the latest innovation has solved some problems. One is related to programming, the next relates to the formation of high shapes like 1-inch or 2-inch flanges. Nowadays it is possible to perform such bends in sheets, that previously could be produced only by press brakes.

The Latest Designs of Punching Presses    

Formation on the traditional punching presses requires 0.984-inch clearance. Some portion of this area is occupied by the forming mold, that brings the sheet up a little, at this point you gain the sheet thickness. Certain tooling allows using considerable portions of this gap. Mostly, reliable formation is performed in an area that is just 50 % of the entire clearance minus the thickness of the materials. It isn`t that much.

Upgraded punching presses offer a clearance taking the formation into consideration. Particular designs produce up to three-inch formation area between the bottom and top punches. It will allow you to significantly form and bend, for example, flanges up to three inches in height. In case the flanges get bent to a level of no more than 90 degrees, the dimensional features of the flanges might be much longer. This press is not featured with the conventional turret set-up, but instead use the so-called tool change design. In standard turret designs, sheets extend from the upper turret to the bottom one. This makes changing of tools rather fast. The main motive of turret invention was this.

However, this design offers limited area, and because of this, troubles concerning partial intervention may arise. 

In case of tool-change punch, the bottom carousel is placed under the brushing desk. Dies appear and disappear through the die channel in the process of each operation. This makes it possible for a die to make movements to the down and off the way. Due to this a range of formation tasks can be carried out. For example, formation of louvers includes high lower dies, capable of scratching materials while moving about the table. The tool-change punch can prevent all this as it makes die move downwards and off the way from hit to hit.

Operation of Punch-Press Bend Tooling

Because of this a lot more new formation opportunities become possible. Besides a rib, a louver or some other shorter shapes, you can form a high flange, commonly formed through press brakes. (Fig. 2) Bend punches and dies in the punching presses are a crossbred of panel benders and press brakes, that combine particular features. The punching press is like a small clamping tool upon the panel bend machine and the dies are of V shape like that of press-brake dies. (Fig. 3) 

Fig. 2
Fig. 3

Dies are a little like a pac-man facing up, which revolves in the bending process. In the result of this spin work pieces get folded to the fixed top punch. Bending angles depend on the die spin degree. (Fig. 4) V-shaped dies determine the accessible radius. This is defined when tools are ordered at the manufacturers. In case you want to reach particular radii, for example, for bending with a deep radius, the die is ​​rotated by a defined degree to raise the sheet as the part gradually makes movements forward. This is a bump bend, punching press style.

Fig. 4

The tolerance is excessively tough, both in terms of the accuracy of the machine position and the tooling processing precision, just like the tolerance accessible for upgraded press brakes carrying precision tools. A change in thickness may be made by a press operator. For example, a series of materials may have less thickness tolerances, the next might have more. Say 0.055 inch for one and 0.061 inch for the other. Bending angles can be different because of this. Though if material thicknesses are checked by operators and necessary changes of parameters are made, the machine will surely consider it. Changes about parameters (commonly made in G06 line) defines the limit that the ram moves prior to operating.

Not just the three-inch height constraint, but some another limitations have to be considered as well. Not like press brakes, punching presses cannot turn the parts over, thus troubles can occur because of positive and negative bending alike. In addition, bending angles have a 90-degree or smaller limitation, sharp angles exceeding 90 degrees are commonly impractical (it depends on the tool available for you). Due to tonnage restrictions, materials can have this thickness. This can be different depended on the punching presses and tools. Yet, most commonly it can be no more than 0.118 inch.

Programming Strategics

While programming with punching presses, the option is more than one. Commonly, the formation succession is programmed at the point that will not allow interference with other parts. This shows that you form closer to the end of the punch sequence of the socket when many or all of the flat punches are accomplished.

This is when you can realize bending of the entirety of flanges on a piece right away. Then the profile can be cut. Tabs are left linked with the socket to make parts stable. Next, flanges are bent and tabs get cut through the final punch. In the next step parts get released and glide down the channel. This option works best in case your aim is to remove already shaped parts off the socket quickly avoiding any tool collision.

Otherwise, profiles might be punched (except for tab materials) upon several parts, for instance, on all parts in the same row. After bending, all these are sent into the channel with the last punches cutting tabs. The option mentioned minimizes the extent of tooling change as well as the cycling duration. Still, this option will work only in case the flange and tools do not interfere with each other.

Each tab provides stability for parts in the bend process. The shapes of flanges determine the exact place, width and number of tabs. Certain parts can require just a few or one tab at the plane space of parts. In other cases bends can lead to tab breakage. It will be helpful in the bump bend. In a succession like this, micro-tabs that hold parts in their place break. When the final punch is completed, parts break and slide into the channel. 

While programming, consider the way that a part slides into the channel. For instance, when big, heavy parts featured with tall flanges slide into the channel improperly, they can cause changes in bending angles as soon as they land, or they might change bending angles of already shaped pieces if they make their landing with a high strength. Programming the necessary changes will help you to cope with this troublesome situation. 

Software Will Make a Difference

Manual programming of all the necessary changes offers complicacy and consumes much time. Many details have to be considered, such as the rotation of bending tools (tooling kit revolves at 360 degrees to get the bending lines aligned in accordance with programming), the positioning and succession of the process to escape interference, the breadth of the bend tooling being used, dependent on the tooling available in the inventory of your workshop, along with all this, the bending lengths required. If your task is more complicated, manual programming might not provide efficiency. Flange formation will take considerably shorter on press brakes.

At this point the last part of the tickler plays its role: the software automates the punching establishment and bending succession. Using this software makes it possible to transfer three-dimensional models of parts onto the punching presses. It can deploy parts suggesting options of punching and bending depended on the accessible tooling. The stand-alone programming performs the same way as that of the bending program on a press brake. It identifies each point of interfering, the rotation way of the tooling and the suitable succession. Programmers are free to accept the recommendations offered by the software or make manual configuration to match them with their requirements. 

Advanced Options, High Bandwidth

In addition to the weld operation, bending is one of the most common bottle-necks in a factory workshop, thus, reduction or elimination of bending operations is so important. Changing designs suitable for the formation on punching presses, whether they be short flanges, various bending locations or others, drastically promotes reducing costs of parts. 

Perhaps punching presses are not capable of forming any type of part, but they eliminate bending bottle-necks. Actually they are not press brakes, yet, they are capable of performing like a press brake.

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