The Production Gap Between Punching and Machining #5

By dev 11/07/2023

There are two great technologies available for manufacturing, CNC Punching, and CNC Machining. Both have their unique advantages and disadvantages but there is a gap that lies between which makes it difficult to decide which process to use. This article is intended to help clarify when it is appropriate to use each of these manufacturing processes and propose a new way to address the gap of short production runs in flat material production.

There are many CNC Punching systems available on the market that range in size, speed, and capabilities. Generally, CNC punching is ideal for punching two-dimensional holes, in flat sheet material for high-volume production runs. The main advantage of this process is the short cycle time per part. One of the disadvantages is the lengthy set-up time to configure the equipment with the many punches required to do a job effectively. In some cases, a custom punch or die might also be needed. So here lies the conundrum when you are faced with a short to medium production run. It can take more time to set the equipment up than run your parts. If you factor in the overall time for the job, it makes it difficult to be competitive. What about just machining the part?

CNC machining does offer some advantages over punching, but it also has some distinct disadvantages as well. Typically, the set-up times are quicker with CNC machining. However, the actual cycle time to machine the part over punching can be significantly more. Therefore, it is only viable for a prototype or one-to-two-piece run. Sometimes these parts can be large or nested in larger sheet materials, which makes it difficult to secure to the bed of a CNC machine. This requires larger equipment that can be expensive and take up a lot of floor space. A well-equipped machine shop may have a range of different-sized CNC machines that allows them flexibility but what if you don’t? There is a solution that opens the possibility of using CNC machining for small to medium-sized production runs in flat, large-sized sheet material.

DATRON machining systems offer unique features and advantages over traditional machining offerings that open the possibility to machining short to medium-production runs in flat material and are a viable alternative to punching.

The DATRON gantry style design offers a large work envelope for sheet material with a relatively small footprint. Integrated in the machine is a large, unique vacuum table system that has revolutionized producing these types of flat parts. A permeable card stock laid over top of an ‘air hockey’ like vacuum table, secures your flat material to the machining table. You can machine precision parts right through the sheet material, into the sacrificial card stock, and the vacuum will hold the part without any movement. You can even secure a part about half the size of a dollar bill. No gasketing, no custom fixturing, just lay down your sheet and hit cycle start. When complete, the machine control turns off the vacuum pump, and the operator or robot removes the permeable sheet off the table with all your precision machined parts on top. Now the machine is ready for a new card stock and sheet material.

The DATRON systems are also equipped with a high-speed spindle that allows you to machine at much higher feed rates than traditional machine tools, thus reducing the overall part-cycle time. Still, it is not the speed of punching but when you factor in the set-up time of just a few minutes with the approximately 5x improved cycle time, the overall production time opens the possibility to economically produce small production runs in sheet material. The 40,000 – 60,000 rpm spindles are capable of tool changes that open more flexibility to punching which reduces the need for secondary operations. Features such as thread milling, chamfering edges, and machining pockets can be done at the same time. You can even engrave or serialize your parts.

There is an integrated spray alcohol mist coolant system that simply evaporates, so you are not dealing with any coolant maintenance or part clean-up. The low-viscosity coolant penetrates right at the cutting tip accommodating the full potential of a high-feed rate from the high-frequency, direct drive spindle. The coolant system can also accommodate oil lubricants when working with ferrous materials.
If you are dealing with precise Z depth tolerances such as a chamfered edge or an engraving of an identification number just a few thousand of an inch deep, DATRON has an option for these production challenges. There is a measuring probe that the operator can instruct to quickly take measurements over the entire surface of the sheet and compensate for any surface variants. You simply program your part as if it was mounted perfectly flat and the machine Z-axis will automatically raise and lower to follow the surface contour of the sheet. This can also be helpful when dealing with materials that vary in thickness, such as acrylics and polycarbonate materials.

Deciding to produce your flat sheet material parts by machining also opens other advantages over punching. Unless you have a very sophisticated punching system, you are limited to two-dimensional holes. With machining, you now have the capability to machine recesses, countersunk holes, threaded holes, and 3D-contoured surfaces. Additionally, a punched hold tends to have a slightly folded edge to the opening with chaffing on the edges. Depending on the setup, a nibbled punched hole can also leave jagged edges. Whereas the machined edge is straighter and more pristine. In some cases, the folded edge is acceptable because a component bezel or part is covering the opening. Our customers have found however the precise, machined appearance of their parts helps them win more business.

Both punching and machining technologies are excellent processes and have expertise in the manufacturing world. When a manufacturer is faced with producing a high volume of flat parts from sheet material, punching is a technology well-suited for this requirement. For a one-piece prototype requirement, traditional CNC machining is the viable approach. More and more, however, manufacturers are quoting short-run, high-mix scenarios in flat sheet material parts and face that gap between the technologies. With the DATRON system, there is now an economical and competitive solution for the gap, of short-run production requirements in sheet material.

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