On the CNC Swiss types Z-axis motions are derived from stock moving opposed to the tool.
When comparing the conventional CNC turning to the CNC Swiss-type machining, the Swiss-type machining offers a very different experience.
The programmers and machinists that shift from the one type to the other need to alter the way they think about the machining cycles in numerous ways. Here are a few of these differences:
1. The Negative Becomes A Positive
On the CNC Swiss types Z-axis motions are derived from stock moving opposed to the tool. This particular change has an effect of the programming offset nature. On the conventional lathes stock extends out from the area of a chuck by specified lengths. The face of these parts is Z zero and anything into this part will be Z negative.
In contrast with the Swiss machines the turning tools will be stationary as the stock will advance. The face of these parts is Z zero like conventional lathes but anything beyond these faces will be Z positive. This difference is very important to keep in mind in
association to the Z-axis offsets. This means making drilling pass any deeper or turning the length longer involves a “minus” offset on conventional lathes but will necessitate a “plus” offset on Swiss-types.
2. The Machine In Segments
The order relating to the cuts that occur in a cycle will also change with the Swiss-type. With the conventional lathes it is standard to finish turn and rough turn work when the machines features threads or OD grooves in order to complete a part. This is not the same when it comes to the Swiss types.
This is because the guide bushing length requires that a part will need to be segmented into sections, otherwise the bar-stock could fall-out from the guide-bushing when retracting the stock. The segmenting usually will mean machining a part into sections of around 15 - 40 mm which is standardized guide for the bushing-land area.
3. The Guide bushing Is Very Important
Guide bushing is known as the central part of Swiss type machines and sizing is vital. This means that using guide bushing which is incorrectly sized for the job can result in various concentricity errors. The guide bushing also comes in different types of materials that include Meehanite, steel and carbide sleeved. This means the potential interactions with work piece materials are another very important factor that needs to be considered.
4. Oil Opposed To Water
The majority of the Swiss type machines will use oil for their cutting fluids opposed to water. This means that the lubricity will be greater. The benefits of oil include the freedom from the odor-causing type bacteria growth and to prevent prune-like looking hands caused from
exposure to the water-based coolants on a daily basis.
However, one main downside when compared to water is that oil is not as effective in dissipating heat. This means that Swiss machine cutting can become hot quickly in the area of the work zone. This means that equipping these machines with fire-suppression systems is a necessity if you plan on lights-out manufacturing.
5. Outstanding Machine Cycles
Many new Swiss-type machine users soon change their mind on the benefits of these machines when they complete one part in a single cycle that usually required multiple machines or multiple operations. The conventional type CNC lathes typically feature 3 or 4 axes. While the Swiss types will have 7 or more axes. Viewing the amount or work that can be performed a lot faster with the machine in smaller work zones has amazed many shop personnel who start using these types of machines for the very first time.
6. Deflection Correction
The aim in supporting a work piece with a guide bushing is to do with maintaining precision throughout the process of machining on the work piece.
Physical objects that are subjected to any force will naturally deflect. When it comes to the conventional lathes, when cutting forces have caused a deflection that is too great, the accuracy associated with the cut will in most cases suffer. The accepted rule with conventional lathes is that when parts are turned that have length-to-diameter ratios which are greater than 3:1, a tailstock is required to prevent any excessive deflection. For the ratios that are greater than 6:1 a follow rest or steady rest is required in order to support the center of a part.
If a work piece is held securely on the one end and then pushed sideways on the end that is not supported, the work piece will bend slightly. When pushing with this exact force on longer work pieces the work piece will bend even more. Deflection for the given force will
increase when the cube-of-distance that comes from the support onto the force will be double in length and 8 times this deflection. This means when applying a side force on the end of a 50 mm part it will usually deflect 0.02mm, while the very same force when applied to the end of 100mm part with the exact diameter will result in a 0,2mm deflection.
When it comes to the Swiss machines, the guide-bushing will support a work piece so closely to the necessary tools that deflection caused from cutting forces is actually zero. This means that the user can use heavier cuts while still maintaining the precise dimensions on these parts.