Find out how these machines keep the production line moving
By Peter Huang and Denise Champagne
PETER HUANG is senior marketing specialist and DENISE CHAMPAGNE is director, corporate communications, Hypertherm Associates, Hanover, N.H.
Reprinted with permission: The AWS Welding Journal
Depending upon the make, model, and manufacturer, an automobile has between 5000 and 7000 spot welds on the white structure body. Many of those welds are on components essential to vehicle integrity and safety. Subframes, bumper and door beams, front headers, and other structural components all contain multiple weld positions — in some cases, more than 50 in a single component. Quality welds are a vital aspect of vehicle performance and safety. In auto-body production, there is no room for error. Defective welds can have catastrophic consequences.
As a result, testing weld integrity is a crucial step in the manufacturing process. Every day, the first components off the line must be checked for any welding imperfections that might cause a failure: cracking, fissures, slag inclusions, incomplete fusion, or any other irregularity that causes the weld to be substandard. Subsequent spot checks are conducted throughout the day to ensure weld and component quality.
To check the weld, manufacturers must get inside it. The joint is cut, polished to a mirror finish, and then examined under a microscope for minuscule defects that could cause significant problems. Production, however, does not stop for testing. The production line is halted only if test data suggests a significant and ongoing issue that requires an adjustment to the welding parameters. Stopping the entire line for weld checks is too costly, given the amount of testing that must be accomplished.
For example, one operator on one line may cut between ten and 25 parts for testing in a single day. In some cases, sample cutting a component with complicated geometries and numerous welds can consume an hour of operator time. To complete the wide variety of test cuts, automotive manufacturers rely on handheld plasma cutting and abrasive waterjet machines.
Cut to the Chase
Plasma cutting provides manufacturers with the fastest, most efficient, and most agile cutting application available to avoid bottlenecks and keep pace with the continuous parade of components. Focusing on ionized gas superheated to some 40,000°F, plasma cutting machines are accessible, easily mastered cutting tools. More importantly, they are safer and cut three to four times faster than grinding wheels.
Versatility and Ease of Use
Cutting, gouging, and flush cutting conductive metals such as carbon, stainless steel, and aluminum are relatively straightforward with plasma cutting machines. However, using a plasma cutting machine with features and capabilities suited to the specific application is important. Some units combine the five elements of a traditional plasma cutting machine into a single-piece cartridge consumable. Operators can change out swirl rings, electrodes, nozzles, retaining caps, and shield caps quickly and all at the same time with a one-piece cartridge system, saving time and ensuring reliable performance. Such cartridge systems also allow operators to quickly change cutting functions by simply changing a cartridge.
Advanced smart technology is also available that uses RFID chips to collect data on arc starts, use time, and machine performance, helping optimize cutting machine application and maintenance. Additionally, some equipment manufacturers have designed systems that sync cartridges with machine functions, making them easy to set up and use for a variety of operations. In many cases, with the right system, workers do not necessarily need to be proficient drag cutting and plasma cutting operators. They only need to understand how to change a cartridge.
Get into a Tight Spot
While a robotic plasma cutting machine can perform a substantial amount of sample cutting, many components must be simplified and require a handheld cutting machine. Most weld sampling is performed on metal only 10 to 12 mm thick. The requirement for efficient, lightweight vehicles has eliminated the use of heavy-gauge metals. However, the complex contours of modern unibodies and subframe components prevent the complete use of robotic plasma cutting machines for weld testing. Highly portable handheld plasma cutting machines can weigh as little as 20 to 30 lb, making them easy to maneuver in various cutting scenarios.
Repair When Possible and Scrap When Not
Plasma-cutting units that use an integrated cartridge system transition between various functions quickly with a simple cartridge change. Where welds are found to be defective but deemed repairable, gouging is appropriate and can be quickly accomplished. The old weld is removed, and the material is ejected in preparation for a new weld. Where repair is neither possible nor appropriate, however, the component must be cut down to unserviceable condition to prevent it from inadvertently entering the market.
Cut Cool with Water
Modern auto manufacturing increasingly integrates a wide range of materials into vehicle design. Alloys, plastics, and composites are growing in popularity with the need to match lighter vehicles for efficient fuel mileage with structural strength. Like with weld sampling, engineers need to know whether the materials they select for a given function are performing as expected. With the sheer number of testing applications — from large components of high-strength steel to tiny microchips in electronic modules — material performance testing requires a tool that is as versatile as it is precise.
Abrasive waterjet machines provide all the capabilities of standard machining and manufacturing cutting operations with versatility that is unmatched by traditional technology. Waterjets can cut virtually any material — from steels, super alloys, and exotics to composites, plastics, stone, and more at a wide range of thicknesses. Equally important, they cut without creating a heat-affected zone (HAZ) caused by traditional machining methods that can alter the physical characteristics of a sample, making accurate testing difficult.
Similarly, the impact of waterjet cutting on the residual stress of an object’s surface is extremely minimal. Residual stresses within and on the surfaces of materials can affect the results of material performance tests. ASTM standards require that these residual stresses must be effectively relieved before testing is conducted. Because of their cutting characteristics, abrasive waterjet machines alter a material’s inherent properties less than any existing technology does.
Waterjet cutting prevents HAZs, minimizes a material’s residual stress, and provides the precise, smooth finish required for detailed inspection and testing. Waterjet machines are available in a variety of sizes, from small, fully enclosed integrated systems to much larger, fully integrated abrasive waterjet systems.
Keeping the Wheels Turning
The economies of automotive manufacturing demand that production lines keep moving with minimum downtime. If defects occur, they must be caught and corrected as quickly as possible. Plasma cutting machines and abrasive waterjets are ideally suited for sample cutting and testing, ensuring a safe, high-quality product while keeping the lines rolling.