WHEN TWO TURRETS ARE NOT ENOUGH

Whether twenty to thirty years ago or today, successful milling and turning operations have always demanded a close examination of processes that will yield optimal productivity, profitability and part quality. However, while these factors were just as important in the past, today the tools, technology and global competitive environment are very different.

Historically, every shop had about the same level of technology ? generally a lathe, vertical mill and grinder. To stay ahead of the competition, job shop owners and manufacturing engineers needed to be more creative with the equipment than the next shop.

Today it is the advancements in technology that keep shops ahead of the competition. Multitasking machines are a great example. Multitasking became a ?buzz word? about fifteen years ago even though the old cam driven screw machines were actually doing multitasking back in the 1800s. They were accomplishing this mechanically vs. electronically, applying two or three tools in the cut.

MULTITASKING ADVANCES
Machine tool builders started making CNC lathes with back working spindles. This allowed the back side of a part to be completed on one machine. Some builders began making true opposing twin spindles with two turrets and milling capability. The turrets had 12 stations with six stations that could mill with at about two hp or three hp.

These platforms allowed manufacturers to reduce cycle time by as much as 50 percent and give greater quality with less handling of the work piece. Complete parts could be produced in one machine. This twin spindle and two turret configuration became popular because it enabled manufacturers to increase production and reduce cost.

In just a few short years builders were adding a Y-axis to this platform. The Y-axis significantly increased productivity by allowing shops to work on one machine to produce more complex parts with features that were not on centerline.

The next significant change occurred because U.S. manufacturing became part of the global economy and had to compete with countries like China, Mexico, India, Turkey and others. The cost of goods sold in these other countries was lower than the U.S. because labor is considerably less expensive. Manufacturers in the U.S. simply could not compete solely against a labor rate which may be as low as 50 cents to $2.00 an hour.

American manufacturers started to see a lot of work going to other countries. Many of the high volume products in manufacturing jobs were given to the lowest bidder. In some cases, the cost of raw material in the U.S. was more than another country?s finished product. This left the U.S. with only low volume, high quality products to be produced here.

Twin spindle, twin turrets multitasking machines were good technology for some applications, but short run production jobs presented a challenge in keeping costs low enough to be profitable. Costs were greater because there was a long setup time on short runs.

In response, the U.S. needed advancements in multitasking technology to address the changing manufacturing environment. Machine tool builders rose to the challenge by delivering a twin spindle with a B-axis tool spindle, replacing the 12-station turret. This is essentially a turning machine with a tool spindle like a machining center. The tool spindle offers good 10 hp, 15 hp and 20 hp, the ability to change tools like a vertical mill, and a Y-axis capability.

This technology also added the tool magazine to the machine, allowing for 40, 60, 80, 100 or more tools, a design of multitasking that reduces setup time because the tools stay resident in the tool magazine and do not need to be removed. Complex parts can be machined complete, including intricate angle features, because a B-axis tool spindle can change to any angle as easily as a new program position.

Although this technology did reduce the setup time, with only one B-axis tool spindle the true multitasking advantage of maximizing with two tools in the cut was lost. Cycle times were actually increasing. To address this, a lower turret was introduced. Some builders even have two lower turrets, and other machines use lower turrets that have milling and a Y-axis.

The lower turret technology made it possible to reduce cycle and setup times when manufacturing small lots of complex parts. Many complex defense components and intricate medical products are now manufactured very effectively with this multitasking technology. Today, some manufacturing is coming back to the U.S. Many U.S. manufacturers are opting to use American labor because they have had quality issues when outsourcing to other countries. Also, the cost of shipping goods has been steadily rising.

THREE TURRETS, TREMENDOUS EFFICIENCY
However, U.S. manufacturers need to reduce costs even more to increase productivity and keep the work here. Advancements in multitasking lathe technology can offer significant benefits. Machine tools builders now offer turning systems with a twin spindle (20 to 30 hp) and three turrets, with all turrets Y-axis capable. The three turrets provide 36 to 72 tool stations capable of 10 hp milling at 40 Nm torque on all stations. This current technology allows production of a family of parts with complex features. Using three tools simultaneously in the cut can produce dramatic cycle time reductions. Since the bar stock actually becomes the fixture, no additional fixtures are necessary to produce complex shapes with tight geometric tolerances.

An example of this was with a gun manufacturer who was producing a gun bolt for their lever action rifle. The volume was 40,000 parts per year and there were three different calibers: 300 Win, Mag, and 338 Win. They used nine operations to complete the part. All of the operations were a single part flow and change over to other sizes was time consuming. The labor and scrap rate was high. They were losing sales because they could not produce parts fast enough. By putting the process on a twin spindle, three turret, 2-Y axis multitasking lathe, a three turret configuration was used because of the number of tools required (31).

