Figure 1: Electron-beam welding machine.

Diagram of electron beam and fixture.

A critical concern when electron beam welding high precision parts, particularly in mass-production situations, is how to substantially eliminate the temperature distortion of weld chamber tooling while simultaneously and continuously providing precise confirmation of the beam’s positional location.

Recently, a manufacturer of aircraft components decided to boost production of a particular assembly from a few parts per hour to hundreds of parts per hour. Part precision and tolerances had to be maintained with the production increase. The assembly consisted of small, cylindrical alloy steel components of various lengths and diameters, and required two circumferential, butt welds.

The company decided to use PTR-Precision Technologies Inc. (www.ptreb.com), a manufacturer of electron beam welding systems, as its supplier to its production needs.

In electron-beam welding, a high concentration of electrons is generated and beamed at the target joint, producing heat that melts and vaporizes the metal. The results are narrow fusion zones and welds with good mechanical properties. The welding often takes place in a vacuum chamber to prevent dispersion of the electron beam. Unfortunately, anything else within in the chamber during welding, such as other parts to be welded and support tooling, also is heated by thermal conduction and radiation. The result may be displacement, drift or distortion of any of the items in the chamber. That can affect the quality of subsequent welds.

To eliminate this problem, PTR designed and fabricated a tooling package that thermally isolates the fixturing that is in direct contact with parts being welded, so that any heat buildup incurred during multiple-part weld runs have a minimal amount of thermal effect on the positioning of weld joints for subsequent parts. The fixtures also were designed to provide clamping force needed to grip the parts throughout the entire welding sequence.

The system, pictured in Figure 1, has a weld chamber with two segments. Parts are loaded into a batch-load container on the rightside, which is the part load/unload area. The parts then are transferred to a rotary fixture on the left-side, which is the weld area. A device devised and installed by PTR verifies the exact location that the electron beam will hit with respect to the position of the joint to be welded.

This device increases the accuracy of the positional relationship from part to part. The mount for this device is designed to minimize relative thermal motion between it and the parts being processed.

The device also is electrically isolated from the chamber and tooling components, which permits it to double as a beamsensing device, able to determine deviations in beam-to-seam alignment of less than 0.001 in. As the assembly is rotated in the fixture during welding, the beam is magnetically deflected from the first seam to the second seam, rather than moving the part physically through the x-and yaxes. This technique eliminates the wear of motion components that, in a high volume production, can increase maintenance and recalibration tasks. The materials and joint configurations of assemblies require multi-weld passes and beam oscillation pattern overlays on welds, to ensure that the final weld characteristics can be achieved consistently. The welding of each assembly is completed in less than 30 seconds, after which the part is deposited into a receiver bin next to the weld chamber. Operating parameters, such as beam power and focus values, and welding speed, can be determined for future jobs in the machine’s PC-based CNC controller. Those parameters can be stored as programs for individual parts.•

Before: Airplane components manufacturer needs to increase output while maintaining qualilty for high-precision componenets.

After: Installs specially designed tooling and an electron beam verification apparatus.

An edge for the wood

Robotec Inc. installs MPC2000 plasma machines.

Rotobec Inc. (www.rotobec.com) wanted to improve the bevel edges of its equipment and cut parts more precisely . Until recently it used a cutting machine it purchased in 1988.

Rotobec is a Canadian company that is a leader in continuous rotation attachments (grapples), including orange peel grapples for the recycling industry. Outside of its core market, the company makes attachments for the forestry industry, such as log loaders and harvesting heads. Rotobec was looking for ways to improve productivity and product quality.

Sylvain Cayouette, the company’s production manager, wanted to improve the precision of bevel angles and holes, while increasing the thickness of steel plate cut by his company. To do so would require replacing Robotec’s 18-year-old plasma cutting machine.

Cayouette considered laser cutting, but decided to buy a MPC2000 plasma machine from MG Systems and Welding Inc. (www.mg-systems-welding.com). He says he based his decision, in part, on the plasma machine having large rails and heavy construction, including an oversized drive motor and gearbox. In addition, he says the rails are protected with brushes, and the control is easy to use.

“Cutting speeds are much higher than before. Cutting costs were lowered considerable for 1-in. plates that were cut ( previously) with oxyfuel. Assembly, welding and machining time were reduced due to cutting precision,” says Cayouette. He also notes that the life of consumables is two times to six times longer than before, and adds, “Cut angles were up to 4 degrees before and now they are less than 1.5 degrees.”

Before: Manufacturer of attachments for equipment needs to boost quality and productivity.

After: Installs new metal cutting equipment that improves edges and precision of parts.