Swiss Precision With CNC Flexibility

Swiss-type automatics have been a production mainstay in screw machine shops better than a hundred years. Originally designed for production of parts for the Swiss watch industry, they are differentiated from other single-spindle machines by a sliding headstock. The cutting tools are fixed and the workpiece is moved

Case Study From: 2/1/1997 Modern Machine Shop

Swiss-type automatics have been a production mainstay in screw machine shops better than a hundred years. Originally designed for production of parts for the Swiss watch industry, they are differentiated from other single-spindle machines by a sliding headstock.

The cutting tools are fixed and the workpiece is moved relative to them. Swiss-type machines produce precision components for virtually every industryfrom automotive to aerospace.

Application of CNC technology to these machines has been relatively slow, compared to other machine tools. Swiss-type automatics have historically been cam actuated. Setup for long production runs, these machines are highly efficient precision part producers.

Like much of metalworking, Swiss-type screw machine shops have felt the industry drive to shorter production runs--driven, in large part, by customer inventory control programs. Orders come into shops for lower volume lots but the orders repeat more frequently.

A run of 500,000 parts which was once setup and run complete now may be spread over a year. For example, a 500,000 piece order may be divided into twelve runs of 42,000 parts. Since most shops can't afford to dedicate a machine exclusively to one job, this means 12 setups and teardowns where once there was just one.

This has put pressure on setup and teardown for these mechanical machines. In general mechanically actuated machines are not conducive to fast changeover. They tend to be very setup intensive with numerous hours and days spent getting the machine set to run a job lot.

Only very recently has CNC technology been competitive with mechanical actuation in terms of speed. A new machine from Tornos Technologies (Brookfield, Connecticut) called DECO 2000 is indicative of a new wave of CNC screw machines. According to the company, this new Swiss-type single-spindle automatic will match or exceed production rates of cam actuated machines with a bonus of setup time savings afforded by full CNC.

This is a new machine from the ground up and has some innovations to go with it. One of the most significant is the use of parallel processing technology in the machine control and servodrive systems. They've even coined a term for this actuation systemPNCfor parallel numerical control.

The PNC system uses two innovations to electronically emulate the functionality of a cam operated machine. The first of these is a central clock.

Its function replaces the main camshaft in a conventional automatic. The clock coordinates timing for when a given motion or function occurs. It automatically updates each programmed step every 8 milliseconds.

In the DECO 2000, virtual electronic cams take the place of their mechanical namesakes. Stroke distance is assigned to a specific axis and stored in memory as a table. Each stroke for the linear axis or, degree of rotation for rotary axes, is programmed individually. Using the clock eliminates the limit of 360 degrees imposed by a cam. The PNC reads data tables in parallel rather than one block at a time.

It's the clock that coordinates these motions assuring each happens at the correct point of the cycle. Other functions, such as cutting oil on or off are also coordinated by the PNC clock.

The DECO 2000 is manufactured in five- or nine-axis models. The difference being the number of endworking and backworking stations.

Designed for work from 1 to 10 mm in diameter, the DECO's 5 hp main spindle generates up 16,000 rpm. The machine has eight turning tools and three driven tool positions. Up to four tools can cut simultaneously. Headstock spindle indexing is standard in 0.1 degree increments with C-axis contouring available optionally.

Tornos has developed an off-line programming system for the DECO 2000. Called TB-DECO, it runs in Windows on a PC platform. Programs can be generated off-line and downloaded to the machine tool or generated in the shop with a portable PC.

The programming software also functions as a simulation package. Operation sequence is selected according to the operator's or programmer's experience. A synchronization function helps the programmer determine simultaneous operations. Relative position of tools, spindles and workpiece is shown as part of the display.

A graphic display of the programmed operation sequence can be run real-time on the PC. The simulation generates the operation cycle time. It also indicates any interference points between tools, spindles or workpiece. Editing the program gives an immediate cycle time update which allows the operator/programmer to optimize the program. MMS

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