High performance for the welding of gears

23/02/2018 - Markus Isgro

In every synchromesh or dual-clutch transmission, there are gears with a synchronizer mechanism: They transmit the torque of the engine to the drive axle via a coupling body (synchro body) and a shift sleeve. There is one gear for each step of the transmission, meaning that a seven-gear transmission requires 7 + 1 gears.

A design that has proven successful is that of a wheel and synchro body, with the two separate parts joined and welded together.

The EMAG ELC 160 HP is a manufacturing system from EMAG specially designed for this operation of joining the wheel and the coupling body together. In a production line, the ELC 160 HP handles the sub-operations of joining (pressing), pre-heating for welding (if required), and finally laser welding. To achieve the quickest possible cycle times, these sub-processes run in parallel. The ELC 160 HP is a rotary transfer machine, making it perfect for high-productivity manufacturing. This also explains its name: the abbreviation “HP” stands for “high performance” or “highly productive.” With this machine, typical gears for car transmissions are produced in about 10 seconds (!).There is nothing new about the principle of a rotary transfer machine. On the contrary, in many areas rotary transfer machines have been deemed too inflexible and have been superseded by other machine designs.

This is where the real innovation of the ELC 160 HP comes into its own: a method of automated retooling for workpiece clamping, patented by EMAG, allows the ELC 160 HP to manufacture a variety of workpieces very flexibly, down to a batch size of one.

Four processes simultaneously—high performance thanks to smart indexing

The machine structure is centralized, in the truest sense of the word, around a central column on which all the components are mounted. A rotary indexing table arranged around this column provides for the transport of parts to the four process stations. A series of special design features ensures that the workpiece is positioned accurately in the machining station despite the high speed of the rotary indexing table. The high machine accuracy of the ELC 160 HP, in combination with EMAG's clamping technology, makes it perfect for even the most demanding, extremely narrow welds.

The machining process begins at the loading/unloading station. Two pick & place units, equipped with pneumatic grippers, transport the parts from the conveyor belt to the rotary indexing table and back. From there the parts proceed to the joining station. This station can be equipped with up to three (different) joining punches, selected by NC commands and set up with no loss of time. This provides full flexibility and retooling freedom for applications such as manufacturing an entire set of gears for one transmission.

The joining operation itself is performed quickly and precisely by a servo press, with an integrated force/stroke monitor for process monitoring.

In the next step of the cycle, the workpiece reaches the third machining station, where it undergoes induction pre-heating. Here too, the user can make use of a slide unit with up to two inductors, which likewise permits automatic retooling. One brief turn of the indexing table later, the workpiece reaches the core of the machine, the laser welding station. Here too there is something special: EMAG clamps the workpieces axially for welding, both to prevent distortion and to protect the workpiece from spatter. This clamp and fixture system can be reset automatically for different workpiece geometries, in time with the cycle of the machine. Up to three fixtures can be made available, which is usually enough.  So maximum flexibility and retooling freedom is provided here as well.

This principle of automated retooling (an EMAG patent) maximizes the efficiency of the ELC 160 HP, as it avoids not only a manual retooling procedure, but also the time spent waiting for the destructive testing of the first workpiece welded, which is required after manual retooling.

By performing the sub-operations of loading/unloading, joining, pre-heating, and laser welding in parallel, the ELC 160 HP attains maximum productivity: Gears for car transmissions are usually produced in a cycle time of just 10 sec. The automated retooling manages to square the circle by eliminating the disadvantage of rotary transfer machines, namely their low flexibility.

Like the two stations before it, this station is also equipped with a slide unit with up to three counter bearings, in order to ensure automatic retooling here as well. The weld head is equipped with an X-axis for the seam position and a Z-axis for adjusting the focal position. As an option, this station can also be equipped with a crosshair camera. 

All four processes described above run in parallel, allowing for extremely quick cycles with a record time of just ten seconds. 

Compact structure—perfect ergonomics

No compromises had to be made in ergonomics or accessibility for maintenance, despite the complex structure of the machine. With the process stations arranged at a 90° angle, the machining areas are all separate and therefore easily accessible. It is theoretically possible to perform maintenance on all four machining areas at the same time without difficulty. All of the technology required for operation of the system is housed in a control cabinet next to the machine unit, compact yet easily accessible. This gives access to all the electrical and pneumatic systems, as well as the induction generator, sensors, welding fume extraction and filtering, and CO2 extinguisher, all in one central location. The fixed beam guide and welding optics are also significant for maintenance tasks. These ensure not only extreme operational reliability, but also highly user-friendly setting and maintenance work. In addition, the fixed welding optics ensures that the laser always points into the interior of the machine, for extra safety in the workplace. The user therefore benefits from a machine layout which is both ergonomic and very safe.

Laser technology—solid-state lasers only 

The ELC 160 HP uses only solid-state lasers, such as the fiber-guided TruDisk laser from TRUMPF with disk laser technology, or direct diode laser systems from IPG. EMAG is one of the pioneers in the use of solid-state lasers for the welding of powertrain components, and is convinced of its advantages. “The diode-pumped solid state lasers have an energy conversion efficiency of around 30%. So a 4 kW unit running at full speed uses only about 25 kW, including the cooling unit. That means a considerable cost saving for the customer, when you compare the operating costs of this system with those of traditional laser systems,” said Nikolas Meyer, head of sales at EMAG Automation.

The use of solid-state lasers also permits welding without shielding gas, allowing further cost savings. Furthermore, solid-state lasers enable considerably faster welding for many applications. In terms of component quality, the heat input per unit length into the component is also reduced, which results in reduced welding distortion—removing the need for expensive reworking. 

It becomes clear why the ELC 160 HP can be called a “High Performance” welding machine. The entire design, including the process sequence, the technology used, and the compact, ergonomic structure of the ELC 160 HP is consistently aimed at performance and productivity. 

With the extremely short cycle times that can be achieved, EMAG is offering a highly attractive laser welding system for the manufacture of powertrain components, one that will no doubt prove very popular in the marketplace. 

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