Punching is one of the most important and most common techniques used in processing sheet metals into countless products. Punching involves the creation of a simple or patterned hole in sheet metals for a variety of purposes. The process, which uses a punching press machine, applies force to punch designs right though sheet metals as the material passes under or through the machine press.
Punching may be done to aid assembly, fabrication or design in sheet metal parts. Several factors culminate for the success of a punching operation. The basic factors include the equipment, the hole-making method, the amount of force applied and the dimensions of the sheet metal. Today, we outline the basic guidelines and simple tips to help you get your sheet metal punching right every time.
Start with surface preparation
The first step to any sheet metal processing operation starts with the sheet preparation. Activities such as cleaning and degreasing are important to prevent misalignment, obstructions and easy maneuverability of the sheet metal during the punching operation.
Next, dimension your parts
Dimensioning and measurements are critical aspects for sheet metal punching. Consider dimensional factors like the thickness, length and width of the sheet metal to determine the best approach for clamping, and choosing what punching method should be used.
Mark the center
Punching is a very positional operation that requires an accurate identification of a center as a reference point. Center marking facilitates accurate punching for hole making, drill positioning and pattern spacing. It also helps with knowing how best to clamp the sheet metal workpiece and prevent deflection. Be sure to mark the sheet center, center of the punch pattern and center of the individual drills to be used properly to line up in x, y and other rotational axes.
Secure the sheet metal
Use a clamp to secure the sheet metal workpiece firmly and stably. Clamp the edge of the sheets to allow accurate punching or drilling to take place without any movements that can derail the punch from missing the mark. Before you begin the punching, try to sway to sheet for any motion. Should you experience any twisting, sliding or slipping between the sheet metal and the clamp, re-check the clamping force or use masking tapes to secure the sheet even more. This will help to prevent errors or damages such as tearing during the punching operation.
Use the right tools
There are several drills and punch equipment that are applicable to making a variety of hole patterns in sheet metals. The ideal choice of tool largely depends on the thickness of the sheet metal and the type of hole to be made. Depending on the desired results, you can choose from twist drills, hole saws, punch presses, portable hand punches and stepped drill bits.
Use appropriate clearances
Factor in the material being worked to plan the clearance between the punch and die. The right amount of clearance will ensure that the punching is done to accuracy. Material like stainless steel will demand up to 20 percent clearance while copper may demand somewhere between 12 and 15 percent.
Keep tools sharp
As your punch and tool see persistent usage, their edges may become blunt and round. Blunt tools will require more force to push through the sheet metal. It also creates larger burrs as their cutting edge have been lost. Regrind and sharpen your tools occasionally to help their efficacy, and ensure that their edge radii never exceed 0.004 inches.
Lubricate and use coated tools
Like almost all manufacturing process, friction is generated during punching. Using lubricants can help you prevent heat buildup and galling on the punch which in turn causes tool dullness and reduced clearance. To prevent this, lubricate the punch and/or lubricate the sheet.
Coated tools may also be used to reduce friction and wear, tools coated with titanium nitride or titanium carbon-nitride can also help reduce galling by keeping the temperature down and mitigating heat build-up.
Consider the material
Another way to prevent galling is to match the tool to the material being processed. Use tougher punches for sheet metal that are generally harder to process, and consider wear-resistant steel punches for materials that are likelier to be abrasive. Generally, matching the tool to the material is a strategy that always makes punching easier and produces better results.
Lastly, if your punching requirements are far more stringent or complex that every day jobs, consider partnering with a supplier with automated punching capabilities. Here, a machine that features a computer-aided design is used along with specific instructions to automate the punching process. Automated punching always delivers on accuracy, precision and productivity.
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