How parts are processed is the key to reducing cycle times, especially when using Swiss-type and turn-mill machines. The goal when running production on these machines is to get as many completed parts off the machines as quickly as possible. And the secret to doing that is taking a systems approach to create a continuous flow from part pick up to part drop and, by doing so, reduce cycle times. A few-second reduction in cycle time translates to huge cost savings for shops cranking out thousands and thousands of parts.
A systems approach to gain continuous part flow starts with the part’s features. These features will determine what machine capabilities are needed, how to go about programming the part, and the type of tooling required.
Machine capabilities must match necessary part operations. However, shops need to justify the expenditure of a more complex machine by the volume of parts to be produced. The reason to purchase a machine with only the necessary capabilities is that by the time a shop adds tooling and other ancillary equipment, the price tag for a Swiss-type machine can be around $300,000.
The more complex a machine, the more capabilities they provide and the more involved programming can be. Shops will need fully experienced programmers.
Most programmers, after some training classes, can get quickly up to speed and program and run simple parts. The more complex parts, on the other hand, will require extensive training paired with lots of experience. CAM software packages can help, but programmers still have to have a complete understanding of the Swiss-type machining concept to successfully program them.
Identify the Operations
When it comes to actual part-machining operations in a systems approach, John Dotday, industry and applications specialist—medical and drilling at Sandvik Coromant, suggests that once part features are identified, they can be grouped into operations such as boring, drilling, threading and so on.
He then recommends that shops first machine all a part’s internal or ID features prior to doing its OD features. This includes completing all the internal drilling, boring, and threading before turning the part’s OD to size. The reason being that once a part’s OD is turned to size, the part loses rigidity and can not be pulled back into the machine’s guide bushing to provide steady holding for internal operations.
If a machine has a subspindle, Mr. Dotday advises shops to do as much of the backworking as possible on that spindle. Doing so frees up time on the machine’s main spindle for simultaneously working on other part features, which reduces cycle times.
As part of a systems approach, tooling is one of the most effective ways to achieve continuous part flow and to reduce cycle times. What tooling a shop chooses is, again, based on part features. However, there are tooling attachments and quick-change-type systems that shops should be aware of to improve continuous part flow.
Optimize Tooling Stations
Typically to increase part flow, shops load machine tooling stations with generic tools such as turning tools, threading tools, and grooving tools used for most jobs. For example, 99 percent of the time, tool station 1 will be designated with a cutoff tool. This station will also be used to locate barstock as it feeds into the machine. And depending on the machine, shops will always keep five to seven commonly used tools in machine gang plates.
While always keeping certain tooling in a machine’s gang plate streamlines part flow, changing these tools out when they break or wear can severely hinder continuous part flow. By incorporating quick-change tooling systems as part of a systems approach, shops make tooling change-outs faster and reduce the amount of time machines sit idle.
However, Mr. Dotday recommends that whatever type of tooling or tooling systems best fit the application, shops should make that decision at the time they purchase a machine. Too often, shops will simply purchase standard tooling for a machine and decide down the road to add a special tooling system or quick-change system that uses its own special components and not the shop’s existing tooling. In essence, they end up paying for tooling twice for the same machine.
Think About Quick-Change
One such quick-change system is the Sandvik Coromant Quick Start (QS) tooling system for specific machine model gang plates. This system is typically a two-piece tool—one piece is the cutting edge side, and the other is the backside, or the stop.
The system significantly reduces downtime and improves productivity. Insert indexing times are reduced by 2 minutes, and diameters can be machined multiple times without having to change the machine’s settings.
Because the system is designed for easy operation and use, a single screw controls clamping and unclamping capabilities. The system also features spring-loaded wedges, which secure short holders in place and eliminate cumbersome handling. The QS system’s insert edge position is automatically set up by contact between the short holder and the stop and does not require adjustments.
To use the system, shops simply remove a machine’s wedges and replace them with QS wedges. There’s no need to remove the machine’s gang plate. Shops then slide in the tool and toolholder, snug them down and take them to the program start location to set the offsets. Once this is complete, the stop is slid in and up against the back of the toolholder, which is then tightened.
Mr. Dotday says using quick-change tooling systems, such as the QS, eliminates a lot of the time spent changing inserts, especially when cutting tough-to-machine materials. Plus additional holders can be set upon a bench while the machine is running and be ready for the next change.
