Making Transfer Machines More Flexible
Are your lot sizes too big for machining centers but too small for dedicated transfer machines? Here's a solution.
In 1933, Luigi, Piero and Giuseppe Dell’Orto, three brothers who shared a passion for motorbikes and motorcycles, started a company, the Industria Nazionale Carburatori Dell’Orto, in Italy to manufacture motorbike carburetors. The Dell’Orto carburetors were adopted by some of some of Europe’s biggest bike manufacturers, and the company prospered.
Demand for Dell’Orto carburetors increased to the point that, in 1948, the company acquired an equipment manufacturer, Industria Meccanica Applicazioni Speciali (IMAS) (Mariano Comense, Italy), and assigned it the task of developing more efficient machines for machining carburetors. The result was a transfer machine capable of mass producing machined carburetors accurately and quickly.
In the 1960s, the company diversified into automobile carburetors, producing them for such prestigious companies as Alfa Romeo, Lotus, Ford and others. However, in the 1980s and ’90s, the market started to change. First, the automakers began converting from naturally aspirated engines (engines with carburetors) to engines with fuel injection systems that required new-fangled parts called throttle bodies. Second, purchasing patterns of Dell’Orto’s customers—and the industry as a whole—changed. Instead of buying carburetors and throttle bodies hundreds of thousands at a time as in the past, the vehicle manufacturers moved to a just-in-time mode, placing orders for smaller quantities on a more frequent basis.
The changes created problems for Dell’Orto: The company’s transfer machines were designed and built to produce specific products in very large volumes. Making the changes to the “dedicated” transfer machine that were necessary to produce another product could take months—if they could be made at all—and was tantamount to rebuilding the machine. Dell’Orto simply could not afford to have its machines idled that long. To respond to customers’ just-in-time production needs, the company needed to be able to efficiently produce smaller batches and be able to switch from one product to another without time-consuming setups.
Once more, Dell’Orto turned to its equipment-manufacturer for help. Rising to the challenge, IMAS developed the IMASFlex flexible, CNC, rotary transfer system for medium to high volume production of parts—in relatively small batches.
The IMASFlex (shown below) is an eight-station rotary transfer machining system. Up to seven stations can be equipped with (typically) three-axis CNC machining modules, all controlled by a master programmable logic controller (PLC). An eighth station is for manual or automatic part loading and unloading.
Parts are moved from station to station by a highly accurate, CNC (within 2 arc seconds) indexing table rotating about a vertical centerline. The table is equipped with eight clamping fixtures, each CNC controlled and capable of rotating 360 degrees in 2-degree increments around a horizontal centerline. The rotation of the clamping fixtures permits machining five sides of a part. Typically, the rotation takes place while the table indexes, reducing cycle time. (On earlier dedicated rotary transfer machines, the table index and clamping fixture rotation occur sequentially.)
Operation of the machine is analogous to a multiple-spindle screw machine: Machining takes place in all seven stations simultaneously, and each time that the machine indexes, a fully machined part is produced.
Each machining module offers three linear axes of movement and can perform interpolated machining operations such as contouring and taper threading. Each module has a turret head with four or six spindles. (See photos on page 34 and 37.) The turret head can be mounted for horizontal- or vertical-spindle applications and can be switched from one orientation to the other simply by changing a mounting bracket.
With each machining module equipped with a multi-spindle turret head, the machine provides 28 to 42 cutting tools for machining. Where possible, combination tooling—for example a combination drill, tap and chamfering tool—is used to reduce cycle time and make the most of tooling capacity.
Additional Tooling Flexibility
Providing additional flexibility, the machining module can also be equipped with any of three single-spindle heads for high speed or heavy duty machining. Attachments are also available for angular machining, grooving, recessing, facing and probing. All spindles can be provided with high-pressure, through-spindle coolant.
Dell’Orto operates some stand-alone flexible transfer machines at its plants in Seregno and Cabiate (both near Milan). However, most of the flexible transfer machines are used in two-machine cells (left) that also contain a CMM. Company president Luigi Dell’Orto explains that the large number of machining operations required for carburetors and throttle bodies necessitates machining them in two stages (Op 10 and Op 20). Each cell has one operator who not only loads both machines but also performs part inspections using the CMM.
The cells are used primarily to machine families of parts, with typical run quantities of 10,000 to 30,000 parts. Where part changeovers on the plants’ dedicated transfer machines can take months, changeovers on the flexible transfer machines can be accomplished in minutes to hours. Machining programs for the part families are stored in the individual machining modules’ CNCs and, when needed, tooling changes are quickly made.
Sergio Scotti, executive vice president of IMAS Transfer USA, Inc. (East Dundee, Illinois), the U.S. sales and service operation for IMAS, adds that the flexibility of the machines includes their ability to be automated for unattended operation. As an example, he cites a turnkey installation for a customer that consists of a pre-machining module, used to qualify cast aluminum parts, and a flexible transfer machine used to finish machine the qualified parts. In this cell, a robot, equipped with a vision system, removes a part from a delivery conveyor and loads it, properly oriented, into the pre-machining module, removes the previously machined part, and places it in the load station of the flexible transfer machine. The same robot offloads the finish-machined part from the flexible transfer machine to an exit conveyor. Large run sizes justified the use of automated load/unload for this customer, Mr. Scotti notes.
The flexible transfer machine can also produce batches of several different parts in a single run. It can be programmed to produce a sequence of as many as eight different parts from a family of parts. With this capability, 100 pieces of one part, 200 of another and so on, can be produced from, say, an aluminum extrusion common to the family of parts being machined.
If dedicated transfer lines are the most efficient way to mass produce parts, the machining center is the most efficient way to machine parts in small to medium quantities. When run sizes get into thousands or tens of thousands of parts, shops usually run the job on several machining centers. The machining centers provide a cost-efficient method for machining the parts, and if the customer’s part requirements increase or decrease, an additional machine can be pressed into service or diverted to other jobs.
More To Offer
However, Mr. Scotti argues that, in many cases, the flexible transfer machine has more to offer than a battery of machining centers. “For companies supplying parts to the automobile industry, quality is a paramount consideration,” he stresses. “When several different machines are involved in production of a part, that presents several different opportunities for errors. By contrast, the flexible transfer machine is first and foremost a transfer machine, which means it is designed to run 24/7 without problems.
“On the flexible transfer machine, the part is clamped only once for machining, and it is precisely transferred from one machining station to the next,” Mr. Scotti explains. “By contrast, machining the part on a battery of machining centers may involve several setups, which may affect machining accuracy.
What do multi-spindle screw machine users need/want in their next machines? Five features are mentioned most frequently by customers: flexibility; easy changeover from one job to the next; ability to use readily available off-the-shelf tooling; greater accuracy and consistency; and ease of operation and maintenance.
A little creativity goes a long way in meeting the challenges that this high-production application presents.
Applying CNC technology to the manufacturing of precision parts is generally accepted as a premium that one must pay for the advantages over conventional actuation systems. Increasingly, however, the gap is narrowing as economies of scale for producing CNC equipped machine tools are incorporated in the unit price of a given machine. In other words, spreading the costs of manufacturing over a larger base of installations will reduce the price of each machine.