For automakers, polishing stamping dies is an essential practice to prevent wear, reduce surface roughness and prolong service life. Industry leaders often use a manual technique called hammer peening where a die is polished by a worker repeatedly striking the surface of the metal with a hammer.
It’s a method favored by manufacturers because it not only increases the service life of the dies, it also improves polishing speed, consistency, surface quality and surface hardness by up to 30 percent.
Despite these benefits, hammer peening is labor intensive and time consuming, and the result is often inconsistent due to varying techniques among workers and worker fatigue. Bottom line, it has some shortcomings.
As a result, the quality and consistency of the die affects the stamped car body components, which may affect how they mount to the vehicle frame. Proper component fit and finish are important for any automaker, but for a manufacturer like Daimler’s Mercedes-Benz – known for luxury vehicles – it is an absolute necessity.
Rooted in robotics
Efforts to improve automotive manufacturing require constant evaluation of current processes and procedures, including the manual hammer peening process. During the search for a way to save the company money while creating a better product, Daimler managers and leaders realized their solution was rooted in the innovative world of robotics.
Robots are less expensive than dedicated CNC machines and provide greater reach on large workpieces, like stamping dies, which in this case weigh up to 25 tons and measure more than 16 ft. long, according to the Mercedes-Benz Ph.D. who spearheaded the development of the hammer peening process. He also notes that robots are more flexible than the common manual process and can work in many different applications.
Enthusiastic about the opportunity to maximize its equipment investment, Daimler took note of the flexibility of robots and anticipated how to leverage them for processes beyond hammer peening. But first, engineers tackled the formidable challenge of how to automate the current peening process.
Programming a robot to manipulate the hammer peening tool with the required frequency and precision using conventional software tools was no easy task. In the process used by Daimler, the stamping die is struck repeatedly with a high-frequency impact spherical hammering tool. The robotic process literally requires millions of impact points by the hammerhead to ensure homogeneous surface quality. The company had a configuration conundrum on their hands.
Attempts to use a combination of existing software platforms to generate code, calculate toolpaths and convert robot motion were unsuccessful; Daimler’s existing programming tools couldn’t handle all of the computations required to program a 6-axis robot for hammer peening. Limited by their resources but not to be defeated, Daimler approached the team responsible for Hypertherm’s Robotmaster CAD/CAM software for insight.
Together, Daimler and the Robotmaster team took on a three-year R&D project between 2014 and 2017, working to enhance and refine the robotic hammer peening process. They collaborated to create a custom toolpath and further develop the Robotmaster software to improve programming time and ease of use.
Daimler attributes much of their success in developing the hammer peening process and other robotic processes that came to follow to the months of hard work and dedication of the Robotmaster team. The team worked not only to understand Daimler’s need but also to adapt its software for their specific applications.
Programming time reduced
Robotmaster offered an offline programming solution that executed all of the complex calculations where previous software failed; it also exceeded Daimler’s expectations by overhauling and revamping the entire robotic hammer peening process. With optimized robot motion, smoother transitions and the ability to program complex dies quickly and easily, the time spent programming was reduced by a staggering 70 percent.
From the initial import of a CAD file and toolpath creation to a final workpiece, total programming time was reduced from 12 hours to 3.5 hours. Robotmaster’s kinematics solution requires just 45 min. of that total programming time, a sizeable improvement compared to previous attempts using other software platforms.
Achieving the Robotmaster solution required one of the fastest kinematics resolution engines available. It swiftly solves singularities, reach and joint limits, and other sudden robot motions that can abruptly change the robot’s configuration or cause errors. The proprietary kinematics and collision detection engines check for errors while the optimization tools smooth the robot motion. The kinematics solution offers clean transitions and minimizes unnecessary joint movements.
“When Daimler asked why it takes this long to process 3 million points, we had to explain how Robotmaster checks for kinematic issues at 150 iterations per point minimum for a 6-axis robot,” says Anbu Lingappan, European business development manager for Intercam SA, a distributor of Robotmaster software and part of the team that collaborated with Daimler on the hammer peening process. “We do this in the background for each point in the path and at a very high speed. Only then do people realize that there are some serious calculations going on behind the scenes. Robotmaster has the best kinematics and collision detection engines on the market.”
To fully optimize the hammer peening process, the software also needed to control external axes easily. Daimler’s hammer peening cell uses a Kuka KR 500 robot mounted on a rail to increase its reach in addition to two rotary axes to position the workpiece. Robotmaster is equipped to manage up to 11 axes simultaneously, including a 6-axis robot and five external axes. Rails and rotaries are automatically supported by the simulation and optimization tools as needed.
Pleased with the results of Robotmaster in the hammer peening application, Daimler began exploring the software’s capabilities for other processes using a second, newly commissioned robotic cell with multifunctional design. The robot could embark on a variety of processes from laser hardening to drilling by simply changing out the end-of-arm tooling.
Daimler soon began using Robotmaster software to program a robotic laser hardening process for their stamping dies. Laser hardening the fillets provides 30 percent more service life from the automaker’s die tools. Robotmaster also proved useful in programming a robotic laser cladding process to build up the worn surfaces of dies.
With the Robotmaster software, Daimler was able to optimize and economize its processes by creating multifunctional robotic cells for hammer peening, laser hardening, laser cladding, milling, drilling and induction hardening. Today, Daimler utilizes Robotmaster software in three Mercedes-Benz die shops and in Daimler’s Digital Factory where the company builds the core of its automobiles.
Ease of use was a significant factor in encouraging Daimler to adopt the Robotmaster software for offline programming. The extremely powerful Robotmaster Interactive Simulation Environment provides an intuitive click-and-drag user interface for modifying the robot’s positions and trajectories.
“The user interface is unique,” explains Norbert Krach, managing director of Robotized RM Systems GmbH, Robotmaster’s local reseller in Germany. “It’s impressive how easily you can get the toolpaths into Robotmaster and easily generate the code, simulate the process and resolve any kinematics challenges. With other software, you have to do a lot of trial and error. With Robotmaster, you resolve toolpaths easily and much faster. You don’t have to sit in front of a computer for hours tweaking points.”
Robotmaster’s user interface and proprietary technology provide unmatched control and flexibility.
As Daimler explores the further uses of robotics for different processes in the die shop, the company continues to rely on Robotmaster to accommodate its robot programming needs. Intercam’s Lingappan says the automotive industry owes a debt to Daimler for its work in this field.
“We give credit to Daimler for helping us innovate the robotic hammer peening process,” he says. “The rest of the market will benefit.”