Punch Nesting Formed Parts
If you are running CNC punch presses or turret punch, you may already be intimately aware of the challenges faced when programming formed features. If not, you may be wondering if creating formed features is a viable option or how it’s done with a CNC punch press.
Either way, today’s discussion is all about cracking open the mystery behind forming features from sheet metal that can only be achieved with CNC punching. Our discussion will roll out along these lines. We’ll first define what formed features are, then look at the issues encountered in programming them, the problems created when the program isn’t done right, and finally, we’ll wrap this up with the solution you may be looking for to this sticky challenge.
What is a Punch Formed Feature?
First a quick definition – for our conversation today, a “formed feature” is any element or attribute given to a finished part or sheet of metal that has depth. This is to distinguish it from conventional punched holes, notches, slits, or separations that only eliminate material from the sheet or separate one sheet into pieces. None of these last punch hits add depth or dimension to the part. Material mass is not moved, molded, or formed. With a formed punch hit mass is moved, molded or extruded.
Examples of Turret Punched Formed Features
It’s not surprising that there are a number of methods to create a formed and get different effects. Here are just a few to provide an overview.
- Louvers – commonly seen in air vents
- Extrusions – forming a flange around a hole in sheet metal
- Countersink holes – for connectors (screws, bolts) to lie flush with the surface
- Counterbore holes – for connectors (screws, bolts) to lie flush with the surface
- Knockouts – for electrical wiring to be run through
- Beads – extended linear recesses
- Hinges / Hinge mounts
- Card edge – for card insertion
- Coining – creating a formed object by fusing two sheets with pressure
- Forming – forcing a relief shape
- Stamping
- Screw holes – for receiving a threaded screw
- Shear buttons – cut guides for easy shearing downstream
As you can see, there are many options to literally build in function to a part through forming features in the metal. Adding in this value to the part or metal can through punching can improve the processing time (eliminating extra downstream processes to add these functions), make the parts easier to use, and improve the part quality and integrity by eliminating extra parts to serve these functions.
Programming Challenges with Turret Punch Formed Features
Programming a turret for normal features without can be challenging in and of itself. Add in this third degree of complexity (width, length, and depth), and we’re in a whole new ball game – indeed, we’ve moved to the major league. Let’s look at some of the challenges a programmer will encounter – or certainly needs to be wary of – when creating part programs that include a depth or formed element.
XY Hit Order
One of the biggest challenges when punching a series of louvers – or any high profile formed feature – is the X, Y hit order. The turret press needs to punch each louver in a bottom to top/bottom to top series to prevent smashing the louvers just punched, the machine or the tool. Programming that order sequence is a priority with louvers.
Tool Clearance
Louvers and some other formed features have fairly tall profiles. The programmer needs to be certain he’s clearing that height when the turret passes overhead. If the turret with the tools including the high station tools isn’t sufficiently elevated to clear the formed feature, again the part, machine, or tool could be damaged.
Turret Configuration
Formed features are typically created with high station dies. That is, the tool has a taller, longer profile than conventional tools to accommodate the depth of the negative image (the formed part). This presents an interesting challenge when configuring the tool turret. The user needs to keep the stations nearest the high station die empty to prevent collateral interference when the high station die is use. You don’t want to accidentally use three tools when you only want to punch with the high station die.
Multi-Hit or Pre-Punch Programming
In the case of a hinge, the part’s metal “fingers” that wrap back and hold the loose hinge are hit multiple times in the same location to achieve the 3D effect from a 2D sheet. In the case of a countersink hole the feature is hit repeatedly on center at different depths to achieve the recessed hole for the joiner head to lie in. With an extrusion, the metal is slit with a punch hit first to create the hole, and then a second hit extrudes part of the metal along the edges out of the interior surface to create a flange and a smooth surface. The point is that multiple hits are done in a specific order and in the same location. In all circumstances they require intelligence in the part program to remain on center, be sensitive to the hit order, and be aware of the Z depth when repeating the hits.
Sheet Stability and Sheet Hit Order
Imagine a sheet that requires hundreds of hits – conventional and formed. In what order do those hits need to occur to avoid sheet, part, and tool damage and retain sheet stability? We’ve addressed the former a bit, so we’ll now turn to sheet stability. As you might imagine creating formed parts or features adds additional stress to the sheet’s integrity, simply because you’re bending and stretching the metal and naturally creating weak or stress spots in the sheet. Punching too close to those already stressed spots when completing the nest can and does fracture the parts or cut loose parts that can cause tip ups. The challenge for the turret program is to both plan the punch sequence or punch tool path correctly and include sufficient and adequately sized tabs to retain sheet integrity.
By now you’ve planned your hit sequence to avoid all of the above dangers, programmed the nest, sent it to the machine and you hear this: the sound of the machine punching the clamps. Just as in programming for regular parts, with those that are formed need to be positioned to avoid the clamp area. It’s an easy oversight when you’re watching all of the other dynamics, too.
The Answer to Punching without Pain
The secret to managing all of the above situations is to use intelligent punch nesting software with tool management. You can set the software parameters to best suit your needs – to avoid the clamps, to maintain sheet stability, etc. The software will plan for these events and proactively warn you if there are any potential hazards.
It is possible. There is punch nesting software with the intelligence to manage all of these nuances. The secret to success is in the knowledge base that acts as an encyclopedia of your manufacturing environment – turret stations, tools, clearances, reaches, etc. and builds each nest relying on facts from the “encyclopedia.” You can calibrate the performance to your liking then trust the nesting software to act according to your plan.
Aside from the time and headaches, this degree of automation can save huge percentages in material, but that’s a discussion for another day.
What’s Your Experience?
How has nesting for your CNC turret punch been working for you? Do you manage formed tools? Here’s your opportunity to weigh in on the conversation.
The Alternative
If your current situation isn’t satisfactory, or you think there might be a better alternative, contact us. We’ve been doing automatic punch nesting for decades. We’d be happy to share our insights and work with you on a project. Contact Optimation.
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