Manufacturing Dilemma

Machine tools are the backbone of manufacturing. But which machine tools are the best for a specific application? This is a question that confuses even the most experienced and knowledgeable machining experts.

Not long ago, high volume production required dedicated machines that could be run without changing for many years. CNC machines were developed essentially to meet the production needs of aerospace companies and were subsequently adopted by short-run job shops. In time, manufacturing companies that built low volume products with many variations discovered the flexibility of CNC machines.

Within the last several years, an evolution has taken place in manufacturing. Large OEMs, especially the Big Three automakers, have been outsourcing machining work to Tier One suppliers. Now, Tier One suppliers are outsourcing to job shops, and shops accustomed to running lot sizes of one to 100 are now faced with contracts that require running the same part 24/7 with a yearly production of a million or more.

To meet that demand, job shops face an economic quandary. Purchasing stand-alone CNC machines to carry out the work requires huge capital expenditures, far more work and a great amount of floor space. But dedicated machines are not feasible due to the relatively short-term nature of the outsourced contracts. The answer that makes the greatest economic sense is the use of flexible technology.

The application of a cell consisting of a CNC flexible trunnion machine and stand-alone CNC machines can provide an excellent solution because the machines can be linked through automation, requiring only one operator to run the cell.

City Machine (Muncie, Indiana) recently shipped one such cell to produce an automotive drive train part. A standard twin spindle CNC chucker, a City Machine CNC heavy duty trunnion (HDT) machine and a converted standard upright drill with a four-spindle head were joined with robot loaders and a conveyor. Using this system, a family of parts can be machined complete at a rate of three per minute with a single operator.

All stations of the CNC trunnion machines are programmable and can be changed to a new part in the family very quickly. Each spindle has the productivity of a stand-alone CNC machine. Although the earlier generation of trunnion machines was dedicated to one part, the company's new generation of CNC trunnion machines features CNC controlled sliding spindle carriers that can perform the same functions as stand-alone CNC turning and machining centers. Additional productivity is gained by applying up to three spindles at one station. The machine can be reconfigured for a new application by rearranging the spindles, changing fixtures and tooling, and reprogramming for the next contracted part.

The configuration of a trunnion machine provides a great amount of flexibility. The drum is located with a large face coupling. Servo indexing time is 1 second or less. Chips fall into the conveyor by gravity and coolant wash. Floor space is comparable to a standard CNC horizontal machining center. Two horizontal heads and one radial head can be mounted at most stations without a center column.

The base allows high thrust and horsepower cuts. The sliding spindle carriers are adjustable so that precision alignments are achieved. Tools are easily changed outside the machine base.

The application of machine tools depends on the requirements of the individual part and the business contract specifications. When production volumes climb, it is time to consider the advantages of using a flexible CNC trunnion machine or a cell consisting of stand-alone CNC machines with automation. Use a CNC trunnion machine to machine the part features it can do best and apply a stand-alone CNC machine to machine what it can do best. Combine the two into a cell using both technologies to create a high production solution that is not a throwaway at the end of the contract.