The result? The part was machined complete from bar stock in a single machine with no changeovers in seven minutes. One machine provided a full production solution. Both short and long production runs can be made with great efficiency because no setup time is required. The three turrets with multiple tools resident means no tool changes are needed ? the operators can change the bar size or workholding, call up a new program and start making the part.

Today there have also been big improvements in the manufacturing of the milling heads used on these machines. The manufacturers are using better bearings and even using four bearings instead of three. Some are using Timken roller bearings for greater rigidity. They have high pressure coolant-thru capability and are offering quick change systems as well.

Multitasking now offers many benefits, the best being process time or cycle time to produce a complete part. Even with complex parts a mill/turn lathe has many advantages. With all the different machine configurations of two turrets, three turrets, three turrets with Y-axis or a B-axis tool changing machine, the possibilities are endless.
This does not mean that a horizontal machine or a 5-axis milling machine can be replaced with a mill/turn lathe. However, when it comes to productivity and profitability, multitasking is hard to beat. So how do you know when to look at a mill/turn process?

The simple answer is any part with turning, drilling or boring, OD or ID threads and a few mill features, such as a square or hex, even a bolt hole pattern. This is a very basic part configuration. There is arguably no better way to produce those types of parts than on a multitasking machine.

What about thinking out of the box? Let?s look at a hypothetical example. Say you need to produce 20,000 pcs/year of a custom hydraulic manifold block. The part is 303 stainless steel, 7/8 in thick x 1.350 in wide x 4.100 in long. There are 2¼-18 NPT holes on each side (a total of eight) and a ½ in hole through the center of the 4.100 length. There is a special round boss on the two ends with an O-ring groove and a ¼-20 bolt hole pattern for mounting. This description sounds like a good horizontal machining application. However, it could be made in a multitasking turning center. For comparison purposes, the two machining processes are hypothetically illustrated in Table 1.

The multitasking process gives a faster cycle time due to more tools in the cut simultaneously. You would need to run the horizontal a full second shift to meet your production needs. The tooling cost should be about the same for either process. This is just a rough example, but the cost savings in productivity and cost-per-piece can make thinking out of the box very profitable and make you more competitive.

To maximize profits even further, manufacturers can reach for a ?lights out? unattended operation to make manufacturing costs even lower and profit higher by using simple automation, such as magazine barfeeders, multi pallet machines and robotics. Unattended running is much more feasible today. The machine tool manufacturers are supplying software features like tool load monitoring and tool life management to make ?lights out? running highly successful.

TIPS FOR IMPLEMENTATION
When a shop first decides it would like to implement multitasking technology there are some basic helpful guidelines to follow:

Choose the Right Personnel

Selecting the appropriate operator/engineer to execute the multitasking machining process is critical for success. The multitasking process may well be a new manufacturing method for an organization and their personnel, who may be accustomed to using more than one system to complete a part. The right personnel will be capable of following a different strategy to machine a complete part on one machine. This will be different, but not difficult.

Changing the Approach to Your Part Manufacturing
The most important element of the multitasking process to address is the transfer of the part to the second spindle. As with most current processes, the operator should ascertain whether there are good features to use for the geometric tolerance or the drawing. For example, look at what features must be done on the same side to hold the print dimensions. With a multi-machine process, one operation is generally reviewed at a time. With multitasking, the whole part must be examined.

Software

Most likely a completely new or upgrade to your current CAM system will be required for a multitasking operation. Software has been developed to utilize the codes that builders were inventing to control the process. Most builders use Wait codes (M100-M199) that synchronize the two programs (Left and Right spindles). When a wait code is commanded by one control, the control hangs up (wait) until a matching wait code is commanded in the opposite control. They are used to avoid interference between the two programs, such as crossing over from one spindle to the other or conflicting turrets between the two while working on the same spindle. With the programming software you can utilize the wait codes to optimize the process and verify that there is time to add in a second operation while another is in process ? again, multitasking. Good levels of simulation and post process capabilities are now available. Most viable CAM systems produce a good part the first time.

A Quality Machine Tool

Just like many things today, all machine tools are not created equal. Proper research is required before a purchase is made. Ensure that the machine offers true multitasking. This includes putting two or three tools in the cut simultaneously. It is a good idea to see a machining demonstration using a familiar sample part because there are a number of mill/turn machines that may have impediments that prevent full multitasking for your application. If you cannot put two tools in the cut, then you are not multitasking. This means cutting on the left and right spindles simultaneously, not just two tools on one spindle. Otherwise you will not obtain the cycle time reduction that is so critical in multitasking. Remember, seeing is believing. This is an important investment.

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Richard Parenteau is the director of applications development and Nakamura-Tome product manager at Methods Machine Tools, Inc., 65 Union Avenue, PO Box 382, Sudbury, MA 01776-0003, 978-443-5388, Fax: 978-440-9405, www.methodsmachine.com.