Hurco Taking advantage of 5-axis machining strategies
Germany – A look at the misinformation that prevents mouldmakers from taking advantage of 5-axis machining strategies to shorten total machining times. By Michael Cope, Senior Applications Engineer from Hurco
Five-axis machining allows the use of shorter tools, enabling you to push faster with increased feed rates. When using simultaneous 5-axis machining for mould work, especially deep-cavity moulds or tall-core moulds, you can make heavier cuts, and Z depths do not present a problem. This yields shorter total machining time.
Simultaneous 5-axis or 5-sided (3+2) machining
Some products require simultaneous movement (true 5-axis) to allow the tool to reach complicated features on the workpiece. However, the majority of parts can be successfully machined by using the two additional rotary axes to position the part at some designated angular orientation and by using a 3-axis tool path to machine the necessary characteristics. Mould work is an instance where a 5-axis machining centre is a worthwhile consideration, especially for deep-cavity moulds or tall-core moulds.
Jason Vawter, general manager of North Vernon, Indiana-based Injection Mold, attests to the true value of employing 5-axis machining for mould manufacture: “The longer we use our 5-axis machining centre, the more applications we uncover. For example, we had a multi-cavity tool with multiple slides per cavity. Each slide had 20-degree-angle holes as well as a 25-degree angle on the back with tapped holes. Prior to our 5-axis machine, machining these would require one setup for each operation on a 3-axis mill and five setups with an hour to an hour-and-a-half on each block. 5-axis machining permitted one setup and 20 minutes for each piece.”
Despite such success, myths and misconceptions regarding 5-axis technology still persist, especially when it comes to its limitations within mould and die work. Before we review some of the more common myths, it’s important to understand the difference between full 5-axis machining and 5-sided machining, in addition to the variety of terminology that is used interchangeably and which has contributed to confusion about the true potential of 5-axis machining.
Simultaneous 5-axis machining uses all five axes at one time. This process is commonly used for manufacturing turbines, impellers, plastic moulds and port surfaces. In 5-sided machining (or 3+2 machining), a 3-axis milling program is executed with the cutting tool locked in a tilted position using the two rotational axes of the 5-axis machine. In this way, the two additional rotary axes are used to position the part at some designated angular orientation. Four Common Myths:
1. You lose rigidity with 5-axis machining
This concern usually involves the swivel-head or articulating-head 5-axis machine, of which there are two types: a head-head configuration with all rotations completed by the head while the table is stationary, and a head-table configuration with a tilting head and a rotating table.
Concern about rigidity is simply due to machine design and the possibility of inadequate clamping to hold the additional two axes in position. In actuality, the B axis will be the least rigid on a swivel-head machine, and this should be a consideration when machining any heavy metal. The trunnion configuration is a more solid design and is preferred for heavy-metal removal.
2. Full 5-axis machining is better than 3+2 machining
For simplicity and increased rigidity, you should use 3+2 machining (also known as 5-sided or positioning) and you will achieve faster cycle times compared to full 5-axis machining (also known as simultaneous 5-axis). With full 5-axis machining, the machine’s movement is limited by the speed of the slowest rotary axis. This isn’t the case with 5-sided or 3+2 machining, because the additional two axes are used for positioning only, which means the linear axes are free to cut at the fastest maximum feed rate allowed by the control.
However, even when you’re using 3-axis toolpath technology, you can still take advantage of the obvious reduction in multiple setups and benefit from many other characteristics associated with 5-axis machining. For example, when using the rotary axes solely to position the part for machining, nothing dictates that the tool axis angle must be perpendicular to the surface being machined. Positioning in a non-perpendicular orientation allows you to cut on the corner radius of a ball- or bull-nose end mill, achieving the desired surface finish and chip load control.
3. A trunnion-style 5-axis machining centre is preferred for mouldmaking over a swivel head 5-axis machine
The type of mould you are manufacturing will dictate which machine is your best option, and every 5-axis machine has its own benefits (see photos previous page). The photo shows a trunnion configuration (also referred to as a table-table configuration), which has both rotary axes contained in the trunnion table itself and a stationary head. This design is a simple progression from standard 3-axis machining, so mouldmakers are typically the most comfortable with the trunnion-style 5-axis machine. The two rotary axes are often used to locate the workpiece into a desired orientation, making it easy to visualize how the machine will position and behave during machining.
Some advantages of trunnion-style 5-axis machines include:
- Larger overall usable work volume. The table tilts and locks into position, and the X, Y and Z axes are allowed their full travel range. A swivel-head machine requires that the overall work envelope be used to accommodate the length of the tool as the head tilts back and forth, and this is magnified when machining with longer tools.
- Better undercut capabilities. The table can tilt farther (at least in one direction) than the swivel-head type of machine, providing greater access to a part’s underside.
- More effective heavy metal removal. The head doesn’t articulate. The trunnion style 5-axis machine design permits the use of geared or belt-driven spindles that provide more torque at lower rpm. The stationary-head design also eliminates the possibility that the head will be pushed out of position while machining, which can occur on swivel-head machines during heavy cuts.
As mentioned previously, an articulating- or swivel-head 5-axis machine can have either a head-head configuration with all rotations completed by the head and a stationary table, or a head-table configuration with a tilting head and a rotating table (see photo previous page). Some benefits of swivel-head-style 5-axis machines include:
- Ability to handle heavier parts. The table doesn’t tilt and the entire weight of the part is transferred directly down through the base of the machine to the floor, making it a very rigid setup for heavier parts.
- Ability to handle larger parts. The table design does not limit the size of the part to one that can be placed between the table risers, as the trunnion-style machine does.
- Ability to use shorter tools. The swivel head allows the use of shorter or more standard-length tooling because all tool rotations occur above the part, whereas on a trunnion-style machine the spindle has to reach out over the tilting table. The closer the table tilts toward 90 degrees, the farther the spindle has to reach.
- Versatility. The head-table design is more versatile than a trunnion- or head-head type of configuration because, in addition to 5-axis machining, the entire table can be used for multiple vise setups, plate work and machining the sixth side of a part (in preparation for a 5-axis setup) in 3-axis mode. A tombstone can also be used on the C-axis table to simulate a horizontal machine setup to enable more parts to be machined in one setup.
4. 5-axis machines break down more often and cost more to repair than 3-axis machines
The reliability of 5-axis machining centres is on par with 3-axis machining centres. As for service, all of the components are the same with the exception of components for the 5-axis trunnion table or the swivel head, which might be a little more expensive to repair and replace. The only additional expense associated with a 5-axis machine is the annual centreline measurement required to retain accuracy, which might be more expensive than the ballbar test on a 3-axis machining centre.
When you prepare to purchase your next machining centre, give serious consideration to adopting 5-axis technology. The incremental increase in costs compared to a 3-axis machine will generally be absorbed quickly by increased efficiency.
* Reprinted with permission from MoldMaking Technology, Gardner Business Media, moldmakingtechnology.com