What makes the QS system so fast is that only the toolholder itself is removed. With conventional systems, the whole tool has to be removed, inserts changed, tool re-installed, and offsets reset.
For a tool change-out on the QS system, shops simply rotate the QS wedge screw about 180 degrees at the bottom, remove the tool, change the insert, and re-install the tool back up against the preset stop. The stop accurately locates the tool, so there’s no need to reset offsets saving valuable time.
Longer Cutter Life
Obviously, the longer a cutter lasts, the less frequent change outs are required, and the fewer the interrup-tions to continuous part flow. On Swiss-type mach-ines, cutter life is an important key to productivity.
Most shops strive to run machines a full shift without having to change over any tooling. Today’s insert technology, such as micro grain carbide inserts with PVD coatings, can extend tool life and help shops meet this goal, especially for exotic materials.
For one of Mr. Dotday’s customers, a change in insert type helped reduce a 3.8-minute part cycle time down to 2 minutes and 12 seconds. First, he evaluated the shop’s process, starting with the longest operation and working backwards to the start point. By changing to inserts that could be run faster with longer and consistent tool life, the shop was able to eliminate some of the part processes and reduce overall part cycle time.
“To economize tooling for Swiss-type machines, shops should evaluate the types of inserts they currently use and try to spec out the tooling needed based on those inserts,” Mr. Dotday says. “Shops using a lot of negative inserts, for example, might want to switch to positive ones because those place less tool pressure on parts. And smaller parts will require different tooling, such as ER collets for rotating tools.”
Lot Sizes and Machine Type
The systems approach with turn-mill and multitasking machines is based on production lot sizes. If a shop changes setups a few times a day, as opposed to maybe once a month, they can benefit from incorporating quick-change tooling technology. However, as with all tooling systems, the decision should be made at the time of machine purchase or run the risk of paying for tooling twice.
“In the systems approach, tooling needs must be part of the machine purchasing decision,” explains Jim Grimes, product manager for machine integration at Sandvik Coromant. “Most shops will opt for standard stick tooling, for example, and later down the road realize they want to incorporate a quick-change system to reduce setup times. The only problem is that those standard tools cannot be used with the quick-change system.”
Quick-change tooling systems, such as Sandvik’s Capto System, not only apply to stick tooling on turn-mill and multitasking machines, but also to live tooling. A lot of today’s machine tools come equipped with Capto couplings for incorporating the quick-change system.
Multitasking machines often perform turning operations using static tools in their main spindles that are locked in place. This puts a completely different rigidity requirement on the tooling coupling, and Grimes says standard V-flange holders are not really designed for handling such static operations. It generally would require a special V-flange tool.
“Shops can’t do both static and rotating operations with the old ‘stand-by’ tooling systems and expect to maintain a good continuous part flow,” Mr. Grimes points out. “On the plus side, Capto is on about 60 percent of today’s multitasking machines. It is truly a universal toolholding system, covering all metalcutting operations. Self-centering and balanced by design, the system’s polygon coupling enables it to operate in any situation from low to high speed machines without changing the properties of the balanced spindle.” In addition, the tapered polygon design provides the necessary torque transmission and accuracy for both rotating and static operations with a clamping repeatability of 80 millionths.
Besides quick-change systems, shops might also consider kitting tools to achieve continuous part flows. These are tools that can be preset for different jobs to avoid having to remove tooling heads from machine turrets when changing over jobs or changing out worn or broken cutters.
In high-production environments, kitting tools change out quicker because redundant heads are used, and insert changes, for example, can be done offline while machines are running. What many shops do is install new inserts and set tool location according to machine wear offsets, so the tool is ready to go when needed.
The goal, according to Mr. Grimes, is to keep as many holders/standard heads in the machine and change only inserts/tools. Shops should then designate a certain amount of holders for OD work and a specific number of them for ID work.
As long as the right amount of holders is in the machine’s turret, shops will not have to change them. Mr. Grimes cited a 12-station turret as an example and says six stations would be for OD work, and the other six for ID work—a combination that would handle most setups.
Both Mr. Dotday and Mr. Grimes agree that an increasing number of shops today, especially those in the aerospace and medical industries, are not so concerned with the cost of tooling if it allows them to achieve their desired results. Basically, the extra cost of tooling is absorbed in the part, especially when machining large volumes of complex parts.